Introduction and Background of the Project

1.Introduction

Malaria is a mosquito-borne, life-threating infectious disease caused by Plasmodium protozoa and an estimated 608,000 people, mainly consisted of children in African countries, died in 2022,. The current standard care for the treatment of malaria typically involves combination therapy with artemisinins. However, there is evidence of emerging resistance to both artemisinins and its partner drugs in some countries such as Cambodia, Thailand, Myanmar and Vietnam. This highlights the urgent need for new classes of compounds with novel mechanisms-of-action (MoA) to treat resistant strains of malaria parasites and support the malaria eradication strategy.

In this project, we aim to investigate back-up candidate of an antimalarial compound with a well-characterized and novel MoA. Glycosylphosphatidylinositol (GPI) is a common moiety in all eukaryotes which has a role in anchoring many proteins to the cell surface. Gwt1p, one of the essential enzymes in the GPI biosynthesis pathway, was identified by Eisai as a novel target for an antifungal drug. After conducting discovery research, Eisai discovered E1210, an antifungal drug clinical candidate, and found that the GWT1 gene encoding Gwt1p enzyme is highly conserved among eukaryotes, including Plasmodium protozoa, the etiological pathogens for malaria. Eisai has screened an internal compound library targeting fungal Gwt1p and found a hit compound with inhibitory activities on plasmodial Gwt1p. This compound showed anti-Plasmodium activities in vitro and in vivo and was subjected to chemical modification in a GHIT Hit-to-Lead Platform and lead optimization in a Product Development Platform. MMV and Eisai created the first candidate compound with improved anti-Plasmodium activity and the long half-life required for single dose malaria treatment. In this project, we plan to investigate a new Gwt1p-inhbitor as the back-up candidate and start preclinical studies.

2.Project objective

The objective of this proposal is to investigate the new Gwt1p-inhibitor and find a back-up candidate with improved activity and safety profile. To deliver this goal, we will focus on the following specific objectives:

(1)  Two chemical series will be chemically optimized and a frontrunner compound will be selected from each series, as precandidates.

(2)  Two precandidates will be evaluated in multiple assays and the most favorable compound will be selected as a Late Lead.

(3)  The synthetic route of Late Lead will be optimized and GLP manufacturing will be conducted.

(4)  Non-rodent DRF study will be conducted and candidate selection will be scheduled following a successful outcome to this study.

3.Project design

In this project, chemical modification of two lead series will be conducted to improve anti-Plasmodium activity and safety profile while securing a long-half-life. Synthesized new compounds will be shipped to Eisai’s Tsukuba Research Laboratories in Japan. They will be tested according to the defined screening cascade starting from the primary screening of anti-Plasmodium activity and cytotoxicity. Compounds which show good anti-Plasmodium activity and safety margin will be tested for solubility at neutral pH and stability against human and murine liver microsomes assays. Based on these results and other profiling, the most promising compound in each series will be selected as pre-candidate and will be further evaluated. Two precandidates will be evaluated in the in vitro/vivo anti-Plasmodium assay, a rat dose range finding (DRF) study, safety profiling, human dose prediction, salt selection, resistant risk assessment and parasite life-cycle assays. The most favorable compound will be selected as a Late Lead. The synthetic route for the Late Lead will be optimized and GLP manufacturing will be conducted. Non-rodent DRF study using the manufactured GLP material will also be conducted. The final goal of this project is the candidate selection in both Eisai and MMV and planned for September 2026. 

How can your partnership (project) address global health challenges?

Malaria is still one of the most life-threating diseases and many children still die, especially in sub-Saharan African countries. In these countries, children catch malaria time and time again, due to a low immunity to malaria. This project is proposed to contribute to the eradication of malaria based on its novel and unique MoA, as described below. To control and eliminate infectious diseases, and particularly for eradication, vector control, prevention of infection by vaccines and treatment with drug are all equally important. For malaria, each of them is under evaluation. Antimalarial drugs have shown memorable improvements in last century, but this great footprint is at risk of being washed away by the appearance of resistant parasites. This project is thought to fulfill several of the target profiles set for the next generation of antimalarial drugs targeting malaria eradication. Our novel MoA is highly expected to lead to new antimalarial drugs with novel characteristics, which have never been seen before, and therefore to save many children’s lives in the future.

