*Article* **The Effect of Dynamic, In Vivo-like Oxaliplatin on HCT116 Spheroids in a Cancer-on-Chip Model Is Representative of the Response in Xenografts**

**Job Komen 1,\*, Sanne M. van Neerven <sup>2</sup> , Elsbeth G. B. M. Bossink <sup>2</sup> , Nina E. de Groot <sup>2</sup> , Lisanne E. Nijman <sup>2</sup> , Albert van den Berg <sup>1</sup> , Louis Vermeulen <sup>2</sup> and Andries D. van der Meer <sup>3</sup>**


**Abstract:** The cancer xenograft model in which human cancer cells are implanted in a mouse is one of the most used preclinical models to test the efficacy of novel cancer drugs. However, the model is imperfect; animal models are ethically burdened, and the imperfect efficacy predictions contribute to high clinical attrition of novel drugs. If microfluidic cancer-on-chip models could recapitulate key elements of the xenograft model, then these models could substitute the xenograft model and subsequently surpass the xenograft model by reducing variation, increasing sensitivity and scale, and adding human factors. Here, we exposed HCT116 colorectal cancer spheroids to dynamic, in vivo-like, concentrations of oxaliplatin, including a 5 day drug-free period, on-chip. Growth inhibition on-chip was comparable to existing xenograft studies. Furthermore, immunohistochemistry showed a similar response in proliferation and apoptosis markers. While small volume changes in xenografts are hard to detect, in the chip-system, we could observe a temporary growth delay. Lastly, histopathology and a pharmacodynamic model showed that the cancer spheroid-on-chip was representative of the proliferating outer part of a HCT116 xenograft, thereby capturing the major driver of the drug response of the xenograft. Hence, the cancer-on-chip model recapitulated the response of HCT116 xenografts to oxaliplatin and provided additional drug efficacy information.

**Keywords:** cancer-on-chip; xenograft; microfluidic; colorectal cancer; pharmacodynamics; pharmacokinetics; drug efficacy; oxaliplatin
