Abstract 3088: Inhibition of CDK5 in colorectal cancer
Authors: Robb Caroline M. 
Published: August 2015

Abstract
Purpose: To investigate the role of CDK5 in Colorectal Cancer.
Background: Colorectal Cancer (CRC) is the fourth most commonly diagnosed form of cancer and is the second leading cause of cancer related deaths in the United States. Most CRC deaths are due to metastatic disease, making the identification of metastatic targets important for the development of therapeutics.
Materials and Methods: Gene expression analysis was performed comparing expression in primary and metastatic tumors from the orthotopic model. Primary colon and corresponding liver metastatic tumors from an orthotopic model and human CRC tissue were analyzed using immunohistochemistry (IHC) to determine the expression of CDK5. Primary antibodies were from Abcam were used at a dilution of 1:300. The negative control contained no primary antibody. Tissue samples were imaged at 40x magnification. Changes in CDK5 expression and activity were analyzed using 150nM CDK5 siRNA. A panel of potential inhibitors was screened for efficacy against CDK5 activity. CDK5 inhibitor studies were further carried out using a small molecule inhibitor, 20-223 and treated at 100nm - 1uM. GEO-GFP CRC cells were injected into athymic nude mice and xenografts were grown to 100mm3. Injections of either DMSO or 8mg/kg of 20-223 were then given S.C daily for the first 7 days then every other day for the remaining two weeks.
Results: Gene expression analysis showed CDK5 expression is upregulated in metastatic tumor compared to primary tumor from the orthotopic model. Additionally, IHC analysis revealed higher expression of CDK5 in metastatic tumors compared to primary tumors in both orthotopic model and human tissues. Knockdown or inhibiting CDK5 decreased CDK5 activity as determined by a decrease in phosphorylation at S732 of FAK, a site specific to CDK5 phosphorylation. Knockdown or inhibition of CDK5 using 20-223 also led to a decrease in expression of anti-apoptotic mediators. Furthermore, treatment with 20-223 reduced cell proliferation and migration, increased cell death, and arrested cells in the G2M transition in vitro. 20-223 halted tumor progression and tumor weight in vivo.
Conclusions: CRC is the second leading cause of cancer related deaths mainly due to the metastatic disease. There are currently no effective pharmacologic treatments for CRC metastases. We have shown that CDK5 is upregulated and overexpressed in metastatic tumors when compared to primary colon tumors. Inhibition of CDK5 either by knockdown or through the use of small molecule inhibitors decreased downstream phosphorylation of specific targets and reduced expression of anti-apoptotic mediators. Together, these data suggest that CDK5 might play a role in metastatic CRC and we’ve identified a potential inhibitor, 20-223 which targets CDK5 in CRC. Future work will include the establishment of a CDK5 knockdown inducible system to verify pharmacological findings and to study the role of CDK5 in establishment and maintenance of metastasis.
Citation Format: Caroline M. Robb. Inhibition of CDK5 in colorectal cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3088. doi:10.1158/1538-7445.AM2015-3088