Treatment of Retinoblastoma 1-Intact Hepatocellular Carcinoma With Cyclin-Dependent Kinase 4/6 Inhibitor Combination Therapy.

BACKGROUND AND AIMS: Synthetic cyclin-dependent kinase (CDK) 4/6 inhibitors exert antitumor effects by forcing RB1 in unphosphorylated status, causing not only cell cycle arrest but also cellular senescence, apoptosis, and increased immunogenicity. These agents currently have an indication in advanced breast cancers and are in clinical trials for many other solid tumors. HCC is one of promising targets of CDK4/6 inhibitors. RB family dysfunction is often associated with the initiation of HCC; however, this is revivable, as RB family members are not frequently mutated or deleted in this malignancy. APPROACH AND RESULTS: Loss of all Rb family members in transformation related protein 53 (Trp53)-/- mouse liver resulted in liver tumor reminiscent of human HCC, and re-expression of RB1 sensitized these tumors to a CDK4/6 inhibitor, palbociclib. Introduction of an unphosphorylatable form of RB1 (RB7LP) into multiple liver tumor cell lines induced effects similar to palbociclib. By screening for compounds that enhance the efficacy of RB7LP, we identified an I kappa B kinase (IKK)ß inhibitor Bay 11-7082. Consistently, RB7LP expression and treatment with palbociclib enhanced IKKα/ß phosphorylation and NF-κB activation. Combination therapy using palbociclib with Bay 11-7082 was significantly more effective in hepatoblastoma and HCC treatment than single administration. Moreover, blockade of IKK-NF-κB or AKT pathway enhanced effects of palbociclib on RB1-intact KRAS Kirsten rat sarcoma viral oncogene homolog mutated lung and colon cancers. CONCLUSIONS: In conclusion, CDK4/6 inhibitors have a potential to treat a wide variety of RB1-intact cancers including HCC when combined with an appropriate kinase inhibitor.

Expression profiles of EphA3 at both the RNA and protein level in the developing mammalian forebrain.

The ephrin/Eph system is well known to regulate various aspects of brain development. In this study, we analyzed the expression profiles of EphA3 at both the RNA and protein level in developing mouse forebrains. Although the EphA3 gene is known to encode two isoforms of the receptors, a full-length transmembrane form, and a short, secretory form, only the full-length isoform was detected in the developing forebrain. We found that, in the early developmental stages, while EphA3 mRNA was expressed in the dorsal thalamus and the cortical intermediate zone (IMZ), the EphA3 protein was detected in the IMZ and the internal capsule, but not in the dorsal thalamus. In the later stages the mRNA was expressed in the most superficial region of the cortical plate, while the protein was expressed in the IMZ. This discrepancy between the mRNA and protein expression patterns might be attributed to the possibility of the protein being transported to the axons to regulate the thalamocortical and corticofugal projection. The results of double-immunostaining for L1 and EphA3 or TAG-1 and EphA3 suggested that EphA3 protein was produced mainly in the thalamocortical axons and only partially in the corticofugal axons. In addition, the EphA3 protein was also detected in various other structures, such as the lateral olfactory tract, anterior commissure, and corpus callosum, suggesting the possibility that EphA3 might regulate the formation of various neuronal networks in the developing brain, including the TC projection and the commissural fibers.