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Background Up to 40% of lung adenocarcinoma have been reported to lack ataxia-telangiectasia mutated (ATM) protein expression. We asked whether ATM-deficient lung cancer cell lines are sensitive to poly-ADP ribose polymerase (PARP) inhibitors and determined the mechanism of action of olaparib in ATM-deficient A549 cells. Methods We analysed drug sensitivity data for olaparib and talazoparib in lung adenocarcinoma cell lines from the Genomics of Drug Sensitivity in Cancer (GDSC) project. We deleted ATM from A549 lung adenocarcinoma cells using CRISPR/Cas9 and determined the effects of olaparib and the ATM/Rad3-related (ATR) inhibitor VE-821 on cell viability. Results IC50 values for both olaparib and talazoparib positively correlated with ATM mRNA levels and gene amplification status in lung adenocarcinoma cell lines. ATM mutation was associated with a significant decrease in the IC50 for olaparib while a similar trend was observed for talazoparib. A549 cells with deletion of ATM were sensitive to ionising radiation and olaparib. Olaparib induced phosphorylation of DNA damage markers and reversible G2 arrest in ATM-deficient cells, while the combination of olaparib and VE-821 induced cell death. Conclusions Patients with tumours characterised by ATM-deficiency may benefit from treatment with a PARP inhibitor in combination with an ATR inhibitor.

BackgroundThe ataxia telangiectasia mutated (ATM) protein kinase is mutated in several human cancers, presenting potential opportunities for targeted cancer therapy. We previously reported that the poly-ADP ribose polymerase (PARP) inhibitor olaparib induced transient G2 arrest but not cell death in ATM-deficient A549 lung cancer cells, while the combination of olaparib with the ATM-, Rad3-related (ATR) inhibitor VE-821 induced cell death. Here, we show that the clinically relevant ATR inhibitor, AZD6738, sensitizes ATM-deficient A549 lung, prostate and pancreatic cancer cells to olaparib.MethodsATM was depleted from A549 lung cancer cells, PC-3 prostate cancer cells and Panc 10.05 pancreatic cancer cells, and the effects of olaparib alone and in combination with AZD6738 were determined.ResultsThe combination of olaparib plus AZD6738 induced cell death in ATM-deficient lung, prostate and pancreatic cancer cells with little effect on their ATM-proficient counterparts.ConclusionsLung, prostate and pancreatic patients whose tumours exhibit loss or inactivation of ATM may benefit from combination of a PARP inhibitor plus an ATR inhibitor.

Poly-ADP ribose polymerase (PARP) inhibitors are currently used in the treatment of several cancers carrying mutations in the breast and ovarian cancer susceptibility genes BRCA1 and BRCA2, with many more potential applications under study and in clinical trials. Here, we discuss the potential for extending PARP inhibitor therapies to tumours with deficiencies in the DNA damage-activated protein kinase, Ataxia-Telangiectasia Mutated (ATM). We highlight our recent findings that PARP inhibition alone is cytostatic but not cytotoxic in ATM-deficient cancer cells and that the combination of a PARP inhibitor with an ATR (ATM, Rad3-related) inhibitor is required to induce cell death.

The 2016 Annual General Meeting of the Canadian Society of Clinician Investigators (CSCI) and Clinician Investigator Trainee Association of Canada/Association des Cliniciens-Chercheurs en Formation du Canada (CITAC/ACCFC) was a national conference held in Toronto November 21-23, 2016, in conjunction with The University of Toronto Clinician Investigator Program Research Day. The theme for this year’s meeting was “Mapping Your Career as a Clinician-Scientist”; emphasizing essential skills for developing a fruitful career as clinician-scientist. The meeting featured an opening presentation by Dr. Alan Underhill, Dr. Nicola Jones and Alexandra Kuzyk. The keynote speakers were Dr. Nada Jabado (McGill University), who discussed the association between cancer and histones, Dr. Norman Rosenblum (University of Toronto), who addressed the career path and the “calling” of the Clinician Scientist, Dr. Martin Schmeing (McGill University), who was the 2016 Joe Doupe Award recipient, and Dr. Linda Rabeneck (Cancer Care Ontario and University of Toronto), who received the Friends of CIHR lectureship. The workshops, focusing on career development for clinician scientists, were hosted by Drs. Alan Underhill, Nicola Jones, Lynn Raymond, Michael Schlossmacher and Norman Rosenblum, as well as University of Toronto communication specialists, Caitlin Johannesson and Suzanne Gold. In addition, the Young Investigators’ Forum included presentations from clinician investigator trainees from across the country. The research topics were diverse and comprehensive: from basic sciences to clinical practice; from epidemiology to medical engineering. All scientific abstracts are summarized in this review. Over 70 abstracts were showcased at this year’s meeting during two poster sessions, with six outstanding abstracts selected for oral presentations during the President’s Forum.

Non-homologous end joining (NHEJ) is the major pathway for the repair of ionizing radiation induced DNA double strand breaks in human cells. Here, we discuss current insights into the mechanism of NHEJ and the interplay between NHEJ and other pathways for repair of IR-induced DNA damage.

