Expert Opinion on Investigational Drugs
ISSN: 1354-3784 (Print) 1744-7658 (Online) Journal homepage: http://www.tandfonline.com/loi/ieid20
Angiotensin 1 – 7 stimulation of platelet recovery Kathleen E Rodgers, Kainoa J Peterson, Holly A Maulhardt & Gere S diZerega MD To cite this article: Kathleen E Rodgers, Kainoa J Peterson, Holly A Maulhardt & Gere S diZerega MD (2014) Angiotensin 1 – 7 stimulation of platelet recovery, Expert Opinion on Investigational Drugs, 23:4, 551-559 To link to this article: http://dx.doi.org/10.1517/13543784.2014.891015
Published online: 20 Feb 2014.
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Angiotensin 1 -- 7 stimulation of platelet recovery Kathleen E Rodgers, Kainoa J Peterson, Holly A Maulhardt & Gere S diZerega†
1.
Introduction
2.
Market overview
3.
Scientific rationale
4.
Renin--angiotensin system
5.
Chemistry
6.
Nonclinical A(1 -- 7) efficacy
7.
Clinical safety and efficacy of A(1 -- 7)
8.
Conclusion
9.
Expert opinion
†
University of Southern California, Keck School of Medicine, Livingston Laboratory, Los Angeles, CA, USA
Introduction: Thrombocytopenia is an abnormally low number of platelets in the blood resulting from either too few platelets being produced or existing platelets being destroyed. Severe thrombocytopenia leads to excessive bleeding and can be the result of numerous medical conditions or a side effect of medications or treatments. Although platelet transfusions are typically administered to correct thrombocytopenia, transfusions represent a temporary and unsustainable solution. As there is a limited supply of platelet units available for transfusion, along with the significant financial cost and risk of infection, investigation to uncover mechanisms that boost platelet production may have important clinical and therapeutic implications. Treatment with angiotensin 1 -- 7 (A(1 -- 7)) has been shown in a preclinical and clinical evaluations to have a positive effect on platelet recovery. Areas covered: The authors provide an overview of the current treatment options available for platelet recovery and highlight the need for alternatives. Following on, the authors discuss the use of A(1 -- 7) as a potential therapeutic option for platelet recovery, including its safety and efficacy. Expert opinion: Current evidence provides a good basis for continued research and evaluation of the benefits of A(1 -- 7) treatment in stimulating platelet recovery following myelosuppression. A(1 -- 7) therapy has the potential to make a significant contribution to healthcare by providing standalone and additive treatments to address unmet medical needs and life-threatening diseases by utilizing the regenerative arm of the renin--angiotensin system. Keywords: angiotensin (1 -- 7), filgrastim, hematopoiesis, hematopoietic stem cell, myelosuppression, platelet recovery, thrombocytopenia, TXA127 Expert Opin. Investig. Drugs (2014) 23(4):551-559
1.
Introduction
Severe thrombocytopenia (platelet count £ 50,000/mcl) can occur as a direct result of disease (e.g., myelodysplastic syndromes), result of cytotoxic therapies (e.g., chemotherapy and radiation), or following a radiological event (e.g., nuclear bomb). As platelets are essential for hemostasis and there are currently no pharmaceutical therapies that are widely used for chemotherapy-induced or radiation-induced thrombocytopenia (CIT or RIT), treatment of thrombocytopenia due to cytotoxic therapy represents a major unmet clinical need. Although platelet transfusions are typically administered to correct thrombocytopenia, transfusions represent a temporary solution and do not address the underlying etiology [1]. Apart from the significant financial costs associated with platelet transfusions and resulting healthcare, there is a limited supply of donated units for transfusion. Over time, repetitive platelet transfusions often stimulate antibody production by the recipient, reducing the clinical utility of treatments. Uncovering mechanisms that boost platelet production can have important clinical implications,
10.1517/13543784.2014.891015 © 2014 Informa UK, Ltd. ISSN 1354-3784, e-ISSN 1744-7658 All rights reserved: reproduction in whole or in part not permitted
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Box 1. Drug summary.
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Drug name Phase Indication Pharmacological description/mechanism of action
Route of administration Chemical structure Pivotal/key trial(s)
Angiotensin 1 -- 7 II clinical trial Hematopoietic recovery A(1 -- 7) increases progenitor numbers through proliferation or improves survival after injury and improves engraftment of exogenous progenitors. These effects on progenitors lead to accelerated recovery of formed elements in the blood Subcutaneous injection Asp-Arg-Val-Tyr-Ile-His-Pro NCT00771810
A(1 - 7): Angiotensin (1 - 7); Asp: Aspartic acid; Arg: Arginine; His: Histidine; Ile: Isoleucine; Pro: Proline; Tyr: Tyrosine.
leading to improvement in supportive care for chemotherapy and bone marrow transplantation [2].
2.
Market overview
CIT is a major morbidity of treating patients with solid tumors including breast, colon, lung, and urothelial cancers. Depending on the chemotherapy regimen used, severe (Grades 3 [< 50,000/mcl] and 4 [< 20,000/mcl]) CIT occurs in up to 50% of patients. Current treatment strategies include use of platelet transfusions and dose reductions or delays in cancer therapy in order to reduce the risk of infection, stroke, and uncontrolled bleeding. The management of CIT through dose reductions and treatment delays often leads to reduced therapeutic efficacy [3]. The use of nuclear energy, in both civilian and military applications as well as exploitation of radiological materials for criminal and terrorist intents, poses risks to public health. Acute radiation syndrome (ARS) occurs after whole-body or significant partial-body (> 60%) irradiation and clinically significant damage to the hematopoietic system can result from exposure to > 1 Gy of radiation [4]. A leading cause of mortality in the hematopoietic subsyndrome is loss of platelet production with the duration of severe thrombocytopenia shown to be a reliable predictor of death [5]. Medical treatment for individuals suffering from the hematopoietic syndrome of ARS include red blood cell and platelet transfusions, growth factors, allogeneic stem-cell transplantation, fluid replacement, antibiotic therapy, and prophylaxis against ulceration [4]. It is estimated that ~ 1.5 million platelet transfusions to prevent severe bleeding are administered yearly, with each transfusion costing > $600 [6]. Platelet recovery (sustained platelet count > 50,000/mcl) following transfusion is often transient and transfusion-associated sepsis represents the 552
largest overall infectious risk in transfusion therapy [7]. Failure to achieve adequate response may result in patients becoming refractory to subsequent transfusions requiring additional transfusions and increased healthcare costs [8]. In the case of a nuclear event, where > 1 million people may be injured, the number of transfusion units required will exceed supply. As a result, development of therapies that reduce the necessity or limit the number of transfusions required will provide a great benefit for treatment of individuals affected by thrombocytopenia in both standard clinical practice and in preparation for a potential mass-casualty nuclear catastrophe. 3.
