Interaction of calicheamicin gamma1(I) and its related carbohydrates with DNA-protein complexes

Structural and mechanistic insight into DNA bending by antitumour calicheamicins

Among the class of enediyne antibiotics endowed with potent antitumour activities, the calicheamicin derivative known as ozogamicin is selectively targeted to several leukaemia cell types by means of tailor-made immunoconjugates. Binding of these drugs to the DNA minor groove in a sequence-specific fashion eventually causes double-stranded cleavage that results in cell death. Use of calicheamicin ε, an unreactive analogue of calicheamicin γ1I, has demonstrated that these structurally sophisticated molecules inflict bending on certain DNA oligonucleotides of defined sequence to the extent that they increase their circularization ratio upon ligation into multimers. By modelling and simulating several linear and circular DNA constructs containing high-affinity 5'-TCCT-3' and low-affinity 5'-TTGT-3' target sites in the presence and absence of calicheamicin ε, we have shed light into the structural distortions introduced by the drug upon binding to DNA. This new insight not only informs about the direction and magnitude of the DNA curvature but also provides a rationale for an improved understanding of the preferred structural and dynamic features associated with DNA target selection by calicheamicins.

Novel insights on the DNA interaction of calicheamicin γ₁(I)

Calicheamicin γ1(I) (Cal) is a unique molecule in which a DNA binding motif (aryl-tetrasaccharide) is linked to a DNA cleaving moiety (calicheamicinone). The hallmark of this natural product rests in the impressive optimization of these two mechanisms leading to a drug that is extremely efficient in cleaving DNA at well-defined sites. However, the relative contributions of these two structurally distinct domains to the overall process have not been fully elucidated yet. Here, we used different experimental approaches to better dissect the role of the aryl-tetrasaccharide and the enediyne moieties in the DNA sequence selective binding step as well as the in the cleavage reaction. Our results highlight the remarkable cooperation of the two components in producing an amazing molecular machine. The herein presented molecular details of this concerted mechanism of action can be further applied to rationally design more druggable compounds.

Gemtuzumab Ozogamicin (CMA-676, Mylotarg) for the treatment of CD33+ acute myeloid leukemia

Gemtuzumab Ozogamicin (GO, CMA-676) is a monoclonal antibody against the cellular surface antigen CD33 conjugated with the cytotoxic antibiotic calicheamicin. In the beginning of 2000 it obtained US Food and Drug Administration approval for the treatment of refractory acute myeloid leukemia (AML) expressing CD33 in patients older than 60 years who are not candidates for other chemotherapy. After ligation with the CD33 on the cell surface, GO is internalized and hydrolyzed. Its two components are released into the cytoplasm and calicheamicin enters the nucleus where it associates with the DNA, causing double helix breaks and finally cell death. GO is in general well tolerated. The most frequent adverse effect observed is myelotoxicity, with prolonged neutropenia and thrombocytopenia. Veno-occlusive disease of the liver is a less frequent but severe adverse effect. A phase II study points towards a percentage of overall hematologic response around 30% in the setting of refractory or relapsed disease. Future phase III trials will show the most suitable place of GO in the treatment of AML.

[Development of novel methodology for rapid conjugated oligosaccharide synthesis]

Glycosylation is one of the most important post-translation modifications of proteins, which affects biological activities by way of controlling higher order structure. Recently, the novel structure of glycoprotein, namely C-glycosyl protein was identified in various proteins. The first total synthesis of the naturally occurring C-glycosyl amino acid and peptide was achieved. The mannose and tryptophan moiety was connected via ring opening reaction of epoxide by lithiated indole derivative. After functional group conversion and deprotection, the glyco-amino acid was synthesized in a concise and stereoselective manner. To develop the rapid oligosaccharide construction methodology, the soluble polymer supported oligosaccharide was investigated. Due to high polarity of polymer support, the purification of PEG bound compound is achieved quite easily. The real-time monitoring of the glycosylation reaction was performed by MALDI-TOF MS, whereas the deprotection reaction of chloroacetyl group was performed by color test using (p-nitrobenzyl) pyridine. The purification of PEG bound compound which has chloroacetyl group, is achieved by capture-release strategy by use of resin bound cysteine derivative. By combination of these methodologies and novel linker, tetrasaccharides were synthesized.

