Chapter 1 Novel Insights/Translational Implication from the Emerging Biology of Melanoma Antoni Ribas Abstract Melanoma is a main example of how applying advances in basic biology, pharmacology, and molecular diagnostics into the clinic results in unprecedented benefits to patients. After many years of lack of advances in the treatment of patients with metastatic melanoma, the advent of new therapies that block driver oncogenic signaling and modulate immune responses to cancer provided the first studies with a positive impact in overall survival (OS) of patients with advanced melanoma. The pace of progress in the treatment of this disease has been greatly accelerated by these initial breakthroughs, and it continues with new generation agents and combinatorial approaches. Key words BRAF, CTLA4, PD-1, Immunotherapy, Targeted therapy
1
Introduction In a short period of time melanoma has become a poster child of how science can be translated into better patient care. This is a big change in this disease where treatment for advanced disease had shown very little progress since the advent of modern oncology. In fact, until 2010 there had never been a therapy that had demonstrated improvement in overall survival in patients with metastatic melanoma. The lack of insight into the biology of this cancer and how it interacts with the host had precluded advances in treatments. Nonspecific genotoxins like chemotherapy and radiotherapy had provided marginal benefits, with occasional patients having tumor responses without an ability to understand what guided response or resistance. Melanoma has a remarkable ability to correct DNA damage by chemotherapy, which is likely endowed from its cell of origin, the melanocyte, which is a pigmented skin cell designed by Nature to withstand DNA damage from ultraviolet light and protect the surrounding skin cells. Furthermore, a series of immunotherapy strategies had repeatedly provided evidence of
Magdalena Thurin and Francesco M. Marincola (eds.), Molecular Diagnostics for Melanoma: Methods and Protocols, Methods in Molecular Biology, vol. 1102, DOI 10.1007/978-1-62703-727-3_1, © Springer Science+Business Media New York 2014
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benefit in occasional patients, with a very low frequency of responses that were highly relevant for those patients with benefit since these tended to be very durable, many times lasting years. However, these immunotherapies were far from desirable since multiple active vaccination approaches had proven to have very low immunological potency, and nonspecific immune stimulating such as the cytokines interleukin-2 (IL-2) or interferon-alpha (IFN-α) had to be administered at the highest (barely tolerated) doses to result in a low frequency of clinical benefit. The big clinical improvements provided by the recently widely available therapies for advanced melanoma are based on a refined understanding of oncogenic signaling pathways in cancer cells and how immune responses to cancer are regulated. Therapies based on inhibiting mutated BRAF signaling and blocking negative immune checkpoint regulatory proteins have provided the first clinical trials demonstrating improvements in overall survival in patients with metastatic melanoma.
2
Targeted Therapies Blocking Melanoma Driver Oncogenic Signaling Insights into the genetic alterations in melanoma allowed understanding what gives this cancer the oncogenic signals to proliferate. Over 70 % of skin and mucosal melanomas have activating mutations in the receptor tyrosine kinase (RTK) KIT, or the oncogenic proteins NRAS or BRAF [1, 2]. These are generally mutually exclusive mutations that all result in constitutive oncogenic signaling through the mitogenactivated protein kinase (MAPK) pathway governing cell proliferation and avoidance of apoptosis [1, 3]. The great majority of uveal melanomas have a distinct set of driver oncogenic mutations in GNAQ and GNA11 [4, 5]. Together with the near universal alterations in cell cycle control, they provide the key oncogenic events to transform normal melanocytes into cancer cells [3]. These mutations are not randomly distributed among melanomas. As noted for the distinct mutations in uveal melanoma, different melanoma subtypes likely with different pathogenic events have a different set of driver oncogenic mutations: KIT mutations are more common in mucosal, acral, and lentiginous melanomas, NRAS mutations are more common in cutaneous melanomas in older adults, and BRAF mutations are more common in melanomas arising from intermittently sun exposed skin in younger adults [1, 6, 7]. The biological significance of the affected proteins and signaling pathways, their mutual exclusivity in the great majority of cases and their nonrandom distribution in distinct clinicopathological subtypes of melanoma provide clues to their importance and potential for therapeutic targeting. The greatest therapeutic advance has been achieved in patients with mutations in BRAFV600, which is present in approximately
New Treatments for Melanoma
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50 % of patients with metastatic melanoma. Small molecule inhibitors that displace ATP in the mutated BRAFV600 threonine-serine kinase have been developed and demonstrated to have unprecedently high response rates [8]. Clinical studies with the type I (which bind to the activation state of the kinase) RAF kinase inhibitors vemurafenib (formerly PLX4032) and dabrafenib (formerly GSK2118436) demonstrated objective tumor responses in excess of 50 % of patients by strict RECIST criteria, with up to 85 % of patients having some kind of tumor response and a very low frequency of innate resistance [9–13]. These two BRAF inhibitors have demonstrated improvement in progression free survival (PFS) against the old standard chemotherapy agent dacarbazine [10, 13], while vemurafenib has also demonstrated improvident in overall survival (OS) in a randomized clinical trial [10]. The high specificity of these agents for the mutated BRAF kinase allows a wide therapeutic window, with most toxicities being manageable with dose adjustments or interruptions. The most common grade 3 or 4 toxicity with these agents is the development of cutaneous squamous cell carcinomas (cuSCC), most of them of keratoacanthoma (KA) subtype. These toxicities are usually easily managed by simple surgical excision and do not preclude continued therapy. The pathobiology of their appearance has been elucidated through the phenomenon of paradoxical