Kevin Tan

Major Research ProgrammesPlasmodium falciparum – Exploiting unique features of cell death for the discovery of novel anti-malarialsMalaria is a potentially fatal infectious disease caused by protozoan parasites of the genus Plasmodium. The most virulent species, Plasmodium falciparum, infects approximately 200 million people and claims 0.5 million lives annually. The parasite infects red blood cells (RBC) of all ages, multiplies within them, before rupturing the host cell to release parasite progeny. Despite the importance of malaria, evidenced by overwhelming number of deaths, there are numerous gaps in our knowledge of P. falciparum biology. Our laboratory has developed numerous assays for the characterization of drug-induced programmed cell death (PCD) pathways in P. falciparum. We have shown that a new mode of action of chloroquine and other lysosomotropic drugs is the disruption of the parasite digestive vacuole (DV), resulting in PCD-like features post DV rupture. We observed that DV rupture can occur in vivo and is a physiologically relevant alternative mode of drug-mediated parasite death. Recent studies from our team have implicated a calcium/ calpain pathway that is universally activated upon drug induced DV rupture.Leveraging on newer technologies such as imaging flow cytometry, we have developed a platform for the discovery of novel molecules that perturb calcium homeostasis. This platform has resulted in a collaboration with industry (GSK) with the objective of identifying DV/ calcium disruption molecules among a focused compound library. Screening the MMV Malaria Box and Pathogen Box have also resulted in the identification of potent DV/ calcium disruptors. Together with partners at the Department of Chemistry and Pharmacy, we have developed fluorescent- and chemosensitizer-tagged chloroquine hybrid molecules that have been validated to be excellent reporter molecules and potent chemoreversal drugs respectively. Our research on malaria has implicated the parasite digestive vacuole and calcium metabolism as an attractive and tractable drug target. With the development of an imaging-based platform, a robust and rapid method for the identification and DV/ calcium disruption compounds is available to the scientific community.Blastocystis – Parasite-host interactions and microbiomes to understand pathogenesisOur laboratory has contributed extensively to the current understanding of Blastocystis biology. Our research on this protist focuses on host-pathogen interactions, which aims to clarify its controversial role in intestinal disease. We have shown that the parasite exhibits IgA, IgM and IgG protease activity and induces contact-independent apoptosis, F-actin rearrangement, and barrier function disruption in IEC-6 cells. We have also observed that parasite cysteine proteases mediate IL-8 production in human colonic epithelial T-84 cells in a NF-kB dependent manner. We subsequently report that Blastocystis-induced tight junction compromise is mediated by host cell rho-ROCK pathway. More recent studies shed new light on the interaction between Blastocystis and host antimicrobial peptides.Humans can be infected by numerous genotypically distinct subtypes of Blastocystis. We have contributed to new knowledge that such a complex nature of the parasite can lead to significant inter- and intra-subtype variation in cell biology, drug sensitivity and cytopathic effects including variations in adhesion, host cell death, barrier compromise and host pathology. Our laboratory has established mouse models of Blastocystis infection and colonization that will provide the scientific community with a means to better define the pathogenesis of Blastocystis.Our laboratory is currently investigating the roles of Blastocystis in the context of parasite-microbiota interactions using in vitro and in vivo (infection and colonization mouse models) approaches. Our current data suggests that Blastocystis modulates host microbiota populations either leading to dysbiosis and intestinal disease or to a healthy gut phenotype depending on the Blastocystis subtype used. Our findings suggest that Blastocystis infections are not homogenous and clinical judgement is necessary when positive cases are seen.