The HSP90 inhibitor 17-AAG induced calcium-mediated apoptosis in filarial parasites

The available antifilarial medications are effective only against the larval stage of the filarial parasite. As a result, there is a pressing need for an adulticidal drug. The development of drugs requires the identification of molecular targets that are critical for parasite life. In this study, we observed the effect of 17-N-allyl-17-demethoxygeldanamycin on the survival of adult filarial parasites. The 17-N-allyl-17-demethoxygeldanamycin (17-AAG) is a derivative of geldanamycin (GA), which is an inhibitor of heat shock protein (HSP)90. It is less toxic as compared to geldanamycin. The motility and viability of the adult filarial parasite Setaria cervi were decreased on exposure to 17-AAG at 2.5 and 5.0 μM/ml concentrations. The 17-AAG treated parasites showed induction of oxidative stress as evidenced by decreased activity of various antioxidant enzymes like glutathione s-transferase, glutathione reductase, thioredoxin reductase, and an increase in ROS production in comparison to control. Oxidative stress may lead to altered calcium homeostasis. Indeed, in 17-AAG treated worms, there was a rise in calcium in the cytosol and mitochondria, as well as a decrease in the ER. We also observed enhanced activity of phospholipase C in the treated parasite, suggesting the opening of calcium channels located on the ER membrane. ER stress is marked by a reduced level of protein disulfide isomerase. Further, 17-AAG treated worms showed an increase in apoptotic marker enzyme activities like calpain, cyt-c, and caspase-3. The 2D-gel electrophoresis technique showed 142 protein spots in the control and 112 spots in the 17-AAG treated parasite. Thus, 17-AAG induced oxidative stress, and altered calcium, and proteostasis of parasites, which led to apoptosis.