Abstract 3463: The role of Atg13 in response to radiotherapy in cervical cancer cells

Introduction The role of autophagy protecting cancer cells against anti-cancer therapy, especially via the Beclin-1 axis, has become more clear. In cervical cancer, functionality of the Beclin-1 axis can be questioned, since promoter methylation and silencing of two components of this axis, C13ORF18 (Rubicon-like) and DAPK, is frequently observed. The involvement of another autophagy pathway, the ULK1 axis is less well studied in this tumor type. The ULK1 axis, consisting of ULK1, Atg13 and FIP200 is under control of mTOR. Here, we investigated the role of the essential component of the ULK1 complex, Atg13 in the response to (chemo)radiation in cervical cancer. Methods and Results Using immunohistochemistry we first analyzed expression of Atg13 in a large cohort of 375 pretreatment tissue samples of advantaged stage cervical cancer patients primarily treated with (chemo)radiation. Positive expression of Atg13 was more frequently observed in adenocarcinoma, known to have a poor response to chemoradiation, compared to squamous carcinoma (75% versus 56 % positive tumors, p< 0.03). Transient overexpression of GFP-tagged Atg13 in HEK293T kidney cells increased radiotherapy resistance (1.5-2 fold). Western blot showed that Atg13 was expressed in several cervical cancer cell lines, including the adenocarcinoma model HeLa. Downregulation of Atg13 expression with siRNA, resulted in a 2-fold increase in radiotherapy sensitivity in HeLa cells as determined with clonogenic assays. In HeLa-GFP-LC3 cells, we found that irradiation caused a strong increase in LC-3 containing autophagosomes, which co-localized with Atg13. The autophagy inhibitor bafilomycin A1 blocks the conversion of autophagosomes into autolysosomes. Bafilomycin A1 treatment indeed resulted in an accumulation of radiation-induced autophagosomes, demonstrating that autophagy was occurring after irradiation. In addition, HeLa cells were sensitized to irradiation, when autophagy was inhibited with bafilomycin A1. These results were confirmed using the less specific autophagy inhibitor 3-methyladenine and the autophagy inducer rapamycin (an mTOR inhibitor). Conclusion We showed that the Atg13 expression is related to the presence of cervical adenocarcinoma. Our in-vitro results indicate that the autophagic ULK1 pathway plays an important role in protecting cervical cancer cells to irradiation. Thus, inhibition of autophagy may be an interesting strategy to sensitize cervical adenocarcinoma to radiotherapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3463. doi:1538-7445.AM2012-3463

The role of ATM and 53BP1 as predictive markers in cervical cancer

Treatment of advanced-stage cervical cancers with (chemo)radiation causes cytotoxicity through induction of high levels of DNA damage. Tumour cells respond to DNA damage by activation of the 'DNA damage response' (DDR), which induces DNA repair and may counteract chemoradiation efficacy. Here, we investigated DDR components as potential therapeutic targets and verified the predictive and prognostic value of DDR activation in patients with cervical cancer treated with (chemo)radiation. In a panel of cervical cancer cell lines, inactivation of ataxia telangiectasia mutated (ATM) or its substrate p53-binding protein-1 (53BP1) clearly gave rise to cell cycle defects in response to irradiation. Concordantly, clonogenic survival analysis revealed that ATM inhibition, but not 53BP1 depletion, strongly radiosensitised cervical cancer cells. In contrast, ATM inhibition did not radiosensitise non-transformed epithelial cells or non-transformed BJ fibroblasts. Interestingly, high levels of active ATM prior to irradiation were related with increased radioresistance. To test whether active ATM in tumours prior to treatment also resulted in resistance to therapy, immunohistochemistry was performed on tumour material of patients with advanced-stage cervical cancer (n = 375) treated with (chemo)radiation. High levels of phosphorylated (p-)ATM [p = 0.006, hazard ratio (HR) = 1.817] were related to poor locoregional disease-free survival. Furthermore, high levels of p-ATM predicted shorter disease-specific survival (p = 0.038, HR = 1.418). The presence of phosphorylated 53BP1 was associated with p-ATM (p = 0.001, odds ratio = 2.206) but was not related to any clinicopathological features or survival. In conclusion, both our in vitro and patient-related findings indicate a protective role for ATM in response to (chemo)radiation in cervical cancer and point at ATM inhibition as a possible means to improve the efficacy of (chemo)radiation.

