Definition

An orally bioavailable selective inhibitor of the ubiquitin specific protease 1 (USP1), with apoptosis-inducing, tumor-sensitizing and antineoplastic activities. Upon oral administration, USP1 inhibitor KSQ-4279 specifically binds to and inhibits the activity of USP1, thereby blocking USP1-mediated deubiquitylating activity. This blocks the ubiquitin proteasome degradation pathway, prevents the degradation of defective proteins, and leads to an accumulation of mono-ubiquinated substrates. This induces the unfolded protein response (UPR). This may induce cell cycle arrest, reduce the expression of certain anti-apoptotic proteins, induce tumor cell apoptosis, inhibit tumor cell growth, and may sensitize tumor cells to DNA-targeting chemotherapeutics. USP1, a deubiquitinating enzyme overexpressed in various tumor cell types, plays a key role in the correct folding and deubiquitination of proteins and facilitates DNA repair via its role regulating the Fanconi anemia complex and translesion synthesis.