Activity of a mycobacterial antineoplastic glycan against human breast cancer

Attenuated Mycobacterium bovis, Bacillus Calmette Guerin, BCG vaccine, is a general immune stimulant and is now an approved clinical treatment for superficial bladder cancer. Isolation and characterization of a series of complex polysaccharides (glycans) from BCG and other mycobacteria has shown that these materials are remarkably heat stable and have considerable in vivo activity against a number of animal cancer models. This present communication describes the testing of a glycan, PS1, obtained from the Tice substrain of BCG against the hormonal dependent human breast cancer cell line MCF-7 and the hormonally independent BT-20 line, using 5-fluorouracil (5-FU) as a positive control.

The PS1 was obtained by methods previously described. Cells were obtained from the American Type Culture Collection (Rockville, MD) and athymic nu/nu mice from Frederick (MD). The cells were implanted into the flanks of 20g female nude mice (n = 10). After two weeks, volumes of phosphate buffered saline (control), 5-FU (positive control) or PS1 solutions were injected and the tumor growth rates followed for up to six weeks.

The 5-FU was effective in slowing tumor growth of both tumors. The MCF-7 cell line was markedly affected by the PS1, especially in the presence of estradiol. The BT-20 cell line was only marginally affected by PS1, with or without estradiol.

Since PS1 is known to have macrophage stimulating activity and nude mice are deficient in both T-cells and natural killer cells, the mechanism of activity is postulated to involve MHC-1 antigen secretion by the hormonal-dependent tumor cells, enhanced in the presence of hormone. These cells are then actively identified and destroyed by local macrophages.