(702a) Hematin Crystallization Mechanisms Suggest How Antimalarial Drugs Operate

Hematin is a byproduct of heme detoxification in malaria parasites. Current antimalarial compounds are thought to inhibit the growth of hematin crystals, referred to as hemozoin (in vivo) or b-hematin (in vitro). Identification of antimalarial drug action on this phase transformation could provide a foundation for drug design to overcome parasite resistance to antimalarials. Continued resurgence of antimalarial drug resistance drives research effort to better characterize drug-crystal interactions from a fundamental perspective. To this end, we aim to better understand the molecular mechanism(s) of hematin crystallization and antimalarial drug action within physiologically-relevant environments as the basis for elucidating growth sites on hematin crystal surfaces and design more effective growth inhibitors that selectively bind to these sites.

We employ in situ atomic force microscopy (AFM) in parallel with bulk solution and crystallization studies as a platform to study the mechanisms of crystal growth and inhibitor-crystal interactions in biomimetic growth solutions. Time-resolved in situ AFM measurements reveal that hematin crystallization occurs by the classical pathway of single molecule incorporation, specifically involving two-dimensional nucleation of layers. We quantified the rate of layer generation and the velocities of anisotropic step advancement as a function of supersaturation in the absence and presence of antimalarials. We identified unique modes of binding for current antimalarials as inhibition pathways: step pinning, kink blocking, and step bunching. In parallel, we studied the prominent functional groups that comprise antimalarial compounds by in situ AFM. Identifying fundamental principles governing the molecular recognition of antimalarial drugs to specific sites could lead to the rational design of new compounds with improved efficiency to overcome parasite resistance to current antimalarials.