Kinase experiment:

Stock solutions of malachite green (0.081% w/v), polyvinyl alcohol (2.3% w/v), and ammonium heptamolybdate tetrahydrate (5.7% w/v in 6 M HCl) are prepared and stored at 4℃. Three solutions are mixed with water in the ratio of 2 : 1 : 1 : 2 to prepare the malachite green reagent. For the determination of the ATPase activity of Hsc70, a master mixture of an ATPase domain of Hsc70 is prepared in assay buffer (100 mM Tris-HCl, 20 mM KCl, and 6 mM MgCl2, pH 7.4) as the final concentration of 1 mM. An aliquot (10 mL) of this mixture is added into each well of a 96-well plate. To this solution is added each compound (including Apoptozole) in assay buffer, and the plate is incubated for 30 min at room temperature. To start the reaction, 1 mL of 4 mM ATP is added to the solution. The final concentrations are 1 mM protein and 200 mM ATP in 20 mL of assay buffer. After 3 h incubation at 37℃, 80 mL of the malachite green reagent is added into each well. The samples are mixed thoroughly and incubated at 37℃ for 15 min, and 10 mL of 34% sodium citrate is added to stop the nonenzymatic hydrolysis of ATP. The absorbance is determined at 620 nm on a SpectraMax 340 PC 384[1].

Cell experiment:

Cells (5 × 105 per well) are plated in triplicate in 96-well plates in 0.1 mL of culture media with 10% FBS. After 24 hr, cells are treated with various concentrations of Apoptozole (0-15 μM) in culture media with 3% FBS (final volume: 0.2 mL per well) for 18, 48, and 72 hr before treatment with MTT. Absorbance at 570 nm is measured using a UV microplate reader[3].

Animal experiment:

Male nude mice are housed in a pathogen-free room under controlled temperature and humidity. Mice aged 4 weeks are injected with tumor cells for the xenograft experiments. Viable A549 and RKO cells (5 × 106) and HeLa cells (5 × 106) are injected subcutaneously into the flank of mice. The A549 and RKO cell xenograft mice are immediately and randomly assigned to two groups. The first group (n = 10) is used as a control group and receives vehicle only. The second group (n = 10) receives intraperitoneal injections of Apoptozole (4 mg/kg/day) every other day for 2 weeks. The HeLa cell xenograft mice are immediately and randomly assigned to four groups. The first group (n = 10) is a control group receiving vehicle only. The second group (n = 10) receives intraperitoneal injections of Apoptozole (4 mg/kg/day) every other day for 2 weeks. The third group (n = 10) receives intraperitoneal injections of doxorubicin (15 mg/kg/day) every other day for 2 weeks. The fourth group (n = 10) receives intraperitoneal injections of Apoptozole (4 mg/kg/day) and doxorubicin (15 mg/kg/day) every other day for 2 weeks. Tumors in all mice are measured in two dimensions with calipers every 3 days and tumor volumes are calculated using the formula volume = w × l2/2, where w is the width at the widest point of the tumor and l is the length perpendicular to w. The results from individual mice are plotted as average tumor volumes versus time[3].

Apoptozole is an inhibitor of ATPase activity of HSP70 [1].

The heat shock protein 70 (HSP70) protein family plays diverse roles in biological processes and has multiple functions involved in suppression of apoptotic pathways through multiple anti-apoptotic processes. The two major members, constitutive Hsc70 and inducible Hsp70, are composed of an N-terminal ATPase domain and a C-terminal substrate binding domain [1][2].

Apoptozole (Az) is an inhibitor of ATPase activity of HSP70. Apoptozole inhibited the ATPase activity of HSP70 by binding to its ATPase domain. In the presence of 200 μM ATP, Apoptozole inhibited the ATPase activity of HSP70 by 32% and 65% at 100 μM and 200 μM, respectively. Apoptozole bound HSP70 but not HSP40, HSP60, and HSP90. In several cancer cell lines, Apoptozole induced apoptosis in a dose-dependent way with IC50 values ranged from 5 to 7 μM. In HeLa cells, Apoptozole decreased the amount of APAF-1 associated with HSP70 without affecting the expression level of APAF-1, and produced cleaved procaspase-9, suggesting that Apoptozole blocked association of HSP70 with APAF-1 and induced caspase-dependent apoptosis.

In the nude mice xenografted with A549, RKO (colorectal carcinoma), and HeLa cells, i.p injection of Apoptozole reduced tumor volumes by 61%, 65%, and 68%, respectively [1]. In mice administered with both protein antigen and Az, Az increased immune responses to administered antigens and produced more antibodies [2].

References:
[1].  Ko SK, Kim J, Na DC, et al. A small molecule inhibitor of ATPase activity of HSP70 induces apoptosis and has antitumor activities. Chem Biol. 2015 Mar 19;22(3):391-403.
[2].  Baek KH, Zhang H, Lee BR, et al. A small molecule inhibitor for ATPase activity of Hsp70 and Hsc70 enhances the immune response to protein antigens. Sci Rep. 2015 Dec 3;5:17642.