Syntheses of Trehalose Monomycolate and Related Compounds, and Their Lethal Toxicity and Adjuvant Activity

Development of immunoadjuvants for immunotherapy of cancer

Previously, we have reported that cell-wall skeleton (CWS) fraction was the major adjuvant-active principle of mycobacterial cells which were used in Freund's complete adjuvant (FCA). We have described the biochemical and immunological properties of CWS of mycobacteria and related bacteria, especially the CWS of Mycobacterium bovis BCG strain (BCG-CWS) in detail. The effectiveness of BCG-CWS for the cancer immunotherapy in patients was shown in several clinical trials. On the action mechanism of BCG-CWS on host immune cells, we have suggested that dendritic cells and macrophages express two sorts of receptors, Toll-like receptors, TLR-2 and TLR-4, and a putative binding receptor for BCG-CWS, whose signaling pathways lead to a sufficient antigen-presenting state in the activation of the innate immune system. We have also reported the usefulness of synthetic immunoadjuvants such as muramyldipeptide (MDP) derivatives, trehalose-dimycolates (TDM) and DNA fraction for the application for the cancer and infectious diseases in experimental systems and cancer patients.

Inhibitory effect of trehalose dimycolate (TDM) and its stereoisometric derivatives, trehalose dicorynomycolates (TDCMs), with low toxicity on lung metastasis of tumour cells in mice

We examined the effect of semisynthetic trehalose-6,6 '-dimycolate (TDM) and its synthetic stereoisomeric derivatives (trehalose 6,6'-dicorynomycolates; TDCMs) prepared in oil-in-water (o/w) emulsion on inhibition of lung metastasis produced by highly metastatic murine tumour cells, colon 26-M3.1 carcinoma and B16-BL6 melanoma cells, using experimental and spontaneous metastasis models. Intravenous (i.v.) administration of TDM (100 microg/mouse) 1, 3 or 8 days before tumour inoculation significantly inhibited lung metastasis of colon 26-M3.1 cells, in a dose-dependent manner. Single administration of TDM 1 day after tumour inoculation also showed the therapeutic effect on experimental lung metastasis of colon 26-M3.1 cells. Similarly, multiple administrations of TDM after tumour inoculation resulted in a significant inhibition of spontaneous lung metastasis of B16-BL6 cells (on day 35), although it showed no effect on suppression of tumour growth (on day 21). In comparison of toxicity in vivo among TDM and four TDCMs such as TDCM(2R,3R), TDCM(2S,3R), TDCM(2R,3S) and TDCM(2S,3S), all of the TDCMs appeared to be less toxic than TDM itself. Furthermore, all of the TDCMs were prophylactically as well as therapeutically active for inhibition of lung metastasis of both colon 26-M3.1 and B16-BL6 tumour cells, showing higher inhibitory activity than that of TDM. In particular, TDCMs induced a marked suppression of the growth of B16-BL6 tumour cells in vivo. These results suggest that systemic administration of TDM as well as TDCMs led to inhibition of tumour metastasis and TDCMs are more potential to suppress tumour growth and inhibit tumour metastasis than TDM.

Synthesis of O-[2-acetamido-2-deoxy-6-O-stearoyl- and -6-O-(2-tetradecylhexadecanoyl)-beta-D-glucopyranosyl]-(1-->4)-N- acetylnormuramoyl-L-alpha-aminobutanoyl-D-isoglutamine, lipophilic disaccharide analogues of MDP

Silver triflate-promoted condensation of 3,4,6-tri-O-acetyl-2-deoxy-2- phthalimido-beta-D-glucopyranosyl bromide (1) with benzyl 2-acetamido-6-O-benzyl-2-deoxy-3-O- (methoxycarbonyl)methyl-alpha-D-glucopyranoside (4) afforded the key compound, benzyl 2-acetamido-6-O-benzyl-2-deoxy-3-O- (methoxy-carbonyl)methyl-4-O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-b eta-D- glucopyranosyl)-alpha-D-glucopyranoside (5), which after deprotection was transformed into acid 10. Condensation of 10 with the benzyl ester of L-alpha-aminobutanoyl-D-isoglutamine and deisopropylidenation of the product 11 afforded the benzyl ester of N-(2-O-[benzyl 2-acetamido-4-O-(2-acetamido-3-O-benzyloxymethyl-2- deoxy-beta-D-glucopyranosyl)-6-O-benzyl-2,3-dideoxy-alpha-D-glucopyra nosid-3- yl]glycoloyl)-L-alpha-aminobutanoyl-D-isoglutamine (12). Partial O-acylation of 12 and hydrogenolysis of protecting groups gave the 6-O-stearoyl- and 6-O-(2-tetradecylhexadecanoyl)-disaccharide-dipeptides 17 and 18, respectively. Pyrogenicity and adjuvant activity in cell-mediated immunity are reported.