Scientific rationale
Hematopoiesis is a dynamic process where hematopoietic stem cells (HSCs) give rise to multipotent progenitor cells which, in turn, generate precursor cells destined to become circulating blood elements [9]. HSCs in the bone marrow differentiate to megakaryocytic progenitors, then megakaryocytes and finally platelets [10]. This process has been shown to be remarkably sensitive to destruction by ionizing radiation [11] and chemotherapy [12]. Platelets are central to hemostasis, but they also have key roles in the inflammatory response [13,14], wound healing [15,16], immunomodulation [17,18], and angiogenesis [19,20]. Activated platelets release a range of chemokines [21] and promote recruitment, adhesion, and proliferation of adult stem cells [22]. The multipotency of stem cells or early progenitors and their ability to augment vascular and tissue repair due to paracrine mechanisms [23] make them promising therapeutic vehicles in regenerative medicine. Additionally, tissue damage itself generates strong chemo-attractive signals for stem cells, providing a basis for regenerative activity. Platelet-regulated recruitment of adult stem cells toward injured cells may therefore be a central mechanism in exerting regenerative cellular responses [22]. 4.
Renin--angiotensin system
The renin--angiotensin system (RAS), a well-defined network for systemic regulation of blood pressure [24], has recently been shown to be present in individual tissues. Every known component of the RAS is contained within bone marrow cells, including mRNA for angiotensinogen, renin, ACE, angiotensin II receptors type 1 and 2 (AT1 and AT2, respectively), Mas, and ACE2 [25-27]. Extensive evidence indicates a significant role for the RAS in regulation of hematopoiesis and the development of hematopoietic progenitor cells [28-33]. Additionally, alterations in the RAS have been implicated in a variety of human hematopoietic diseases including myelodysplastic syndrome [34] and anemia [35,36]. Angiotensin (1 -- 7) (A(1 -- 7); Box 1) is an active member of the RAS that is generated through the actions of enzymes on angiotensin I, A(1 -- 9) or angiotensin II (Figure 1) [32,37]. A (1 -- 7) exhibits high specificity for the Mas receptor [38,39]
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Angiotensin 1 -- 7
- Neoplastic haematopoiesis - Neoplastic erythropoiesis - Early stages of BC formation - Mature peripheral BC formation
Angiotensinogen
- Primitive haematopoiesis - Leukaemogesis
Renin
Angiotensin-I
Angiotensin-(1-9) ACE2
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ACE - Haematopoiesis - Leukaemogensis - Thrombopoiesis - JAK-STAT signal transduction pathway activation
ACE
Angiotensin-II
Angiotensin-(1-7) ACE2
AT1 receptor
- Myeloma cell survival - BC formation - Erythropoiesis - Atherosclerosis
- Neoplastic haematopoiesis - Leukaemogensis - Lymphomagenesis - Early stages of BC formation - Down-regulation of Ac SDKP
AT2 receptor
MAS receptor
- BC formation - BC mobilization - Haematopoietic cell proliferation
- Anti-proliferative - Anti-neoplastic - Apoptosis
Figure 1. Potential role(s) of the essential peptides of the RAS in primitive and neoplastic hematopoiesis. Reproduced from [32] with permission of Portland Press Limited. RAS: Renin--Angiotensin system.
and A(1 -- 7) stimulation of hematopoiesis is hypothesized to be through the Mas receptor. The ability of A(1 -- 7) to accelerate hematopoietic recovery was blocked by administration of Mas, but not AT1 or AT2 antagonists [31,40]. Although expression of Mas in normal bone marrow is low, A(1 -- 7) increases the number of early and late progenitor cells that express Mas. This increase in Mas expression is further increased following chemotherapy and radiation [41,42]. Immature stem and progenitor cells (e.g., epidermal stem cells or hematopoietic progenitors) are most sensitive to induction of proliferation by A(1 -- 7), with effects most pronounced after injury [25,41,43-49]. Megakaryocytes, the precursors to platelets, have been found to be the most sensitive hematopoietic lineage to A(1 -- 7) therapy after myelosuppression [47].
Formulation in development TXA127, the clinical formulation of A(1 -- 7), is manufactured, stored, and distributed under GMP and is formulated as a sterile, preservative-free, nonpyrogenic solution for injection. The parenteral formulation is produced as a pHbuffered solution, adjusted for the proper osmolality with the addition of 4% mannitol to provide a final osmolality of 295 -- 415 mOsm for the dosing concentrations of A(1 -- 7). The product is packaged in a 2 ml, single-use, stoppered vial with a ~ 1.2 ml fill. The individual components used to manufacture the drug product are commonly used in other parenteral drug products. Sterilization is achieved via 0.22-µm filtration of the final solution into vials, which are filled under aseptic conditions. 5.1
6. 5.
Chemistry
Nonclinical A(1 -- 7) efficacy
Chemotherapy Data from preclinical studies demonstrate the effectiveness of A (1 -- 7), the active ingredient of the pharmaceutical TXA127, in accelerating megakaryocyte and platelet recovery following chemotherapy-induced myelosuppression [41,45,46,50]. Administration of A(1 -- 7) in vivo following chemotherapy increased numbers of hematopoietic progenitor cells in the bone marrow and formed elements in the peripheral blood, with the most profound effect seen in platelets [41,44-46,50]. The observed 6.1
A(1 -- 7) is a naturally occurring heptapeptide that is a nonhypertensive metabolite of Angiotensin-II (molecular weight 899.03 Da) with the amino-acid sequence, Asp-Arg-Val-TyrIle-His-Pro. A(1 -- 7) has been manufactured under GMP conditions for the conduct of preclinical safety and clinical studies. It is soluble in water, alcohol, propylene glycol, and organic solvents as well as hydrolysable by strong acids and bases at pH > 9.5. It is soluble in aqueous solutions at pH 5 -- 8.
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A.
**
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*
500 mcg/kg/day A(1 – 7)
1000
1000 mcg/kg/day A(1 – 7)
*
0 Baseline Day 3
Day 7 Day 15 Day 21 Day 30
Figure 2. A. CD2F1 mice underwent TBI and 24 h later various doses of A(1 -- 7) given by subcutaneous administration were started and administered daily until necropsy. Animals were euthanized on day 30 and their bone marrow harvested. Results represent the mean and SEM of data from five mice per group for CFU-Meg progenitor cells. Mice given higher dose of TBI have a lower recovery across all bone marrow progenitors. B. CD2F1 mice underwent TBI and 48 h later, daily administration of various doses of A(1 -- 7) by subcutaneous injection was initiated and continued until necropsy. Animals were bled prior to TBI, and on days 3, 7, 10, 14, 21 and 30. Animals received 400 cGy TBI. Results represent the mean and SEM of data from five mice per group. Reproduced from [31] with permission of Informa Healthcare. A. Bars marked with asterisk are significantly different from saline treated control (p < 0.05). B. Bars marked with asterisk are significantly different from saline treated control (p < 0.05).