MAPK activation [14, 15], where cells with preexisting upstream mutations, most frequently in HRAS and KRAS, are transactivated to proliferate through MAPK signaling [16, 17]. Despite the initial tumor responses and early benefit in PFS and OS, the majority of patients demonstrate disease progression frequently within months. The mechanisms how BRAFV600 mutant metastatic melanoma develops acquired resistance to BRAF inhibitors are different from the prevalent gatekeeper mutations with other ATP-competitive small molecule targeted inhibitor therapies for cancer. In fact, melanomas seem to develop a wide array of mechanisms to overcome BRAF inhibition. These mechanisms either reactivate the MAPK pathway through secondary NRAS mutations, BRAF amplification, BRAF truncation, or MEK mutations, or provide alternative survival signaling by activating RTKs and downstream signaling through the PI3K/AKT pathway [18–26]. Furthermore, inhibiting MAPK signaling immediately downstream of mutated BRAF can be achieved with MEK inhibitors, which preclinical studies had shown to have preferential activity in the setting of the BRAFV6000 mutations [27]. In patients who had not previously received BRAF inhibitor-based therapy, a randomized clinical trial demonstrated that the MEK inhibitor trametinib (GSK1120211) improved both PFS and OS over dacarbazine [28], providing another active agent for these patients. However, the antitumor activity is lower and the toxicities are higher with single agent MEK inhibitors compared to single agent BRAF inhibitors.
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The rapid phase of development of targeted treatments for BRAF mutant metastatic melanoma has resulted in the testing of combined therapy with BRAF and MEK inhibitors. This combination has the theoretical ability to provide improved initial antitumor activity resultant from double inhibition of oncogenic signaling through the MAPK pathway [29], as well and providing longer duration of responses by preventing or treating acquired resistance [30]. At the same time, the combination of BRAF and MEK inhibitors has the potential to also decrease toxicities resultant from paradoxical MAPK activation, since the MEK inhibitor would block the BRAF inhibitor-induced MAPK activation in cells that are wild type for BRAF and have strong upstream signaling [16]. Early clinical testing of this combined therapy is highly encouraging [31], and formal testing of improvements in PFS and OS over single agent BRAF inhibitor therapy is ongoing.
3
Immune Modulation Overcoming Negative Regulatory Pathways Therapies that attempt to activate a cytotoxic T lymphocyte (CTL) immune response against chronically expressed self-antigens, as are most tumor antigens, are negatively regulated by T cell-intrinsic negative costimulatory signaling known as immune checkpoints [32]. The recent advances in immunotherapy for melanoma have been based on the clinical application of antibodies blocking these immune checkpoints, in particular the cytotoxic T lymphocyteassociated antigen-4 (CTLA-4) and the programmed death receptor 1 (PD-1) [33]. These two negative immune regulatory receptors have very different biological roles, which may allow understanding their effects in the clinic [33, 34]. CTLA-4 is a negative costimulatory receptor that competes with CD28 for costimulatory signaling through CD80/CD86 upon T cell activation. The blockade of CTLA-4 releases negative regulation upon T cell activation in secondary lymphoid organs, and these T cells then need to circulate through the periphery and recognize cells expressing their cognate targets. Therefore, CTLA-4 blockade is relatively nonspecific for antitumor T cells and its clinical effects are likely to be delayed. On the contrary, PD-1 is expressed by chronically antigen-exposed T cells and it is engaged primarily in peripheral tissues upon recognition of the PD ligand 1 (PD-L1), which is an activation-induced ligand expressed in inflamed tissues and cancers. Therefore, PD-1 inhibits the final effector mechanism of CTLs that have already recognized antigen and have been negatively regulated by PD-L1 in the periphery. This predicts a more specific activation of T cells to cancer and chronic infections, while it should also provide more rapid antitumor activity.
New Treatments for Melanoma
7
These preclinical predictions correlate well with the clinical effects of CTLA-4 and PD-1/PD-L1 blocking antibodies. Two CTLA-4 blocking antibodies have been extensively tested in the clinic, ipilimumab (formerly MDX010) and tremelimumab (formerly CP-675,206) [35]. They both provided a low but reproducible level of antitumor activity in patients with metastatic melanoma, with the main feature of providing very long duration of tumor responses in roughly 10 % of treated patients, with responses lasting years [36–39]. Ipilimumab has been demonstrated to improve OS in two randomized clinical trials, one against a gp100 peptide vaccine and another in combination with dacarbazine against single agent dacarbazine [40, 41], leading to its regulatory approval in several countries. Tremelimumab was tested in a randomized clinical trial against dacarbazine or temozolomide but failed to demonstrate a statistically significant improvement in OS, with the major reason being a relatively high rate of use of ipilimumab in patients in the control chemotherapy arm [42]. These two agents are limited by their low frequency of tumor responses, their delayed tumor responses, and their frequency of 15–20 % of serious inflammatory and autoimmune toxicities, in particular colitis and endocrinopathies. Early clinical testing of PD-1 and PD-L1 blocking antibodies suggests that they may have higher antitumor activity, more rapid tumor responses, and a lower frequency of toxicities. There are several PD-1 axis inhibitors in current clinical testing, with the most advanced programs using the anti-PD-1 nivolumab (formerly MDX1106) and the anti-PD-L1 MDX1105 [33]. Both of these agents have provided evidence of objective tumor responses in 20–30 % of patients with metastatic melanoma in phase 1 testing, with the majority being durable responses [43–45]. These encouraging results are being pursued in larger series and randomized clinical trials. Furthermore, the ability to detect PD-L1 in tumors may allow selecting patients whose immune response to melanoma is being blocked through the PD-1/PD-L1 interaction, with the potential for enriching for patients who are more likely to respond to these antibodies.
