Abstract 4778: Covalent bonding of a C8-conjugated pyrrolobenzodiazepine (PBD) monomer and dimer to a terminal guanine residue of DNA duplex and hairpin fragments

Abstract

Abstract The pyrrolobenzodiazepines (PBDs) are a family of covalent-binding DNA-interactive minor-groove binding agents that are of growing interest due to their potential as stand-alone anticancer agents, and for their use as payloads in Antibody Drug Conjugates (ADCs). For example, one PBD Dimer, SJG-136 has reached Phase II evaluation in the clinic for ovarian and haematological cancers, and a number of PBD-based ADCs are now being evaluated in pre-clinical, Phase I and II clinical trials (e.g., SGN-CD19B, SGN-CD33A [vadastuximab talirine], SGN-CD70A, SGN-CD123A, SC16LD6.5 [Rova-T, rovalpituzumab tesirine] and ADCT-402). Until now, PBDs, which bind in the minor groove of DNA and covalently bond to a guanine residue through its C2-NH2 functional group, were thought to require a three-base-pair recognition sequence prior to covalent bonding to the central guanine (with a thermodynamic preference for binding to 5’-Pu-G-Pu-3’ sequences but a kinetic preference for 5’-Py-G-Py-3’; Pu = Purine, Py = Pyrimidine). Using HPLC/MS methodology with designed hairpin and duplex oligonucleotides, we have now demonstrated that the PBD dimer SJG-136 and the C8-conjugated PBD Monomer GWL-78 can covalently bond to a terminal guanine of DNA, with the PBD skeleton spanning only two base pairs. Control experiments with the non-C8-conjugated anthramycin along with molecular dynamics simulations suggest that the C8-substituent of a PBD monomer, or one-half of a PBD Dimer, may provide stability for the adduct. This observation highlights the importance of PBD C8-substituents, and also suggests that PBDs may bind to terminal guanines within stretches of DNA in cells, thus representing a potentially novel mechanism of action at the end of DNA strand breaks. Citation Format: Julia Mantaj, Paul J. M. Jackson, Khondaker Miraz Jackson, David E. Thurston. Covalent bonding of a C8-conjugated pyrrolobenzodiazepine (PBD) monomer and dimer to a terminal guanine residue of DNA duplex and hairpin fragments. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4778.