Metformin attenuates transforming growth factor beta (TGF-β) mediated oncogenesis in mesenchymal stem-like/claudin-low triple negative breast cancer

Abstract

Mesenchymal stem-like/claudin-low (MSL/CL) breast cancers are highly aggressive, express low cell-cell adhesion cluster containing claudins (CLDN3/CLDN4/CLDN7) with enrichment of epithelial-to-mesenchymal transition (EMT), immunomodulatory, and transforming growth factor-β (TGF-β) genes. We examined the biological, molecular and prognostic impact of TGF-β upregulation and/or inhibition using in vivo and in vitro methods. Using publically available breast cancer gene expression databases, we show that upregulation and enrichment of a TGF-β gene signature is most frequent in MSL/CL breast cancers and is associated with a worse outcome. Using several MSL/CL breast cancer cell lines, we show that TGF-β elicits significant increases in cellular proliferation, migration, invasion, and motility, whereas these effects can be abrogated by a specific inhibitor against TGF-β receptor I and the anti-diabetic agent metformin, alone or in combination. Prior reports from our lab show that TNBC is exquisitely sensitive to metformin treatment. Mechanistically, metformin blocks endogenous activation of Smad2 and Smad3 and dampens TGF-β-mediated activation of Smad2, Smad3, and ID1 both at the transcriptional and translational level. We report the use of ID1 and ID3 as clinical surrogate markers, where high expression of these TGF-β target genes was correlated to poor prognosis in claudin-low patients. Given TGF-β's role in tumorigenesis and immunomodulation, blockade of this pathway using direct kinase inhibitors or more broadly acting inhibitors may dampen or abolish pro-carcinogenic and metastatic signaling in patients with MCL/CL TNBC. Metformin therapy (with or without other agents) may be a heretofore unrecognized approach to reduce the oncogenic activities associated with TGF-β mediated oncogenesis.

Metformin Accumulation Correlates with Organic Cation Transporter 2 Protein Expression and Predicts Mammary Tumor Regression In Vivo

“…Epidemiological studies consistently suggest an anti-cancer effect of metformin in individuals with diabetes, including breast cancer (1-3). A number of preclinical studies of mammary carcinogenesis and in vitro studies using breast cancer cell lines are consistent with this assertion of metformin's beneficial effects (4-9). Even so, other preclinical studies of mammary carcinogenic models failed to see any effect of metformin when the animals were fed a low fat diet and exhibited no metabolic dysfunction (10,11).…”

“…Numerous preclinical in vivo (4,6,12,27,28) and in vitro (5,7-9,14,29) cancer models have provided evidence of metformin's anti-tumorigenic potential, which is commonly attributed to indirect whole-body effects (insulin-dependent) and/or direct (insulin-independent) effects (30). Metformin has been shown to reduce hyperinsulinemia and glycemia thereby reducing tumor cell insulin receptor (IR) expression and downstream signaling (30).…”

“…Even so, numerous studies in breast cancer cell lines have shown that metformin directly affects growth and proliferation through inhibition of mammalian target of rapamycin complex I (mTORC1) in both AMPK-dependent (8) and independent (14) processes. Additional mechanistic observations using triple negative breast cancer cell lines implicate inhibition of Stat3 with subsequent growth inhibition and apoptosis induction (8), as well as inhibition of TGF-β-mediated activation of Smad2, Smad3, and ID1 (9). Preclinical rodent studies showing an effect of metformin support these putative direct effects, with AMPK activation and subsequent inhibition of mTORC1 and/or acetyl CoA carboxylase (12,15).…”

CD155 contributes to the mesenchymal phenotype of triple‐negative breast cancer

“…Our study revealed that CD155 knockdown significantly weakened TGF‐β expression, indicating that CD155 also cross‐talked with TGF‐β signaling. In TNBC, TGF‐β was shown to induce EMT and metastasis . Smad family members such as Smad2, Smad3 and Smad4 mediated these processes .…”

Androgen Deprivation Therapy (ADT), Metabolic Syndrome and Metastatic Prostate Cancer: In Vivo and In Vitro Assessments of Effects of Metformin

“…For example, cell death mediated by metformin is autophagy mediated in particular cells of colon, melanoma and lymphoma cancers [286]. On the other hand, apoptosis is often observed with metformin treatment in breast, prostate, lung and head and neck cancers mediated by AMPK activation and p38 MAPK pathway [310]. One of the mechanisms for cell survival preference includes the cell's sensitivity to tumournecrosis-factor-related-apoptosis-inducing-ligand [212] induced apoptosis.…”