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IGV plot of RNA-Seq from YUMM1.1, YUMM1.7 and YUMM2.1; western blot analysis of cytoplasmic and nuclear beta-catenin in YUMM1.7 and YUMM2.1 cell lines with or without exposure to 10 uM 4HT for 48 hours; top-flash activity of total beta-catenin in YUMM1.7 and YUMM2.1 with or without exposure to 10uM 4HT for 48 hours; representative immunofluorescence of beta-catenin stained non-treated tumors.

IGV plot exome sequencing from YUMM1.1, YUMM1.7 and YUMM2.1, tumor growth curve of YUMM1.7 and B16 with 4 mice in each group, analysis of the non-synonymous mutational load compared to a strain-matched normal with known dbSNP variants excluded.

Gating strategy of CD11c+B220-, CD11c+B220+, CD11c+B220-CD8+ and CD11c+B220-CD103+ cells; gating strategy of CD11b+MHC-IIhigh DCs in CD11c+ cells; gating strategy of CD11b+F4/80+TAMs, CD11b+F4/80+MHC-IIlow TAMs and CD11b+F4/80+MHC-IIhigh TAMs; gating strategy of MO-MDSC (CD11b+Ly6ChighLy6Glow) and PMN-MDSC (CD11b+Ly6ClowLy6Ghigh); gating strategy of Tregs (CD4+CD25+FoxP3+); corresponding normalized enrichment scores (NES), P values and false discovery rates (FDR) of the GSEA plots for YUMM2.1 versus YUMM1.1 enriched pathways involved in immune response, cytokine production and inflammatory response.

Quantification of CD3+CD8+ (CD8 T-cells) and (B) CD3+CD4+ (CD4 T-cells) in both tumors and spleens in YUMM2.1; gating strategy after exclusion of dead cells of CD3+CD8+ and CD3+CD4+ cells after gating for CD3+ cells; quantification of CD3+CD8+ (CD8 T-cells) in MC38 and YUMM2.1 spleens; CD3+CD4+ (CD4 T-cells) in MC38 and YUMM 2.1 spleens CD8 T-cells in both tumors and spleens in YUMM1.1.

The supplementary data contains supplemental methods, figures, tables and the clinical trial protocol in which patients from this study were enrolled.

The programmed cell death protein 1 (PD-1) limits effector T-cell functions in peripheral tissues, and its inhibition leads to clinical benefit in different cancers. To better understand how PD-1 blockade therapy modulates the tumor–host interactions, we evaluated three syngeneic murine tumor models, the BRAFV600E-driven YUMM1.1 and YUMM2.1 melanomas, and the carcinogen-induced murine colon adenocarcinoma MC38. The YUMM cell lines were established from mice with melanocyte-specific BRAFV600E mutation and PTEN loss (BRAFV600E/PTEN−/−). Anti–PD-1 or anti–PD-L1 therapy engendered strong antitumor activity against MC38 and YUMM2.1, but not YUMM1.1. PD-L1 expression did not differ between the three models at baseline or upon interferon stimulation. Whereas mutational load was high in MC38, it was lower in both YUMM models. In YUMM2.1, the antitumor activity of PD-1 blockade had a critical requirement for both CD4 and CD8 T cells, as well as CD28 and CD80/86 costimulation, with an increase in CD11c+CD11b+MHC-IIhigh dendritic cells and tumor-associated macrophages in the tumors after PD-1 blockade. Compared with YUMM1.1, YUMM2.1 exhibited a more inflammatory profile by RNA sequencing analysis, with an increase in expression of chemokine-trafficking genes that are related to immune cell recruitment and T-cell priming. In conclusion, response to PD-1 blockade therapy in tumor models requires CD4 and CD8 T cells and costimulation that is mediated by dendritic cells and macrophages. Cancer Immunol Res; 4(10); 845–57. ©2016 AACR.

A promising arsenal of targeted and immunotherapy treatments for metastatic melanoma has emerged over the last decade. With these therapies, we now face new mechanisms of tumor-acquired resistance. We report here a patient whose metastatic melanoma underwent dedifferentiation as a resistance mechanism to adoptive T-cell transfer therapy (ACT) to the MART1 antigen, a phenomenon that had been observed only in mouse studies to date. After an initial period of tumor regression, the patient presented in relapse with tumors lacking melanocytic antigens (MART1, gp100) and expressing an inflammation-induced neural crest marker (NGFR). We demonstrate using human melanoma cell lines that this resistance phenotype can be induced in vitro by treatment with MART1 T cell receptor–expressing T cells or with TNFα, and that the phenotype is reversible with withdrawal of inflammatory stimuli. This supports the hypothesis that acquired resistance to cancer immunotherapy can be mediated by inflammation-induced cancer dedifferentiation.Significance: We report a patient whose metastatic melanoma underwent inflammation-induced dedifferentiation as a resistance mechanism to ACT to the MART1 antigen. Our results suggest that future melanoma ACT protocols may benefit from the simultaneous targeting of multiple tumor antigens, modulating the inflammatory response, and inhibition of inflammatory dedifferentiation-inducing signals. Cancer Discov; 8(8); 935–43. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 899

Supplementary figure legends

PDF file - 48KB, Lack of correlations between changes in ALC (x axis) and changes in the unique productive sequences (y axis) expressed in % of change both. Each dot corresponds to a GA patient.

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.

PDF file - 411KB, Scatter plots for all patients with a rank-rank analysis . For every GA patient a dot plot was generated ranking each single clone according to abundance in baseline (x axis) and post-treatment (y axis). Values range from highest frequency (0) to lowest frequency.

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.

PDF file - 247KB, MAPK pathway is almost inactive in resting PBMCs.

PDF file - 65KB, Table S1 Summary for TCR V-beta CDR3 sequence analysis. Table S2 Number of unique Productive Sequences in Top 25% abundance at four different timepoints. Table S3 Number of unique productive Sequences in Top 25% clones at baseline and at Day 30-60.

