Biomedical subjects

H P Hofs

Publications and source records attributed to H P Hofs.

15 recordsLinked to original sources

PubMed1997

The effect of ethyldeshydroxy-sparsomycin and cisplatin on the intracellular glutathione level and glutathione S-transferase activity.

Ethyldeshydroxy-sparsomycin (EdSm) is a ribosomal protein synthesis inhibitor which synergistically enhances the antitumor activity of cisplatin against L1210 leukemia in vivo. Because cellular glutathione (GSH) and glutathione S-transferases (GST) are reported to interfere with the antitumor activity of cisplatin, we analyzed the effect of EdSm and cisplatin on GSH and GST activity in selected tumor cells. For this purpose we used three murine leukemia tumors with different sensitivities towards EdSm and cisplatin: L1210-WT, sensitive to both drugs, L1210-Sm, resistant to EdSm, and L1210-CDDP, resistant to cisplatin. No significant differences were detectable between these three cell lines regarding the population doubling time, the cell size, and the cellular level of protein and glutathione. Neither of the resistant L1210 subclones showed P-glycoprotein expression. Drug exposure, however, changed the intracellular dynamics. Exposure to EdSm strongly decreased the amount of cellular protein, decreased the overall GST activity and led to GSH depletion, whereas exposure to cisplatin induced a rise in the amount of protein, in GSH, and in the total GST activity. These effects are dose-dependent and correlate well with the sensitivity of the tumor cells for EdSm or cisplatin. In addition, exposure to EdSm lowered the V(max) of GST in L1210-WT and L1210-Sm; however, in L1210-CDDP both the V(max) and the K(m) were increased. That this was not a direct effect of EdSm on GST was shown in a cell-free system, where EdSm did not influence the GST activity nor could it act as a substrate for GST. Our results suggest that the synergistic combination of EdSm and cisplatin might be explained by EdSm switching off the cellular detoxification mechanism for cisplatin, i.e. by inhibition of de novo synthesis and subsequent depletion of GSH and GST.

Animals↗

PubMed1995

Preclinical antitumor activity of ethyldeshydroxysparsomycin in combination with cisplatin.

The efficacy of cisplatin (CDDP) in combination with the protein synthesis inhibitor ethyldeshydroxysparsomycin (EDSM) has been tested in two tumor models at various schedules. Mice with L1210 leukemia or B16 melanoma were treated with CDDP alone or in combination with EDSM. Against L1210 leukemia, which is sensitive to CDDP, combinations elicited increases in life-span for all treatment schedules compared to those achieved with the corresponding dose of CDDP. Moreover, the combination of EDSM with this platinum compound yielded a cure rate > 80%, compared to < 35% for single CDDP treatment. Although the B16 melanoma is rather resistant to both CDDP and EDSM, combinations of these agents against B16 melanoma showed schedule dependent efficacy and in certain schedules significant therapeutic advantage over individual drug treatment, but cures were not observed. Our results suggest that EDSM has significant synergistic capabilities in both animal tumor models, but strong therapeutic enhancement of cisplatin efficacy is only seen when the tumor is sensitive to CDDP.

Animals↗

PubMed1995

Antitumour activity and retinotoxicity of ethyldeshydroxy-sparsomycin in mice.

The colony formation in agar of human tumour xenografts was used as a test system to study the cytostatic activity of ethyldeshydroxy-sparsomycin (EdSm) at the cellular level. EdSm was additionally studied in vivo in human tumour xenografts and murine tumour models. EdSm showed a clear dose-response effect in vitro. At continuous exposure with 0.01 micrograms/ml, 2 out of 11 of the tumours responded (a gastric and a small cell lung carcinoma). At 0.1 mu/ml EdSm, the tumour response was 5/11 tumours and at 1 microgram/ml the compound was active in all tumours. The maximal tolerable doses of EdSm in vivo have been determined in non-tumour bearing CDF1 mice. In the intraperitoneally (i.p.) given multiple dose schedules the respective LD10 doses indicated that the tolerable cumulative dose increases when lower doses are given more frequently. This also enhances the antitumour activity in L1210 leukaemia to 172% T/C. On the other hand, continuous infusion strongly diminished the tolerable dose as well as the antitumour activity. EdSm was also active against i.p. inoculated P388 leukaemia (150% T/C), B16 melanoma (156% T/C), and RC carcinoma (197% T/C), and the subcutaneously (s.c.) inoculated L1210 (139% T/C) and RC (138% T/C). Absence of tumour responses was found in the following s.c. implanted murine tumours: M5076 sarcoma, osteosarcomas C22LR and CP369, and the LL carcinoma, as well as in the human tumour xenografts: LXFG 529, a non-small cell lung carcinoma; GXF 251, a gastric carcinoma; and FMa, an ovary carcinoma. Possible long-range retinotoxic effects of EdSm were investigated in tumour-bearing mice, cured after surviving treatment with LD50 doses of EdSm, by assaying the protein biosynthetic capacity of the retinal by assaying the ocular rhodopsin and opsin levels as parameters. In none of these cases could a significant reduction in either opsin or rhodopsin levels be measured and no changes were seen histologically.

