This difference leads to the specula tion that constitutive activation of EGFR

Thymidine is the substrate of TK1 in the pyrimidine salvage INNO-406 887650-05-7 pathway and our data suggested that TK1 activ ity is increased in mutNRAS cells. Indeed, we found a significant overexpression of TK1 in mutNRAS cells compared to mutBRAF cells in our panel of melanoma cell lines. This finding was supported by two independent datasets analysed in Oncomine. NRAS mutant melanoma cells are more resistant to DNA de novo synthesis inhibitors than BRAF mutant cells Our data show that in mutNRAS melanoma cells elevated TK1 activity contributes to enhanced pyrimidine salvaging. However, the inhibitory effect of 2 AzaHX is on the purine salvage pathway, where after conversion into 2 Aza inositol monophosphate it suppresses IMP dehydro genase. Thus, the difference in the response of mutNRAS and mutBRAF cells to DTIC could be based on differences in IMPDH.<br><br> Indeed, mutNRAS cells were significantly more resistant to two IMPDH inhibitors, Lapatinib HER2 阻害剤 Mycophenolic Acid and AVN944, compared to mutBRAF cells. IMPDH expression levels did not differ in the individual cell lines, indi cating that the resistance in mutNRAS cells is not due to higher IMPDH expression levels. In summary, mutNRAS melanoma cells are more effi cient in nucleotide salvaging than mutBRAF melanoma cells, which is at least part due to enhanced TK1 expres sion and IMPDH activity. This finding sug gests that mutNRAS melanoma cells would be more resistant to drugs targeting DNA de novo synthesis than mutBRAF cells. Indeed, when we determined the GI50 of our panel of melanoma cells for the DHFR inhibitors ami nopterin, pyrimethamine and methrotrexate, we found that mutNRAS cells were significantly more resistant than mutBRAF cells.<br><br> Moreover, when we analysed a dataset derived from a drug screen using a large panel of cancer cell lines, we found not only that Lonafarnib 臨床試験 NRAS mu tant melanoma cell lines were more resistant to pyrimeth amine than BRAF mutant melanoma cells, but that independently of cancer type, mutRAS cancer cells were significantly more resistant to pyrimethamine than mutBRAF cells. Discussion The aim of this study was to determine whether the muta tional status of melanoma cells would correlate with their response to chemotherapeutic agents. Our results demon strate that in melanoma the presence of mutually exclusive BRAF and NRAS mutations has no influence on the re sponse to DNA alkylating agents such as TMZ.<br><br> Similar re sults considering BRAF or RAS mutation status are found in a large data set containing drug treatment data from 732 cancer cell lines of different origin. Thus, it appears that mutBRAF and mutNRAS share common mechanisms of resistance to methylating agents such as drug efflux, or deregulation of pro apoptotic or DNA repair pathways. Surprisingly, we found that mutBRAF and mutNRAS cells respond very differently to light activated DTIC. Acti vation of DTIC by exposure to white light has been de scribed to recapitulate its chemotherapeutic activity in vitro but our results provide experimental evidence that the toxic effect described for light activated DTIC is inde pendent of DNA methylation.