PDF file - 206KB, Restoration of the MAPK pathway activity by vemurafenib in lymphocytes exposed to PD-L1.

In melanoma, dysregulation of the MAPK pathway, usually via BRAF(V600) or NRAS(Q61) somatic mutations, leads to constitutive ERK signaling. While BRAF inhibitors are initially effective for BRAF-mutant melanoma, no FDA-approved targeted therapies exist for BRAF-inhibitor-resistant BRAF(V600), NRAS mutant, or wild-type melanoma.The 50% inhibitory concentration (IC50) of SCH772984, a novel inhibitor of ERK1/2, was determined in a panel of 50 melanoma cell lines. Effects on MAPK and AKT signaling by western blotting and cell cycle by flow cytometry were determined.Sensitivity fell into three groups: sensitive, 50% inhibitory concentration (IC50)1 μM; intermediately sensitive, IC50 1-2 μM; and resistant,2 μM. Fifteen of 21 (71%) BRAF mutants, including 4 with innate vemurafenib resistance, were sensitive to SCH772984. All three (100%) BRAF/NRAS double mutants, 11 of 14 (78%) NRAS mutants and 5 of 7 (71%) wild-type melanomas were sensitive. Among BRAF(V600) mutants with in vitro acquired resistance to vemurafenib, those with MAPK pathway reactivation as the mechanism of resistance were sensitive to SCH772984. SCH772984 caused G1 arrest and induced apoptosis.Combining vemurafenib and SCH722984 in BRAF mutant melanoma was synergistic in a majority of cell lines and significantly delayed the onset of acquired resistance in long term in vitro assays. Therefore, SCH772984 may be clinically applicable as a treatment for non-BRAF mutant melanoma or in BRAF-mutant melanoma with innate or acquired resistance, alone or in combination with BRAF inhibitors.

Background The MORPHEUS platform comprises multiple randomized Phase Ib/II trials to identify early safety and efficacy signals for treatment combinations across cancers. Seli interacts with CD40 on antigen presenting cells, resulting in activation and priming of CD8 T-cells. Atezo (anti-PD-L1)+seli (CD40 agonist) was evaluated with gem+nabP for pancreatic ductal adenocarcinoma (PDAC), or with bev for triple-negative breast cancer (TNBC) and colorectal cancer (CRC). Methods MORPHEUS-PDAC, MORPHEUS-TNBC and MORPHEUS-CRC enrolled 1L metastatic (m) PDAC, 2L locally advanced or mTNBC or 3L mCRC patients, respectively. Experimental arm patients received atezo (840 mg IV q2w) and seli (16 mg SC on D1 every 28-day cycle for C1-4 and every third cycle thereafter). Patients also received gem (1000 mg/m2) and nabP (1000 mg/m2, 125 mg/m2 respectively, IV on D1, 8, 15 every 28-day cycle) in PDAC or bev (10 mg/kg IV q2w) in TNBC and CRC. Control treatments were gem+nabP in PDAC, capecitabine in TNBC, and regorafenib in CRC. Primary endpoints were safety and objective response rate (ORR; investigator-assessed RECIST 1.1). PD-L1 and CD8/panCK IHC were tested in all biopsies. Results All treated patients were safety evaluable. MORPHEUS-PDAC (20-week interim analysis): 9 patients received atezo+seli+gem+nabP and 4 received control. Treatment-related adverse events (TRAEs) were seen in all. Treatment-related serious AEs (SAEs) occurred in 6 patients (67%) receiving atezo+seli+gem+nabP and 1 (25%) receiving control. Confirmed ORRs: 44% (95%CI:14–79) and 25% (95%CI:6–81), respectively. MORPHEUS-TNBC (27-week interim analysis): 6 patients received atezo+seli+bev and 24 received control. TRAEs were seen in 5 patients (83%) receiving atezo+seli+bev and 18 (75%) receiving control. Treatment-related SAEs occurred in 1 patient in each arm (17% and 4%, respectively). Confirmed ORRs: 17% (95%CI:0.4–64) and 21% (95%CI:7–42), respectively. All 6 patients receiving atezo+seli+bev were PD-L1 negative (SP142 IHC assay) at baseline; the only patient with partial response (PR) showed upregulation of PD-L1 expression at week 3. MORPHEUS-CRC (18-week interim analysis): 6 patients received atezo+seli+bev and 13 received control. TRAEs were seen in all patients receiving atezo+seli+bev and 12 (92%) receiving control. Treatment-related SAEs occurred in 3 patients (50%) receiving atezo+seli+bev and 1 (8%) receiving control. No responses occurred in either study arm. Paired biopsies for 3 patients (60%) receiving atezo+seli+bev suggest on-treatment increases in CD8 T-cell infiltration into tumors. Conclusions Toxicities related to the atezo+seli combinations were consistent with individual study treatments. Preliminary efficacy was observed for atezo+seli+gem+nabP in PDAC. Together with preliminary evidence of on-treatment pharmacodynamic effects in CRC and TNBC tumor samples, CD40 agonist strategies warrant further investigation. Trial Registration MORPHEUS-PDAC: NCT03193190; MORPHEUS-TNBC: NCT03424005; MORPHEUS-CRC: NCT03555149. Ethics Approval The trial was conducted according to the principles of the Declaration of Helsinki. All patients provided written informed consent. Protocol approval was obtained from independent review boards or ethics committees at each site.

