Junctions in DNA: underexplored targets for therapeutic intervention

DNA has been a key target for cancer therapy, with a range of compounds able to bind and either impair its processing or induce damage. Targeting DNA with small molecules in a truly sequence specific way, to impair gene specific processes, remains out of reach. The ability of DNA to assume different structures from the classical double helix allows access to more specific ligand binding modes and, potentially, to new avenues of treatment. In this review, we illustrate the small molecules that have been reported to bind to three- and four-way junctions

The development of potent, competitive CXCR4 antagonists for the prevention of cancer metastasis

Cancer metastasis is the cause of up to 90 % of cancer related mortality. The CXCR4 receptor and its cognate ligand, CXCL12, have major roles in enabling cancer metastasis and consequently, the CXCR4 receptor has become an attractive therapeutic target for the prevention of metastasis. Despite this, CXCR4 antagonists have had limited success in clinical trials due to cellular toxicity and poor stability and efficacy. In this study, we developed a novel, competitive CXCR4 antagonist (IS4) that through copper-catalysed-azide-alkyne-cycloaddition can be clicked to other chemical moieties such as fluorescent dyes (IS4-FAM) for CXCR4-based imaging. We determined that these CXCR4 antagonists were non-toxic and could be used to specifically label the CXCR4 receptor. Furthermore, IS4 and IS4-FAM inhibited both CXCL12-stimulated cancer cell migration and Ca2+ release in both adherent and suspension cell lines with similar or improved potency as compared to two literature CXCR4 antagonists. Our results highlight the potential of IS4 and IS4-FAM as research tools and as potent CXCR4 antagonists for the prevention of metastasis

A peptide-duocarmycin conjugate targeting the Thomsen-Friedenreich antigen has potent and selective antitumour activity

Solid phase synthesis allowed the rapid generation of a peptide-drug conjugate. A peptide targeting the Thomsen-Friedenreich antigen (TFα) was conjugated to the alkylating subunit of the potent cytotoxin duocarmycin SA. The compound, containing a cathepsin B cleavable linker, was shown to be active and selective against TFα expressing tumour cell lines

Cytotoxicity of Pyrazine-Based Cyclometalated (C^Npz^C)Au(III) Carbene Complexes: Impact of the Nature of the Ancillary Ligand on the Biological Properties

The synthesis of a series of cyclometalated gold(III) complexes supported by pyrazine-based (C^N^C)-type pincer ligands is reported, including the crystal structure of a cationic example. The compounds provide a new platform for the study of antiproliferative properties of gold(III) complexes. Seven complexes were tested: the neutral series (C^Npz^C)AuX [X = Cl (1), 6-thioguanine (4), C≡CPh (5), SPh (6)] and an ionic series that included the N-methyl complex [(C^NpzMe^C)AuCl]BF4 (7) and the N-heterocyclic carbene complexes [(C^Npz^C)AuL]+ with L = 1,3-dimethylbenzimidazol-2-ylidene (2) or 1,3,7,9-tetramethylxanthin-8-ylidene (3). Tests against human leukemia cells identified 1, 2, 3, and 4 as particularly promising, whereas protecting the noncoordinated N atom on the pyrazine ring by methylation (as in 7) reduced the cytotoxicity. Complex 2 proved to be the most effective of the entire series against the HL60 leukemia, MCF-7 breast cancer, and A549 lung cancer cell lines, with IC50 values down to submicromolar levels, associated with a lower toxicity toward healthy human lung fibroblast cells. The benzimidazolylidene complex 2 accumulated more effectively in human lung cancer cells than its caffeine-based analogue 3 and the gold(III) chloride 1. Compound 2 proved to be unaffected by glutathione under physiological conditions for periods of up to 6 days and stabilizes the DNA G-quadruplex and i-motif structures; the latter is the first such report for gold compounds. We also show the first evidence of inhibition of MDM2–p53 protein–protein interactions by a gold-based compound and identified the binding mode of the compound with MDM2 using saturation transfer difference NMR spectroscopy combined with docking calculations