increased sensitivity of immature stem or early progenitor cells to the proliferative and regenerative effects of angiotensin peptides offers unique therapeutic opportunities including significantly enhanced hematopoietic recovery after chemotherapy and potential bone marrow regeneration. Synergy Treatment with A(1 -- 7) following chemotherapy (intravenous 5-fluorouracil) significantly increased the concentration of megakaryocytes in the bone marrow. The observed increase was heightened and recovery was accelerated when A(1 -- 7) was coadministered with Neupogen (filgrastim). Effects seen in megakaryocyte progenitors were also found when evaluating platelet levels, where there was sustained platelet 6.2
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recovery following coadministration [41]. The observed synergistic effect was not limited to the megakaryocyte lineage. Coadministration of suboptimal doses of filgrastim and A (1 -- 7) resulted in superior white blood cell recovery to that observed in full dose filgrastim treatment, while maintaining the observed A(1 -- 7) improvement on platelet recovery [41]. A second study showed confirmatory results in megakaryocyte recovery when evaluating coadministration after gemcitabine-induced bone marrow suppression [50]. Shortterm administration of one tenth the dose of filgrastim in combination with A(1 -- 7) resulted in recovery consistent with full dose filgrastim. The combination of filgrastim and A(1 -- 7) had more potent effects on platelet recovery that A (1 -- 7) alone [50].
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Angiotensin 1 -- 7
Platelets ¥ 10 (3)/ul (mean ± SEM )
500 400 300 200 100 0 Visit
Cycle 0 1 2
Cycle 1 3 4
5 6 7
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8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Ang 1 – 7 10 – 100 mcg (n = 12)
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Cycle 3
Filgrastim (n = 5)
Figure 3. Concentration of platelets measured over the course of the study. Data are displayed as mean ± SEM for patients receiving doses from 10 to 100 mcg/kg. Cycle 0 is the treatment 14 days prior to the first chemotherapy administration. Cycles are 21 days in length. Visit 6, 12 and 18 represent prechemotherapy concentrations at the start of cycle 1, 2 and 3, respectively. Visit 7, 13 and 19 occurred 3 days after chemotherapy administration. Visit 8, 14 and 20 occurred 7 days after chemotherapy administration. Visit 9, 15 and 21 occurred 10 days after chemotherapy administration. Visit 10, 16 and 22 occurred 12 days after chemotherapy administration. Visit 11, 17 and 23 occurred 15 days after chemotherapy administration. Reproduced from [47] with permission of Springer-Velag.
Radiation Optimization of the appropriate dosing regimen has been performed in murine models of total body irradiation (TBI), with dosing initiated up to 10 days post-irradiation [31,45]. Studies showed that daily dosing with A(1 -- 7) resulted in a dose-dependent improvement in bone marrow progenitors and circulating formed elements, including platelets, and that the effects and higher doses were optimal when treatment was started at least 48 h after irradiation [31]. Overall, A(1 -- 7) significantly improved platelet levels compared to saline-treated controls, improved survival (from 60 to > 90%) and reduced bleeding time 30 days after TBI. As previously demonstrated in models of chemotherapy, A(1 -- 7) treatment also increased the concentration of megakaryocyte progenitors (two- to threefold increase) in the bone marrow and reduced RIT (twofold reduction) (Figure 2). Results were improved when A(1 -- 7) was delayed greater than 24 h post-TBI, which is consistent with the hypothesis that immature progenitor cells are more sensitive to the proliferative effects of A(1 -- 7) than mature cells [31]. 6.3
7.
Clinical safety and efficacy of A(1 -- 7)
A Phase I/IIa prospective, open-label, dose-escalation study of TXA127 was conducted in 15 breast cancer subjects receiving three cycles of adjuvant doxorubicin and cyclophosphamide [47]. The study compared the effects of up to 100 mcg/kg of TXA127 to filgrastim. The filgrastim comparator arm was used to compare safety and response variables,
and TXA127 was found to be safe and was well tolerated. No dose-limiting toxicity (DLT) was observed following subcutaneous administration of up to 100 mcg/kg of TXA127 for periods of up to 14 days. Subjects treated with TXA127 showed reduced frequency and severity of thrombocytopenia, anemia, and lymphopenia as compared to subjects who received filgrastim. Additionally, by the third cycle mean platelet nadirs were significantly higher (p < 0.012) with TXA127 than filgrastim (Figure 3). The preservation of platelet counts was not dose dependent and there were no occurrences of thrombocytopenia in TXA127-treated patients [47]. More recently, a Phase IIb study evaluating the safety and efficacy of TXA127 in reducing the incidence and severity of thrombocytopenia in subjects receiving a combination of gemcitabine and platinum therapy for ovarian carcinoma was completed [51]. Subjects receiving up to six cycles of gemcitabine and platinum therapy were randomized in a 1:1:1 ratio to receive placebo, 100 or 300 mcg/kg/day TXA127. The primary end point of the study was the severity and incidence of thrombocytopenia as determined by the number of chemotherapy cycles during which the platelet count measured < 50,000/mm3 (NCI-CTCAE Version 4.0, Grades 3 or 4 thrombocytopenia). A significant reduction of Grade 4 thrombocytopenia was seen in the 100 mcg/kg group, and there was a significant increase in the maximal percent increase in platelet count (p = 0.02) and relative dose intensity (p = 0.04) in subjects treated with 100 mcg/kg/day versus placebo-controlled (Figure 4). Interestingly, there was a nonsignificant increase in the incidence of Grade 4 thrombocytopenia in the subjects treated with 300 mcg/kg/day versus
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200 175
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p = 0.02
p = 0.42
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n = 9 n = 12
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Gemcitabine only 300 mcg/kg TXA127
Figure 4. A. maximal percentage platelet count increase from baseline. Median platelet counts in patients treated with 100 mcg/kg TXA127 (A(1 -- 7)) increased by 67% (345 to 546 109/l) from baseline levels, while placebo and 300 mcg/kg TXA127-treated patients showed more modest increases of 22% (343 to 399 109/l) and 29% (319 to 430 109/l), respectively. The difference between 100 mcg/kg-treated and placebo-treated patients was statistically significant (p < 0.05). B. Maintenance of dose intensity is displayed as the percent of planned chemotherapy delivered to patients. Patients treated with 100 mcg/kg TXA127 (A(1 -- 7)) received, on average, 88.7% (gemcitabine + platinum, n = 9) and 86.5% (gemcitabine only, n = 10) of the intended dose. In comparison, patients treated with placebo received 76.7% (gemcitabine + platinum, n = 8) and 67.6% (gemcitabine only, n = 10). Comparisons between placebo-treated and TXA127-treated patients yielded statistically significant (p < 0.05) differences in the 100 mcg/kg group. Number of patients differs due to three patients changing treatment from carboplatin to cisplatin mid-study. Reproduced from [51] with permission of Springer-Velag.
