Evaluation of ON 01910.Na, a novel modulator of polo-like kinase 1 (Plk1) pathway, and development of a cyclin-B1-based predictive assay in pancreatic cancer

Abstract

3569 Background: Plk1 is a key mitotic regulator of the transition through the G2/M checkpoint in the cell cycle. This work aimed to evaluate the activity of ON 01910.Na, a Plk1 pathway modulator, in in vitro and in vivo models of pancreatic cancer (PaCa) and to discover biomarkers predictive of efficacy. Methods: ON 01910.Na was tested in 12 PaCa cell lines. Studies assessing Plk1 related markers were conducted to identify biomarkers. For validation a live collection of PaCa xenografts from fresh tumor samples obtained at the time of surgical resection was used (PancXenoBank). The ex vivo assay was based on fine-needle aspirate (FNA) biopsies. Results: ON 01910.Na showed equal activity to gemcitabine against PaCa cell lines. The activity of ON 01910.Na correlated with suppression of two downstream mediators of PLK1, CDC25C and cyclin B1 (by mRNA and protein). ON 01910.Na was tested in xenografts from representative pancreatic cell lines. The selected markers were evaluated in an ex vivo assay, using intra-tumor pharmacokinetics to select the dose of the assay. Cyclin B1 mRNA evaluation yielded the most optimal combination of accuracy and reproducibility. Knockdown of cyclin B1 by siRNA had no effect per se or in the response of the resistant MiaPaca2 to either of the drugs. We next used the ex vivo assay to profile ten patient-derived cases from the PancXenoBank. Two cases were catalogued as potential responders. From each of these ten cases, a group of mice bearing at least 20 tumors received vehicle or ON 01910.Na for 28 days. There was a correlation between the ex vivo cyclin B1 assay and the sensitivity to the tested agent, as the 2 cases prospectively identified as sensitive met pre-specified criteria for response. Of the 8 tumors predicted to be resistant, only one was sensitive. In IHC testing cases showing ex vivo cyclin B1 down-regulation had also decreases in cyclin B1 protein, and there was a correlation between activity and IHC changes in cyclin B1. Conclusions: ON 01910.Na demonstrated significant activity in a preclinical model of PaCa. A rationally designed ex vivo cyclin B1-based assay not only identified cases sensitive to ON 01910.Na, but also replicated the pharmacodynamic events occurring after in vivo exposure. No significant financial relationships to disclose.