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Pretreatment with DNA-damaging agents permits selective killing of checkpoint-deficient cells by microtubule-active
M V Blagosklonny1, R Robey, S Bates
1Medicine Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA. mikhailb@box-m.nih.gov
Abstract:
Cell-cycle checkpoint mechanisms, including the p53- and p21-dependent G(2) arrest that follows DNA damage, are often lost during tumorigenesis. We have exploited the ability of DNA-damaging drugs to elicit this checkpoint, and we show here that such treatment allows microtubule drugs, which cause cell death secondary to mitotic arrest, to kill checkpoint-deficient tumor cells while sparing checkpoint-competent cells. Low doses of the DNA-damaging drug doxorubicin cause predominantly G(2) arrest without killing HCT116 cells that harbor wt p53. Doxorubicin treatment prevented mitotic arrest, Bcl-2 phosphorylation, and cell death caused by paclitaxel, epothilones, and vinblastine. In contrast, doxorubicin enhanced cytotoxicity of FR901228, an agent that does not affect microtubules. Low doses of doxorubicin did not arrest p21-deficient clones of HCT116 cells and did not protect these cells from cytotoxicity caused by microtubule drugs, but cells in which p21 expression was restored enjoyed partial protection under these conditions. Moreover, in p53-deficient clones of HCT116 cells doxorubicin did not induce either p53 or p21 and provided no protection against paclitaxel-induced cytotoxicity. Therefore, (a) p53-dependent p21 induction caused by doxorubicin protects from microtubule drug-induced cytotoxicity, and (b) pretreatment with cytostatic doses of DNA-damaging drugs before treatment with microtubule drugs results in selective cytotoxicity to cancer cells with defective p53/p21-dependent checkpoint.
Insights
DNA-damaging drugs can selectively kill cancer cells lacking cell-cycle checkpoints. This strategy uses DNA-damaging drugs to sensitize checkpoint-deficient tumor cells to microtubule-targeting drugs, sparing healthy cells.
Area of Science:
- Oncology
- Cell Biology
- Molecular Biology
Background:
- Cell-cycle checkpoints, particularly those involving p53 and p21, are crucial for preventing tumor progression.
- Loss of these checkpoints is a common event during tumorigenesis, contributing to cancer development.
- Microtubule-targeting drugs induce cell death via mitotic arrest, but their efficacy is limited in checkpoint-deficient cancer cells.
Purpose of the Study:
- To investigate whether DNA-damaging drugs can be used to selectively eliminate cancer cells with defective cell-cycle checkpoints.
- To determine if pre-treatment with DNA-damaging agents can sensitize checkpoint-deficient tumor cells to microtubule-targeting drugs.
Main Methods:
- Utilized low doses of doxorubicin (a DNA-damaging drug) to induce G2 arrest in cancer cells.
- Administered microtubule-targeting drugs (paclitaxel, epothilones, vinblastine) after doxorubicin pre-treatment.
- Examined the effects of doxorubicin on p53 and p21 expression and their role in cell-cycle arrest and drug sensitivity.
- Compared cytotoxicity in cancer cells with wild-type versus deficient p53/p21 pathways.
Main Results:
- Doxorubicin induced G2 arrest in p53-proficient cells, protecting them from microtubule drug-induced death.
- In p21-deficient or p53-deficient cells, doxorubicin did not induce G2 arrest and did not protect against microtubule drug cytotoxicity.
- Doxorubicin enhanced the cytotoxicity of FR901228 (a non-microtubule agent), indicating pathway specificity.
- Restoration of p21 expression partially protected cells from microtubule drug cytotoxicity.
Conclusions:
- p53-dependent p21 induction is critical for doxorubicin-mediated protection against microtubule drug cytotoxicity.
- Pre-treatment with cytostatic doses of DNA-damaging drugs selectively enhances the cytotoxicity of microtubule drugs in cancer cells with defective p53/p21 checkpoints.
- This approach offers a potential strategy for targeting cancers with compromised cell-cycle regulation.
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