The determination of individual cell trajectories through a high-dimensional cell-state space is an outstanding challenge for understanding biological changes ranging from cellular differentiation to epigenetic responses of diseased cells upon drugging. We integrate experiments and theory to determine the trajectories that single BRAFV600E mutant melanoma cancer cells take between drug-naive and drug-tolerant states. Although single-cell omics tools can yield snapshots of the cell-state landscape, the determination of individual cell trajectories through that space can be confounded by stochastic cell-state switching. We assayed for a panel of signaling, phenotypic, and metabolic regulators at points across 5 days of drug treatment to uncover a cell-state landscape with two paths connecting drug-naive and drug-tolerant states. The trajectory a given cell takes depends upon the drug-naive level of a lineage-restricted transcription factor. Each trajectory exhibits unique druggable susceptibilities, thus updating the paradigm of adaptive resistance development in an isogenic cell population., Detailed understanding of how cancer cells transition from a drug sensitive to a tolerant state is lacking. Here, using single cell proteomic and metabolic data the authors uncover that isogenic BRAF mutant melanoma cells can take two distinct paths to become tolerant to BRAF inhibition.

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.

The determination of individual cell trajectories through a high-dimensional cell-state space is an outstanding challenge, with relevance towards understanding biological changes ranging from cellular differentiation to epigenetic (adaptive) responses of diseased cells to drugging. We report on a combined experimental and theoretic method for determining the trajectories that specific highly plastic BRAFV600E mutant patient-derived melanoma cancer cells take between drug-naïve and drug-tolerant states. Recent studies have implicated non-genetic, fast-acting resistance mechanisms are activated in these cells following BRAF inhibition. While single-cell highly multiplex omics tools can yield snapshots of the cell state space landscape sampled at any given time point, individual cell trajectories must be inferred from a kinetic series of snapshots, and that inference can be confounded by stochastic cell state switching. Using a microfludic-based single-cell integrated proteomic and metabolic assay, we assayed for a panel of signaling, phenotypic, and metabolic regulators at four time points during the first five days of drug treatment. Dimensional reduction of the resultant data set, coupled with information theoretic analysis, uncovered a complex cell state landscape and identified two distinct paths connecting drug-naïve and drug-tolerant states. Cells are shown to exclusively traverse one of the two pathways depending on the level of the lineage restricted transcription factor MITF in the drug-naïve cells. The two trajectories are associated with distinct signaling and metabolic susceptibilities, and are independently druggable. Our results update the paradigm of adaptive resistance development in an isogenic cell population and offer insight into the design of more effective combination therapies.

SummaryWe resolved a mechanism connecting tumor epigenetic plasticity with non-genetic adaptive resistance to therapy, with MAPK inhibition ofBRAF-mutant melanomas providing the model. These cancer cells undergo multiple, reversible drug-induced cell-state transitions, ultimately yielding a drug-resistant mesenchymal-like phenotype. A kinetic series of transcriptome and epigenome data, collected over two months of drug treatment and release, revealed changing levels of thousands of genes and extensive chromatin remodeling. However, a 3-step computational algorithm greatly simplified the interpretation of these changes, and revealed that the whole adaptive process was controlled by a gene module activated within just three days of treatment, with RelA driving chromatin remodeling to establish an epigenetic program encoding long-term phenotype changes. These findings were confirmed across several patient-derived cell lines and in melanoma patients under MAPK inhibitor treatment. Co-targeting BRAF and histone-modifying enzymes arrests adaptive transitions towards drug tolerance in epigenetically plastic melanoma cells and may be exploited therapeutically.

Phenotypic plasticity is associated with non-genetic drug tolerance in several cancers. Such plasticity can arise from chromatin remodeling, transcriptomic reprogramming, and/or protein signaling rewiring, and is characterized as a cell state transition in response to molecular or physical perturbations. This, in turn, can confound interpretations of drug responses and resistance development. Using BRAF-mutant melanoma cell lines as the prototype, we report on a joint theoretical and experimental investigation of the cell-state transition dynamics associated with BRAF inhibitor drug tolerance. Thermodynamically motivated surprisal analysis of transcriptome data was used to treat the cell population as an entropy maximizing system under the influence of time-dependent constraints. This permits the extraction of an epigenetic potential landscape for drug-induced phenotypic evolution. Single-cell flow cytometry data of the same system were modeled with a modified Fokker-Planck-type kinetic model. The two approaches yield a consistent picture that accounts for the phenotypic heterogeneity observed over the course of drug tolerance development. The results reveal that, in certain plastic cancers, the population heterogeneity and evolution of cell phenotypes may be understood by accounting for the competing interactions of the epigenetic potential landscape and state-dependent cell proliferation. Accounting for such competition permits accurate, experimentally verifiable predictions that can potentially guide the design of effective treatment strategies., Author summary Cancer cells exhibit varied degrees of phenotypic heterogeneity. These phenotypes, each of them with unique molecular and functional profiles, display dynamic interconversion in response to drug perturbations, and can evolve to form new drug-tolerant phenotypes. Such phenotypic plasticity, in turn, renders tumor cells extremely difficult to treat. To get a quantitative biophysical understanding of the origins of the phenotypic equilibrium and evolution associated with drug tolerance development in highly plastic patient-derived melanoma cells, we employed joint experimental and computational approaches, using either bulk or single cell measurements as input, to interrogate the epigenetic landscape of the phenotypic evolution. We found that the observed phenotypic equilibria were established via competition between state-dependent net proliferation rates and landscape potential. The results reveal how the tumor cells maintain a phenotypic heterogeneity that facilitates appropriate responses to external cues. They implicate that, in certain phenotypically plastic tumor cells, drug targeting the driver oncogenes may not have sustained efficacy unless the phenotypic plasticity of the tumor is co-targeted.

