Abstract 598: Use of fluorescent imaging to monitor drug responses in mouse models of tumorigenesis.
Authors: Balderstone Lucy A. , Muir Morwenna , Welman Arkadiusz , Serrels Alan , Wedge Stephen R. , Brunton Val 
Published: August 2014

Abstract
As our understanding of the complexities of cancer biology has increased, the ability to exploit unique features of tumour cells with molecularly targeted therapies has become a reality. However, intrinsic and acquired resistance to these agents means their full potential is not being reached, and despite unprecedented volumes of new molecules in clinical trials, the number of highly efficacious drugs approved by the regulatory authorities remains disappointingly low. The frequent emergence of resistance mechanisms, necessitates better preclinical platforms to be able to prospectively identify and optimise relevant combination strategies.
Fluorescence imaging is a potentially powerful modality for preclinical drug development, and the production of fluorescent cell death imaging agents would be a valuable tool. A novel in house reporter construct identifying cells undergoing caspase mediated cell death, namely apoptosis, has been generated (pCasFSwitch). Validation of pCasFSwitch in stably transfected squamous carcinoma cells revealed a consistent kinetic profile of caspase activity upon staurosporine treatment. Specificity studies using caspase inhibitors demonstrated that the construct was specific for cleavage by caspases, and was not cleaved by other members of the cysteine protease family. With activity confirmed, pCasFSwitch will be utilized to explore drug efficacy in a mouse model of breast carcinogenesis, driven by overexpression of the human epidermal growth factor receptor 2 (HER2) oncogene coupled with / without the loss of the phosphatase and tensin (PTEN) tumour suppressor. Multifocal tumours arose in mice from both lines and displayed a histopathology consistent with a HER2 type neoplasm. Disruption of PTEN rapidly accelerated tumour onset (from 138 to 82 days) and tumour growth (with the time from tumour onset to maximum tumour size reduced from 38 to 21 days), significantly reducing overall survival (from 165 to 102 days).
Tumours arising in both mouse genotypes have been utilized to generate cell lines, which have been stably transfected with pCasFSwitch. Growth of these cells is currently being established in vivo, with a view to examining tumours by intravital imaging. Since PTEN loss is associated with resistance to the HER2 targeted therapy Herceptin, these cell lines will be used to identify drugs that are suitable for combination with HER2 directed therapies and which promote tumour cell apoptosis. Utilizing this model, combination sequencing will be further optimized in vivo through the use of temporal reporter imaging. Collectively, this integration of mouse tumour models and imaging represents an advanced preclinical strategy for examining therapeutic response.
Citation Format: Lucy A. Balderstone, Morwenna Muir, Arkadiusz Welman, Alan Serrels, Stephen R. Wedge, Val Brunton. Use of fluorescent imaging to monitor drug responses in mouse models of tumorigenesis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 598. doi:10.1158/1538-7445.AM2013-598