Transformation-defective adenovirus 5 E1A mutants exhibit antioncogenic properties in human BLM melanoma cells

Adenoviral E1A proteins exhibit a strong tumor-suppressive activity in huma n tumor cells. However, E1A is capable of transforming rodent and human cel ls in cooperation with other oncoproteins, such as activated RAS. Thus, the therapeutic use of wild-type E1A harbors the principal risk of enhancing t umor malignancy. This prompted us to construct E1A 13S cDNA-derived mutants that were unable to transform baby mouse kidney cells in cooperation with E1B and to test their tumor-suppressive activity in BLM human melanoma cell s. Anchorage-independent growth in soft agar was reduced for those cell lin es expressing the E1A(delCR2) mutant, which lacks the entire conserved regi on 2 (CR2) sequences, or for cells expressing the E1A(CR3Ex2) mutant, which contains CR3 plus exon 2 sequences. In contrast, cell lines expressing the entire E1A wild-type (E1A(WT)) or only the exon 2 sequences (E1A(Ex2)) gre w like the parental BLM cells. Moreover, inoculation of nude mice with BLM cells or cells expressing E1A(Ex2) revealed large tumors after 2 weeks. In contrast, tumors derived from E1A(delCR2)- or E1A(CR3Ex2)-expressing cells exhibited a substantial delay in tumor growth accompanied by a loss of E1A expression in the outgrown tumors. Cell lines expressing E1A(WT) showed an intermediate phenotype. Thus, expression of CR3 plus exon 2 sequences is su fficient to enhance both the antioncogenic properties and the therapeutic s afety of E1A in our system.