Abstract 3091: Targeting low molecular weight (LMW) cyclin E-Cdk2 pathway for the prevention of breast cancer

Abstract

Abstract Our laboratory was first to discover that full length cyclin E is proteolytically cleaved into low-molecular weight isoforms (LMW-E) specifically in tumor cells. The LMW-E isoforms are hyperactive and over-expressed in 70% of all triple negative breast cancer (TNBC) compared to only 30% of non-TNBC patients. Overexpression of LMW-E in transgenic mice induces mammary tumors similar to the basal subtype of breast cancer, which accounts for 70% of all human TNBCs. We have reported that Cdk2 deficient mice were completely resistant to LMW-cyclin E mediated mammary tumors. In this study, we have interrogated the ability of roscovitine in preventing the development of triple negative mammary tumors in the MMTV-LMW-E; p53+/- mouse model. Initially, a group of mice were treated from age 3 months with vehicle (DMSO/PBS, 40:60v/v, N = 8) or roscovitine (100 mg/kg, N = 8) once every 4 and 5 days alternatively by intraperitoneal injection and were followed up for mammary tumor development. Mice did not show any signs of toxicity. In this schedule of treatment, we did not find any difference in time to tumor formation or survival between the 2 groups (8.3 vs 7.9 months, P = 0.70, and 8.9 vs 8.4 months, P = 0.98, respectively). However, we found a 2.8-fold increase in tumor doubling time in the roscovitine-treated group indicating that roscovitine treatment decreased tumor growth (12.1+/-4.4 vs 4.4+/-0.9 days, P<0.05). This was due to a decreased proliferation as measured by BrdU immunohistochemistry (IHC) (13.6+/-0.9% vs 30.0 +/- 7.7%, P<0.05) and an increased apoptotic index as measured by cleaved caspase 3 IHC (49.6+/-9.4 CC3+ cells/x40 field vs 25.9 +/- 9.9, P<0.05). A second group of mice were treated at age 3 months with the same schedule but were killed after 2 months of treatment and the mammary glands were collected to investigate the effects of drug treatment on normal and premalignant mammary cells. The BrdU staining showed that 2 months of roscovitine treatment caused a 3-fold decrease in the number of BrdU positive cells (5.4+/-1.5% vs 14.6+/-3.8%, P<0.05) but did not completely block cyclin E-induced proliferation. This result may explain why the roscovitine-treated mice developed tumor with similar kinetics as the control group. Our ongoing work is to use gene expression profiling to determine the RNA changes induced by roscovitine for the discovery of potential biomarkers. The results from the first trial is suggestive that the mice need to be treated on a continued schedule to ensure that proliferation of the cyclin E overexpressing mammary tissue is completely inhibited. To this end, we are now treating the mice twice a day, 7 days on, 21 days off. We predict that the new treatment schedule will be more efficacious in inhibiting tumor formation. These preliminary data could support the development of a clinical trial testing cyclin-dependent kinase inhibitors for the prevention of human triple negative breast cancer especially those with LMW-E overexpression. Citation Format: Said Akli, Dong Yang, Tuyen N. Bui, Khandan Keyomarsi. Targeting low molecular weight (LMW) cyclin E-Cdk2 pathway for the prevention of breast 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 3091. doi:10.1158/1538-7445.AM2015-3091