Begoña Comin-Anduix

Mutations Associated with Acquired Resistance to PD-1 Blockade in Melanoma

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.).

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

PURPOSE Cytotoxic T lymphocyte-associated antigen 4 (CTLA4) blockade with CP-675,206, a fully human anti-CTLA4 monoclonal antibody, may break peripheral immunologic tolerance leading to effective immune responses to cancer in humans. A phase I trial was conducted to test the safety of CP-675,206. PATIENTS AND METHODS Thirty-nine patients with solid malignancies (melanoma, n = 34; renal cell, n = 4; colon, n = 1) received an intravenous (IV) infusion of CP-675,206 at seven dose levels. The primary objective was to determine the maximum-tolerated dose and the recommended phase II dose. RESULTS Dose-limiting toxicities and autoimmune phenomena included diarrhea, dermatitis, vitiligo, panhypopituitarism and hyperthyroidism. Two patients experienced complete responses (maintained for 34+ and 25+ months), and there were two partial responses (26+ and 25+ months) among 29 patients with measurable melanoma. There have been no relapses thus far after objective response to therapy. Four other patients had stable disease at end of study evaluation (16, 7, 7, and 4 months). Additionally, five patients had extended periods without disease progression (36+, 35+, 26+, 24+, and 23+ months) after local treatment of progressive metastases. Longer systemic exposure to CP-675,206 achieved in higher dose cohorts predicted for a higher probability of response. CONCLUSION CP-675,206 can be administered safely to humans as a single IV dose up to 15 mg/kg, resulting in breaking of peripheral immune tolerance to self-tissues and antitumor activity in melanoma.

Differential sensitivity of melanoma cell lines with BRAFV600E mutation to the specific Raf inhibitor PLX4032

Blocking oncogenic signaling induced by the BRAFV600E mutation is a promising approach for melanoma treatment. We tested the anti-tumor effects of a specific inhibitor of Raf protein kinases, PLX4032/RG7204, in melanoma cell lines. PLX4032 decreased signaling through the MAPK pathway only in cell lines with the BRAFV600E mutation. Seven out of 10 BRAFV600E mutant cell lines displayed sensitivity based on cell viability assays and three were resistant at concentrations up to 10 μM. Among the sensitive cell lines, four were highly sensitive with IC50 values below 1 μM, and three were moderately sensitive with IC50 values between 1 and 10 μM. There was evidence of MAPK pathway inhibition and cell cycle arrest in both sensitive and resistant cell lines. Genomic analysis by sequencing, genotyping of close to 400 oncogeninc mutations by mass spectrometry, and SNP arrays demonstrated no major differences in BRAF locus amplification or in other oncogenic events between sensitive and resistant cell lines. However, metabolic tracer uptake studies demonstrated that sensitive cell lines had a more profound inhibition of FDG uptake upon exposure to PLX4032 than resistant cell lines. In conclusion, BRAFV600E mutant melanoma cell lines displayed a range of sensitivities to PLX4032 and metabolic imaging using PET probes can be used to assess sensitivity.

Dendritic Cell Vaccination Combined with CTLA4 Blockade in Patients with Metastatic Melanoma

Purpose: Tumor antigen–loaded dendritic cells (DC) are believed to activate antitumor immunity by stimulating T cells, and CTL-associated antigen 4 (CTLA4)–blocking antibodies should release a key negative regulatory pathway on T cells. The combination was tested in a phase I clinical trial in patients with advanced melanoma. Experimental Design: Autologous DC were pulsed with MART-126-35 peptide and administered with a dose escalation of the CTLA4-blocking antibody tremelimumab. Sixteen patients were accrued to five dose levels. Primary end points were safety and immune effects; clinical efficacy was a secondary end point. Results: Dose-limiting toxicities of grade 3 diarrhea and grade 2 hypophysitis developed in two of three patients receiving tremelimumab at 10 mg/kg monthly. Four patients had an objective tumor response, two partial responses and two complete responses, all melanoma free between 2 and 4 years after study initiation. There was no difference in immune monitoring results between patients with an objective tumor response and those without a response. Exploratory gene expression analysis suggested that immune-related gene signatures, in particular for B-cell function, may be important in predicting response. Conclusion: The combination of MART-1 peptide–pulsed DC and tremelimumab results in objective and durable tumor responses at the higher range of the expected response rate with either agent alone. (Clin Cancer Res 2009;15(19):6267–76)

Improved antitumor activity of immunotherapy with BRAF and MEK inhibitors in BRAFV600E melanoma

