<p>Multidrug resistance (MDR) remains the principal impediment to curative oncology, driven by complex interplays between cancer cells and the tumor microenvironment (TME). While nanomedicines have sought to overcome these delivery barriers, their clinical translation is often hampered by the heterogeneity of the enhanced permeability and retention (EPR) effect and by inefficient intratumoral delivery. In this review, we argue that overcoming MDR requires a transition beyond traditional passive drug delivery, advocating active, localized remodeling of the tumor ecosystem. Next-generation injectable hydrogels are increasingly recognized as localized viscoelastic niches that combine controlled intratumoral retention with the capacity to actively modulate biological responses within tumor TME. By converging principles of mechanobiology and immunometabolism, these hydrogels enable a multi-tiered strategy to dismantle multidimensional MDR. This approach begins with the biomechanical softening of the extracellular matrix to decouple mechanotransduction driven by Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ), followed by the metabolic disruption of hypoxia-driven bioenergetics. Beyond the extracellular landscape, nanogel-enabled trafficking allows payloads to circumvent intracellular sequestration and efflux transporters, while immunomodulatory niches mobilize antitumor immunity through in situ vaccination and myeloid reprogramming. Finally, we evaluate the integration of artificial intelligence-driven design and patient-derived organoids as a technical bridge to reconcile laboratory ingenuity with clinical utility, aiming to transform the TME into a vulnerable therapeutic target.</p>