Cell experiment:

Treatments consists of 3 thiopurines (azathioprine, 6-mercaptopurine, and 6-Thioguanine (Thioguanine)) at each of 6 concentrations (0.468, 0.937, 1.875, 3.750, 7.500, and 15.000 μM). Each thiopurinee is dissolved in DMSO solution to achieve a concentration of 10 mg/mL. Sterile filtered maintenance medium is used to further dilute each thiopurine solution to each of the 6 treatment concentrations. Twenty-four hours after the hepatocytes are plated on 96-well culture[3].

6-Thioguanine (Thioguanine; 2-Amino-6-purinethiol) is an anti-leukemia and immunosuppressant agent, acts as an inhibitor of SARS and MERS coronavirus papain-like proteases (PLpros) and also potently inhibits USP2 activity, with IC50s of 25 μM and 40 μM for Plpros and recombinant human USP2, respectively.

6-Thioguanine (Thioguanine; 2-Amino-6-purinethiol) is an anti-leukemia and immunosuppressant agent, acts as an inhibitor of SARS and MERS coronavirus papain-like proteases (PLpros) and also potently inhibits USP2 activity, with IC50s of 25 μM and 40 μM for Plpros and recombinant human USP2, respectively[1]. 6-Thioguanine (Thioguanine) affects the methylation of cytosine residues by purified DNA methyltransferases including human DNMT1 and bacterial HpaII methylase. 6-Thioguanine (Thioguanine) (1 or 3 μM) decreases global cytosine methylation in Jurkat T cells and cytosine methylation in human cells at 3 μM[2]. 6-Thioguanine (Thioguanine) (18.75, 37.50, or 75.00 μM) adversely affects cell viability, but with no effect on LDH or ALT activity[3].

References:
[1]. Chuang SJ, et al. 6-Thioguanine is a noncompetitive and slow binding inhibitor of human deubiquitinating protease USP2. Sci Rep. 2018 Feb 15;8(1):3102.
[2]. Wang H, et al. 6-Thioguanine perturbs cytosine methylation at the CpG dinucleotide site by DNA methyltransferases in vitro and acts as a DNA demethylating agent in vivo. Biochemistry. 2009 Mar 17;48(10):2290-9.
[3]. LaDuke KE, et al. Effects of azathioprine, 6-mercaptopurine, and 6-thioguanine on canine primary hepatocytes. Am J Vet Res. 2015 Jul;76(7):649-55.