Cancer associated fibroblasts (CAFs) are the most abundant components of cancer-microenvironment. They play important roles in cancer initiation, progression, and metastasis. In addition, CAFs can confer drug-resistance to cancer cells. Considering their pro-tumorigenic roles, it is recommended to remove CAFs to prevent cancer recurrence after chemotherapy. Despite their clinical significance, few anti-CAF drugs have been developed. The objective of this study was to find a drug that could suppress the viability of patient-derived CAFs through repurposed screening of 51 drugs that were in clinical trials or received FDA approval. As a result, bortezomib (BTZ), carfilzomib (CFZ), and panobinostat (PST) were identified as anti-CAF drug candidates. It was confirmed that BTZ and PST could decrease the viability of various patients derived CAFs through inducing of caspase-3 mediated apoptosis. Interestingly, combination therapy with BTZ and PST showed better efficacy of inhibiting CAFs than single treatment. The synergistic effect between BTZ and PST on viability of CAFs was observed both in vitro CAF culture and in vivo mouse model. Furthermore, combination therapy with BTZ/PST and conventional anticancer compound docetaxel strongly inhibited tumor growth in xenografts of mouse breast cancer cells with mouse CAFs. In conclusion, our present study revealed that BTZ and PST could significantly reduce the viability of CAFs. Therefore, a combination therapy with BTZ/PST and anticancer drugs might be considered as a new rational for the development of anticancer therapy.

Cancer-associated fibroblasts (CAFs) are the most abundant stromal cells in tumor microenvironments. These cells strongly support tumor progression and are considered to be potent therapeutic targets. Therefore, drugs targeting CAFs have been developed, but most of them have failed in clinical trials. The discovery of additional drugs to inactivate or eliminate CAFs is thus essential. In this study, we developed a high-throughput screening system to find anti-CAF drugs using reporter cells that express Twist1 promoter-GFP. This screening system uses the activity of the Twist1 promoter as an indicator of CAF activation because Twist1 is known to be a central player in CAF activation. Using this screening system, we found that dihydrorotenone (DHR), an inhibitor of electron transfer chain complex 1 in mitochondria, can effectively deactivate CAFs. DHR-treated CAFs exhibited reduced expression of CAF-enriched markers, decreased capability of collagen gel contraction, and impaired ability to engage in tumor-promoting activities, such as facilitating the proliferation and colonization of cancer cells. Furthermore, conditioned media from DHR-treated CAFs attenuated tumor progression in mice grafted with MNK28 cells. In conclusion, DHR can be considered as a candidate drug targeting CAFs.