HAT1 is a central regulator of chromatin synthesis that acetylates nascent histone H4. To ascertain whether targeting HAT1 is a viable anticancer treatment strategy, we sought to identify small-molecule inhibitors of HAT1 by developing a high-throughput HAT1 acetyl-click assay. Screening of small-molecule libraries led to the discovery of multiple riboflavin analogs that inhibited HAT1 enzymatic activity. Compounds were refined by synthesis and testing of over 70 analogs, which yielded structure–activity relationships. The isoalloxazine core was required for enzymatic inhibition, whereas modifications of the ribityl side chain improved enzymatic potency and cellular growth suppression. One compound (JG-2016 [24a]) showed relative specificity toward HAT1 compared to other acetyltransferases, suppressed the growth of human cancer cell lines, impaired enzymatic activity in cellulo, and interfered with tumor growth. This is the first report of a small-molecule inhibitor of the HAT1 enzyme complex and represents a step toward targeting this pathway for cancer therapy.

Despite remarkable advances within the field of molecular cancer therapeutics over the preceding decades, DNA-damaging agents retain a central role in the pharmacotherapy of neoplastic diseases. The clinical response to DNA-damaging therapies is varied within and across cancer subtypes where a robust DNA damage response (DDR) predicts recalcitrance. Replication protein A (RPA) is the predominant human single-stranded DNA (ssDNA)-binding protein, playing essential roles in DNA replication, repair, recombination, and the DNA-damage response (DDR). Inhibition of the RPA−DNA interaction is an approach to cancer drug discovery that holds potential to provide single-agent activity and/or synergy with existing therapeutics. Proteolysis targeting chimera (PROTAC) based drug design presages a paradigm shift within drug discovery as PROTACs begin to carve out a space in the clinical landscape. The PROTAC platform is particularly suited for drugging overexpressed proteins such as RPA because iterative target degradation improves drug:target stoichiometry and precludes RPA’s role in protein scaffolding. Herein, we describe the synthesis and biological evaluation of an RPA targeted PROTAC library conceived by conjugation of the diaryl pyrazole RPA inhibitor TDRL-551 and an E3-ligand via a linker of variable length and composition. Residing within the beyond rule of five (bRo5) chemical space, careful consideration was given to minimize the liability to cell permeability imposed by the high molecular weight of PROTACs. Excitingly, cellular uptake across the compound library was broadly improved relative to the unconjugated warhead TDRL-551. Similarly, RPA engagement by the PROTAC series was widely unhindered and, in many cases, improved relative to the warhead TDRL-551. A subset of the compound library unified by flexible linkers and alkyne attachment of the E3-ligand (typified by GL-3311) display low single-digit micromolar IC50 values in viability assays across H460, A549, and A2780 cell lines. Citation Format: Jeremy M. Kelm, Jitender Dev Gaddameedi, Pamela S. VanderVere-Carozza, Amirreza Samarbakhsh, Nivisa Vakeesan, Hussein W. Kansou, Sara Serafimovski, Katherine S. Pawelczak, John J. Turchi, Navnath S. Gavande. Development of replication protein A (RPA) targeted PROTACs for the treatment of lung and ovarian cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 802.

A series of novel N-triazole/isoxazole alkyl quinolin-2(1H)-one derivatives 6a-m, 9a-d, and 7a-r were prepared. Compounds 6d and 6k, which showed promising anticancer activity at micromolar concentration, have been identified.