Abstract A37: Complex crosstalk between MAPK signaling and energy metabolism in melanoma

The notoriously high glucose uptake by metastatic melanoma (MM) lesions is commonly exploited clinically using PET/CT imaging to evaluate disease progression and treatment. The purpose of this study was to use patient-derived xenograft (PDX) MM models and a PDX derived (MM8.1) cell line, to determine how driver oncogene mutations and drugs targeting the RAS-RAF-MEK signaling pathways impact glucose uptake, ATP production and mitochondrial plasticity of MM cells both in vivo and in vitro and the implications on drug resistance. MM BRAF V600E+ patients are routinely treated targeting either mutant BRAF kinase (vemurafenib), or the MAPK downstream signaling intermediate; MEK. To begin exploring links between oncogenic BRAF and metabolism, we first conducted differential gene expression (DGE) profiling of 30 different MM lesions (n=15 patients: pre- and post-engraftment). Focusing on PGC1α; a master mitochondrial regulator promoting oxidative phosphorylation (OXPHOS) revealed lower expression levels in BRAF V600E+ tumors compared to BRAF V600V+ tumors. Further analysis of a BRAF V600E+ MM PDX model revealed strong glucose uptake by PET/CT imaging at baseline. However, 48 hrs. after treatment with vemurafenib triggered growth arrest, accompanied by increased PGC1α; mRNA levels and significant reduction in glucose uptake without change in tumor volume. Upon acquisition of acquired vemurafenib resistance in the PDX model (day 70), rapidly growing tumors displayed reversal to high glucose uptake; which was again diminished by targeting MEK (PD0325901). DGE analysis of vehicle vs. 48 hrs. day 50 and day 70 vemurafenib treated tumors revealed oscillation in the expression of genes regulating glycolysis and oxidative phosphorylation (OXPHOS) that is reflected in the PET/CT imaging. To gain deeper insight, a cell line derived from a vehicle treated tumor, was examined using the Seahorse metabolic analyzer. Vehicle treated MM8.1 cells display high glycolytic capacity and predominantly glycolytic-derived ATP production, which is reflected by only minor inhibition of ATP production with oligomycin (an inhibitor of ATP synthase, a component of the OXHPOS system). Upon treatment with PLX4032, there was rapid reduction in glycolytic capacity along with a concurrent increase in maximum oxygen consumption capacity. PLX4032 treatment additionally enhanced MM8.1 sensitivity to oligomycin, but only transiently (24 hrs. pre-treatment), as later exposure times did not induce oligomycin sensitivity despite DGE changes to indicate otherwise. In conclusion, caution is warranted in evaluating drug responses in patients using PET/CT depending on duration of treatment. Cross-talk involving MAPK signaling and energy metabolism is a dynamic process, with more of a rheostat than switch-type properties, requiring further evaluation to identify therapeutic approaches exploiting metabolic events within MM cells. Citation Format: Nathan J. Lanning, Pimiento Jose, Noel R. Monks, Paula J. Davidson, Andrew S. Borgman, Ting-Tung Chang, Anderson S. Peck, David J. Monsma, Chelsea A. Peterson, Mackeigan P. Jeff, Brian J. Nickoloff. Complex crosstalk between MAPK signaling and energy metabolism in melanoma. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr A37. doi: 10.1158/1557-3125.RASONC14-A37