“Long-term outcomes for BRAF-mutant melanoma patients treated with BRAF and MEK inhibitors are influenced by a number of baseline factors including BRAF genotype, gender, and serum lactate dehydrogenase (LDH) levels, according to a new study.
“Treatment of V600 BRAF-mutant metastatic melanoma has improved with inhibition of the MAPK pathway with BRAF inhibitors and MEK inhibitors. But ‘the degree of response and the duration of survival are highly variable,’ wrote study authors led by Alexander M. Menzies, MBBS, of the Melanoma Institute Australia in Sydney. ‘Whether clinicopathologic factors can be used to predict the clinical course of these patients is largely unknown, and there have been few studies examining this issue.’
“The study included 142 consecutive immunotherapy- and MAPK inhibitor–naive patients with BRAF-mutant metastatic melanoma. All were treated either with BRAF inhibitors (111 patients) or with a combination of dabrafenib and trametinib (31 patients), and the median follow-up was 15.7 months. Results were published online ahead of print in Cancer.”
The gist: Two new, similar melanoma treatments have been tested in clinical trials—research studies with volunteer patients. Both of the trials are focused on people with advanced melanoma whose tumors have mutations in the BRAF gene. Such patients are often treated with a targeted therapy called a BRAF inhibitor, but their tumors often become resistant and keep growing. In these two trials, the researchers hope that combining BRAF inhibitors with other targeted drugs known as MEK inhibitors might help patients avoid resistance. One of the trials tested a combination of the drugs vemurafenib and cobimetinib. The other trial combined dabrafenib and trametinib. In both trials, patients treated with the combination treatment fared better than patients treated with just a BRAF inhibitor alone.
“For patients with advanced melanoma that isBRAF-mutation positive, the combination of a BRAF and MEK inhibitor works better than a BRAF inhibitor alone. The data come from 2 phase 3 trials presented here at the presidential session of the European Society for Medical Oncology (ESMO) Congress 2014.
“Experts here say that such combinations should be the new standard of care in this patient population, which accounts for about 40% of all melanoma.
“At present, the first-line treatment for these patients is a BRAF inhibitor used alone, but while these drugs can elicit dramatic responses, they do not last, and after about 5 or 6 months, patients relapse. The tumor develops resistance to the drug via the MAPK pathway, and this is blocked by a MEK inhibitor. Adding a MEK inhibitor to the BRAF inhibitor from the beginning of treatment blocks this resistance pathway and improves outcomes.
“The 2 new trials are known as COMBI-v and coBRIM.
“Both studies used vemurafenib (Zelboraf, Roche/Plexxikon) as the single BRAF inhibitor, but each used a different combination of BRAF and MEK inhibitor.”
We already knew that melanomas can resist BRAF inhibitor drugs by activating a particular cancer pathway (a group of proteins in a cell that work together to control cell multiplication, which can lead to tumor growth)—but new research shows that this resistance can also be caused by activating a second cancer pathway. The first pathway is called MAPK and the second is called PI3K-PTEN-AKT. The researchers studied 100 melanomas that resisted the BRAF inhibitors vemurafenib or dabrafenib, and found that 70% had mutations in the first pathway, while 22% had mutations in the second pathway. Moreover, mutations in both pathways could occur in the same tumor, suggesting that thwarting resistance to BRAF inhibitors may require targeting both pathways with a combination treatment.
Basile KJ, Abel EV, Dadpey N, Hartsough EJ, et al. Cancer Research. Oct 11, 2013.
“Activation of the ERK1/2 mitogen-activated protein kinases (MAPKs) confers resistance to the RAF inhibitors vemurafenib and dabrafenib in mutant BRAF-driven melanomas. Methods to understand how resistance develops are important to optimize the clinical utility of RAF inhibitors in patients. Here we report the development of a novel ERK1/2 reporter system that provides a non-invasive, quantitative and temporal analysis of RAF inhibitor efficacy in vivo. Use of this system revealed heterogeneity in the level of ERK1/2 reactivation associated with acquired resistance to RAF inhibition. We identified several distinct novel and known molecular changes in resistant tumors emerging from treatment-naïve cell populations including BRAF V600E variants and HRAS mutation, both of which were required and sufficient for ERK1/2 reactivation and drug resistance. Our work offers an advance in understanding RAF inhibitor resistance and the heterogeneity in resistance mechanisms, which emerge from a malignant cell population.”
Kwong MLM, Neyns B, Yang JC, et al. Clinical Cancer Research. Oct 1, 2013.
