Xiaohuan Gao

Tissue microarray constructs to predict a response to chemoradiation in rectal cancer

PURPOSE To identify, using tissue microarray (TMA), an immunohistochemical panel predictive of response to ionizing radiation (IR) in rectal cancer. METHODS TMA constructs were prepared from archived stage II/III rectal tumors and matching adjacent mucosa (n=38) from patients treated with pre-operative chemoradiation. Immunohistochemistry (IHC) was performed for MIB, Cyclin E, p21, p27, p53, survivin, Bcl-2, and BAX. Immunoreactivity along with clinical variables was subjected to univariate and forward stepwise logistic regression analyses. RESULTS Pathological complete response (pCR) was 23.9%. The number of positive lymph nodes obtained in the resected specimen was associated with pCR. Immunoreactivity for MIB (Sn 15%, Sp 65%, OR 0.33), p53 (Sn 3%, Sp 84%, OR 0.16), Bcl-2 (Sn 11%, Sp 74%, OR 0.35), and BAX (Sn 92%, Sp 80%, OR 46) was associated with pathological response (all ps<0.001). Forward stepwise logistic regression analysis demonstrated that MIB was an independent predictor of a response to chemoradiation (p=0.001). CONCLUSIONS A combined panel of mediators of apoptosis alone or combined with clinical factors is a feasible approach that can be applied to rectal tumor biopsies to predict a response to chemoradiation. The most sensitive factor was BAX; while MIB independently predicted a response to chemoradiation.

Mechanisms of resistance to ionizing radiation in rectal cancer

While patients with breast cancers are not subjected to the adverse side effects of tamoxifen or trastuzumab if their tumors are negative for estrogen, progesterone or Her-2/Neu, neoadjuvant ionizing radiation with concurrent chemotherapeutic agents is administered almost universally to patients with stage II/III rectal cancers. There is, however, a tremendously wide range of response to this preoperative modality from complete pathological response to continuous tumor growth in patients receiving the same form of treatment. The specific phenotype of the tumor plays a major role in rendering tumor cells survival advantage to the cytotoxic effects of chemoradiation. Pathways such as proliferation, cell cycle, apoptosis and hypoxia have been investigated under a variety of conditions in preirradiated tissues and postirradiated tumors. This article reviews the current evidence available to identify a molecular profile predictive of the best response to ionizing radiation.

Role of p53, Bax, p21, and DNA-PKcs in radiation sensitivity of HCT-116 cells and xenografts.

BACKGROUND Molecular factors that dictate tumor response to ionizing radiation in rectal cancer are not well described. METHODS We investigated the contribution of p53, p21, Bax, and DNA-PKcs in response to ionizing radiation in an isogeneic colorectal cancer system in vitro and in vivo. RESULTS HCT-116 DNA-PKcs(-/-) cells and xenografts were radiosensitive compared with wild-type (WT) HCT-116 cells. HCT-116 p53(-/-) cells and tumor xenografts displayed a radioresistant phenotype. Separately, p21 or Bax deficiency was associated with a radiosensitive phenotype in vitro and in vivo. In vivo, Bax deficiency led to increased tumor necrosis and decreased microvessel density. In vitro, HCT-116 Bax(-/-) cells had decreased levels of vascular endothelial growth factor. HCT-116 WT cells had a more radioresistant phenotype after pancaspase inhibition, but pancaspase inhibition did not alter radiosensitivity in HCT-116 Bax(-/-) cells subjected to ionizing radiation. There was no difference in cell growth in HCT-116 WT cells subjected to transient apoptosis-inducing factor (AIF) inhibition; however, HCT-116 Bax(-/-) cells treated with AIF siRNA followed by ionizing radiation had a significant survival advantage compared with control-treated cells, implicating AIF in the radiosensitivity of Bax(-/-) cells. CONCLUSION These data might be used along with other markers to predict response to radiation in patients with rectal cancer.

In vitro and in vivo radiosensitization of colorectal cancer HT-29 cells by the smac mimetic JP-1201