Integrated proteomic and metabolic single-cell assays reveal multiple independent adaptive responses to drug tolerance in a BRAF-mutant melanoma cell line Cancers commonly develop resistance against chemotherapeutics or targeted therapies through various types of genetic or non-genetic mechanisms. Non-genetic mechanisms have been shown to occur early on and can provide a latent reservoir of cells for the emergence of various different type of mechanisms, yet very limited understanding of process were resolve main from bulk analysis. Considering the heterogeneous nature of the tumor cells, a single-cell level characterization of the process worth detailed further investigation. Using MAPK inhibition of BRAF-mutant melanomas as a model system, we resolved that cells take different paths to go from drug-sensitive to drug-resistant state. Using a microfludic-based single-cell integrated proteomic and metabolic assay, we assayed for a panel of signaling, phenotypic, and metabolic regulators at four time points during the first five days of drug treatment. Dimensional reduction of the resultant data set, coupled with information theoretic analysis, uncovered a complex cell state landscape and identified two distinct paths connecting drug-naïve and drug-tolerant states. Cells are shown to exclusively traverse one of the two pathways depending on the level of the lineage restricted transcription factor MITF in the drug-naïve cells. The two trajectories are associated with distinct signaling and metabolic susceptibilities, and are independently druggable. Our results update the paradigm of adaptive resistance development in an isogenic cell population and offer insight into the design of more effective combination therapies. Citation Format: Yapeng Su, Guideng Li, Melissa Ko, Hanjun Cheng, Ronghui Zhu, Min Xue, Lidia Robert, Raphael Levine, Antoni Ribas, Garry Nolan, Wei Wei, Sylvia Plevritis, David Baltimore, James R. Heath. Systems biology for investigating drug resistance mechanism of melanoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6585.

A promising arsenal of targeted and immunotherapy treatments for metastatic melanoma has emerged over the last decade. With these therapies, we now face new mechanisms of tumor-acquired resistance. We report here a patient whose metastatic melanoma underwent dedifferentiation as a resistance mechanism to adoptive T-cell transfer therapy (ACT) to the MART1 antigen, a phenomenon that had been observed only in mouse studies to date. After an initial period of tumor regression, the patient presented in relapse with tumors lacking melanocytic antigens (MART1, gp100) and expressing an inflammation-induced neural crest marker (NGFR). We demonstrate using human melanoma cell lines that this resistance phenotype can be induced in vitro by treatment with MART1 T cell receptor–expressing T cells or with TNFα, and that the phenotype is reversible with withdrawal of inflammatory stimuli. This supports the hypothesis that acquired resistance to cancer immunotherapy can be mediated by inflammation-induced cancer dedifferentiation. Significance: We report a patient whose metastatic melanoma underwent inflammation-induced dedifferentiation as a resistance mechanism to ACT to the MART1 antigen. Our results suggest that future melanoma ACT protocols may benefit from the simultaneous targeting of multiple tumor antigens, modulating the inflammatory response, and inhibition of inflammatory dedifferentiation-inducing signals. Cancer Discov; 8(8); 935–43. ©2018 AACR. This article is highlighted in the In This Issue feature, p. 899

Malignant transformation can result in melanoma cells that resemble different stages of their embryonic development. Our gene expression analysis of human melanoma cell lines and patient tumors revealed that melanoma follows a two-dimensional differentiation trajectory that can be subclassified into four progressive subtypes. This differentiation model is associated with subtype-specific sensitivity to iron-dependent oxidative stress and cell death known as ferroptosis. Receptor tyrosine kinase-mediated resistance to mitogen-activated protein kinase targeted therapies and activation of the inflammatory signaling associated with immune therapy involves transitions along this differentiation trajectory, which lead to increased sensitivity to ferroptosis. Therefore, ferroptosis-inducing drugs present an orthogonal therapeutic approach to target the differentiation plasticity of melanoma cells to increase the efficacy of targeted and immune therapies.

BACKGROUND. Constitutive activation of ERK1/2 occurs in various cancers, and its reactivation is a well-described resistance mechanism to MAPK inhibitors. ERK inhibitors may overcome the limitations of MAPK inhibitor blockade. The dual mechanism inhibitor SCH772984 has shown promising preclinical activity across various BRAFV600/RAS-mutant cancer cell lines and human cancer xenografts. METHODS. We have developed an orally bioavailable ERK inhibitor, MK-8353; conducted preclinical studies to demonstrate activity, pharmacodynamic endpoints, dosing, and schedule; completed a study in healthy volunteers (P07652); and subsequently performed a phase I clinical trial in patients with advanced solid tumors (MK-8353-001). In the P07652 study, MK-8353 was administered as a single dose in 10- to 400-mg dose cohorts, whereas in the MK-8353-001 study, MK-8353 was administered in 100- to 800-mg dose cohorts orally twice daily. Safety, tolerability, pharmacokinetics, pharmacodynamics, and antitumor activity were analyzed. RESULTS. MK-8353 exhibited comparable potency with SCH772984 across various preclinical cancer models. Forty-eight patients were enrolled in the P07652 study, and twenty-six patients were enrolled in the MK-8353-001 study. Adverse events included diarrhea (44%), fatigue (40%), nausea (32%), and rash (28%). Dose-limiting toxicity was observed in the 400-mg and 800-mg dose cohorts. Sufficient exposure to MK-8353 was noted that correlated with biological activity in preclinical data. Three of fifteen patients evaluable for treatment response in the MK-8353-001 study had partial response, all with BRAFV600-mutant melanomas. CONCLUSION. MK-8353 was well tolerated up to 400 mg twice daily and exhibited antitumor activity in patients with BRAFV600-mutant melanoma. However, antitumor activity was not particularly correlated with pharmacodynamic parameters. TRIAL REGISTRATION. ClinicalTrials.gov NCT01358331. FUNDING. Merck Sharp & Dohme Corp., a subsidiary of Merck & Co. Inc., and NIH (P01 CA168585 and R35 CA197633).