Identification of a new p53/MDM2 inhibitor motif inspired by studies of chlorofusin

Previous studies on the natural product chlorofusin have shown that the full peptide and azaphilone structure are required for inhibition of the interaction between MDM2 and p53. In the current work, we utilized the cyclic peptide as a template and introduced an azidonorvaline amino acid in place of the ornithine/azaphilone of the natural product and carried out click chemistry with the resulting peptide. From this small library the first ever non-azaphilone containing chlorofusin analogue with MDM2/p53 activity was identified. Further studies then suggested that the simple structure of the Fmoc-norvaline amino acid that had undergone a click reaction was also able to inhibit MDM2/p53 interaction. This is an example where studies of a natural product have led to the serendipitous identification of a new small molecule inhibitor of a protein-protein interaction

Peptide directed phthalocyanine-gold nanoparticles for selective photodynamic therapy of EGFR overexpressing cancers

Gold nanoparticles, covalently functionalised with the photosensitiser C11Pc and PEG, were actively targeted towards epidermal growth factor receptor overexpressing cancers using the peptide FITC-βAAEYLRK. Selective phototoxicity was observed at nanomolar concentrations with minimal dark toxicity

Probing cytochrome P450 (CYP) bioactivation with chloromethylindoline bioprecursors derived from the duocarmycin family of compounds

YesThe duocarmycins belong to a class of agent which has great potential for use in cancer therapy. Their exquisite potency means they are too toxic for systemic use, and targeted approaches are required to unlock their clinical potential. In this study, we have explored seco-OH-chloromethylindoline (CI) duocarmycin-based bioprecursors for their potential for cytochrome P450 (CYP)-mediated cancer cell kill. We report on synthetic and biological explorations of racemic seco-CI-MI, where MI is a 5-methoxy indole motif, and dehydroxylated analogues. We show up to a 10-fold bioactivation of de-OH CI-MI and a fluoro bioprecursor analogue in CYP1A1-transfected cells. Using CYP bactosomes, we also demonstrate that CYP1A2 but not CYP1B1 or CYP3A4 has propensity for potentiating these compounds, indicating preference for CYP1A bioactivation.The authors would like to thank Yorkshire Cancer Research (Program grant B381PA) for supporting our work focused on exploring CYPs as targets for prodrug development. The human recombinant CYP1A1 was a gift from Prof Emily E. Scott, University of Michigan; the enzyme was produced via NIH funded grant (R37 GM076343)

Duocarmycins as Antibody–Drug Conjugate (ADC) Payloads

The duocarmycins are a family of natural products first described in 1978 with the discovery of CC-1065. These DNA alkylating spirocyclopropyl-cyclohexadienones demonstrate ultrapotent cytotoxic activity, provided by the sequence-selective alkylation of the N3 of adenine. The medicinal chemistry community immediately saw great potential in the picomolar potency of the duocarmycins in cell lines, but inherent toxicity in vivo has hindered their progression through to clinical use. Consequently, a variety of strategies have been developed to harness the power of the duocarmycins and to begin to realise the potential of their highly interesting mode of action, the most exciting of which is the development of antibody–drug conjugates (ADCs). This chapter will present the most recent understanding of the mechanism of action of the duocarmycins and the downstream effects of DNA alkylation. Innovative approaches to the synthesis of the duocarmycins, including stereoselective synthesis and new approaches for solid-phase synthesis, are discussed. This chapter also highlights the approaches of medicinal chemists to harness the duocarmycins for clinical use and an overview of prodrug strategies is presented, emphasising the most effective and creative methods to release the duocarmycins at the desired site of action. Finally, the use of duocarmycins as ADCs is reviewed, underlining the inventive chemical approaches to direct and deliver this ultrapotent payload