Transcriptional effects of the potent enediyne anti-cancer agent Calicheamicin gamma(I)(1)

We have investigated the mode of action of calicheamicin in living cells by using oligonucleotide microarrays to monitor its effects on gene expression across the entire yeast genome. Transcriptional effects were observed as early as 2 min into drug exposure. Among these effects were the upregulation of two nuclear proteins encoding a Y'-helicase (a subtelomerically encoded protein whose function is to maintain telomeres) and a suppressor of rpc10 and rpb40 mutations (both rpc10 and rpb40 encode RNA polymerase subunits). With longer calicheamicin exposure, genes involved in chromatin arrangement, DNA repair and/or oxidative damage, DNA synthesis and cell cycle checkpoint control as well as other nuclear proteins were all differentially expressed. Additionally, ribosomal proteins and a variety of metabolic, biosynthetic, and stress response genes were also altered in their expression.

Mylotarg: antibody-targeted chemotherapy comes of age

Mylotarg (gemtuzumab ozogamicin, CMA-676; Wyeth-Ayerst Laboratories, Philadelphia, PA) recently was approved by the US Food and Drug Administration for the treatment of patients with CD33-positive acute myeloid leukemia in first relapse, age 60 years or older, who are not considered candidates for other types of cytotoxic chemotherapy. In combined phase II studies of 142 patients with CD33-positive acute myeloid leukemia in first relapse, Mylotarg monotherapy was associated with a 30% overall response rate. Although treated patients had relatively high incidences of myelosuppression, hyperbilirubinemia, and elevated hepatic transaminases, the incidences of severe mucositis and infections were low compared with what might be expected in association with conventional chemotherapeutic treatment. Preliminary data in pediatric patients also suggest that the immunoconjugate is reasonably well tolerated. Studies of Mylotarg in combination with anthracycline, cytarabine, and agents that inhibit P-glycoprotein are underway.

Antigen-specific downregulation of T cells by doxorubicin delivered through a recombinant MHC II--peptide chimera

As the number of drugs with potential therapeutic use for T-cell-mediated diseases increases, there is a need to find methods of delivering such drugs to T cells. The major histocompatibility complex (MHC)--peptide complexes are the only antigen-specific ligands for the T-cell receptor (TCR) expressed on T cells, and they may be an appropriate drug delivery system. We engineered a soluble bivalent MHC class II-peptide chimera on the immunoglobulin scaffold (I-E(d)alpha beta/Fc gamma 2a/HA110-120, DEF) that binds stably and specifically to CD4 T cells recognizing the HA110-120 peptide. Doxorubicin, a powerful antimitogenic anthracycline, was enzymatically assembled on the galactose residues of a DEF chimera. The DEF-gal-Dox construct preserved both the binding capacity to hemagglutinin (HA)-specific T cells, and the drug toxicity. Brief exposure of HA-specific T cells to DEF-gal-Dox construct in vitro was followed by drug internalization in the lysosomes, translocation to the nucleus, and apoptosis. Administration of DEF-gal-Dox to mice expressing the TCR-HA transgene reduced the frequency of TCR-HA T cells in the spleen and thymus by 27% and 42%, and inhibited HA proliferative capacity by 40% and 60%, respectively. It has not been demonstrated previously that pharmacologically active drugs able to modulate T-cell functions can be delivered to T cells in an antigen-specific manner by soluble, bivalent MHC II-peptide chimeras.

Chemical approaches to control gene expression

A current goal in molecular medicine is the development of new strategies to interfere with gene expression in living cells in the hope that novel therapies for human disease will result from these efforts. This review focuses on small-molecule or chemical approaches to manipulate gene expression by modulating either transcription of messenger RNA-coding genes or protein translation. The molecules under study include natural products, designed ligands, and compounds identified through functional screens of combinatorial libraries. The cellular targets for these molecules include DNA, messenger RNA, and the protein components of the transcription, RNA processing, and translational machinery. Studies with model systems have shown promise in the inhibition of both cellular and viral gene transcription and mRNA utilization. Moreover, strategies for both repression and activation of gene transcription have been described. These studies offer promise for treatment of diseases of pathogenic (viral, bacterial, etc.) and cellular origin (cancer, genetic diseases, etc.).