Abstract 2685: Targeting TGFβ signaling pathways in bone metastatic breast cancer cells to limit metastatic progression using curcuminoids, a turmeric-derived natural product

Tumor-cell TGFβ signaling has been demonstrated to drive osteolytic breast cancer bone metastases (BrCa BMET) in mouse models. This established an important link between the microenvironment and tumor cells in bone, wherein osteoclast-mediated bone resorption stimulates the release of TGFβ from bone matrix, which induces tumoral secretion of osteolytic factors, such as parathyroid-related protein (PTHrP) that drive further osteoclast-mediated bone destruction in a positive feedback loop. These findings have prompted interest in the use of pharmacologic TGFβ inhibitors, currently under development, for the treatment of BrCa BMET. Interestingly, studies have demonstrated antagonistic effects of a natural product, turmeric-derived polyphenols called curcuminoids (CURC), on BrCa BMET progression and TGFβ-inducible, Smad-dependent signaling in a TGFβ-dependent human xenograft model (human MDA-MB-231 [MDA-SA]).The studies described here were undertaken to determine whether this inhibitory effect is generalizable to other BrCa cells that form TGFβ-dependent BMETs (human MDA-1833 and MDA-2287; murine 4T1) and to begin to elucidate the mechanism by which CURC block BrCa cell TGFβ signaling. Analogous to prior findings using MDA-SA cells forming BMET that are dependent on TGFβ-inducible tumoral secretion of PTHrP via Smad and non-Smad (specifically, p38) dependent pathways, CURC inhibited TGFβ inducible activation (phosphorylation) of receptor Smad2 (Western) in all TGFβ-dependent BrCa cell lines tested.In MDA-SA cells, CURC inhibition of TGFβ-stimulated Smad2 phosphorylation was time- and dose-dependent (Western), and associated with decreased expression of a Smad-dependent luciferase reporter gene in transiently transfected cells. In both MDA-SA and 4T1 cells, these changes were accompanied by decreased TGFβ-stimulated PTHrP secretion (RIA). These effects in MDA-SA cells were not associated with changes in the expression of canonical TGFβ signaling proteins, such as Smad anchor for receptor activation (SARA), which is involved in Smad phosphorylation, or Smad4, a required cofactor for Smad-mediated gene transcription. Also unchanged were noncanonical TGFβ-stimulated, Smad-independent signaling pathways (e.g., p38, ERK1/2 or JNK). Of note, however, in all cell lines tested, CURC inhibition of Smad2 phosphorylation was accompanied by a decrease in constitutive Smad2 levels, with variable decreases in the ratio of phosphorylated vs. total Smad levels. These results suggest that CURC can specifically and uniformly inhibit Smad-regulated TGFβ signaling in bone metastatic BCa cells forming TGFβ-dependent osteolytic lesions, an effect that may be mediated, at least in part, by changes in constitutive levels of receptor-regulated Smad expression. Citation Format: Andrew Kunihiro, Julia A. Brickey, Jen B. Frye, Janet L. Funk. Targeting TGFβ signaling pathways in bone metastatic breast cancer cells to limit metastatic progression using curcuminoids, a turmeric-derived natural product [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2685.