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Differential chemosensitivity to antifolate drugs between RAS and BRAF melanoma cells
Imanol Arozarena1, Ibai Goicoechea, Oihane Erice
1Manchester Cancer Research Centre, The University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK. Imanol.Arozarena@manchester.ac.uk.
Background:
The importance of the genetic background of cancer cells for the individual susceptibility to cancer treatments is increasingly apparent. In melanoma, the existence of a BRAF mutation is a main predictor for successful BRAF-targeted therapy. However, despite initial successes with these therapies, patients relapse within a year and have to move on to other therapies. Moreover, patients harbouring a wild type BRAF gene (including 25% with NRAS mutations) still require alternative treatment such as chemotherapy. Multiple genetic parameters have been associated with response to chemotherapy, but despite their high frequency in melanoma nothing is known about the impact of BRAF or NRAS mutations on the response to chemotherapeutic agents.
Methods:
Using cell proliferation and DNA methylation assays, FACS analysis and quantitative-RT-PCR we have characterised the response of a panel of NRAS and BRAF mutant melanoma cell lines to various chemotherapy drugs, amongst them dacarbazine (DTIC) and temozolomide (TMZ) and DNA synthesis inhibitors.
Results:
Although both, DTIC and TMZ act as alkylating agents through the same intermediate, NRAS and BRAF mutant cells responded differentially only to DTIC. Further analysis revealed that the growth-inhibitory effects mediated by DTIC were rather due to interference with nucleotide salvaging, and that NRAS mutant melanoma cells exhibit higher activity of the nucleotide synthesis enzymes IMPDH and TK1. Importantly, the enhanced ability of RAS mutant cells to use nucleotide salvaging resulted in resistance to DHFR inhibitors.
Conclusion:
In summary, our data suggest that the genetic background in melanoma cells influences the response to inhibitors blocking de novo DNA synthesis, and that defining the RAS mutation status could be used to stratify patients for the use of antifolate drugs.
Insights
Melanoma cell genetics impact chemotherapy response. NRAS-mutant cells show resistance to certain DNA synthesis inhibitors due to nucleotide salvaging, suggesting RAS mutation status can guide treatment selection.
Area of Science:
- Oncology
- Cancer Genetics
- Melanoma Research
Background:
- Genetic mutations like BRAF and NRAS significantly influence melanoma patient susceptibility to targeted therapies and chemotherapy.
- While BRAF inhibitors are effective, patient relapse is common, necessitating alternative treatments for both BRAF-mutant and wild-type cases, including those with NRAS mutations.
- The impact of BRAF or NRAS mutations on chemotherapy response in melanoma remains largely unexplored.
Purpose of the Study:
- To investigate the differential response of NRAS-mutant versus BRAF-mutant melanoma cell lines to various chemotherapy drugs.
- To elucidate the mechanisms underlying chemotherapy resistance in melanoma based on specific genetic mutations.
- To assess the potential of using RAS mutation status for patient stratification in chemotherapy treatment.
Main Methods:
- Characterization of melanoma cell line responses using cell proliferation assays, DNA methylation assays, Fluorescence-Activated Cell Sorting (FACS), and quantitative-RT-PCR.
- Evaluation of sensitivity to chemotherapy agents including dacarbazine (DTIC), temozolomide (TMZ), and DNA synthesis inhibitors.
- Assay of nucleotide synthesis enzyme activity (IMPDH, TK1) and assessment of resistance to dihydrofolate reductase (DHFR) inhibitors.
Main Results:
- NRAS and BRAF mutant melanoma cells exhibited differential responses to dacarbazine (DTIC), but not temozolomide (TMZ), despite both being alkylating agents.
- DTIC's growth-inhibitory effects were primarily linked to interference with nucleotide salvaging pathways.
- NRAS-mutant melanoma cells demonstrated higher activity of nucleotide synthesis enzymes IMPDH and TK1, contributing to resistance against DHFR inhibitors.
Conclusions:
- The genetic background of melanoma cells, specifically RAS mutation status, significantly influences response to DNA synthesis inhibitors.
- Enhanced nucleotide salvaging in NRAS-mutant cells confers resistance to certain chemotherapy agents, including antifolates.
- RAS mutation status can serve as a biomarker for stratifying melanoma patients for antifolate-based therapies.
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