Edward M. Acton

Further studies on the generation of reactive oxygen species from activated anthracyclines and the relationship to cytotoxic action and cardiotoxic effects

The relative ease of generation of reactive oxygen species from a series of reductively activated aglycone and sugar modified anthracyclines was compared by the extents of single strand scission in supercoiled PM2-covalently closed circular (CCC)-DNA. The electrochemical properties of these agents were used as a quantitative measure of the ease of reduction and subsequent reoxidation of the reduced species. The relationship of these processes to various biological properties of the anthracyclines, in particular to the measured cardiotoxicity of the drugs, was examined. An attempt was made to identify those structural changes which ameliorate the cardiotoxic effects measured in other test systems while permitting the expression of antitumor properties.

Diminished superoxide anion generation by reduced 5-iminodaunorubicin relative to daunorubicin and the relationship to cardiotoxicity of the anthracycline antitumor agents

Abstract 5-Iminodaunorubicin, when reductively activated, produces single strand scission in PM2-CCC-DNA by a mechanism which proceeds via production of Superoxide anion and hydroxyl radicals. Under comparable conditions, 5-iminodaunorubicin produces much less nicking than daunorubicin. With the aid of N -cyclohexyl-5-iminoquinizarin, as a model, assignment of polarographic waves to the quinone moiety of 5-iminodaunorubicin was possible. The electrochemical results indicate that 5-iminodaunorubicin is more difficult to reduce than daunorubicin and that reoxidation of the reduced form, 5,11-dihydro-5-iminodaunorubicin, is much more difficult than reoxidation of reduced daunorubicin. The latter conclusion is supported by independent chemical studies. By comparison of 5-iminodaunorubicin with daunorubicin and N -cyclohexyl-5-iminoquinizarine, the unusual stability of the reduced 5-iminodaunorubicin, is tentatively attributed to strong hydrogen bonding. The results suggest a correlation between the diminished generation of Superoxide anion by 5-iminodaunorubicin and its observed suppressed cardiotoxicity relative to other anthracyclines.

Synthetic C-nucleosides: 3-(α- and β-D-arabinofuranosyl)pyrazolo[4,3-d]pyrimidine-5,7-diones

Abstract 2,3,5-Tri- O -benzyl- D -arabinofuranosyl bromide ( 4 ) was converted into 2,5-anhydro-3,4,6-tri- O -benzyl- D -glucononitrile ( 5 ), mixed with 20% of the D - manno epimer 6 . The mixture was reduced to the amine 7 , which via the N -nitrosoacetamide 10 afforded the 1-deoxy-l-diazo sugar 11 . Dipolar addition to dimethyl acetylene-dicarboxylate afforded the C -nucleoside derivative, dimethyl 3-(2,3,5-tri- O -benzyl-α-β- D -arabinofuranosyl)pyrazole-4,5-dicarboxylate ( 20 ). Selective ammonolysis afforded the 4-ester-5-carboxamide 21 , which was separated chromatographically into the α-(minor) and β-(major) anomers. Hydrazinolysis and Curtius reaction of the pair of 4-acid hydrazides (α- 22 and β- 22 ) afforded the anomeric 3-glycosyl-1 H -pyrazolo-[4,3- d ]pyrimidine-5,7-diones (α- 24 and β- 24 ). Hydrogenolytic debenzylation yielded the β- D )- arabino epimer ( 1 ) of oxoformycin B , and the α- D - arabino form 2 . These anomeric C -nucleosides were distinguished by circular dichroism spectra that showed the same relationship as α- and β- D - arabino anomers of normal purine nucleosides.

Comparative cytotoxicities of various morpholinyl anthracyclines

SummaryA series of quinone- and sugar-modified analogs of adriamycin have been tested for growth inhibition of adriamycin-sensitive (P388/S) and -resistant (P388/ADR) sublines of P388 murine leukemia cells in vitro. P388/ADR is less resistant to analogs of adriamycin containing either a 3′-deamino-3′-(4″-morpholinyl) group, MRA; or a-(3″-cyano-4″-morpholinyl) group, MRA-CN, than to adriamycin. However, MRA-CN was the most potent growth inhibitor of either subline. This potency is reduced by either modification of the quinone unit with a 5-imino substituent or restriction of the cyano-morpholinyl ring by an oxygen bridge to the daunosamine sugar. The calcium antagonist verapamil substantially increases the cytotoxicity of adriamycin to P388/ADR but has no appreciable effect on the cytotoxicity of either MRA or MRA-CN. The results suggest that increased uptake and retention by both MRA and MRA-CN may contribute to their increased cytotoxicity, but that the intense potency of the cyano-morpholinyl analogs must be due to other unique properties of these compounds.