Synthetic immunoadjuvants: application to non-specific host stimulation and potentiation of vaccine immunogenicity

It is well recognized that immunoadjuvants mainly play two roles; non-specific stimulation of host resistance against infections and cancer, and the potentiation of vaccine immunogenicity. This article reviews the recent results of the development of synthetic immunoadjuvants in our laboratory with special reference to muramyldipeptide (MDP), trehalose dimycolate (TDM), lipid A, chitin and their related compounds. The usefulness of MDP derivative MDP-Lys(L18), which has recently gone on the market as a haematopoietic agent for restoration of leukopenia in cancer patients treated with radiotherapy and chemotherapy, is reviewed. The various approaches to application of synthetic immunoadjuvants to the potentiation of vaccine immunogenicity, including adjuvant formulation, are also discussed.

An improved synthesis of trehalose 6-mono- and 6,6'-di-corynomycolates and related esters

A simplified synthesis of 6-mono- and 6,6'-di-corynomycolate esters of alpha,alpha-trehalose, and related compounds, was achieved by coupling the (hydroxyl-protected) acids to the partially trimethylsilylated sugar in the presence of dicyclohexylcarbodiimide and 4-dimethylaminopyridine. As acid reactants, (2-RS,3-RS)-3-hydroxy-2-tetradecyloctadecanoic acid (DL-corynomycolic acid) and its 2RS,3SR diastereomer were prepared from methyl palmitate by sequential Claisen condensation, reduction, chromatographic separation, and saponification. Reaction with tert-butylchlorodimethylsilane (imidazole) gave the disubstituted ether-esters, which were converted into the required 3-tert-butyldimethylsilyl ethers by partial hydrolysis. 6-Linked monocorynomycolate was obtained in excellent yield (78%) from the reaction of the RS,SR acid with the known heptakis-O-(trimethylsilyl)trehalose, and in good yield from equimolar portions of RS,RS acid and hexakis-O-(trimethylsilyl)trehalose. An excess (2.5-molar portions) of the RS,RS acid gave the 6,6'-diester (69%). The mono- and di-palmitate were similarly obtained from (Me3Si)6-trehalose. The mono (RS,RS)-(Me3Si)6-trehalose coupling product was partially resolved on a silica gel column into its RR and SS diastereomers, the former corresponding to the naturally occurring trehalose monocorynomycolate. All coupling products were deprotected to free trehalose esters by treatment first with K2CO3 in methanol, then tetrabutylammonium fluoride-trifluoracetic acid in oxolane.

Chemical synthesis and biological activities of 6,6'-di-O-mycoloyl-beta,beta- and -alpha,beta-trehalose

6,6'Di-O-mycoloyl-beta,beta-trehalose (beta,beta-TDM) and 6,6'-di-O-mycoloyl-alpha,beta-trehalose (alpha,beta-TDM) were synthesized and their toxicity and ability to activate peritoneal macrophages in situ were examined in mice, in comparison with 6,6'-di-O-mycoloyl-alpha,alpha-trehalose (TDM). Both beta,beta-TDM and alpha,beta-TDM caused a decrease in body weight two days after injection, however the weights reverted to a normal level. No deaths were caused by either analog. On the other hand, TDM showed potent toxicity, causing decrease in body weight and death of all animals injected. Beta,beta-TDM and alpha,beta-TDM were effective in the in situ activation of mouse peritoneal macrophages.

Lethal toxicity and adjuvant activities of synthetic TDM and its related compounds in mice

Trehalose-6,6'-dimycolate (TDM) and its monosaccharide-type analogues were synthesized, and their lethal and adjuvant activities were examined in mice. All the monosaccharide-type analogues with a glucose or N-acetylglucosamine moiety were devoid of lethal toxicity to mice; in particular, D-GlcNAcM(1-deoxy) and D-GlcNM did not cause any loss of body weight at an early stage after intravenous administration as a 9% oil-in-water emulsion. Intraperitoneal administration of D-GlcNAcM(1-deoxy) in aqueous suspension, as well as TDM, could activate macrophages to become tumoricidal against tumour cells, whereas D-GlcNAcM(1-deoxy) in oil emulsion, unlike TDM, caused no granulomatous formation in the lung after intravenous injection. Squalane-treated D-GlcNAcM(1-deoxy) showed significant inhibition of spontaneous lung metastases by B16-BL6 melanoma cells when it was administered twice intratumorally. The non-toxic monosaccharide-type analogue of TDM [D-GlcNAcM(1-deoxy)] was a beneficial adjuvant for the activation of macrophages and the prevention of cancer metastasis.

Regression of line-10 hepatocellular carcinoma by a less toxic cord factor analogue combined with L18-MDP or synthetic lipid A analogues

A transplantable hepatocarcinoma of strain 2 guinea pigs was used as an experimental model for immunotherapy of cancer. 6,6'-Dideoxy-6,6'-bis-mycoloylamino-alpha,alpha- trehalose (TDNM) was found to be more effective in producing regression of transplantable line-10 tumours than 6,6'-di-O-mycoloyl-alpha,alpha-trehalose (TDM) when combined with 6-O-stearoyl muramyldipeptide (L18-MDP). TDNM showed potent antitumour activity in combination with synthetic lipid A of Escherichia coli (compound 506), but not with the lipid A analogues (GLA-59 and 60). As with the combination of MDP derivative and lipid A analogue, MDP derivatives conjugated with GLA-60 (GMD compounds) showed no tumour regression activity of line-10 cells in guinea-pigs.