Abstract 1874: The role of functional polymorphisms in folate metabolism on 6-mercaptopurine-mediated hematological toxicity in children with acute lymphoblastic leukemia

Abstract

Abstract Purpose: Defective S-methylation of 6-mercarptopurine (6-MP) either due to reduced activity of thiopurine s-methyltransferase (TPMT) or due to reduced synthesis of S-adenosyl methionine (SAM) induces hematological toxicity in children undergoing 6-MP treatment for acute lymphoblastic leukemia (ALL). Recently, we have demonstrated the genetic variants of TMPT results in hematological toxicity when on 6-MP. In the current study, we have aimed to explore the role of seven functional polymorphisms in folate metabolism as pharmacogenomic determinants of 6-MP mediated toxicity. Experimental Procedures: In 126 children with ALL being treated with 6-MP, Glutamate carboxypeptidase II (GCPII) C1561T, Reduced folate carrier 1 (RFC1) G80A, cytosolic serine hydroxymethyl transferase (cSHMT) C1420T, Thymidylate synthase (TYMS) 3′-UTR ins6/del6, Methylene tetrahydrofolate reductase (MTHFR) C677T, Methionine synthase (MTR) A2756G polymorphisms were analysed by PCR-RFLP method while TYMS 5′-UTR 28 bp tandem repeat analysis was done by PCR-AFLP method. Summary: Univariate analysis showed positive association of GCPII C1561T (r= 0.23) and cSHMT C1420T (r=0.15) variants with hematological toxicity. Multi dimensionality reduction analysis confirmed synergetic gene-gene interaction between these two loci (×2=5.9, p=0.02) apart from showing an interesting tri-variate interaction i.e, RFC1 G80A/cSHMT C1420T/TYMS 5′-2R3R. RFC1 G80A showed additive interaction with cSHMT while TYMS 2R alleles showed counteracting interaction. Toxicity grade prediction model was developed using multiple linear regression approach, which showed moderate predictability of aberrations in folate metabolism and TPMT*3C (Area under the receiver operating characteristic curve=0.69) thus explaining 36% variation in toxicity. Conclusion: Aberrations in folate metabolism and TPMT*3C contribute to 36% 6-MP mediated toxicity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1874. doi:1538-7445.AM2012-1874