Brandon Nadres

Resistance to checkpoint blockade therapy through inactivation of antigen presentation

Treatment with immune checkpoint blockade (CPB) therapies often leads to prolonged responses in patients with metastatic melanoma, but the common mechanisms of primary and acquired resistance to these agents remain incompletely characterized and have yet to be validated in large cohorts. By analyzing longitudinal tumor biopsies from 17 metastatic melanoma patients treated with CPB therapies, we observed point mutations, deletions or loss of heterozygosity (LOH) in beta-2-microglobulin (B2M), an essential component of MHC class I antigen presentation, in 29.4% of patients with progressing disease. In two independent cohorts of melanoma patients treated with anti-CTLA4 and anti-PD1, respectively, we find that B2M LOH is enriched threefold in non-responders (~30%) compared to responders (~10%) and associated with poorer overall survival. Loss of both copies of B2M is found only in non-responders. B2M loss is likely a common mechanism of resistance to therapies targeting CTLA4 or PD1.Resistance to immune-checkpoint blockade often occurs in treated patients. Here, the authors demonstrate that B2M loss is a mechanism of primary and acquired resistance to therapies targeting CTLA4 or PD-1 in melanoma patients.

Real-time Genomic Characterization of Advanced Pancreatic Cancer to Enable Precision Medicine

Clinically relevant subtypes exist for pancreatic ductal adenocarcinoma (PDAC), but molecular characterization is not yet standard in clinical care. We implemented a biopsy protocol to perform time-sensitive whole-exome sequencing and RNA sequencing for patients with advanced PDAC. Therapeutically relevant genomic alterations were identified in 48% (34/71) and pathogenic/likely pathogenic germline alterations in 18% (13/71) of patients. Overall, 30% (21/71) of enrolled patients experienced a change in clinical management as a result of genomic data. Twenty-six patients had germline and/or somatic alterations in DNA-damage repair genes, and 5 additional patients had mutational signatures of homologous recombination deficiency but no identified causal genomic alteration. Two patients had oncogenic in-frame BRAF deletions, and we report the first clinical evidence that this alteration confers sensitivity to MAPK pathway inhibition. Moreover, we identified tumor/stroma gene expression signatures with clinical relevance. Collectively, these data demonstrate the feasibility and value of real-time genomic characterization of advanced PDAC.Significance: Molecular analyses of metastatic PDAC tumors are challenging due to the heterogeneous cellular composition of biopsy specimens and rapid progression of the disease. Using an integrated multidisciplinary biopsy program, we demonstrate that real-time genomic characterization of advanced PDAC can identify clinically relevant alterations that inform management of this difficult disease. Cancer Discov; 8(9); 1096-111. ©2018 AACR.See related commentary by Collisson, p. 1062This article is highlighted in the In This Issue feature, p. 1047.

Convergent Therapeutic Strategies to Overcome the Heterogeneity of Acquired Resistance in BRAFV600E Colorectal Cancer

Clonal heterogeneity associated with acquired resistance presents a critical therapeutic challenge. Whole-exome sequencing of paired tumor biopsies and targeted sequencing of cell-free DNA (cfDNA) from patients with BRAFV600E colorectal cancer receiving BRAF inhibitor combinations identified 14 distinct alterations in MAPK pathway components driving acquired resistance, with as many as eight alterations in a single patient. We developed a pooled clone system to study clonal outgrowth during acquired resistance, in vitro and in vivoIn vitro, the dynamics of individual resistant clones could be monitored in real time in cfDNA isolated from culture media during therapy. Outgrowth of multiple resistant clones was observed during therapy with BRAF, EGFR, and MEK inhibitor combinations. However, ERK inhibition, particularly in combination with BRAF and EGFR inhibition, markedly abrogated clonal outgrowth in vitro and in vivo Thus, convergent, up-front therapy may suppress outgrowth of heterogeneous clones harboring clinically observed resistance alterations, which may improve clinical outcome.Significance: We observed heterogeneous, recurrent alterations in the MAPK pathway as key drivers of acquired resistance in BRAFV600E colorectal cancer, with multiple concurrent resistance alterations detectable in individual patients. Using a novel pooled clone system, we identify convergent up-front therapeutic strategies capable of intercepting multiple resistance mechanisms as potential approaches to suppress emergence of acquired resistance. Cancer Discov; 8(4); 417-27. ©2018 AACR.See related commentary by Janku, p. 389See related article by Corcoran et al., p. 428This article is highlighted in the In This Issue feature, p. 371.