MEK inhibition enhanced the antitumor activity of combined BRAF inhibition and immunotherapy. Melanoma’s triple threat Combination therapy is the favored approach to fight drug-resistant cancer. For BRAF-mutated melanoma, combining a BRAF inhibitor and checkpoint inhibitors was hoped to improve the antitumor response; however, an early clinical trial was stopped because of liver toxicity. Hu-Lieskovan et al. test the addition of MEK [MAPK (mitogen-activated protein kinase) kinase] inhibitors to this combination therapy in an effort to potentiate the MAPK inhibition of BRAF inhibitors while concurrently decreasing the toxicity. They show in a mouse model of BRAFV600E-driven melanoma that triple therapy with BRAF and MEK inhibitors together with adoptive cell transfer (ACT) immunotherapy induced complete tumor regression in a manner consistent with immune activation. In addition, replacing ACT with anti-PD1 in the triple therapy had similar results, supporting the testing of MEK and BRAF inhibitions with various immunotherapies in patients with BRAF-mutated melanoma. 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 BRAFV600E-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 BRAFV600E mutant metastatic melanoma.

Effects of MAPK and PI3K Pathways on PD-L1 Expression in Melanoma

Purpose: PD-L1 is the main ligand for the immune inhibitory receptor PD-1. This ligand is frequently expressed by melanoma cells. In this study, we investigated whether PD-L1 expression is controlled by melanoma driver mutations and modified by oncogenic signaling inhibition. Experimental Design: Expression of PD-L1 was investigated in a panel of 51 melanoma cell lines containing different oncogenic mutations, including cell lines with innate and acquired resistance to BRAF inhibitors (BRAFi). The effects of targeted therapy drugs on expression of PD-L1 by melanoma cells were investigated. Results: No association was found between the level of PD-L1 expression and mutations in BRAF, NRAS, PTEN, or amplification of AKT. Resistance to vemurafenib due to the activation of alternative signaling pathways was accompanied with the induction of PD-L1 expression, whereas the resistance due to the reactivation of the MAPK pathway had no effect on PD-L1 expression. In melanoma cell lines, the effects of BRAF, MEK, and PI3K inhibitors on expression of PD-L1 were variable from reduction to induction, particularly in the presence of INFγ. In PD-L1–exposed lymphocytes, vemurafenib paradoxically restored activity of the MAPK pathway and increased the secretion of cytokines. Conclusions: In melanoma cell lines, including BRAFi-resistant cells, PD-L1 expression is variably regulated by oncogenic signaling pathways. PD-L1–exposed lymphocytes decrease MAPK signaling, which is corrected by exposure to vemurafenib, providing potential benefits of combining this drug with immunotherapies. Clin Cancer Res; 20(13); 3446–57. ©2014 AACR.

CTLA4 Blockade Broadens the Peripheral T-Cell Receptor Repertoire

Purpose: To evaluate the immunomodulatory effects of cytotoxic T–lymphocyte-associated protein 4 (CTLA4) blockade with tremelimumab in peripheral blood mononuclear cells (PBMC). Experimental Design: We used next-generation sequencing to study the complementarity-determining region 3 (CDR3) from the rearranged T-cell receptor (TCR) variable beta (V-beta) in PBMCs of 21 patients, at baseline and 30 to 60 days after receiving tremelimumab. Results: After receiving tremelimumab, there was a median of 30% increase in unique productive sequences of TCR V-beta CDR3 in 19 out of 21 patients, and a median decrease of 30% in only 2 out of 21 patients. These changes were significant for richness (P = 0.01) and for Shannon index diversity (P = 0.04). In comparison, serially collected PBMCs from four healthy donors did not show a significant change in TCR V-beta CDR3 diversity over 1 year. There was a significant difference in the total unique productive TCR V-beta CDR3 sequences between patients experiencing toxicity with tremelimumab compared with patients without toxicity (P = 0.05). No relevant differences were noted between clinical responders and nonresponders. Conclusions: CTLA4 blockade with tremelimumab diversifies the peripheral T-cell pool, representing a pharmacodynamic effect of how this class of antibodies modulates the human immune system. Clin Cancer Res; 20(9); 2424–32. ©2014 AACR.

The Oncogenic BRAF Kinase Inhibitor PLX4032/RG7204 Does Not Affect the Viability or Function of Human Lymphocytes across a Wide Range of Concentrations

