Saporin 6 and lonidamine in primary cell cultures from human breast carcinomas: a synergistic effect.

Lonidamine (LND) is a potential chemotherapeutic agent which can positively modulate the efficacy of several antineoplastic agents. The ribosome-inactivating protein Saporin 6 (SO 6), which acts as a rRNA N-glycosidase and a DNA nuclease, has recently attracted interest as a novel potential anticancer and antiviral agent. Synergism between LND and SO 6 was previously demonstrated by us in the human metastatic MAST breast cancer cell line in vitro. In the present study, the antiproliferative effect of the drugs, either alone or in combination, was investigated in vitro at various concentrations in 17 primary cell cultures established from patients carrying infiltrating ductal carcinomas of the breast. Results indicate a strong synergistic effect in 11/17 cases, when LND was administered as a second drug. This is in agreement with previous results in the MAST cell line. Synergism was evident at SO 6 concentrations between 3.3 x 10(-10) and 1.7 x 10(-9) M.