[Synergistic antitumor activity of human breast cancer immunotoxins].

Three anti-breast carcinoma monoclonal antibodies 317G5, 260F9 and 741F8 linked to ricin A chain (rRTA) were selected for the present investigation. Attempts were made to understand the relative efficiency of these immunotoxins in relation to: a) binding, b) internalization, and c) clonogenic suppression of breast cancer cells in vitro. The results indicated that 317G5-rRTA combined with 260F9-rRTA had synergistic antitumor activity against SKBr3 breast carcinoma cell line. Individually, 10 micrograms/ml 260F9-rRTA or 317 G5-rRTA alone could only eliminate 2-3 logs of clonogenic SKBr3 cells. When used in combination, 260F9-rRTA and 317G5-rRTA, 1 microgram/ml each, could kill 4 logs of clonogenic tumor cells. The mechanism of the synergistic action is discussed.