Many targeted therapies against cancer are aimed at inhibiting the enzymatic activity of kinases. Thus far, this approach has undoubtedly yielded significant clinical improvements, but has only rarely achieved cures. Other drugs, which selectively elicit proteasome-dependent degradation of oncoproteins, induce the loss of cancer cell self-renewal and promote cell differentiation and/or apoptosis. In acute promyelocytic leukemia, the cooperative degradation of PML/RARA by arsenic and retinoic acid cures most patients. In this condition and others, drug-induced proteolysis of oncoproteins is feasible and underlies improved clinical outcome. Several transcription factors, nuclear receptors, or fusion proteins driving cancer growth could be candidates for proteolysis-based drug-discovery programs.

Summary: Some cancer therapies may degrade oncoproteins. Loss of the driver oncoprotein is associated with loss of cancer cell self-renewal. Leukemia- or sarcoma-associated fusion proteins are the best candidates for small-molecule screens aimed at initiating oncoprotein degradation. Cancer Discovery; 1(2). 117–27. ©2011 AACR.