Heat Shock Protein 90 as a Drug Target against Protozoan Infections

Abstract

Using a pharmacological inhibitor of Hsp90 in cultured malarial parasite, we have previously implicated Plasmodium falciparum Hsp90 (PfHsp90) as a drug target against malaria. In this study, we have biochemically characterized PfHsp90 in terms of its ATPase activity and interaction with its inhibitor geldanamycin (GA) and evaluated its potential as a drug target in a preclinical mouse model of malaria. In addition, we have explored the potential of Hsp90 inhibitors as drugs for the treatment of Trypanosoma infection in animals. Our studies with full-length PfHsp90 showed it to have the highest ATPase activity of all known Hsp90s; its ATPase activity was 6 times higher than that of human Hsp90. Also, GA brought about more robust inhibition of PfHsp90 ATPase activity as compared with human Hsp90. Mass spectrometric analysis of PfHsp90 expressed in P. falciparum identified a site of acetylation that overlapped with Aha1 and p23 binding domain, suggesting its role in modulating Hsp90 multichaperone complex assembly. Indeed, treatment of P. falciparum cultures with a histone deacetylase inhibitor resulted in a partial dissociation of PfHsp90 complex. Furthermore, we found a well known, semisynthetic Hsp90 inhibitor, namely 17-(allylamino)-17-demethoxygeldanamycin, to be effective in attenuating parasite growth and prolonging survival in a mouse model of malaria. We also characterized GA binding to Hsp90 from another protozoan parasite, namely Trypanosoma evansi. We found 17-(allylamino)-17-demethoxygeldanamycin to potently inhibit T. evansi growth in a mouse model of trypanosomiasis. In all, our biochemical characterization, drug interaction, and animal studies supported Hsp90 as a drug target and its inhibitor as a potential drug against protozoan diseases.

Radicicol Confers Mid-Schizont Arrest by Inhibiting Mitochondrial Replication in Plasmodium falciparum

“…In order to determine whether decrement of mitochondrial replication is specific to radicicol treatment, we performed a similar study by exposing the parasites with 17AAG, a potent Hsp90 inhibitor. It was previously reported that 17AAG inhibits the growth of 3D7 with an IC 50 of 160 nM when treated for 48 h (24). With our experimental conditions, we determined the IC 50 of 17AAG as 170 nM, which is very close to the previously reported value.…”

Hsp90 Inhibitors as New Leads To Target Parasitic Diarrheal Diseases

“…Moreover, protozoan Hsp90 differs in biochemical characteristics from Hsp90 of the mammalian host. For example, Hsp90 from P. falciparum exhibits about six times higher ATPase activity than its human counterpart (34,62). Furthermore, the ATP-binding pocket of E. histolytica Hsp90 may mediate unique ligand interactions, based on the presence of Cys49 and Arg109 relative to the corresponding Ser52 and Lys112 in the human Hsp90 ATP-binding domain.…”

“…Hsp90 is implicated in growth and development in many protozoan species, including Dictyostelium, Leishmania, Plasmodium, Trypanosoma, and Giardia species (31)(32)(33)(34)(35). Inhibition of parasite Hsp90 activity by geldanamycin resulted in lethality in Plasmodium fal-ciparum (36), but this compound has not been pursued for clinical development due to unacceptable toxicity.…”

Post-transcriptional Repair of a Split Heat Shock Protein 90 Gene by mRNA trans-Splicing

“…In addition to its ability to fold proteins and regulate cell cycle and development, recent studies also suggest an ability to guide evolution in eukaryotes (11-13). The function of Hsp90 as a sensor of environmental cues is especially crucial in protozoan parasites, which often need to respond to radical changes of milieus within and outside their hosts (7,10).In all organisms investigated to date, Hsp90 proteins are encoded by a single open reading frame (ORF), which usually contains multiple introns. In the genome sequence of three Giardia isolates, no contiguous hsp90 ORF was predicted, but two fragments separated by a large stretch of sequence on the same scaffold were detected and annotated as hsp90.…”