Spontaneous Regression of Human Cancer Cells In Vitro: Potential Role of Disruption of Cdk1/Cdk4 Co-expression

Background: Although well-acknowledged in vivo, spontaneous death of cancer cells in vitro is less widely appreciated. Materials and Methods: Colony formation was studied in untreated control plates of standard clonogenic assays and measurements of actual and potential doubling times performed in asynchronous cultures of human cancer cells lines. Western blotting of lung large cell carcinoma, COR-L23 cells actively undergoing spontaneous cell death was also carried out. Results: Catastrophic disintegration of mature colonies could be seen in the untreated plates of lung large cell carcinoma, H460 and colon adenocarcinoma, SW620 human cancer cell lines and a significant cell loss factor was present in the cell lines growing as adherent cells in continuous culture. Western blotting demonstrated alterations of relative cyclin dependent kinase (Cdk)1 to Cdk4 protein expression in dying COR-L23 cells. Conclusion: The phenomenon of spontaneous cell death should be considered a hallmark of cancer and may be the result of failure to stabilise unstable, fully developed cancer cells due to the disruption of Cdk1/Cdk4 co-expression in those cells.