Rhein potentiates doxorubicin in treating triple negative breast cancer by inhibiting cancer-associated fibroblasts

Cancer-associated fibroblasts (CAFs), one of the most abundant stromal cells in the tumor microenvironment, mediate desmoplastic responses. CAFs are major drivers for the failure of triple-negative breast cancer (TNBC) chemotherapy. It is well-documented that many traditional Chinese medicines (TCMs) exhibit potent anti-fibrotic effects based on their capacity to suppress the production of ECM proteins. Therefore, the combination of TCMs exhausting CAFs with chemotherapy is a potential regimen for treating TNBC. Here, TGF-β was used to induce the transformation of NIH/3T3 cells into CAFs for screening TCMs to inhibit tumor fibrosis. After screening 11 candidate TCMs for inhibiting CAFs using the TMS method, rhein (Rhe) was found to strongly inhibit the proliferation of CAFs. Therefore, Rhe was chosen as a representative TCM to inhibit CAFs in TNBC. A 4T1Fluc/CAFs tumor sphere resembling the TME in vivo was constructed to explore the feasibility of inhibiting CAFs to sensitize DOX in treating TNBC. It was found that CAFs apparently hindered the penetration of DOX into 4T1Fluc/CAFs tumor spheres and decreased the the sensitivity of 4T1Fluc cells to DOX, while Rhe significantly restored the sensitivity of 4T1Fluc cells to DOX by inhibiting the proliferation of CAFs. Consistent with in vitro results, Rhe reversed the abnormal activation of CAFs and diminished the accumulation of collagen in 4T1Fluc mouse xenograft models. This removal of stromal barrier facilitated the antitumor efficacy of DOX. Altogether, this study demonstrated for the first time that Rhe could inhibit tumor tissue fibrosis and synergize DOX to treat TNBC.