plx-4720 and palbociclib

Increased CDK4 activity occurs in the majority of melanomas and CDK4/6 inhibitors in combination with BRAF and MEK inhibitors are currently in clinical trials for the treatment of melanoma. We hypothesize that the timing of the addition of CDK4/6 inhibitors to the current BRAF and MEK inhibitor regime will impact on the efficacy of this triplet drug combination. The efficacy of BRAF, MEK and CDK4/6 inhibitors as single agents and in combination was assessed in human BRAF mutant cell lines that were treatment naïve, BRAF inhibitor tolerant or had acquired resistance to BRAF inhibitors. Xenograft studies were then performed to test the in vivo efficacy of the BRAF and CDK4/6 inhibitor combination. Melanoma cells that had developed early reversible tolerance or acquired resistance to BRAF inhibition remained sensitive to palbociclib. In drug-tolerant cells, the efficacy of the combination of palbociclib with BRAF and/or MEK inhibitors was equivalent to single agent palbociclib. Similarly, acquired BRAF inhibitor resistance cells lost efficacy to the palbociclib and BRAF combination. In contrast, upfront treatment of melanoma cells with palbociclib in combination with BRAF and/or MEK inhibitors induced either cell death or senescence and was superior to a BRAF plus MEK inhibitor combination. In vivo palbociclib plus BRAF inhibitor induced rapid and sustained tumor regression without the development of therapy resistance. In summary, upfront dual targeting of CDK4/6 and mutant BRAF signaling enables tumor cells to evade resistance to monotherapy and is required for robust and sustained tumor regression. Melanoma patients whose tumors have acquired resistance to BRAF inhibition are less likely to have favorable responses to subsequent treatment with the triplet combination of BRAF, MEK and CDK4/6 inhibitors.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Cell Line, Tumor; Cyclin-Dependent Kinase 4; Cyclin-Dependent Kinase 6; Drug Resistance, Neoplasm; Drug Synergism; Female; Humans; Indoles; MAP Kinase Kinase Kinases; Melanoma; Mice; Mice, SCID; Piperazines; Protein Kinase Inhibitors; Proto-Oncogene Proteins B-raf; Pyridines; Sulfonamides; Xenograft Model Antitumor Assays

Deregulated glucose metabolism fulfills the energetic and biosynthetic requirements for tumor growth driven by oncogenes. Because inhibition of oncogenic BRAF causes profound reductions in glucose uptake and a strong clinical benefit in BRAF-mutant melanoma, we examined the role of energy metabolism in responses to BRAF inhibition. We observed pronounced and consistent decreases in glycolytic activity in BRAF-mutant melanoma cells. Moreover, we identified a network of BRAF-regulated transcription factors that control glycolysis in melanoma cells. Remarkably, this network of transcription factors, including hypoxia-inducible factor-1α, MYC, and MONDOA (MLXIP), drives glycolysis downstream of BRAF(V600), is critical for responses to BRAF inhibition, and is modulated by BRAF inhibition in clinical melanoma specimens. Furthermore, we show that concurrent inhibition of BRAF and glycolysis induces cell death in BRAF inhibitor (BRAFi)-resistant melanoma cells. Thus, we provide a proof-of-principle for treatment of melanoma with combinations of BRAFis and glycolysis inhibitors.. BRAF is suppress glycolysis and provide strong clinical benefi t in BRAF V600 melanoma. We show that BRAF inhibition suppresses glycolysis via a network of transcription factors that are critical for complete BRAFi responses. Furthermore, we provide evidence for the clinical potential of therapies that combine BRAFis with glycolysis inhibitors.

Topics: Cell Line, Tumor; Drug Resistance, Neoplasm; Glycolysis; HEK293 Cells; Humans; Indoles; MAP Kinase Signaling System; Melanoma; Piperazines; Protein Kinase Inhibitors; Proto-Oncogene Proteins B-raf; Pyridines; Sulfonamides; Transcription Factors; Vemurafenib

Although malignant astrocytomas are a leading cause of cancer-related death in children, rational therapeutic strategies are lacking. We previously identified activating mutations of v-raf murine sarcoma viral oncogene homolog B1 (BRAF) (BRAF(T1799A) encoding BRAF(V600E)) in association with homozygous cyclin-dependent kinase inhibitor 2A (CDKN2A, encoding p14ARF and p16Ink4a) deletions in pediatric infiltrative astrocytomas. Here we report that BRAF(V600E) expression in neural progenitors (NPs) is insufficient for tumorigenesis and increases NP cellular differentiation as well as apoptosis. In contrast, astrocytomas are readily generated from NPs with additional Ink4a-Arf deletion. The BRAF(V600E) inhibitor PLX4720 significantly increased survival of mice after intracranial transplant of genetically relevant murine or human astrocytoma cells. Moreover, combination therapy using PLX4720 plus the Cyclin-dependent kinase (CDK) 4/6-specific inhibitor PD0332991 further extended survival relative to either monotherapy. Our findings indicate a rational therapeutic strategy for treating a subset of pediatric astrocytomas with BRAF(V600E) mutation and CDKN2A deficiency.

Topics: Animals; Apoptosis; Astrocytoma; Blotting, Western; Cell Differentiation; Cell Line, Tumor; Cell Proliferation; Cells, Cultured; Child; Cyclin-Dependent Kinase Inhibitor p16; Extracellular Signal-Regulated MAP Kinases; Female; Humans; Immunohistochemistry; Indoles; Mice; Mice, Inbred BALB C; Mice, Knockout; Mice, Nude; Mice, SCID; Neural Stem Cells; Phosphorylation; Piperazines; Proto-Oncogene Proteins B-raf; Pyridines; Sulfonamides; Xenograft Model Antitumor Assays

Topics: Animals; Antineoplastic Agents; Astrocytoma; Brain Neoplasms; Disease Models, Animal; Humans; Indoles; Mice; Pediatrics; Piperazines; Proto-Oncogene Proteins B-raf; Pyridines; Sulfonamides