Using curcumin to turn the innate immune system against cancer

Curcumin has been at the center of vigorous research and major debate during the past decade. Inspired by its anti-inflammatory properties, many curcumin-based products are being sold now to manage various forms of arthritis. Parallel preclinical studies have established its role in dissolving beta-amyloid plaques, tau-based neurofibrillary tangles, and also alpha-synuclein-linked protein aggregates typically observed in Parkinson's disease. In cancer research, most cancer cells in culture are eliminated by curcumin at an IC50 of 15-30 µM, whereas the maximum in vivo curcumin concentration achieved in humans is only about 6 µM. Additionally, a decade ago, no improvement over the placebo groups was observed in clinical studies using free curcumin as an anticancer agent. The lack of anticancer efficacy was attributed to its low bioavailability, which results from the low water-solubility and high metabolic rate in vivo. Newer lipid-complexed or antibody-targeted forms have been used and these studies have revealed an exciting property of curcumin, which involves repolarization of the tumor-promoting, tumor-associated microglia/macrophages (TAMs) into a tumoricidal form and recruitment of natural killer cells from the periphery. This review will cover some efforts to explore the effect of appropriately-delivered curcumin to dramatically alter the tumor microenvironment, thereby launching an indirect attack on the tumor cells and the tumor stem cells. Reviewing some aspects of immunotherapy, this article will argue for the use of the innate immune cells in cancer therapy.