Carboxylesterase 2-Engineered Stem Cell Therapy Shows Superior Efficacy over Cytosine Deaminase in Castration-Resistant Prostate Cancer.

Purpose: Castration-resistant prostate cancer (CRPC) responds poorly to conventional chemotherapy. We evaluated a cell-based enzyme-prodrug therapy using adipose-derived stem cells (ADSCs) engineered to express cytosine deaminase (CD) or carboxylesterase 2 (CE2), paired with their respective prodrugs 5-fluorocytosine (5-FC) or irinotecan (CPT-11), to compare their antitumor efficacy. Materials and

Methods

Human telomerase reverse transcriptase (hTERT)-immortalized ADSCs were transduced with CD or CE2, and transgene expression and stem cell phenotype were confirmed. CD expression was verified at the transcript level and by functional 5-FC-to-5-fluorouracil (5-FU) conversion, whereas CE2 expression was verified by transcript analysis and immunoblotting. Tumor tropism toward PC3 prostate cancer cells was tested using migration assays and analysis of chemoattractant ligand/receptor expression. Prodrug-induced self-killing and bystander tumor cell killing were assessed through viability assays and co-culture with PC3 cells. For the CE2/CPT-11 system, SN-38 was not directly quantified; functional activity was inferred from prodrug-dependent cytotoxicity and in vivo efficacy. In vivo efficacy was evaluated in nude mice with PC3 tumors treated systemically with engineered ADSCs plus prodrug.

Results

CD- and CE2-expressing ADSCs were successfully established and retained mesenchymal stem cell (MSC) characteristics. Both cell types exhibited significant migration toward PC3 cells. The CE2/CPT-11 system produced stronger prodrug-mediated cytotoxicity than CD/5-FC, with CE2-modified ADSCs showing higher sensitivity to CPT-11 and inducing greater apoptosis in co-cultured PC3 cells. In vivo, both treatments suppressed tumor growth, but CE2/CPT-11 achieved greater inhibition (tumor volume ~26% of control vs. ~32% for CD/5-FC at day 14). No overt clinical toxicity was observed based on body weight and daily clinical monitoring; however, hematology/serum chemistry were not assessed.

Conclusions

Engineered ADSCs home to CRPC tumors and enable local prodrug activation, producing significant antitumor effects. Within the constraints of our in vitro assays and subcutaneous xenograft model, CE2/CPT-11 demonstrated stronger efficacy outcomes than CD/5-FC. Mechanistic attribution to intratumoral SN-38 exposure should be confirmed by direct metabolite measurements in future studies.