Platinum-based drugs, in particular cisplatin, are among the most widely used chemotherapeutic agents, used in the treatment of a wide array of solid malignancies. Despite initial therapeutic success, cisplatin treatment often results in the development of resistance, which can lead to therapeutic failure. Despite significant advances in understanding mechanisms of cisplatin resistance in other tumor sites, there are substantial gaps in our molecular knowledge of resistance in cervical cancer. Our group has examined the role of the PI3K/AKT/mTOR pathway in cervical cancer patients treated with cisplatin and radiation therapy. The PI3K/AKT/mTOR pathway is a promising therapeutic target because it is activated in several human cancers, which is frequently mediated by “hotspot” mutations including E542K, E545K and H1047R in the PIK3CA gene. Moreover, multiple PI3K/AKT/mTOR pathway inhibitors have been developed and are currently being evaluated in clinical trials. We previously reported that PIK3CA mutation in patients with early stage (IB/II) cervical cancer was associated with poor survival after treatment with radiation and cisplatin (McIntyre et al. Gynecol Oncol. 2013, PMID: 23266353), and that PIK3CA-E545K mutation renders cervical cancer cells more resistant to cisplatin or cisplatin plus radiation and results in a more migratory phenotype than cell lines with wild type-PIK3CA. Moreover, these phenotypes were reversed by the PI3K inhibitor GDC-0941 (Wani et al. Oncotarget. 2016, PMID: 27489350). The aim of the present study is to explore the mechanism of cisplatin resistance and enhanced migration in cervical cancer cells engineered to express PIK3CA-E545K mutation. Gene expression analysis identified 161 genes that were up regulated and 189 that were down regulated in cervical cancer cells stably expressing PIK3CA-E545K, some of which are involved in pathways relevant to cisplatin resistance. On further validation, we found that Fibronectin1 (FN1) was upregulated at both the mRNA and protein level in cervical cancer cells expressing PIK3CA-E545K. FN1 is a glycoprotein that is widely expressed in multiple cell types and is involved in cellular adhesion and migration. Recent studies have reported that FN1 might have a role in regulating chemoresistance in tumors. However, the effect of FN1 on cisplatin resistance in cervical cancer cells expressing E545K mutation has not been investigated. The present study aims to determine the effect of FN1 expression on cisplatin resistance in cervical cancer cells expressing the PIK3CA-E545K mutation and to explore potential mechanisms of cisplatin resistance and enhanced cell migration in cervical cancer cells. Citation Format: Arjumand Wani, Shiekh Tanveer Ahmad, Nicholas Jette, Siddhartha Goutam, Corinne M. Doll, Susan P. Miller. Mechanism of cisplatin resistance and enhanced cell migration in cervical cancer cells expressing PIK3CA-E545K mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4026.

The phosphatidylinositol-3 kinase (PI3K)/AKT/ mTOR signaling pathway is activated in several human cancers and activation is frequently mediated by “hotspot” mutations including E542K, E545K and H1047R in the PIK3CA gene. Approximately 30% of cervical cancer patients have the PIK3CA-E545K mutation. Cisplatin with radiotherapy (RT) is the standard treatment of cervical cancer world-wide, used in both the radical and post-operative adjuvant settings. However, details of the molecular mechanisms responsible for cisplatin resistance remain unclear. We previously reported PIK3CA mutation in patients with earlier stage (IB/II) cervical cancer was associated with poor survival (McIntyre et al. Gynecol Oncol. 2013, PMID:23266353), and in our recent study we observed that PIK3CA-E545K mutation renders cervical cancer cells more resistant to cisplatin or cisplatin plus RT and results in a more migratory phenotype than isogenic cell lines with wild type-PIK3CA. Moreover, these phenotypes are reversed by the PI3K inhibitor GDC-0941/Pictilisib (Wani et al. Oncotarget. 2016, PMID:27489350). The aim of the present study is to identify the expression of genes related to cisplatin resistance in cervical cancer cells engineered to express PIK3CA-E545K. Microarray analysis identified 161 genes that were up-regulated and 189 that were down-regulated in the cervical cancer cells stably expressing PIK3CA-E545K, some of which are involved in well-characterized mechanisms that could be relevant to cisplatin resistance. We are currently validating some of those genes by Real-time PCR that will help us to determine the mechanism of PIK3CA-E545K induced cisplatin resistance and enhanced migration in cervical cancer cells expressing PIK3CA-E545K and extending our in vitro findings to animal models. Together, our data will provide a useful basis for screening candidate targets for risk stratification and provide valuable information for potential targeted intervention in patients whose tumors harbor cisplatin-resistant molecular characteristics. Citation Format: Wani Arjumand, Nicholas Jette, Jb McIntyre, Prafull Ghatage, Corinne M. Doll, Susan P. Lees-Miller. Identification of genes associated with the cisplatin resistance in cervical cancer cells expressing E545K mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3149. doi:10.1158/1538-7445.AM2017-3149

The DNA-dependent protein kinase (DNA-PK) is a serine/threonine protein kinase composed of a large catalytic subunit (DNA-PKcs) and the Ku70/80 heterodimer. Over the past two decades, significant progress has been made in elucidating the role of DNA-PK in non-homologous end joining (NHEJ), the major pathway for repair of ionizing radiation-induced DNA double strand breaks in human cells and recently, additional roles for DNA-PK have been reported. In this review, we will describe the biochemistry, structure and function of DNA-PK, its roles in DNA double strand break repair and its newly described roles in mitosis and other cellular processes.