Correlation of in vitro Sensitivity of Chloroquine and other Antimalarials with the Partner Drug Resistance to Plasmodium falciparum Malaria in Selected Sites of India

Background: Antimalarial drug resistance is a potential threat for control and elimination of malaria. To ascertain the status of antimalarial drug resistance at the study sites, correlation between in vitro drug sensitivity pattern and drug resistance molecular markers in Plasmodium falciparum malaria was undertaken. Materials and Methods: Polymorphisms in P. falciparum chloroquine resistance transporter (pfcrt) K76T and pfmdr1 N86Y were studied in relation to the in vitro susceptibility of P. falciparum in culture (n = 10) and field isolates (n = 40) to chloroquine (CQ), amodiaquine (AQ), quinine (QN), mefloquine (MQ) and artemisinin (ART). The prevalence of drug resistance molecular markers, pfdhfr (codon S108N, C59R, N51I, I164 L and A16V), pfdhps (codon S436F and A437G), pfATPase6 (codon D639G and E431K) and mutation in the propeller domain of pfK13 gene were also analysed. Chi-square test and parametric Pearson correlation test were performed using SPSS version 17. Results: In vitro assay showed 18% resistance to CQ, 8% to AQ and 4% to QN. However, no resistance was observed towards MQ and ART. The mutations in pfcrt and pfmdr1 were statistically not significantly associated with susceptibility responses for antimalarials; however, increased IC50 values of drugs were reflected as mutant and/or mixed isolates for both gene polymorphisms. CQ was found as independent predictor for other antimalarials, i.e., AQ, QN and ART, with r(2) score 0.241, 0.241 and 0.091, respectively. Mutation in the pfATPase6 gene at codon E431K was observed in only one sample from Tripura which also had increased IC50 value of 6.28 nM. However, moderate numbers of mutations at codon S108N, C59R and I164 L for pfdhfr gene and S436F and A437G for pfdhps gene were also observed. None of the samples showed mutation in propeller domain of pfK13 gene. Conclusion: The correlation between IC50 and molecular markers for antimalarial drug resistance is reported for the first time through this study. A positive correlation between in vitro drug resistance with molecular markers for antimalarial drug resistance could make in vitro assay a reliable tool to predict drug efficacy which is needed for detection of emerging resistance in the country.