Evaluating the effect of new antimalarial N-89 for gametocytes in P. berghei-infected mice

We have developed a transdermal formulation of 1,2,6,7-tetraoxaspiro [7.11] nonadecane (td N-89) for children under the age of five, who account for the majority of malaria deaths, as multiple oral doses are difficult to administer to pediatric. Td N-89 shows promise as a new antimalarial candidate for targeting trophozoites using Plasmodium berghei in vivo. Primaquine (PQ) is currently the only drug that targets the liver stage parasites against P. vivax and P. ovale. When PQ is used in combination to target gametocytes, caution is required to prevent PQ resistance. To investigate the effect of td N-89 on gametocytes, we assess the gametocytocidal activity by measuring the expression levels of gametocyte-related genes following td N-89 treatment. The P. berghei ookinete surface protein (Pbs21) and generative cell-specific 1(GCS) were used as markers for female and male gametocytes. Expression levels of Pbs21 and GCS increased during td N-89 at ED₉₀ dose. In mice with td artemisinin as a reference, Pbs21 and GCS expression levels were higher than those in the td N-89 group, suggesting that td artemisinin exhibited higher anti-asexual parasite activity compared to td N-89. However, all mice treated with td artemisinin showed recrudescence and died. In contrast, 33.3 % of mice treated with td N-89 achieved a cure despite 1.7 % parasitemia. We report for the first time that gametocyte-related genes expression progressively changes in the td N-89 group and can be detected for a long period. Taken together, our results suggest that target of td N-89 is mainly trophozoites and not gametocytes.