4
Conclusions The rapid advancement of new therapies active in patients with metastatic melanoma has been achieved thanks to the clinical translation of preclinical scientific knowledge. These advances are in sharp contrast with the lack of significant progress when attempting to treat melanoma with nonspecific agents, in particular chemotherapy. The ability to understand mechanisms of response and resistance to BRAF inhibitor-based therapies and immune checkpoint
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blockade at a molecular level, and the rapid advancement of the knowledge brought through by the scientific community’s renewed interest in melanoma, predicts that the pace of improvements in further developing effective therapies for this disease will continue in the near future. References 1. Curtin JA, Fridlyand J, Kageshita T, Patel HN, Busam KJ, Kutzner H et al (2005) Distinct sets of genetic alterations in melanoma. N Engl J Med 353:2135–2147 2. Curtin JA, Busam K, Pinkel D, Bastian BC (2006) Somatic activation of KIT in distinct subtypes of melanoma. J Clin Oncol 24:4340–4346 3. Gray-Schopfer V, Wellbrock C, Marais R (2007) Melanoma biology and new targeted therapy. Nature 445:851–857 4. Van Raamsdonk CD, Bezrookove V, Green G, Bauer J, Gaugler L, O’Brien JM et al (2009) Frequent somatic mutations of GNAQ in uveal melanoma and blue naevi. Nature 457: 599–602 5. Van Raamsdonk CD, Griewank KG, Crosby MB, Garrido MC, Vemula S, Wiesner T et al (2010) Mutations in GNA11 in uveal melanoma. N Engl J Med 363:2191–2199 6. Viros A, Fridlyand J, Bauer J, Lasithiotakis K, Garbe C, Pinkel D et al (2008) Improving melanoma classification by integrating genetic and morphologic features. PLoS Med 5:e120 7. Long GV, Menzies AM, Nagrial AM, Haydu LE, Hamilton AL, Mann GJ et al (2011) Prognostic and clinicopathologic associations of oncogenic BRAF in metastatic melanoma. J Clin Oncol 29:1239–1246 8. Ribas A, Flaherty KT (2011) BRAF targeted therapy changes the treatment paradigm in melanoma. Nat Rev Clin Oncol 8:426–433 9. Flaherty KT, Puzanov I, Kim KB, Ribas A, McArthur GA, Sosman JA et al (2010) Inhibition of mutated, activated BRAF in metastatic melanoma. N Engl J Med 363: 809–819 10. Chapman PB, Hauschild A, Robert C, Haanen JB, Ascierto P, Larkin J et al (2011) Improved survival with vemurafenib in melanoma with BRAF V600E mutation. N Engl J Med 364:2507–2516 11. Sosman JA, Kim KB, Schuchter L, Gonzalez R, Pavlick AC, Weber JS et al (2012) Survival in BRAF V600-mutant advanced melanoma treated with vemurafenib. N Engl J Med 366:707–714 12. Falchook GS, Long GV, Kurzrock R, Kim KB, Arkenau TH, Brown MP et al (2012)
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Dabrafenib in patients with melanoma, untreated brain metastases, and other solid tumours: a phase 1 dose-escalation trial. Lancet 379:1893–1901 Hauschild A, Grob JJ, Demidov LV, Jouary T, Gutzmer R, Millward M et al (2012) Dabrafenib in BRAF-mutated metastatic melanoma: a multicentre, open-label, phase 3 randomised controlled trial. Lancet 380:358–365 Heidorn SJ, Milagre C, Whittaker S, Nourry A, Niculescu-Duvas I, Dhomen N et al (2010) Kinase-dead BRAF and oncogenic RAS cooperate to drive tumor progression through CRAF. Cell 140:209–221 Poulikakos PI, Zhang C, Bollag G, Shokat KM, Rosen N (2010) RAF inhibitors transactivate RAF dimers and ERK signalling in cells with wild-type BRAF. Nature 464:427–430 Su F, Viros A, Milagre C, Trunzer K, Bollag G, Spleiss O et al (2012) RAS mutations in cutaneous squamous-cell carcinomas in patients treated with BRAF inhibitors. N Engl J Med 366:207–215 Oberholzer PA, Kee D, Dziunycz P, Sucker A, Kamsukom N, Jones R et al (2012) RAS mutations are associated with the development of cutaneous squamous cell tumors in patients treated with RAF inhibitors. J Clin Oncol 30:316–321 Nazarian R, Shi H, Wang Q, Kong X, Koya RC, Lee H et al (2010) Melanomas acquire resistance to B-RAF(V600E) inhibition by RTK or N-RAS upregulation. Nature 468: 973–977 Poulikakos PI, Persaud Y, Janakiraman M, Kong X, Ng C, Moriceau G et al (2011) RAF inhibitor resistance is mediated by dimerization of aberrantly spliced BRAF(V600E). Nature 480:387–390 Shi H, Moriceau G, Kong X, Koya RC, Nazarian R, Pupo G et al (2012) Sensitivity of B-RAF/MEK1 double-mutant melanomas to B-RAF inhibitors. Cancer Discov 2(5): 414–424 Shi H, Moriceau G, Kong X, Lee MK, Lee H, Koya RC et al (2012) Melanoma whole-exome sequencing identifies (V600E)B-RAF amplification-mediated acquired B-RAF inhibitor resistance. Nat Commun 3:724
