J Cancer 2011; 2:36-51. doi:10.7150/jca.2.36

Research Paper

Effects of an Indolocarbazole-Derived CDK4 Inhibitor on Breast Cancer Cells

Yuan Sun1,4, Ying-xia Li2✉, Hai-jun Wu2, Si-hung Wu1, Y. Alan Wang3, Dian-zhong Luo4, D. Joshua Liao1✉

1. Hormel Institute, University of Minnesota, Austin, MN 55912, USA
2. School of Pharmacy, Fudan University, Pudong, Shanghai, 201203, P.R. China
3. Discovery Center for Applied Cancer Science, Dana-Farber Cancer Institute, Harvard University, Boston, MA 02115, USA
4. Department of Pathology, Guanxi Medical University, Nanning, Guangxi, 530021, P.R.China

Abstract

Introduction: Cyclin D1 (D1) binds to cyclin-dependent kinases (CDK) 4 or 6 to form a holoenzyme that phosphorylates the Rb protein to promote cell cycle progression from G1 to S phase. Therefore, targeting CDK4/6 may be a good strategy for chemotherapy of cancer. We performed a proof-of-principle study to determine the effect of Naphtho [2, 1-α] pyrrolo [3, 4-c] carbazole-5, 7 (6H, 12H)-dione (NPCD), a novel CDK4 inhibitor, on breast cancer cell lines.

Methods: NPCD was synthesized and purified to over 99% purity verified by HPLC. MCF7, MB231, MCF15, T47D and GI101Ap human breast cancer cells were analyzed for the efficacy of NPCD with MTT and clonogenic assays, with FACS and staining for ethidium bromide and acridine orange for cell death and cell cycle profile. Western blot, reverse transcription and PCR were used for studies of gene expression, and co-immunoprecipitation for protein-complex formation.

Results: MTT assay showed that NPCD caused growth arrest and apoptosis of MCF7, MDA-MB231, T47D, MCF15 and GI101Ap cells with an IC50 ranging between 3 to 8 µM given as a single dose. The growth arrest persisted for many days after cessation of the treatment, as shown in a clonogenic assay. NPCD could induce or reduce the D1 and CDK4 protein levels, depending on the cell line, but this effect was not correlated with its efficacy. Phosphorylation of D1 at Thr286 was decreased but it unexpectedly did not correlate with the change in D1 level in the cell lines studied. Phosphorylation of the Rb protein was decreased as expected whereas the p27kip1 protein level was decreased unexpectedly. Protein levels of p21cip1, CDK2 and cyclin E were also decreased in some, but not all, of the cell lines, whereas the mRNA levels of D1, CDK4, cyclin E, CDK2, p27kip1 and p21cip1 were increased in different cell lines.

Conclusions: NPCD can cause long-lasting growth arrest and cell death of breast cancer cell lines at an IC50 of 3-8 µM. Decreased phosphorylation of Rb by D1-CDK4/6 and decreased p27kip1 protein level may be part of the underlying mechanism.

Keywords: NPCD, CDK4 Inhibitor, breast cancer cell lines

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How to cite this article:
Sun Y, Li Yx, Wu Hj, Wu Sh, Wang YA, Luo Dz, Liao DJ. Effects of an Indolocarbazole-Derived CDK4 Inhibitor on Breast Cancer Cells. J Cancer 2011; 2:36-51. doi:10.7150/jca.2.36. Available from http://www.jcancer.org/v02p0036.htm