Abstract
BACKGROUND: Interest in immunotherapy for breast cancer is rapidly emerging, and applicable animal models that mimic human cancer are urgently needed for preclinical studies. This study aimed to improve a technique for orthotopic inoculation of syngeneic breast cancer cells to be used as a preclinical animal model for immunotherapy. MATERIALS AND METHODS: We used our previously reported murine model of orthotopic cancer cell inoculation under direct vision and compared the efficiency of tumorigenesis with tumor cells suspended in either phosphate-buffered saline or Matrigel containing varying numbers of cells. As a model for immune rejection, murine BALB/c-derived 4T1-luc2 breast cancer cells were inoculated orthotopically into both BALB/c and C57BL/6 mice. RESULTS: Matrigel-suspended cells formed larger tumors with higher efficiency than phosphate-buffered saline-suspended cells. The maximum volume of Matrigel that could be inoculated without spillage was 20 μL and 30 μL in the #2 and #4 mammary fat pads, respectively. Tumor take rates increased as the injected cell number increased. In this immune rejection model, there were no significant differences in tumor weight between the strains up to day 7, after which tumor weight decreased in C57BL/6 mice. Bioluminescence in C57BL/6 mice was also significantly less than that in BALB/c mice and increased up to day 7, then swiftly decreased thereafter. CONCLUSIONS: This improved technique of innoculating murine breast cancer cells using bioluminescence technology may be useful in evaluating the efficacy of tumor regression mediated by immune responses, as shown by an allogeneic response in C57BL/6 mice.