New Treatments for Melanoma 22. Straussman R, Morikawa T, Shee K, BarzilyRokni M, Qian ZR, Du J et al (2012) Tumour micro-environment elicits innate resistance to RAF inhibitors through HGF secretion. Nature 487:500–504 23. Wilson TR, Fridlyand J, Yan Y, Penuel E, Burton L, Chan E et al (2012) Widespread potential for growth-factor-driven resistance to anticancer kinase inhibitors. Nature 487:505–509 24. Villanueva J, Vultur A, Lee JT, Somasundaram R, Fukunaga-Kalabis M, Cipolla AK et al (2010) Acquired resistance to BRAF inhibitors mediated by a RAF kinase switch in melanoma can be overcome by cotargeting MEK and IGF-1R/PI3K. Cancer Cell 18:683–695 25. Johannessen CM, Boehm JS, Kim SY, Thomas SR, Wardwell L, Johnson LA et al (2010) COT drives resistance to RAF inhibition through MAP kinase pathway reactivation. Nature 468:968–972 26. Wagle N, Emery C, Berger MF, Davis MJ, Sawyer A, Pochanard P et al (2011) Dissecting therapeutic resistance to RAF inhibition in melanoma by tumor genomic profiling. J Clin Oncol 29(22):3085–3096 27. Solit DB, Garraway LA, Pratilas CA, Sawai A, Getz G, Basso A et al (2006) BRAF mutation predicts sensitivity to MEK inhibition. Nature 439:358–362 28. Flaherty KT, Robert C, Hersey P, Nathan P, Garbe C, Milhem M et al (2012) Improved survival with MEK inhibition in BRAF-mutated melanoma. N Engl J Med 367:107–114 29. Smalley KS, Flaherty KT (2009) Integrating BRAF/MEK inhibitors into combination therapy for melanoma. Br J Cancer 100:431–435 30. Lo RS (2012) Combinatorial therapies to overcome B-RAF inhibitor resistance in melanomas. Pharmacogenomics 13:125–128 31. Flaherty KT, Infante JR, Daud A, Gonzalez R, Kefford RF, Sosman J et al (2012) Combined BRAF and MEK inhibition in melanoma with BRAF V600 mutations. N Engl J Med 367:1694–1703 32. Korman AJ, Peggs KS, Allison JP (2006) Checkpoint blockade in cancer immunotherapy. Adv Immunol 90:297–339 33. Pardoll DM (2012) The blockade of immune checkpoints in cancer immunotherapy. Nat Rev Cancer 12:252–264 34. Ribas A (2012) Tumor immunotherapy directed at PD-1. N Engl J Med 366(26): 2517–2519 35. Agarwala SS, Ribas A (2010) Current experience with CTLA4-blocking monoclonal antibodies for the treatment of solid tumors. J Immunother 33:557–569
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36. Ribas A, Camacho LH, Lopez-Berestein G, Pavlov D, Bulanhagui CA, Millham R et al (2005) Antitumor activity in melanoma and anti-self responses in a phase I trial with the anti-cytotoxic T lymphocyte-associated antigen 4 monoclonal antibody CP-675,206. J Clin Oncol 23:8968–8977 37. Hodi FS, Mihm MC, Soiffer RJ, Haluska FG, Butler M, Seiden MV et al (2003) Biologic activity of cytotoxic T lymphocyte-associated antigen 4 antibody blockade in previously vaccinated metastatic melanoma and ovarian carcinoma patients. Proc Natl Acad Sci USA 100:4712–4717 38. O’Day SJ, Maio M, Chiarion-Sileni V, Gajewski TF, Pehamberger H, Bondarenko IN et al (2010) Efficacy and safety of ipilimumab monotherapy in patients with pretreated advanced melanoma: a multicenter single-arm phase II study. Ann Oncol 21:1712–1717 39. Camacho LH, Antonia S, Sosman J, Kirkwood JM, Gajewski TF, Redman B et al (2009) Phase I/II trial of tremelimumab in patients with metastatic melanoma. J Clin Oncol 27: 1075–1081 40. Hodi FS, O’Day SJ, McDermott DF, Weber RW, Sosman JA, Haanen JB et al (2010) Improved survival with ipilimumab in patients with metastatic melanoma. N Engl J Med 363:711–723 41. Robert C, Thomas L, Bondarenko I, O’Day S, M DJ, Garbe C et al (2011) Ipilimumab plus dacarbazine for previously untreated metastatic melanoma. N Engl J Med 364:2517–2526 42. Ribas A, Kefford R, Marshall MA, Punt CJA, Haanen JB, Marmol M et al (2013) A phase III randomized clinical trial comparing tremelimumab with standard-of-care chemotherapy in patients with advanced melanoma. J Clin Oncol 31(5):616–622 43. Brahmer JR, Drake CG, Wollner I, Powderly JD, Picus J, Sharfman WH et al (2010) Phase I study of single-agent anti-programmed death-1 (MDX-1106) in refractory solid tumors: safety, clinical activity, pharmacodynamics, and immunologic correlates. J Clin Oncol 28: 3167–3175 44. Brahmer JR, Tykodi SS, Chow LQ, Hwu WJ, Topalian SL, Hwu P et al (2012) Safety and activity of anti-PD-L1 antibody in patients with advanced cancer. N Engl J Med 366: 2455–2465 45. Topalian SL, Hodi FS, Brahmer JR, Gettinger SN, Smith DC, McDermott DF et al (2012) Safety, activity, and immune correlates of antiPD-1 antibody in cancer. N Engl J Med 366:2443–2454
1
