GAP31 (Gelonium protein of 31 kDa) and MAP30 (Momordica protein of 30 kDa) are agents isolated from the medicinal plants Gelonium multiflorum and Momordica charantia, respectively. The current study was conducted to investigate the efficacy of GAP31 and MAP30 on estrogen-independent and highly metastatic human breast tumor MDA-MB-231 both in vitro and in vivo. The effect of these agents on the expression of breast tumor antigen HER2 (also known as neu or as c-erbB 2) was also examined. Treatment of MDA-MB-231 breast cancer cells with GAP31 and MAP30 resulted in inhibition of cancer cell proliferation as well as inhibition of the expression of HER2 gene in vitro. When MDA-MB-231 human breast cancer cells were transferred into SCID mice, the mice developed extensive metastases and all mice succumbed to tumor by day 46. Treatment of the human breast cancer bearing SCID mice with GAP31 or MAP30 at 10 micrograms/injection EOD for 10 injections resulted in significant increases in survival, with 20-25% of the mice remaining tumor free for 96 days. Thus, anti-tumor agents GAP31 and MAP30 are effective against human breast cancer MDA-MB-231 in vitro and in vivo. These agents may therefore be a potential therapeutic use against breast carcinomas.