Oridonin derivative DLC13 targeting proliferating cell nuclear antigen to overcome oxaliplatin resistance in colorectal cancer.

Novel therapeutic strategies are urgently needed for the treatment of colorectal cancer (CRC), which is the third most common cancer and the second leading cause of cancer-related mortality worldwide. Natural products are a pivotal source for the discovery of new anticancer agents. Oridonin (DLC) and its derivatives have demonstrated the ability to inhibit malignancy through regulating multiple pathways, presenting promising options for CRC therapy. In this work, we identified an DLC derivative, oridonin 13 (DLC13), which exhibited 11.5-fold and 4.8-fold greater potency against HCT116 and HT29 cell proliferation than DLC, and achieved equivalent tumor suppression in HCT116 xenografts at half the dosage. DLC13 effectively inhibited DNA damage repair, cell cycle progression, stemness, and migration of CRC cells. As a first-line chemotherapeutic agent for CRC, oxaliplatin (OXA) drives aberrant expression of genes involved in DNA damage repair, cell cycle progression, stemness, and migration, leading to the development of OXA resistance. DLC13 was shown to suppress the abnormal gene expression driven by OXA, indicating its potential to reverse OXA resistance. Indeed, we found that DLC13 and OXA synergistically inhibited the malignant proliferation of CRC cells, and DLC13 enhanced the sensitivity of OXA-resistant CRC cells to OXA treatment. Activity-based protein profiling (ABPP) proteomics identified proliferating cell nuclear antigen (PCNA), a critical regulator of DNA replication and repair, as a direct target of DLC13. Importantly, PCNA is a critical driver of OXA resistance in CRC. Further mechanistic studies revealed that DLC13 binds to the QSMDSSH motif of PCNA, facilitating its K48-linked polyubiquitination and subsequent proteasomal degradation, thereby inhibiting the biological function of PCNA. Knockdown of PCNA suppressed CRC cell proliferation, DNA damage repair, cell cycle progression, stemness, and migration, while restoring OXA sensitivity in resistant cells. In summary, PCNA is a direct target of DLC13. DLC13 inhibits malignant proliferation and reverses OXA resistance in CRC by promoting ubiquitination-dependent degradation of PCNA. The combination of oridonin derivatives with OXA may represent a promising approach for treating refractory CRC. Additionally, targeted inhibition of PCNA offers a potential approach to suppress CRC malignancy and overcome OXA resistance.