Objective The present study evaluated the anti-cancer effects of irradiation (Ir) alone, Ir after heat shock protein 90 inhibitor; 17allylamino-17-demethoxygeldanamycin (17-AAG) and gold nanoparticle (GNP) treatments in human colorectal cancer cell line (HCT-116), with the targeting of related mechanisms. Methods Water-soluble tetrazolium salt-1 assay was utilized to study the cytotoxic effects of 17-AAG, GNP, Ir in single and combination cases on the cell viability of HCT-116 cells. The cells were examined with DNA fragmentation electrophoresis and evaluated for apoptosis induction. Caspase-3 expression as a critical apoptosis element in protein level was detected by western blotting.Results Treatment with 17-AAG in a dose dependent manner for 24 h inhibited the cellular viability of HCT-116 cells. GNP at a dose of 70 μM had the lowest cytotoxic effects and was thus selected for combination treatment studies. Based on the results, GNP at a dose of 70 μM did not have a significant effect on cellular viability of HCT-116. In contrast, the evaluation of double and triple combinations, GNP with Ir (2 Gy of 6 MV X-ray radiation) and 17-AAG in double combinations induced significant cytotoxicity. Both DNA damage pattern and caspase-3 protein upregulation were present in Ir,GNP/17-AAG,GNP and Ir,17-AAG combinations compared to single treatments. Furthermore, in the three combination of GNP,Ir,17-AAG, radiosensitization effects (increased caspase-3 expression) occurred with a minimum concentration of 17-AAG. Conclusion According to the results of this study, 17-AAG as chemotherapeutic agent in combination with Ir and GNP exerts noticeable anti-cancer effects, inhibited cell viability, and increased apoptosis occurrence by upregulating caspase-3 expression. It is suggested that these combinations should be more evaluated as a promising candidate for colorectal cancer treatment.

Introduction: In this study, the cytotoxic and anti-cancer effects of Irinotecan as a conventional chemotherapeutic agent compared to 17-(allyl amino)-17-demethoxygeldanamycin (17-AAG) as possible radiosensitizers in the HCT-116 cell line were investigated. Methods: HCT-116 cells were treated with various concentrations of irinotecan and 17-AAG and also irradiated with a 2-Gy of X-ray radiation. Then, the cell viability was examined by a water-soluble tetrazolium-1 assay after 24 hours. For single therapies and double and triple combination cases, IC50, 0.5×IC50 and 0.25×IC50 concentrations of each drug were selected respectively for a terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) assay and other tests. In treated and untreated cells, the caspase 3 and Bcl-2 gene expression ratios were evaluated by the real-time PCR method. Likewise, caspase 3 activity was detected with a colorimetric assay. Results: In all combined treatments, including 17-AAG- radiation, irinotecan - radiation, irinotecan -17-AAG, and irinotecan-17-AAG-radiation, decreased cellular viability and increased TUNEL positive cells were presented versus the control group (P<0.05). There were increased TUNEL positive cells in the triple combination, in concentrations of 0.25×IC50 of each drug, in comparison with single and double agent treatments. Moreover, in triple combination, the caspase 3 mRNA level and caspase 3 activity increased versus related single treatments. Likewise, in the irinotecan-17-AAG-radiation combined treatment and the 17-AAG-radiation double treatment, the Bcl-2 gene expression level decreased in comparison with single therapies. Conclusion: It can be indicated that the combination of chemo-radiotherapy versus single treatments has significant anti-cancer effects.