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placebo-controlled. Additionally, there was no observed difference in the maximal percent increase in platelet count and relative dose intensity in subjects treated with 300 mcg/kg/day versus placebo-controlled. No DLT was observed during the course of the study and no TXA127-related SAEs or deaths occurred. No bone marrow biopsies were taken during conduct of the clinical trials, and there were no TXA127 related side effects observed in organs outside of the blood.
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8.
Conclusion
A(1 -- 7) has a profound effect on the stimulation of the megakaryocytic lineage which in turn leads to a downstream effect on platelet formation and recovery. Administration of A (1 -- 7) has been shown to facilitate enhanced and accelerated platelet recovery in both preclinical and clinical evaluations of myelosuppressive therapies while presenting no observed safety concerns. 9.
Expert opinion
Convincing evidence of local RAS effect on cellular activity, tissue injury, and tissue regeneration has been accumulating over the past two decades. The RAS is highly conserved and the corroborative results between preclinical and clinical evaluations are consistent with the homology of A(1 -- 7) across mammalian species. The increase in sensitivity of immature stem and early hematopoietic progenitor cells to the proliferative and regenerative effects of A(1 -- 7), alone and in combination with currently marketed hematopoietic stimulants (e.g., filgrastim), offers therapeutic opportunities. Clinical data from patients receiving chemotherapy show a significant improvement in platelet recovery following low dose (£ 100 mcg/kg/day) A(1 -- 7) administration in comparison to filgrastim or placebo-treated patients [47,51]. A reduction in efficacy is observed when a higher dose (300 mcg/kg/day) of A(1 -- 7) is administered [51]. It is hypothesized that, in this dosing regimen, the drug has a significant effect of over-stimulating progenitor cells. The demonstrated sensitivity of hematopoietic progenitors to A(1 -- 7) stimulation [31,41,45] as well as their sensitivity to chemotherapy [12] suggest that there is a fine balance which must be maintained to allow for downstream platelet recovery without continued stimulation of the progenitors during chemotherapy administration. This observation can be extended to oncology patients receiving fractionated doses of radiation, with the repeated insult to bone marrow resulting in cell death of immature progenitors. It is the opinion of these authors
that lower doses of A(1 -- 7) warrant further evaluation as a chemotherapy-adjuvant as they provide the most compelling evidence for maintaining a balance of HSC stimulation and downstream platelet recovery. To date, no clinical evidence exists for the evaluation of A(1 -- 7) in patients treated for radiation exposure. Preclinical evidence suggests that a higher dose of A(1 -- 7) provided the most accelerated and sustained platelet recovery following a single dose of TBI [31]. It is hypothesized that this is due to the one-time delivery of TBI, in comparison to repeated delivery of chemotherapy cycles. As proliferating progenitors are able to differentiate to formed blood cells without receiving recurrent insult, extensive repopulation of hematopoietic cells by A(1 -- 7) serves to enhance recovery. Due to the limited number of patients that present with this type of injury, FDA approval of A(1 -- 7) as a medical countermeasure following radiation would be pursued by way of the Animal Rule (21 CFR 314.600) for the indication of mitigation of consequences of lethal radiation. It is the opinion of these authors that further investigation may include currently approved treatments (e.g., filgrastim) and given the demonstration of synergy [50], combined application may provide a significantly improved hematopoietic response to either drug alone. Current evidence provides the basis for continued research and evaluation of the benefit A(1 -- 7) treatment has in stimulating platelet recovery following myelosuppression. A(1 -- 7) therapy has the potential to make a significant contribution to healthcare by providing standalone and additive treatments to address unmet medical needs and life-threatening diseases by utilizing the regenerative arm of the RAS. Potential patient populations include cancer patients receiving antineoplastic or radiation therapy with myelosuppressive side effects, stem-cell transplant patients after myeloablative conditioning, patients with conditions resulting in ineffective myelopoiesis and apoptosis of hematopoietic progenitors, and individuals exposed to radiation.
Declaration of interest K Rodgers and G diZerega are inventors on patents covering this peptide and may have royalties associated. G diZerega is the owner and founder of US Biotest, the company that received the funding from Tarix Pharmaceuticals which funded much of the work described. K Peterson and H Maulhardt are employees of US Biotest.
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Gnecchi M, Zhang Z, Ni A, Dzau VJ. Paracrine mechanisms in adult stem cell signaling and therapy. Circ Res 2008;103(11):1204-19
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Haznedaroglu IC, Beyazit Y. Local bone marrow renin-angiotensin system in primitive, definitive and neoplastic haematopoiesis. Clin Sci(Lond) 2013;124(5):307-23 Describes the renin-angiotensin system and it’s role in the bone marrow.
33.
Passos-Silva DG, Verano-Braga T, Santos RA. Angiotensin-(1 -- 7): beyond the cardio-renal actions. Clin Sci (Lond) 2013;124(7):443-56
34.
Marusic Vrsalovic M, Dominis M, Jaksic B, Kusec R. Angiotensin
Angiotensin 1 -- 7
I-converting enzyme is expressed by erythropoietic cells of normal and myeloproliferative bone marrow. Br Haematol 2003;123(3):539-41 35.
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Brunton LL, Lazo JS, Parker KL. Renin and angiotensin. In: Jackson E, editor, Goodman, Gilman’s the pharmacological basis of therapeutics. 11th edition. McGraw-Hill, New York; 2006. p. 789-821
44.
Bader M, Santos RA, Unger T,
40.
Rodgers K, Xiong S, Felix J, et al. Development of angiotensin (1 -- 7) as an agent to accelerate dermal repair. Wound Repair Regen 2001;9(3):238-47
41.
Ellefson DD, Espinoza T, Roda N, et al. Synergistic effects of co-administration of angiotensin 1 -- 7 and Neupogen on hematopoietic recovery in mice. Cancer Chemother Pharmacol 2004;53(1): 15-24 Jadhav SS, Sharma N, Meeks CJ, et al. Effects of combined radiation and burn
Gallinat S, Yu M, Dorst A, et al. Sciatic nerve transection evokes lasting up-regulation of angiotensin AT2 and AT 1receptor mRNA in adult rat dorsal root ganglia and sciatic nerves. Brain Res Mol Brain Res 1998;57(1):111-22
Heringer-Walther S, Eckert K, Schumacher SM, et al. Angiotensin(1 -- 7) stimulates hematopoietic progenitor cells in vitro and in vivo. Haematologica 2009;94(6):857-60
50.
Rodgers KE, Xiong S, Steer R, DiZerega GS. Effect of angiotensin II on hematopoietic progenitor cell proliferation. Stem Cells 2000;18(4):287-94
Rodgers KE, Espinoza TB, Roda N, Meeks CJ. Angiotensin-(1 -- 7) synergizes with colony-stimulating factors in hematopoietic recovery. Cancer Chemother Pharmacol 2013;72(6):1235-45
51.
Pham H, Schwartz BM, Delmore JE, et al. Pharmacodynamic stimulation of thrombogenesis by angiotensin (1 -- 7) in recurrent ovarian cancer patients receiving gemcitabine and platinumbased chemotherapy. Cancer Chemother Pharmacol 2013;71(4):965-72 Describes the ability of A(1 -- 7) to facilitate platelet recovery following chemotherapy in a clinical indication.