Animals↗

PubMed1995

Schedule-dependent enhancement of antitumor activity of ethyldeshydroxy-sparsomycin in combination with classical antineoplastic agents.

The efficacy of the protein synthesis inhibitor ethyldeshydroxy-sparsomycin (EDSM) as a biochemical response modifier of several antitumor agents against L1210 leukemia and B16 melanoma is described. Seven drugs with different intracellular targets were selected for this combination study. Tumor implantation and drug treatment were both i.p., and the time interval between the administration of EDSM and the cytostatic agent was varied. Our results show that in the B16 tumor model EDSM is not able to potentiate any of these drugs, whereas antagonism is seen in combination with doxo-rubicin (DX). In the L1210 tumor model, however, no loss of activity is seen for this specific combination. The effect of the combination of cytosar (Ara-C), 5-fluorouracil (5-FU) or vincristine (VCR) with EDSM in the L1210 model is strongly time interval dependent. Loss of 5-FU antitumor activity is seen when EDSM is given 3 or 24 h after 5-FU; however, no effect is observed when EDSM is given 6 h after 5-FU. Enhancement of the 5-FU activity is not noticed. The VCR activity is potentiated when EDSM is given at least 6 h after VCR administration, which increases the antitumor response from 32 to > 60 days and the percentage survivors from 33 to 83% (p = 0.04). In combination with Ara-C, potentiation of antitumor activity is seen only when EDSM is given 24 h after Ara-C, which increases the antitumor response from 32 to > 55 days and the percentage survivors from 11 to 50% (p = 0.008). No modulatory effects are found when EDSM is combined with carmustine or DX.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Effect of modulators on 5-fluorouracil metabolite patterns in murine colon carcinoma determined by in vitro 19F nuclear magnetic resonance spectroscopy.

High-resolution 19F nuclear magnetic resonance spectroscopy at 7 T was used to study the effect of modulators on the metabolism of 5-fluorouracil (5-FUra, 115 mg/kg i.p.) in C38 murine colon tumors grown in C57BL/6 mice. Distinct 5-FUra metabolite patterns were found in perchloric acid extracts of these tumors after treatment. The 19F nuclear magnetic resonance spectra exhibited resonances representing 5-FUra, the catabolites alpha-fluoro-beta-ureidopropionic acid and alpha-fluoro-beta-alanine, as well as four distinct fluoronucleotide anabolites. Using this model system the effect of several modulators on 5-FUra tumor metabolite patterns was investigated: methotrexate (300 mg/kg); alpha-interferon (10(5) IU/animal); N-(phosphonacetyl)-L-aspartate (100 and 250 mg/kg); and leucovorin (300 and 750 mg/kg). A significant increase in the anabolite:catabolite ratio was observed for the groups treated with 5-FUra in combination with the modulators methotrexate (n = 8), alpha-interferon (n = 7), and high-dose leucovorin (n = 14), but not for low-dose leucovorin (n = 7). Cotreatment with high-dose N-(phosphonacetyl)-L-aspartate (n = 8) resulted in a significant decrease in the anabolite: catabolite ratio compared to treatment with 5-FUra alone (n = 16). Possible correlations of metabolite profiles with therapy response are discussed.

Animals↗

PubMed1994

Concentration and sequence dependent synergism of ethyldeshydroxy-sparsomycin in combination with antitumor agents.

The modulating effect of ethyldeshydroxy-sparsomycin (EDSM), an inhibitor of ribosomal protein synthesis, on cytostatic agents was studied on cultured B16 melanoma cells using the microculture tetrazolium test (MTT). The data were analyzed for true synergism using the combination index and the median effect principle. The extent of cytotoxic drug interaction was influenced by the duration of drug exposure, the dose ratio, as well as the treatment schedule. When drug ratios were used, synergism was observed upon pre- and post-treatment in combination with cisplatin, cytosine arabinoside (Ara-C), methotrexate (MTX) and 5-fluorouracil (5-FU). The combination of a fixed dose of EDSM was synergistic with cisplatin, Ara-C, vincristine (VCR) and MTX, in the order MTX > Ara-C > VCR > cisplatin, while the combinations with doxorubicin, 5-FU and etoposide (VP-16) were shown to be antagonistic. These results suggest that only certain drugs and treatment schedules might be worthwhile for combination studies with EDSM in vivo and indicate a role for EDSM as modifier of antitumor responses in cancer chemotherapy.

