Stage-specific pharmacodynamic chloroquine and pyronaridine action on artemisinin ring-stage resistant Kelch C580Y mutation <i>Plasmodium falciparum</i> correlates to hemozoin inhibition process

The antimalarial quinolines pyronaridine and chloroquine both inhibit hemozoin crystallization, predominately produced by <i>Plasmodium falciparum</i> intra-erythrocytic trophozoite stage parasites. Pyronaridine extends activity to ring-stage chloroquine-sensitive parasites, in contrast to chloroquine. Here, we investigated chloroquine and pyronaridine hemozoin inhibition type correlated to stage-specific activity on chloroquine-resistant ring-stage artemisinin sensitive and resistant <i>P. falciparum</i> CamWT and CamWT-C580Y parasites. Pyronaridine (2.8 μM) is tenfold more potent at beta-hematin nucleation than chloroquine (40 μM). Both pyronaridine and chloroquine (0.2 and 0.7 μM, respectively) had similar sub-μM inhibition of beta-hematin extension. <i>P. falciparum</i> CamWT-C580Y parasites produce smaller width hemozoin crystals which extend less than isogenic CamWT hemozoin. Stage-specific pulse dose pyronaridine and chloroquine on CamWT-C580Y or CamWT isogenic parasites observed 3- to 4-fold higher pyronaridine IC₅₀s compared to 10- to 15-fold higher chloroquine on most CamWT-C580Y to CamWT stages. These findings collectively show that hemozoin nucleation inhibition widens stage-specific pyronaridine activity on <i>P. falciparum</i> drug-resistant parasites.