“The clinical strengths of immunotherapy and small-molecule inhibitors targeting the mitogen-activated protein kinase (MAPK) pathway appear to be largely complementary for the treatment of advanced melanoma. In current practice, most patients with BRAF V600 mutant melanomas will see both modalities. Several in vitro and in vivo studies suggest that combining immunotherapy with MAPK inhibition may have synergistic effects. First, mouse models show that adoptive cell therapy (ACT) can be enhanced by vaccination. Rapid tumor destruction by vemurafenib could provide a vaccine-like stimulus to adoptively transferred T cells. Second, both in mice and in early clinical trials, melanoma metastases treated with MAPK inhibitors seem to display increased T-cell infiltrates. Third, MAPK inhibition upregulates the expression of some melanoma antigens and, therefore, may enhance T-cell recognition of vemurafenib-treated melanomas. Fourth, vemurafenib may sensitize tumor cells to immune destruction. Finally, some investigators have found that an optimal antitumor effect from MAPK inhibition is dependent on an intact host immune response. Currently, the Surgery Branch of the National Cancer Institute has initiated a phase II trial combining the BRAF inhibitor vemurafenib with ACT using tumor-infiltrating lymphocytes in patients with BRAF-mutant tumors to investigate the safety and efficacy of this combination. The proposed mechanisms for synergy between these two modalities can be complex, and their optimal combination may require testing a variety of sequences and schedules.”
Ott PA, Hodi FS, Robert C. Clinical Cancer Research. Oct 1, 2013.
“Immune checkpoint blockade with monoclonal antibodies directed at the inhibitory immune receptors CTLA-4, PD-1, and PD-L1 has emerged as a successful treatment approach for patients with advanced melanoma. Ipilimumab is the first agent associated with a documented improved overall survival benefit in this patient population. A striking attribute of CTLA-4 blockade is the durability of objective responses, leading to speculation of a possible cure for some patients. Many tumor responses achieved with PD-1 and PD-L1 inhibition were durable in the phase I trials and were seen in a higher proportion of patients with melanoma than typically observed with ipilimumab. Biomarker development to identify the subset of patients with melanoma who will achieve durable clinical benefit with checkpoint blockade is critical; tumor PD-L1 expression has been promising in early studies. The contrast between unprecedented response rates but limited durability of responses achieved with BRAF and MEK inhibition in BRAFV600-mutated melanoma and the impressive durability but relatively low rate of response achieved with immune checkpoint blockade is striking. Preclinical data on potential synergies between CTLA-4/PD-1/PD-L1 inhibition and MAPK-targeted therapy is emerging, and combined immune checkpoint blockade and MAPK inhibition are being explored in clinical trials. Other promising approaches to increase the number of patients with melanoma who benefit from durable responses with immune checkpoint blockade include concurrent or sequenced CTLA-4 and PD-1/PD-L1 inhibition and combination with other immunotherapeutic strategies.”
Villanueva J, Infante JR, Krepler C, Reyes-Uribe P. et al. Cell Reports. Sep 19, 2013.
“Although BRAF and MEK inhibitors have proven clinical benefits in melanoma, most patients develop resistance. We report a de novo MEK2-Q60P mutation and BRAF gain in a melanoma from a patient who progressed on the MEK inhibitor trametinib and did not respond to the BRAF inhibitor dabrafenib. We also identified the same MEK2-Q60P mutation along with BRAF amplification in a xenograft tumor derived from a second melanoma patient resistant to the combination of dabrafenib and trametinib. Melanoma cells chronically exposed to trametinib acquired concurrent MEK2-Q60P mutation and BRAF-V600E amplification, which conferred resistance to MEK and BRAF inhibitors. The resistant cells had sustained MAPK activation and persistent phosphorylation of S6K. A triple combination of dabrafenib, trametinib, and the PI3K/mTOR inhibitor GSK2126458 led to sustained tumor growth inhibition. Hence, concurrent genetic events that sustain MAPK signaling can underlie resistance to both BRAF and MEK inhibitors, requiring novel therapeutic strategies to overcome it.”
Zhu Y, Regunath K, Jacq X, Prives C. Genes Dev. Aug 15, 2013.
“The interdependence of p53 and MDM2 is critical for proper cell survival and cell death and, when altered, can lead to tumorigenesis. Mitogen-activated protein kinase (MAPK) signaling pathways function in a wide variety of cellular processes, including cell growth, migration, differentiation, and death. Here we discovered that transforming growth factor β-activated kinase 1 (TAK1)-binding protein 1 (TAB1), an activator of TAK1 and of p38α, associates with and inhibits the E3 ligase activity of MDM2 toward p53 and its homolog, MDMX. Depletion of TAB1 inhibits MDM2 siRNA-mediated p53 accumulation and p21 induction, partially rescuing cell cycle arrest induced by MDM2 ablation. Interestingly, of several agents commonly used as DNA-damaging therapeutics, only cell death caused by cisplatin is mitigated by knockdown of TAB1. Two mechanisms are required for TAB1 to regulate apoptosis in cisplatin-treated cells. First, p38α is activated by TAB1 to phosphorylate p53 N-terminal sites, leading to selective induction of p53 targets such as NOXA. Second, MDMX is stabilized in a TAB1-dependent manner and is required for cell death after cisplatin treatment. Interestingly TAB1 levels are relatively low in cisplatin-resistant clones of ovarian cells and in ovarian patient’s tumors compared with normal ovarian tissue. Together, our results indicate that TAB1 is a potential tumor suppressor that serves as a functional link between p53-MDM2 circuitry and a key MAPK signaling pathway.”