Effective process for screening melanin binding affinity of small molecule drugs and new drug candidates

Melanin binding of small molecule drugs can lead to targeted disposition to the pigmented tissues and prolonged pharmacological responses in the eye. Melanin binding of drugs in vitro correlates with in vivo binding, but current workflows for binding affinity require multiple slow steps, and analytical method development, and/or they may result in high data variability. We developed tangential flow filtration-based methodology to produce size-specific fractions of water-soluble melanin nanoparticles (MNPs), reducing production time from 2-3 days to just a few hours and yielding MNPs with enhanced fluorescence signal. Improved MNPs enabled modifications to a previously published microscale thermophoresis-based melanin binding protocol, shifting analytical focus toward thermophoretic behavior, reducing data variability, and improving reproducibility. The process was tested with nine compounds with varying melanin binding affinities, and the results were consistent with literature, confirming the ability of the method to differentiate compounds based on melanin binding. Fast and reliable workflow will be useful in screening binding affinity for therapeutics and new drug candidates to melanin thereby facilitating ocular drug discovery and construction of predictive pharmacokinetic simulation models.