Therapeutic resistance is a major obstacle to achieving durable clinical responses with targeted therapies, highlighting a need to elucidate the underlying mechanisms responsible for resistance and identify strategies to overcome this challenge. An emerging body of data implicates the tyrosine kinase MET in mediating resistance to BRAF inhibitors in BRAFV600E mutant melanoma. In this study we observed a dominant role for the HGF/MET axis in mediating resistance to BRAF and MEK inhibitors in models of BRAFV600E and NRAS mutant melanoma. In addition, we showed that MAPK pathway inhibition induced rapid increases in MET and GAB1 levels, providing novel mechanistic insight into how BRAFV600E mutant melanoma is primed for HGF-mediated rescue. We also determined that tumor-derived HGF, not systemic HGF, may be required to convey resistance to BRAF inhibition in vivo and that resistance could be reversed following treatment with AMG 337, a selective MET inhibitor. In summary, these findings support the clinical evaluation of MET-directed targeted therapy to circumvent resistance to BRAF and MEK inhibitors in BRAFV600E mutant melanoma. In addition, the induction of MET following treatment with BRAF and MEK inhibitors has the potential to serve as a predictive biomarker for identifying patients best suited for MET inhibitor combination therapy.

The treatment landscape for metastatic melanoma has changed considerably over the last several years with the approval of targeted therapy, such as BRAF inhibitors, and immunotherapy, such as immune checkpoint inhibitors that block cytotoxic T lymphocyte associated protein 4 (CTLA-4) and programmed cell death 1 (PD-1). However, approximately 40% of patients do not respond to the current standard of care, and up to one-third of patients who initially respond to therapy can relapse. Novel therapies that act by a distinct mechanism of action may be needed to increase durable response rates in metastatic melanoma. Bispecific T cell engager (BiTE®) antibody constructs directly connect T cells to tumor cells and redirect T cell lysis to achieve tumor cell killing. BiTE®-mediated cytotoxicity is not dependent on a specific T cell receptor or peptide-MHC complex and has the potential to circumvent common immune resistance mechanisms. We have generated a BiTE® with half-life extension (HLE) that targets the atypical cadherin CDH19 on melanoma cells and CD3 on T cells (anti-CDH19/CD3 HLE BiTE®). We have also generated an HLE BiTE® that targets delta-like ligand 3 (DLL3) on tumor cells and CD3 on T cells, anti-DLL3/CD3 HLE BiTE®, or AMG 757. CDH19 and DLL3 are expressed on about half of primary and metastatic melanoma tumors prior to treatment. In this study, we investigated the expression of CDH19 and DLL3 and the activity of the corresponding BiTE® antibody constructs in a panel of 14 melanoma cell lines that were derived from patients that were resistant to either targeted therapy or immune checkpoint therapy and expanded the spectrum of recently defined multistage differentiation melanoma subtypes from melanocytic, transitional, neural crest-like and de-differentiated subtypes (Tsoi et al. Cancer Cell 2017). The cell surface expression of CDH19 and DLL3 was determined by flow cytometry. We then used T cell-dependent cytotoxicity (TDCC) assays to assess the activity of the anti-CDH19/CD3 HLE BiTE® and AMG 757 against the cell lines. 13/14 (93%) of the treatment-resistant melanoma cell lines expressed CDH19 on the cell surface, and 9/14 (64%) of the cell lines expressed cell surface DLL3. The anti-CDH19/CD3 HLE BiTE® and AMG 757 demonstrated potent cell killing of CDH19-positive or DLL3-positive melanoma cells, respectively, in TDCC assays, with EC50 values in the low picomolar range. These data show that melanoma cells that become resistant to targeted therapy and/or immune checkpoint blockade can be effectively targeted with BiTE® antibody constructs and suggest that the anti-CDH19/CD3 HLE BiTE® and AMG 757 may be potential novel therapies for treatment of relapsed and/or refractory metastatic melanoma. Citation Format: Julie M. Bailis, Fei Lee, Michael Giffin, Paul Hughes, Jennifer Tsoi, Lidia Robert, Thomas G. Graeber, Antoni Ribas, Angela Coxon. Melanoma subtypes that emerge during adaptive resistance to therapy are targets for bispecific T cell engager (BiTE®) antibody constructs directed to CDH19 and DLL3 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 553.

The programmed cell death protein 1 (PD-1) limits effector T-cell functions in peripheral tissues, and its inhibition leads to clinical benefit in different cancers. To better understand how PD-1 blockade therapy modulates the tumor–host interactions, we evaluated three syngeneic murine tumor models, the BRAFV600E-driven YUMM1.1 and YUMM2.1 melanomas, and the carcinogen-induced murine colon adenocarcinoma MC38. The YUMM cell lines were established from mice with melanocyte-specific BRAFV600E mutation and PTEN loss (BRAFV600E/PTEN−/−). Anti–PD-1 or anti–PD-L1 therapy engendered strong antitumor activity against MC38 and YUMM2.1, but not YUMM1.1. PD-L1 expression did not differ between the three models at baseline or upon interferon stimulation. Whereas mutational load was high in MC38, it was lower in both YUMM models. In YUMM2.1, the antitumor activity of PD-1 blockade had a critical requirement for both CD4 and CD8 T cells, as well as CD28 and CD80/86 costimulation, with an increase in CD11c+CD11b+MHC-IIhigh dendritic cells and tumor-associated macrophages in the tumors after PD-1 blockade. Compared with YUMM1.1, YUMM2.1 exhibited a more inflammatory profile by RNA sequencing analysis, with an increase in expression of chemokine-trafficking genes that are related to immune cell recruitment and T-cell priming. In conclusion, response to PD-1 blockade therapy in tumor models requires CD4 and CD8 T cells and costimulation that is mediated by dendritic cells and macrophages. Cancer Immunol Res; 4(10); 845–57. ©2016 AACR.

Increased expression of the Microphthalmia-associated transcription factor (MITF) contributes to melanoma progression and resistance to BRAF pathway inhibition. Here we show that the lack of MITF is associated with more severe resistance to a range of inhibitors, while its presence is required for robust drug responses. Both in primary and acquired resistance, MITF levels inversely correlate with the expression of several activated receptor tyrosine kinases, most frequently AXL. The MITF-low/AXL-high/drug-resistance phenotype is common among mutant BRAF and NRAS melanoma cell lines. The dichotomous behaviour of MITF in drug response is corroborated in vemurafenib-resistant biopsies, including MITF-high and -low clones in a relapsed patient. Furthermore, drug cocktails containing AXL inhibitor enhance melanoma cell elimination by BRAF or ERK inhibition. Our results demonstrate that a low MITF/AXL ratio predicts early resistance to multiple targeted drugs, and warrant clinical validation of AXL inhibitors to combat resistance of BRAF and NRAS mutant MITF-low melanomas.

