Non-cytotoxic dose of paclitaxel influences invasion, dissemination and cell phenotype in oral squamous cell carcinoma

The development of chemotherapeutics has been based on the concept that cancer is a cell-autonomous genetic disease. The idea that transformed cells proliferate and invade in an unrestricted manner neglects the fact that malignant cells are embedded within a tumor microenvironment. Paclitaxel is a well-known cytotoxic drug used in the treatment of breast, ovarian and non-small cell lung cancer and its mechanism of action involves cell death of cancer cells through apoptosis. There is evidence that, at reduced non-cytotoxic concentrations, paclitaxel has anti-tumoral biological effects that involve modulation of the microenvironment. In this study, we used a model of oral squamous cells carcinoma (OSCC) microenvironment to assess the effect of a non-cytotoxic concentration/dose of paclitaxel on tumor progression and dissemination. We investigated the influence of non-cytotoxic paclitaxel on cancer-associated fibroblast (CAFs) and monocytes in addition to neoplastic cells. Invasion was assessed in vitro, using 3D cell cultures comprised of OSCC cell lines (SCC9 or H314), monocytes and CAFs. Tumor dissemination was assessed in vivo by injecting SCC9 cells, monocytes, and CAFs into zebrafish larvae, which were subsequently treated for three days with paclitaxel. Outcomes assessed were tumor size, metastasis and phenotype of the cells by immunofluorescence (vimentin and α-SMA). We also used a heterotopic xenograft model in male Balb/c nude mice injected with H314 cells. Fifteen days post-injection, mice were treated with a low dose of paclitaxel or vehicle. After an additional 12 days, mice were euthanized, and the tumors were measured and collected. The outcomes assessed were tumor volume, morphology and phenotype of the cells. Tumor tissues were analyzed by hematoxylin/eosin staining (morphology), immunohistochemistry (cytokeratin and ki67), and immunofluorescence (CD80 and CD163). Paclitaxel decreased the invasion of tumor cells in vitro and reduced tumor size and metastasis in vivo. Non-cytotoxic paclitaxel reduced expression of vimentin in cancer cells, and of α-SMA in CAFs/monocytes in the zebrafish model. Monocyte/macrophages were skewed towards an anti-tumoral phenotype. In conclusion, the results demonstrate that paclitaxel has cytotoxicity-independent anti-tumoral effects, reducing tumor progression and dissemination by modulating cells in the microenvironment. Repurposing of paclitaxel in reduced doses may have potential as an adjunct treatment in OSCC.

Corresponding author: Natalie Aparecida Rodrigues Fernandes (e-mail: natalie.fernandes@unesp.br).