45.
Rodgers KE, Xiong S. Accelerated recovery from irradiation injury by angiotensin peptides. Cancer Chemother Pharmacol 2002;49(5):403-11
46.
Rodgers K, Xiong S. Effect of angiotensin II and angiotensin (1 -- 7) on hematopoietic recovery after intravenous chemotherapy. Cancer Chemother Pharmacol 2003;51(2):97-106
Santos RA, e Silva ACS, Maric C, et al. Angiotensin-(1 -- 7) is an endogenous ligand for the G protein-coupled receptor Mas. Proc Natl Acad Sci USA 2003;100(14):8258-63
39.
42.
43.
Sica DA. ACE inhibitors and anemia in congestive heart failure. Congest Heart Fail 2000;6(6):330-2 Naito M, Kawashima A, Akiba T, et al. Effects of an angiotensin II receptor antagonist and angiotensin-converting enzyme inhibitors on burst forming units-erythroid in chronic hemodialysis patients. Am J Nephrol 2003;23(5):287-93
49.
injury on the renin--angiotensin system. Wound Repair Regen 2013;21(1):131-40
47.
Rodgers KE, Oliver J. Phase I/II dose escalation study of angiotensin 1 -- 7 [A (1 -- 7)] administered before and after chemotherapy in patients with newly diagnosed breast cancer. Cancer Chemother Pharmacol 2006;57(5):559-68
48.
Zambidis ET, Park TS, Yu W, et al. Expression of angiotensin-converting enzyme (CD143) identifies and regulates primitive hemangioblasts derived from human pluripotent stem cells. Blood 2008;112(9):3601-14
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Affiliation Kathleen E Rodgers1, Kainoa J Peterson2, Holly A Maulhardt2 & Gere S diZerega†2,3 MD † Author for correspondence 1 University of Southern California, School of Pharmacy, 1985 Zonal Avenue, Los Angeles, CA 90089, USA 2 US Biotest, Inc., 231 Bonetti Drive, Suite 240, San Luis Obispo, CA 93401, USA 3 Professor, University of Southern California, Keck School of Medicine, Livingston Laboratory, 1321 N. Mission Road, Los Angeles, CA 90033, USA Tel: +1 805 595 1300; E-mail: [email protected]
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ISSN: 1354-3784 (Print) 1744-7658 (Online) Journal homepage: http://www.tandfonline.com/loi/ieid20
Angiotensin 1 – 7 stimulation of platelet recovery Kathleen E Rodgers, Kainoa J Peterson, Holly A Maulhardt & Gere S diZerega MD To cite this article: Kathleen E Rodgers, Kainoa J Peterson, Holly A Maulhardt & Gere S diZerega MD (2014) Angiotensin 1 – 7 stimulation of platelet recovery, Expert Opinion on Investigational Drugs, 23:4, 551-559 To link to this article: http://dx.doi.org/10.1517/13543784.2014.891015
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Drug Evaluation
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Angiotensin 1 -- 7 stimulation of platelet recovery Kathleen E Rodgers, Kainoa J Peterson, Holly A Maulhardt & Gere S diZerega†
1.
Introduction
2.
Market overview
3.
Scientific rationale
4.
Renin--angiotensin system
5.
Chemistry
6.
Nonclinical A(1 -- 7) efficacy
7.
Clinical safety and efficacy of A(1 -- 7)
8.
Conclusion
9.
Expert opinion
†
University of Southern California, Keck School of Medicine, Livingston Laboratory, Los Angeles, CA, USA
Introduction: Thrombocytopenia is an abnormally low number of platelets in the blood resulting from either too few platelets being produced or existing platelets being destroyed. Severe thrombocytopenia leads to excessive bleeding and can be the result of numerous medical conditions or a side effect of medications or treatments. Although platelet transfusions are typically administered to correct thrombocytopenia, transfusions represent a temporary and unsustainable solution. As there is a limited supply of platelet units available for transfusion, along with the significant financial cost and risk of infection, investigation to uncover mechanisms that boost platelet production may have important clinical and therapeutic implications. Treatment with angiotensin 1 -- 7 (A(1 -- 7)) has been shown in a preclinical and clinical evaluations to have a positive effect on platelet recovery. Areas covered: The authors provide an overview of the current treatment options available for platelet recovery and highlight the need for alternatives. Following on, the authors discuss the use of A(1 -- 7) as a potential therapeutic option for platelet recovery, including its safety and efficacy. Expert opinion: Current evidence provides a good basis for continued research and evaluation of the benefits of A(1 -- 7) treatment in stimulating platelet recovery following myelosuppression. A(1 -- 7) therapy has the potential to make a significant contribution to healthcare by providing standalone and additive treatments to address unmet medical needs and life-threatening diseases by utilizing the regenerative arm of the renin--angiotensin system. Keywords: angiotensin (1 -- 7), filgrastim, hematopoiesis, hematopoietic stem cell, myelosuppression, platelet recovery, thrombocytopenia, TXA127 Expert Opin. Investig. Drugs (2014) 23(4):551-559
1.
Introduction
Severe thrombocytopenia (platelet count £ 50,000/mcl) can occur as a direct result of disease (e.g., myelodysplastic syndromes), result of cytotoxic therapies (e.g., chemotherapy and radiation), or following a radiological event (e.g., nuclear bomb). As platelets are essential for hemostasis and there are currently no pharmaceutical therapies that are widely used for chemotherapy-induced or radiation-induced thrombocytopenia (CIT or RIT), treatment of thrombocytopenia due to cytotoxic therapy represents a major unmet clinical need. Although platelet transfusions are typically administered to correct thrombocytopenia, transfusions represent a temporary solution and do not address the underlying etiology [1]. Apart from the significant financial costs associated with platelet transfusions and resulting healthcare, there is a limited supply of donated units for transfusion. Over time, repetitive platelet transfusions often stimulate antibody production by the recipient, reducing the clinical utility of treatments. Uncovering mechanisms that boost platelet production can have important clinical implications,
10.1517/13543784.2014.891015 © 2014 Informa UK, Ltd. ISSN 1354-3784, e-ISSN 1744-7658 All rights reserved: reproduction in whole or in part not permitted
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Box 1. Drug summary.
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Drug name Phase Indication Pharmacological description/mechanism of action
Route of administration Chemical structure Pivotal/key trial(s)
Angiotensin 1 -- 7 II clinical trial Hematopoietic recovery A(1 -- 7) increases progenitor numbers through proliferation or improves survival after injury and improves engraftment of exogenous progenitors. These effects on progenitors lead to accelerated recovery of formed elements in the blood Subcutaneous injection Asp-Arg-Val-Tyr-Ile-His-Pro NCT00771810
A(1 - 7): Angiotensin (1 - 7); Asp: Aspartic acid; Arg: Arginine; His: Histidine; Ile: Isoleucine; Pro: Proline; Tyr: Tyrosine.
leading to improvement in supportive care for chemotherapy and bone marrow transplantation [2].
