Inhibition of type 1 insulin-like growth factor receptor (IGF-1R) enhances tumor cell sensitivity to ionizing radiation. It is not clear how this effect is mediated, nor whether this approach can be applied effectively in the clinic. We previously showed that IGF-1R depletion delays repair of radiation-induced DNA double-strand breaks (DSBs), unlikely to be explained entirely by reduction in homologous recombination (HR) repair. The current study tested the hypothesis that IGF-1R inhibition induces a repair defect that involves non-homologous end-joining (NHEJ). IGF-1R inhibitor AZ12253801 blocked cell survival and radiosensitized IGF-1R over-expressing murine fibroblasts but not isogenic IGF-1R null cells, supporting specificity for IGF-1R. IGF-1R inhibition enhanced radiosensitivity in DU145, PC3 and 22Rv1 prostate cancer cells, comparable to effects of ATM inhibition. AZ12253801-treated DU145 cells showed delayed resolution of γH2AX foci, apparent within 1hr of irradiation and persisting for 24hr. In contrast, IGF-1R inhibition did not influence radiosensitivity or γH2AX focus resolution in LNCaP-LN3 cells, suggesting that radiosensitization tracks with the ability of IGF-1R to influence DSB repair. To differentiate effects on repair from growth and cell survival responses, we tested AZ12253801 in DU145 cells at sub-SF50 concentrations that had no early (≤48hr) effects on cell cycle distribution or apoptosis induction. Irradiated cultures contained abnormal mitoses, and after 5 days IGF-1R inhibited cells showed enhanced radiation-induced polyploidy and nuclear fragmentation, consistent with the consequences of entry into mitosis with incompletely repaired DNA. AZ12253801 radiosensitized DNA-PK proficient but not DNA-PK deficient glioblastoma cells, and did not radiosensitize DNA-PK-inhibited DU145 cells, suggesting that in the context of DSB repair, IGF-1R functions in the same pathway as DNA-PK. Finally, IGF-1R inhibition attenuated repair by both NHEJ and HR in HEK293 reporter assays. These data indicate that IGF-1R influences DSB repair by both major DSB repair pathways, findings that may inform clinical application of this approach.

These data indicate a role for IGF-1R in DSB repair, at least in part via HR, and support use of IGF-1R inhibitors with DNA damaging cancer treatments.

Type 1 insulin like growth factor receptor (IGF-1R) targeted therapies showed compelling pre-clinical evidence; however, to date, this has failed to translate into patient benefit in Phase 2/3 trials in unselected patients. This was further complicated by the toxicity, including hyperglycemia, which largely results from the overlap between IGF and insulin signaling systems and associated feedback mechanisms. This has halted the clinical development of inhibitors targeting IGF signaling, which has limited the availability of biopsy samples for correlative studies to understand biomarkers of response. Indeed, a major factor contributing to lack of clinical benefit of IGF targeting agents has been difficulty in identifying patients with tumors driven by IGF signaling due to the lack of predictive biomarkers. In this review, we will describe the IGF system, rationale for targeting IGF signaling, the potential liabilities of targeting strategies, and potential biomarkers that may improve success.

Effective systemic treatment of cancer relies on the delivery of agents with optimal therapeutic potential. The molecular age of medicine has provided genomic tools that can identify a large number of potential therapeutic targets in individual patients, heralding the promise of personalized treatment. However, determining which potential targets actually drive tumor growth and should be prioritized for therapy is challenging. Indeed, reliable molecular matches of target and therapeutic agent have been stringently validated in the clinic for only a small number of targets. Patient-derived xenografts (PDX) are tumor models developed in immunocompromised mice using tumor procured directly from the patient. As patient surrogates, PDX models represent a powerful tool for addressing individualized therapy. Challenges include humanizing the immune system of PDX models and ensuring high quality molecular annotation, in order to maximise insights for the clinic. Importantly, PDX can be sampled repeatedly and in parallel, to reveal clonal evolution, which may predict mechanisms of drug resistance and inform therapeutic strategy design.

