Editorial For reprint orders, please contact [email protected]
Cancer therapy using oligonucleotide-based STAT3 inhibitors: will they deliver? “The research on STAT3 targeting for cancer therapy produced three most promising strategies to date: decoy oligodeoxynucleotides, antisense oligonucleotides and siRNAs.” Keywords: antisense oligonucleotides n aptamer n cancer immunotherapy n decoy n siRNA n STAT3 n TLR9
Transcription factors have long been considered as attractive targets for cancer therapy [1]. Targeting transcription factors as nodes of cell signaling networks provides the most efficient strategy to modulate target cell functions. From the beginning, this hypothesis was best exemplified by targeting STAT3. The interest in blocking STAT3 activity was originally related to its oncogenic role in human cancers, which often depend on STAT3 for survival and angiogenesis [2]. In contrast to cancer cells, the loss of STAT3 is not toxic for normal adult human cells or tissues [2]. Finally, a strong argument for STAT3 targeting is its unique function as a central regulator of inflammation and tumor immune tolerance [2]. Unfortunately, direct inhibition of STAT3 activity proved to be challenging for pharmacologic drugs. Small molecule inhibitors of Jak, which transmit signals from cytokine receptors to STATs, are intensely studied as potential cancer and autoimmune disease therapeutics [3]. Although several Jak inhibitors showed significant antitumor efficacy, some of them caused unexpected adverse effects in clinical trials [3]. These challenges emphasize the need for direct and specific targeting of STAT3 expression or function using alternative strategies, such as oligonucleotide-based therapeutics. Although pharmacokinetic properties of oligonucleotides require chemical modification and their targeted delivery still remains an issue, the ease of design and target specificity give these molecules an advantage over standard drugs. The research on STAT3 targeting for cancer therapy produced three most promising strategies to date: decoy oligodeoxynucleotides (dODN), antisense oligonucleotides (ASO) and siRNAs. Blocking of STAT3 binding to DNA, using synthetic dODNs as competitive inhibitors, was originally utilized for in vitro assays
identifying STAT3-dependent regulation of various genes [1]. Grandis and colleagues successfully developed this approach into clinically relevant strategy for therapy of head and neck cancers [4]. The STAT3 decoy used in the recent Phase 0 trial was an unmodified, double-stranded ODN with limited serum stability. Nonetheless, when injected intratumorally, STAT3 dODN produced remarkable effects reducing protein levels of two STAT3dependent targets without detectable toxicities. To enable systemic delivery of STAT3 decoy in future clinical trials, the group improved the serum half-life of the molecule. Instead of using nucleotide analogs that sometimes interfere with decoy binding to STAT3, the nucleolytic degradation of new molecules was prevented by closed-end, cyclic dODN design and partial phosphorothioation [4]. Broader application of STAT3 decoys will require better understanding of their biodistribution and improved cellspecific delivery, however, they have already shown feasibility as a therapeutic strategy for head and neck cancers. Therapeutic approaches preventing STAT3 binding to DNA are likely to also inactivate another closely related STAT family member, STAT1 [1]. Despite their structural similarities, STAT1 plays an opposite role in control of antitumor immune responses and is critical for successful immunosurveillance and antitumor immunity [2]. Thus, unlike Jak inhibitors, higher specificity of oligonucleotide STAT3 inhibitors may enhance their overall antitumor effects. The development of ASO, short singlestranded oligonucleotides that bind to mRNA of selected genes and turn off their expression, has over 30 years history [5]. Until recently, delivery of ASO required transfection or gene transfer and therefore was limiting their application. However, continued industry efforts resulted
10.4155/TDE.13.152 © 2014 Future Science Ltd
Ther. Deliv. (2014) 5(3), 239–242
