Development of macrocycle-based ligands for challenging disease targets

Macrocycles are a promising class of therapeutics because they can bind targets considered undruggable with small molecules. A focused KRAS macrocycle library designed and synthesized to make smaller and potent KRAS (G12D) inhibitors using the salt bridge, essential to ensure selectivity and to induce allosteric pocket (switch-II pocket (S-IIP)), has been screened against KRAS. The library screening against KRAS with TR-FRET displacement assay gave some trouble due to the positive charge in macrocycle which led to a decrease in Cy5 intensity; at the same time, it has been observed that for neutral or negative charged macrocycles, the effect is scarce. So, the positively charged macrocycle library has been screened against another challenging target: KLK5, a trypsin-like serine protease involved in the cleavage of cell adhesion and skin-shedding. This study led to finding some suitable binders with a good IC50. This is the beginning of a new path for the development of binders for another challenging target.