Cutaneous squamous-cell carcinomas and keratoacanthomas are common findings in patients treated with BRAF inhibitors.We performed a molecular analysis to identify oncogenic mutations (HRAS, KRAS, NRAS, CDKN2A, and TP53) in the lesions from patients treated with the BRAF inhibitor vemurafenib. An analysis of an independent validation set and functional studies with BRAF inhibitors in the presence of the prevalent RAS mutation was also performed.Among 21 tumor samples, 13 had RAS mutations (12 in HRAS). In a validation set of 14 samples, 8 had RAS mutations (4 in HRAS). Thus, 60% (21 of 35) of the specimens harbored RAS mutations, the most prevalent being HRAS Q61L. Increased proliferation of HRAS Q61L-mutant cell lines exposed to vemurafenib was associated with mitogen-activated protein kinase (MAPK)-pathway signaling and activation of ERK-mediated transcription. In a mouse model of HRAS Q61L-mediated skin carcinogenesis, the vemurafenib analogue PLX4720 was not an initiator or a promoter of carcinogenesis but accelerated growth of the lesions harboring HRAS mutations, and this growth was blocked by concomitant treatment with a MEK inhibitor.Mutations in RAS, particularly HRAS, are frequent in cutaneous squamous-cell carcinomas and keratoacanthomas that develop in patients treated with vemurafenib. The molecular mechanism is consistent with the paradoxical activation of MAPK signaling and leads to accelerated growth of these lesions. (Funded by Hoffmann-La Roche and others; ClinicalTrials.gov numbers, NCT00405587, NCT00949702, NCT01001299, and NCT01006980.).

Targeted therapies have induced high response rates and improved survival in patients with cancer. However, the long-term effectiveness of targeted therapies has been limited by the development of acquired resistance in the majority of patients. On the other hand, the modern immunotherapy strategies have been associated with durable responses but in limited number of patients. Accordingly, research efforts have been focused on examining the effects of combinations of targeted therapy and immunotherapy in several different histological subtypes of cancer. There has been accumulated evidence to suggest that targeted therapy can induce immune effects in the tumor cells, the host immune system, and the tumor microenvironment. Subsequently, clinical trials have been designed to examine the efficacy of combining immune checkpoint blockade or adoptive cell transfer with tyrosine kinase inhibitors, HER family blockade, anti-angiogenic agents, histone deacetylase inhibitors, and cancer stem cell inhibitors. To date, the combination of immunotherapy with targeted therapy has demonstrated potential as a cancer treatment strategy, but further optimizations are required and caution must be taken to avoid toxicity. The current review summarizes existing evidence and provides rationale supporting the use of combined targeted and immune-therapy approaches in patients with different types of cancer.

Immune-regulatory mechanisms are used by cancer to hide from the immune system. Advances and in-depth understanding of the biology of melanoma and its interaction with the immune system have led to the development of some of antagonistic antibodies to the programmed death 1 pathway (PD-1) and one of its ligands, programmed death ligand 1 (PD-L1), which are demonstrating high clinical benefit rates and tolerability. Blocking the immune-regulatory checkpoints that limit T-cell responses to melanoma upon PD-1/PD-L1 modulation has provided clinically validated targets for cancer immunotherapy. Combinations with other anti-melanoma agents may result in additional benefits. Nivolumab, pembrolizumab (formerly known as MK-3475 and lambrolizumab), and pidilizumab are anti-PD-1 antibodies in clinical development for melanoma, non-small cell lung cancer, renal cell carcinoma, head and neck cancers, lymphoma, and several other cancers. Long-term survivors already have been reported with these therapies. In this review, we discuss the current state of anti-PD-1 agents, the evidence in the literature to support the combination of anti-PD-1 antibodies with other anti-cancer agents and discuss the future directions for rational design of clinical trials that keep on increasing the number of long-term survivors.

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.

Canonical Wnt signaling plays an important role in development and disease, regulating transcription of target genes and stabilizing many proteins phosphorylated by glycogen synthase kinase 3 (GSK3). We observed that the MiT family of transcription factors, which includes the melanoma oncogene MITF (micropthalmiaassociated transcription factor) and the lysosomal master regulator TFEB, had the highest phylogenetic conservation of three consecutive putative GSK3 phosphorylation sites in animal proteomes. This finding prompted us to examine the relationship between MITF, endolysosomal biogenesis, and Wnt signaling. Here we report that MITF expression levels correlated with the expression of a large subset of lysosomal genes in melanoma cell lines. MITF expression in the tetracycline-inducible C32 melanoma model caused a marked increase in vesicular structures, and increased expression of late endosomal proteins, such as Rab7, LAMP1, and CD63. These late endosomes were not functional lysosomes as they were less active in proteolysis, yet were able to concentrate Axin1, phospho-LRP6, phospho-β-catenin, and GSK3 in the presence of Wnt ligands. This relocalization significantly enhanced Wnt signaling by increasing the number of multivesicular bodies into which the Wnt signalosome/ destruction complex becomes localized upon Wnt signaling. We also show that the MITF protein was stabilized by Wnt signaling, through the novel C-terminal GSK3 phosphorylations identified here. MITF stabilization caused an increase in multivesicular body biosynthesis, which in turn increased Wnt signaling, generating a positive-feedback loop that may function during the proliferative stages of melanoma. The results underscore the importance of misregulated endolysosomal biogenesis in Wnt signaling and cancer. MITF Wnt-STOP lysosome melanoma multivesicular body.