Marcin Kortylewski Author for correspondence: Department of Cancer Immunotherapeutics & Tumor Immunology, Beckman Research Institute at City of Hope National Medical Center, 1500 East Duarte Road, Duarte, CA, 91010, USA Tel.: +1 626 256 4673 (ext. 64120) Fax: +1 626 471 3602 [email protected]
Sergey Nechaev Irell & Manella Graduate School of Biological Sciences, Beckman Research Institute at City of Hope National Medical Center, 1500 East Duarte Road, Duarte, CA, 91010, USA
ISSN 2041-5990
239
Editorial | Kortylewski & Nechaev in the development of clinically relevant ASO platforms [6]. The constrained ethyl/phosphorothiote modifications improve serum stability of these ASO and allow for direct uptake by certain cancer cells through an, as yet, unknown mechanism [6]. The STAT3-specific ASO is currently being tested in Phase II clinical trials in advanced lymphoma and B-cell lymphoma, and in recently initiated Phase I/ Ib study in metastatic liver cancer (as reported on [7]). These studies will establish safety and tolerability of systemic STAT3 ASO treatment, which are two major concerns for clinical use of ASO [5]. Other than gene knockdown, a recent report demonstrated that morpholino ASO can induce alternative STAT3 splicing, generating truncated STAT3b isoforms in vivo [8]. Although the effect of STAT3b expression is not identical to STAT3 knockdown, it was still shown to induce potent antitumor effects in several tumor models [8].
“The major advantage of STAT3 over other oncogenic targets clearly lies in the role of STAT3 as a unique and central immune checkpoint regulator.” The experience gained during the development of ASO methodology fueled rapid growth of RNAi applications [9,10]. Compared with ASO, the siRNAs provide a potentially more effective method of specific gene silencing using natural mechanisms. Antitumor effects of STAT3 siRNAs were demonstrated in several xenotransplanted tumor models in vivo [9]. Nonetheless, clinical application of siRNA technology is still complicated by poor cellular uptake of naked siRNA and challenges in tissue-specific delivery for siRNAs formulated in lipids or nanoparticles [9]. At the same time, advances in chemical modification of siRNA allow for the development of unformulated molecules for systemic delivery [10,11]. To enable cell-specific delivery STAT3 siRNA molecules can be conjugated to monoclonal antibody (mAb) or a receptor agonist. The first approach was used to target STAT3 siRNA to LewisY-expressing human cancer cells [12]. The mAbLewisY-STAT3 siRNA conjugates succeeded in cell-specific delivery of STAT3 siRNA but the efficacy of gene silencing was limited by poor endosomal escape of siRNA. The endosomal retention remains the major hurdle for 240
Ther. Deliv. (2014) 5(3)
receptor-mediated delivery of naked siRNA without complex and potentially toxic lipid or polymer formulations [11,13]. However, certain immune cells are known for transporting the content of endosomes to other cell compartments in the process of antigen cross-presentation [14]. Endosome trafficking is triggered by activation of intracellular immune receptors, such as TLR9. TLR9 recognizes single stranded oligodeoxynucleotides (ODN) with unmethylated CpG motif (CpG ODN), which are quickly internalized into endosomes likely through scavenger receptors [14,15]. This mechanism can be harnessed for targeted delivery of STAT3 siRNA into TLR9-positive dendritic cells, macrophages and B cells, all of which are critical for generation of antitumor immunity [16,17]. Synthetic combination of CpG ODN with STAT3 siRNA (CpG-STAT3 siRNA) produces a molecule combining enhanced internalization, typical for phosphorothioated ODNs, with cell-specific STAT3 silencing [15]. Efficient target-gene silencing results from TLR9-mediated release of the diced STAT3 siRNA from endosomes [16]. Our studies demonstrated that CpG-siRNAs silence various target genes in mouse and human TLR9-positive cells in vitro and in vivo, although, STAT3 targeting had the most potent antitumor effects [15,17]. CpG-STAT3 siRNA was able to unleash maximum potential of TLR9-induced immune responses against cancer cells as it released the immune ‘brake’ by STAT3 inhibition [16,18]. TLR9 is also commonly expressed by hematologic malignancies such as acute