BACKGROUND The response to neoadjuvant chemoradiation in rectal cancer is variable and unpredictable. Resistance to chemoradiation has been directly correlated with the levels of the inhibitors of apoptosis (IAPs) in several malignancies. Because smac-DIABLO is a pro-apoptotic gene product that directly inhibits the activity of the IAPs, molecules with similar activity might radiosensitize rectal tumors with phenotypes that express high levels of IAPs. This study was undertaken to assess the radiosensitizing properties of the smac mimetic JP-1201 in radioresistant HT-29 colorectal cancer cells in vitro and established xenografts in SCID mice. METHODS Survival was determined by clonogenic assays. PARP-1, caspase-8 cleavage, and IAP levels were assessed by Western blot analysis. SCID mice bearing HT-29 xenografts were treated with ionizing radiation: 2.0 Gy x 5; (n = 6), JP-1201 (5.0 mg/Kg i.p., n = 5) or combination treatment (n = 7) and compared to control (n = 8). DNA repair mechanisms were interrogated by gammaH2AX positive foci. RESULTS Pretreatment of HT-29 cells with JP-1201 (5.0 microM) prior to ionizing radiation (IR) significantly decreased the survival of these cells. SCID mice bearing HT-29 xenografts demonstrated no difference in tumor load in the group receiving exclusively JP-1201 versus control. At the end of the treatment (day 40), a 46% reduction of tumor load was observed in the IR+JP-1201-treated group compared to the IR-only treated group. Radiosensitization was achieved with a substantial elevation of cleaved PARP-1 in JP-1201- treated HT-29 cells versus control cells with a concomitant decrease of XIAP, but not of survivin or cIAP1/2. JP-1201-treated HT-29 cells had a reduced ability to repair double-stranded DNA breaks (DSBs). CONCLUSION The smac mimetic JP-1201 decreased the survival of HT-29 cells and tumor growth by an additive effect in apoptosis and a reduction in the level of XIAP and an impairment of DNA repair mechanisms. The pathways leading to this response need to be further investigated.

Radiosensitization of HT-29 cells and xenografts by the nitric oxide donor DETANONOate†

Mechanisms of radioresistance in rectal cancer remain unclear.

Murine orthotopic model for the assessment of chemoradiotherapeutic interventions in rectal cancer.

A murine orthotopic model for the study of colon cancer has been described earlier. However, for the study of rectal cancer, three issues remain: (i) the relative sensitivity of the implanted tumors to ionizing radiation (IR); (ii) the location of the tumor for the delivery of external beam IR; and (iii) the assessment of a given modality over time before necropsy. In this protocol, we have modified an orthotopic model for colon cancer described earlier for the specific assessment of chemoradiation in rectal cancer by (i) cecal transplantation of tumors with a known response to IR; (ii) securing the tumor to the lateral abdominal wall with a permanent suture for the administration of IR; and (iii) transfection of cells with luciferase before tumor implantation for the assessment of the chemoradiotherapeutic interventions over time by bioluminescence imaging before the end on the study. This technique allows targeted delivery of IR in an intraperitoneal tumor. Imaging throughout the course of the treatment is possible such that the timing of chemoradiation can be determined and permits comparison between groups before the end of the treatment. This model represents a modified technique that allows the assessment of chemoradiotherapeutic interventions in rectal cancer.

HIF-1α and Resistance to Ionizing Radiation in Rectal Cancer

Introduction: There is a wide range of responses to pre-operative chemoradiation (CRT) in patients with rectal cancer. Factors that dictate tumors response have not been identified. The objective of this study was to determine the role of hypoxia-inducible factor 1-alpha (HIF-1α) in in vitro and ex vivo models of rectal cancer. Methods: Levels of HIF-1α were assessed in radiosensitive (HCT-116) and a radioresistant (HT-29) cells. Radioresistant HT-29 cells were exposed to a potent radiosensitizing agent (a nitric oxide donor: DETANONOate [1 mM]) and IR followed by Western blot analysis with anti- HIF-1α antibodies. Patients with rectal cancer that were treated with CRT were separated based on good responders (≥ 50% reduction in tumor by comparing tumor size pre-operatively and postoperatively) compared to those that did not respond (<50% reduction in tumor). Blocks were stained for HIF-1α. Tissues collected from normal colonic epithelium from all these patients were subjected to the same treatments. Results: In vitro, radiosensitive HCT-116 colorectal cancer cells demonstrated low levels of HIF-1α following treatment IR. Western blot analysis showed high protein levels of HIF-1α in radioresistant HT-29 cells subjected to IR with induction at 2.0 and 4.0 Gy. Protein levels of HIF-1α were attenuated by treatment of cells HT-29 with the radiosensitizing agent DETANONOate following exposure to IR. Ex vivo, tissue microarrays demonstrated no difference in HIF-1α expression between patients with a poor response to CRT (418.1 ± 32.6) vs. good responders (371.1 ± 31.5; p=0.3). However, examination tumor tissue compared to normal epithelium showed an increase in HIF-1α (1.5 fold; p<0.001) in patients who responded poorly to IR. This effect was not observed in the cohort of patients who responded well to IR. Conclusions: The results of this study further support the potential role of HIF-1α in resistance to IR. This study implicates it a potential role of HIF-1α in rectal cancers.