Bioactive nanomedicines for multidrug-resistant colorectal cancer: Actionable mechanisms, emerging particle classes, and translational barriers.
Multidrug resistance (MDR) in colorectal cancer (CRC) arises from interacting tumour-cell, pharmacological and microenvironmental programmes that undermine both drug activity and delivery. Chemotherapy-associated MDR is the principal focus of this review, while resistance to targeted therapy and immunotherapy is considered where it directly affects delivery design or patient selection. Bioactive compounds can modulate several resistance pathways, but their translational value is constrained by poor solubility, instability, rapid metabolism and inadequate exposure at resistant lesions. This review critically examines when nanomedicine can make such mechanistic activity pharmacologically and translationally meaningful. We link resistance biology to delivery functions, evaluate bioactive chemosensitiser candidates against human exposure, compare major nanomedicine design strategies, and assess nano-bio interactions, repeat-dose safety, manufacturing and clinical positioning. Across the evidence, three limitations recur. First, concentrations associated with chemosensitisation for curcumin, resveratrol, epigallocatechin gallate and quercetin generally exceed measured human parent-analyte exposure. Second, many resistance claims rely on parental or poorly characterised models, whereas studies combining defined resistance provenance with functional mechanism and exposure confirmation remain uncommon. Third, human studies demonstrate feasibility, tissue exposure or treatment response, but not mechanism-specific reversal of CRC MDR by a bioactive compound or bioactive nanomedicine. Progress therefore depends less on adding new particle classes than on matching a necessary formulation function to a defined resistance or spatial barrier, quantifying active exposure in the relevant compartment, validating mechanism in appropriate models, and integrating repeat-dose safety, scalable manufacturing and biomarker-guided clinical development.