In 1990 and 1991, samples of Cancell/Cantron/Protocel were evaluated in NCI’s in vitro NCI-60 DTP Human Tumor Cell Line Screen. In the screen, the cell lines are grown in artificial media under conditions that do not truly mimic the in vivo situation in animals or humans. The important information used in assessing a drug’s effectiveness in the NCI in vitro screen includes drug concentrations necessary to achieve the following:
- 50% inhibition of cell growth (GI50; the concentration needed to reduce the growth of treated cells to half that of untreated [i.e., control] cells).
- 100% (total) growth inhibition (TGI; the concentration required to completely halt the growth of treated cells).
- 50% cell kill or lethal concentration (LC50; the concentration that kills 50% of treated cells).
The log10 values for GI50, TGI, and LC50 for the 60 cell lines are available online.
The variations in log10 values for GI50 are 0.4 to 1.8 (mean = 1.15), equivalent to concentrations of 2.5 to 63 μg /mL (mean = 14); the variations in log10 values for TGI are 1.0 to 2.5 (mean = 1.62), equivalent to 10 to 320 μg/mL (mean = 41); and the variations in log10 values for LC50 are 1.6 to 3.9 (mean = 3.17), equivalent to 39 to 7,943 μg/mL (mean = 1,479).
|Parameter Measured||60 Cell-line Range (μg/mL)||Mean (μg/mL)|
|50% growth inhibition (GI50)||2.5–63||14|
|Total growth inhibition (TGI)||10–320||41|
|Concentration for 50% lethality (LC50)||39–7,943||1,479|
|Maximum theoretical human plasma concentration (for comparison)||—||29 (calculated)|
Based on the manufacturer's recommended doses of a marketed brand of Cancell/Cantron/Protocel it has been calculated that under idealized conditions of absolutely no loss of the constituents after administration to a patient (i.e., 100% bioavailability, meaning no loss due to degradation, absorption in the body, or rapid excretion—an unlikely situation), the maximum concentration that could be achieved in the plasma of an average 154-lb male is 29 μg/mL (antilog of 1.46). Thus, under these highly idealized conditions Cancell/Cantron/Protocel may exhibit some mild inhibitory effect on the growth of some cancer cells, but it would not be expected to inhibit their growth completely or to kill them. There is little evidence that any of the constituents of Cancell/Cantron/Protocel would be available in the bloodstream of a patient.
Activity was seen in two-thirds of the cell lines, though at levels that would be roughly 275 times higher than the theoretical maximum concentration achievable in serum. Therefore, the in vitro effects are likely due to nonspecific effects of changes in salt concentration. Furthermore, cells in the NCI Tumor Cell Line Screen are grown in artificial media under conditions that do not truly mimic the in vivo situation in animals or humans, and results obtained with the screen may not accurately reflect possible effects in humans. To place the findings for Cancell/Cantron/Protocel in perspective, any conventional drug exhibiting this low level of in vitro activity in the NCI human cancer cell line screen would normally not be investigated further by NCI.
The principal manufacturers of Cancell/Cantron/Protocel have stated that they have performed numerous animal experiments with the mixture involving tens of thousands of mice.[1,2] Results of these experiments, however, have not been published in peer-reviewed scientific journals and no information beyond stating that some of the experiments tested the toxicity of Cancell/Cantron/Protocel has been provided.