Introduction In a short period of time melanoma has become a poster child of how science can be translated into better patient care. This is a big change in this disease where treatment for advanced disease had shown very little progress since the advent of modern oncology. In fact, until 2010 there had never been a therapy that had demonstrated improvement in overall survival in patients with metastatic melanoma. The lack of insight into the biology of this cancer and how it interacts with the host had precluded advances in treatments. Nonspecific genotoxins like chemotherapy and radiotherapy had provided marginal benefits, with occasional patients having tumor responses without an ability to understand what guided response or resistance. Melanoma has a remarkable ability to correct DNA damage by chemotherapy, which is likely endowed from its cell of origin, the melanocyte, which is a pigmented skin cell designed by Nature to withstand DNA damage from ultraviolet light and protect the surrounding skin cells. Furthermore, a series of immunotherapy strategies had repeatedly provided evidence of
Magdalena Thurin and Francesco M. Marincola (eds.), Molecular Diagnostics for Melanoma: Methods and Protocols, Methods in Molecular Biology, vol. 1102, DOI 10.1007/978-1-62703-727-3_1, © Springer Science+Business Media New York 2014
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Antoni Ribas
benefit in occasional patients, with a very low frequency of responses that were highly relevant for those patients with benefit since these tended to be very durable, many times lasting years. However, these immunotherapies were far from desirable since multiple active vaccination approaches had proven to have very low immunological potency, and nonspecific immune stimulating such as the cytokines interleukin-2 (IL-2) or interferon-alpha (IFN-α) had to be administered at the highest (barely tolerated) doses to result in a low frequency of clinical benefit. The big clinical improvements provided by the recently widely available therapies for advanced melanoma are based on a refined understanding of oncogenic signaling pathways in cancer cells and how immune responses to cancer are regulated. Therapies based on inhibiting mutated BRAF signaling and blocking negative immune checkpoint regulatory proteins have provided the first clinical trials demonstrating improvements in overall survival in patients with metastatic melanoma.
2
Targeted Therapies Blocking Melanoma Driver Oncogenic Signaling Insights into the genetic alterations in melanoma allowed understanding what gives this cancer the oncogenic signals to proliferate. Over 70 % of skin and mucosal melanomas have activating mutations in the receptor tyrosine kinase (RTK) KIT, or the oncogenic proteins NRAS or BRAF [1, 2]. These are generally mutually exclusive mutations that all result in constitutive oncogenic signaling through the mitogenactivated protein kinase (MAPK) pathway governing cell proliferation and avoidance of apoptosis [1, 3]. The great majority of uveal melanomas have a distinct set of driver oncogenic mutations in GNAQ and GNA11 [4, 5]. Together with the near universal alterations in cell cycle control, they provide the key oncogenic events to transform normal melanocytes into cancer cells [3]. These mutations are not randomly distributed among melanomas. As noted for the distinct mutations in uveal melanoma, different melanoma subtypes likely with different pathogenic events have a different set of driver oncogenic mutations: KIT mutations are more common in mucosal, acral, and lentiginous melanomas, NRAS mutations are more common in cutaneous melanomas in older adults, and BRAF mutations are more common in melanomas arising from intermittently sun exposed skin in younger adults [1, 6, 7]. The biological significance of the affected proteins and signaling pathways, their mutual exclusivity in the great majority of cases and their nonrandom distribution in distinct clinicopathological subtypes of melanoma provide clues to their importance and potential for therapeutic targeting. The greatest therapeutic advance has been achieved in patients with mutations in BRAFV600, which is present in approximately
New Treatments for Melanoma
5
50 % of patients with metastatic melanoma. Small molecule inhibitors that displace ATP in the mutated BRAFV600 threonine-serine kinase have been developed and demonstrated to have unprecedently high response rates [8]. Clinical studies with the type I (which bind to the activation state of the kinase) RAF kinase inhibitors vemurafenib (formerly PLX4032) and dabrafenib (formerly GSK2118436) demonstrated objective tumor responses in excess of 50 % of patients by strict RECIST criteria, with up to 85 % of patients having some kind of tumor response and a very low frequency of innate resistance [9–13]. These two BRAF inhibitors have demonstrated improvement in progression free survival (PFS) against the old standard chemotherapy agent dacarbazine [10, 13], while vemurafenib has also demonstrated improvident in overall survival (OS) in a randomized clinical trial [10]. The high specificity of these agents for the mutated BRAF kinase allows a wide therapeutic window, with most