Silibinin and STAT3: A natural way of targeting transcription factors for cancer therapy

•STAT3 is constitutively activated in many different types of cancer.•pSTAT3 is a poor prognostic marker for breast, colon, prostate and non-small cell lung cancer.•Silibinin inhibits pSTAT3 expression in preclinical studies of prostate, breast, skin, gastric and lung cancer.•New clinical trials are necessary to determine the role of silibinin as a pSTAT3 inhibitor in cancer.

Signal transducer and activator of transcription 3 (STAT3) is constitutively activated in many different types of cancer and plays a pivotal role in tumor growth and metastasis. Retrospective studies have established that STAT3 expression or phospho-STAT3 (pSTAT3 or activated STAT3) are poor prognostic markers for breast, colon, prostate and non-small cell lung cancer. Silibinin or silybin is a natural polyphenolic flavonoid which is present in seed extracts of milk thistle (Silybum marianum). Silibinin has been shown to inhibit multiple cancer cell signaling pathways in preclinical models, demonstrating promising anticancer effects in vitro and in vivo. This review summarizes evidence suggesting that silibinin can inhibit pSTAT3 in preclinical cancer models. We also discuss current strategies to overcome the limitations of oral administration of silibinin to cancer patients to translate the bench results to the bed side. Finally, we review the ongoing clinical trials exploring the role of silibinin in cancer.