Effect of Osmotic Pressure on Uptake of Chemotherapeutic Agents by Carcinoma Cells

Robert L. Stephen, Jeanne M. Novak, Elizabeth M. Jensen, Carl Kabilitz, and Saundra S. Buys. "Effect of Osmotic Pressure on Uptake of Chemotherapeutic Agents by Carcinoma Cells". Cancer Research (1990), Volume 50, 4704-4708

Summary:

Intraperitoneal chemotherapy, a treatment in which chemotherapeutic drugs are injected directly into the abdomen, has been a widely accepted treatment for intraabdominal tumors such as ovarian cancer and colon cancer. This study focuses on examining the osmolarity of the fluid used for drug administration and its effect on the pharmacokinetics of drugs administered. The authors employed both the cell culture model and the animal model to explore the drug uptake in hypotonic, isotonic and hypertonic solutions. With the cell model, two tumor cell types, HeLa and Murine Teratoma primary cells, were incubated with 5-fluorouracil (5-FU), which is an anticancer drug with autofluorescence, and [C14]dextran/sucrose, which are extracellular markers, in different osmolar solution. The total 5-FU uptake is then measured at a regular interval up to 30 minutes after the subtraction of background radioactivity from the extracellular fluid content. With the animal model, six-to-eight-week old female mice were injected with teratoma cells initially, and doxorubicin, also a chemotherapeutic drug, four days later in different osmolar solutions. The mice were sacrificed and the cellular doxorubicin content was measured using fluorometry.

Results indicate that the uptake of chemotherapeutic drug into tumor cells is increased significantly when in a hypotonic solution (lower osmolarity) with both the cell model and the animal model. In a hypotonic solution, the effect of convective flux causes water to flow into cells and drags the drug infused along, therefore, increases drug uptake. The study also compares the binding pattern of the two cell lines used. The paper points out that for HeLa cells, the amount of 5-FU uptake decreases over time, and this can be due to the regulatory volume adjustment process in a hypotonic solution (5-FU eventually flows out of cells to reach equilibrium). The amount of 5-FU uptake for the teratoma primary cells, however, increases steadily over time. The paper proposes the possibility of intracellular drug binding sites to retain chemotherapeutic agents in these primary cells. Comparing the animal model and the cell model, the amount of drug uptake in animal model is significant, but less than in cell models. The paper suggests that this may be caused by the accumulation of ascitic fluid that may dilute the drug concentration and adjust the infusate toward isotonicity. Finally, the paper defines some practical application of the results to drug delivery in intraperitoneal chemotherapy. The use of hypotonic solution will increase the depth of drug penetration into the tumor mass due to higher drug accumulation. Also, the hypotonic solution will facilitate drug uptake into the afferent arteriole through convective flux and directly affect vascularized areas of the tumor. Through a recent pilot study, this change in osmolarity of the infusate seems promising.

Cell model result:

Animal model result:

Critique:

One concern I have for this study is the lack of negative control. For the cell model experiment, the amount of fluorescence from 5-FU is measured in hypotonic, isotonic and hypertonic solutions. However, the study fails to mention subtracting background fluorescence from the culture by using a negative control. There might be proteins present in cultures that may autofluoresce and be added to the measurement. The study also uses different chemotherapeutic agents in the cell culture experiment and the animal experiment without explaining the reason and the potential effects of comparing the two results. The difference in chemical property of the anticancer drugs and the pathway of drug intake might affect the experimental outcomes, causing the different results in the two models. In terms of flaw in conclusion, the paper compares the differential effects on pharmacokinetic in different osmolar solutions without investigating and analyzing the possible impacts of these solutions on the cells. With a hypotonic solution, there is a greater chemotherapeutic drug intake but this may lead to a rise in cytotoxicity level, and the sudden application of osmotic stress may also induce apoptosis in normal healthy cells, which are undesirable. A more comprehensive study of these negative impacts needs to be done before any conclusion can be drawn for clinical application.