Apoptosis, p53, and tumor cell sensitivity to anticancer agents

Area of Science:

• Oncology
• Molecular Biology
• Cancer Genetics

Background:

• Current oncology dogma posits that tumor cells die via apoptosis, and resistance to apoptosis equates to resistance to cancer therapy.
• This tenet is primarily based on studies of normal cells and short-term assays, potentially overlooking tumor-specific adaptations.
• Solid human tumors often exhibit an apoptotically resistant phenotype due to evolutionary selection pressures.

Purpose of the Study:

• To critically reexamine the tenet that apoptosis resistance dictates cancer treatment resistance in nonhematological human tumors.
• To investigate the influence of assay methodology and p53 mutations on assessing cell killing by anticancer agents.

Main Methods:

• Review of existing literature on cancer cell killing assays and apoptosis.
• Analysis of the impact of short-term versus clonogenic survival assays on evaluating drug and radiation sensitivity.
• Examination of the role of p53 and bcl-2 in apoptosis and their influence on treatment response in solid tumors.

Main Results:

• Short-term assays can underestimate cell killing in apoptosis-resistant cells or those with mutant p53.
• Wild-type p53 promotes faster cell death after DNA damage in normal cells, leading to misinterpretations of p53 mutations conferring resistance.
• Clonogenic survival assays in solid human tumor cells indicate that apoptosis-related genes (p53, bcl-2) play a minimal role in sensitivity to anticancer drugs and radiation.

Conclusions:

• The established link between apoptosis resistance and cancer treatment resistance may be overstated for solid human tumors.
• Assay methodology significantly impacts the interpretation of cell killing and the role of apoptosis in treatment response.
• Apoptosis-independent mechanisms are crucial for determining the sensitivity of solid tumors to genotoxic anticancer therapies.