Shaping Antimalarials: A Geometry-First Approach to PfCLK3 Covalent Inhibitors

Area of Science:

• Medicinal Chemistry
• Parasitology
• Drug Discovery

Background:

• Antimalarial drug resistance in Plasmodium falciparum necessitates novel therapeutic strategies.
• Plasmodium falciparum Clk3 (PfCLK3) is a validated target for antimalarial drug development.
• Covalent kinase inhibitors (CKIs) offer durable inhibition but often prioritize warhead reactivity over optimal geometry.

Purpose of the Study:

• To develop optimized covalent inhibitors of PfCLK3 using a geometry-first approach.
• To investigate the impact of warhead and linker geometry on covalent bond formation with PfCLK3.
• To identify novel CKI drug candidates with potent antimalarial activity and favorable drug-like properties.

Main Methods:

• Systematic structural modification of a chloroacetamide-based covalent inhibitor scaffold.
• Evaluation of covalent engagement with PfCLK3 Cys368 residue.
• Assessment of antiparasitic activity and metabolic stability of optimized compounds.

Main Results:

• A geometry-first approach successfully optimized covalent PfCLK3 inhibitors.
• Maintaining the α-reactive geometry allowed covalent engagement with less reactive electrophiles.
• The methyl sulfamate analogue SB5-171 demonstrated potent antimalarial activity (EC50 = 104 nM) and enhanced metabolic stability (t1/2 = 35 min).

Conclusions:

• Geometric optimization is a viable strategy for designing selective and effective covalent kinase inhibitors.
• This approach decouples covalent engagement from high intrinsic reactivity, leading to improved drug-like properties.
• The developed compounds provide a rational framework for future antimalarial CKI drug discovery.