Effects of the Bowman-Birk inhibitor on clonogenic survival and cisplatin-or radiation-induced cytotoxicity in human breast, cervical, and head and neck cancer cells

Bowman-Birk inhibitor (BBI) is a soybean-derived anticarcinogenic protease inhibitor previously shown to potentiate cisplatin-induced cytoxicity in hu man lung and ovarian cancer cells. To further assess the potential of BBI a s a sensitizing agent for cancer radiotherapy and chemotherapy, we evaluate d the effects of BBI and a soybean concentrate enriched in BBI known as BBI concentrate (BBIC) on clonogenic survival and radiation- or cisplatin-indu ced cell killing in MCF7 human breast carcinoma cells, SCC61 and SQ20B huma n head and neck carcinoma cells, HeLa, HeLa-R1, and HeLa-R3 human cervical carcinoma cells, MCF10 nontumorigenic human epithelial cells, HTori-3 nontu morigenic human thyroid epithelial cells, and C3H10T1/2 mouse fibroblast ce lls. BBI and BBIC significantly sup pressed the clonogenic survival of MCF7 and SCC61 cells. BBIC also suppressed the survival of SQ20B cells and enha nced radiation-induced cell killing in SCC61 and SQ20B cells and cisplatin- induced cell killing in HeLa, HeLa-R1, and HeLa-R3 cells. In contrast, BBI and/or BBIC did not enhance radiation-induced cell killing in MCF10 cells o r cisplatin-induced cell killing in C3H10T1/2 cells. BBI did nor significan tly affect the survival of SQ20B cells or enhance radiation-induced cell ki lling in SCC61 and SQ20B cells. The clonogenic survivals of MCF10 and C3H10 T1/2 cells were not adversely affected by treatment with BBI or BBIC. The c lonogenic survival of HTori-3 cells was only moderately suppressed by treat ment with BBIC at greater than or equal to 80 mu g/ml. These results sugges t that BBIC could be a useful agent for the potentiation of radiation- and cisplatin-mediated cancer treatment without significant adverse effects on surrounding normal tissues.