A Sulfated Acidic Heteropolysaccharide from Sea Cucumber Cooking Liquid Suppresses HCT-15 Colorectal Cancer Cell Proliferation by Inducing ROS-Associated Mitochondrial Apoptosis and DNA Damage Response

Sea cucumber cooking liquid contains water-soluble macromolecules, but its bioactive polysaccharide fractions remain insufficiently characterized. In this study, a polysaccharide-rich fraction, P0.7, was isolated from sea cucumber cooking liquid and evaluated for its antitumor activity against HCT-15 colorectal cancer. P0.7 was characterized as a relatively homogeneous sulfated acidic heteropolysaccharide-rich fraction containing 83.61 ± 3.65% total sugar, 13.67 ± 2.48% sulfate, 9.98 ± 1.22% uronic acid, and 5.11 ± 0.34% protein. It was mainly composed of galactose, mannose, and glucose, accounting for 34.12%, 26.93%, and 17.99%, respectively. Among the tested tumor cell lines, HCT-15 cells showed the highest sensitivity to P0.7, with inhibition rates of approximately 45% and 63% at 100 and 200 μg/mL, respectively. P0.7 promoted apoptosis, induced G2/M-phase accumulation, increased ROS production, disrupted mitochondrial membrane potential, regulated Bax, Bcl-2, and cleaved caspase-3 expression, and enhanced γ-H2AX-related DNA damage-response signaling in HCT-15 cells. In an HCT-15 xenograft mouse model, P0.7 reduced terminal tumor volume and tumor weight without causing obvious body weight loss. Histological and immunohistochemical analyses further showed reduced Ki67 staining, increased TUNEL-positive signals, and enhanced γ-H2AX staining in tumor tissues. These findings indicate that P0.7 suppresses HCT-15 colorectal cancer growth in vitro and in vivo, possibly through mechanisms associated with ROS accumulation, mitochondrial apoptosis, and γ-H2AX-related DNA damage response. These findings provide additional experimental evidence supporting the investigation of sea cucumber-derived polysaccharides for potential pharmaceutical applications.