Regression of tumors in guinea pigs after treatment with synthetic muramyl dipeptides and trehalose dimycolate.

A high incidence of tumor regression was observed in guinea pigs bearing transplantable, line-10 hepatocellular carcinomas when synthetic muramyl dipeptides combined with trehalose dimycolate in oil-in-water emulsions were injected directly into the tumors. These compounds are promising candidates to replace viable bacillus Calmette-Guérin in cancer immunotherapy in humans and animals.

A shortened synthesis of adjuvant dipeptide (MDP).

N-acetylmuramyl-L-alanyl-D-isoglutamine, or muramyl dipeptide (MDP), has been shown to be the minimal structure necessary for adjuvant activity. This compound can replace whole mycobacteria in Freund's complete adjuvant. In our continuing investigation of bacterial cell wall fragments of biological and immunotherapeutic interest, the necessity of obtaining MDP analogs of varying structure has proven to be of primary importance. We have found that the published routes to MDP could be effectively shortened to four steps starting from commercially available starting materials. As an example of this scheme, synthesis of the seryl analog will be detailed. gamma-benzyl glutamic acid could be elaborated in one step to the N-tertiary butoxycarbonyl seryl-gamma-benzyl isoglutamine. Deprotection of the Boc group followed by condensation with 1-O-benzyl-4, 6-O-benzylidine N-acetyl muramic acid provided the protected MDP. Deprotection of this product by hydrogenolysis gave the final product. Physical chemical and biological data as proof of structure is presented. Utility of these compounds in the line-10 tumor system is demonstrated.

Enhancement of endotoxic shock by N-acetylmuramyl-L-alanyl-(L-seryl)-D-isoglutamine (muramyl dipeptide).

We described elsewhere that the synergistic antitumor activity of endotoxic extracts from Re mutants of gram-negative bacteria and trehalose mycolate against guinea pig syngeneic line 10 tumor was abrogated after peptide substances accompanying these extracts had been removed. This activity could be restored by combining peptide-free endotoxin either with cell wall skeleton from Bacillus Calmette-Guérin, a polymeric mycolic acid-arabinogalactan-mucopeptide complex, or with a combination of two separate components, trehalose dimycolate and N-acetylmuramyl-L-alanyl-(L-seryl)-D-isoglutamine (MDP). We report here that when a combination of endotoxin (150 microgram) and a mixture of MDP (150 microgram) and trehalose dimycolate (150 microgram) was inoculated into established dermal tumors, a significant number of the animals died, presumably of endotoxic shock. All surviving animals suffered severe but temporary lethargy. When administered alone intradermally in the dose levels tested, none of the components caused severe lethargy or lethality. The lethal effects of 159 microgram of MDP also occurred in combination with relatively weak endotoxic products, such as Pseudomonas vaccine (Pseudogen), and these effects did not depend upon the presence of malignant tissue. Guinea pigs inoculated i.v. were even more susceptible inasmuch as the addition of as little as 6 microgram of MDP to 150 microgram of Pseudogen, itself not lethal, caused the death of 80% of the animals.