The use of Trichomonas vaginalis purine nucleoside phosphorylase to activate fludarabine in the treatment of solid tumors

In this study, we investigated a panel of naturally occurring PNPs to identify more efficient enzymes that may be suitable for metabolizing F-araA as part of experimental cancer therapy. We show thatTrichomonas vaginalis PNP (TvPNP) cleaves F-araA with a catalytic efficiency 25-fold greater than the prototypicE. coli enzyme. Cellular extracts from human glioma cells (D54) transduced with lentivirus stably expressingTvPNP (D54/TvPNP) were found to cleave F-araA at a rate similar to extracts from D54 cells expressingEcPNP, although much less enzyme was expressed per cell in theTvPNP transduced condition. As a test of safety and efficacy usingTvPNP, human head and neck squamous cell carcinoma (FaDu) xenografts expressingTvPNP were studied in nude mice and shown to exhibit robust tumor regressions, albeit with partial weight loss that resolved post-therapy. F-araAMP was also a very effective treatment for mice bearing D54/TvPNP xenografts in which approximately 10% of tumor cells expressed the enzyme, indicating pronounced ability to kill non-transduced tumor cells (high bystander activity). Moreover, F-araAMP demonstrated activity against D54 tumors injected with an E1, E3 deleted adenoviral vector encodingTvPNP. In that setting, despite higher F-araA cleavage activity usingTvPNP, tumor responses were similar to those obtained withEcPNP, indicating factors other than F-Ade production may limit regressions of the D54 murine xenograft model. Our results establish thatTvPNP is a fa...
Source: Cancer Chemotherapy and Pharmacology - Category: Cancer & Oncology Source Type: research