*Article* **Chemomodulatory Effect of the Marine-Derived Metabolite "Terrein" on the Anticancer Properties of Gemcitabine in Colorectal Cancer Cells**

**Reham Khaled Abuhijjleh 1, Dalia Yousef Al Saeedy 1, Naglaa S. Ashmawy 2,3, Ahmed E. Gouda 4, Sameh S. Elhady <sup>5</sup> and Ahmed Mohamed Al-Abd 4,6,\***


**Abstract:** Background: Terrein (Terr) is a bioactive marine secondary metabolite that possesses antiproliferative/cytotoxic properties by interrupting various molecular pathways. Gemcitabine (GCB) is an anticancer drug used to treat several types of tumors such as colorectal cancer; however, it suffers from tumor cell resistance, and therefore, treatment failure. Methods: The potential anticancer properties of terrein, its antiproliferative effects, and its chemomodulatory effects on GCB were assessed against various colorectal cancer cell lines (HCT-116, HT-29, and SW620) under normoxic and hypoxic (pO2 ≤ 1%) conditions. Further analysis via flow cytometry was carried out in addition to quantitative gene expression and 1HNMR metabolomic analysis. Results: In normoxia, the effect of the combination treatment (GCB + Terr) was synergistic in HCT-116 and SW620 cell lines. In HT-29, the effect was antagonistic when the cells were treated with (GCB + Terr) under both normoxic and hypoxic conditions. The combination treatment was found to induce apoptosis in HCT-116 and SW620. Metabolomic analysis revealed that the change in oxygen levels significantly affected extracellular amino acid metabolite profiling. Conclusions: Terrein influenced GCB's anti-colorectal cancer properties which are reflected in different aspects such as cytotoxicity, cell cycle progression, apoptosis, autophagy, and intra-tumoral metabolism under normoxic and hypoxic conditions.

**Keywords:** terrein; gemcitabine; combination analysis; colorectal cancer; cell cycle; apoptosis; autophagy; metabolomics; qPCR
