Identification and characterization of novel chemical scaffolds to overcome drug resistance in malaria

• Main Author: Tay, Donald Wen Jun
• Other Authors: Peter Preiser
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Science::Biological sciences::Biochemistry; Science::Biological sciences::Microbiology
• Online Access: https://hdl.handle.net/10356/144514
• Institution: Nanyang Technological University

Till today, malaria remains one of the most prominent infectious diseases in the world. Since the beginning of the decade, the number of malaria cases has drastically decreased, in no small part due to the availability of a plethora of chemotherapeutic strategies. In the last five years however, this progress has seemed to have stalled, with drug resistance, especially to frontline treatments, playing no small part. Without an efficacious vaccine, strong emphasis is placed on discovering and developing new chemotherapeutics with novel mechanisms of action to prevent and control malaria infections. However, drug development in malaria is a challenging task, faced by the canonical hurdles of drug discovery and further compounded by the lack of understanding of the parasite’s complex biology. These issues not only result in prolonged pre-clinical and clinical testing, but also starve the community of starting points for therapeutic design. Therefore, it might take too long before a new antimalarial may reach the hands of clinicians and patients. Hence, we used two distinct drug discovery approaches in an attempt to augment the antimalarial development pipeline. Here, we report two FDA-approved anticancer compounds for repurposing in malaria, as well as a third chemotype, unique to existing antimalarials, both as a promising candidate for drug development and a tool to uncover drug targets. These compounds were identified by screening a collection of anticancer drugs undergoing clinical development as well as an in-house library of compounds previously unintended for biological study. With large number of hits from both screens, we applied a distinct triage workflow to narrow down our candidates from each library. By comparison of pharmacokinetic properties in humans against their efficacy against Plasmodium falciparum, this allowed us to shortlist the two candidates which were documented to achieve doses in excess of their minimum inhibitory concentrations for at least 24hrs post administration in a single dose. The extrapolation suggests that these compounds have the potential to be expedited for development into clinical drugs by taking their first step into controlled-human malaria infection studies. While it may not immediately lead to the next clinical candidate, novel chemical scaffolds may serve as good starting points for anti-drug resistant therapies, as well as to probe the proteome of the parasite for new avenues for therapeutic design. Therefore, our second approach was to biologically characterize the screened hits for suitable candidates displaying as many ideal antimalarial traits possible, and use it as a tool to study the parasite’s druggable biology. This led to the identified a chemical scaffold with low nanomolar asexual stage-killing activity and parasite-to-host specificity, herein known as A1. Amongst its ideal antimalarial properties, A1 not only shows to inhibit the growth of not only ring stages of the asexual cycle, but also disrupts gametocyte development. Hypothesizing that its activity against the parasite may disrupt a lesser understood cellular function, we subjected A1 to a target identification screen using Cellular Thermal Shift Assay (CETSA). Interestingly the metalloprotease, Falcilysin (FLN), best described for its critical role in haemoglobin degradation, was identified and subsequently validated as its target in both asexual and sexual developmental stages of the parasite. Our pilot structural activity relation (SAR) studies have also shown that the compound has the potential to be improved into a proper candidate for early clinical testing. Taken together, we anticipate that the findings of this study have supplemented the antimalarial development community with novel candidates to be seriously considered for therapeutic development, as well as a promising start point for which the next generation of drugs can be designed upon.