Immunotherapy of BALB/c mice bearing Ehrlich ascites tumor with vitamin D-binding protein-derived macrophage activating factor

Abstract

Vitamin D3-binding protein (DBP; human DBP is known as Gc protein) is the precursor of macrophage activating factor (MAF). Treatment of mouse DBP with immobilized β-galactosidase or treatment of human Gc protein with immobilized β-galactosidase and sialidase generated a remarkably potent MAF, termed DBPMAF or GcMAF, respectively. The domain of Gc protein responsible for macrophage activation was cloned and enzymatically converted to the cloned MAF, designated CdMAF. In Ehrlich ascites tumor-bearing mice, tumor- specific serum α-N-acetyl-galactosaminidase (NaGalase) activity increased linearly with time as the transplanted tumor cells grew in the peritoneal cavity. Therapeutic effects of DBPMAF, GcMAF, and CdMAF on mice bearing Ehrlich ascites tumor were assessed by survival time, the total tumor cell count in the peritoneal cavity, and serum NaGalase activity. Mice that received a single administration of DBPMAF or GcMAF (100) pg/mouse) on the same day after transplantation of tumor (1 x 105 cells) showed a mean survival time of 35 ± 4 days, whereas tumor-bearing controls had a mean survival time of 16 ± 2 days. When mice received the second DBPMAE or GcMAF administration at day 4, they survived more than 50 days. Mice that received two DBPMAF administrations, at days 4 and 8 after transplantation of 1 x 105 tumor cells, survived up to 32 ± 4 days. At day 4 posttransplantation, the total tumor cell count in the peritoneal cavity was approximately 5 x 105 cells. Mice that received two DBPMAF administrations, at days 0 and 4 after transplantation of 5 x 105 tumor cells, also survived up to 32 ± 4 days, while control mice that received the 5 X 105 ascites tumor cells only survived for 14 ± 2 days. Four DBPMAF, GcMAF, or CdMAF administrations to mice transplanted with 5 x 105 Ehrlich ascites tumor cells with 4-day intervals showed an extended survival of at least 90 days and an insignificantly low serum NaGalase level between days 30 and 90.