myeloid leukemia, B cell lymphoma and by certain solid tumors [17], providing an opportunity for direct targeting of cancer cells. Our recent study demonstrated that CpG-STAT3 siRNA had direct immunogenic effect on TLR9positive leukemia cells, which exposed tumorspecific antigens and allowed for CD8 T cellmediated tumor eradication [18]. The successful completion of toxicology studies should enable clinical testing of local CpG-STAT3 siRNA administration in blood cancers planned in the near future. Oligonucleotide-based therapeutics started to gain recognition for tackling STAT3 known for a long time as an ‘undruggable’ target in cancer therapy. A continuously growing repertoire of chemical modifications and new oligonucleotide designs, such as cyclic dODN or single-stranded siRNA [4,10], have already demonstrated the feasibility of generating future science group
Cancer therapy using oligonucleotide-based STAT3 inhibitors: will they deliver? oligonucleotides with clinically relevant pharmacokinetic properties. A major concern for clinical application of STAT3 ODN inhibitors remains with their safety, which has been also emphasized by recent discontinuation of several promising Jak inhibitors due to unexpected adverse effects in clinical trials. In spite of the exceptional target specificity of siRNA and ASO compared to small molecule drugs, this issue emphasizes the need for cell- or tissue-specific delivery of STAT3 inhibitors. It is likely that the growing collection of aptamersiRNA conjugates will substitute mAb-siRNAs on the path to cell-specific oligonucleotide therapeutics [11]. Aptamers are synthetic DNA or RNA molecules that recognize protein targets with specificity and affinity rivaling antibodies. The list of aptamer-siRNAs with confirmed efficacy began with the pioneering PSMA apt-siRNA molecule specifically targeting oncogenes in prostate cancer cells [19] and was later followed by T cell-specific CD4 aptand gp120apt-siRNAs inhibiting survivin and HIV proteins, respectively [11]. Lately, Rossi and colleagues presented an innovative design of dual function BAFFR apt-STAT3 siRNA [20]. The molecule was shown to inhibit B cell lymphoma proliferation through aptamer-mediated neutralization of the mitogenic receptor and concomitant intracellular delivery of STAT3 siRNA [21]. Similarly to mAb-siRNA, aptamersiRNAs are limited by the rate of the siRNA release from endosomes. It remains to be tested whether activation of endosomal immune receptors, as in case of CpG-siRNA [15], could enhance efficacy of aptamer-STAT3 siRNAs. The recent advances in the development of oligonucleotide-based STAT3 inhibitiors for cancer therapy highlighted both pitfalls and
| Editorial
potentials of this concept. The major advantage of STAT3 over other oncogenic targets clearly lies in the role of STAT3 as a unique and central immune checkpoint regulator. Maximization of therapeutic gain may critically depend on targeted delivery of STAT3 inhibitors into appropriate immune cell populations. The preclinical data suggest that locally administered ODN STAT3 inhibitors succeed in engaging immune cells to generate systemic antitumor immune responses [16,17]. In addition, they seem to synergize very well with standard anticancer therapies, such as radiotherapy [21]. Therefore, cancer immunotherapy seems to be feasible and a very attractive avenue for clinical application of currently available and future STAT3 targeting ODN. Disclaimer The content of this editorial is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.
Financial & competing interests disclosure The authors’ work was supported in part by the NCI/NIH award (R01CA155367), Department of Defense Prostate Cancer Program Grant (W81XWH-12–1–0132) and V Foundation Translational Research Grant (M Kortylewski). M Kortylewski is a co-inventor on the patent US07951374 and a pending patent application US20120065125. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this manuscript.
References 1
Darnell JE Jr. Transcription factors as targets for cancer therapy. Nat. Rev. Cancer 2(10), 740–749 (2002).
2
Yu H, Pardoll D, Jove R. STATs in cancer inflammation and immunity: a leading role for STAT3. Nat. Rev. Cancer 9(11), 798–809 (2009).
