Identification of the Serine Biosynthesis Pathway as a Critical Component of BRAF Inhibitor Resistance of Melanoma, Pancreatic, and Non-Small Cell Lung Cancer Cells

• Published in: Molecular cancer therapeutics 2017-08, Vol.16 (8), p.1596-1609
• Main Authors: Ross, Kayleigh C, Andrews, Andrew J, Marion, Christopher D, Yen, Timothy J, Bhattacharjee, Vikram
• Format: Article
• Language: English
• Subjects: Biosynthesis; Biosynthetic Pathways - drug effects; Biotechnology; Cancer; Carcinoma, Non-Small-Cell Lung - drug therapy; Carcinoma, Non-Small-Cell Lung - pathology; Cell Line, Tumor; Cell Proliferation - drug effects; Deoxycytidine - analogs & derivatives; Deoxycytidine - pharmacology; Deoxycytidine - therapeutic use; Deoxyribonucleic acid; DNA; DNA damage; Drug resistance; Drug Resistance, Neoplasm - drug effects; Folic acid; Gemcitabine; Humans; Imidazoles - pharmacology; Imidazoles - therapeutic use; Indoles - pharmacology; Indoles - therapeutic use; Inhibitors; Lung cancer; Lung Neoplasms - drug therapy; Lung Neoplasms - pathology; Melanoma; Melanoma - drug therapy; Melanoma - pathology; Metastases; Methotrexate; Methotrexate - pharmacology; Methotrexate - therapeutic use; Models, Biological; Oximes - pharmacology; Oximes - therapeutic use; Pancreatic cancer; Pancreatic Neoplasms - drug therapy; Pancreatic Neoplasms - pathology; Phosphoglycerate Dehydrogenase - metabolism; Proto-Oncogene Proteins B-raf - antagonists & inhibitors; Proto-Oncogene Proteins B-raf - metabolism; Serine; Serine - metabolism; siRNA; Sulfonamides - pharmacology; Sulfonamides - therapeutic use; Tumor cell lines; Tumor cells; Vemurafenib
• ISSN: 1535-7163; 1538-8514
• DOI: 10.1158/1535-7163.MCT-16-0798

Metastatic melanoma cells commonly acquire resistance to V600E inhibitors (BRAFi). In this study, we identified serine biosynthesis as a critical mechanism of resistance. Proteomic assays revealed differential protein expression of serine biosynthetic enzymes PHGDH, PSPH, and PSAT1 following vemurafenib (BRAFi) treatment in sensitive versus acquired resistant melanoma cells. Ablation of PHGDH via siRNA sensitized acquired resistant cells to vemurafenib. Inhibiting the folate cycle, directly downstream of serine synthesis, with methotrexate also displayed similar sensitization. Using the DNA-damaging drug gemcitabine, we show that gemcitabine pretreatment sensitized resistant melanoma cells to BRAFis vemurafenib and dabrafenib. We extended our findings to BRAF WT tumor cell lines that are intrinsically resistant to vemurafenib and dabrafenib. Pretreatment of pancreatic cancer and non-small cell lung cancer cell lines with sublethal doses of 50 and 5 nmol/L of gemcitabine, respectively, enhanced killing by both vemurafenib and dabrafenib. The novel aspects of this study are the direct identification of serine biosynthesis as a critical mechanism of V600E inhibitor resistance and the first successful example of using gemcitabine + BRAFis in combination to kill previously drug-resistant cancer cells, creating the translational potential of pretreatment with gemcitabine prior to BRAFi treatment of tumor cells to reverse resistance within the mutational profile and the WT. .