Breast cancer is the leading cause of cancer-related mortality in women worldwide. Liver metastasis is involved in upwards of 30% of cases with breast cancer metastasis, and results in poor outcomes with median survival rates of only 4.8 -15 months. Current rodent models of breast cancer metastasis, including primary tumor cell xenograft and spontaneous tumor models, rarely metastasize to the liver. Intracardiac and intrasplenic injection models do result in liver metastases, however these models can be confounded by concomitant secondary-site metastasis, or by compromised immunity due to removal of the spleen to avoid tumor growth at the injection site. To address the need for improved liver metastasis models, a murine portal vein injection method that delivers tumor cells firstly and directly to the liver was developed. This model delivers tumor cells to the liver without complications of concurrent metastases in other organs or removal of the spleen. The optimized portal vein protocol employs small injection volumes of 5 -10 μl, ≥ 32 gauge needles, and hemostatic gauze at the injection site to control for blood loss. The portal vein injection approach in Balb/c female mice using three syngeneic mammary tumor lines of varying metastatic potential was tested; high-metastatic 4T1 cells, moderate-metastatic D2A1 cells, and low-metastatic D2.OR cells. Concentrations of ≤ 10,000 cells/injection results in a latency of ~ 20 -40 days for development of liver metastases with the higher metastatic 4T1 and D2A1 lines, and > 55 days for the less aggressive D2.OR line. This model represents an important tool to study breast cancer metastasis to the liver, and may be applicable to other cancers that frequently metastasize to the liver including colorectal and pancreatic adenocarcinomas.

The conformational analysis of the ionophore metal complex salinomycin-Na by N M R spectroscopy and molecular dynamics (MD) calculation was carried out in solution to study a model for ion transport across biological membranes. The first N M R solution structure of an ionophore metal complex using NOE-derived distances is reported. The 51 distance constaints derived from a 600-MHz NOESY spectrum of this molecule in the extreme narrowing limit were in agreement with an overall macrocyclic solution structure. The back-calculation of the NOESY spectrum confirmed the reliability of the NOE data. The structure was first refined by MD simulation in vacuo without a sodium ion present and subsequently in solution in the presence of a sodium ion. The complex shows a hydrophobic surface and a hydrophilic core, with the ion coordinated by a distorted pentagonal pyramid of oxygen atoms. Additional free MD simulations with and without the ion provide further information about the exact hinge regions and a possible mechanism of ionophoric action.

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