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  • Title: 212Pb-radioimmunotherapy potentiates paclitaxel-induced cell killing efficacy by perturbing the mitotic spindle checkpoint.
    Author: Yong KJ, Milenic DE, Baidoo KE, Brechbiel MW.
    Journal: Br J Cancer; 2013 May 28; 108(10):2013-20. PubMed ID: 23632482.
    Abstract:
    BACKGROUND: Paclitaxel has recently been reported by this laboratory to potentiate the high-LET radiation therapeutic (212)Pb-TCMC-trastuzumab, which targets HER2. To elucidate mechanisms associated with this therapy, targeted α-particle radiation therapeutic (212)Pb-TCMC-trastuzumab together with paclitaxel was investigated for the treatment of disseminated peritoneal cancers. METHODS: Mice bearing human colon cancer LS-174T intraperitoneal xenografts were pre-treated with paclitaxel, followed by treatment with (212)Pb-TCMC-trastuzumab and compared with groups treated with paclitaxel alone, (212)Pb-TCMC-HuIgG, (212)Pb-TCMC-trastuzumab and (212)Pb-TCMC-HuIgG after paclitaxel pre-treatment. RESULTS: (212)Pb-TCMC-trastuzumab with paclitaxel given 24 h earlier induced increased mitotic catastrophe and apoptosis. The combined modality of paclitaxel and (212)Pb-TCMC-trastuzumab markedly reduced DNA content in the S-phase of the cell cycle with a concomitant increase observed in the G2/M-phase. This treatment regimen also diminished phosphorylation of histone H3, accompanied by an increase in multi-micronuclei, or mitotic catastrophe in nuclear profiles and positively stained γH2AX foci. The data suggests, possible effects on the mitotic spindle checkpoint by the paclitaxel and (212)Pb-TCMC-trastuzumab treatment. Consistent with this hypothesis, (212)Pb-TCMC-trastuzumab treatment in response to paclitaxel reduced expression and phosphorylation of BubR1, which is likely attributable to disruption of a functional Aurora B, leading to impairment of the mitotic spindle checkpoint. In addition, the reduction of BubR1 expression may be mediated by the association of a repressive transcription factor, E2F4, on the promoter region of BubR1 gene. CONCLUSION: These findings suggest that the sensitisation to therapy of (212)Pb-TCMC-trastuzumab by paclitaxel may be associated with perturbation of the mitotic spindle checkpoint, leading to increased mitotic catastrophe and cell death.
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