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Published on: March 7, 2011
Radiosensitization of HT-29 cells and xenografts by the nitric oxide donor DETANONOate
Xiaohuan Gao1, Debabrata Saha, Payal Kapur
1Department of Surgery, Dallas VA Medical Center, University of Texas Southwestern, Dallas, Texas, USA.
Background:
Mechanisms of radioresistance in rectal cancer remain unclear.
Objectives:
To determine mechanisms of radioresistance in rectal cancer cells and to assess the role of the nitric oxide donor DETANONOate as a radiosensitizing agent.
Methods:
Survival was determined by clonogenic assays, apoptosis by PARP-1 cleavage, and phenotypic differences by Western blot analysis. SCID mice bearing HT-29 xenografts were treated with ionizing radiation (IR) [2.0 Gy x 5], DETANONOate [0.4 mg/kg i.p.], or combination treatment.
Results:
Colorectal cancer HT-29-p53-null cells were resistant and HCT-116-p53 wild-type cells sensitive to IR, which correlated with cleaved PARP-1. Increased levels of p21 occurred in HCT-116 cells, while Bcl-2 and survivin were elevated in HT-29 cells. Radiosensitization was achieved with a substantial elevation of cleaved PARP-1 in DETANONOate-HT-29-treated versus control cells, which was accompanied by elevation of p21, p27, and BAX, and a concomitant decrease in Bcl-2. SCID mice bearing HT-29 xenografts demonstrated a 37.6%, 51.1%, and 70.1% inhibition in tumor growth in mice receiving IR, DETANONOate, and combination treatment versus control, respectively.
Conclusions:
Radioresistant HT-29 cells are p53-null and have substantially decreased levels of p21. DETANONOate radiosensitized HT-29 cells in vitro and in vivo by an additive effect in apoptosis.
Insights
Mechanisms of radioresistance in rectal cancer were investigated. The nitric oxide donor DETANONOate sensitized radioresistant HT-29 cells by increasing apoptosis, offering a potential radiosensitizing strategy.
Area of Science:
- Oncology
- Radiation Oncology
- Molecular Biology
Background:
- Rectal cancer radioresistance mechanisms are not fully understood.
- Investigating novel radiosensitizing agents is crucial for improving treatment outcomes.
Purpose of the Study:
- To elucidate mechanisms of radioresistance in rectal cancer cells.
- To evaluate the efficacy of the nitric oxide donor DETANONOate as a radiosensitizing agent.
Main Methods:
- Clonogenic assays and Western blot analysis were used to assess cell survival and protein expression.
- Apoptosis was measured by poly (ADP-ribose) polymerase-1 (PARP-1) cleavage.
- In vivo efficacy was tested using HT-29 xenografts in SCID mice treated with ionizing radiation (IR) and/or DETANONOate.
Main Results:
- p53-null HT-29 cells exhibited radioresistance, unlike p53 wild-type HCT-116 cells, correlating with PARP-1 cleavage.
- DETANONOate treatment in HT-29 cells significantly increased apoptosis markers (cleaved PARP-1, p21, p27, BAX) and reduced anti-apoptotic proteins (Bcl-2).
- Combination therapy demonstrated the greatest tumor growth inhibition (70.1%) in vivo.
Conclusions:
- Radioresistant HT-29 cells are characterized by p53-null status and low p21 levels.
- DETANONOate effectively radiosensitized HT-29 cells in vitro and in vivo.
- The radiosensitizing effect of DETANONOate is attributed to an additive effect on apoptosis.
