| The taxanes are microtubule-targeting chemotherapeutics that form the basis of most chemotherapy regimens. Despite their success, acquisition of taxane resistance and disease progression hampers their clinical efficacy. The molecular mechanisms that drive clinical taxane resistance remain poorly understood, and biomarkers that identify patient sub-populations likely to respond to taxane chemotherapy have yet to be validated. Recent clinical data correlate low BRCA1 transcript or protein levels with poor taxane response in non-small cell lung cancer (NSCLC). However, no literature exists that links BRCA1 with microtubule biology, thus, we set out to determine the role of BRCA1 in taxane resistance. We generated a BRCA1 loss-of-function model in A549 NSCLC cells. BRCA1-knockdown made cells taxane-resistant phenocopying the clinical data. We describe novel roles for BRCA1 in regulating microtubule dynamics and biology. Also, BRCA1-knockdown resulted in microtubules less sensitive to paclitaxel treatment and paclitaxel-induced microtubule-mediated apoptotic signaling. This work implicates BRCA1 in microtubule biology and suggests the potential use of BRCA1 as a biomarker for taxane response. In the second part of this work, we describe the development and clinical application of a novel microfluidic device designed to capture circulating tumor cells (CTCs) from the peripheral blood of cancer patients, in order to discover new biomarkers for clinical taxane activity. Live patient CTCs are captured as a real-time "liquid biopsy" and assayed for functional response to taxane treatment. CTC-based bioassays, including a novel Drug-Target Engagement assay and RNA-Sequencing, have been developed to extract information from this tumor tissue source and assess functional CTC response to drug treatment. This suite of CTC bioassays are being tested in an ongoing phase II clinical trial, TAXYNERGY. In this prospective trial, CTC response will be correlated with clinical taxane response of 100 chemo-naive patients. Each patient will be longitudinally followed with 17 CTC-based assays before, during and after taxane chemotherapy. RNA-sequencing of same patient CTCs captured pre-and post-development of taxane resistance has the potential to identify new, unappreciated pathways that are responsible for clinical taxane resistance. Thus, the TAXYNERGY clinical trial has the potential to discover biomarkers predictive of clinical taxane response using a personalized medicine approach. |