Therapies that target the programmed death-1 (PD-1) receptor have shown unprecedented rates of durable clinical responses in patients with various cancer types. One mechanism by which cancer tissues limit the host immune response is via upregulation of PD-1 ligand (PD-L1) and its ligation to PD-1 on antigen-specific CD8(+) T cells (termed adaptive immune resistance). Here we show that pre-existing CD8(+) T cells distinctly located at the invasive tumour margin are associated with expression of the PD-1/PD-L1 immune inhibitory axis and may predict response to therapy. We analysed samples from 46 patients with metastatic melanoma obtained before and during anti-PD-1 therapy (pembrolizumab) using quantitative immunohistochemistry, quantitative multiplex immunofluorescence, and next-generation sequencing for T-cell antigen receptors (TCRs). In serially sampled tumours, patients responding to treatment showed proliferation of intratumoral CD8(+) T cells that directly correlated with radiographic reduction in tumour size. Pre-treatment samples obtained from responding patients showed higher numbers of CD8-, PD-1- and PD-L1-expressing cells at the invasive tumour margin and inside tumours, with close proximity between PD-1 and PD-L1, and a more clonal TCR repertoire. Using multivariate analysis, we established a predictive model based on CD8 expression at the invasive margin and validated the model in an independent cohort of 15 patients. Our findings indicate that tumour regression after therapeutic PD-1 blockade requires pre-existing CD8(+) T cells that are negatively regulated by PD-1/PD-L1-mediated adaptive immune resistance.

Cancer cell proliferation relies on the ability of cancer cells to grow, transition through the cell cycle, and divide. To identify novel chemical probes for dissecting the mechanisms governing cell cycle progression and cell division, and for developing new anti-cancer therapeutics, we developed and performed a novel cancer cell-based high-throughput chemical screen for cell cycle modulators. This approach identified novel G1, S, G2, and M-phase specific inhibitors with drug-like properties and diverse chemotypes likely targeting a broad array of processes. We further characterized the M-phase inhibitors and highlight the most potent M-phase inhibitor MI-181, which targets tubulin, inhibits tubulin polymerization, activates the spindle assembly checkpoint, arrests cells in mitosis, and triggers a fast apoptotic cell death. Importantly, MI-181 has broad anti-cancer activity, especially against BRAFV600E melanomas.

Background In melanoma, dysregulation of the MAPK pathway, usually via BRAFV600 or NRASQ61 somatic mutations, leads to constitutive ERK signaling. While BRAF inhibitors are initially effective for BRAF-mutant melanoma, no FDA-approved targeted therapies exist for BRAF-inhibitor-resistant BRAFV600, NRAS mutant, or wild-type melanoma. Methods The 50% inhibitory concentration (IC50) of SCH772984, a novel inhibitor of ERK1/2, was determined in a panel of 50 melanoma cell lines. Effects on MAPK and AKT signaling by western blotting and cell cycle by flow cytometry were determined. Results Sensitivity fell into three groups: sensitive, 50% inhibitory concentration (IC50) 2 μM. Fifteen of 21 (71%) BRAF mutants, including 4 with innate vemurafenib resistance, were sensitive to SCH772984. All three (100%) BRAF/NRAS double mutants, 11 of 14 (78%) NRAS mutants and 5 of 7 (71%) wild-type melanomas were sensitive. Among BRAFV600 mutants with in vitro acquired resistance to vemurafenib, those with MAPK pathway reactivation as the mechanism of resistance were sensitive to SCH772984. SCH772984 caused G1 arrest and induced apoptosis. Conclusions Combining vemurafenib and SCH722984 in BRAF mutant melanoma was synergistic in a majority of cell lines and significantly delayed the onset of acquired resistance in long term in vitro assays. Therefore, SCH772984 may be clinically applicable as a treatment for non-BRAF mutant melanoma or in BRAF-mutant melanoma with innate or acquired resistance, alone or in combination with BRAF inhibitors. Electronic supplementary material The online version of this article (doi:10.1186/1476-4598-13-194) contains supplementary material, which is available to authorized users.

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 BRAFV600-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 BRAFV600 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.

Targeting immune inhibitory receptors has brought excitement, innovation and hope to cancer patients. Our recent work revealed the immunological effects of blocking the CTLA4 and PD-1 immune checkpoints on T cell receptor usage among peripheral blood cells, and further uncovers how the expansion of the T cell repertoire matches the immunotoxicity profile of the therapy.

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.

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.

Colony stimulating factor 1 (CSF-1) recruits tumor-infiltrating myeloid cells (TIM) that suppress tumor immunity, including M2 macrophages and myeloid-derived suppressor cells (MDSC). The CSF-1 receptor (CSF-1R) is a tyrosine kinase that is targetable by small molecule inhibitors such as PLX3397. In this study, we used a syngeneic mouse model of BRAFV600E-driven melanoma to evaluate the ability of PLX3397 to improve the efficacy of adoptive cell therapy (ACT). In this model, we found that combined treatment produced superior antitumor responses compared with single treatments. In mice receiving the combined treatment, a dramatic reduction of TIMs and a skewing of MHCIIlow to MHCIIhi macrophages were observed. Furthermore, mice receiving the combined treatment exhibited an increase in tumor-infiltrating lymphocytes (TIL) and T cells, as revealed by real-time imaging in vivo. In support of these observations, TILs from these mice released higher levels of IFN-γ. In conclusion, CSF-1R blockade with PLX3397 improved the efficacy of ACT immunotherapy by inhibiting the intratumoral accumulation of immunosuppressive macrophages. Cancer Res; 74(1); 153–61. ©2013 AACR.

To study lytic lesions in a patient with past history of renal cancer.A 62 year-old man was admitted to hospital for investigation of the cause of polyostotic bone pain.Brown tumors due to hyperparathyroidism turned out to be the cause of bone pain.Differential diagnosis is important in daily practice in order to provide a correct treatment for each condition.

