3-Position Biaryl Endochin-like Quinolones with Enhanced Antimalarial Performance.

ELQ-300 is a potent antimalarial drug with activity against blood, liver, and vector stages of the disease. A prodrug, ELQ-331, exhibits reduced crystallinity and improved in vivo efficacy in preclinical testing, and currently, it is in the developmental pipeline for once-a-week dosing for oral prophylaxis against malaria. Because of the high cost of developing a new drug for human use and the high risk of drug failure, it is prudent to have a back-up plan in place. Here we describe ELQ-596, a member of a new subseries of 3-biaryl-ELQs, with enhanced potency in vitro against multidrug-resistant Plasmodium falciparum parasites. ELQ-598, a prodrug of ELQ-596 with diminished crystallinity, is more effective vs murine malaria than its progenitor ELQ-331 by 4- to 10-fold, suggesting that correspondingly lower doses could be used to protect and cure humans of malaria. With a longer bloodstream half-life in mice compared to its progenitor, ELQ-596 highlights a novel series of next-generation ELQs with the potential for once-monthly dosing for protection against malaria infection. Advances in the preparation of 3-biaryl-ELQs are presented along with preliminary results from experiments to explore key structure-activity relationships for drug potency, selectivity, pharmacokinetics, and safety.

Lipophilic Permeability Efficiency Reconciles the Opposing Roles of Lipophilicity in Membrane Permeability and Aqueous Solubility.

As drug discovery moves increasingly toward previously "undruggable" targets such as protein-protein interactions, lead compounds are becoming larger and more lipophilic. Although increasing lipophilicity can improve membrane permeability, it can also incur serious liabilities, including poor water solubility, increased toxicity, and faster metabolic clearance. Here we introduce a new efficiency metric, especially relevant to "beyond rule of 5" molecules, that captures, in a simple, unitless value, these opposing effects of lipophilicity on molecular properties. Lipophilic permeability efficiency (LPE) is defined as log D7.4dec/w - mlipocLogP + bscaffold, where log D7.4dec/w is the experimental decadiene-water distribution coefficient (pH 7.4), cLogP is the calculated octanol-water partition coefficient, and mlipo and bscaffold are scaling factors to standardize LPE values across different cLogP metrics and scaffolds. Using a variety of peptidic and nonpeptidic macrocycle drugs, we show that LPE provides a functional assessment of the efficiency with which a compound achieves passive membrane permeability at a given lipophilicity.