Abstract 3098: Structure-based design rules for potent quadruplex-binding compounds based on the naphthalene diimide core
Authors: Neidle Stephen 
Published: June 2023

Abstract
Quadruplex nucleic acids (G4s) are four-stranded arrangements formed by guanine-rich tracts of DNA or RNA, held together by Hoogsteen hydrogen-bonded guanine quartets. G4 sequences are widely though not randomly distributed in the human genome. They are over-represented in telomeres and in the regulatory regions of many cancer-related genes such as KIT, MYC, VEGF, RAS and HIF. G4 structures can be unwound by helicase activity but can be stabilized by the binding of high-affinity small molecules. The compound QN-302, a tetra-substituted naphthalene diimide (ND) derivative, has nanomolar affinity and selectivity for several DNA and RNA G4s over duplex DNA. QN-302 has single-digit nM anti-proliferative activity in a panel of human pancreatic cancer (PDAC) cell lines (Ahmed et al., ACS Med Chem Lett, 2020, 11, 1634-1644). It has significant anti-tumor activity in several models for PDAC - in a MIA-PACA2 xenograft, in the genetic KPC model and in an orthotopic BX-PC3 model. QN-302 is currently in an advanced stage of pre-IND development by Qualigen Inc as a novel anti-cancer agent. QN-302 is the latest in several generations of NDs developed by us and designed by computer modelling based on earlier G4 co-crystal structures determined in this laboratory. The database of seven ND-containing crystal structures includes four different NDs with distinct side chain end groups, all with intramolecular telomeric parallel G4s. End-groups include N-methyl piperazine, hydroxyl, morpholino and N-dimethyl. These structures have been systematically compared for example using least-squares overlays of the structures. All the structures have their four substituents positioned each in a G4 groove, although there are significant differences in orientations of the end groups. Surprisingly, the naphthalene diimide cores do not retain the same orientation in each structure, with three distinct orientations being apparent. Examination of ND core overlap with the adjacent G-quartet has revealed variation in the degree of heterocycle-guanine base overlap, which is dependent on the nature and size of each substituent. However, all structures show minimal ND-guanine overlap, with typically just one out of four guanines in a G-quartet being involved. This strongly implies that most of the contribution to ND-G4 affinity comes from the side chains, and especially from the protonated end groups. These and other observations have led us to develop a structure-activity framework for tetra-substituted NDs, which has culminated in their optimization and the design of QN-302, with enhanced cellular potency and G4 affinity compared to previous NDs.
Citation Format: Stephen Neidle. Structure-based design rules for potent quadruplex-binding compounds based on the naphthalene diimide core [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3098.