Nebularine

Nebularine (9-β-D-Ribofuranosylpurine) is a naturally occurring cytotoxic purine riboside antibiotic. Nebularine competitively inhibits adenine deaminase and xanthine oxidase, and acts as a template for thymine insertion during DNA elongation and replication. Nebularine serves as a cytokinin antagonist and induces mitotic aberrations in plant cells. Nebularine exhibits cytotoxicity against plants, mammals, fungal organisms and cancer cells. Nebularine can be used in research related to fungal infections, plant growth, as well as chronic myeloid leukemia, acute lymphoblastic leukemia and breast cancer^[1][2][3][4]. In Vitro:Nebularine acts as a template to guide the insertion of thymine by the nuclease-deficient Escherichia coli DNA polymerase I Klenow fragment in vitro^[1].
Nebularine (4 μM-2.0 mM; 1 week) potently inhibits the growth of seedlings of spinach, lettuce, carrot, alfalfa, snapdragon and wheat; at 2.0 mM, it inhibits the axis length, root length and aboveground fresh weight of wheat seedlings by 90%, 97% and 60%, respectively, and induces chromosomal abnormalities in root tip cells of all tested species^[2].
Nebularine (2.5-20 μM; 3-36 h) acts as a cytokinin antagonist in *Amaranthus caudatus* seedlings. When its concentration is 8-fold that of cytokinins, it inhibits kinetin- or zeatin-induced betalain biosynthesis, with a maximum inhibition rate of up to 60%, and increasing kinetin concentration reverses this inhibitory effect^[2].
Nebularine (20 μM; 5 days) antagonizes the green-retaining effect of kinetin in leaf segments of 7-day-old wheat seedlings; when 20 μM of this substance is present together with 2.5 μM kinetin, it reduces the activity of kinetin by 35%^[2].
Nebularine (4-20 μM) acts as a non-competitive inhibitor of xanthine oxidase, and inhibits 85% of the enzyme activity at a substrate xanthine concentration of 40 μM and its own concentration of 20 μM^[2].
Nebularine (72 h) potently inhibits the viability of human K562, CEM and MCF-7 cell lines, with IC₅₀ values of 2.2 μM, 1.1 μM and 3.6 μM, respectively^[3].
Nebularine (10-100 μM; 24-48 h) inhibits the viability of tobacco BY-2 cells, with an IC₅₀ of 20 μM after 48 h of incubation^[3].
Nebularine (0.067 mM) inhibits human erythrocyte adenosine deaminase ADA1 by reducing inosine production to 60%^[3].
Nebularine (0.25-1 μM; 7 days) concentration-dependently shortens the primary root and promotes lateral root formation in Arabidopsis thaliana Col-0 seedlings, and also reverses the lateral root inhibition induced by 0.01 μM BAP (HY-B0941)^[3].
Nebularine (10-100 μM; 6 days) antagonizes the chlorophyll retention effect of 30 μM BAP on isolated wheat leaf tips, reducing this effect to 55% after 6 days of incubation at equimolar concentrations^[3].
Nebularine (1-50 μM) inhibits the growth of cytokinin-dependent tobacco calli stimulated by 1 μM BAP in a concentration-dependent manner^[3].
Nebularine (10-50 μM; 16 h) reduces the expression levels of cytokinin-responsive ARR5:GUS and auxin-responsive DR5:GUS in Arabidopsis thaliana seedlings; after incubation at 10 μM or higher concentrations for 16 h, the induced expression levels are reduced to approximately 70%^[3].
Nebularine (500 μg per paper disc; 2-5 days) exhibits moderate antifungal activity against Magnaporthe grisea and Trichophyton mentagrophytes, with an inhibition zone diameter of 9 mm (including the diameter of the paper disc), and shows no activity against other tested fungi and bacteria^[4].