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Dasatinib Overcomes Acquired Resistance to BRAF/MEK Inhibitor Therapy

ABSTRACT: Despite high initial activity, resistance to combination BRAF/MEK inhibitor (BRAFi/MEKi) therapy arises in virtually all patients with BRAFV600E/K melanoma. There remains a critical unmet need to identify strategies to overcome acquired BRAFi/MEKi resistance. To better personalize therapy in cancer patients and address therapy relapse, umbrella trials have commenced whereby genomic sequencing of a panel of potentially actionable targets guide therapy selection for patients. However, the superior efficacy of such approaches remains to be seen. We here test the robustness of the umbrella trial rationale by analyzing relationships between genomic status of a gene and the downstream consequences at the protein level of related pathways, and find poor relationships between mutations, copy number amplification, and protein expression and activation. To profile candidate therapeutic strategies that may offer clinical benefit in the context of acquired BRAFi/MEKi resistance, we utilized a repository of patient-derived xenograft models from heavily pretreated patients with resistance to BRAFi/MEKi and/or immunotherapy (R-PDX). With these R-PDXs, we executed in vivo compound repurposing screens using 11 FDA-approved agents from an NCI-portfolio with pan-RTK, non-RTK and/or PI3K-mTOR specificity. We identify dasatinib as capable of restoring sensitivity to BRAFi/MEKi in ~70% of R-PDX models tested. Elevated baseline protein expression of canonical drivers of therapy resistance (e.g., AXL, YAP, HSP70, phospho-AKT) predicts BRAFi/MEKi plus dasatinib treatment sensitivity. We therefore propose that dasatinib plus BRAFi/MEKi combination therapy may restore antitumor efficacy in patients that have relapsed to standard-of-care therapy by broadly targeting proteins critical in melanoma therapy escape. Further, we submit that this experimental PDX paradigm could potentially improve preclinical evaluation of therapeutic modalities and augment our ability to identify biomarker-defined patient subsets that may respond to a given clinical trial. Furthermore, the aged patient population has suboptimal responses to SARS-CoV-2 vaccine antigens. Here, we characterize vaccine-induced responses to SARS-CoV-2 synthetic DNA vaccine antigens in 18-month-old mice and interrogate protection. Aged mice have altered cellular responses, including decreased IFNγ secretion and increased TNFα secretion as compared to young mice. Aged mice had significantly decreased binding and neutralizing antibodies in their serum compared to their young counterparts. Co-immunization with the plasmid-encoded molecular adjuvant adenosine deaminase-1 (pADA) enhanced cellular responses and expanded the breadth of humoral responses in aged mice. pADA co-delivery also altered the gene expression profiles of lymph node lymphocytes in aged animals. Upon challenge pADA co-immunization modestly decreased age-associated morbidity and mortality in ACE2 transgenic and mouse-adapted SARS-CoV-2 challenge models. These data support the use of aged mice as a model for age-associated decreased vaccine immunogenicity and infection-mediated morbidity and mortality in the context of SARS-CoV-2 and provide further support of the use of adenosine deaminase as a molecular adjuvant.

ORGANISM(S): Homo sapiens

PROVIDER: GSE273120 | GEO | 2025/07/24

REPOSITORIES: GEO

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Project description:Despite the clinical success of targeted therapy inhibitors, tumor responses are transient, and a subpopulation of residual drug-tolerant cells may seed resistance. Understanding minimal residual disease (MRD) mechanisms and the connection with dormancy-like traits may guide strategies to target drug-tolerant persister cells and optimize target therapies. Here, we studied the relationship between persister cell tolerance to BRAF and MEK inhibitors (BRAFi + MEKi) and expression of nuclear receptor subfamily 2 group F member 1 (NR2F1), which has been linked to tumor dormancy in the context of cutaneous melanoma. In previously published RNA-seq datasets, NR2F1 expression was enriched in melanoma samples following BRAF inhibitor and MEK inhibitor (BRAFi + MEKi) treatment compared to pre-treatment patient-matched samples. We also found that NR2F1 is highly expressed in the residual drug-tolerant cell state following BRAFi + MEKi treatment in patient-derived and cell line-derived melanoma xenografts. Additionally, xenografts overexpressing NR2F1 displayed higher tumor growth and poorer animal survival following BRAFi + MEKi treatment compared to control xenografts expressing basal levels of NR2F1. In vitro, NR2F1-overexpressing cells showed increased tumor proliferation and higher expression of cell cycle and survival-related proteins on targeted therapy, such as phosphorylation of both RB and S6K proteins. In addition, NR2F1, highly expressed in invasive melanoma cells, was sufficient to promote invasiveness following BRAFi + MEKi in 3D tumor spheroid assays. Furthermore, when compared to young mice, NR2F1 was overexpressed in tumor xenografts in an old microenvironment. The use of shRNA NR2F1 in older mice led to slower tumor growth and the highest survival in animals on BRAFi + MEKi treatment. We also tested a pharmacological approach to target drug-tolerant persister cells that overexpress NR2F1 on BRAFi + MEKi treatment. The inhibition of mTORC1 delayed NR2F1-overexpressing cell proliferation compared to non-NR2F1-overexpressing cells on targeted therapy. Altogether, our findings suggest that NR2F1 plays a role in the persistence of MRD in melanoma, indicating that targeting NR2F1 expression could improve targeted therapy outcomes in melanoma patients.

Project description:Nearly 50% of cutaneous melanomas carry activating mutations on the BRAF oncogene, and the combination of BRAF- and MEK-inhibitors (BRAF/MEKi) is frequently used for their clinical management. One major drawback of BRAF/MEKi targeted therapy is the rapid development of therapeutic resistance, which can occur via multiple mechanisms, including the metabolic rewiring of cancer cells that often involves the upregulation of mitochondrial bionergetics and NAD+ biosynthetic pathways. mTORC2 is a signaling complex that requires the presence of its essential RICTOR subunit to play its regulatory functions in cell growth and metabolism. mTORC2 is believed to play mostly pro-oncogenic roles in several tumor types, including melanoma. However, bioinformatics analysis of TCGA melanoma patients’ database revealed that low RICTOR levels in tumors correlate with an overall worse clinical outcome. GSEA analysis of low-RICTOR tumors evidenced also a gene expression signature suggestive of activation of mitochondrial energy producing pathways. On these bases, we have hypothesized that inhibition of mTORC2 activity may render BRAFV600E melanoma cells resistant to BRAFi/MEKi. We show here that RICTOR/mTORC2-deficient cells are intrinsically tolerant to BRAFi/MEKi, and anticipate the onset of resistance to BRAFi after sustained drug exposure both in vitro and in vivo, indicating that mTORC2 activity normally opposes the acquisition of targeted therapy resistance in BRAFV600E melanomas. Mechanistically, RICTOR-deficient cells show an enhanced mitochondrial respiratory potential and increased expression of nicotinamide phosphoribosyltransferase (NAMPT) protein, the rate-limiting enzyme of NAD+ salvage pathway, and pharmacological inhibition of these processes in RICTOR-deficient cells is sufficient to restore sensitivity to BRAFi. Thus, our work identifies a novel role for mTORC2 in favoring the responses of BRAF-mutated melanoma cells to targeted therapy, and suggest that the evaluation of the intratumor level of RICTOR may help to predict the responses of melanoma patients to these treatments.

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Dasatinib Overcomes Acquired Resistance to BRAF/MEK Inhibitor Therapy

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