Concomitant expression of urokinase type plasminogen activator (uPA) and its surface receptor (uPAR) has been shown to correlate strongly with a more invasive tumor cell phenotype. A highly malignant human epidermoid carcinoma cell line (HEp3) was transfected with a vector capable of expressing an antisense transcript complementary to 300 bases of the 5' end of uPAR, including the ATG codon. Six stably transfected antisense (AS-2, 3, 5, 9, 10, 12) and eight control clones were characterized. All clones produced high levels of uPA activity. Examination of collagenase production and doubling time showed that all of the clones tested produced similar activities. The antisense clones showed a 20-74% reduction in the uPAR sites; the uPAR mRNA level was also reduced. A test of the invasive ability of all clones in a modified chorioallantoic membrane (CAM) showed that invasiveness of the antisense-inhibited clones was directly proportional to the density of surface uPAR. The AS-2 clone, which expressed the lowest number of uPARs showed a significantly reduced level of invasion. The invasiveness of additional AS-inhibited clones was also reduced. Seven control and four AS-inhibited clones were tested for tumorigenicity on CAMs of chick embryos. Inoculation of control cells produced large tumors, while the As clones were non-tumorigenic. AS-2 did not produce tumors even if kept in vivo for up to 10 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)