A novel attenuated replication-competent adenovirus for melanoma therapy

To generate a replication-competent adenovirus (Ad) with specificity for melanoma, we constructed a tissue-specific promoter restricting E1A expression to melanoma cells. The combination of four copies of a mouse tyrosinase enhancer element (TE) fused to the human tyrosinase promoter (TP) yielded up to 2000-fold higher luciferase reporter activity in tyrosinase-expressing melanoma cells than in nonmelanoma cells. Insertion of the composite TETP construct upstream of the E1A gene was combined with deleting as far as possible the intertwined endogenous Ad enhancer/promoter (EP). The resulting AdDeltaEP-TETP vector, also deleted for the E3 region, was found to replicate in tyrosinase-positive melanoma cells, such as SK-Mel23 as efficiently as wild-type Ad5, but at a more than 50-fold reduced level in nonmelanoma tumour cells and primary human cells. Injection of AdDeltaEP-TETP into xenotransplanted melanomas, but not into HeLa-derived tumours led to long-lasting tumour regression in nude mice. This AdDeltaEP-TETP virus might be useful for the treatment of accessible lesions in advanced melanoma patients.