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Synthetic calicheamicin mimics with novel initiation mechanisms: DNA cleavage, cytotoxicity, and apoptosis
K C Nicolaou1, E N Pitsinos, E A Theodorakis
1Department of Chemistry, Scripps Research Institute, La Jolla, CA 92037, USA.
Background:
Calicheamicin gamma 1I is a bacterial product that is a prominent member of the enediyne class of antitumor antibiotics, and has been extensively studied. Calicheamicin gamma 1I binds to DNA, causing double-stranded breaks, and cells exposed to it eventually become apoptotic. It can now be made synthetically, and highly potent biological mimics have been designed. Such molecules have many potential clinical applications, but are complex to make. We therefore investigated whether simplified versions of these molecules are biologically active.
Results:
We designed and synthesized a number of simple calicheamicin mimics and evaluated their biological activity. We also constructed mimics that are particularly suitable for conjugation to proteins, oligonucleotides, and other delivery systems. Several active mimics were found, and two in particular, which lack the trisulfide and oligosaccharide moieties of calicheamicin, had potent DNA-cleaving and cytotoxic activities. They caused chiefly single-stranded cuts in DNA, however, unlike the natural molecule, which causes double-stranded DNA cuts. Although they were able to induce apoptosis, they were less potent than the natural compound in this assay.
Conclusions:
The simple enediyne mimics were less potent than calicheamicin gamma 1I, presumably because they lack the oligosaccharide DNA-binding domain. Nevertheless, considering their relatively primitive structures, they have remarkable biological properties. They may be useful biological tools and are potential leads for the development of chemotherapeutic agents. We propose that the ability of the enediynes to induce apoptosis is related to their ability to make double-stranded cuts in DNA.
Insights
Simplified calicheamicin mimics show potent cytotoxic and DNA-cleaving activity, offering potential as chemotherapeutic agents despite reduced potency compared to the natural compound.
Area of Science:
- Medicinal Chemistry
- Molecular Biology
- Drug Discovery
Background:
- Calicheamicin gamma 1I is a potent enediyne antibiotic with antitumor properties, known to induce DNA double-strand breaks and apoptosis.
- Synthetic calicheamicin analogs have been designed, but their complexity limits clinical applications.
- Research is needed to explore simplified, biologically active calicheamicin mimics.
Purpose of the Study:
- To design and synthesize simplified analogs of calicheamicin.
- To evaluate the biological activity, including DNA cleavage and cytotoxicity, of these simplified mimics.
- To assess the potential of these mimics for drug development and as biological tools.
Main Methods:
- Chemical synthesis of simplified calicheamicin mimics.
- Evaluation of DNA cleavage activity (single- vs. double-strand breaks).
- Assessment of cytotoxic effects and apoptosis induction in cells.
Main Results:
- Several active simplified calicheamicin mimics were synthesized and identified.
- Two potent mimics, lacking trisulfide and oligosaccharide, exhibited significant DNA-cleaving and cytotoxic effects.
- These mimics primarily induced single-strand DNA breaks and were less potent in apoptosis induction than the natural calicheamicin gamma 1I.
Conclusions:
- Simplified enediyne mimics possess remarkable biological properties despite reduced potency compared to calicheamicin gamma 1I.
- The lack of the oligosaccharide DNA-binding domain likely contributes to the reduced potency.
- These mimics represent promising leads for chemotherapeutic agent development and valuable biological tools.