Carcinostatic activity of methylglyoxal and related substances in tumour-bearing mice.

Methylglyoxal treatment of tumour cells in vitro primarily depresses protein synthesis, in contrast to trans-4-hydroxypent-2-enal (HPE) which preferentially inhibits DNA synthesis. Methylglyoxal and hpe are potent carcinostatic agents in vitro but relatively ineffective in vivo. Both aldehydes have a short half-life in vivo which may explain their poor carcinostatic properties when administered other than peritumorally. Several possibilities of increasing the effective half-life were investigated including (i) multiple intraperitoneal injections, (ii) concomitant administration of an inhibitor of glyoxalase I, (iii) administration of aldehyde-cysteine adducts, and (iv continuous intravenous infusion. Methylglyoxal (36 mg/kg i.p., twice daily) was slightly less effective in inhibiting the growth of the solid form of Ehrlich carcinoma than a dose of 72 mg/kg (inj. 1); 36 mg/kg (inj. 2) 46.2% compared to 51%. The aldehyde was more effective aginst the ascitic form of the tumour, with 99.76% inhibition of growth after giving 72 mg/kg twice daily for five days followed by 36 mg/kg for five days. The glyoxalase I inhibitor S-(p-bromobenzyl)-glutathione didnot significantly enhance the activity of methylglyoxal against the solid form of the tumour. Nicotinamide (1% w/v in the drink) was similarily inactive. Methylglyoxal in combination with nicotinamide was significantly more effect (P less than 0.05) than methylglyoxal alone (36 mg/kg, twice daily) in inhibiting the growth of the ascitic tumour. Methylglyoxal-N-acetyl-L-cysteine was four times less toxic than methylglyoxalalone but was marginally less effective against the ascitic form of the tumour. Doses of these adducts equivalent to 144 mg/kg per day of methylglyoxal were more effective P less than 0.05) than the optimal regime of methylglyoxal in inhibiting the solid tumour (67.5% inhibition compared to 51%). Treatment of mice bearing the ascitic form of Sarcoma 180 with five daily doses (i.p.) of an HPE-cysteine adduct equivalent to a dose of HPE alone of 32-256 mg/kg per day significantly increased survival time by comparison with controls. The adduct was 2-3 times more effective, dose-for-dose, than HPE alone in inhibiting tumour growth. Purified buffered methylglyoxal has an LD50 on continuous infusion into the right lateral tail vein in mice of more than 3.0 mg/g per day (seven days at 2.8 ml/day). Local oedema followed by tail necrosis occurs at doses in excess of 0.25-0.5 mg/g per day in mice bearing the solid forms of the syngeneic tumours: squamous carcinoma D; lymphosarcoma 1 (WH/Ht mice); and spontaneous mammary D5056 (CBA/CA mice). A maximum tumour volume growth delay of 3.4 days at Day 17 (P less than 0.001) after transplantation was observed after infusion of 0.5 mg/g per day methylglyoxal on Days 11-17 in the CBA/CA D40 syngeneic mammary tumour. Tumour regrowth after termination of therapy eliminated the significant difference between control and methylglyoxal-treated tumours by Day 27. Methylglyoxal infusion (0...