Ladislav Novotný

Antileukemic activity of 4-pyranone derivatives

In a search for new compounds possessing antitumor activity, we examined the effects of a group of oxygen containing heterocyclic derivatives on L1210 murine leukemia cell growth. Several 5-hydroxy-2-hydroxymethyl-4-pyranone derivatives were tested in a growth assay employing a human leukemia K562 cells line. IC50 was extrapolated from the growth inhibition curves at compound concentrations ranging from 0.1 to 100 microM. The halogen derivatives of 5-hydroxy-2-hydroxymethyl-4-pyranone inhibited L1210 cell growth in suspension culture after 96 hr incubation in the following order: 5-hydroxy-2-iodomethyl-4-pyranone (IC50 3.15 microM) > 6-bromo-2-bromomethyl-5-hydroxy-4-pyranone (IC50 3.40 microM) > 6-bromo-5-hydroxy-2-hydroxy-methyl-4-pyranone (IC50 3.75 microM) > 2-bromomethyl-5-hydroxy-4-pyranone (IC50 4.30 microM) > 5-benzyloxy-2-chloromethyl-4-pyranone (IC50 5 microM) > 6-bromo-2-chloromethyl-4-pyranone (IC50 13.50 microM) > 6-chloro-2-chloromethyl-5-hydroxy-4-pyranone (IC50 18 microM) > 2-chloromethyl-5-hydroxy-4-pyranone (IC50 20 microM). The compound, 5-hydroxy-2-hydroxymethyl-4-pyranone has no effect on L1210 cell growth. These results suggest that 5-hydroxy-2-hydroxymethyl-4-pyranone derivatives might represent a new class of compounds with antileukemic activity.

PREPARATION, PROPERTIES AND ANTILEUKEMIC ACTIVITY OF ARABINOSYLCYTOSINE POLYSACCHARIDE CONJUGATES

1. Conjugates of 1-beta-D-arabinofuranosylcytosine (araC) with polysaccharides containing carboxyl groups, such as polygalacturonic acid (PGA) and carboxymethylated yeast beta-D-glucan (CMG) were prepared. 2. Activation of the polysaccharidic carboxyl group by isobutylchloroformiate and formation of a peptide bond via 4-NH2 group of araC was used for a coupling reaction. 3. Elementary analysis, u.v. and i.r. spectra confirmed the structures of the conjugates. 4. The conjugates were most stable against the hydrolysis under the mild acid conditions. 5. It was also shown that under the physiological conditions trypsin catalyze the conjugate hydrolysis and the catalytic effect is higher than that of chymotrypsine. 6. It is suggested that trypsin or trypsin-like proteases could participate in the hydrolysis of the conjugates in vivo. PGA-araC and CMG-araC showed 1.5- or 2.5-times higher antileukemic activity than both free araC or polysaccharides.

DNA breakage and inactivation resulting from hydroxylamine and/or cis-diamminedichloroplatinum(II) interactions with plasmid DNA

1. Occurrence of lesions induced in plasmid DNA by cis-DDP and by HA was quantified both as a transforming activity and as conformation integrity of supercoiled pBR322 DNA. Fifty per cent decrease of the biological activity of plasmid DNA, not accompanied by measurable change of DNA conformation, was observed after a single exposure of DNA to cis-DDP (1 hr/37 degrees C). 2. HA induced conversion of supercoiled DNA to other topological forms in a dose-dependent manner. 3. One- and two-strand DNA breaks were determined electrophoretically with high sensitivity. Cis-DDP exposed DNA relaxed at 30 times lower HA concentration compared to intact DNA. 4. This effect may be connected with a local distortion of DNA structure at the cis-DDP--DNA bond, which makes possible high effectivity of HA-DNA interaction. 5. On other hand, biological activity stayed at the 50% level despite breaks induced in DNA. 6. This finding supports the idea that DNA breaks occur at the locations which were modified during the exposure of DNA to cis-DDP. 7. The importance of the DNA structure during interaction with HA may be seen during HA-DNA interaction at heat-denaturation of supercoiled DNA. At this condition, the DNA breaks were induced at 100 times lower concentration of HA. 8. We conclude, on the basis of these results published earlier, that local distortion of supercoiled DNA structure, which is caused by the cis-DDP bond, and the local DNA uncoiling caused by heat-denaturation are related to high HA-DNA reactivity.

