Evaluation of arginine deiminase treatment in melanoma xenografts using (18)F-FLT PET

This study aims to develop a molecular imaging strategy for response assessment of arginine deiminase (ADI) treatment in melanoma xenografts using 3'-[(18)F]fluoro-3'-deoxythymidine ([(18)F]-FLT) positron emission tomography (PET).F-FLT response to ADI therapy was studied in preclinical models of melanoma in vitro and in vivo. The molecular mechanism of response to ADI therapy was investigated, with a particular emphasis on biological pathways known to regulate (18)F-FLT metabolism.Proliferation of SK-MEL-28 melanoma tumors was potently inhibited by ADI treatment. However, no metabolic response was observed in FLT PET, presumably based on the known ADI-induced degradation of PTEN, followed by instability of the tumor suppressor p53 and a relative overexpression of thymidine kinase 1, the enzyme mainly responsible for intracellular FLT processing.The specific pharmacological properties of ADI preclude using (18)F-FLT to evaluate clinical response in melanoma and argue for further studies to explore the use of other clinically applicable PET tracers in ADI treatment.