IN-VIVO HUMAN CARBOXYLESTERASE CDNA GENE-TRANSFER TO ACTIVATE THE PRODRUG CPT-11 FOR LOCAL TREATMENT OF SOLID TUMORS

To evaluate the concept that in vivo transfer of the human carboxylest erase gene will confer sensitivity of a solid tumor to the prodrug CPT -11 (irinotecan), we constructed an adenovirus vector (AdCMV.CE) carry ing the human carboxylesterase gene driven by the cytomegalovirus (CMV ) promoter, infected A549 human lung adenocarcinoma cells in vitro and in vivo, and evaluated cell growth Dyer time. AdCMV.CE produced a fun ctional carboxylesterase protein in A549 cells in vitro and in vivo as evidenced by ability of lysates from the infected cells to convert CP T-11 to its active metabolite SN-38. The AdCMV.CE vector effectively s uppressed A549 cell growth in vitro in the presence of CPT-11. Cell mi xing studies demonstrated that when as few as 10% of cells expressed t he human carboxylesterase gene, there was bystander growth suppression in the presence of CPT-11. Consistent with these in vitro observation s, when AdCMV.CE was directly injected into established subcutaneous A 549 tumors in nude mice receiving CPT-11, there was 35% reduction in t umor size at day 27 compared to controls, and a 41% reduction at day 3 4 (P < 0.01, both comparisons to controls). Similar observations were made with the cell line H157 and HeLa, These observations suggest that local gene transfer of the human carboxylesterase gene and concomitan t local administration of CP=T-11 may have potential as a strategy for control of the growth of solid tumors.