Untersuchung der Reaktivität und Selektivität DNA-alkylierender Duocarmycin-Analoga mittels hochauflösender Massenspektrometrie

CD-spectroscopy as a powerful tool for investigating the mode of action of unmodified drugs in live cells

Circular dichroism (CD) spectroscopy is a well-known method for the analysis of chiral chemical compounds and is often used for studying the structure and interaction of proteins, DNA and bioactive compounds in solution. Here we demonstrate that CD spectroscopy is also a powerful tool for investigating the cellular uptake and mode of action of drugs in live cells. By means of CD spectroscopy, we identified DNA as the cellular target of several novel anticancer agents based on the highly cytotoxic natural antibiotic CC-1065. Furthermore, time-dependent changes in the CD spectra of drug-treated cells enabled us to rationalize differences in drug cytotoxicity. The anticancer agents rapidly penetrate the cell membrane and bind to cellular DNA as their intracellular target. Thereby, the formation of a reversible noncovalent complex with the DNA is followed by a covalent binding of the drugs to the DNA and the more toxic compounds show a higher stability and a lower alkylation rate. Since no drug manipulation is necessary for this kind of investigation and achiral compounds bound to chiral biomolecules may also show induced CD signals, CD spectroscopy of live cells is not limited to the study of analogues of CC-1065. Thus, it constitutes a general approach for studying the mode of action of bioactive compounds on the cellular and molecular level.

Asymmetric synthesis and biological evaluation of glycosidic prodrugs for a selective cancer therapy

A severe limitation in cancer therapy is the often insufficient differentiation between malign and benign tissue using known chemotherapeutics. One approach to decrease side effects is antibody-directed enzyme prodrug therapy (ADEPT). We have developed new glycosidic prodrugs such as (-)-(1S)-26 b based on the antibiotic (+)-duocarmycin SA ((+)-1) with a QIC(50) value of 3500 (QIC(50)=IC(50) of prodrug/IC(50) of prodrug+enzyme) and an IC(50) value for the corresponding drug (prodrug+enzyme) of 16 pM. The asymmetric synthesis of the precursor (-)-(1S)-19 was performed by arylation of the enantiomerically pure epoxide (+)-(S)-29 (> or = 98 % ee).

Probing the mechanism of action of potential anticancer agents at a molecular level using electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry

Treating cancer without harming healthy tissue is an important goal in modern medicine. Our research group has developed a series of novel, relatively non-toxic glycosidic prodrugs that are activated to give the corresponding highly cytotoxic drugs selectively in the tumour tissue. Our first investigations have shown a high duplex DNA alkylation efficiency of the drugs, whereas the prodrugs showed almost no tendency for alkylation of duplex DNA. Herein we report on novel investigations of the mode of action of the anti-cancer drugs on a molecular level. Using high-resolution mass spectrometry, we determined the reactivity of these drugs as well as of other drugs of similar structure against different nucleophiles such as RNA and the tripeptide glutathione. In addition, the new drugs were also tested for their interaction with duplex DNA. All compounds show a high reactivity against duplex DNA, whereas the alkylation efficiency regarding RNA and glutathione is only poor. Furthermore, the alkylation of duplex DNA correlates qualitatively but not quantitatively with the cytotoxicity of the drugs. Consequently, other factors besides the alkylation efficiency such as the stability of the drugs seem to influence their biological activity. Altogether the results show that high-resolution mass spectrometry constitutes a powerful method for studying the mode of action of drugs on a molecular level.

Selective Treatment of Cancer: Synthesis, Biological Evaluation and Structural Elucidation of Novel Analogues of the Antibiotic CC-1065 and the Duocarmycins

Novel diastereomerically pure beta-D-galactosidic prodrugs (+)-12 a-e of the cytotoxic antibiotics CC-1065 and the duocarmycins were prepared for an antibody directed enzyme prodrug therapy (ADEPT) using 4 as a substrate via a radical cyclization to give rac-5 and rac-6 followed by a chromatographic resolution of the enantiomers of rac-5, glycosidation and linkage to the DNA-binding units 10 a-e. These only slightly toxic compounds can be toxified enzymatically by an antibody-beta-D-galactosidase conjugate at the surface of malignant cells to give the cytotoxic drugs, which then alkylate DNA. The new prodrugs were tested in in vitro cytotoxicity assays showing excellent QIC(50) values of 4800 and 4300 for (+)-12 a and (+)-12 b, respectively. The absolute configuration of precursor (+)-5 was determined by comparison of the experimental CD spectrum with the theoretically predicted CD spectra and by X-ray structure analysis.