3-AP

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.