Hypoxia is a key characteristic of the tumor microenvironment, too rarely considered during drug development due to the lack of a user-friendly method to culture naturally hypoxic 3D tumor models. In this study, we used soft lithography to engineer a microfluidic platform allowing the culture of up to 240 naturally hypoxic tumor spheroids within an 80 mm by 82.5 mm chip. These jumbo spheroids on a chip are the largest to date (>750 µm), and express gold-standard hypoxic protein CAIX at their core only, a feature absent from smaller spheroids of the same cell lines. Using histopathology, we investigated response to combined radiotherapy (RT) and hypoxic prodrug Tirapazamine (TPZ) on our jumbo spheroids produced using two sarcoma cell lines (STS117 and SK-LMS-1). Our results demonstrate that TPZ preferentially targets the hypoxic core (STS117: p = 0.0009; SK-LMS-1: p = 0.0038), but the spheroids’ hypoxic core harbored as much DNA damage 24 h after irradiation as normoxic spheroid cells. These results validate our microfluidic device and jumbo spheroids as potent fundamental and pre-clinical tools for the study of hypoxia and its effects on treatment response.

We describe the first microfluidic device for in vitro testing of brachytherapy (BT), with applications in translational cancer research. Our PDMS-made BT-on-chip system allows highly precise manual insertion of clinical BT seeds, reliable dose calculation using standard clinically-used TG-43 formalism and easy culture of naturally hypoxic spheroids in less than 3 days, thereby increasing the translational potential of the device. As the BT-on-chip platform is designed to be versatile, we showcase three different gold-standard post-irradiation bioassays and recapitulate, for the first time on-chip, key clinical observations such as dose rate effect and hypoxia-induced radioresistance. Our results suggest that BT-on-chip can be used to safely and efficiently integrate BT and radiotherapy to translational research and drug development pipelines, without expensive equipment or complex workflows.

Enniatins (ENNs) are emerging Fusarium mycotoxins detected in food and feed. Despite their widespread occurrence, their toxicity remains poorly understood; thus, advanced in vitro systems that can mimic human physiology are of interest. We evaluated the cytotoxic and genotoxic effects of ENN A1 and ENN B1 exposure on differentiated (DIFF) and undifferentiated (UND) HepaRG liver cells cultured as 2D monolayers and 3D spheroids. Cytotoxicity, assessed by ATP-based luminescence, revealed a time-dependent decrease in inhibitory concentration 50 (IC₅₀) values between 24 h and 48 h across all models. In DIFF HepaRG cells, ENN A1 IC₅₀ values in 3D spheroids decreased from 14.4–18.2 µM at 24 h to 2.2–3.0 µM at 48 h, reaching values comparable to those measured in 2D DIFF cells at 48 h (2.2–2.6 µM), while no IC₅₀ could be determined in 2D at 24 h. For ENN B1, a pronounced time-dependent toxicity was observed, with IC₅₀ values in 3D DIFF spheroids decreasing from 4.1–6.6 µM at 24 h to 1.3–1.6 µM at 48 h, remaining lower than those measured in 2D DIFF cells at 48 h (2.4–3.0 µM). ENN A1 primarily induced apoptotic responses, whereas both ENN A1 and B1 were associated with necrotic responses, and ENN B1 induced a transient and limited autophagic signal, suggesting a minor role for autophagy. To further characterize cellular responses to ENN exposure, spheroids cultured in microfluidic chips were sectioned, and proliferation (Ki67), DNA damage (γH2AX), and apoptosis (cleaved caspase-3) was assessed. Immunostaining revealed no proliferative response, whereas significant DNA damage was detected, particularly in DIFF spheroids. At low, sub-cytotoxic concentrations (~5 µM, 24 h), ENN A1 induced significant DNA damage, as shown by increased γH2AX levels, while cytotoxic effects were only observed at higher concentrations (IC₅₀ ~ 18 µM, 24 h), supporting a potential genotoxic effect independent of cytotoxicity. Despite the structural similarities between ENN A1 and ENN B1, our results highlighted distinct cell death pathways between the two analogues. Both ENNs were detected throughout spheroids without evidence of peripheral restriction, although a homogeneous functional test could not be conclusively demonstrated. Overall, the 3D HepaRG spheroid model proved to be a more physiologically relevant system, offering differential sensitivity, as well as enhanced mechanistic insight, compared to 2D cultures.

Hypoxia influences the biology and response of cancers. No user-friendly device allows the study of hypoxia on highly-controlled clinically-relevant tumor models. Here, we describe how hypoxic-core (HyCo) spheroids generated using our unique non-perfused microfluidic device recapitulate key clinical hallmarks of hypoxia in vitro . Our PDMS-made system can generate up to 240 spheroids naturally exhibiting a diffusion-driven hypoxic core in only 4 days, here from two sarcoma cell lines. Compared to smaller normoxic spheroids from the same cell lines, known hypoxia-related genes are upregulated in HyCo spheroids. In addition, HyCo spheroids display hallmark hypoxia-induced resistance to radiotherapy and chemotherapy, along with increased invasiveness. Finally, to demonstrate applications of our HyCo spheroids and on-chip framework in drug development, we used our HyCo-derived gene expression dataset to select a drug candidate (diethyl-pythiDC) and confirmed its effect on spheroid invasiveness. Our results suggest that HyCo spheroids can be efficiently used as translational tools to integrate hypoxia in cancer research, without complex workflows or setups. Teaser: On-chip spheroids with a natural hypoxic-core emulate clinical cancer hypoxia hallmarks essential for novel therapy development.

Background: Hypoxia influences the biology and response of tumors. Current methods to study hypoxia are low-throughput or use artificial induction, limiting the translational potential of findings. We previously described a user-friendly microfluidic chip to rapidly generate 240 large spheroids naturally harboring a hypoxic core. However, we had yet to validate the clinical relevance of these hypoxic-core (HyCo) spheroids, their use in understanding treatment resistance and their applications in targeted therapy testing. Methods: HyCo and small normoxic spheroids were generated on-chip from commercial and patient-derived soft-tissue sarcoma (STS) cell lines. Presence of hypoxia was validated through in silico modelling, immunofluorescence staining and RTqPCR. Whole-genome RNA sequencing was used to establish HyCo gene expression profile, compared to clinically-derived datasets, and used to identify target genes in hypoxic STSs. Apoptosis staining and clonogenic assay were used to evaluate HyCo therapy resistance to chemotherapy and radiotherapy. Matrigel invasion assay was used to quantify HyCo invasiveness and aggressivity. Diethyl-pythiDC was used to demonstrate the efficacy of P4HA1-inhibition on reducing HyCo invasiveness. Results: Large STSs spheroids generated on-chip naturally exhibit a diffusion-driven hypoxic core in only a few days. These HyCo spheroids recapitulate clinical hallmarks of hypoxia in STS: upregulation of hypoxia-related genes, resistance to chemotherapy/radiotherapy, and increased invasiveness. Our results suggest evidence of treatment resistance driven by hypoxia-induced paracrine signaling in STS. We identified P4HA1 gene as both upregulated in HyCo and prognostic in clinical STS and demonstrated that P4HA1-inhibition using diethyl-pythiDC reduced HyCo invasiveness. Conclusions: Our results demonstrate HyCo spheroids as efficient translational tools to integrate hypoxia in cancer research and drug development. We uncovered evidence of hypoxia-mediated chemoresistance in normoxic regions and successfully identified P4HA1-inhibition as a viable strategy for the treatment of hypoxic STSs, warranting further exploration.