Abstract P6-18-01: Site-specific activation of curcuminoids in the breast cancer bone metastases microenvironment

Abstract

Abstract The majority of women with advanced breast cancer (BCa) develop incurable osteolytic bone metastases. Our laboratory has previously demonstrated that curcuminoids, bioactive compounds isolated from turmeric rhizomes, prevent the development of lytic bone lesions in a murine xenograft model of human BCa bone metastasis and inhibit tumor cell secretion of TGFβ-stimulated parathyroid-related protein (PTHrP), a signaling pathway known to drive bone metastasis progression. In both humans and mice, glucuronidated phase II metabolites of curcumin, which are thought to be biologically inactive, are the primary form detected in circulation after consuming curcuminoid-containing foods or supplements. This has led to an untested postulate that curcuminoids may be deglucuronidated at sites of action to form bioactive, aglycone (free) curcumin. Studies were therefore undertaken to test this hypothesis in the context of the murine BCa bone metastasis model, assessing site-specific deconjugation of curcuminoids in the tumor-bone microenvironment. Effects of curcumin-glucuronide (G-CURC) vs. curcumin (CURC) on TGFβ-stimulated PTHrP secretion by bone-tropic MDA-MB-231 (MDA) cells was determined by immunoradiometric assay. G-CURC and CURC levels were quantified by LC-MS in plasma and bone marrow specimens isolated from curcuminoid-treated female nude mice. Endogenous β-glucuronidase enzyme expression was localized by immunohistochemical (IHC) staining in paraffin-embedded sections of decalcified, MDA metastases-containing hind limbs of nude mice inoculated, via intracardiac injection 21 days prior, with MDA cells. Glucuronide deconjugation activity of bone marrow lysates was determined by colorimetric assay. In contrast to the inhibitory effects of a naturally occurring curcuminoid mixture or pure CURC, G-CURC did not alter TGFβ-stimulated PTHrP secretion, confirming its postulated lack of biologic activity. In mice treated with curcuminoids, the majority of circulating curcumin was conjugated (91%). In contrast, the majority of curcumin in the bone marrow (56%) was unconjugated free (aglycone) curcumin (p <0.01). IHC staining of MDA tumor-bearing hind limbs of nude mice demonstrated expression of β-glucuronidase (GUSB), an enzyme that deconjugates compounds in mice and humans, by bone marrow cells, but not by tumor cells. Consistent with IHC, bone marrow from female nude mice displayed significantly higher (30-fold) deconjugation enzyme activity compared to MDA cells (p < 0.01). Female C3H/HeJ mice, which possess a partial loss-of-function mutation in the GUSB gene, had significantly decreased (66% lower) deconjugation enzyme activity compared to normal female C57BL/6 (p < 0.001) or nude (p < 0.01) mice. In addition, treatment with the β-glucuronidase inhibitor, saccharolactone (SL), also decreased deconjugation enzyme activity in marrow lysates from female nude mice. These results suggest that curcuminoids, in the setting of breast cancer bone metastases, may act as a pro-drug, becoming activated within the tumor-bone microenvironment by glucuronidase-expressing hematopoietic bone marrow cells, to limit the progression of osteolytic lesion formation in a murine model of BCa bone metastasis. Supported by: R01CA174926-01, R01AT006896, and R03CA159382. Citation Format: Kunihiro AG, Frye JB, Brickey JA, Luis PB, Schneider C, Funk JL. Site-specific activation of curcuminoids in the breast cancer bone metastases microenvironment [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-18-01.