5
Kole R, Krainer AR, Altman S. RNA therapeutics: beyond RNA interference and antisense oligonucleotides. Nat. Rev. Drug Discov. 11(2), 125–140 (2012).
3
Kontzias A, Kotlyar A, Laurence A, Changelian P, O’Shea JJ. Jakinibs: a new class of kinase inhibitors in cancer and autoimmune disease. Curr. Opin. Pharmacol. 12(4), 464–470 (2012).
6
4
Sen M, Thomas SM, Kim S et al. First-inhuman trial of a STAT3 decoy oligonucleotide
Burel SA, Han SR, Lee HS et al. Preclinical evaluation of the toxicological effects of a novel constrained ethyl modified antisense compound targeting signal transducer and activator of transcription 3 in mice and cynomolgus monkeys. Nucleic Acid Ther. 23(3), 213–227 (2013).
future science group
in head and neck tumors: implications for cancer therapy. Cancer Discov. 2(8), 694–705 (2012).
www.future-science.com
7
ClinicalTrials Database. www.clinicaltrials.gov
8
Zammarchi F, De Stanchina E, Bournazou E et al. Antitumorigenic potential of STAT3 alternative splicing modulation. Proc. Natl Acad. Sci. USA 108(43), 17779–17784 (2011).
9
Rettig GR, Behlke MA. Progress toward in vivo use of siRNAs-II. Mol. Ther. 20(3), 483–512 (2012).
10 Peschansky VJ, Liang Z, Wahlestedt C. RNAi
joins the ‘singles club’. Mol. Ther. 20(11), 2010–2011 (2012).
241
Editorial | Kortylewski & Nechaev 11 Thiel KW, Giangrande Ph. Intracellular
delivery of RNA-based therapeutics using aptamers. Ther. Deliv. 1(6), 849–861 (2010). 12 Ma Y, Kowolik CM, Swiderski PM et al.
Humanized Lewis-Y specific antibody based delivery of STAT3 siRNA. ACS Chem. Biol. 6(9), 962–970 (2011). 13 Zhou J, Bobbin ML, Burnett JC, Rossi JJ.
Current progress of RNA aptamer-based therapeutics. Front. Genet. 3, 234 (2012). 14 Latz E, Schoenemeyer A, Visintin A et al.
TLR9 signals after translocating from the ER to CpG DNA in the lysosome. Nat. Immunol. 5(2), 190–198 (2004). 15 Nechaev S, Gao C, Moreira D et al.
Intracellular processing of
242
immunostimulatory CpG-siRNA: Toll-like receptor 9 facilitates siRNA dicing and endosomal escape. J. Control. Release 170, 307–315 (2013). 16 Kortylewski M, Swiderski P, Herrmann A
et al. In vivo delivery of siRNA to immune cells by conjugation to a TLR9 agonist enhances antitumor immune responses. Nat. Biotechnol. 27(10), 925–932 (2009). 17 Zhang Q, Hossain DM, Nechaev S et al.
TLR9-mediated siRNA delivery for targeting of normal and malignant human hematopoietic cells in vivo. Blood 121(8), 1304–1315 (2013). 18 Hossain DM, Dos Santos C, Zhang Q et al.
Leukemia cell-targeted STAT3 silencing and TLR9-triggering generate systemic
Ther. Deliv. (2014) 5(3)
antitumor immunity. Blood 123(1) 15–25, (2013). 19 Mcnamara JO 2nd, Andrechek ER, Wang Y
et al. Cell type-specific delivery of siRNAs with aptamer-siRNA chimeras. Nat. Biotechnol. 24(8), 1005–1015 (2006). 20 Zhou J, Tiemann K, Chomchan P et al. Dual
functional BAFF receptor aptamers inhibit ligand-induced proliferation and deliver siRNAs to NHL cells. Nucleic Acids Res. 41(7), 4266–4283 (2013). 21 Gao C, Kozlowska A, Nechaev S et al. TLR9
signaling in the tumor microenvironment initiates cancer recurrence after radiation therapy. Cancer Res. 73(24), 7211–7221 (2013).
