One obstacle to the success of cancer chemotherapy is the development of tumor resistance. Resistance to cisplatin commonly occurs during ovarian cancer treatment and how to overcome it has become a key issue in cancer research. Previous studies have identified alpha-enolase and pyruvate kinase as two intracellular binding partners of cisplatin which may reduce its cytotoxic effect. Moreover, these two proteins play a critical role in tumor energy metabolism. Therefore, an inhibitor of ENO1, sodium fluoride (NaF), as well as an inhibitor and an inducer of PKM2, shikonin and fructose-1, 6-bisphosphate (FBP), respectively, were selected to explore if these two enzymes affect cisplatin sensitivity in ovarian cancer cells. Thus, one aim of this work was to investigate whether the inhibition of ENO1 and PKM2 can enhance cisplatin sensitivity through reduction of intracellular binding of cisplatin and/or via blocking the glycolytic pathway. Another aim was to identify whether the induction of PKM2 can reduce cisplatin cytotoxicity in ovarian cancer cells and in this way to understand the relevance of PKM2 for cisplatin sensitivity. 

The cytotoxicity of cisplatin in A2780 and cisplatin-resistant A2780cis cells after co-incubation with NaF, shikonin and FBP was determined using the MTT assay. The expression of ENO1 and PKM2 after incubation with NaF, shikonin and FBP was investigated by Western Blot. siRNA transfection aiming at silencing ENO1 and PKM2 mRNA was performed to compare cisplatin cytotoxicity before and after transfection.  

Cisplatin sensitivity in A2780 and A2780cis cells did not change significantly upon co-incubation with shikonin and FBP. However, the sensitivity of cisplatin to A2780cis cells was significantly enhanced after co-incubation with NaF, whereas no significant improvement could be observed in A2780 cells. The investigation of ENO1 and PKM2 expression showed that the treatment with NaF, shikonin and FBP did not have an impact on the intracellular protein levels in both cell lines. Because the efficiency of the siRNA transfection of ENO1 and PKM2 was low, it was not possible to reveal whether the down-regulation of ENO1 and PKM2 can enhance cisplatin cytotoxicity.  

In conclusion, neither the inhibition nor the induction of PKM2 influenced cisplatin cytotoxicity in A2780 and A2780cis cells. The inhibition of ENO1 by NaF was able to increase cisplatin sensitivity in A2780cis cells but not in A2780 cells. Whereas PKM2 does not seem to affect cisplatin sensitivity, the role of ENO1 warrants further investigation.