Animals↗

PubMed1993

Correlation of the in vitro cytotoxicity of ethyldeshydroxysparsomycin and cisplatin with the in vivo antitumour activity in murine L1210 leukaemia and two resistant L1210 subclones.

The cultured murine leukaemia L1210 cell populations used in the present study were derived from L1210 cells that had been grown in vivo. Subclones resistant to sparsomycin (L1210/Sm) or cisplatin (L1210/CDDP) were also developed in vivo. The doubling times of the cultured cell populations were identical. Fractions surviving after drug treatment in vitro were determined by colony formation in soft agar. The results, based on the differential sensitivity of the cell populations to ethyldeshydroxysparsomycin (EdSm) and CDDP, indicated that after a short exposure, cultured L1210/CDDP cells were cross-resistant to EdSm. L1210/Sm cells, however, were not cross-resistant to CDDP. The results obtained in cultured cell populations were confirmed in vivo. CD2f1 mice bearing i.p. implants of 1 x 10(5) tumour cells were given EdSm or CDDP and a combination of the two agents. Drugs were given once daily every 4 days for 3 doses starting at 24 h after tumour implantation. Treatment of mice bearing L1210/wt leukaemia with combined EdSm and CDDP caused strongly synergistic antitumour activity. In animals bearing the two resistant subclones, however, combined drug treatment did not improve the antitumour activity. The corresponding median survival of mice receiving combined drug treatment was 60 days in each group containing 6 mice bearing L1210/wt, with 4-6 cures being noted; 19 days in animals harbouring L1210/Sm, with 2 cures being recorded among 6 mice; and 11 days in mice bearing L1210/CDDP, with no cure being obtained. The results of this study indicate that the synergism resulting from combined treatment with CDDP and EdSm is a function of the cellular properties of the target tumour-cell populations and is independent of host factors.

Animals↗

PubMed1991

Effects of benzoylphenyl ureas on growth of B16 melanoma cells in vitro and in vivo.

New analogs of diflubenzuron, a benzoylphenyl urea, are tested on their in vitro cytostatic activity against B16 melanoma cells. The following structure-activity relationship was established: substitution by a hydroxylated function at the ortho, meta or para position or by a dimethylamino function at the ortho position of the benzoyl moiety appeared to be necessary for cytostatic activity in vitro. Acetoxy functions at the ortho position or hydroxy functions at the para position of the aniline ring resulted also in active compounds. A number of these benzoylphenyl ureas are selected for in vivo evaluation of antitumor activity on B16 melanoma growing s.c.. Although many of the tested benzoylphenyl ureas delayed tumor growth during the first ten days of drug treatment, only a few increased animal life span. The best results (% T/C) were obtained with compounds 5 (127%), 7 (147%), 13 (135%) and 16 (135%), which all have hydroxylated functions in the benzoyl moiety.

Animals↗

PubMed1989

Potentiation of cisplatin antitumor activity on L1210 leukemia s.c. by sparsomycin and three of its analogues.

Sparsomycin (Sm) is a known antibiotic derived from Streptomyces. Its potential antitumor activity stimulated the search for a synthetic production method and the development of new derivatives. In a recent screening investigation, three Sm analogues appeared to be more active and considerably less toxic than the parent drug. Sparsomycins became especially interesting when it was shown that Sm potentiates the antitumor activity of cisplatin. In the present study Sm and its three promising analogues: deshydroxy-Sm (dSm), ethyl-deshydroxy-Sm (EdSm) and n-pentyl-Sm (PSm) were studied for their cisplatin potentiating effect. The experiments were performed on CD2F1 mice inoculated with 10(6) L1210 cells s.c. Sparsomycins were administered i.p. 3 h before cisplatin on days 1, 5 and 9. Three of the drugs, Sm, dSm and PSm, showed no potentiating effect in this tumor model. At a dose of 10 mg/kg, EdSm potentiated cisplatin antitumor activity 2.8 times (P less than 0.01) without an increase in weight loss. These results warrant further investigation.

Animals↗

PubMed1987

Synthesis and biological properties of side-chain-modified bleomycins.

