Use of Green Fluorescent Protein (GFP)-imaging to visualise in vivo responses to the anti-tumour agent TRAIL


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Neil Cross1, Anne Fowles2, Jenny Lippitt2, Srdjan Hamdy2, Freddie Vitovski2, Colby Eaton2

1Sheffield Hallam University, Sheffield, UK, 2University of Sheffield, UK

Abstract

Background

Tumour Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) is a potential anti-cancer agent due to its selective activity on tumour cells, but not normal cells. TRAIL/Death Receptor-4/5 agonist-based therapies are currently in clinical trials, however insensitivity to TRAIL occurs in many tumours. Furthermore, our in vitro studies demonstrate that TRAIL resistant populations exist within cell lines, such as PC3, which are considered TRAIL sensitive (Cross et al, J Cell Biochem, 2008;104(4):1452-64). In this study, we have used the generally TRAIL sensitive PC3 prostate cancer cell line as a model system to investigate TRAIL responses in vivo using a Green Fluorescence Protein (GFP) imaging-based approach.

Method

PC3 cells were transfected with GFP and injected into the bone marrow cavity (intratibial injection), or by sub-cutaneous (SC) injection, in nude mice. Tumour burden was assessed by GFP-imaging using a Lightools illumination system. GFP signal was monitored daily after TRAIL treatment of 6mg/kg i.p. daily for 3 days, or 0.5ug injected locally around SC tumours.

Results

Tumours of 1mm diameter in bone, and non-palpable SC tumours, were both visible using GFP imaging of live animals. Injection of TRAIL (i.p.) induced complete loss of signal in 1/6 intratibial tumours and partial regression observed in one tumour. TRAIL (i.p.) did not affect any SC tumours (n=8). SC injection of TRAIL (0.5ug) near the SC tumour site resulted in apparent complete regression of 2/12 tumours, one of which returned after 4 weeks without TRAIL treatment. Most tumours (10/12) responded initially, and many continued grow despite subsequent TRAIL treatments.

Conclusion

GFP imaging can be used to visualise responses to anti-tumour agents, such as TRAIL, at internal sites in live animals. PC3 prostate cancer cells are generally TRAIL sensitive in vitro, however pre-existing TRAIL-insensitive populations result in rapid emergence of TRAIL-resistant tumour cell growth both in vitro and in vivo.