A novel 5Fu-TQ hybrid targets chemo-resistant colorectal cancer stem cell self-renewal capacity -

Abstract

In the clinic, 5-fluorouracil (5-Fu) remains the standard chemotherapy for metastatic colorectal cancer (CRC), but its effectiveness is limited by drug resistance and unpredictable cardiotoxicity. The high recurrence rates and the common resistance are thought to be due to a population of chemo-resistant clones as well as a population of self-renewing cancer stem cells (CSCs). Just like CSCs, chemo-resistant tumor cells represent a subpopulation of cells molecularly and phenotypically distinct from the original tumor. Thus, the identification of a common drug that simultaneously targets both populations is of clinical significance for an effective eradication of CRC. To address the issue of targeting chemo-resistant cells, we generated a 5-Fu chemo-resistant HCT116 cell line by continuous exposure to increasing doses of 5-Fu. In the quest for using a novel multi-targeted drug, we synthesized a hybrid between the clinical drug 5-Fu and the plant derived promising compound thymoquinone (TQ) which was recently shown by our group to target colon CSCs. This newly synthesized 5Fu-TQ hybrid is considered as an advanced form of combination therapy on HCT116 cell lines sensitive or resistant to 5-Fu. Our main aim was to investigate the potency of the 5Fu-TQ hybrid in overcoming chemo-resistance by targeting the heterogeneous population of the tumor and preventing recurrence. Sphere-formation and propagation assays were used to assess the efficacy of hybrid treatment, in comparison to the parent drugs, on targeting self-renewal capacity of colon CSCs enriched from the sensitive and resistant cell lines in 3D cultures over several generations. Our results of the hybrid efficacy in 2D cell culture system showed that the hybrid reduced the cell viability in both cell lines, and was twice as potent as TQ. More importantly, our 3D results showed that the 5Fu-TQ hybrid induced significant inhibition, greater than that of either 5-Fu or TQ alone, on the sphere formation, size, and self-renewal capacity of CSCs derived from both