What sort of innovation are you bringing in your project?

The most promising advantage of this project is a novel MoA with an identified target protein. The MoA is inhibition of GPI-biosynthesis and this is a completely novel concept in the treatment of malaria. Furthermore, the target protein Gwt1p, an acyltransferase essential in GPI-biosynthesis, was discovered in Eisai and no other discovery activities targeting this enzyme are reported. Based on its novel MoA, Gwt1p-inhibitors are expected to act on Plasmodium strains resistant to existing antimalarials, including artemisinins. The existing data suggests that the character of Gwt1p-inhibitors is consistent with TCP1 for malaria treatment and also the target candidate profile for prophylaxis, set by MMV. As a second advantage, inhibition of GPI-biosynthesis is expected to lead to anti-Plasmodium activities against multiple parasite life stages, because many kinds of stage-specific GPI-anchored proteins are expressed in each life stage of the malaria parasite. For example, in the sexual stages of P. falciparum, a GPI-anchored protein named Pfs48/45 is expressed in male gametocytes and this protein is essential for sexual mating. These expected efficacies would be consistent with other TCP’s, such as transmission blocking (TCP5) or chemoprotection (TCP4). As a third advantage, in addition to these direct anti-Plasmodium activities, inhibition of Gwt1p is expected to show additional preferable characteristics such as activation of the immune system of the host or a decrease in the inflammatory response caused by malaria infection.

Role and Responsibility of Each Partner

Eisai will be responsible for primary screening with anti-Plasmodium and cytotoxicity assays, and medicinal chemistry to synthesize new compounds. Compounds with improved activity will be further screened at Eisai’s laboratory for physical chemistry and DMPK characters. Toward the candidate selection, Eisai will conduct human dose prediction, safety assessment including rodent/non-rodent DRF studies. Eisai will lead CMC activities including salt screen, process development and preparation of intermediates for GLP drug substances.

MMV is responsible for the compound characterization at malaria expert laboratories in their network laboratories and input scientific insight for the discovery research with broad expertise.

Others (including references if necessary)

1. https://www.who.int/teams/global-malaria-programme/reports/world-malaria-report-2023

2. Yeung S, Socheat D, Moorthy VS et al. Artemisinin resistance on the Thai-Cambodian border. Lancet 2009; 374: 1418-9.

3. Hawkes M, Conroy AL, Kain KC. Spread of artemisinin resistance in malaria. The New England journal of medicine 2014; 371: 1944-5.

4. Okamoto M, Yoko-o T, Umemura M et al. Glycosylphosphatidylinositol-anchored proteins are required for the transport of detergent-resistant microdomain-associated membrane proteins Tat2p and Fur4p. The Journal of biological chemistry 2006; 281: 4013-23.

5. Sagane K, Umemura M, Ogawa-Mitsuhashi K et al. Analysis of membrane topology and identification of essential residues for the yeast endoplasmic reticulum inositol acyltransferase Gwt1p. The Journal of biological chemistry 2011; 286: 14649-58.

6. Tsukahara K, Hata K, Nakamoto K et al. Medicinal genetics approach towards identifying the molecular target of a novel inhibitor of fungal cell wall assembly. Mol Microbiol 2003; 48: 1029-42.

7. Umemura M, Okamoto M, Nakayama K et al. GWT1 gene is required for inositol acylation of glycosylphosphatidylinositol anchors in yeast. The Journal of biological chemistry 2003; 278: 23639-47.

8. Miyazaki M, Horii T, Hata K et al. In vitro activity of E1210, a novel antifungal, against clinically important yeasts and molds. Antimicrobial agents and chemotherapy 2011; 55: 4652-8.

9. Burrows et al. New Developments in Anti-Malarial Target Candidate and Product Profiles. Malar J 2017; 16:26