Purpose: PLX4032 (RG7204), an oncogenic BRAF kinase inhibitor undergoing clinical evaluation, has high response rates in early clinical trials in patients with advanced BRAFV600E mutant melanoma. Combining PLX4032 with immunotherapy may allow expanding the durability of responses. The effects of PLX4032 on immune cells were studied to explore the feasibility of future combinatorial approaches with immunotherapy for melanoma. Experimental Design: Peripheral blood mononuclear cells (PBMC) and BRAFV600E mutant melanoma cells were exposed to increasing concentrations of PLX4032 and the cell viability, proliferation, cell cycle, apoptosis, and phosphorylation of signaling proteins were analyzed. Effects of PLX4032 on antigen-specific T-cell function were analyzed by specific cytokine release and cytotoxicity activity. Results: The 50% inhibition concentration (IC50) of PLX4032 for resting human PBMC was between 50 and 150 μmol/L compared with an IC50 below 1 μmol/L for sensitive BRAFV600E mutant melanoma cell lines. Activated lymphocytes were even more resistant with no growth inhibition up to concentrations of 250 μmol/L. PLX4032 had a marginal effect on cell-cycle arrest, apoptotic cell changes or alteration of phosphorylated signaling molecules in lymphocytes. Functional analysis of specific antigen recognition showed preserved T-cell function up to 10-μmol/L concentration of PLX4032, whereas the cytotoxic activity of PLX4032 was maintained up to high concentrations of 50 μmol/L. Conclusions: The preserved viability and function of lymphocytes exposed to high concentrations of PLX4032 suggest that this agent could be a potential candidate for combining with immunotherapy strategies for the treatment of patients with BRAFV600E mutant melanoma. Clin Cancer Res; 16(24); 6040–8. ©2010 AACR.

Intratumoral Immune Cell Infiltrates, FoxP3, and Indoleamine 2,3-Dioxygenase in Patients with Melanoma Undergoing CTLA4 Blockade

Purpose: CTL-associated antigen 4 (CTLA4)-blocking monoclonal antibodies induce long-term regression of metastatic melanoma in some patients, but the exact mechanism is unknown. In this study, biopsies of selected accessible tumor lesions from patients treated with tremelimumab were examined to further elucidate the mechanism of its antitumor activity. Experimental Design: Fifteen tumor biopsies from 7 patients who had been treated with tremelimumab (CP-675,206) were collected. Samples were analyzed for melanoma markers, immune cell subset markers, the presence of the T regulatory-specific transcription factor FoxP3 and the immunosuppressive enzyme indoleamine 2,3-dioxygenase (IDO). Results: Clinically responding lesions had diffuse intratumoral infiltrates of CD8+ T cells that were markedly increased in cases where comparison with a baseline biopsy was available. Nonregressing lesions had sparse, patchy CD8+ intratumoral infiltrates. Patients with regressing lesions had an increased frequency of CD8+ cells with or without a concomitant increase in CD4+ cells. Two of 3 responding patients with paired samples showed a slight increase in the number of FoxP3+ cells in the postdosing biopsies. In patients with regressing lesions who had paired samples, the intensity of IDO staining in macrophages and/or melanoma cells showed no clear pattern of change postdosing. Conclusions: Administration of tremelimumab was associated with massive intratumoral infiltrates of CD8+ CTLs in patients with regressing tumors but had varying effects on intratumoral infiltrates of CD4+ and FoxP3+ cells or intratumoral expression of IDO.

Detailed analysis of immunologic effects of the cytotoxic T lymphocyte-associated antigen 4-blocking monoclonal antibody tremelimumab in peripheral blood of patients with melanoma.

BackgroundCTLA4-blocking antibodies induce tumor regression in a subset of patients with melanoma. Analysis of immune parameters in peripheral blood may help define how responses are mediated.MethodsPeripheral blood from HLA-A*0201-positive patients with advanced melanoma receiving tremelimumab (formerly CP-675,206) at 10 mg/kg monthly was repeatedly sampled during the first 4 cycles. Samples were analyzed by 1) tetramer and ELISPOT assays for reactivity to CMV, EBV, MART1, gp100, and tyrosinase; 2) activation HLA-DR and memory CD45RO markers on CD4+/CD8+ cells; and 3) real-time quantitative PCR of mRNA for FoxP3 transcription factor, preferentially expressed by T regulatory cells. The primary endpoint was difference in MART1-specific T cells by tetramer assay. Immunological data were explored for significant trends using clustering analysis.ResultsThree of 12 patients eligible for immune monitoring had tumor regression lasting > 2 years without relapse. There was no significant change in percent of MART1-specific T cells by tetramer assay. Additionally, there was no generalized trend toward postdosing changes in other antigen-specific CD8+ cell populations, FoxP3 transcripts, or overall changes in surface expression of T-cell activation or memory markers. Unsupervised hierarchical clustering based on immune monitoring data segregated patients randomly. However, clustering according to T-cell activation or memory markers separated patients with clinical response and most patients with inflammatory toxicity into a common subgroup.ConclusionAdministration of CTLA4-blocking antibody tremelimumab to patients with advanced melanoma results in a subset of patients with long-lived tumor responses. T-cell activation and memory markers served as the only readout of the pharmacodynamic effects of this antibody in peripheral blood.Clinical trial registration numberNCT00086489