New side-chain-modified bleomycins (BLMs) 3a-k have been synthesized by the reaction of demethyl BLM A2 with alpha-bromoacetamides (2a-k). The structures of these BLM analogues have been established by comparison of their NMR spectra with the corresponding spectra of model thiazole derivatives. Mass spectra (FAB) of the modified BLMs are not informative, since the fragmentation patterns exhibit a loss of the modified chain moiety, presumably in the matrix. The purity of the compounds is attested by TLC and HPLC analyses. Biological evaluation of 3a-k in in vitro (survival of B16 melanoma cells) shows that the compounds are almost as effective as bleomycin. Examination of the effects of 3c, 3e, and 3f on lungs of male mice indicates that the analogues do not exhibit lower pulmonary toxicity than bleomycin.

Animals↗

PubMed1984

The effect of temperature on spontaneous, and ovulation hormone-induced female reproduction in Lymnaea stagnalis.

Spontaneous oviposition of the freshwater pulmonate snail Lymnaea stagnalis stopped after transfer from 20 degrees to low temperatures (8 and 4 degrees). This was due to a reduction in the activities of the neurosecretory caudodorsal cells (CDC), which produce the ovulation hormone (CDCH). Oviposition latencies (time interval between CDCH-injection and start of oviposition) increased with decreasing temperature. The ovotestis and the female accessory sex organs of snails placed at 8 degrees became less sensitive, and those at 4 degrees became completely insensitive to injected CDCH. This was probably caused by a reduction in activities of the endocrine dorsal bodies (DB), which control vitellogenesis and the activities of the female accessory sex organs. After a change from 4 to 20 degrees, CDCH injections rapidly became effective in inducing egg mass production, and spontaneous oviposition also restarted quickly, suggesting a rapid increase in DB and CDC activities.

Animals↗

PubMed1977

Comparison between the size of granular vesicles in intact cells and vesicles obtained by fragmentation of biomembranes.

Preparations of biomembranes, consisting of membrane vesicles, were analyzed with the analytical ultracentrifuge. Under certain conditions depending on the speed of rotation and the temperature, a sedimentation profile was observed that was highly characteristic for membranous material. From the sedimentation coefficients obtained, we calculated particle weights for the various well-defined membrane components. In certain types of preparations the particle weights of two adjacent components differed on average by a factor of 2. When vesicles obtained by fragmentation of biomembranes were compared with the granular vesicles present in intact cells, the accordance in diameters was striking. This may indicate that the size of vesicles is determined by purely physical factors.

Animals↗

PubMed1976

Sedimentation studies on membrane vesicles.

Analytical centrifugation was used in order to investigate the size distribution of vesicles in various membrane preparations. Under certain conditions depending among others on the speed of rotation and the temperature, a sedimentation profile was observed that was characteristic for membraneous material. Since the membrane vesicles exhibited a discontinuous distribution of sedimentation coefficients it was concluded that membrane vesicles only occur in a few size classes.

Cell Fractionation↗

PubMedDate not supplied

Potentiation of cisplatin antitumour activity by Ethyldeshydroxy-Sparsomycin in L1210 leukemia.

The combination of Ethyldeshydroxy-Sparsomycin (EdSm) with cisdiamminedichloroplatinum(II) (CDDP) caused significant antitumour activity against murine L1210 leukemia. Although single drug treatment by cisplatin generated some cures, all schedules of combined treatment, using nontoxic doses of EdSm (5mg/kg) and cisplatin (3 mg/kg), resulted in the cure of 4 to 6 mice in each group consisting of 6 mice. No differences in antitumour activity were observed between pretreatment, simultaneous treatment or posttreatment of cisplatin with EdSm. Increasing the number of tumour cells implanted i.p. diminished the antitumour effect of both EdSm as well as CDDP, but not for the drug combination. Changing the route of administration from i.p. to i.v. for one of the drugs out of the combination resulted in loss of antitumour activity.

Animals↗

PubMedDate not supplied

Modulation of the in vitro cytotoxicity of seven anticancer drugs by protein synthesis inhibition using sparsomycin.

Inhibitors of protein synthesis may modify cell response to cytotoxic drugs. The influence of protein synthesis inhibition using sparsomycin (Sm) on the cytotoxicity of seven classical cytotoxic drugs, 5-FU, ARA-C, MTX, doxorubicin, melphalan, bleomycin and vincristine, was studied. Preincubations, simultaneous incubations and postincubations with Sm were investigated in vitro on CHO cells. Preincubation with Sm antagonized the activity of the S phase specific drugs 5-FU, ARA-C, MTX as well as vincristine, while postincubation with Sm enhanced their effect. A similar pattern was observed with doxorubicin. Preincubation with Sm had a potentiated non-S phase specific like bleomycin and cisplatin, but not melphalan. Postincubation with Sm had a potentiating effect on bleomycin but had no effect on melphalan. These results indicate a strong, schedule dependent effect of Sm on various drugs and suggest some potentially useful combinations to be tested in vivo.

Adjuvants, Pharmaceutic↗