The effect of structural modifications of 5-fluorouracil derivatives on their transport and biodegradation by isolated rat jejunum

SummaryThe continuous-perfusion technique was used in an isolated segment of everted rat jejunum to study transport and biotransformation processes in a series of cancerostatic derivatives of 5-fluorouracil. Metabolic alterations during penetration of the intestinal wall were assessed by high-performance liquid chromatography (HPLC). Octanol-buffer partition coefficients were measured, and the lipophilicity of the study compounds and fragmental constants for their sugar moieties were assessed. In the present series of 5-fluorouracil derivatives, there was no correlation between lipophilicity and metabolic cleavage to 5-fluorouracil, but a correlation was found between lipophilicity and the transport rate. Remarkable stability of the nucleoside bond and high biotransport were observed with 5′-chloro-5-fluorouridine, suggesting a different mode of activation for this derivative.

Polarographic behavior of flavanoids from propolis and their potential carcinogenity

Abstract The electrochemical reduction of 12 flavanoids isolated from propolis and synthetic 7,8-benzoflavone was investigated in anhydrous dimethylformamide (DMF) in the absence or presence of the growth factor α-lipoic acid. In anhydrous conditions α-lipoic acid influences the polarographic reduction of compounds with carcinogenic activity. The same effect is not observed with non-carcinogens. In the presence of α-lipoic acid in the polarographed solution of carcinogen, a new polarographic wave is observed. This wave increases linearly with increasing concentration of α-lipoic acid. This increase was used to evaluate the potential carcinogenity of the compounds examined by polarography. The index of potential carcinogenity tan α was estimated for all flavanoids investigated. The relationship between chemical structure and potential carcinogeneity was analyzed. Values of tan α indicating possible mutagenic or carcinogenic properties were found only for quercetin, rhamnetin and kempferol.

Evaluation of synergism of drugs cis-mdiamminedichloroplatinum (II) and arabinosylcytosine on the level of chemical interaction with DNA and on the growth of mouse leukemia

1. Cytotoxic synergism of drugs cis-diamminedichloroplatinum(II) (cis-DDP) and arabinosylcytosine (araC) was studied both on the level of interaction with DNA in chemically determined conditions and on leukemia L1210 bearing mice. 2. AraC and its structural natural precursor cytidine were tested for the modulation of kinetics of bifunctional adducts production induced by cis-DDP in DNA. 3. This process plays the basic role in cytotoxic mechanism and antitumor activity of cis-DDP. 4. No interaction was seen between cis-DDP and araC. Further, presence of araC in reaction mixture had no effect on cis-DDP-DNA interaction. 5. Therefore, cytotoxic synergism does not arise in the araC-cis-DDP-DNA interaction and its origin is different. 6. Finding that cytidine has no synergistic effect on life span of leukemia L1210 bearing mice when administered together with cis-DDP it shows the difference between cytidine and araC. 7. The small structural difference between cytidine and araC is very important for synergism of cytotoxicity.

Effect of thioredoxin on the sensitivity of bacteria to chemical damage

The ability of thioredoxin (Trx) to protect cells from chemical damage was determined by comparing the growth of a control strain of Escherichia coli JM101 and isogenic strain transformed with the plasmid pKKTS1 containing the Streptomyces aureofacien thioredoxin gene, in the presence of the nucleoside analogs arabinosylcytosine, 5‐fluorouridine, ftorafur and carcinogen β‐naftylamine. Arabinosylcytosine showed no effect on the growth of either of the two strains. 5‐fluorouridine, ftorafur [1‐((R,S)‐tetrahydrofuran‐2‐yl)‐5‐fluorouracil] and β‐naftylamine demonstrated lower inhibitory effects on the growth of the thioredoxin overproducing strain than on the growth of the control strain. These results suggested that Trx could protect the cells from chemical damage under certain metabolic conditions.

Effect of arabinosylcytosine derivative cyclocytidine on hepatal functions in rats and on Zajdela hepatoma

1. The effectivity of the arabinosylcytosine (araC) derivative, cyclocytidine (cC), against Zajdela hepatoma was evaluated. It was established that the cC effect was dose-dependent. 2. Zajdela hepatoma-bearing rats, given a single dose of 500 mg of cC per kg of body weight, showed an increased life span of 48 and 39%. 3. cC significantly decreased the number of Zajdela hepatoma cells in ascitic fluid and affected the cytochrome content in hepatal mitochondria. 4. The overall cC effect on the hepatal function of normal and hepatectomized liver was marginal, thus making this araC derivative an interesting candidate for further evaluation of its effectivity against non-hematological tumors.