Anti‑proliferative and pro‑apoptotic effects of rosemary and constituent terpenoids in a model for the HER‑2‑enriched molecular subtype of clinical breast cancer

Abstract

Neoadjuvant treatment options for human epidermal growth factor receptor-2 (HER-2)-enriched and luminal B molecular subtypes of clinical breast cancer include HER-2-targeted therapy with chemotherapy or anti-hormonal therapy. These treatment options result in systemic toxicity and acquired tumor resistance. Minimally toxic naturally occurring phytochemicals may represent testable alternatives to conventional therapy. HER-2-overexpressing tumorigenic human mammary epithelial 184-B5/HER cells represent a model for the HER-2-enriched breast cancer subtype. Non-fractionated rosemary extract (RME) and constituent phenolic terpenoids ursolic acid (UA), carnosol (CSOL) and carnosic acid (CA) represented the test agents. Anchorage-independent (AI) proliferation, cell cycle progression, cellular apoptosis and expression of cell cycle-regulatory and apoptosis-specific proteins represented the mechanistic end point biomarkers. Relative to the parental non-tumorigenic 184-B5 cells, tumorigenic 184-B5/HER cells exhibited decreased population doubling, increased saturation density, accelerated cell cycle progression and downregulated cellular apoptosis, confirming the loss of homeostatic control of proliferation. Treatment with the test agents resulted in a dose-dependent decrease in AI colony number, indicating a decrease in cancer risk. Mechanistically, RME and UA inhibited G-S phase transition resulting in an increased G:S+G/M ratio and decreased cyclin D1 expression. The pro-apoptotic effect of RME and UA was indicated by increased sub-G (apoptotic) cell population, and relevant reciprocal modulation, as demonstrated by decreased anti-apoptotic B-cell lymphoma-2 (Bcl-2) and increased pro-apoptotic Bcl-2-associated X protein expression. In contrast, treatment with CA and CSOL resulted in cytostatic G/M arrest and an increase in cyclin B1 expression; thus, naturally-occurring rosemary and its constitutive terpenoids re-establish homeostatic control of proliferation and decrease cancer risk via distinct mechanisms. These data validate an experimental approach to prioritize efficacious natural compounds as testable alternatives for conventional chemo-endocrine and HER-2-targeted therapies in HER-2-enriched breast cancer.

Anticancer Properties of Carnosol: A Summary of In Vitro and In Vivo Evidence

“…In a study by Telang et al (2018), treatment of HER-2 overexpressing tumorigenic human mammary epithelial cells (184–B5/HER) with carnosol (1–5 μM) for 21 days dose-dependently inhibited colony formation and increased G2/M phase arrest [ 48 ]. Additionally, G2 phase specific cyclin B1 expression was upregulated with carnosol treatment compared to control cells ( Table 3 ) [ 48 ].…”

Targeting drug resistant stem cells in a human epidermal growth factor receptor‑2‑enriched breast cancer model

“…Naturally occurring phytochemicals and herbal extracts possessing minimal systemic toxicity may represent testable alternatives to conventional chemoendocrine therapy for clinical breast cancer (6,7). Published evidence on the present model for HER-2 enriched breast cancer has demonstrated potent anti-proliferative and pro-apoptotic effects of several mechanistically distinct naturally occurring compounds, including phytoalexins (8), isoflavones (9-11), vitamin A derivatives (12,13) and phenolic terpenoids (14,15). This documented evidence for the susceptibility of the present model raises a possibility that natural products may also be effective as testable alternatives for cancer stem cell targeted therapeutic efficacy.…”

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“…MV1 had higher terpenoid content than MS36 among the extracts. The anti-cancer properties of terpenoids have been demonstrated in various medicinal plants and has exhibited a protective role majorly in breast and gastrointestinal cancers [37][38][39][40][41] . Selection of solvent for extraction of bioactive compounds of target plays a major role in determining the biological activity and therefore, studying the nature of target compounds becomes vital.…”