The Immune System As a New Possible Cell Target for AFP 464 in a Spontaneous Mammary Cancer Mouse Model

Abstract

Aminoflavone (AFP 464, NSC 710464), an antitumor agent which recently entered phase II clinical trials, acts against estrogen-positive breast cancer (ER +). AFP 464, which has a unique mechanism of action by activating aryl hydrocarbon receptor (AhR) signaling pathway, decreased tumor size and growth rate in the estrogen dependent, Tamoxifen-sensitive spontaneous M05 mouse model. Considering that AhR has recently emerged as a physiological regulator of the innate and adaptive immune responses, we investigated whether AFP 464 modulates the immune response in our mouse model. Studies on the effect of AFP 464 on the immune system were carried in BALB/c mice bearing M05 semi-differentiated mammary adenocarcinomas that express estrogen and progesterone receptors. Splenic cells and tumor inflammatory infiltrates were studied by cytometric analyses. The modulation of splenocytes cytotoxic activity by AFP 464 was also evaluated. We further investigated the effects of AFP 464 on peritoneal macrophages by evaluating metalloproteinase, arginase and iNOS activities. We found that AFP 464 increased splenic cytotoxic activity, diminished the number of systemic and local Treg lymphocytes and MDSCs, and induced a M1 phenotype in peritoneal macrophages of M05 tumor bearing mice. Therefore, we conclude that AFP 464 modulates immune response which collaborates with its anti-tumor activity. Our results place the immune system as a novel target for this anti-cancer agent to strengthen the rationale for its inclusion in breast cancer treatment regimens.