2.
Market overview
CIT is a major morbidity of treating patients with solid tumors including breast, colon, lung, and urothelial cancers. Depending on the chemotherapy regimen used, severe (Grades 3 [< 50,000/mcl] and 4 [< 20,000/mcl]) CIT occurs in up to 50% of patients. Current treatment strategies include use of platelet transfusions and dose reductions or delays in cancer therapy in order to reduce the risk of infection, stroke, and uncontrolled bleeding. The management of CIT through dose reductions and treatment delays often leads to reduced therapeutic efficacy [3]. The use of nuclear energy, in both civilian and military applications as well as exploitation of radiological materials for criminal and terrorist intents, poses risks to public health. Acute radiation syndrome (ARS) occurs after whole-body or significant partial-body (> 60%) irradiation and clinically significant damage to the hematopoietic system can result from exposure to > 1 Gy of radiation [4]. A leading cause of mortality in the hematopoietic subsyndrome is loss of platelet production with the duration of severe thrombocytopenia shown to be a reliable predictor of death [5]. Medical treatment for individuals suffering from the hematopoietic syndrome of ARS include red blood cell and platelet transfusions, growth factors, allogeneic stem-cell transplantation, fluid replacement, antibiotic therapy, and prophylaxis against ulceration [4]. It is estimated that ~ 1.5 million platelet transfusions to prevent severe bleeding are administered yearly, with each transfusion costing > $600 [6]. Platelet recovery (sustained platelet count > 50,000/mcl) following transfusion is often transient and transfusion-associated sepsis represents the 552
largest overall infectious risk in transfusion therapy [7]. Failure to achieve adequate response may result in patients becoming refractory to subsequent transfusions requiring additional transfusions and increased healthcare costs [8]. In the case of a nuclear event, where > 1 million people may be injured, the number of transfusion units required will exceed supply. As a result, development of therapies that reduce the necessity or limit the number of transfusions required will provide a great benefit for treatment of individuals affected by thrombocytopenia in both standard clinical practice and in preparation for a potential mass-casualty nuclear catastrophe. 3.
Scientific rationale
Hematopoiesis is a dynamic process where hematopoietic stem cells (HSCs) give rise to multipotent progenitor cells which, in turn, generate precursor cells destined to become circulating blood elements [9]. HSCs in the bone marrow differentiate to megakaryocytic progenitors, then megakaryocytes and finally platelets [10]. This process has been shown to be remarkably sensitive to destruction by ionizing radiation [11] and chemotherapy [12]. Platelets are central to hemostasis, but they also have key roles in the inflammatory response [13,14], wound healing [15,16], immunomodulation [17,18], and angiogenesis [19,20]. Activated platelets release a range of chemokines [21] and promote recruitment, adhesion, and proliferation of adult stem cells [22]. The multipotency of stem cells or early progenitors and their ability to augment vascular and tissue repair due to paracrine mechanisms [23] make them promising therapeutic vehicles in regenerative medicine. Additionally, tissue damage itself generates strong chemo-attractive signals for stem cells, providing a basis for regenerative activity. Platelet-regulated recruitment of adult stem cells toward injured cells may therefore be a central mechanism in exerting regenerative cellular responses [22]. 4.
Renin--angiotensin system
The renin--angiotensin system (RAS), a well-defined network for systemic regulation of blood pressure [24], has recently been shown to be present in individual tissues. Every known component of the RAS is contained within bone marrow cells, including mRNA for angiotensinogen, renin, ACE, angiotensin II receptors type 1 and 2 (AT1 and AT2, respectively), Mas, and ACE2 [25-27]. Extensive evidence indicates a significant role for the RAS in regulation of hematopoiesis and the development of hematopoietic progenitor cells [28-33]. Additionally, alterations in the RAS have been implicated in a variety of human hematopoietic diseases including myelodysplastic syndrome [34] and anemia [35,36]. Angiotensin (1 -- 7) (A(1 -- 7); Box 1) is an active member of the RAS that is generated through the actions of enzymes on angiotensin I, A(1 -- 9) or angiotensin II (Figure 1) [32,37]. A (1 -- 7) exhibits high specificity for the Mas receptor [38,39]
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Angiotensin 1 -- 7
- Neoplastic haematopoiesis - Neoplastic erythropoiesis - Early stages of BC formation - Mature peripheral BC formation
Angiotensinogen
- Primitive haematopoiesis - Leukaemogesis
Renin
Angiotensin-I
Angiotensin-(1-9) ACE2
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ACE - Haematopoiesis - Leukaemogensis - Thrombopoiesis - JAK-STAT signal transduction pathway activation
ACE
Angiotensin-II
Angiotensin-(1-7) ACE2
AT1 receptor
- Myeloma cell survival - BC formation - Erythropoiesis - Atherosclerosis
- Neoplastic haematopoiesis - Leukaemogensis - Lymphomagenesis - Early stages of BC formation - Down-regulation of Ac SDKP
AT2 receptor
MAS receptor
- BC formation - BC mobilization - Haematopoietic cell proliferation
- Anti-proliferative - Anti-neoplastic - Apoptosis
Figure 1. Potential role(s) of the essential peptides of the RAS in primitive and neoplastic hematopoiesis. Reproduced from [32] with permission of Portland Press Limited. RAS: Renin--Angiotensin system.
and A(1 -- 7) stimulation of hematopoiesis is hypothesized to be through the Mas receptor. The ability of A(1 -- 7) to accelerate hematopoietic recovery was blocked by administration of Mas, but not AT1 or AT2 antagonists [31,40]. Although expression of Mas in normal bone marrow is low, A(1 -- 7) increases the number of early and late progenitor cells that express Mas. This increase in Mas expression is further increased following chemotherapy and radiation [41,42]. Immature stem and progenitor cells (e.g., epidermal stem cells or hematopoietic progenitors) are most sensitive to induction of proliferation by A(1 -- 7), with effects most pronounced after injury [25,41,43-49]. Megakaryocytes, the precursors to platelets, have been found to be the most sensitive hematopoietic lineage to A(1 -- 7) therapy after myelosuppression [47].
Formulation in development TXA127, the clinical formulation of A(1 -- 7), is manufactured, stored, and distributed under GMP and is formulated as a sterile, preservative-free, nonpyrogenic solution for injection. The parenteral formulation is produced as a pHbuffered solution, adjusted for the proper osmolality with the addition of 4% mannitol to provide a final osmolality of 295 -- 415 mOsm for the dosing concentrations of A(1 -- 7). The product is packaged in a 2 ml, single-use, stoppered vial with a ~ 1.2 ml fill. The individual components used to manufacture the drug product are commonly used in other parenteral drug products. Sterilization is achieved via 0.22-µm filtration of the final solution into vials, which are filled under aseptic conditions. 5.1
6. 5.
