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Evaluating the Effectiveness of Cancer Drug Sensitization In Vitro and In Vivo
Published on: February 6, 2015
Disruption of p53 function sensitizes breast cancer MCF-7 cells to cisplatin and pentoxifylline
1Laboratory of Molecular Pharmacology, National Cancer Institute, NIH, Bethesda, Maryland 20892, USA.
Abstract:
The possibility that appropriately designed chemotherapy could act selectively against p53-defective tumor cells was explored in MCF-7 human breast cancer cells. These cells were chosen because they have normal p53 function but are representative of a tumor cell type that does not readily undergo p53-dependent apoptosis. Two sublines (MCF-7/E6 and MCF-7/mu-p53) were established in which p53 function was disrupted by transfection with either the human papillomavirus type-16 E6 gene or a dominant-negative mutant p53 gene. p53 function in MCF-7/E6 and MCF-7/mu-p53 cells was defective relative to control cells in that there were no increases in p53 or p21Waf1/Cip1 protein levels and no G1 arrest following exposure to ionizing radiation. Survival assays showed that p53 disruption sensitized MCF-7 cells to cisplatin (CDDP) but not to several other DNA-damaging agents. CDDP sensitization was not limited to MCF-7 cells since p53 disruption in human colon carcinoma RKO cells also enhanced sensitivity to CDDP. Contrary to the other DNA-damaging agents tested, CDDP-induced DNA lesions are repaired extensively by nucleotide excision, and in agreement with a defect in this process, MCF-7/E6 and MCF-7/mu-p53 cells exhibited a reduced ability to repair a CDDP-damaged chloramphenicol acetyltransferase-reporter plasmid transfected into the cells. Therefore, we attributed the increased CDDP sensitivity of MCF-7 cells with disrupted p53 to defects in G1 checkpoint control, nucleotide excision repair, or both. The G2 checkpoint inhibitor pentoxifylline exhibited synergism with CDDP in killing MCF-7/E6 cells but did not affect sensitivity of the control cells. Moreover, pentoxifylline inhibited G2 checkpoint function to a greater extent in MCF-7/E6 than in the parental cells. These results suggested that, in the absence of p53 function, cancer cells are more vulnerable to G2 checkpoint abrogators. Our results show that a combination of CDDP and pentoxifylline is capable of synergistic and preferential killing of p53-defective tumor cells that do not readily undergo apoptosis.
Insights
Disrupting tumor suppressor p53 function sensitizes cancer cells to cisplatin chemotherapy and G2 checkpoint inhibitors. This combination therapy offers a targeted approach for p53-defective tumors resistant to apoptosis.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Genetics
Background:
- The tumor suppressor protein p53 plays a crucial role in cell cycle control and apoptosis.
- Dysfunctional p53 is common in many cancers, contributing to tumor development and therapy resistance.
- Targeting p53-defective cancer cells presents a potential strategy for selective cancer treatment.
Purpose of the Study:
- To investigate whether chemotherapy can be designed to selectively target tumor cells with defective p53 (tumor suppressor) function.
- To explore the role of p53 in cellular response to DNA-damaging agents and checkpoint control.
- To evaluate the potential of combining cisplatin with G2 checkpoint inhibitors for selective cancer therapy.
Main Methods:
- Established MCF-7 human breast cancer cell lines with disrupted p53 function using viral E6 gene or dominant-negative mutant p53.
- Assessed p53 and p21Waf1/Cip1 protein levels and G1 arrest following ionizing radiation exposure.
- Performed survival assays using cisplatin (CDDP) and other DNA-damaging agents.
- Evaluated DNA repair capacity for CDDP-induced lesions.
- Investigated the synergistic effect of CDDP and pentoxifylline (a G2 checkpoint inhibitor) on cancer cell killing.
Main Results:
- p53 disruption in MCF-7 cells led to defective G1 arrest and sensitization to cisplatin (CDDP), but not other DNA-damaging agents.
- p53-defective RKO colon cancer cells also showed enhanced sensitivity to CDDP.
- MCF-7 cells with disrupted p53 exhibited reduced repair of CDDP-induced DNA damage, suggesting defects in nucleotide excision repair or G1 checkpoint control.
- The G2 checkpoint inhibitor pentoxifylline synergized with CDDP to kill p53-defective MCF-7/E6 cells, with a greater effect on G2 checkpoint inhibition compared to control cells.
Conclusions:
- Disruption of p53 function sensitizes cancer cells to cisplatin, potentially due to impaired G1 checkpoint control and/or nucleotide excision repair.
- Cancer cells lacking p53 function are more vulnerable to G2 checkpoint abrogators.
- A combination of cisplatin and pentoxifylline demonstrates synergistic and preferential killing of p53-defective tumor cells that are resistant to apoptosis.
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