PRPS1 Mutants Drive 6-MP Resistance And MTX Reverses The Drug Resistance Induced By PRPS1 Gene Mutation In ALL

Acute lymphoblastic leukemia(ALL)is the most common childhood malignancy,and drug resistance is one of the causes of treatment failure and recurrece.Understanding the molecular mechanisms of drug resistance is crucial to predicting the risk of recurrence.Our group has identified relapse-specific mutations in the phosphoribosyl pyrophosphate synthetase 1 gene(PRPS1)in relapsed childhood ALL cases,this gene encodes the first rate-limiting enzyme in the purine biosynthesis pathway.However,the role of mutations in PRPS1 gene in relapsed ALL is unknown.Using several experiments such as cell apoptosis assay,Western Blot and LC-MS,we found that:(1)Reh cells expressing PRRS1 mutants were resistant to the drug 6-mercaptopurine(6-MP);(2)relapse-specific PRPS1 mutants significantly increased the activity of de novo purine biosynthesis pathway,and elevated hypoxanthine(HX)could competitively inhibit 6-MP conversion;(3)as compared with methotrexate(MTX)or 6-MP alone,the combination of MTX and 6-MP could significantly suppress the proliferation of Reh cells expressing drug-resisrant PRPS1 mutants,increase the levels of cell apoptosis,and enhance the expression of DNA damage- and apoptosis-associated proteins.;(4)MTX can reverse the drug resistance induced by PRPS1 gene mutation in ALL cells to 6-MP,and the molecular mechanism is related to inhibiting the abnormal accumulation of HX.In this study,we found that relapse-specific PRPS1 mutants drive 6-MP resistance in ALL.Meanwhile,we revealed that MTX reverses the drug resistance induced by PRPS1 gene mutation in ALL cells to 6-MP.