Harmine Is a Potent Antimalarial Targeting Hsp90 and Synergizes with Chloroquine and Artemisinin

Abstract

Previous studies have shown an antimalarial effect of total alkaloids extracted from leaves of Guiera senegalensis from Mali in West Africa. We independently observed that the beta-carboline alkaloid harmine obtained from a natural product library screen inhibited Plasmodium falciparum heat shock protein 90 (PfHsp90) ATP-binding domain. In this study, we confirmed harmine-PfHsp90-specific affinity using surface plasmon resonance analysis (dissociation constant [K d ] of 40 M). In contrast, the related compound harmalol bound human Hsp90 (HsHsp90) (K d of 224 M) more tightly than PfHsp90 (K d of 7,010 M). Site-directed mutagenesis revealed that Arg98 in PfHsp90 is essential for harmine selectivity. In keeping with our model indicating that Hsp90 inhibition affords synergistic combinations with existing antimalarials, we demonstrated that harmine potentiates the effect of chloroquine and artemisinin in vitro and in the Plasmodium berghei mouse model. These findings have implications for the development of novel therapeutic combinations that are synergistic with existing antimalarials.

Differences in Conformational Dynamics between Plasmodium falciparum and Human Hsp90 Orthologues Enable the Structure-Based Discovery of Pathogen-Selective Inhibitors

“…30,31 Likewise, harmine displays synergy with CQ and artemisinin in vitro and in a mouse model of malaria. 31 Recently, the crystal structure of ADP-bound PfHsp90 became available, 32 which opened the possibility for structurebased drug screening and design. Notably methods of virtual drug screening (VS) 33,34 make it possible to explore a much larger number of chemotypes and compounds at a fraction of the cost, time and effort required to screen compound libraries with more traditional approaches.…”

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

“…As a result, it is hypothesized that it is possible to inhibit the activity of Hsp of a pathogen without significant deleterious effects on the Hsps of the host [5, 17]. It has been shown previously that natural compounds such as harmine and the ATP mimetic PU-H71 exert anti- Plasmodium activity by targeting PfHsp90 [21, 26]. In this study, 42 different derivatives of harmine were synthesized and the in vitro and in vivo anti-malarial activities of two of the harmine analogues was tested as single agents and in combination with artemisinin.…”

“…Unlike 17A, treatment with 21A significantly prolonged the survival time of treated mice. This property was not seen with the parent molecule harmine [26]. Therefore, 21A was selected for the dose-ranging and combination experiments.…”

“…Recently, it has been demonstrated that PU-H71 has a good anti-malarial activity in vitro and in mice [21]. Harmine, a beta carboline alkaloid, is able to selectively bind PfHsp90 to a greater extent than human Hsp90 (HsHsp90) [26]. Harmine has been reported as having a specific high-affinity interaction with the ATP-binding domain of PfHsp90 with strong inhibition of P. falciparum in cell culture systems.…”

“…In the P. berghei ANKA infection model in mice, harmine showed a significant reduction in parasitaemia. However, it did not significantly prolong the survival of the infected mice [17, 26]. …”