future science group
Cancer therapy using oligonucleotide-based STAT3 inhibitors: will they deliver? “The research on STAT3 targeting for cancer therapy produced three most promising strategies to date: decoy oligodeoxynucleotides, antisense oligonucleotides and siRNAs.” Keywords: antisense oligonucleotides n aptamer n cancer immunotherapy n decoy n siRNA n STAT3 n TLR9
Transcription factors have long been considered as attractive targets for cancer therapy [1]. Targeting transcription factors as nodes of cell signaling networks provides the most efficient strategy to modulate target cell functions. From the beginning, this hypothesis was best exemplified by targeting STAT3. The interest in blocking STAT3 activity was originally related to its oncogenic role in human cancers, which often depend on STAT3 for survival and angiogenesis [2]. In contrast to cancer cells, the loss of STAT3 is not toxic for normal adult human cells or tissues [2]. Finally, a strong argument for STAT3 targeting is its unique function as a central regulator of inflammation and tumor immune tolerance [2]. Unfortunately, direct inhibition of STAT3 activity proved to be challenging for pharmacologic drugs. Small molecule inhibitors of Jak, which transmit signals from cytokine receptors to STATs, are intensely studied as potential cancer and autoimmune disease therapeutics [3]. Although several Jak inhibitors showed significant antitumor efficacy, some of them caused unexpected adverse effects in clinical trials [3]. These challenges emphasize the need for direct and specific targeting of STAT3 expression or function using alternative strategies, such as oligonucleotide-based therapeutics. Although pharmacokinetic properties of oligonucleotides require chemical modification and their targeted delivery still remains an issue, the ease of design and target specificity give these molecules an advantage over standard drugs. The research on STAT3 targeting for cancer therapy produced three most promising strategies to date: decoy oligodeoxynucleotides (dODN), antisense oligonucleotides (ASO) and siRNAs. Blocking of STAT3 binding to DNA, using synthetic dODNs as competitive inhibitors, was originally utilized for in vitro assays
identifying STAT3-dependent regulation of various genes [1]. Grandis and colleagues successfully developed this approach into clinically relevant strategy for therapy of head and neck cancers [4]. The STAT3 decoy used in the recent Phase 0 trial was an unmodified, double-stranded ODN with limited serum stability. Nonetheless, when injected intratumorally, STAT3 dODN produced remarkable effects reducing protein levels of two STAT3dependent targets without detectable toxicities. To enable systemic delivery of STAT3 decoy in future clinical trials, the group improved the serum half-life of the molecule. Instead of using nucleotide analogs that sometimes interfere with decoy binding to STAT3, the nucleolytic degradation of new molecules was prevented by closed-end, cyclic dODN design and partial phosphorothioation [4]. Broader application of STAT3 decoys will require better understanding of their biodistribution and improved cellspecific delivery, however, they have already shown feasibility as a therapeutic strategy for head and neck cancers. Therapeutic approaches preventing STAT3 binding to DNA are likely to also inactivate another closely related STAT family member, STAT1 [1]. Despite their structural similarities, STAT1 plays an opposite role in control of antitumor immune responses and is critical for successful immunosurveillance and antitumor immunity [2]. Thus, unlike Jak inhibitors, higher specificity of oligonucleotide STAT3 inhibitors may enhance their overall antitumor effects. The development of ASO, short singlestranded oligonucleotides that bind to mRNA of selected genes and turn off their expression, has over 30 years history [5]. Until recently, delivery of ASO required transfection or gene transfer and therefore was limiting their application. However, continued industry efforts resulted
10.4155/TDE.13.152 © 2014 Future Science Ltd
Ther. Deliv. (2014) 5(3), 239–242
Marcin Kortylewski Author for correspondence: Department of Cancer Immunotherapeutics & Tumor Immunology, Beckman Research Institute at City of Hope National Medical Center, 1500 East Duarte Road, Duarte, CA, 91010, USA Tel.: +1 626 256 4673 (ext. 64120) Fax: +1 626 471 3602 [email protected]
Sergey Nechaev Irell & Manella Graduate School of Biological Sciences, Beckman Research Institute at City of Hope National Medical Center, 1500 East Duarte Road, Duarte, CA, 91010, USA
ISSN 2041-5990
239
Editorial | Kortylewski & Nechaev in the development of clinically relevant ASO platforms [6]. The constrained ethyl/phosphorothiote modifications improve serum stability of these ASO and allow for direct uptake by certain cancer cells through an, as yet, unknown mechanism [6]. The STAT3-specific ASO is currently being tested in Phase II clinical trials in advanced lymphoma and B-cell lymphoma, and in recently initiated Phase I/ Ib study in metastatic liver cancer (as reported on [7]). These studies will establish safety and tolerability of systemic STAT3 ASO treatment, which are two major concerns for clinical use of ASO [5]. Other than gene knockdown, a recent report demonstrated that morpholino ASO can induce alternative STAT3 splicing, generating truncated STAT3b isoforms in vivo [8]. Although the effect of STAT3b expression is not identical to STAT3 knockdown, it was still shown to induce potent antitumor effects in several tumor models [8].
