DHFR and ovarian cancer: After first line treatment of ovarian cancer (OC) patients with platinum drugs, drug resistance occurs rapidly inducing the overexpression of folate-dependent proteins such as thymidylate synthase (TS, TYSY) (Ozasa et al., 2010), dihydrofolate reductase (DHFR, DYR), the trifunctional purine biosynthetic protein adenosine-3 (GART, PUR2) and other enzymes involved in cell replication.