Adenovirus-mediated p53 gene therapy inhibits human sarcoma tumorigenicity

Mutations of the p53 tumor-suppressor gene are the most frequent genetic ab normality in soft tissue sarcomas, Because these rare rumors also respond p oorly to standard chemotherapy and bear a 50% 5-year mortality rate, we inv estigated the possible therapeutic benefits of p53 gene restoration in sarc omas. We constructed Ad5pS3, which is an E1A-deleted, replication-deficient adenovirus expressing a cytomegalovirus promoter-driven wild-type p53 cDNA with a Flag sequence tag. SKLMS-1 human leiomyosarcoma cells containing a mis-sense p53 point mutation were effectively transduced with Ad5p53. Incre asing levels of Flag-p53 protein, as well as dose-dependent p21(Cip1) induc tion, were observed through a dose range of 10-500 plaque-forming units (PF U)/cell. in vitro administration of Ad5p53 as a single 100 PFU/cell dose ca used 40-60% growth inhibition of SKLMS-1 cells at posttreatment days 4, 6, and 8 compared with untreated or viral control treated-cells (P < .05, Stud ent's t test). Relative to these same controls, in vivo treatment of SKLMS- 1-bearing severe combined immunodeficient mice with 6 x 10(9) PFU of Ad5p53 by intratumoral injection resulted in a 35-day tumor growth delay and comp lete tumor regression in 40% of mice (P < .05, Student's t test). The expre ssion of virally derived p53 mRNA in Ad5p53-treated tumor tissues was detec ted in treated tumor specimens by reverse transcriptase polymerase chain re action. Reduced intratumoral cellularity and the presence of p53 staining i n adjacent normal tissue, consistent with delivery of exogenous p53 to the tumor target, were evident only in Ad5p53-treated tumors after immunohistoc hemical staining for p53. These results indicate that wild-type p53 gene re storation in sarcomas retards tumor growth and may come to be usefully appl ied to the clinical treatment of this disease as a single regimen or in com bination with conventional therapies.