Knockdown of TKTL1 additively complements cisplatin-induced cytotoxicity in nasopharyngeal carcinoma cells by regulating the levels of NADPH and ribose-5-phosphate.

Background: Transketolase-like 1 (TKTL1) plays an important role in pentose phosphate pathway (PPP) branch, the main pathway generating nicotinamide adenine dinucleotide phosphate (NADPH) and nucleotides for DNA synthesis. TKTL1 is closely related to DNA damage and has a close relationship with incidence and progression of cancers. Cisplatin is the main chemotherapeutic drug by inducing DNA damage. Whether TKTL1 knockdown additively complements cisplatin-induced cytotoxicity in nasopharyngeal carcinoma cells, however, remains largely undefined.

Methods: Lipofectamine 2000 was used to transfect si-TKTL1s with different sequences into the CNE2 and HONE1 cells. The mRNA and protein levels of TKTL1 were determined by qRT-PCR and western blot, respectively. MTT assay and flow cytometry were used to access the viability and apoptosis of CNE2 and HONE1 cells. The NADPH and ribose-5-phosphate levels in both CNE2 and HONE1 cells were determined by NADPH examination kit and HPCE analysis, respectively. The effect of TKTL1 knockdown and NADPH/ribose-5-phosphate supplement on DNA damage was assessed by using Comet assay.

Results: TKTL1 knockdown significantly decreased TKTL1 level in CNE2 and HONE1 cells. A significant decrease in cell viability and an obvious increase in cell apoptosis rate were found in si-TKTL1+cisplatin group compared with si-TKTL1 group or si-control+cisplatin group. The levels of NADPH and ribose-5-phosphate in CNE1 and HONE1 cells were dramatically decreased in si-TKTL1 group compared with si-control group. TKTL1 knockdown additively complemented cisplatin-induced cytotoxicity, which was partly reversed by the supplements of NADPH and ribose-5-phosphate, including the increased survival rate, decreased apoptosis and DNA damage.

Conclusions: Knockdown of TKTL1 additively complements cisplatin-induced cytotoxicity in the nasopharyngeal carcinoma cells by inhibiting the levels of NADPH and ribose-5-phosphate, indicating that TKTL1 may be a promising target to improve the therapeutic effect combining with cisplatin for the patients with nasopharyngeal carcinoma.