Cell Cycle Regulation and Apoptotic Cell Death in Experimental Colon Carcinogenesis: Intervening with Cyclooxygenase-2 Inhibitors

Abstract

Relative imbalance in the pathways regulating cell cycle, cell proliferation, or cell death marks a prerequisite for neoplasm. C-phycocyanin, a biliprotein from Spirulina platensis and a selective COX-2 inhibitor along with piroxicam, a traditional nonsteroidal antiinflammatory drug was used to investigate the role of cell cycle regulatory proteins and proinflammatory transcription factor NFκB in 1,2-dimethylhydrazine dihydrochloride (DMH)-induced rat colon carcinogenesis. Cell cycle regulators [cyclin D1, cyclin E, cyclin dependent kinase 2 (CDK2), CDK4, and p53], NFκB (p65) pathway, and proliferating cell nuclear antigen (PCNA) were evaluated by gene and protein expression, whereas apoptosis was studied by terminal deoxynucleotidyl transferase dUTP nick end labeling and apoptotic bleb assay. Molecular docking of ligand protein interaction was done to validate the in vivo results. Cyclin D1, cyclin E, CDK2, and CDK4 were overexpressed in DMH, whereas piroxicam and c-phycocyanin promoted the cell cycle arrest by downregulating them. Both drugs mediated apoptosis through p53 activation. Piroxicam and c-phycocyanin also stimulated antiproliferation by restraining PCNA expression and reduced cell survival via inhibiting NFκB (p65) pathway. Molecular docking revealed that phycocyanobilin (a chromophore of c-phycocyanin) interact with DNA binding site of NFκB. Inhibition of cyclin/CDK complex by piroxicam and c-phycocyanin affects the expression of p53 in colon cancer followed by downregulation of NFκB and PCNA levels, thus substantiating the antineoplastic role of these agents.

Funding

Financial assistance for this study was received from the Indian Council of Medical Research, Govt. of India [Reference No. (3/2/2/83/2011/NCD-III)]. The support is gratefully acknowledged. We also acknowledge the contributions of Dr. Ravi Kumar, Application Specialist, SCHRODINGER, India for helping us in performing the docking studies.