All-human microphysical model of metastasis therapy

Abstract

The vast majority of cancer mortalities result from distant metastases. The metastatic microenvironment provides unique protection to ectopic tumors as the primary tumors often respond to specific agents. Although significant interventional progress has been made on primary tumors, the lack of relevant accessible model in vitro systems in which to study metastases has plagued metastatic therapeutic development--particularly among micrometastases. A real-time, all-human model of metastatic seeding and cancer cells that recapitulate metastatic growth and can be probed in real time by a variety of measures and challenges would provide a critical window into the pathophysiology of metastasis and pharmacology of metastatic tumor resistance. To achieve this we are advancing our microscale bioreactor that incorporates human hepatocytes, human nonparenchymal liver cells, and human breast cancer cells to mimic the hepatic niche in three dimensions with functional tissue. This bioreactor is instrumented with oxygen sensors, micropumps capable of generating diurnally varying profiles of nutrients and hormones, while enabling real-time sampling. Since the liver is a major metastatic site for a wide variety of carcinomas and other tumors, this bioreactor uniquely allows us to more accurately recreate the human metastatic microenvironment and probe the paracrine effects between the liver parenchyma and metastatic cells. Further, as the liver is the principal site of xenobiotic metabolism, this reactor will help us investigate the chemotherapeutic response within a metabolically challenged liver microenvironment. This model is anticipated to yield markers of metastatic behavior and pharmacologic metabolism that will enable better clinical monitoring, and will guide the design of clinical studies to understand drug efficacy and safety in cancer therapeutics. This highly instrumented bioreactor format, hosting a growing tumor within a microenvironment and monitoring its responses, is readily transferable to other organs, giving this work impact beyond the liver.

Figure 1

Micrometastasis progression in standard and diurnal cultures. Conceptual view of (top) micrometastasis progression in three-dimensional perfused liver microreactors maintained with controlled circadian profiles of key components of the portal circulation (nutrients, insulin) and the systemic circulation (cortisol) compared with (bottom) micrometastasis progression in standard culture with daily medium changes. Approximate relative values of diurnal fluctuations in the tissue microenvironment are shown for each case; absolute magnitudes of cortisol and insulin are conventionally supraphysiological in the standard culture. Micrometastases are created by seeding individual tumor cells within the parenchyma of the tissue mimic, where flow of oxygenated culture medium into the tissue supports survival and proliferation. Carcinoma cells may re-express cadherin and integrate into the tissue, or may exhibit unrestrained growth. As tumors grow, the tissue becomes hypoxic, stromal cells proliferate, and the mix of cytokines and acute phase proteins becomes altered. Parameters listed (nutrient and hormone levels, cytokine levels, oxygen) are measured noninvasively to assess the progression of metastases. A premise is that the uncontrolled metastases stimulated by supraphysiological levels of hormones and nutrients in standard culture will be easier to eradicate by traditional chemotherapeutic agents that target proliferation, and thus fail to represent the full spectrum of behaviors of clinically important metastases compared with the case of controlled diurnal stimulation. P_O2, oxygen partial pressure.