Anti-malarial activity of geldanamycin derivatives in mice infected with Plasmodium yoelii

Abstract

BackgroundGeldanamycin (GA), a benzoquinone ansamycin antibiotic has been shown in vitro to possess anti-plasmodial activity. Pharmacological activity of this drug is attributed to its ability to inhibit PfHSP90. The parasite growth arrest has been shown to be due to drug-induced blockage of the transition from ring to trophozoite stage. To further evaluate the consequences of this pharmacodyamic feature, the anti-malarial activity of GA analogs with enhanced drug properties in a Plasmodium-infected animal model have been evaluated for their capacity to induce clearance of the parasite. In the process, a hypothesis was subsequently tested regarding the susceptibility of the cured animals to malaria reflected in an attenuated parasite load that may be evoked by a protective immune response in the host.MethodsSix weeks old Swiss mice were infected with a lethal Plasmodium yoelii (17XL) strain. On appearance of clinical symptoms of malaria, these animals were treated with two different GA derivatives and the parasite load was monitored over 15-16 days. Drug-treated animals cured of the parasite were then re-challenged with a lethal dose of P. yoelii 17XL. Serum samples from GA cured mice that were re-challenged with P. yoelii 17XL were examined for the presence of antibodies against the parasite proteins using western blot analysis.ResultsTreatment of P. yoelii 17XL infected mice with GA derivatives showed slow recovery from clinical symptoms of the disease. Blood smears from drug treated mice indicated a dominance of ring stage parasites when compared to controls. Although, P. yoelii preferentially invades normocytes (mature rbcs), in drug-treated animals there was an increased invasion of reticulocytes. Cured animals exhibited robust protection against subsequent infection and serum samples from these animals showed antibodies against a vast majority of parasite proteins.ConclusionsTreatment with GA derivatives blocked the transition from ring to trophozoite stage presumably by the inhibition of HSP90 associated functions. Persistence of parasite in ring stage leads to robust humoral immune response as well as a shift in invasion specificity from normocytes to reticulocyte. It is likely that the treatment with the water-soluble GA derivative creates an attenuated state (less virulent with altered invasion specificity) that persists in the host system, allowing it to mount a robust immune response.

A Review of Recent Patents on the Protozoan Parasite HSP90 as a Drug Target

“…More recently, 17-AAG and 17-N-(3-(2-(-2(3-aminopropoxy) ethoxy)propyl)pent-4-ynamide-17-demethoxygeldanamycin (17-PEG-Alkyn-GA) Fig. ( 1 ), a highly water soluble pegylated derivative of GA, were tested against a murine model infection with P. yoelii [49]. The drug was inoculated on day 6 after infection, when malaria symptoms were evident.…”

“…The administration of 17-AAG or 17-PEG-Alkyn-GA on day 6 post-infection resulted in control of parasitemia. However, a second dose was needed for complete clearance of the parasites and cure of mice [49]. In this case, by using either 17-AAG or 17-PEG-Alkyn-GA, three out of four mice survived the experiment.…”

“…The in vivo analysis suggests that the anti-HSP90 treatment could have an anti-parasitic effect, at least for Plasmodium spp and T. evansi [42, 49]. Therefore, it is reasonable to expect future studies that involve animal models of malaria, Chagas, leishmaniosis and toxoplasmosis either using some of the compounds described above or new synthesized molecules.…”

In vitro and in vivo anti-malarial activity of novel harmine-analog heat shock protein 90 inhibitors: a possible partner for artemisinin

“…Therefore, targeting the Hsp90 ATP-binding using a small molecule is expected to inhibit its chaperoning activity and render the client proteins to degradation via the cytosolic proteasome, which consequently inhibit major metabolic activities of the cell [40]. Several studies have tested the use of small molecules that bind to and competitively inhibit the ATPase activity of Hsp90 as candidate drugs for different infectious diseases and cancer [23, 41, 42]. Although the Hsp90 in humans and the malaria parasite have a high degree of homology, there are subtle and potentially significant structural differences that can be exploited when designing selective small-molecule inhibitors [16].…”

“…As a result, different derivatives of geldanamycin have been developed that have an acceptable level of hepatotoxicity [22]. In vitro and in vivo experiments have shown that the geldanamycin-derivatives, 17AAG and 17-PEG-Alkyn-GA, are promising anti-malarial compounds targeting PfHsp90 [23, 24]. …”