6-Diazo-5-oxo-L-norleucine (DON) is a glutamineantagonist, which was isolated originally from Streptomyces in a sample of Peruvian soil. This diazo compound is biosynthesized from lysine by three enzymes in bacteria.[2] It is one of the most famous non-proteinogenic amino acid and was characterized in 1956 by Henry W Dion et al.,[3] who suggested a possible use in cancer therapy. This antitumoral efficacy was confirmed in different animal models.[4] DON was tested as chemotherapeutic agent in different clinical studies, but was never approved. In 2019, DON was shown to kill tumor cells while reversing disease symptoms and improve overall survival in late-stage experimental glioblastoma in mice, when combined with calorie-restricted ketogenic diet.[5]
Chemistry
DON is a water-soluble yellowish powder, which can be dissolved also in aqueous solutions of methanol, acetone or ethanol, but dissolution in absolute alcohols is difficult. Solutions of at least 50 μM DON in 0.9% NaCl are lightly yellowish. The crystalline form appears as yellowish greenish needles. The specific rotation is [α]26D +21° (c = 5.4% in H2O). In phosphate buffer, pH 7 are the ultraviolet absorption maxima at 274 nm (E1%1 cm. 683) and 244 nm (E1%1 cm 376).[3][6]
Biochemistry
DON is used as inhibitor of different glutamine utilizing enzymes. Due to its similarity to glutamine, it can enter catalytic centres of these enzymes and inhibits them by covalent binding, or more precisely, by alkylation.[7][8] The following table gives a survey of DON targets.
DON is a cytotoxic inhibitor of many enzymes of nucleotide synthesis. It could be shown in vitro that DON treatment led to apoptosis, or programmed cell death. Different pathways were investigated; it could be shown that the inner mitochondrial membrane was damaged,[14] and that single strand DNA breaks occurred.[15] The exact mode of action remains unclear and needs further research.
DON has not been approved as a pharmaceutical agent; however, it has been tested in combination with a recombinant glutaminase in clinical trials for the treatment of different solid tumors.[16]
^"CID 5359375". PubChem. United States National Library of Medicine.
^Kawai S, Sugaya Y, Hagihara R, Tomita H, Katsuyama Y, Ohnishi Y (April 2021). "Complete Biosynthetic Pathway of Alazopeptin, a Tripeptide Consisting of Two Molecules of 6-Diazo-5-oxo-l-norleucine and One Molecule of Alanine". Angewandte Chemie. 60 (18): 10319–10325. doi:10.1002/anie.202100462. PMID33624374. S2CID232039107.
^ abDion HW, Fusari SA, Jakubowski ZL, Zora JG, Bartz QR, et al. (1954). 6-diazo-5-oxo-L-norleucine, A new tumor inhibitory substance. II: Isolation and Characterization. Antibiotics and Chemotherapy. Vol. 78. pp. 3075–7.
^Yoshioka K, Takehara H, Okada A, Komi N (June 1992). "Glutamine antagonist with diet deficient in glutamine and aspartate reduce tumor growth". The Tokushima Journal of Experimental Medicine. 39 (1–2): 69–76. PMID1412455.
^DeWald HA, Moore AM (August 1958). "6-Diazo-5-oxo-L-norleucine, a New Tumor-inhibitory Substance.1a Preparation of L-, D- and DL-Forms1b". Journal of the American Chemical Society. 80 (15): 3941–3945. doi:10.1021/ja01548a036.
^Ortlund E, Lacount MW, Lewinski K, Lebioda L (February 2000). "Reactions of Pseudomonas 7A glutaminase-asparaginase with diazo analogues of glutamine and asparagine result in unexpected covalent inhibitions and suggests an unusual catalytic triad Thr-Tyr-Glu". Biochemistry. 39 (6): 1199–1204. doi:10.1021/bi991797d. PMID10684596.
^Rosenbluth RJ, Cooney DA, Jayaram HN, Milman HA, Homan ER (August 1976). "DON, CONV and DONV-II. Inhibition of L-'asparagine synthetase in vivo". Biochemical Pharmacology. 25 (16): 1851–1858. doi:10.1016/0006-2952(76)90189-1. PMID9091.
^Wu F, Lukinius A, Bergström M, Eriksson B, Watanabe Y, Långström B (July 1999). "A mechanism behind the antitumour effect of 6-diazo-5-oxo-L-norleucine (DON): disruption of mitochondria". European Journal of Cancer. 35 (7): 1155–1161. doi:10.1016/S0959-8049(99)00099-4. PMID10533463.
^Mueller C, Al-Batran S, Jaeger E, Schmidt B, Bausch M, Unger C, Sethuraman N (2008). "A phase IIa study of PEGylated glutaminase (PEG-PGA) plus 6-diazo-5-oxo-L-norleucine (DON) in patients with advanced refractory solid tumors". J Clin Oncol. 26 (May 20 Suppl): abstr 2533. doi:10.1200/jco.2008.26.15_suppl.2533.