Calotropis Procera Induced Caspase-Dependent Apoptosis and Impaired Akt/mTOR Signaling in 4T1 Breast Cancer Cells

Abstract

Introduction: Calotropis procera (Aiton) Dryand (Apocynaceae) is an herb that has been commonly used in folk medicine to treat various diseases for more than 1500 years.

Aims: Our goal was to investigate the anti-metastatic effects of phenolics extracted from C. procera (CphE) against 4T1 breast cancer cells and in BALB/c mice.

Methods: 4T1 cells were treated with CphE and quercetin (positive control) at concentrations that inhibited cell viability by 50% (IC₅₀). Levels of reactive oxygen species (ROS), wound healing, and protein expressions were determined following standard protocols. For the in vivo pilot study, the syngeneic BALB/c mouse model was used. 4T1 cells were injected into mammary fat pads. Tumors were allowed to grow for 9 days before gavage treatment with CphE (150 mg GAE/kg/day) or PBS (controls) for one week. Excised tumors, liver, and lungs were analyzed for gene and protein expression and histology.

Results: In vitro results showed that CphE suppressed cell viability through apoptosis induction, via caspase-3 cleavage and total PARP reduction. CphE also scavenged ROS and suppressed Akt, mTOR, ERK1/2, CREB, and Src activation contributing to cell motility inhibition. CphE reduced IR, PTEN, TSC2, p70S6, and RPS6, protein levels, which are proteins involved in the PI3K/Akt/mTOR pathway, suggesting this pathway as CphE primary target. In vivo results showed downregulation of ERK1/2 activation by phosphorylation in tumor tissues, accompanied by angiogenesis reduction in tumor and lung tissues. A reduction of Cenpf mRNA levels in liver and lung tissues strongly suggested anti-invasive cancer activity of CphE.

Conclusion: CphE inhibited 4T1 cell signal pathways that play a key role in cell growth and invasion. The potential for in vitro results to be translated in vivo was confirmed. A complete animal study is a guarantee to confirm the CphE anticancer and antimetastatic activity in vivo.

Keywords: MAPK/ERK1/2; angiogenesis; medicinal plants; metastasis; milkweed (Calotropis procera); stage IV human breast cancer.