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MINI 38 - Biology and Prognosis (ID 167)
- Event: WCLC 2015
- Type: Mini Oral
- Track: Thymoma, Mesothelioma and Other Thoracic Malignancies
- Presentations: 1
MINI38.04 - BRCA1/OCT1/MAD2L1 Axis Regulates a Bifurcating Apoptotic Pathway Induced by Vinorelbine in Mesothelioma (ID 2675)
18:30 - 20:00 | Author(s): L. O'Regan
There is currently no licenced second line therapy for mesothelioma patients upon relapse after pemetrexed cisplatin. The vinca alkaloid spindle poison, vinorelbine, exhibits useful activity in mesothelioma, warranting evaluation in a new UK randomised clinical trial, VIM. However the molecular determinants of efficacy are unclear. We have reported that BRCA1 is an essential regulator of vinorelbine-induced apoptosis, and loss of detectable BRCA1 occurs in 39% of mesotheliomas. However the mechanisms governing BRCA1 dependent lethality has been lacking. We have utilized a functional genetic approach to uncover critical genes required for vinorelbine efficacy.
Apoptosis was analysed by PARP cleavage and caspase 3/7 activity assay. Focused RNAi targeting Caspase 8, BAX and BAK was conducted to delineate critical death activators. Mouse embryonic fibroblasts (MEFs) wild type (WT) or double knockout (DKO) for BAX/BAK cells were also used. MAD2L1 expression was studied by western blot and qRT-PCR. Tumour explants were derived from 10 MPM patients.
Mitochondrial and caspase-8 dependent apoptosis pathways were shown by triple knockdown of BAX, BAK and Caspase 8 to be required to rescue completely from vinorelbine-induced apoptosis. Loss of BRCA1 recapitulated this apoptosis block and was associated with loss of Oct1 dependent MAD2L1 associated transcriptional upregulation. RNAi mediated silencing of MAD2L12 phenocopied BRCA1 loss. In cells selected for resistance to vinorelbine, MAD2L1 failed to upregulate, secondly to constitutive downregulation of BRCA1. Using mesothelioma explants derived at extrapleural decortication, exhibited either marked resistance or sensitivity to vinorelbine induced apoptosis; correlation with regulation of BRCA1/Oct1/MAD2L is ongoing and will be presented.
BRCA1 functions through an Oct1/MAD2L1-dependent activation of both mitochondria dependent and independent pathways to induce apoptosis. This implicates a requirement for a functional spindle assembly checkpoint, with implications for expanding the biomarker repertoire governing vinorelbine efficacy in mesothelioma
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