Effect of Incubation With Rabbit Serum on Toxicity and Tumor-Necrotizing Action of Polysaccharide From S. marcescens

¹ From the Laboratory of Chemical Pharmacology and the Clinical Pharmacology and Experimental Therapeutics Section, National Cancer Institute, National Institutes of Health, Bethesda, Maryland

Effect of incubation with rabbit serum on the lethality and tumor-necrotizing activity of two pyrogenic polysaccharide preparations was studied in mice carrying i.m. implants of sarcoma 37. The polysaccharide materials were isolated from the same strain of S. marcescens, but were prepared in different laboratories and obtained by different methods. One preparation was a crude, insoluble fraction containing protein, the other was a soluble, trypsin-digested material giving negative protein color tests. Incubation in serum reduced the lethality of the crude preparation by about 50%, but had no effect on the lethality of the more highly purified polysaccharide; it had no demonstrable effect, moreover, on the tumor-necrotizing activity of either preparation. Similar results were obtained with mice rendered tolerant by two injections of polysaccharide in saline. The factor in serum responsible for the decrease in toxicity of the crude preparation was stable to heating at 56°C for 30 minutes, but was inactivated by heating to 70°C for 8 minutes. Tumor implants exhibited apparent refractoriness to the tumor-necrotizing action of the polysaccharide preparations after 6 days growth in hosts rendered tolerant to the lethal action of the material before tumor implantation.