Development of a Novel Therapeutic Class of Antimalarials Targeting PfGARP as Treatments for Severe Malaria

Rhode Island Hospital, Providence RI

Investigators

Abstract

ABSTRACT- Our overall objective is to develop a novel therapeutic class of antimalarials targeting PfGARP as treatments for severe malaria. Half of the world's population lives in malaria endemic regions with an estimated 247 million malaria cases recorded in 2021 alone. These cases resulted in over half a million deaths, of which ~80% occur in children under the age five 1. Clearly, malaria continues to pose an enduring threat to humanity. This situation is compounded by newly emerging parasites that are resistant to our most effective antimalarial, Artemisinin (ART), which mandates an expedited drug development initiative. Prior work from our group identified P falciparum Glutamic Acid Rich Protein (PfGARP) as a vaccine candidate for falciparum malaria 2. PfGARP is a ~80 kDa protein found only on exofacial surface of P falciparum infected RBCs which: 1) lacks homology with host proteins, 2) is essential for parasite survival in vivo, 3) has markedly limited sequence variation across ~3000 field isolates, and 4) is the target of both polyclonal and monoclonal antibodies that kill parasites at the trophozoite stage by inducing parasite apoptosis in the absence of immune cells or complement. These data provide a robust scientific basis for investigating PfGARP as a promising antimalarial drug target. We propose to screen a small molecule drug library to identify compounds that bind to PfGARP in the same location as our lethal anti-PfGARP antibodies, thus enriching for small molecules that also activate PfGARP leading to parasite death. We propose a “hit” discovery and then lead candidate development program for an anti-malarial drug targeting PfGARP. The prioritized leads will be down-selected using in vitro parasite killing assays and an innovative cell-based suite of pharmacokinetic analyses with our COBRE Pharmacology Core. Prioritized leads will be further down-selected with murine pharmacokinetic (PK) studies, and finally in efficacy studies in the NSG/P. falciparum murine model 3. In our preliminary work, we have developed an antibody inhibition assay to screen for small molecules that inhibit the binding of polyclonal anti-PfGARP to PfGARP coated beads, screened 6,400 compounds from the ChemBridge DIVERSet library and identified two compounds which bind PfGARP, kill parasites in the low μM range and yet have no observable toxicity in human cells at up to 100-fold higher concentration. To ensure we have identified the most promising hits covering the broadest possible chemical space, we propose to use two newly developed, parasite lethal, human monoclonal antibodies (mAb) to screen 50,000 additional compounds from this library. This research will identify novel antimalarials and yield key preliminary data for follow-on, independent grant proposals. In future studies, we will conduct preclinical, and ultimately, IND-enabling studies to develop these compounds as novel therapies for the most important single-agent killer of children on the planet.