A novel targeting modality to enhance adenoviral replication by vitamin D₃ in androgen-independent human prostate cancer cells and tumors

We report the development of a novel replication-competent adenoviral vector, Ad-hOC-E1, containing a single bidirectional human osteocalcin (hOC) promoter to drive both the early viral E1A and E1B gene. This vector selectively replicated in OC-expressing but not non-OC-expressing cells, with viral replication enhanced at least 10-fold on vitamin D₃ exposure. Both the artificial TATA-box and hOC promoter element in this bidirectional promoter construct were controlled by a common OC regulatory element which selectively activated OC expression in cells. The expression of E1A and E1B gene by Ad-hOC-E1 can be markedly induced by vitamin D₃. Unlike Ad-sPSA-E1, an adenoviral vector with viral replication controlled by a strong super prostate-specific antigen (sPSA) promoter which only replicates in PSA-expressing cells with androgen receptor (AR), Ad-hOC-E1 retarded the growth of both androgen-dependent and androgen-independent prostate cancer cells irrespective of their basal level of AR and PSA expression. A single i.v. administration of 2 × 10⁹ plaque-forming units of Ad-hOC-E1 inhibited the growth of previously established s.c. DU145 tumors (an AR- and PSA-negative cell line). Viral replication is highly enhanced by i.p. administration of vitamin D₃. Ultimately, enhancing Ad-hOC-E1 viral replication by vitamin D₃ may be used clinically to treat localized and osseous metastatic prostate cancer in men.