RESUMEN
Cullin-RING (really intersting new gene) E3 ubiquitin ligases (CRLs) are the largest E3 family and direct numerous protein substrates for proteasomal degradation, thereby impacting a myriad of physiological and pathological processes including cancer. To date, there are no reported small-molecule inhibitors of the catalytic activity of CRLs. Here, we describe high-throughput screening and medicinal chemistry optimization efforts that led to the identification of two compounds, 33-11 and KH-4-43, which inhibit E3 CRL4 and exhibit antitumor potential. These compounds bind to CRL4's core catalytic complex, inhibit CRL4-mediated ubiquitination, and cause stabilization of CRL4's substrate CDT1 in cells. Treatment with 33-11 or KH-4-43 in a panel of 36 tumor cell lines revealed cytotoxicity. The antitumor activity was validated by the ability of the compounds to suppress the growth of human tumor xenografts in mice. Mechanistically, the compounds' cytotoxicity was linked to aberrant accumulation of CDT1 that is known to trigger apoptosis. Moreover, a subset of tumor cells was found to express cullin4 proteins at levels as much as 70-fold lower than those in other tumor lines. The low-cullin4-expressing tumor cells appeared to exhibit increased sensitivity to 33-11/KH-4-43, raising a provocative hypothesis for the role of low E3 abundance as a cancer vulnerability.
Asunto(s)
Antineoplásicos/farmacología , Biomarcadores de Tumor/metabolismo , Inhibidores Enzimáticos/farmacología , Regulación Enzimológica de la Expresión Génica/efectos de los fármacos , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Leucemia Mieloide Aguda/tratamiento farmacológico , Ubiquitina-Proteína Ligasas/antagonistas & inhibidores , Animales , Antineoplásicos/química , Apoptosis , Biomarcadores de Tumor/genética , Proliferación Celular , Inhibidores Enzimáticos/química , Femenino , Humanos , Leucemia Mieloide Aguda/enzimología , Leucemia Mieloide Aguda/patología , Ratones , Ratones Endogámicos BALB C , Ratones Desnudos , Células Tumorales Cultivadas , Ubiquitina/metabolismo , Ubiquitinación , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
Formal syntheses of tetracyclic terpenoids frondosin B and liphagal are described. Both synthetic routes rely on the use of platinum-catalyzed α,ß-unsaturated carbene formation for the key C-C bond forming transformations. The successful route toward frondosin B utilizes a formal (4 + 3) cycloaddition, while the liphagal synthesis features the vinylogous addition of an enol nucleophile as a key step. Both synthetic routes are discussed, revealing insights into structural requirements in the catalytic α,ß-unsaturated carbene reaction manifold.