Cell experiment:

An MTT assay is used to determine cell growth inhibition of CHO cells. Human leukemia K562 cells and K/VP.5 cells (a 26-fold etoposide-resistant K562-derived sub-line with decreased levels of topoisomerase IIα mRNA and protein) are maintained as suspension cultures in MEM containing 10% fetal calf serum (FCS). For growth inhibition assays, K562 and K/VP.5 cells are plated at a concentration of 1.5×105 cell/mL, and incubated 5 d with various concentrations of Dp44mT, 3-AP or vehicle (DMSO) for 48 h, after which cells are counted on a model ZBF Coulter counter. The IC50 growth inhibitory concentration for each cell line is calculated from a non-linear least-squares fit to a 2-parameter logistic equation[2].

Animal experiment:

Mice[3]Female BALB/c nu/nu mice are used at 8-10 weeks of age. Tumor cells in culture are harvested, and 107 cells are suspended in Matrigel and injected s.c. into the right flanks of mice. After engraftment, tumor size is measured by Vernier calipers. Tumor volumes (in cubic millimeters) are calculated. When tumor volumes reached 120 mm3, i.v. treatment began (day 0). Chelators (e.g., 3-AP) are dissolved in 15% propylene glycol in 0.9% saline and injected i.v. over 5 consecutive days per week for up to 7 weeks. Control mice are treated with vehicle alone.

3-AP is a ribonucleotide reductase inhibitor and iron chelator with antitumor activity.

Ribonucleotide reductase, the rate-limiting enzyme for de novo DNA synthesis, is an excellent target for chemotherapy. The increased activity of ribonucleotide reductase in cancer cells has been reported to be associated with malignant proliferation and transformation.

In vitro: Previous study found that the exposure of the tumor cell lines to 3-AP before or immediately after irradiation resulted in an increase in radiosensitivity. In contrast, 3-AP could enhance the radiosensitivity of the normal fibroblast cell line only when the exposure was before irradiation. There were no consistent differences between cell lines with respect to the expression of the RR subunits. Whereas 3-AP had no effect on radiation-induced gammaH2AX foci at 1 hour, the number of gammaH2AX foci per cell was significantly greater in the 3-AP-treated cells at 24 hours after irradiation, demonstrating the presence of unrepaired DNA damage [1].

In vivo: Animal study found that 3-AP administration to mice bearing tumor xenografts immediately after irradiation led to a greater than additive increase in radiation-induced tumor growth delay [1].

Clinical trial: Clinical study shows that triapine radiochemotherapy was safe, active, and effective in patients with untreated advanced-stage cervical cancer, worthy of randomized clinical trial study [2].

References:
[1] Barker, C. A.,Burgan, W.E.,Carter, D.J., et al. In vitro and in vivo radiosensitization induced by the ribonucleotide reductase inhibitor triapine (3-aminopyridine-2-carboxaldehyde-thiosemicarbazone). Clinical Cancer Research 12(9), 2912-2918 (2006).
[2] Kunos CA, Sherertz TM.  Long-Term Disease Control with Triapine-Based Radiochemotherapy for Patients with Stage IB2-IIIB Cervical Cancer. Front Oncol. 2014 Jul 24;4:184.