Cardiac toxicity and antitumor activity of 4'-deoxy-4'-iodo-doxorubicinol

Antimycobacterial activity of DNA intercalator inhibitors of Mycobacterium tuberculosis primase DnaG

Owing to the rise in drug resistance in tuberculosis combined with the global spread of its causative pathogen, Mycobacterium tuberculosis (Mtb), innovative anti mycobacterial agents are urgently needed. Recently, we developed a novel primase-pyrophosphatase assay and used it to discover inhibitors of an essential Mtb enzyme, primase DnaG (Mtb DnaG), a promising and unexplored potential target for novel antituberculosis chemotherapeutics. Doxorubicin, an anthracycline antibiotic used as an anticancer drug, was found to be a potent inhibitor of Mtb DnaG. In this study, we investigated both inhibition of Mtb DnaG and the inhibitory activity against in vitro growth of Mtb and M. smegmatis (Msm) by other anthracyclines, daunorubicin and idarubicin, as well as by less cytotoxic DNA intercalators: aloe-emodin, rhein and a mitoxantrone derivative. Generally, low-μM inhibition of Mtb DnaG by the anthracyclines was correlated with their low-μM minimum inhibitory concentrations. Aloe-emodin displayed threefold weaker potency than doxorubicin against Mtb DnaG and similar inhibition of Msm (but not Mtb) in the mid-μM range, whereas rhein (a close analog of aloe-emodin) and a di-glucosylated mitoxantrone derivative did not show significant inhibition of Mtb DnaG or antimycobacterial activity. Taken together, these observations strongly suggest that several clinically used anthracyclines and aloe-emodin target mycobacterial primase, setting the stage for a more extensive exploration of this enzyme as an antibacterial target.

4'-iodo-4'-deoxydoxorubicin and tetracyclines disrupt transthyretin amyloid fibrils in vitro producing noncytotoxic species: screening for TTR fibril disrupters

Transthyretin Leu55Pro is one of the most aggressive mutations in familial amyloidotic polyneuropathy, an autosomal dominant disorder characterized by extracellular deposition of fibrillar amyloid protein. This variant has the ability to form fibrils in vitro under physiological conditions (PBS, pH 7.4). We studied by transmission electron microscopy the effect of the drug 4'-iodo-4'-deoxydoxorubicin (I-DOX) on the in vitro assembly of TTR Leu55Pro fibrils by following fibril growth over a 15 day period. Our results showed that I-DOX at a concentration of 10-5 M/100 microg fibrils does not inhibit fibril formation in up to 10 days since fibrils identical to the ones present in the untreated sample were observed. However, after 15 days of treatment, only round particles, resembling soluble native TTR, were observed. We also tested the ability of tetracyclines and nitrophenols to interfere with amyloid fibril formation for 17 days; the group of compounds tested showed fibril disruption activity to different extents: doxycycline and 2,4-dinitrophenol resulted in complete disaggregation of fibrils. The species generated upon I-DOX and tetracyclines treatments were nontoxic, as revealed by the lack of significant caspase-3 activation on a Schwannoma cell line, making them potential therapeutic drugs in TTR-related and other amyloidosis.

The molecular interaction of 4'-iodo-4'-deoxydoxorubicin with Leu-55Pro transthyretin 'amyloid-like' oligomer leading to disaggregation

The crystal structure of the amyloidogenic Leu-55Pro transthyretin (TTR) variant has revealed an oligomer structure that may represent a putative amyloid protofibril [Sebastião, Saraiva and Damas (1998) J. Biol. Chem. 273, 24715-24722]. Here we report biochemical evidence that corroborates the isolation of an intermediate structure, an 'amyloid-like' oligomer, which is most probably present in the biochemical pathway that leads to amyloid deposition and that was isolated by the crystallization of the Leu-55Pro TTR variant. 4'-Iodo-4'-deoxydoxorubicin (IDOX) is a compound that interacts with amyloid fibrils of various compositions and it has been reported to reduce the amyloid load in immunoglobulin light chain amyloidosis [Merlini, Ascari, Amboldi, Bellotti, Arbustini, Perfetti, Ferrari, Zorzoli, Marinone, Garini et al. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 2959-2963]. In this work, we observed that the monoclinic Leu-55Pro TTR crystals, soaked with IDOX, undergo rapid dissociation. Moreover, under the same conditions, the orthorhombic wild-type TTR crystals are quite stable. This is explained by the different TTR conformations isolated upon crystallization of the two proteins; while the Leu-55Pro TTR exhibits the necessary conformation for IDOX binding, the same structure is not present in the crystallized wild-type protein. A theoretical model concerning the interaction of Leu-55Pro TTR with IDOX, which is consistent with the dissociation of the amyloid-like oligomer, is presented. In this model the IDOX iodine atom is buried in a pocket located between the two beta-sheets of the Leu-55Pro TTR monomer with the IDOX aromatic-moiety long axis nearly perpendicular to the direction of the beta-sheets.

