A study published in the peer-reviewed journal Cell & Bioscience found that cannabidiol (CBD) may help restore sensitivity to tamoxifen in estrogen receptor-positive breast cancer, potentially improving the effectiveness of a widely used endocrine therapy.

Researchers from Korea University College of Medicine investigated the effects of CBD on tamoxifen-resistant breast cancer models, focusing on ER-positive breast cancer cells. Tamoxifen remains a key treatment for this type of breast cancer, but resistance to the therapy can develop over time, limiting its effectiveness and creating a major challenge for patients and clinicians.

Using human breast cancer cell lines MCF7 and T47D, researchers treated cells with CBD, tamoxifen or a combination of the two. They found that CBD significantly increased tamoxifen-induced cell death and apoptosis in ER-positive breast cancer cells.

The study found that CBD suppressed the cAMP/CREB signaling pathway, which led to lower levels of estrogen receptor alpha and related target genes, including TFF1, GREB1 and CCND1. Researchers also found that CBD disrupted the interaction between phosphorylated CREB and CBP, contributing to reduced ERα signaling.

In animal models, the combination of CBD and tamoxifen synergistically inhibited tumor growth while reducing ERα and p-CREB expression in tumor tissues.

The researchers concluded that CBD restored tamoxifen sensitivity by downregulating ERα signaling through a CREB-mediated mechanism. They said the findings suggest CBD could have potential as an adjuvant agent to help overcome tamoxifen resistance and improve outcomes for patients with ER-positive breast cancer.