New methods to study breast cancer metastasis and invasion are required to advance our treatments of this most morbid aspect of the disease. We propose to utilize an extracorporeal functional liver bioreactor that can be viewed continuously for weeks to make it functional for investigating breast cancer metastasis. In this initial study, we will examine the role of motility in metastatic attainment and growth.

Breast cancer kills when it spreads from its original site in the mammary gland to distant organs. Current interventions are successful at removing the tumor from the breast and are curative if the spread has not occurred. However, once the tumor escapes from its original location, chemotherapy must find and target the disseminated metastases. Unfortunately, therapies have less than satisfactory response rates, let alone cures. What is needed is a better understanding of the tumor biology during metastatic growth, so as to identify key molecular targets for development of rational therapies. Our overall objective is to understand which tumor cell behaviors contribute to invasion and metastasis.

Scientific investigation into the biology of metastasis is limited by the tools available. We can study the tumor biology either outside the body or in surrogate hosts or tumor models. The main challenge is to understand metastasis, which is the sum of the tumor itself and the host organ. Current in vitro assays are manipulatable and accessible but suffer from loss of organ context. Relevant organ environments are provided by animal tumors, xenografts, and other in vivo systems, but these can be monitored only at static endpoints or over a very limited time period, while metastasis occurs over weeks to months. Further, specific alterations and interventions of tumor or host organ cells are cumbersome at best. Also, such in vivo systems are not human, with the inherent difficulties in directly extrapolating results, as many of key chemokines and cytokines do not cross species.

Our goal is to create an ex vivo organ system that can be used to study tumor cell behavior in an environment that mimics metastasis in patients. We have chosen the liver since it is a major site of metastasis for breast cancer. We have, as a starting point, an extracorporeal liver bioreactor that contains functioning liver cells in a representative architecture and functions similarly to normal liver cells. This system is stable for weeks and can be repeatedly or continuously imaged throughout.

In this proposal, we will use the first-generation reactor and a humanized, endothelial one being developed in studies to define the key determinants of tumor metastasis. Herein, we will determine whether cell motility is required for attainment of the liver parenchyma by metastatic cells and subsequent expansion.

The successful completion of these aims will provide a new organ model system for studying tumor progression. Even a limited system that supports only one of these stages of tumor progression would be a step forward, as it is coupled with long-term visualization and easy manipulability. We will determine what event in progression is limited by motility, attainment of the target organ parenchyma, or further expansive growth. This is key as new agents are being targeted at this biophysical process. In future studies, we will focus on defining both the molecular determinants of progression during the act of tumor progression, as well as other cell biological processes that might contribute to invasion and metastasis at the molecular level. This would provide for novel targets or known molecules in a new context for rational therapy design. A second thrust of future investigations will be to evaluate this system for human tumor specimens. We have access to sets of primary human tumor cells with linked clinical information and follow-up. These include, in total, over 1,000 early-passage lines from breast, ovarian, prostate, and lung carcinomas.