Targeting metabolism as a therapeutic strategy in malignant melanoma.

摘要

The approval of vemurafenib by the FDA in 2011 marked the beginning of a new era in therapeutics for malignant melanoma. Fueled by the concomitant rise of high-throughput gene sequencing, therapy for metastatic disease evolved beyond the broad-spectrum cytotoxic chemotherapeutics of the previous 50 years, targeting the specific driver oncogenes now known to fuel the disease's unchecked growth. Unfortunately, promising early responses to BRAF inhibitors did not prove durable, with long-term overall survival left relatively unchanged. Though later addition of MEK inhibitors as a combination therapy increased progression-free survival by a matter of months, virtually 100% of patients would still eventually develop resistance and succumb to metastatic disease. Due to this emerging pattern of eventual resistance to newer and newer MAPK pathway inhibitors, new therapeutic strategies needed to be developed. Studies of the unique metabolic properties of melanoma cells, as well as their metabolic adaptations to resist existing treatment, provided an attractive new paradigm for discovering novel anticancer agents, as well as improving existing methods for surveillance and therapeutic response tracking.;One of the most encouraging early observations regarding BRAF inhibitors in the clinic was the dramatic reduction in [18F]fluorodeoxyglucose uptake-positron emission tomography (FDG-PET) signal within weeks of starting therapy. However the reappearance of PET-avid lesions eventually occured in nearly all cases, frequently at sites of treated metastatic disease. Given the basis of FDG-PET on the Warburg Effect, this likely non-random occurrence was an early clue that changes in metabolic activity might be a hallmark of BRAF inhibition. Here, our study provides evidence of melanoma cell volume reduction in a patient cohort treated with BRAF inhibitors. We present data demonstrating that BRAF inhibition reduces melanoma glucose uptake per cell, but that this change is no longer significant following normalization for cell volume changes. We also demonstrate that volume normalization greatly reduces differences in transmembrane glucose transport and hexokinase-mediated phosphorylation. Mechanistic studies suggest that this loss of cell volume is due in large part to decreases in new protein translation as a consequence of vemurafenib treatment, possibly through a downstream effector of ERK: p9ORSK. Ultimately, our findings suggest that cell volume regulation constitutes an important physiologic parameter that may significantly contribute to radiographic changes observed in clinic.;Having identified a role for p9ORSK family kinases as key factors for cell volume regulation, glucose uptake, and protein synthesis, we sought to better understand their control over protein synthesis. This centered around RSKmediated regulation of assembly of the m7-GTP cap-dependent translation complex. We evaluated inhibitors of p9ORSK family members BI-D1870 and BRD 7389 for their ability to inhibit both proliferation and protein synthesis in patient-derived melanoma cell lines with acquired resistance to combined BRAF inhibitor vemurafenib and MEK inhibitor selumetinib treatment. We found that the RSK inhibitors blocked cell proliferation and protein synthesis in multiple dual-resistant melanoma lines. In addition, RSK inhibitor monotherapy was effective in drug-naive lines, two of which are innately vemurafenib-resistant. We also used Reverse Phase Protein Array screening to identify differential protein expression that correlates with BI-D1870 sensitivity, and demonstrated new prognostic biomarkers for survival in human melanoma patients. These findings established p9ORSK inhibition as a therapeutic strategy in treatment-resistant melanoma and provide insight into their mechanism of action.;While statins have been previously identified as potential anti-cancer therapeutic agents, in vivo toxicity appeared to limit their utility in a small number of studies. We previously conducted a high-throughput drug screening study to identify synergy between a large number of compounds with known anti-melanoma activity. This study suggested that simvastatin and other lipophilic statins might have favorable interactions with MAPK pathway inhibitors such as vemurafenib and selumetinib. We found that MAPK blockade synergized with simvastatin in BRAFdriven melanoma and non-melanoma cancers, likely due to statins' inhibition of farnesyl and geranylgeranyl post-translational modification groups. We also showed efficacy for simvastatin in xenograft mouse model using a vemurafenibresistant human melanoma cell line. Using detailed characterization of the metabolic properties of melanoma both on and off of current standard of care therapy, our work has provided insight into new targets for therapeutic intervention, as well as a refined our understanding of the implications of changes in FDG PET-based tumor surveillance. Future studies may be directed at better adapting these findings for in vivo application, as well as expansion of our investigation to changes in carbon flux and macromolecular synthesis.