Recent breakthroughs in the treatment of advanced melanoma are based on scientific advances in understanding oncogenic signaling and the immunobiology of this cancer. Targeted therapy can successfully block oncogenic signaling in BRAF(V600)-mutant melanoma with high initial clinical responses, but relapse rates are also high. Activation of an immune response by releasing inhibitory check points can induce durable responses in a subset of patients with melanoma. These advances have driven interest in combining both modes of therapy with the goal of achieving high response rates with prolonged duration. Combining BRAF inhibitors and immunotherapy can specifically target the BRAF(V600) driver mutation in the tumor cells and potentially sensitize the immune system to target tumors. However, it is becoming evident that the effects of paradoxical mitogen-activated protein kinase pathway activation by BRAF inhibitors in non-BRAF-mutant cells needs to be taken into account, which may be implicated in the problems encountered in the first clinical trial testing a combination of the BRAF inhibitor vemurafenib with ipilimumab (anti-CTLA4), with significant liver toxicities. Here, we present the concept and potential mechanisms of combinatorial activity of targeted therapy and immunotherapy, review the literature for evidence to support the combination, and discuss the potential challenges and future directions for rational conduct of clinical trials.

Combining immunotherapy and BRAF targeted therapy may result in improved antitumor activity with the high response rates of targeted therapy and the durability of responses with immunotherapy. However, the first clinical trial testing the combination of the BRAF inhibitor vemurafenib and the CTLA4 antibody ipilimumab was terminated early because of substantial liver toxicities. MEK [MAPK (mitogen-activated protein kinase) kinase] inhibitors can potentiate the MAPK inhibition in BRAF mutant cells while potentially alleviating the unwanted paradoxical MAPK activation in BRAF wild-type cells that lead to side effects when using BRAF inhibitors alone. However, there is the concern of MEK inhibitors being detrimental to T cell functionality. Using a mouse model of syngeneic BRAF(V600E)-driven melanoma, SM1, we tested whether addition of the MEK inhibitor trametinib would enhance the antitumor activity of combined immunotherapy with the BRAF inhibitor dabrafenib. Combination of dabrafenib and trametinib with pmel-1 adoptive cell transfer (ACT) showed complete tumor regression, increased T cell infiltration into tumors, and improved in vivo cytotoxicity. Single-agent dabrafenib increased tumor-associated macrophages and T regulatory cells (Tregs) in tumors, which decreased with the addition of trametinib. The triple combination therapy resulted in increased melanosomal antigen and major histocompatibility complex (MHC) expression and global immune-related gene up-regulation. Given the up-regulation of PD-L1 seen with dabrafenib and/or trametinib combined with antigen-specific ACT, we tested the combination of dabrafenib, trametinib, and anti-PD1 therapy in SM1 tumors, and observed superior antitumor effect. Our findings support the testing of triple combination therapy of BRAF and MEK inhibitors with immunotherapy in patients with BRAF(V600E) mutant metastatic melanoma.

Continuous BRAF inhibition of BRAF mutant melanomas triggers a series of cell state changes that lead to therapy resistance and escape from immune control before establishing acquired resistance genetically. We used genome-wide transcriptomics and single-cell phenotyping to explore the response kinetics to BRAF inhibition for a panel of patient-derived BRAF^V600 -mutant melanoma cell lines. A subset of plastic cell lines, which followed a trajectory covering multiple known cell state transitions, provided models for more detailed biophysical investigations. Markov modeling revealed that the cell state transitions were reversible and mediated by both Lamarckian induction and nongenetic Darwinian selection of drug-tolerant states. Single-cell functional proteomics revealed activation of certain signaling networks shortly after BRAF inhibition, and before the appearance of drug-resistant phenotypes. Drug targeting those networks, in combination with BRAF inhibition, halted the adaptive transition and led to prolonged growth inhibition in multiple patient-derived cell lines.

PURPOSE: Patients with locally advanced or metastatic urothelial cancer (la/mUC) who are ineligible for cisplatin-based therapy have limited first-line (1L) treatment options and significant need for improved therapies. Enfortumab vedotin (EV) and pembrolizumab (Pembro) individually have shown a survival benefit in urothelial cancer in second-line + la/mUC settings. Here, we present data from the pivotal trial of EV plus Pembro (EV + Pembro) in the 1L setting. PATIENTS AND METHODS: In Cohort K of the EV-103 phase Ib/II study, cisplatin-ineligible patients with previously untreated la/mUC were randomly assigned 1:1 to receive EV as monotherapy or in combination with Pembro. The primary end point was confirmed objective response rate (cORR) per blinded independent central review. Secondary end points included duration of response (DOR) and safety. There were no formal statistical comparisons between treatment arms. RESULTS: The cORR was 64.5% (95% CI, 52.7 to 75.1) and 45.2% (95% CI, 33.5 to 57.3) for patients treated with EV + Pembro (N = 76) and EV monotherapy (N = 73), respectively. The median DOR was not reached for the combination and was 13.2 months for monotherapy; 65.4% and 56.3% of patients who responded to the combination and monotherapy, respectively, maintained a response at 12 months. The most common grade 3 or higher treatment-related adverse events (TRAEs) in patients treated with the combination were maculopapular rash (17.1%), fatigue (9.2%), and neutropenia (9.2%). EV TRAEs of special interest (any grade) in the combination arm included skin reactions (67.1%) and peripheral neuropathy (60.5%). CONCLUSION: EV + Pembro showed a high cORR with durable responses as 1L treatment in cisplatin-ineligible patients with la/mUC. Patients who received EV monotherapy had a response and safety profile consistent with previous studies. Adverse events for EV + Pembro were manageable, with no new safety signals observed.

Background

Approximately 75% of objective responses to anti-programmed death 1 (PD-1) therapy in patients with melanoma are durable, lasting for years, but delayed relapses have been noted long after initial objective tumor regression despite continuous therapy. Mechanisms of immune escape in this context are unknown.

Methods

We analyzed biopsy samples from paired baseline and relapsing lesions in four patients with metastatic melanoma who had had an initial objective tumor regression in response to anti-PD-1 therapy (pembrolizumab) followed by disease progression months to years later.

Results

Whole-exome sequencing detected clonal selection and outgrowth of the acquired resistant tumors and, in two of the four patients, revealed resistance-associated loss-of-function mutations in the genes encoding interferon-receptor-associated Janus kinase 1 (JAK1) or Janus kinase 2 (JAK2), concurrent with deletion of the wild-type allele. A truncating mutation in the gene encoding the antigen-presenting protein beta-2-microglobulin (B2M) was identified in a third patient. JAK1 and JAK2 truncating mutations resulted in a lack of response to interferon gamma, including insensitivity to its antiproliferative effects on cancer cells. The B2M truncating mutation led to loss of surface expression of major histocompatibility complex class I.

Conclusions

In this study, acquired resistance to PD-1 blockade immunotherapy in patients with melanoma was associated with defects in the pathways involved in interferon-receptor signaling and in antigen presentation. (Funded by the National Institutes of Health and others.).