Abstract 4171: The role of ATM and 53BP1 as predictive markers and therapeutic targets in advanced stage cervical cancer

Chemoradiation is the standard of care for advanced stage cervical cancer patients and induces cytotoxicity by inducing high levels of DNA breaks in the tumor. The ability of tumor cells to repair therapy-induced DNA damage may counteract the effects of chemoradiation. The pathway responsible for DNA double strand break repair is called the ‘DNA damage response’.

In vitro we observed robust radiation-induced G1 and G2 cell cycle arrests in cervical cancer cell lines, despite the expression of HPV oncogenes, which impact the DNA damage response through rapid p53 degradation. Moreover, the DNA damage checkpoint protein ATM and its substrate 53BP1 are required for proper induction of cell cycle checkpoint arrests. Yet, when long-term survival effects were measured, inhibition of ATM, but not 53BP1, strongly sensitized cervical cancer cells to irradiation. To validate the putative role of ATM and 53BP1 in advanced stage cervical cancer we investigated presence and activity of ATM as well as 53BP1 in relation to response-to-treatment in a large, well documented, series of advanced stage cervical cancer patients (n=375). We found that high levels of ATM were related to poor response to chemoradiation (P=0.013). Importantly, high phosho-ATM immunostaining, reflecting active ATM, predicted poor responses to chemoradiation even better (P=0.004). In addition, high phospho-ATM levels predicted shorter disease-specific survival (P=0.020).

Although presence of phosphorylated 53BP1 did relate to phospho-ATM (P=0.001), it was not significantly related to any clinicopathological features or survival.

Combined, our data suggest the prognostic value of ATM signaling for responses to chemoradiation and point at ATM inhibition as a potential therapeutic target to increase treatment efficacy in advanced stage cervical cancers.

Acknowledgements

This research is supported by the Dutch Cancer Society (RUG 2007-3719) and the Netherlands Organization for Scientific Research (NWO-VENI 916.76.062).

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4171. doi:10.1158/1538-7445.AM2011-4171

Prognostic cell biological markers in cervical cancer patients primarily treated with (chemo)radiation: a systematic review

The aim of this study was to systematically review the prognostic and predictive significance of cell biological markers in cervical cancer patients primarily treated with (chemo)radiation. A PubMed, Embase, and Cochrane literature search was performed. Studies describing a relation between a cell biological marker and survival in ≥50 cervical cancer patients primarily treated with (chemo)radiation were selected. Study quality was assessed, and studies with a quality score of 4 or lower were excluded. Cell biological markers were clustered on biological function, and the prognostic and predictive significance of these markers was described. In total, 42 studies concerning 82 cell biological markers were included in this systematic review. In addition to cyclooxygenase-2 (COX-2) and serum squamous cell carcinoma antigen (SCC-ag) levels, markers associated with poor prognosis were involved in epidermal growth factor receptor (EGFR) signaling (EGFR and C-erbB-2) and in angiogenesis and hypoxia (carbonic anhydrase 9 and hypoxia-inducible factor-1α). Epidermal growth factor receptor and C-erbB-2 were also associated with poor response to (chemo)radiation. In conclusion, EGFR signaling is associated with poor prognosis and response to therapy in cervical cancer patients primarily treated with (chemo)radiation, whereas markers involved in angiogenesis and hypoxia, COX-2, and serum SCC-ag levels are associated with a poor prognosis. Therefore, targeting these pathways in combination with chemoradiation may improve survival in advanced-stage cervical cancer patients.

Construction of a triple modified p53 containing DNA vaccine to enhance processing and presentation of the p53 antigen

More effective and less toxic treatments are urgently needed in the treatment of patients with cancer. The tumour suppressor protein p53 is a tumour-associated antigen that could serve that purpose when applied in an immunologic approval to cancer. It is mutated in approximately 50% of the tumours resulting in p53 overexpression, which can serve as target for therapy. To improve the immunisation results in patients with p53 overexpression tumours we constructed a DNA vaccine that could lead to improved processing and presentation of p53 peptides in the MHC-class I. We constructed a triple modified p53 fusion protein containing DNA vaccine by (1) addition of a xeno-antigen (mouse or rat p53 fragment), (2) potentiation of intra-cytoplasmatic accumulation of p53 by deleting the nuclear signalling part, (3) improving the processing to peptides of p53 by addition of ubiquitin. In-vitro experiments confirmed correct construction of the DNA vaccine. Preliminary testing in normal and HLA-A2 mice of this triple modified p53 containing DNA construct meant for human application showed a trend towards a superior immunogenicity.