AUTHOR=Eschenbrenner Julia , Winsel Sebastian , Hammer Stefanie , Sommer Anette , Mittelstaedt Kevin , Drosch Michael , Klar Ulrich , Sachse Christoph , Hannus Michael , Seidel Monika , Weiss Bertram , Merz Claudia , Siemeister Gerhard , Hoffmann Jens TITLE=Evaluation of Activity and Combination Strategies with the Microtubule-Targeting Drug Sagopilone in Breast Cancer Cell Lines JOURNAL=Frontiers in Oncology VOLUME=1 YEAR=2011 URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2011.00044 DOI=10.3389/fonc.2011.00044 ISSN=2234-943X ABSTRACT=

Sagopilone, a fully synthetic epothilone, is a microtubule-stabilizing agent optimized for high in vitro and in vivo activity against a broad range of tumor models, including those resistant to paclitaxel and other systemic treatments. Sagopilone development is accompanied by translational research studies to evaluate the molecular mode of action, to recognize mechanisms leading to resistance, to identify predictive response biomarkers, and to establish a rationale for combination with different therapies. Here, we profiled sagopilone activity in breast cancer cell lines. To analyze the mechanisms of mitotic arrest and apoptosis and to identify additional targets and biomarkers, an siRNA-based RNAi drug modifier screen interrogating 300 genes was performed in four cancer cell lines. Defects of the spindle assembly checkpoint (SAC) were identified to cause resistance against sagopilone-induced mitotic arrest and apoptosis. Potential biomarkers for resistance could therefore be functional defects like polymorphisms or mutations in the SAC, particularly in the central SAC kinase BUB1B. Moreover, chromosomal heterogeneity and polyploidy are also potential biomarkers of sagopilone resistance since they imply an increased tolerance for aberrant mitosis. RNAi screening further demonstrated that the sagopilone-induced mitotic arrest can be enhanced by concomitant inhibition of mitotic kinesins, thus suggesting a potential combination therapy of sagopilone with a KIF2C (MCAK) kinesin inhibitor. However, the combination of sagopilone and inhibition of the prophase kinesin KIF11 (EG5) is antagonistic, indicating that the kinesin inhibitor has to be highly specific to bring about the required therapeutic benefit.