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.

Phytosomal curcumin causes natural killer cell-dependent repolarization of glioblastoma (GBM) tumor-associated microglia/macrophages and elimination of GBM and GBM stem cells.

BACKGROUND: Glioblastoma (GBM) is a primary brain tumor with a 5-year survival rate of ≤5%. We have shown earlier that GBM-antibody-linked curcumin (CC) and also phytosomal curcumin (CCP) rescue 50-60% of GBM-bearing mice while repolarizing the tumor-associated microglia/macrophages (TAM) from the tumor-promoting M2-type to the tumoricidal M1-type. However, systemic application of CCP yields only sub-IC50 concentrations of CC in the plasma, which is unlikely to kill GBM cells directly. This study investigates the role of CC-evoked intra-GBM recruitment of activated natural killer (NK) cells in the elimination of GBM and GBM stem cells. METHODS: We have used an immune-competent syngeneic C57BL6 mouse model with the mouse-GBM GL261 cells orthotopically implanted in the brain. Using immunohistochemistry and flow cytometry, we have quantitatively analyzed the role of the intra-GBM-recruited NK cells by (i) injecting (i.p.) the NK1.1 antibody (NK1.1Ab) to temporarily eliminate the NK cells and (ii) blocking NK recruitment by injecting an IL12 antibody (IL12Ab). The treatment cohorts used randomly-chosen GL261-implanted mice and data sets were compared using two-tailed t-test or ANOVA. RESULTS: CCP treatment caused the GBM tumor to acquire M1-type macrophages (50-60% of the TAM) and activated NK cells. The treatment also elicited (a) suppression of the M2-linked tumor-promoting proteins STAT3, ARG1, and IL10, (b) induction of the M1-linked anti-tumor proteins STAT1 and inducible nitric oxide synthase in the TAM, (c) elimination of CD133(+) GBM stem cells, and (d) activation of caspase3 in the GBM cells. Eliminating intra-GBM NK cell recruitment caused a partial reversal of each of these effects. Concomitantly, we observed a CCP-evoked dramatic induction of the chemokine monocyte chemotactic protein-1 (MCP-1) in the TAM. CONCLUSIONS: The recruited NK cells mediate a major part of the CCP-evoked elimination of GBM and GBM stem cells and stabilization of the TAM in the M1-like state. MCP-1 is known to activate peripheral M1-type macrophages to secrete IL12, an activator of NK cells. Based on such observations, we postulate that by binding to peripheral M1-type macrophages and IL12-activated NK cells, the brain-released chemokine MCP-1 causes recruitment of peripheral immune cells into the GBM, thereby causing destruction of the GBM cells and GBM stem cells.

TriCurin, a synergistic formulation of curcumin, resveratrol, and epicatechin gallate, repolarizes tumor-associated macrophages and triggers an immune response to cause suppression of HPV+ tumors.

Our earlier studies reported a unique potentiated combination (TriCurin) of curcumin (C) with two other polyphenols. The TriCurin-associated C displays an IC50 in the low micromolar range for cultured HPV+ TC-1 cells. In contrast, because of rapid degradation in vivo, the TriCurin-associated C reaches only low nano-molar concentrations in the plasma, which are sub-lethal to tumor cells. Yet, injected TriCurin causes a dramatic suppression of tumors in TC-1 cell-implanted mice (TC-1 mice) and xenografts of Head and Neck Squamous Cell Carcinoma (HNSCC) cells in nude/nude mice. Here, we use the TC-1 mice to test our hypothesis that a major part of the anti-tumor activity of TriCurin is evoked by innate and adaptive immune responses. TriCurin injection repolarized arginase1high (ARG1high), IL10high, inducible nitric oxide synthaselow (iNOSlow), IL12low M2-type tumor-associated macrophages (TAM) into ARG1low, IL10low, iNOShigh, and IL12high M1-type TAM in HPV+ tumors. The M1 TAM displayed sharply suppressed STAT3 and induced STAT1 and NF-kB(p65). STAT1 and NF-kB(p65) function synergistically to induce iNOS and IL12 transcription. Neutralizing IL12 signaling with an IL12 antibody abrogated TriCurin-induced intra-tumor entry of activated natural killer (NK) cells and Cytotoxic T lymphocytes (CTL), thereby confirming that IL12 triggers recruitment of NK cells and CTL. These activated NK cells and CTL join the M1 TAM to elicit apoptosis of the E6+ tumor cells. Corroboratively, neutralizing IL12 signaling partially reversed this TriCurin-mediated apoptosis. Thus, injected TriCurin elicits an M2→M1 switch in TAM, accompanied by IL12-dependent intra-tumor recruitment of NK cells and CTL and elimination of cancer cells.

Curcumin changes the polarity of tumor-associated microglia and eliminates glioblastoma.

Glioblastoma (GBM) is one of the most pernicious forms of cancer and currently chances of survival from this malady are extremely low. We have used the noninvasive strategy of intranasal (IN) delivery of a glioblastoma-directed adduct of curcumin (CC), CC-CD68Ab, into the brain of mouse GBM GL261-implanted mice to study the effect of CC on tumor remission and on the phenotype of the tumor-associated microglial cells (TAMs). The treatment caused tumor remission in 50% of GL261-implanted GBM mice. A similar rescue rate was also achieved through intraperitoneal infusion of a lipid-encapsulated formulation of CC, Curcumin Phytosome, into the GL261-implanted GBM mice. Most strikingly, both forms of CC elicited a dramatic change in the tumor-associated Iba1+ TAMs, suppressing the tumor-promoting Arginase1high , iNOSlow M2-type TAM population while inducing the Arginase1low , iNOShigh M1-type tumoricidal microglia. Concomitantly, we observed a marked induction and activation of microglial NF-kB and STAT1, which are known to function in coordination to cause induction of iNOS. Therefore, our novel findings indicate that appropriately delivered CC can directly kill GBM cells and also repolarize the TAMs to the tumoricidal M1 state.