Nonclassical mechanisms to irreversibly suppress & beta;-hematin crystal growth

Hematin crystallization is an essential element of heme detoxification of malaria parasites and its inhibition by antimalarial drugs is a common treatment avenue. We demonstrate at biomimetic conditions in vitro irreversible inhibition of hematin crystal growth due to distinct cooperative mechanisms that activate at high crystallization driving forces. The evolution of crystal shape after limited-time exposure to both artemisinin metabolites and quinoline-class antimalarials indicates that crystal growth remains suppressed after the artemisinin metabolites and the drugs are purged from the solution. Treating malaria parasites with the same agents reveals that three- and six-hour inhibitor pulses inhibit parasite growth with efficacy comparable to that of inhibitor exposure during the entire parasite lifetime. Time-resolved in situ atomic force microscopy (AFM), complemented by light scattering, reveals two molecular-level mechanisms of inhibitor action that prevent & beta;-hematin growth recovery. Hematin adducts of artemisinins incite copious nucleation of nonextendable nanocrystals, which incorporate into larger growing crystals, whereas pyronaridine, a quinoline-class drug, promotes step bunches, which evolve to engender abundant dislocations. Both incorporated crystals and dislocations are known to induce lattice strain, which persists and permanently impedes crystal growth. Nucleation, step bunching, and other cooperative behaviors can be amplified or curtailed as means to control crystal sizes, size distributions, aspect ratios, and other properties essential for numerous fields that rely on crystalline materials. Experiments under biomimetic conditions in vitro reveal molecular-level mechanisms of action of antimalarial drugs via irreversible inhibition of hematin crystal growth and crystalline hematin sequestration by P. falciparum.

Automated summary

Hematin crystallization is crucial for heme detoxification in malaria parasites, and inhibiting this process is a common approach in antimalarial treatment. Our study reveals irreversible inhibition of hematin crystal growth due to distinct cooperative mechanisms under biomimetic conditions. The findings demonstrate that both artemisinin metabolites and quinoline-class antimalarials can suppress crystal growth even after being eliminated from the solution. Furthermore, the research shows that short-term exposure to inhibitors has comparable efficacy in inhibiting parasite growth as long-term exposure. These molecular-level mechanisms of action of antimalarial drugs provide valuable insights into inhibiting hematin crystal growth and sequestering crystalline hematin by Plasmodium falciparum.