px-866 and Melanoma

Targeted therapies for mutant BRAF metastatic melanoma are effective but not curative due to acquisition of resistance. PI3K signaling is a common mediator of therapy resistance in melanoma; thus, the need for effective PI3K inhibitors is critical. However, testing PI3K inhibitors in adherent cultures is not always reflective of their potential in vivo. To emphasize this, we compared PI3K inhibitors of different specificity in two- and three-dimensional (2D, 3D) melanoma models and show that drug response predictions gain from evaluation using 3D models. Our results in 3D demonstrate the anti-invasive potential of PI3K inhibitors and that drugs such as PX-866 have beneficial activity in physiological models alone and when combined with BRAF inhibition. These assays finally help highlight pathway effectors that could be involved in drug response in different environments (e.g. p4E-BP1). Our findings show the advantages of 3D melanoma models to enhance our understanding of PI3K inhibitors.

Topics: Animals; Cell Adhesion; Cell Line, Tumor; Cell Proliferation; Collagen; Gonanes; Indoles; Melanoma; Mice, Inbred NOD; Models, Biological; Mutation; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Protein Kinase Inhibitors; Proto-Oncogene Proteins B-raf; Proto-Oncogene Proteins c-akt; Signal Transduction; Spheroids, Cellular; Sulfonamides; Tumor Microenvironment

BRAF inhibition is highly active in BRAF-mutant melanoma, but the degree and duration of responses is quite variable. Improved understanding of the mechanisms of de novo resistance may lead to rational therapeutic strategies with improved efficacy. Proteomic analysis of BRAF-mutant, PTEN-wild-type human melanoma cell lines treated with PLX4720 demonstrated that sensitive and de novo resistant lines exhibit similar RAS-RAF-MEK-ERK pathway inhibition, but the resistant cells exhibited durable activation of S6 and P70S6K. Treatment with the mTOR inhibitor rapamycin blocked activation of P70S6K and S6, but it also increased activation of AKT and failed to induce cell death. Combined treatment with rapamycin and PX-866, a PI3K inhibitor, blocked the activation of S6 and AKT and resulted in marked cell death when combined with PLX4720. The results support the rationale for combined targeting of BRAF and the PI3K-AKT pathways and illustrate how target selection will be critical to such strategies.

Topics: Antineoplastic Combined Chemotherapy Protocols; Blotting, Western; Cell Line, Tumor; Cell Proliferation; Cell Survival; Drug Resistance, Neoplasm; Drug Screening Assays, Antitumor; Extracellular Signal-Regulated MAP Kinases; Gonanes; Humans; Indoles; Melanoma; Molecular Targeted Therapy; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Protein Interaction Maps; Protein Kinase Inhibitors; Proto-Oncogene Proteins B-raf; Signal Transduction; Sirolimus; Sulfonamides; TOR Serine-Threonine Kinases