Identifying the modes and mechanisms of action of transmission-blocking antimalarials against Plasmodium falciparum
File(s)
Author(s)
Yahiya, Sabrina
Type
Thesis
Abstract
Phenotypic drug screening has transformed the antimalarial development pipeline,
facilitating the discovery of compounds targeting unexplored parasite proteins
at a drastically accelerated rate. Breaking the cycle of malaria transmission is
crucial to eradication and centres around inhibition of the sexual stage gametocytes
and gametes. Transmissible sexual stages represent a population bottleneck of the
Plasmodium life-cycle which face little selective pressure and are hence a desirable
target of drug intervention. Recently discovered in a phenotypic screen, the N-((4-
hydroxychroman-4-yl)methyl)-sulphonamide (N-4HCS) compounds potently inhibit
P. falciparum male gamete formation (microgametogenesis) in the mosquito. By
combining study of the remarkable Plasmodium gametocyte cellular biology with
medicinal chemistry and chemical proteomics, here we performed a detailed analysis
of N-4HCS compound activity.
Adhering to a traditional drug developmental pipeline, we first performed N-
4HCS hit-to-lead development and yielded compounds with activity in the nanomolar
concentration range and favourable safety profiles. Furthermore, an N-4HCS
photoaffinity probe was utilised in a proteome-wide photoaffinity labelling study,
identifying the P. falciparum sexual stage-specific protein, Pfs16, as the compound
target. Notably, the Cellular Thermal Shift Assay confirmed label-free specificity
of N-4HCS compounds to Pfs16. Flow cytometry and phase-contrast, widefield-
fluorescence and electron microscopy revealed compounds exclusively inhibited microgametogenesis, with a cellular phenotype consistent with published reports on the
targeted gene disruption of Pfs16. We therefore present the 16kDa parasitophorous
vacuole membrane protein, Pfs16, as a desirable antimalarial target and the N-4HCS
compounds as potent candidates for future development. Additionally, a live-cell fluorescence microscopy workflow was devised to enable visualisation of microgametogenesis from the onset of activation through to exflagellation. Crucially, our imaging approach was applicable to drug discovery and is accessible to the malaria
research community, thereby facilitating future study of transmission-blocking drug
candidates. This thesis hence addressed the urgent requirement for novel antimalarial
interventions, developing and aiding future discovery of transmission-blocking
drugs.
facilitating the discovery of compounds targeting unexplored parasite proteins
at a drastically accelerated rate. Breaking the cycle of malaria transmission is
crucial to eradication and centres around inhibition of the sexual stage gametocytes
and gametes. Transmissible sexual stages represent a population bottleneck of the
Plasmodium life-cycle which face little selective pressure and are hence a desirable
target of drug intervention. Recently discovered in a phenotypic screen, the N-((4-
hydroxychroman-4-yl)methyl)-sulphonamide (N-4HCS) compounds potently inhibit
P. falciparum male gamete formation (microgametogenesis) in the mosquito. By
combining study of the remarkable Plasmodium gametocyte cellular biology with
medicinal chemistry and chemical proteomics, here we performed a detailed analysis
of N-4HCS compound activity.
Adhering to a traditional drug developmental pipeline, we first performed N-
4HCS hit-to-lead development and yielded compounds with activity in the nanomolar
concentration range and favourable safety profiles. Furthermore, an N-4HCS
photoaffinity probe was utilised in a proteome-wide photoaffinity labelling study,
identifying the P. falciparum sexual stage-specific protein, Pfs16, as the compound
target. Notably, the Cellular Thermal Shift Assay confirmed label-free specificity
of N-4HCS compounds to Pfs16. Flow cytometry and phase-contrast, widefield-
fluorescence and electron microscopy revealed compounds exclusively inhibited microgametogenesis, with a cellular phenotype consistent with published reports on the
targeted gene disruption of Pfs16. We therefore present the 16kDa parasitophorous
vacuole membrane protein, Pfs16, as a desirable antimalarial target and the N-4HCS
compounds as potent candidates for future development. Additionally, a live-cell fluorescence microscopy workflow was devised to enable visualisation of microgametogenesis from the onset of activation through to exflagellation. Crucially, our imaging approach was applicable to drug discovery and is accessible to the malaria
research community, thereby facilitating future study of transmission-blocking drug
candidates. This thesis hence addressed the urgent requirement for novel antimalarial
interventions, developing and aiding future discovery of transmission-blocking
drugs.
Version
Open Access
Date Issued
2021-10
Date Awarded
2022-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Baum, Jake
Fuchter, Matthew
Delves, Michael
Sponsor
Engineering and Physical Sciences Research Council
Grant Number
EP/R512540/1
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)