Guanazole

Guanazole is a ribonucleotide reductase (RNR) inhibitor that blocks replicative DNA synthesis by inhibiting deoxyribonucleotide biosynthesis. Guanazole selectively inhibits DNA synthesis in rapidly proliferating tissues, induces replication stress and G2/M phase arrest in Schizosaccharomyces pombe, and exhibits myelosuppressive, immunosuppressive, and anti-L1210 leukemia activities. Guanazole does not induce DNA repair and only shows slight mutagenicity towards Salmonella typhimurium TA102. Guanazole serves as an alternative tool to Hydroxyurea (HY-B0313) for replication checkpoint studies in Schizosaccharomyces pombe. Guanazole can be applied in research related to leukemia and solid tumors^{[1][2][3][4][5]}. In Vitro:Guanazole (2.52-252 μmole/plate) exhibits weak mutagenicity against Salmonella typhimurium strain TA102, with a mutagenic activity range of 0.60 to 1.63 mutants/μmole^[1].
Guanazole (0.05-50.0 mM) does not induce DNA repair in primary rat hepatocyte cultures^[1].
Guanazole (15 mM; 18 h) inhibits replicative DNA synthesis in primary rat hepatocyte cultures^[1].
Guanazole (15 mM; 18 h) supports the detection of DNA repair synthesis in primary cultured rat hepatocytes induced by a variety of genotoxic agents. Its detection sensitivity is comparable to that of Hydroxyurea (HY-B0313) for most agents, higher for MNNG, and lower for aflatoxin B₁ and H₂O₂^[1].
Guanazole (48 h) exhibits acute toxicity to Daphnia magna, with an EC50 of 4.13 mg/L^[4].
Guanazole (15-30 mM; 3 days) specifically induces replication stress in Schizosaccharomyces pombe replication checkpoint mutants (rad3Δ, cds1Δ), and its cytotoxicity against metabolic mutants (erg11-1, hem13-1) is far lower than that of hydroxyurea^[3].
Guanazole (50-250 mM; 8 h) induces acute replication stress in rad3Δ Schizosaccharomyces pombe cells; due to the presence of additional stress responses, the cytotoxicity at high doses is unexpectedly reduced^[3].
Guanazole (200 mM; 6 h) induces acute replication stress in Schizosaccharomyces pombe rad3Δ and cds1Δ cells, and both mutants exhibit comparable sensitivity due to additional G₂/M checkpoint stress^[3].
Guanazole (50-300 mM; 3 h) induces Rad3-dependent phosphorylation of Mrc1-Thr645 in wild-type Schizosaccharomyces pombe cells, and this site is a marker of replication stress^[3].
Guanazole (200 mM; 6 h) induces G₂/M phase cell cycle arrest accompanied by replication stress in both wild-type and rad3Δ Schizosaccharomyces pombe cells after 6 h ^[3].
Guanazole (200 mM; 3 h) inhibits the "cut" phenotype of premature mitosis in rad3Δ Schizosaccharomyces pombe cells, and does not induce elongation in wild-type, mrc1Δ, or erg11-1 cells. This result is consistent with G2/M cell cycle arrest^[3].
Guanazole inhibits purified calf thymus ribonucleotide reductase with an IC₅₀ of 460 μM by disrupting the tyrosyl radical of the enzyme^[5].
Guanazole is an inhibitor of the ribonucleotide reductase M2 subunit, with a potency approximately one-quarter that of Hydroxyurea, and its inhibitory activity can be enhanced by iron chelators ^[5].
Guanazole exhibits cross-resistance in hydroxyurea-resistant Chinese hamster ovary cells and mouse L cells with upregulated or altered expression of ribonucleotide reductase^[5]. In Vivo:Guanazole (30 mg/mL; i.v.; 0.3 mL/hr; 47 hr) causes marked inhibition of ¹⁴C-uridine incorporation into DNA in rapidly proliferating healthy mouse tissues, with the greatest inhibition in spleen (16.4% of control), followed by thymus (33.6% of control) and bone marrow (58.4% of control), while increasing incorporation in liver DNA (177.0% of control)^[2].
Guanazole has low acute toxicity to zebrafish embryos, with 72-hour LC₅₀ values ranging from ≥29.70 mg/L to 17320 mg/L across replicate tests^[4].