“The major advantage of STAT3 over other oncogenic targets clearly lies in the role of STAT3 as a unique and central immune checkpoint regulator.” The experience gained during the development of ASO methodology fueled rapid growth of RNAi applications [9,10]. Compared with ASO, the siRNAs provide a potentially more effective method of specific gene silencing using natural mechanisms. Antitumor effects of STAT3 siRNAs were demonstrated in several xenotransplanted tumor models in vivo [9]. Nonetheless, clinical application of siRNA technology is still complicated by poor cellular uptake of naked siRNA and challenges in tissue-specific delivery for siRNAs formulated in lipids or nanoparticles [9]. At the same time, advances in chemical modification of siRNA allow for the development of unformulated molecules for systemic delivery [10,11]. To enable cell-specific delivery STAT3 siRNA molecules can be conjugated to monoclonal antibody (mAb) or a receptor agonist. The first approach was used to target STAT3 siRNA to LewisY-expressing human cancer cells [12]. The mAbLewisY-STAT3 siRNA conjugates succeeded in cell-specific delivery of STAT3 siRNA but the efficacy of gene silencing was limited by poor endosomal escape of siRNA. The endosomal retention remains the major hurdle for 240
Ther. Deliv. (2014) 5(3)
receptor-mediated delivery of naked siRNA without complex and potentially toxic lipid or polymer formulations [11,13]. However, certain immune cells are known for transporting the content of endosomes to other cell compartments in the process of antigen cross-presentation [14]. Endosome trafficking is triggered by activation of intracellular immune receptors, such as TLR9. TLR9 recognizes single stranded oligodeoxynucleotides (ODN) with unmethylated CpG motif (CpG ODN), which are quickly internalized into endosomes likely through scavenger receptors [14,15]. This mechanism can be harnessed for targeted delivery of STAT3 siRNA into TLR9-positive dendritic cells, macrophages and B cells, all of which are critical for generation of antitumor immunity [16,17]. Synthetic combination of CpG ODN with STAT3 siRNA (CpG-STAT3 siRNA) produces a molecule combining enhanced internalization, typical for phosphorothioated ODNs, with cell-specific STAT3 silencing [15]. Efficient target-gene silencing results from TLR9-mediated release of the diced STAT3 siRNA from endosomes [16]. Our studies demonstrated that CpG-siRNAs silence various target genes in mouse and human TLR9-positive cells in vitro and in vivo, although, STAT3 targeting had the most potent antitumor effects [15,17]. CpG-STAT3 siRNA was able to unleash maximum potential of TLR9-induced immune responses against cancer cells as it released the immune ‘brake’ by STAT3 inhibition [16,18]. TLR9 is also commonly expressed by hematologic malignancies such as acute myeloid leukemia, B cell lymphoma and by certain solid tumors [17], providing an opportunity for direct targeting of cancer cells. Our recent study demonstrated that CpG-STAT3 siRNA had direct immunogenic effect on TLR9positive leukemia cells, which exposed tumorspecific antigens and allowed for CD8 T cellmediated tumor eradication [18]. The successful completion of toxicology studies should enable clinical testing of local CpG-STAT3 siRNA administration in blood cancers planned in the near future. Oligonucleotide-based therapeutics started to gain recognition for tackling STAT3 known for a long time as an ‘undruggable’ target in cancer therapy. A continuously growing repertoire of chemical modifications and new oligonucleotide designs, such as cyclic dODN or single-stranded siRNA [4,10], have already demonstrated the feasibility of generating future science group
