Mutated in multiple advanced cancers 1/phosphatase and tensin homologue (MMAC1/PTEN) is a novel tumor suppressor gene candidate located on chromosome 10 that is commonly mutated in human glioblastoma multiforme and several other cancer types. To evaluate the function of this gene as a tumor suppressor, we constructed a replication-defective adenovirus (MMCB) for efficient, transient transduction of MMAC1 into tumor cells. Infection of MMAC1-mutated U87MG glioblastoma cells with MMCB resulted in dose-dependent exogenous MMAC1 protein expression as detected by Western blotting of cell lysates. In vitro prliferation of U87MG cells was inhibited by MMCB in comparison to several control adenoviruses at equal viral doses, implying a specific effect of MMAC1 expression. Anchorage-independent growth in soft agar was also inhibited by MMCB compared to control adenovirus. Tumorigenicity in nude mice of transiently transduced mass cell cultures was then assessed. MMCB-infected U87MG cells were almost completely nontumorigenic compared to untreated and several control adenovirus-treated cells at equal viral doses. These data support an in vivo tumor suppression activity of MMAC1/PTEN and suggest that in vivo gene transfer with this recombinant adenoviral vector has a potential use in cancer gene therapy.