Optimization of novel phenotypic screening hits for treatment of Malaria
To identify novel chemical starting points for the discovery of new anti-malarial drugs by phenotypic screening against erythrocytic stage P. falciparum.
Malaria remains one of the most serious infectious diseases, globally threatening nearly 50% of the world population, and leading to >400,000 deaths annually, mostly among young African children. There are no effective vaccines and the disease is managed through a combination of insecticides and drugs for both treatment and chemoprevention. The relentless ability of the parasite to acquire drug resistance necessitates that a continual pipeline of new drug candidates is maintained.
We undertook a high-throughput screen of a newly acquired (in 2017) 100K chemical library reasoning that since it was recently purchased it might contain new chemical space that had not been previously screened. As part of our hit validation process we prioritized hits from the screen based on the following experimental measures: 1) potency versus the parasite against two cell lines, 2) selectivity versus a human cell line, 3) novelty of the chemical matter, 4) parasite kill rate (medium and fast kill being desirable) and 5) in vitro ADME properties including metabolic stability and solubility. We identified 16 chemical series that met our objectives of novelty and from these have selected 3 series for hit to lead chemistry. These include a piperidine carboxamide series (Alchm18) that has a moderate rate of kill, good starting potency (P. falciparum 3D7 EC50 <100 nM), and strong starting in vitro and in vivo ADME properties; a a tetrazole-based series (Alchm3) that shows fast kill kinetics, and a an azetidine amide (Alchm17), with good potency and solubility. We have validated synthetic strategies for all three series through synthesis of both the parent compound and analogs.