Model-dependent transport limitations shape the in vitro evaluation of platinum-based nanotherapeutics.

Platinum-based chemotherapeutics remain central in oncology but are limited by systemic toxicity and poor tumor selectivity. Here, we investigate hydroxyapatite nanoparticles (HA NPs) as carriers for Pt(II) complexes, and compare the activity of free and NP-conjugated formulations across 2D cultures, static 3D tumor models, and flow-conditioned 3D systems using identical formulations, doses, and biological endpoints. Static 3D models impose diffusion-driven constraints that limit NP penetration, promote peripheral accumulation, and attenuate the apparent efficacy of NP-conjugated formulations. In contrast, quantitative spatial fluorescence profiling show that dynamic flow conditions partially alleviate these limitations, enhancing distal NP distribution and therapeutic activity. Notably, these transport-dependent effects influence the relative performance of free and nano-formulated drugs across models. Overall, our findings demonstrate that transport limitations in static systems can distort nanomedicine evaluation, highlighting the importance of incorporating flow-controlled conditions in preclinical screening.