Cancer therapy using oligonucleotide-based STAT3 inhibitors: will they deliver? oligonucleotides with clinically relevant pharmacokinetic properties. A major concern for clinical application of STAT3 ODN inhibitors remains with their safety, which has been also emphasized by recent discontinuation of several promising Jak inhibitors due to unexpected adverse effects in clinical trials. In spite of the exceptional target specificity of siRNA and ASO compared to small molecule drugs, this issue emphasizes the need for cell- or tissue-specific delivery of STAT3 inhibitors. It is likely that the growing collection of aptamersiRNA conjugates will substitute mAb-siRNAs on the path to cell-specific oligonucleotide therapeutics [11]. Aptamers are synthetic DNA or RNA molecules that recognize protein targets with specificity and affinity rivaling antibodies. The list of aptamer-siRNAs with confirmed efficacy began with the pioneering PSMA apt-siRNA molecule specifically targeting oncogenes in prostate cancer cells [19] and was later followed by T cell-specific CD4 aptand gp120apt-siRNAs inhibiting survivin and HIV proteins, respectively [11]. Lately, Rossi and colleagues presented an innovative design of dual function BAFFR apt-STAT3 siRNA [20]. The molecule was shown to inhibit B cell lymphoma proliferation through aptamer-mediated neutralization of the mitogenic receptor and concomitant intracellular delivery of STAT3 siRNA [21]. Similarly to mAb-siRNA, aptamersiRNAs are limited by the rate of the siRNA release from endosomes. It remains to be tested whether activation of endosomal immune receptors, as in case of CpG-siRNA [15], could enhance efficacy of aptamer-STAT3 siRNAs. The recent advances in the development of oligonucleotide-based STAT3 inhibitiors for cancer therapy highlighted both pitfalls and
| Editorial
potentials of this concept. The major advantage of STAT3 over other oncogenic targets clearly lies in the role of STAT3 as a unique and central immune checkpoint regulator. Maximization of therapeutic gain may critically depend on targeted delivery of STAT3 inhibitors into appropriate immune cell populations. The preclinical data suggest that locally administered ODN STAT3 inhibitors succeed in engaging immune cells to generate systemic antitumor immune responses [16,17]. In addition, they seem to synergize very well with standard anticancer therapies, such as radiotherapy [21]. Therefore, cancer immunotherapy seems to be feasible and a very attractive avenue for clinical application of currently available and future STAT3 targeting ODN. Disclaimer The content of this editorial is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.
Financial & competing interests disclosure The authors’ work was supported in part by the NCI/NIH award (R01CA155367), Department of Defense Prostate Cancer Program Grant (W81XWH-12–1–0132) and V Foundation Translational Research Grant (M Kortylewski). M Kortylewski is a co-inventor on the patent US07951374 and a pending patent application US20120065125. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this manuscript.
References 1
Darnell JE Jr. Transcription factors as targets for cancer therapy. Nat. Rev. Cancer 2(10), 740–749 (2002).
2
Yu H, Pardoll D, Jove R. STATs in cancer inflammation and immunity: a leading role for STAT3. Nat. Rev. Cancer 9(11), 798–809 (2009).
5
Kole R, Krainer AR, Altman S. RNA therapeutics: beyond RNA interference and antisense oligonucleotides. Nat. Rev. Drug Discov. 11(2), 125–140 (2012).
