Intratumor injections of oil-in-water emulsions containing mycobacterial whole-cell extraction residues, cell walls, or cell wall skeletons combined with a phenol:water extract of heptoseless (Re) mutant Salmonella typhimurium produced high percentages of regression of line 10 hepatocellular carcinomas in strain 2 guinea pigs. Injection of one of the mycobacterial components plus Salmonella extract cured higher percentages of tumor-bearing animals than did treatment with either microbial substance alone.

Mycobacterial whole-cell extraction residues and cell wall skeletons exposed to hydrochloric acid, potassium hydroxide, or organic solvents produced residues with varying antitumor activity. Interaction of these microbial substances with oil droplets was measured by determining the nitrogen content of the oil and aqueous phases of oil-in-water emulsions containing the test substances. A linear, positive correlation was found between tumor regressive activity and capability of the mycobacterial substances to interact with oil droplets of oil-in-water emulsions.

However, interaction of radiolabeled Salmonella extract and radiolabeled cell wall skeleton with oil droplets revealed that neither of these materials affected the binding of the other with oil droplets. Thus, the synergistic antitumor activity obtained by combined treatment with cell wall skeleton and Salmonella extract was not a consequence of the enhanced interaction of the microbial materials with the oil phase of the therapeutic oil-in-water emulsions. Presumably, the synergistic antitumor effect of combined therapy was due to individual, host-mediated responses to the two microbial substances. These as yet unknown biological responses culminated in expression of potent tumor regressive activity.

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