toxicities being manageable with dose adjustments or interruptions. The most common grade 3 or 4 toxicity with these agents is the development of cutaneous squamous cell carcinomas (cuSCC), most of them of keratoacanthoma (KA) subtype. These toxicities are usually easily managed by simple surgical excision and do not preclude continued therapy. The pathobiology of their appearance has been elucidated through the phenomenon of paradoxical MAPK activation [14, 15], where cells with preexisting upstream mutations, most frequently in HRAS and KRAS, are transactivated to proliferate through MAPK signaling [16, 17]. Despite the initial tumor responses and early benefit in PFS and OS, the majority of patients demonstrate disease progression frequently within months. The mechanisms how BRAFV600 mutant metastatic melanoma develops acquired resistance to BRAF inhibitors are different from the prevalent gatekeeper mutations with other ATP-competitive small molecule targeted inhibitor therapies for cancer. In fact, melanomas seem to develop a wide array of mechanisms to overcome BRAF inhibition. These mechanisms either reactivate the MAPK pathway through secondary NRAS mutations, BRAF amplification, BRAF truncation, or MEK mutations, or provide alternative survival signaling by activating RTKs and downstream signaling through the PI3K/AKT pathway [18–26]. Furthermore, inhibiting MAPK signaling immediately downstream of mutated BRAF can be achieved with MEK inhibitors, which preclinical studies had shown to have preferential activity in the setting of the BRAFV6000 mutations [27]. In patients who had not previously received BRAF inhibitor-based therapy, a randomized clinical trial demonstrated that the MEK inhibitor trametinib (GSK1120211) improved both PFS and OS over dacarbazine [28], providing another active agent for these patients. However, the antitumor activity is lower and the toxicities are higher with single agent MEK inhibitors compared to single agent BRAF inhibitors.
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Antoni Ribas
The rapid phase of development of targeted treatments for BRAF mutant metastatic melanoma has resulted in the testing of combined therapy with BRAF and MEK inhibitors. This combination has the theoretical ability to provide improved initial antitumor activity resultant from double inhibition of oncogenic signaling through the MAPK pathway [29], as well and providing longer duration of responses by preventing or treating acquired resistance [30]. At the same time, the combination of BRAF and MEK inhibitors has the potential to also decrease toxicities resultant from paradoxical MAPK activation, since the MEK inhibitor would block the BRAF inhibitor-induced MAPK activation in cells that are wild type for BRAF and have strong upstream signaling [16]. Early clinical testing of this combined therapy is highly encouraging [31], and formal testing of improvements in PFS and OS over single agent BRAF inhibitor therapy is ongoing.
3
Immune Modulation Overcoming Negative Regulatory Pathways Therapies that attempt to activate a cytotoxic T lymphocyte (CTL) immune response against chronically expressed self-antigens, as are most tumor antigens, are negatively regulated by T cell-intrinsic negative costimulatory signaling known as immune checkpoints [32]. The recent advances in immunotherapy for melanoma have been based on the clinical application of antibodies blocking these immune checkpoints, in particular the cytotoxic T lymphocyteassociated antigen-4 (CTLA-4) and the programmed death receptor 1 (PD-1) [33]. These two negative immune regulatory receptors have very different biological roles, which may allow understanding their effects in the clinic [33, 34]. CTLA-4 is a negative costimulatory receptor that competes with CD28 for costimulatory signaling through CD80/CD86 upon T cell activation. The blockade of CTLA-4 releases negative regulation upon T cell activation in secondary lymphoid organs, and these T cells then need to circulate through the periphery and recognize cells expressing their cognate targets. Therefore, CTLA-4 blockade is relatively nonspecific for antitumor T cells and its clinical effects are likely to be delayed. On the contrary, PD-1 is expressed by chronically antigen-exposed T cells and it is engaged primarily in peripheral tissues upon recognition of the PD ligand 1 (PD-L1), which is an activation-induced ligand expressed in inflamed tissues and cancers. Therefore, PD-1 inhibits the final effector mechanism of CTLs that have already recognized antigen and have been negatively regulated by PD-L1 in the periphery. This predicts a more specific activation of T cells to cancer and chronic infections, while it should also provide more rapid antitumor activity.
