Folate antagonist MTX is preferred because of its cost and long term experience. However, ~50% patients experience good clinical response. Inconsistent non genetic prediction (treatment response) variables, significant variability in MTX response and expensive alternative biologic DMARDs demand better predictive markers for MTX response. We investigated SNPs in folate metabolic pathway in Indian (Asian) RA patients treated with MTX. We hypothesized that these SNP would affect MTX pharmacokinetics (PK) and MTX treatment outcome.
A total of 336 ACR classified RA patients (Female 85%, RF 79%) undergoing supervised MTX therapy for > 3 months were randomly selected from a community rheumatology clinic; 217 patients were analyzed; maximum (usually limited by tolerability) MTX dose 3.75-20 mg, median 17.5mg. We retrospectively analyzed standard CRF but recalled several patients to confirm events. Responders were classified as patients having ACR 50 at 12 months plus ACR 20 response at 6 months; ACR improvement response as per ACR. 12 SNPs in 9 genes of folate-MTX metabolism (including transporters) were genotyped using PCR-RFLP and Real-time Taqman allelic discrimination that also included 144 healthy controls (HC). To evaluate the effect of SNPs on MTX PK; PK analysis was performed on 94 patients (weekly dose ranging 3.75 mg – 20 mg). Plasma MTX and its metabolite 7-OH MTX levels were determined at 0, 2 and 8 hr. by HPLC post column photoxidation- fluorescence detection and plasma homocysteine was estimated at 0 hr.
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ACR 50 response
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(1) MTHFR A1298C ‘C' allele (OR =2.6, 95% CI 1.9- 3.5, P<0.0001) and RFC1 G80A ‘G' allele (OR=2.0, 95% CI, 1.5- 2.7, P<0.0001) were significantly associated with RA when compared to HC. (2) The table shows frequency distribution of genotypes associated with ACR 50 response. At 12 months patients with MTHFR 1298 CC genotype and RFC1 80 GG genotype were more likely to have poor MTX efficacy relative to MTHFR 1298 AA-AC (OR= 3.3, 95% CI 1.3-8.5, P=0.01) and RFC1 80 AA-GA (OR= 2.2, 95% CI 1.0-4.9, P=0.04) respectively. None of the other SNPs in folate-MTX pathway were associated with MTX efficacy in our RA population. (3) PK analysis revealed no significant difference in the plasma concentration of MTX, 7OH MTX and Hcy at 0hr, 2hr and 8 hrs between responders and non responders. However patients having 1298 CC genotype showed higher 7 OH MTX levels at 8 hrs.
Conclusion: Patients with MTHFR 1298 CC and RFC1 80 GG showed poor clinical improvement with MTX. PK study show some associations with genetic polymorphisms but need to be further validated. SNPs in folate pathway may contribute to MTX efficacy in Indian RA patients. Large sample size validation cohort would be required to confirm our observations with an attempted higher dose to treat.
Disclosure: Y. Ghodke, None; A. Chopra, None; A. S. Puranik, None; P. Shintre, None; A. Radkar, None; K. Joshi, None; B. Patwardhan, None.