Chemistry
Nonclinical A(1 -- 7) efficacy
Chemotherapy Data from preclinical studies demonstrate the effectiveness of A (1 -- 7), the active ingredient of the pharmaceutical TXA127, in accelerating megakaryocyte and platelet recovery following chemotherapy-induced myelosuppression [41,45,46,50]. Administration of A(1 -- 7) in vivo following chemotherapy increased numbers of hematopoietic progenitor cells in the bone marrow and formed elements in the peripheral blood, with the most profound effect seen in platelets [41,44-46,50]. The observed 6.1
A(1 -- 7) is a naturally occurring heptapeptide that is a nonhypertensive metabolite of Angiotensin-II (molecular weight 899.03 Da) with the amino-acid sequence, Asp-Arg-Val-TyrIle-His-Pro. A(1 -- 7) has been manufactured under GMP conditions for the conduct of preclinical safety and clinical studies. It is soluble in water, alcohol, propylene glycol, and organic solvents as well as hydrolysable by strong acids and bases at pH > 9.5. It is soluble in aqueous solutions at pH 5 -- 8.
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A.
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*
500 mcg/kg/day A(1 – 7)
1000
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*
0 Baseline Day 3
Day 7 Day 15 Day 21 Day 30
Figure 2. A. CD2F1 mice underwent TBI and 24 h later various doses of A(1 -- 7) given by subcutaneous administration were started and administered daily until necropsy. Animals were euthanized on day 30 and their bone marrow harvested. Results represent the mean and SEM of data from five mice per group for CFU-Meg progenitor cells. Mice given higher dose of TBI have a lower recovery across all bone marrow progenitors. B. CD2F1 mice underwent TBI and 48 h later, daily administration of various doses of A(1 -- 7) by subcutaneous injection was initiated and continued until necropsy. Animals were bled prior to TBI, and on days 3, 7, 10, 14, 21 and 30. Animals received 400 cGy TBI. Results represent the mean and SEM of data from five mice per group. Reproduced from [31] with permission of Informa Healthcare. A. Bars marked with asterisk are significantly different from saline treated control (p < 0.05). B. Bars marked with asterisk are significantly different from saline treated control (p < 0.05).
increased sensitivity of immature stem or early progenitor cells to the proliferative and regenerative effects of angiotensin peptides offers unique therapeutic opportunities including significantly enhanced hematopoietic recovery after chemotherapy and potential bone marrow regeneration. Synergy Treatment with A(1 -- 7) following chemotherapy (intravenous 5-fluorouracil) significantly increased the concentration of megakaryocytes in the bone marrow. The observed increase was heightened and recovery was accelerated when A(1 -- 7) was coadministered with Neupogen (filgrastim). Effects seen in megakaryocyte progenitors were also found when evaluating platelet levels, where there was sustained platelet 6.2
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recovery following coadministration [41]. The observed synergistic effect was not limited to the megakaryocyte lineage. Coadministration of suboptimal doses of filgrastim and A (1 -- 7) resulted in superior white blood cell recovery to that observed in full dose filgrastim treatment, while maintaining the observed A(1 -- 7) improvement on platelet recovery [41]. A second study showed confirmatory results in megakaryocyte recovery when evaluating coadministration after gemcitabine-induced bone marrow suppression [50]. Shortterm administration of one tenth the dose of filgrastim in combination with A(1 -- 7) resulted in recovery consistent with full dose filgrastim. The combination of filgrastim and A(1 -- 7) had more potent effects on platelet recovery that A (1 -- 7) alone [50].
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Angiotensin 1 -- 7
Platelets ¥ 10 (3)/ul (mean ± SEM )
500 400 300 200 100 0 Visit
Cycle 0 1 2
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5 6 7
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Ang 1 – 7 10 – 100 mcg (n = 12)
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Cycle 3
Filgrastim (n = 5)
Figure 3. Concentration of platelets measured over the course of the study. Data are displayed as mean ± SEM for patients receiving doses from 10 to 100 mcg/kg. Cycle 0 is the treatment 14 days prior to the first chemotherapy administration. Cycles are 21 days in length. Visit 6, 12 and 18 represent prechemotherapy concentrations at the start of cycle 1, 2 and 3, respectively. Visit 7, 13 and 19 occurred 3 days after chemotherapy administration. Visit 8, 14 and 20 occurred 7 days after chemotherapy administration. Visit 9, 15 and 21 occurred 10 days after chemotherapy administration. Visit 10, 16 and 22 occurred 12 days after chemotherapy administration. Visit 11, 17 and 23 occurred 15 days after chemotherapy administration. Reproduced from [47] with permission of Springer-Velag.
Radiation Optimization of the appropriate dosing regimen has been performed in murine models of total body irradiation (TBI), with dosing initiated up to 10 days post-irradiation [31,45]. Studies showed that daily dosing with A(1 -- 7) resulted in a dose-dependent improvement in bone marrow progenitors and circulating formed elements, including platelets, and that the effects and higher doses were optimal when treatment was started at least 48 h after irradiation [31]. Overall, A(1 -- 7) significantly improved platelet levels compared to saline-treated controls, improved survival (from 60 to > 90%) and reduced bleeding time 30 days after TBI. As previously demonstrated in models of chemotherapy, A(1 -- 7) treatment also increased the concentration of megakaryocyte progenitors (two- to threefold increase) in the bone marrow and reduced RIT (twofold reduction) (Figure 2). Results were improved when A(1 -- 7) was delayed greater than 24 h post-TBI, which is consistent with the hypothesis that immature progenitor cells are more sensitive to the proliferative effects of A(1 -- 7) than mature cells [31]. 6.3
7.
