Soybean Extract Rich in Lunasin Enhances p21 Expression in DMBA-Induced Breast Cancer Rat: A Potential Adjuvant Therapy

Background: Breast cancer treatment in Indonesia faces challenges due to side effects, limited accessibility, and resistance to therapies like tamoxifen, highlighting the need for effective adjuvants strategies. Lunasin, a soybean-derived peptide, exhibits anticancer potential by upregulating p21, a tumor suppressor involved in cell cycle arrest and apoptosis. This study examines the effect of soybean extract rich in lunasin on p21 expression in a DMBA-induced breast cancer rat model. Methods: Thirty female Sprague-Dawley rats were induced with breast cancer via intragastric injection of 7,12-Dimethylbenz[a]anthracene (DMBA), 20 mg/kgBW was given twice weekly for a total of 11 injections. Once the tumor volume reached 1-2 cm3, the rats were given 10 mg/kgBW of tamoxifen (positive control), 500 mg/kgBW of soybean extract rich in lunasin (lunasin), and a combination of both (combination) for eight weeks. Rats in the negative control group did not receive any medication. Afterwards, the rats were terminated to extract the tumor tissue. This tumor tissue was examined for the expression of p21 protein using immunohistochemistry staining. Results: The highest average p21 expression was observed in the normal group, followed by combination, lunasin, positive control, and negative control groups. The combination group showed significantly higher p21 expression than negative control (p<0.05), while no significant difference was observed between the positive control and lunasin groups (p>0.05). Conclusion: Soybean extract rich in lunasin upregulates p21, supporting its role in tumor suppression. While lunasin alone had no significant advantage over tamoxifen, their combination significantly increased p21 expression, suggesting a synergistic effect, making it a promising adjuvant therapy.