Cell Implantation Application

New technology has been developed by the National Cancer Institute for the screening of anti-cancer compounds. The in vivo method of identifying compounds with potential chemotherapeutic activity against cancer and HIV is not routinely used by many researchers.

The technology allows human cells to be implanted into host animals and subsequently harvested en masse. While in the host, cells can be exposed to potential chemotherapeutic agents and the impact of that exposure can be measured after retrieval.

Target cell are macroencapsulated in biocompatible hollow fibers that are then implanted into the subcutaneous or intraperitoneal compartments of laboratory rodents. After selecting a subset of compounds with the hollow fiber encapsulation assay, the activity of the compounds is confirmed using the classical testing models currently used for evaluating these types of chemotherapeutic agents.

This methodology results in significant saving of time, labor, amount of compound required and the number of animals used in the evaluation of the potential therapeutic activity of these candidate compounds.

The hollow fiber assay is a unique in vivo model permitting the simultaneous evaluation of compound efficacy against six cell lines at subcutaneous (s.c.) and peritoneal (i.p.) sites (Hollingshead, et al. Life Sci. 57: 131, 1995). As an example, this model was used to investigate the relationship between cell density and compound activity. Additionally, the model was adapted for mechanism of action studies. A racemic mixture of flavorpiriodal (YZ149, a literature standard and a cyclin-dependent kinase inhibitor) was used. NCT116 cells (human colon carcinoma) were loaded into hollow fibers at cell densities of 1.0, 5.0 or 7.5 x 10⁶ cells/mL, and implanted s.c. or i.p. into nude mice. YZ149 was dosed daily by i.p. bolus at 6, 12, 18 and 25 mg/kg on days 3 through 6 after implantation. Cell growth was determined by the MTT dye conversion assay. In controls, increasing cell density decreased net cell growth with maximum cell growth at 1 x 10⁶ cells/mL, indicating the compound is more active against higher cell densities. After dosing, cells were removed from the fibers and changes in expression of cell cycle related proteins such a SCk, cyclins and Rb were monitored by Western Blot analysis. The protein changes were correlated with in vivo activity.

The data demonstrates the efficacy of a compound is a function of cell density, suggesting that the degree of stringency for drug activity can be targeted with the manipulation of cell density using this assay.

CellMax implants have the following advantaged over the current xenographic model: 10 day assay versus 60 day assay; small assay variability; fewer animals needed; uses small amounts of test compounds; multiple cell lines can be tested in the same animal model and they are compatible with different cell lines.