Clinical safety and efficacy of A(1 -- 7)
A Phase I/IIa prospective, open-label, dose-escalation study of TXA127 was conducted in 15 breast cancer subjects receiving three cycles of adjuvant doxorubicin and cyclophosphamide [47]. The study compared the effects of up to 100 mcg/kg of TXA127 to filgrastim. The filgrastim comparator arm was used to compare safety and response variables,
and TXA127 was found to be safe and was well tolerated. No dose-limiting toxicity (DLT) was observed following subcutaneous administration of up to 100 mcg/kg of TXA127 for periods of up to 14 days. Subjects treated with TXA127 showed reduced frequency and severity of thrombocytopenia, anemia, and lymphopenia as compared to subjects who received filgrastim. Additionally, by the third cycle mean platelet nadirs were significantly higher (p < 0.012) with TXA127 than filgrastim (Figure 3). The preservation of platelet counts was not dose dependent and there were no occurrences of thrombocytopenia in TXA127-treated patients [47]. More recently, a Phase IIb study evaluating the safety and efficacy of TXA127 in reducing the incidence and severity of thrombocytopenia in subjects receiving a combination of gemcitabine and platinum therapy for ovarian carcinoma was completed [51]. Subjects receiving up to six cycles of gemcitabine and platinum therapy were randomized in a 1:1:1 ratio to receive placebo, 100 or 300 mcg/kg/day TXA127. The primary end point of the study was the severity and incidence of thrombocytopenia as determined by the number of chemotherapy cycles during which the platelet count measured < 50,000/mm3 (NCI-CTCAE Version 4.0, Grades 3 or 4 thrombocytopenia). A significant reduction of Grade 4 thrombocytopenia was seen in the 100 mcg/kg group, and there was a significant increase in the maximal percent increase in platelet count (p = 0.02) and relative dose intensity (p = 0.04) in subjects treated with 100 mcg/kg/day versus placebo-controlled (Figure 4). Interestingly, there was a nonsignificant increase in the incidence of Grade 4 thrombocytopenia in the subjects treated with 300 mcg/kg/day versus
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200 175
p (Dose-Response) = 0.45 p (vs Placebo)
p = 0.02
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Maximal increase (%)
150 125 100 75 50 25 0 –25 –50 0 (n = 10)
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Figure 4. A. maximal percentage platelet count increase from baseline. Median platelet counts in patients treated with 100 mcg/kg TXA127 (A(1 -- 7)) increased by 67% (345 to 546 109/l) from baseline levels, while placebo and 300 mcg/kg TXA127-treated patients showed more modest increases of 22% (343 to 399 109/l) and 29% (319 to 430 109/l), respectively. The difference between 100 mcg/kg-treated and placebo-treated patients was statistically significant (p < 0.05). B. Maintenance of dose intensity is displayed as the percent of planned chemotherapy delivered to patients. Patients treated with 100 mcg/kg TXA127 (A(1 -- 7)) received, on average, 88.7% (gemcitabine + platinum, n = 9) and 86.5% (gemcitabine only, n = 10) of the intended dose. In comparison, patients treated with placebo received 76.7% (gemcitabine + platinum, n = 8) and 67.6% (gemcitabine only, n = 10). Comparisons between placebo-treated and TXA127-treated patients yielded statistically significant (p < 0.05) differences in the 100 mcg/kg group. Number of patients differs due to three patients changing treatment from carboplatin to cisplatin mid-study. Reproduced from [51] with permission of Springer-Velag.
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placebo-controlled. Additionally, there was no observed difference in the maximal percent increase in platelet count and relative dose intensity in subjects treated with 300 mcg/kg/day versus placebo-controlled. No DLT was observed during the course of the study and no TXA127-related SAEs or deaths occurred. No bone marrow biopsies were taken during conduct of the clinical trials, and there were no TXA127 related side effects observed in organs outside of the blood.
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8.
Conclusion
A(1 -- 7) has a profound effect on the stimulation of the megakaryocytic lineage which in turn leads to a downstream effect on platelet formation and recovery. Administration of A (1 -- 7) has been shown to facilitate enhanced and accelerated platelet recovery in both preclinical and clinical evaluations of myelosuppressive therapies while presenting no observed safety concerns. 9.
Expert opinion
Convincing evidence of local RAS effect on cellular activity, tissue injury, and tissue regeneration has been accumulating over the past two decades. The RAS is highly conserved and the corroborative results between preclinical and clinical evaluations are consistent with the homology of A(1 -- 7) across mammalian species. The increase in sensitivity of immature stem and early hematopoietic progenitor cells to the proliferative and regenerative effects of A(1 -- 7), alone and in combination with currently marketed hematopoietic stimulants (e.g., filgrastim), offers therapeutic opportunities. Clinical data from patients receiving chemotherapy show a significant improvement in platelet recovery following low dose (£ 100 mcg/kg/day) A(1 -- 7) administration in comparison to filgrastim or placebo-treated patients [47,51]. A reduction in efficacy is observed when a higher dose (300 mcg/kg/day) of A(1 -- 7) is administered [51]. It is hypothesized that, in this dosing regimen, the drug has a significant effect of over-stimulating progenitor cells. The demonstrated sensitivity of hematopoietic progenitors to A(1 -- 7) stimulation [31,41,45] as well as their sensitivity to chemotherapy [12] suggest that there is a fine balance which must be maintained to allow for downstream platelet recovery without continued stimulation of the progenitors during chemotherapy administration. This observation can be extended to oncology patients receiving fractionated doses of radiation, with the repeated insult to bone marrow resulting in cell death of immature progenitors. It is the opinion of these authors
that lower doses of A(1 -- 7) warrant further evaluation as a chemotherapy-adjuvant as they provide the most compelling evidence for maintaining a balance of HSC stimulation and downstream platelet recovery. To date, no clinical evidence exists for the evaluation of A(1 -- 7) in patients treated for radiation exposure. Preclinical evidence suggests that a higher dose of A(1 -- 7) provided the most accelerated and sustained platelet recovery following a single dose of TBI [31]. It is hypothesized that this is due to the one-time delivery of TBI, in comparison to repeated delivery of chemotherapy cycles. As proliferating progenitors are able to differentiate to formed blood cells without receiving recurrent insult, extensive repopulation of hematopoietic cells by A(1 -- 7) serves to enhance recovery. Due to the limited number of patients that present with this type of injury, FDA approval of A(1 -- 7) as a medical countermeasure following radiation would be pursued by way of the Animal Rule (21 CFR 314.600) for the indication of mitigation of consequences of lethal radiation. It is the opinion of these authors that further investigation may include currently approved treatments (e.g., filgrastim) and given the demonstration of synergy [50], combined application may provide a significantly improved hematopoietic response to either drug alone. Current evidence provides the basis for continued research and evaluation of the benefit A(1 -- 7) treatment has in stimulating platelet recovery following myelosuppression. A(1 -- 7) therapy has the potential to make a significant contribution to healthcare by providing standalone and additive treatments to address unmet medical needs and life-threatening diseases by utilizing the regenerative arm of the RAS. Potential patient populations include cancer patients receiving antineoplastic or radiation therapy with myelosuppressive side effects, stem-cell transplant patients after myeloablative conditioning, patients with conditions resulting in ineffective myelopoiesis and apoptosis of hematopoietic progenitors, and individuals exposed to radiation.
Declaration of interest K Rodgers and G diZerega are inventors on patents covering this peptide and may have royalties associated. G diZerega is the owner and founder of US Biotest, the company that received the funding from Tarix Pharmaceuticals which funded much of the work described. K Peterson and H Maulhardt are employees of US Biotest.
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Affiliation Kathleen E Rodgers1, Kainoa J Peterson2, Holly A Maulhardt2 & Gere S diZerega†2,3 MD † Author for correspondence 1 University of Southern California, School of Pharmacy, 1985 Zonal Avenue, Los Angeles, CA 90089, USA 2 US Biotest, Inc., 231 Bonetti Drive, Suite 240, San Luis Obispo, CA 93401, USA 3 Professor, University of Southern California, Keck School of Medicine, Livingston Laboratory, 1321 N. Mission Road, Los Angeles, CA 90033, USA Tel: +1 805 595 1300; E-mail: [email protected]
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