Objectives: The anti-cancer activity of doxycycline has been reported in many cancers but not renal cell carcinoma (RCC). This study aimed to determine the efficacy of doxycycline alone and in combination with paclitaxel and analyze the underlying mechanism in RCC.
Methods: Proliferation, colony formation and apoptosis assays were performed in RCC cell lines after drug treatments. An RCC xenograft mouse model was generated, and tumor growth was monitored. Mechanistic studies focused on mitochondrial translation and functions.
Results: Doxycycline at clinically achievable concentrations inhibited proliferation and colony formation and induced apoptosis in RCC cell lines. In normal kidney cells, doxycycline at the same concentrations either had no effect or was less effective. The combination index value demonstrated that doxycycline and paclitaxel were synergistic in vitro. Consistently, this combination therapy was significantly more effective than the monotherapy in RCC xenograft mice without causing significant toxicity. Mechanistic studies revealed that doxycycline acts on RCC cells via preferentially inhibiting mitochondrial DNA translation, thereby disrupting multiple mitochondrial complexes and impairing mitochondrial respiration.
Conclusions: Doxycycline is a useful addition to the treatment strategy for RCC. Our work also highlights the therapeutic value of mitochondrial translation inhibition in sensitizing RCC to chemotherapy.
Keywords: Renal cell carcinoma; chemotherapy; doxycycline; mitochondrial translation; paclitaxel; synergism.