Solubility at the molecular level: development of a critical aggregation concentration (CAC) assay for estimating...

In drug discovery research the formation of soluble compound aggregates is a major cause of false positives, false negatives, and distorted values in High-Throughput Screening assays that measure either binding or functional activity. These aggregation-based artifacts lead to serious distortions in the SAR which are critical to successful lead optimization. In this work we introduce a new approach by which the "critical aggregation concentration" (CAC) is determined, thereby overcoming limitations inherent to traditional solubility methods and enabling estimation of small molecule monomer solubility.

The theoretical and experimental basis of a new confocal Static Light Scattering plate reader assay is presented.

Tests conducted with model systems, commercial compounds, and Abbott library compounds show that the CAC assay can measure aqueous monomer solubilities reproducibly and reliably, achieving a sensitivity of ~0.2 μm, which is an improvement of approximately two orders of magnitude over nephelometry.

Determination of compound monomer solubilities in a screening format is possible for the first time with the cSLS-CAC methodology. It is currently in routine use in Abbott's drug discovery program, and has enabled identification of many compound induced artifacts in binding or activity assays that are missed by traditional kinetic solubility measurements.