Si-Jun-Zi-Tang potentiates temozolomide's anti-melanoma efficacy and reduces its hepatotoxicity

Background:
Malignant melanoma remains a major challenge in oncology, largely due to the limited efficacy and significant toxicity associated with treatments such as temozolomide (TMZ). Si-Jun-Zi-Tang (SJZT), a traditional Chinese medicine formula with documented anti-cancer properties, has shown potential in enhancing chemotherapy effectiveness and reducing treatment-related toxicity.

Purpose:
This study investigated the role of SJZT in improving TMZ treatment outcomes in melanoma.

Methods:
The effects of SJZT on TMZ treatment outcomes were evaluated in melanoma cell lines and mouse models. Cell proliferation, apoptosis, DNA damage, and cell cycle distribution were assessed using CCK-8 assays, Annexin V/PI staining, γ-H2AX immunofluorescence, and flow cytometry, respectively. In vivo antitumor efficacy and hepatotoxicity were evaluated in melanoma-bearing mice. Mechanistic insights were explored via network pharmacology and RNA sequencing, and validated by RT-qPCR, Western blotting, and rescue experiments.

Results:
SJZT enhanced TMZ-induced inhibition of cell proliferation, apoptosis, and DNA strand breaks in melanoma cells. SJZT also attenuated TMZ-induced G2/M arrest, promoting mitotic catastrophe. In mouse models, SJZT enhanced the anti-tumor effects of TMZ and mitigated TMZ-induced hepatotoxicity. Mechanistically, network pharmacology and experimental validation revealed that simultaneous inhibition of Chk1 and promotion of MGMT proteasomal degradation mediated the enhanced anti-melanoma effects of TMZ with SJZT. RNA sequencing and experimental validation demonstrated that TMZ upregulated the bile salt transporter Slc10a1/Ntcp and downregulated detoxifying enzymes Ugt1a1 and Slco1b2/Oatp2, disrupting bile acid homeostasis. Notably, SJZT co-administration reversed these changes, restoring bile acid balance.

Conclusion:
These findings reveal that SJZT can enhance TMZ’s therapeutic efficacy while reducing hepatotoxicity, supporting its use as a promising adjuvant in melanoma treatment.