CYTOTOXIC EFFECT OF A FUSION PROTEIN FROM TRANSFORMING GROWTH-FACTOR-ALPHA AND PSEUDOMONAS EXOTOXIN ON RAT AND HUMAN BLADDER-CARCINOMA CELLS IN-VITRO

A protein formed by fusion of transforming growth factor alpha with Pseudomonas exotoxin (TGFalpha-PE40) has been shown to have the ability to kill or inhibit the growth of several carcinoma cell lines. This study was designed to evaluate the in vitro cytotoxic effects of TGFalpha-PE40 on rat and human bladder carcinoma cell lines with different biological potential, and normal rat urothelial cells. The rat cell lines used were D44c, LMC19, and MYU3L, which were established in our laboratory. Human cell lines used were RT4, T24, and 253J. As a normal control, we used the first-passage culture of normal rat bladder urothelium (RU-P1). We examined the number and affinity of epidermal growth factor receptors (EGFR) in these cells, the ability of TGFalpha-PE40 to bind EGFR, and the cytotoxic effect of TGFalpha-PE40 and PE40. Rat cell lines, D44c, LMC19, and MYU3L (EGFR = 4.9 x 10(3)-11.4 x 10(3)/cell) had ED50 values (the concentration of TGFalpha-PE40 needed to reduce the viable cell population by 50%) of 180 pM, 540 pM and 6000 pM respectively; for c(I) (the concentration required to achieve complete inhibition of growth under continuous serum stimulation) TGFalpha-PE40 concentrations of 10(4) pM, 10(4) pM and higher than 10(4) pM respectively were required. Human cell lines, RT4, T24, and 253J (EGFR = 32 x 10(3) 126 x 10(3)/cell) had ED50 values of 20 pM, 66 pM, and 330 pM respectively and T24 showed c(I) values of 10(3) pM. RU-P1 (EGFR = 92.6 x 10(3)/cell) had the highest ED50 value of 8000 pM. These data indicate that the susceptibility to TGFalpha-PE40 does not always depend on the number of EGFR, that cells having a relatively small number of EGFR respond well to TGFalpha-PE40, and that normal urothelial cells are more resistant to TGFalpha-PE40 than are cancer cells. The differential effect of TGFalpha-PE40 on normal and neoplastic cells provides a rational basis for its use in vivo to control tumor growth.