Interactions between drug combinations and resistance acquisition risk for antimalarial ATP4 inhibitors

ABSTRACT The overall goals of this proposal are to develop an understanding of the factors driving the efficacy of potential clinical combinations of a new class of fast acting antimalarial, the ATP4 inhibitors (ATP4i), including pharmacology enforcing speed of action and total cidality and the selection of new ATP4i resistant strains of P. falciparum that are competent to propagate in vivo and thus would provide clinically relevant ATP4i resistance. The key goal is to understand how specific drug partners could potentially prevent development of ATP4i resistant parasites. The project centers on the ATP4i SJ733, which has recently successfully completed Phase 2a trials and provides rapid pharmacodynamics in humans for both P. falciparum and P. vivax malarias. The basic approach will be examining patterns of efficacy and resistance acquisition in both in vitro and in vivo models. This approach allows understanding how ATP4i inhibitor’s unique host-mediated clearance mechanism – the removal of infected, treated erythrocytes by macrophages and the spleen – leads to disparities between predicting resistance risk using in vitro methods and the actual clinical risk. Drug combinations to be examined include: pyronaridine, lumefantrine, piperaquine, artesunate, tafenoquine and the triple combination artemether- lumefantrine. The health relatedness of this project is the potential to develop new ATP4i based combination antimalarial drugs that possess intrinsically low risk for resistance development and could replace the ACTs. We have previously developed and carried out all the required in vitro and in vivo pharmacological modeling, genomics, and genetic methods for testing candidate resistance-conferring mutations. In Aim 1, we will carry out in vitro experiments using combination drug exposure patterns matched to what would be seen in patients to both examine total cidality of the combinations and the frequency and nature of resistance-conferring mutations selected in cultured parasites. In Aim 2, we will carry out in vivo experiments using combination drugs dosed so to match blood drug exposure patterns seen in patients to both examine total cidality of the combinations and the frequency and nature of resistance-conferring mutations selected during infections in humanized mice. In Aim 3, we will characterize genomic changes in parasites selected by both approaches, identify candidate resistance-conferring changes, and generate knock-in strains of P. falciparum to test the function of candidate changes. Overall, this innovative project will teach us how ATP4i drug combinations reinforce the fast-acting pharmacodynamics of the class, how resistance develops to ATP4i, and how the genomic changes in the parasite interact with the host-driven clearance mechanism to define which mutants are competent for growth in vivo. Ultimately this should allow designing the optimal drug combination to best protect the ATP4i from resistance acquisition and allow development of a drug to replace the ACTs.