Tissue distribution of doxorubicin and doxorubicinol in rats receiving multiple doses of doxorubicin

SummaryPlasma and tissue levels of doxorubicin (DXR) and doxorubicinol (DXR-OL) were measured fluorometrically after high-pressure liquid chromatography at 1, 3, and 24 h following one, nine, and 24 doses of 1.0 mg DXR/kg or one and eight doses of 4.0 mg DXR/kg, IP, to rats. Comparison of plasma levels of DXR found following single and multiple doses suggests significant build-up of DXR at 1 h with successive doses, but not at 3 h. Liver exhibited substantially higher levels of DXR (on a per gram of protein basis) than did plasma, and multiple doses did not produce higher levels than did a single dose. In contrast, the heart accumulated DXR slowly, attaining levels after multiple dosing in excess of those found in the liver. Skeletal muscle exhibited dose-related levels similar to those for heart but the absolute levels of DXR in muscle were only about one-tenth of those observed in heart. DXR-OL was at very low levels of ≤4% of the DXR levels in the tissues; it was, however, a major circulatory metabolite, attaining levels in the plasma as high as 85% of the concentration of DXR.

Effects of 5-iminodaunorubicin on nucleoli of rats

SummaryWe have confirmed that doxorubicin induces irreversible changes in the nucleolar ultrastructure of myocardial cells of rats. Similar changes were not caused by an equal dose of the synthetic analogue, 5-iminodaunomycin. These results combined with previous and current comparative tests with this analogue, doxorubicin, and daunomycin suggest that 5-iminodaunomycin may serve as a less cardiotoxic anthracycline derivative.

Synthetic approach to anthracyclinone C-glycosides

Abstract Stereospecific coupling of a pentadienyl chain to C.1 of daunosamine followed by Diels-Alder reactions with quinones gave a new synthesis of C-glycosides, including the first intermediates to anthracycline C-glycosyl isosteres.

C-daunosaminyl derivatives by the wittig reaction

Abstract C -Glycosylation of a 2-deoxypyranose has been achieved for the first time by conversion of 4- O-p -nitrobenzoyl- N -trifluoroacetyldaunosamine in a Wittig reaction into the corresponding derivative of ethyl 2-(daunosaminyl)acetate. The product was predominantly (54%) in the desired α- l configuration (separated from the β- l anomer, 15%) required for further elaboration of C -daunosaminyl derivatives. Conversion into the corresponding derivatives of 2-(α- l -daunosaminyl)acetaldehyde and 2-(α- l -daunosaminyl)ethanol was also achieved.

Synthesis of anthracycline C-glycosyl isosteres

Abstract The C-glycosyl isostere of 4-demethoxy-9-desacetyldaunorubicin and its 7,9-diepi isomer have been synthesized via Diels-Alder reaction of a protected daunosaminyl-2,4-pentadiene with quinizarin quinone.

Inhibition of nucleoside transport by nitrobenzylthioformycin analogs

The formycin analogs of nitrobenzylthioinosine and nitrobenzylthioguanosine were synthesized and evaluated as nucleoside transport inhibitors. These analogs have a potential therapeutic advantage over their parent compounds in that their C-nucleosidic linkages prevent them from being degraded to the immunosuppressive agents, 6-mercaptopurine and 6-thioguanine. 7-[(4-Nitrobenzyl)-thio]-3-(beta-D-ribofuranosyl)pyrazolo[4,3- d]pyrimidine (NBTF) and 5-amino-7-[(4-nitrobenzyl)thio]-3-(beta-D- ribofuranosyl)pyrazolo[4,3-d]pyrimidine (NBTGF) were inhibitors of nucleoside transport in human erythrocytes and HL-60 leukemia cells. The IC50 value for nitrobenzylthioinosine, NBTF and NBTGF with 10% erythrocyte suspensions were 18, 18 and 40 nM respectively. Specific binding studies with [3H]NBTF yielded a Kd of 3.4 nM with erythrocytes, approximately 10-fold higher than values reported for nitrobenzylthioinosine. NBTF and nitrobenzylthioinosine bound to HL-60 cells with Kd values of 8.1 and 0.81 nM respectively. The octanol/water partition coefficients of nitrobenzylthioinosine, NBTF and NBTGF were 3.5, 3.2, and 2.8 respectively. NBTF could be expected to be equipotent with nitrobenzylthioinosine in whole blood where inhibitor concentrations of 10(-7) to 10(-6) M are required in order to saturate erythrocytic binding sites; hence, it may exhibit the advantages inherent in a C-nucleoside.