3
Kontzias A, Kotlyar A, Laurence A, Changelian P, O’Shea JJ. Jakinibs: a new class of kinase inhibitors in cancer and autoimmune disease. Curr. Opin. Pharmacol. 12(4), 464–470 (2012).
6
4
Sen M, Thomas SM, Kim S et al. First-inhuman trial of a STAT3 decoy oligonucleotide
Burel SA, Han SR, Lee HS et al. Preclinical evaluation of the toxicological effects of a novel constrained ethyl modified antisense compound targeting signal transducer and activator of transcription 3 in mice and cynomolgus monkeys. Nucleic Acid Ther. 23(3), 213–227 (2013).
future science group
in head and neck tumors: implications for cancer therapy. Cancer Discov. 2(8), 694–705 (2012).
www.future-science.com
7
ClinicalTrials Database. www.clinicaltrials.gov
8
Zammarchi F, De Stanchina E, Bournazou E et al. Antitumorigenic potential of STAT3 alternative splicing modulation. Proc. Natl Acad. Sci. USA 108(43), 17779–17784 (2011).
9
Rettig GR, Behlke MA. Progress toward in vivo use of siRNAs-II. Mol. Ther. 20(3), 483–512 (2012).
10 Peschansky VJ, Liang Z, Wahlestedt C. RNAi
joins the ‘singles club’. Mol. Ther. 20(11), 2010–2011 (2012).
241
Editorial | Kortylewski & Nechaev 11 Thiel KW, Giangrande Ph. Intracellular
delivery of RNA-based therapeutics using aptamers. Ther. Deliv. 1(6), 849–861 (2010). 12 Ma Y, Kowolik CM, Swiderski PM et al.
Humanized Lewis-Y specific antibody based delivery of STAT3 siRNA. ACS Chem. Biol. 6(9), 962–970 (2011). 13 Zhou J, Bobbin ML, Burnett JC, Rossi JJ.
Current progress of RNA aptamer-based therapeutics. Front. Genet. 3, 234 (2012). 14 Latz E, Schoenemeyer A, Visintin A et al.
TLR9 signals after translocating from the ER to CpG DNA in the lysosome. Nat. Immunol. 5(2), 190–198 (2004). 15 Nechaev S, Gao C, Moreira D et al.
Intracellular processing of
242
immunostimulatory CpG-siRNA: Toll-like receptor 9 facilitates siRNA dicing and endosomal escape. J. Control. Release 170, 307–315 (2013). 16 Kortylewski M, Swiderski P, Herrmann A
et al. In vivo delivery of siRNA to immune cells by conjugation to a TLR9 agonist enhances antitumor immune responses. Nat. Biotechnol. 27(10), 925–932 (2009). 17 Zhang Q, Hossain DM, Nechaev S et al.
TLR9-mediated siRNA delivery for targeting of normal and malignant human hematopoietic cells in vivo. Blood 121(8), 1304–1315 (2013). 18 Hossain DM, Dos Santos C, Zhang Q et al.
Leukemia cell-targeted STAT3 silencing and TLR9-triggering generate systemic
Ther. Deliv. (2014) 5(3)
antitumor immunity. Blood 123(1) 15–25, (2013). 19 Mcnamara JO 2nd, Andrechek ER, Wang Y
et al. Cell type-specific delivery of siRNAs with aptamer-siRNA chimeras. Nat. Biotechnol. 24(8), 1005–1015 (2006). 20 Zhou J, Tiemann K, Chomchan P et al. Dual
functional BAFF receptor aptamers inhibit ligand-induced proliferation and deliver siRNAs to NHL cells. Nucleic Acids Res. 41(7), 4266–4283 (2013). 21 Gao C, Kozlowska A, Nechaev S et al. TLR9
signaling in the tumor microenvironment initiates cancer recurrence after radiation therapy. Cancer Res. 73(24), 7211–7221 (2013).
future science group