Targeted therapy that inhibits the BRAF (V600E) protein has shown impressive initial responses in metastatic melanoma patients. However, acquired drug resistance, derived from tumor heterogeneity, always limits its efficacy and compromises its treatment outcomes. Melanocyte to neural crest transition (MNT) has been observed to play crucial role in early stage adaptive drug tolerance, and the mathematic modeling indicates the transition is contributed from both stochastic phenotypic transition and non-genetic selection. Whole transcriptomic analysis enriched important signaling proteins that are involved in the resistance development process. Single cell proteomic analysis of those proteins was performed on patient-derived melanoma models to further study the early stage drug tolerance. This resolves how protein signaling network coordination rewires in the process, which cannot be resolved from proteomic analysis of bulk tumor tissue. Signaling network coordination analysis indicates that co-inhibiting the hubs of the network (MEK, NFKB-p65) could keep cells in the drug-susceptible stages. The combination therapy that co-inhibits mutant BRAF, MEK and NFKB-p65 together successfully arrested the MNT transition and induced a sustained tumor growth suppression in multiple patient-derived melanoma cell lines. This study provides us a brand-new way of using single cell proteomic analysis to infer effective combinations by resolving protein signaling network coordination that is inaccessible through traditional bulk-level proteomic measurement. Citation Format: Yapeng Su, Wei Wei, Min Xue, Lidia Robert, Jennifer Tsoi, Thomas Graeber, Antoni Ribas, James Heath. Single cell analysis resolves combinatory targeted therapy for arresting the BRAFi-induced cellular dedifferentiation of metastatic melanomas. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 879.

Purpose To confirm the efficacy of a risk-adapted treatment approach for patients with clinical stage I seminoma. The aim was to reduce both the risk of relapse and the proportion of patients receiving adjuvant chemotherapy while maintaining a high cure rate. Patients and Methods From 2004 to 2008, 227 patients were included after orchiectomy in a multicenter study. Eighty-four patients (37%) presented no local risk factors, 44 patients (19%) had tumors larger than 4 cm, 25 patients (11%) had rete testis involvement, and 74 patients (33%) had both criteria. Only the latter group received two courses of adjuvant carboplatin, whereas the rest were managed by surveillance. Results After a median follow-up time of 34 months, 16 relapses (7%) have been documented (15 [9.8%] among patients on surveillance and one [1.4%] among those treated with carboplatin). All relapses occurred in retroperitoneal lymph nodes, except for one case in pelvic nodes. Median node size was 25 mm, and median time to recurrence was 14 months. All patients were rendered disease-free with chemotherapy. The actuarial 3-year disease-free survival rate was 88.1% (95% CI, 82.3% to 93.9%) for patients on surveillance and 98.0% (95% CI, 94.0% to 100%) for those treated with adjuvant chemotherapy. Overall 3-year survival was 100%. Conclusion With the limitations of the short follow-up duration, we confirm that a risk-adapted approach is effective for stage I seminoma. Adjuvant carboplatin seems adequate treatment for patients with 2 risk criteria, as is active surveillance for those with 0 to one risk factors. More reliable predictive factors are needed to improve the applicability of this model.

Melanoma can adapt to several stress factors, such as TNF treatment, by changing its phenotype from a highly differentiated (MITF and MART-1 positive) to undifferentiated (neural crest markers) states. We studied this phenomenon as a mechanism of adaptive resistance to BRAF inhibition since melanomas with both MITF high and low have been reported to result in BRAF inhibitor resistance. We treated 17 BRAFV600E mutant melanoma cell lines with the BRAF inhibitor vemurafenib for short term (3 days) or long term (17 days), and compared them to no treatment or TNF treated conditions. We profiled them phenotypically for MART1 antigen (differentiated phenotype) and nerve growth factor receptor (NGFR, neural crest phenotype) expression by flow cytometry. Results comparing median fluorescence intensity (MFI) showed a wide spectrum of adaptive responses to short term BRAF inhibition, followed by solidification or further evolution of these changes upon long term exposure and development of drug tolerance. According to each cell line distribution, we calculated a (x,y) value that organized the cell lines and conditions in four quadrants according to MART1 (x axis) or NGFR (y axis) expression. Two double negative (MART1-/NGFR-) cell lines that were unaffected by treatment and stayed in the same quadrant. Seven MART1-/NGFR+ and four MART1+/NGFR- cell lines slightly changed phenotype with vemurafenib exposure but stayed in the same quadrant. Four cell lines with MART1+/NGFR+ phenotype were greatly influenced by treatment, showing wide plasticity with cells shifting towards NGFR+/MART1- and others towards NGFR-/MART1+. Changes in position between baseline and tolerance to vemurafenib after 17days treatment were numerically quantified as an inferred number from plasticity. Cell lines with double positive (MART1+/NGFR+) phenotype had a significant change in plasticity compared to the rest of cell lines in other quadrants (p = 0.0004). This arranges cells in a four-quadrant pattern that could be likened to a U-turn toward de-differentiation. Cells that de-differentiated with BRAF inhibition mimicked the effect induced by TNF. This effect was driven by a decrease in MITF activity confirmed with a tyrosinase promoter-luciferase assay. In conclusion, baseline melanoma differentiation phenotypes guide the phenotype switch response, with those double positive for differentiation and neural crest markers being at a semi-stable state that can be prone to different plastic changes upon BRAF inhibition. Citation Format: Lidia Robert, Jennifer Tsoi, Angel Garica Diaz, Blanca Homet Moreno, Nhat Truong, Thomas Graeber, Antoni Ribas. Melanoma phenotype switching to adapt to BRAF inhibition. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2682. doi:10.1158/1538-7445.AM2015-2682

3027 Background: PD-1 blockade releases effector T-cells in the tumor microenvironment, but little is known on the effects in peripheral blood. We used T cell receptor (TCR) sequencing and multiple...