Abstract A243: SCH727965, a novel potent cyclin dependent kinase inhibitor, inhibits pancreatic tumor growth and Ras-mediated tumorigenic signaling

Abstract

Abstract We have previously shown activation of cyclin-dependent kinase 5 (CDK5), a kinase associated with neuronal migration, in human pancreatic cancer. Abrogation of CDK5 function using a dominant-negative protein, RNA interference, or pharmacological disruption significantly mitigated invasion, migration and anchorage independent growth in vitro, and orthotopic tumor formation and systemic metastases in vivo. CDK5 blockade resulted in inhibition of RalA, a key effector pathway downstream of oncogenic Ras, central to tumorigenesis in pancreatic cancer. Restitution of Ral function rescued the effects of CDK5 inhibition in pancreatic cancer cells. Thus, CDK5 is important for Ras signaling in pancreatic cancer, suggesting that CDK5 inhibition may be an effective therapeutic strategy in pancreatic cancer. To begin to explore the therapeutic potential of CDK5 inhibitors in pancreatic cancer, we have examined the effect of the semi-selective CDK5 inhibitor SCH727965 (Schering-Plough). SCH727965 is a potent inhibitor of CDK1, CDK2, CDK5 and CDK9, with in vitro IC50 values of 3, 1, 1 and 4 nM, respectively. In this study, we evaluated the effect of SCH727965 on pancreatic tumor growth and migration. MTT assay results demonstrated that the IC50 for 2 pancreatic tumor cell lines, MiaPaCa-2 and Panc1.98, was 12nM and 24nM respectively. Migration and anchorage independent growth were significantly more sensitive to SCH727965. Thus, Boyden chamber assay, wound-healing assay and soft agar assays indicated 50% inhibition of migration and soft agar growth inhibition at 5nM, and complete inhibition at 10nM drug concentration — concentrations at which the effects on anchorage dependent growth were relatively minor. Tumors from low passage pancreatic tumor xenografts, or from pancreatic cell line orthotopic xenografts, showed 40–75% reduction of tumor growth after treatment with SCH727965, with significant reduction of metastases. SCH727965 treatment resulted in inhibition of RalA activation. Ral activity could be restored by enforced RalA activation, via expression of Rgl2-CAAX, a constitutively active form of a RalGEF (Ral guanine exchange factor) gene. Our results show that SCH727965 is very effective against pancreatic cancer growth and metastasis. These results also suggest that SCH727965 blocks pancreatic tumor growth, migration and metastasis, at least in part by inhibition of dysregulated Ras signaling, by inhibiting CDK5. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A243.