rifampin and artemisinin

The current anti-TB treatment consists of a prolonged multi-drug therapy. Interventional strategies are required to reduce the chemotherapeutic load. In this regard, we have previously identified a synergistic interaction between hydroperoxides and rifampicin. This strategy has been extended here to repurpose a new drug against TB. A hydrophobic antimalarial drug, artemisinin, with an unstable endoperoxide bridge structure, has been investigated as a potential candidate. In combination with rifampicin, artemisinin was found to be synergistic against M. bovis BCG and M. tuberculosis H37Ra. Furthermore, artemisinin was observed to induce peroxides in a time and concentration dependent manner and the levels of the peroxides were significantly higher in cells treated with the drug pair. Coupled with rapid disintegration of the membrane, this enhanced the clearance of the bacterial culture in vitro. On the other hand, formation of the peroxides was significantly reduced in the presence of ascorbic acid, an antioxidant. This translated to a loss of the synergistic effect of the combination, indicating the importance of peroxide formation in the mode of action of artemisinin. Interestingly, artemisinin also had a synergistic interaction with isoniazid, amikacin and ethambutol and an additive interaction with moxifloxacin, other drugs commonly used against TB.

Topics: Analysis of Variance; Antitubercular Agents; Artemisinins; Cell Membrane; Drug Combinations; Drug Repositioning; Drug Synergism; Drug Therapy, Combination; Microbial Sensitivity Tests; Mycobacterium bovis; Mycobacterium tuberculosis; Peroxides; Rifampin

Artemisinin drugs have become the first-line antimalarials in areas of multidrug resistance. However, monotherapy with artemisinin drugs results in comparatively high recrudescence rates. Autoinduction of cytochrome P450 (P450)-mediated metabolism, resulting in reduced exposure, has been supposed to be the underlying mechanism. To better understand the autoinduction and metabolic drug-drug interactions (DDIs), we evaluated the P450s (particularly CYP2B6 and CYP3A4) inhibited or induced by two artemisinin drugs, Qing-hao-su (QHS) and dihydroartemisinin (DHA) using human liver microsome, recombinant P450 enzymes, and primary human hepatocytes. The results suggested that QHS was a weak reversible inhibitor of CYP2B6 (K(i) 4.6 μM), but not CYP3A4 (IC₅₀ ∼ 50 μM) and did not show measurable time-dependent inhibition of either CYP2B6 or CYP3A4. DHA inhibited neither CYP2B6 nor CYP3A4 (IC₅₀ > 125 μM). In addition, it was found that QHS induced the activity of CYP3A4 (E(max) 3.5-fold and EC₅₀ 5.9 μM) and CYP2B6 (E(max) 1.9-fold and EC₅₀ 0.6 μM). Of the other P450s, UDP glucuronosyltransferases, and transporters studied, QHS and DHA had no significant effect except for minor induction of mRNA expression of CYP1A2 (E(max) 7.9-fold and EC₅₀ 5.2 μM) and CYP2A6 (E(max) 11.7-fold and EC₅₀ 4.0 μM) by QHS. Quantitative prediction of P450-mediated DDIs indicate autoinduction of QHS clearance with the AUC(i)/AUC ratio decreasing to 59%, as a result of a 1.9-fold increase in CYP3A4 and a 1.6-fold increase in CYP2B6 activity. These data suggest that QHS drugs are potential inducers of P450 enzymes, and the possible drug interactions (or lack thereof) with artemisinin drugs may be clinically relevant.

Topics: Antimalarials; Artemisinins; Aryl Hydrocarbon Hydroxylases; Biotransformation; Cells, Cultured; Cytochrome P-450 CYP2B6; Cytochrome P-450 CYP3A; Cytochrome P-450 CYP3A Inhibitors; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Induction; Enzyme Inhibitors; Hepatocytes; Humans; Kinetics; Liver; Microsomes, Liver; Models, Biological; Oxidoreductases, N-Demethylating; Primary Cell Culture; Recombinant Proteins; RNA, Messenger