DHA sensitizes HCT116 and DLD-1 spheroids to TRAIL-induced apoptosis. The 3D spheroids of HCT116 (A) and DLD-1 (B) were constructed in ultra-low attachment 96-well plates after 72 h incubation. Then, the spheroids were treated with 10 μM DHA for 30 min, followed with/without 25 ng/mL rhTRAIL WT, DHER, or 4C7 for 24 h. The cell viability of the spheroids was determined after 25 min incubation with CellTiter-Glo® 3D Reagent. Data shown are mean ± SEM from three independent experiments performed in triplicate. p values were analyzed by two-way ANOVA with Sidak’s multiple comparisons test with Graphpad Prism version 8.0. ** 0.001 < p ≤ 0.01, *** 0.0001 < p ≤ 0.001.