New Treatments for Melanoma
7
These preclinical predictions correlate well with the clinical effects of CTLA-4 and PD-1/PD-L1 blocking antibodies. Two CTLA-4 blocking antibodies have been extensively tested in the clinic, ipilimumab (formerly MDX010) and tremelimumab (formerly CP-675,206) [35]. They both provided a low but reproducible level of antitumor activity in patients with metastatic melanoma, with the main feature of providing very long duration of tumor responses in roughly 10 % of treated patients, with responses lasting years [36–39]. Ipilimumab has been demonstrated to improve OS in two randomized clinical trials, one against a gp100 peptide vaccine and another in combination with dacarbazine against single agent dacarbazine [40, 41], leading to its regulatory approval in several countries. Tremelimumab was tested in a randomized clinical trial against dacarbazine or temozolomide but failed to demonstrate a statistically significant improvement in OS, with the major reason being a relatively high rate of use of ipilimumab in patients in the control chemotherapy arm [42]. These two agents are limited by their low frequency of tumor responses, their delayed tumor responses, and their frequency of 15–20 % of serious inflammatory and autoimmune toxicities, in particular colitis and endocrinopathies. Early clinical testing of PD-1 and PD-L1 blocking antibodies suggests that they may have higher antitumor activity, more rapid tumor responses, and a lower frequency of toxicities. There are several PD-1 axis inhibitors in current clinical testing, with the most advanced programs using the anti-PD-1 nivolumab (formerly MDX1106) and the anti-PD-L1 MDX1105 [33]. Both of these agents have provided evidence of objective tumor responses in 20–30 % of patients with metastatic melanoma in phase 1 testing, with the majority being durable responses [43–45]. These encouraging results are being pursued in larger series and randomized clinical trials. Furthermore, the ability to detect PD-L1 in tumors may allow selecting patients whose immune response to melanoma is being blocked through the PD-1/PD-L1 interaction, with the potential for enriching for patients who are more likely to respond to these antibodies.
4
Conclusions The rapid advancement of new therapies active in patients with metastatic melanoma has been achieved thanks to the clinical translation of preclinical scientific knowledge. These advances are in sharp contrast with the lack of significant progress when attempting to treat melanoma with nonspecific agents, in particular chemotherapy. The ability to understand mechanisms of response and resistance to BRAF inhibitor-based therapies and immune checkpoint
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Antoni Ribas
blockade at a molecular level, and the rapid advancement of the knowledge brought through by the scientific community’s renewed interest in melanoma, predicts that the pace of improvements in further developing effective therapies for this disease will continue in the near future. References 1. Curtin JA, Fridlyand J, Kageshita T, Patel HN, Busam KJ, Kutzner H et al (2005) Distinct sets of genetic alterations in melanoma. N Engl J Med 353:2135–2147 2. Curtin JA, Busam K, Pinkel D, Bastian BC (2006) Somatic activation of KIT in distinct subtypes of melanoma. J Clin Oncol 24:4340–4346 3. Gray-Schopfer V, Wellbrock C, Marais R (2007) Melanoma biology and new targeted therapy. Nature 445:851–857 4. Van Raamsdonk CD, Bezrookove V, Green G, Bauer J, Gaugler L, O’Brien JM et al (2009) Frequent somatic mutations of GNAQ in uveal melanoma and blue naevi. Nature 457: 599–602 5. Van Raamsdonk CD, Griewank KG, Crosby MB, Garrido MC, Vemula S, Wiesner T et al (2010) Mutations in GNA11 in uveal melanoma. N Engl J Med 363:2191–2199 6. Viros A, Fridlyand J, Bauer J, Lasithiotakis K, Garbe C, Pinkel D et al (2008) Improving melanoma classification by integrating genetic and morphologic features. PLoS Med 5:e120 7. Long GV, Menzies AM, Nagrial AM, Haydu LE, Hamilton AL, Mann GJ et al (2011) Prognostic and clinicopathologic associations of oncogenic BRAF in metastatic melanoma. J Clin Oncol 29:1239–1246 8. Ribas A, Flaherty KT (2011) BRAF targeted therapy changes the treatment paradigm in melanoma. Nat Rev Clin Oncol 8:426–433 9. Flaherty KT, Puzanov I, Kim KB, Ribas A, McArthur GA, Sosman JA et al (2010) Inhibition of mutated, activated BRAF in metastatic melanoma. N Engl J Med 363: 809–819 10. Chapman PB, Hauschild A, Robert C, Haanen JB, Ascierto P, Larkin J et al (2011) Improved survival with vemurafenib in melanoma with BRAF V600E mutation. N Engl J Med 364:2507–2516 11. Sosman JA, Kim KB, Schuchter L, Gonzalez R, Pavlick AC, Weber JS et al (2012) Survival in BRAF V600-mutant advanced melanoma treated with vemurafenib. N Engl J Med 366:707–714 12. Falchook GS, Long GV, Kurzrock R, Kim KB, Arkenau TH, Brown MP et al (2012)