A phase II study of combined therapy with a BRAF inhibitor (vemurafenib) and interleukin-2 (aldesleukin) in patients with metastatic melanoma

ABSTRACT Background: Approximately 50% of melanomas harbor BRAF mutations. Treatment with BRAF +/− MEK inhibition is associated with favorable changes in the tumor microenvironment thus providing the rationale for combining targeted agents with immunotherapy. Methods: Patients with unresectable Stage III or IV BRAFV600E mutant melanoma were enrolled in a single-center prospective study (n = 6). Patients were eligible to receive two courses of HD-IL-2 and vemurafenib twice daily. The primary endpoint was progression-free survival (PFS) with secondary objectives including overall survival (OS), response rates (RR), and safety of combination therapy as compared to historical controls. Immune profiling was performed in longitudinal tissue samples, when available. Results: Overall RR was 83.3% (95% CI: 36%–99%) and 66.6% at 12 weeks. All patients eventually progressed, with three progressing on treatment and three progressing after the vemurafenib continuation phase ended. Median PFS was 35.8 weeks (95% CI: 16–57 weeks). Median OS was not reached; however, the time at which 75% of patients were still alive was 104.4 weeks. Change in circulating BRAFV600E levels correlated with response. Though combination therapy was associated with enhanced CD8 T cell infiltrate, an increase in regulatory T cell frequency was seen with HD-IL-2 administration, suggesting a potential limitation in this strategy. Conclusion: Combination vemurafenib and HD-IL-2 is well tolerated and associated with treatment responses. However, the HD-IL-2 induced increase in Tregs may abrogate potential synergy. Given the efficacy of regimens targeting the PD-1 pathway, strategies combining these regimens with BRAF-targeted therapy are currently underway, and the role of combination vemurafenib and HD-IL-2 is uncertain. Trial Registration: Clinical trial information: NCT01754376; https://clinicaltrials.gov/show/NCT01754376

Co-occurring genetic alterations in the RAS pathway promote resistance to MET inhibitor treatment in non-small cell lung cancer with a MET exon 14 skipping mutation

Abstract PURPOSE While patients with advanced-stage non-small cell lung cancers (NSCLCs) harboring MET exon 14 skipping mutations (METex14) often benefit from MET tyrosine kinase inhibitor (TKI) treatment, clinical benefit is limited by primary and acquired drug resistance. The molecular basis for this resistance remains incompletely understood. METHODS Targeted sequencing analysis was performed on cell-free circulating tumor DNA obtained from 289 patients with advanced-stage METex14-mutated NSCLC. RESULTS Prominent co-occurring RAS-MAPK pathway gene alterations (e.g. in KRAS, NF1) were detected in NSCLCs with METex14 skipping alterations as compared to EGFR-mutated NSCLCs. There was an association between decreased MET TKI treatment response and RAS-MAPK pathway co-occurring alterations. In a preclinical model expressing a canonical METex14 mutation, KRAS overexpression or NF1 downregulation hyperactivated MAPK signaling to promote MET TKI resistance. This resistance was overcome by co-treatment with crizotinib and the MEK inhibitor trametinib. CONCLUSION Our study provides a genomic landscape of co-occurring alterations in advanced-stage METex14-mutated NSCLC and suggests a potential combination therapy strategy targeting MAPK pathway signaling to enhance clinical outcomes.While patients with advanced-stage non-small cell lung cancers (NSCLCs) harboring MET exon 14 skipping mutations (METex14) often benefit from MET tyrosine kinase inhibitor (TKI) treatment, their long-term survival is limited by drug resistance. The molecular basis for this resistance remains incompletely understood. Through targeted sequencing analysis of cell-free circulating tumor DNA obtained from 289 patients with advanced-stage METex14 NSCLC, we find prominent co-occurring RAS pathway gene alterations (e.g. in KRAS/NRAS, NF1). Clinical resistance to MET TKI treatment was associated with the presence of these co-occurring alterations. In a new preclinical model expressing a METex14 mutation, KRAS overexpression promoted MET TKI resistance, which was overcome by co-treatment with crizotinib and the MEK inhibitor trametinib. Our study provides a genetic landscape of co-occurring alterations in advanced-stage METex14-mutated NSCLC and suggests a potential combination therapy strategy to enhance clinical outcomes. Statement of Significance This report describes targeted sequencing of the largest reported cohort of advanced-stage NSCLC with a MET exon 14 skipping mutation. The data uncover certain RAS pathway genetic alterations as potential mediators of MEK TKI resistance, which could be overcome by MEK and MET co-inhibition in NSCLC.

Heterogeneity and Coexistence of T790M and T790 Wild-Type Resistant Subclones Drive Mixed Response to Third-Generation Epidermal Growth Factor Receptor Inhibitors in Lung Cancer

Purpose Third-generation epidermal growth factor receptor (EGFR) inhibitors like nazartinib are active against EGFR mutation-positive lung cancers with T790M-mediated acquired resistance to initial anti-EGFR treatment, but some patients have mixed responses. Methods Multiple serial tumor and liquid biopsies were obtained from two patients before, during, and after treatment with nazartinib. Next-generation sequencing and droplet digital polymerase chain reaction were performed to assess heterogeneity and clonal dynamics. Results We observed the simultaneous emergence of T790M-dependent and -independent clones in both patients. Serial plasma droplet digital polymerase chain reaction illustrated shifts in relative clonal abundance in response to various systemic therapies, confirming a molecular basis for the clinical mixed radiographic responses observed. Conclusion Heterogeneous responses to treatment targeting a solitary resistance mechanism can be explained by coexistent tumor subclones harboring distinct genetic signatures. Serial liquid biopsies offer an opportunity to monitor clonal dynamics and the emergence of resistance and may represent a useful tool to guide therapeutic strategies.