Synergistic Action between PfHsp90 Inhibitor and PfRad51 Inhibitor Induces Elevated DNA Damage Sensitivity in the Malaria Parasite

Abstract

The DNA recombinase Rad51 from human malaria parasite Plasmodium falciparum has emerged as a potential drug target due to its central role in the homologous recombination (HR) mediated double strand break (DSB) repair pathway. Inhibition of the ATPase and strand exchange activity of PfRad51, by a small molecule inhibitor B02 (3-(Phenylmethyl)-2-[(1E)-2-(3-pyridinyl)ethenyl]-4(3H)-quinazolinone), renders the parasite more sensitive towards the genotoxic agents. Here, we investigated whether the inhibition of the molecular chaperone PfHsp90 potentiates the anti-malarial action of B02. We found that PfHsp90 inhibitor 17-AAG ( 17 -(Allylamino)- 17 -demethoxygeldanamycin) exhibits strong synergism with B02 in both drug sensitive (3D7) and multi-drug resistant (Dd2) P. falciparum parasites. 17-AAG causes more than 200-fold decrease in the half-maximal inhibitory concentration (IC 50 ) of B02 in 3D7 parasites. Our results provide mechanistic insights into such profound synergism between 17-AAG and B02. We report that PfHsp90 physically interacts with PfRad51 and promotes the UV irradiation-induced DNA repair activity of PfRad51 by controlling its stability. We find that 17-AAG reduces PfRad51 protein levels by accelerating proteasomal degradation. Consequently, PfHsp90 inhibition renders the parasites more susceptible to the potent DNA damaging agent methyl-methane-sulfonate (MMS) in a dose dependent manner. Thus, our study provides a rationale of targeting PfHsp90 along with the recombinase PfRad51 for controlling malaria propagation.

Heat Shock Protein 90 Regulates the Activity of Histone Deacetylase Sir2 in Plasmodium falciparum

“… P. falciparum in vitro cultures at the ring stage were treated with various concentration of 17-AAG or Radicicol, and the steady-state level of PfSir2A protein was determined with a specific antibody. In a previous study investigating the dose dependent inhibition of PfHsp90 function in terms of providing the client stability, it was found that the treatment with 850 nM 17-AAG could result in a significant loss of PfRad51 protein, a client of PfHsp90, while a more dramatic effect was observed with 1.7 μM 17-AAG ( 16 ). The same study has also found that the treatment of 1.5 μM Radicicol could significantly lower-down the function of the PfHsp90 client PfRad51.…”

“…Additionally, functional inhibition of PfHsp90 by another chemical, Radicicol has also been observed in yeast surrogate system ( 13 ). Both the chemicals have also exhibited anti-plasmodial activity in in vitro culture system ( 14 – 16 ). The list of PfHsp90 clientele remained enigmatic.…”