A1874 - CAS 2064292-12-0

Psychotic disorders such as schizophrenia are associated with severe psychological suffering for the patient and high healthcare costs. The initial symptoms typically emerge in adolescence and early adulthood. The incidence varies considerably from place to place and among different groups of immigrants. The symptoms, clinical course, and treatment response differs per individual. Genetic vulnerability for psychotic disorders is shared in part with bipolar disorder, and recent molecular genetic findings also indicate an overlap with developmental disorders such as autism. The diagnosis of schizophrenia is associated with demonstrable alterations in brain structure and changes in dopamine neurotransmission, the latter being directly related to hallucinations and delusions. Antipsychotics, which block the dopamine system, are effective for delusions and hallucinations but less so for disabling cognitive and motivational impairments. A better understanding of the biological mechanisms and the psychosocial factors underlying psychotic disorders may contribute to new treatments.

Although the number of proteins effectively targeted for posttranslational degradation by PROTAC has grown steadily, the number of E3 ligases successfully exploited to accomplish this has been limited to the few for which small-molecule ligands have been discovered. Although the E3 ligase MDM2 is bound by the nutlin class of small-molecule ligands, there are few nutlin-based PROTAC. Because a nutlin-based PROTAC should both knockdown its target protein and upregulate the tumor suppressor p53, we examined the ability of such a PROTAC to decrease cancer cell viability. A nutlin-based, BRD4-degrading PROTAC, A1874, was able to degrade its target protein by 98% with nanomolar potency. Given the complementary ability of A1874 to stabilize p53, we discovered that the nutlin-based PROTAC was more effective in inhibiting proliferation of many cancer cell lines with wild-type p53 than was a corresponding VHL-utilizing PROTAC with similar potency and efficacy to degrade BRD4. This is the first report of a PROTAC in which the E3 ligase ligand and targeting warhead combine to exert a synergistic antiproliferative effect. Our study highlights the untapped potential that may be unlocked by expanding the repertoire of E3 ligases that can be recruited by PROTAC. SIGNIFICANCE: These findings present the first BRD4-targeting MDM2-based PROTAC that possesses potent, distinct, and synergistic biological activities associated with both ends of this heterobifunctional molecule.

A1874 is a novel BRD4-degrading proteolysis targeting chimera (PROTAC). In primary colon cancer cells and established HCT116 cells, A1874 potently inhibited cell viability, proliferation, cell cycle progression, as well as cell migration and invasion. The BRD4-degrading PROTAC was able to induce caspase and apoptosis activation in colon cancer cells. Furthermore, A1874-induced degradation of BRD4 protein and downregulated BRD-dependent genes (c-Myc, Bcl-2, and cyclin D1) in colon cancer cells. Significantly, A1874-induced anti-colon cancer cell activity was more potent than the known BRD4 inhibitors (JQ1, CPI203, and I-BET151). In BRD4-knockout colon cancer cells A1874 remained cytotoxic, indicating the existence of BRD4-independent mechanisms. In addition to BRD4 degradation, A1874 cytotoxicity in colon cancer cells was also associated with p53 protein stabilization and reactive oxygen species production. Importantly, the antioxidant N-acetyl-cysteine and the p53 inhibitor pifithrin-α attenuated A1874-induced cell death and apoptosis in colon cancer cells. In vivo, A1874 oral administration potently inhibited colon cancer xenograft growth in severe combined immuno-deficient mice. BRD4 degradation and p53 protein elevation, as well as apoptosis induction and oxidative stress were detected in A1874-treated colon cancer tissues. Together, A1874 inhibits colon cancer cell growth through both BRD4-dependent and -independent mechanisms.