Colorectal cancer (CRC) is a recurring cancer that is often resistant to conventional therapies and therefore requires the development of molecular-based therapeutic approaches. Dopamine receptor D2 (DRD2) is associated with the growth of many types of tumors, but its oncogenic role in CRC is unclear. Here, we observed that elevated DRD2 expression was associated with a poor survival rate among patients with CRC. Depletion of DRD2 suppressed CRC cell growth and motility by downregulating β-catenin/ZEB signaling in vitro and in vivo, whereas overexpression of DRD2 promoted CRC cells progression. Inhibition of DRD2 by the antagonist pimozide inhibited tumor growth and lymph node metastasis in vivo and enhanced the cytotoxic effects of conventional agents in vitro. Taken together, our findings indicate that targeting the DRD2/β-catenin/ZEB1 signaling axis is a potentially promising therapeutic strategy for patients with CRC.

The primary cause of colorectal cancer (CRC) recurrence is increased distant metastasis after radiotherapy, so there is a need for targeted therapeutic approaches to reduce the metastatic-relapse risk. Dysregulation of the cell-surface glycoprotein podocalyxin-like protein (PODXL) plays an important role in promoting cancer-cell motility and is associated with poor prognoses for many malignancy types. We found that CRC cells exposed to radiation demonstrated increased TGFβ and PODXL expressions, resulting in increased migration and invasiveness due to increased extracellular matrix deposition. In addition, both TGFβ and PODXL were highly expressed in tissue samples from radiotherapy-treated CRC patients compared to those from patients without this treatment. However, it is unclear whether TGFβ and PODXL interactions are involved in cancer-progression resistance after radiation exposure in CRC. Here, using CRC cells, we showed that silencing PODXL blocked radiation-induced cell migration and invasiveness. Cell treatment with galunisertib (a TGFβ-pathway inhibitor) also led to reduced viability and migration, suggesting that its clinical use may enhance the cytotoxic effects of radiation and lead to the effective inhibition of CRC progression. Overall, the results demonstrate that downregulation of TGFβ and its-mediated PODXL may provide potential therapeutic targets for patients with radiotherapy-resistant CRC.