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New Treatments for Melanoma 22. Straussman R, Morikawa T, Shee K, BarzilyRokni M, Qian ZR, Du J et al (2012) Tumour micro-environment elicits innate resistance to RAF inhibitors through HGF secretion. Nature 487:500–504 23. Wilson TR, Fridlyand J, Yan Y, Penuel E, Burton L, Chan E et al (2012) Widespread potential for growth-factor-driven resistance to anticancer kinase inhibitors. Nature 487:505–509 24. Villanueva J, Vultur A, Lee JT, Somasundaram R, Fukunaga-Kalabis M, Cipolla AK et al (2010) Acquired resistance to BRAF inhibitors mediated by a RAF kinase switch in melanoma can be overcome by cotargeting MEK and IGF-1R/PI3K. Cancer Cell 18:683–695 25. Johannessen CM, Boehm JS, Kim SY, Thomas SR, Wardwell L, Johnson LA et al (2010) COT drives resistance to RAF inhibition through MAP kinase pathway reactivation. Nature 468:968–972 26. Wagle N, Emery C, Berger MF, Davis MJ, Sawyer A, Pochanard P et al (2011) Dissecting therapeutic resistance to RAF inhibition in melanoma by tumor genomic profiling. J Clin Oncol 29(22):3085–3096 27. Solit DB, Garraway LA, Pratilas CA, Sawai A, Getz G, Basso A et al (2006) BRAF mutation predicts sensitivity to MEK inhibition. Nature 439:358–362 28. Flaherty KT, Robert C, Hersey P, Nathan P, Garbe C, Milhem M et al (2012) Improved survival with MEK inhibition in BRAF-mutated melanoma. N Engl J Med 367:107–114 29. Smalley KS, Flaherty KT (2009) Integrating BRAF/MEK inhibitors into combination therapy for melanoma. Br J Cancer 100:431–435 30. Lo RS (2012) Combinatorial therapies to overcome B-RAF inhibitor resistance in melanomas. Pharmacogenomics 13:125–128 31. Flaherty KT, Infante JR, Daud A, Gonzalez R, Kefford RF, Sosman J et al (2012) Combined BRAF and MEK inhibition in melanoma with BRAF V600 mutations. N Engl J Med 367:1694–1703 32. Korman AJ, Peggs KS, Allison JP (2006) Checkpoint blockade in cancer immunotherapy. Adv Immunol 90:297–339 33. Pardoll DM (2012) The blockade of immune checkpoints in cancer immunotherapy. Nat Rev Cancer 12:252–264 34. Ribas A (2012) Tumor immunotherapy directed at PD-1. N Engl J Med 366(26): 2517–2519 35. Agarwala SS, Ribas A (2010) Current experience with CTLA4-blocking monoclonal antibodies for the treatment of solid tumors. J Immunother 33:557–569
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36. Ribas A, Camacho LH, Lopez-Berestein G, Pavlov D, Bulanhagui CA, Millham R et al (2005) Antitumor activity in melanoma and anti-self responses in a phase I trial with the anti-cytotoxic T lymphocyte-associated antigen 4 monoclonal antibody CP-675,206. J Clin Oncol 23:8968–8977 37. Hodi FS, Mihm MC, Soiffer RJ, Haluska FG, Butler M, Seiden MV et al (2003) Biologic activity of cytotoxic T lymphocyte-associated antigen 4 antibody blockade in previously vaccinated metastatic melanoma and ovarian carcinoma patients. Proc Natl Acad Sci USA 100:4712–4717 38. O’Day SJ, Maio M, Chiarion-Sileni V, Gajewski TF, Pehamberger H, Bondarenko IN et al (2010) Efficacy and safety of ipilimumab monotherapy in patients with pretreated advanced melanoma: a multicenter single-arm phase II study. Ann Oncol 21:1712–1717 39. Camacho LH, Antonia S, Sosman J, Kirkwood JM, Gajewski TF, Redman B et al (2009) Phase I/II trial of tremelimumab in patients with metastatic melanoma. J Clin Oncol 27: 1075–1081 40. Hodi FS, O’Day SJ, McDermott DF, Weber RW, Sosman JA, Haanen JB et al (2010) Improved survival with ipilimumab in patients with metastatic melanoma. N Engl J Med 363:711–723 41. Robert C, Thomas L, Bondarenko I, O’Day S, M DJ, Garbe C et al (2011) Ipilimumab plus dacarbazine for previously untreated metastatic melanoma. N Engl J Med 364:2517–2526 42. Ribas A, Kefford R, Marshall MA, Punt CJA, Haanen JB, Marmol M et al (2013) A phase III randomized clinical trial comparing tremelimumab with standard-of-care chemotherapy in patients with advanced melanoma. J Clin Oncol 31(5):616–622 43. Brahmer JR, Drake CG, Wollner I, Powderly JD, Picus J, Sharfman WH et al (2010) Phase I study of single-agent anti-programmed death-1 (MDX-1106) in refractory solid tumors: safety, clinical activity, pharmacodynamics, and immunologic correlates. J Clin Oncol 28: 3167–3175 44. Brahmer JR, Tykodi SS, Chow LQ, Hwu WJ, Topalian SL, Hwu P et al (2012) Safety and activity of anti-PD-L1 antibody in patients with advanced cancer. N Engl J Med 366: 2455–2465 45. Topalian SL, Hodi FS, Brahmer JR, Gettinger SN, Smith DC, McDermott DF et al (2012) Safety, activity, and immune correlates of antiPD-1 antibody in cancer. N Engl J Med 366:2443–2454