Chronic effects of a novel synthetic anthracycline derivative (SM-5887) on normal heart and doxorubicin-induced cardiomyopathy in beagle dogs

This study was designed to investigate the chronic cardiotoxic potential of SM-5887 and a possible deteriorating effect of SM-5887 on low-grade cardiotoxicity pre-induced by doxorubicin in beagle dogs. In the chronic treatment, beagle dogs of each sex were given intravenously once every 3 weeks, either a sublethal dose of doxorubicin (1.5 mg/kg) or SM-5887 (2.5 mg/kg). The experiment was terminated 3 weeks after the ninth dosing. Animals which received over six courses of doxorubicin demonstrated the electrocardiogram (ECG) changes, decrease of blood pressure and high-grade histopathological cardiomyopathy, while animals which were terminally sacrificed after the SM-5887 administration did not show any changes in ECG, blood pressure and histopathological examinations. To examine a possibly deteriorating cardiotoxic effect of SM-5887, low-grade cardiomyopathy was induced in dogs by four courses of doxorubicin (1.5 mg/kg). Nine weeks after pre-treatment, dogs were given four courses of either doxorubicin (1.5 mg/kg) or SM-5887 (2.5 mg/kg) once every 3 weeks. The low-grade cardiotoxic changes were enhanced by the additional doxorubicin treatment. On the contrary, the SM-5887 treatment did not progress the grade of cardiomyopathy. In conclusion, SM-5887 does not have any potential of chronic cardiotoxicity and deteriorating effect on doxorubicin-induced cardiotoxicity in dogs.

Iododoxorubicin in advanced breast cancer: a phase II evaluation of clinical activity, pharmacology and quality of life

Iododoxorubicin 80 mg m-2 i.v. was given 3 weekly for a maximum of six cycles as first-line chemotherapy to 14 evaluable women with metastatic breast cancer. The response rate was 14% (95% confidence intervals 4-40%); median time to progression was 3.5 months (range 0.7 to > 9.3) and median survival was 10.2 months (range 2.3 to > 20.4). Neutropenia was the main toxicity but was not associated with severe sepsis. Two patients had a significant (> 10%) but asymptomatic fall in cardiac ejection fraction; other toxicities were mild. Plasma pharmacokinetics was studied during the first cycle of treatment. Iododoxorubicin was extensively metabolised to iododoxorubicinol. Neutropenia and thrombocytopenia were both significantly correlated with the area under the concentration-time curve (AUC) for iododoxorubicin and the total AUC for iododoxorubicin and iododoxorubicinol. Quality of life (QOL), evaluated by self-report questionnaire and interview, showed little evidence of benefit in terms of physical symptom relief, level of activity, psychological symptoms or global evaluation of QOL during treatment. Iododoxorubicin is subjectively less toxic than standard anthracyclines, but at the dose and schedule used has limited activity in metastatic breast cancer, possibly because iododoxorubicinol is not clinically active.

Comparative activity of doxorubicin and its major metabolite, doxorubicinol, on V79/AP4 fibroblasts: a morphofunctional study

Doxorubicin (DXR), an anthracycline antineoplastic drug, is mainly metabolized to the C-13 dihydroderivative doxorubicinol (DXR-ol), which displays cytotoxic activity on various cell lines. To better characterize the cytotoxic activity of this metabolite, we have studied the effect of DXR (0.1-10 micrograms/ml) or DXR-ol (1-100 micrograms/ml) on the transformed fibroblast cell line V79/AP4 by means of the clonogenic assay, cytofluorescence, and light and electron microscopy. Both DXR and DXR-ol displayed a dose-dependent inhibition of colony formation with an IC50 factor DXR-ol/DXR of 19.5. A striking nuclear fluorescence was observed after DXR but not after DXR-ol. A low number of mitoses and a decrease in nucleoli staining affinity were the most evident alterations induced by DXR. Electron microscopy showed both nuclear and cytoplasmic changes in DXR treated cells: nucleolar segregation, cytoplasmic vacuoles, and mitochondrial swelling with dense needle-shaped material were observed. Exposure to formic acid confirmed the calcific nature of the mitochondrial bodies. Only the highest dose of DXR-ol brought about nuclear and cytoplasmic ultrastructural changes similar to those induced by DXR. Our data describe new in vitro findings on the cytotoxicity and morphological alterations induced by both DXR and DXR-ol, with a lower activity of DXR-ol against V79/AP4 fibroblasts.