Therapeutic Targeting of Nuclear γ‐tubulin in RB1‐negative Tumors

Reduced protein levels of nuclear γ‐tubulin increase the transcriptional activities of E2Fs and raise the protein levels of Retinoblastoma (RB1) and in tumor cells lacking RB1 expression, decreased γ‐tubulin protein levels induce cell death in an E2 promoter‐binding factors (E2F) dependent manner. Consequently, impairment of the nuclear activity of γ‐tubulin may be used as a new strategy for RB1 deficient targeted chemotherapy. Here, we searched for compounds that interfere with the nuclear activity of γ‐tubulin including known α‐ and β‐tubulin inhibitors. However, neither the microtubule‐destabilizing colcemid nor the microtubule‐stabilizing Paclitaxel affected E2Fs activities in a Luciferase assay. In contrast, we found that MsP increased E2Fs' activities, but it also impaired astral microtubule outgrowth. Among tested MsP analogues, we found that Gz increased E2Fs' activities without impairing microtubule dynamics. Gz's cytotoxic effect on tumor cells was attenuated by either an increase expression of RB1 or γ‐tubulin, and potentiated by reduced protein levels of either RB1 or γ‐tubulin. In vivo, tumor progression was diminished by Gz in a RB1 dependent manner. Our results demonstrate that drugs developed to specifically inhibit the nuclear activity of γ‐tubulin have the potential to single out tumor cells and may aid the design of safer and more efficient chemotherapeutic.