Inhibition of type 1 IGF receptor (IGF-1R) sensitizes to DNA-damaging cancer treatments, and delays repair of DNA double strand breaks (DSBs) by non-homologous end-joining and homologous recombination (HR). In a recent screen for mediators of resistance to IGF-1R inhibitor AZ12253801, we identified RAD51, required for the strand invasion step of HR. These findings prompted us to test the hypothesis that IGF-1R-inhibited cells accumulate DSBs formed at endogenous DNA lesions, and depend on residual HR for their repair. Indeed, initial experiments showed time-dependent accumulation of cH2AX foci in IGF-1R -inhibited or -depleted prostate cancer cells. We then tested effects of suppressing HR, and found that RAD51 depletion enhanced AZ12253801 sensitivity in PTEN wild-type prostate cancer cells but not in cells lacking functional PTEN. Similar sensitization was induced in prostate cancer cells by depletion of BRCA2, required for RAD51 loading onto DNA, and in BRCA2 2/2 colorectal cancer cells, compared with isogenic BRCA21/2 cells. We also assessed chemical HR inhibitors, finding that RAD51inhibitor BO2 blocked RAD51 focus formation and sensitized to AZ12253801. Finally, we tested CDK1 inhibitor RO-3306, which impairs HR by inhibiting CDK1-mediated BRCA1 phosphorylation. R0-3306 suppressed RAD51 focus formation consistent with HR attenuation, and sensitized prostate cancer cells to IGF-1R inhibition, with 2.4-fold reduction in AZ12253801 GI 50 and 13-fold reduction in GI 80 . These data suggest that responses to IGF-1R inhibition are enhanced by genetic and chemical approaches to suppress HR, defining a population of cancers (PTEN wild-type, BRCA mutant) that may be intrinsically sensitive to IGF-1R inhibitory drugs.

These data suggest a significant difference in the cytocidal effect of commonly used irrigation solutions on head and neck cancer cells in an in vitro model.

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Ovarian cancer is the most lethal gynecologic malignancy and the fifth leading cause of cancer deaths among women. The current standard of care post surgical cytoreduction is combination platinum/taxane chemotherapy. The initial response varies widely; subsets of carcinomas demonstrate resistance or sensitivity from the onset. The underlying cause of this response heterogeneity remains incompletely understood. Patient-derived xenografts (PDX) serve as useful in vivo models to study molecular response markers and test the efficacy of targeted therapies. Our group has demonstrated a high engraftment rate (>70%) of ovarian cancer PDXs (Avatars) by injecting treatment naïve patient tumor directly into the peritoneal cavity of an in immunocompromised mouse host in an effort to better mimic the anatomic context by which ovarian cancer naturally develops. We now have 328 engrafted Avatar models representing the wide range of ovarian cancer subtypes, including serous (65%), mixed epithelial (10%), endometrioid (7%), clear cell (4%), mucinous (3%), carcinosarcoma (1%) and other (10%). Using these models, we are performing a massively parallel sequencing strategy referred to as BROCA-HR to detect all mutation classes (e.g. gene rearrangements, copy number variations, etc.) and gene aberrations within the Fanconi Anemia-BRCA homologous recombination (HR), non-homologous end joining (NHEJ), PTEN, and DNA Mismatch repair pathways. To date, 148 Avatar models have undergone BROCA sequencing. Observed deleterious mutations included 12 BRCA1 (8%), 6 BRCA2 (4%), and 4 PIK3CA (3%); additional loss of function mutations were also evident in the following genes: ATM, RAD51C, FANCM, FANCD2, FANCA, CHEK2, PALB2, MHS6, CDK12 and GEN1. These models are representative of mutations seen in the TCGA mutation set. Models harboring said mutations are currently being tested with platinum agents and/or PARP inhibitors. Taken together, the Avatars represent a high throughput model system for pre-clinical testing in vivo that effectively recapitulates ovarian cancer (e.g. mutations in BRCA1, BRCA2 and other DNA damage response proteins). We have been able to establish avatars at a high rate, including those with mutations in BRCA1, BRCA2 and other DNA damage response genes. These models will be a unique resource for future studies of biomarkers and novel therapeutic approaches. This work is funded by the Ovarian Cancer Research Fund (750563), Mayo Ovarian SPORE (CA136393), National Cancer Institute (RO1 CA184502). Note: This abstract was not presented at the meeting. Citation Format: Kunal A. Lodhia, Marc A. Becker, Xiaonan Hou, Kimberly R. Kalli, Maria I. Harrell, Elizabeth M. Swisher, John S. Weroha, Paul Haluska. Characterization of 148 ovarian cancer tumografts (Avatars) using BROCA-HR deep sequencing. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1474. doi:10.1158/1538-7445.AM2015-1474