Fibrous Rich Tumor Models Reveals Microenvironment Dependent Drug Interactions in Colorectal Cancer

Abstract Background: Tumor response to therapy is strongly influenced by multicellular interactions within the tumor microenvironment, particularly fibroblast and tumor communication mediated by gap junctions. Traditional monoculture models fail to capture these dynamics, limiting the understanding of drug combination effects. This study evaluates the role of a gap junction enhancer (PQ) in modulating antineoplastic drug responses in three dimensional (3D) colorectal cancer models. Methods: 3D monoculture and fibroblast coculture spheroids were generated using colorectal cancer cell lines (Caco-2, HT-29, SW480, SW620) and CCD-112CoN fibroblasts. Spheroids were treated with antineoplastic agents (Doxorubicin, Nilotinib, Cediranib, Erlotinib) alone or in combination with PQ across full dose matrices. Cell viability was measured using the RealTime-Glo assay. Drug interactions were quantified using the Zero Interaction Potency (ZIP) model, with results visualized as 2D synergy maps and 3D interaction landscapes. Results: PQ alone produced limited and variable effects on spheroid metabolic activity. When combined with Doxorubicin, PQ altered response profiles, with higher ZIP scores observed in Caco-2–CCD-112 co-culture spheroids than in Caco-2 monoculture spheroids. PQ–drug interactions were not uniform across dose matrices, with regions of synergy, additivity, and antagonism observed depending on drug type, concentration, and culture condition. PQ and Erlotinib in co-culture spheroids showed mostly additive to weakly antagonistic interaction patterns. Conclusions: PQ modified antineoplastic drug response in 3D colorectal cancer spheroid models, but its effects were dependent on drug type, dose, and culture context. These findings support the use of 3D co-culture systems and full dose–matrix analyses to evaluate context-dependent drug interactions in colorectal cancer models.