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H J Broxterman

Publications and source records attributed to H J Broxterman.

85 records · Page 5Linked to original sources
PubMed1988

Induction by verapamil of a rapid increase in ATP consumption in multidrug-resistant tumor cells.

A marked increase in cellular ATP consumption was induced by verapamil in the multidrug-resistant (MDR) cell line 2780AD, but not in the drug-sensitive parental cell line A2780. A group of structurally unrelated drugs in concentrations known to reverse MDR, but not the verapamil analog tiapamil, a weak modulator of MDR, had similar effects. This effect was saturated at verapamil concentrations of about 1 microM. These data demonstrate that verapamil concentrations in MDR cells are maintained at a low level at the expense of ATP hydrolysis, and provide a first indication of the amount of metabolic energy used in this process.

Adenosine Triphosphate↗
PubMed1987

Analysis of human ascites effect on clonogenic growth of human tumor cell lines and NRK-49F cells in soft agar.

We studied the factors that control the capacity of tumor cells to grow in soft agar. And, we analyzed the effect of cell-free ascites (CFA) obtained from ovarian cancer patients in combination with various media on the cloning efficiency of H-134 and OVCAR-3nu ovarian carcinoma cell lines and the WiDr colon carcinoma cell line. Seven batches of CFA consistently enhanced the soft agar growth of tumor cells more efficiently than tested sera. The addition of charcoal-treated bovine serum albumin (BSA) lowered the amount of CFA required for optimal tumor cell growth. As little as 1.25 ng of epidermal growth factor (EGF)/ml further improved OVCAR-3nu soft agar growth in combination with all of the amounts of CFA tested. Thus, neither BSA nor EGF seems to account for the colony-stimulating effect of ascites on tumor cells. Four batches of CFA were tested for stimulating soft agar growth of normal rat kidney (NRK-49F) fibroblasts; all induced colonies of different morphologies. This effect was potentiated by EGF, which suggests the presence of several transforming growth factor-like activities in CFA. The results show that differences in cloning efficiency of tumor cells of one or two orders of magnitude can be found between standard (anchorage-dependent growth-supporting) media and media optimalized for soft agar growth, such as CFA in the presence of EGF. This paper will discuss the similarity in effects of CFA on various tumor cells and NRK cells, and possible implications of the stimulatory effects of CFA.

Agar↗
PubMed1987

Potentiation of doxorubicin cytotoxicity by the calcium antagonist bepridil in anthracycline-resistant and -sensitive cell lines. A comparison with verapamil.

The ability of the calcium channel blocker bepridil (Bp) to potentiate doxorubicin (Dx) cytotoxicity and enhance its accumulation in anthracycline-sensitive and -resistant human ovarian carcinoma cells (A2780 and 2780AD) and Chinese hamster ovarian (CHO) cells (AUXB1 and CHRC5) was compared with that of verapamil (Vp). A continuous exposure (48-72 h) to Bp as well as Vp potentiated Dx cytotoxicity in 2780AD cells. In short-term incubations (2 h Dx and 4 h calcium channel blocker) the same effects were observed: 4 microM Bp (4Bp) and Vp (4Vp) were equipotent, but at concentrations of 1 and 2 microM, Vp was more active (4Vp = 4Bp greater than 2Vp greater than 2Bp greater than 1Vp greater than 1Bp). In CHRC5 cells the corresponding sequence was: 4Vp greater than 4Bp greater than 2Vp greater than 2Bp greater than 1Vp greater than 1Bp. At high (marginally inhibitory) concentrations, Bp and Vp reversed Dx resistance completely in CHRC5 cells and partly in 2780AD cells. No significant potentiation of Dx cytotoxicity by Bp or Vp was found in A2780 cells, but both were active in AUXB1 cells. In studies with radiolabelled Dx (2 microM), Bp and Vp (16.5 microM) stimulated accumulation in CHRC5 cells almost up to the level in AUXB1 cells. Dx accumulation in 2780AD cells (52 pmol/10(6) cells) could be stimulated to a maximum of about 90 pmol/10(6) cells (drug level in A2780 cells was 153 pmol/10(6) cells). Also, Bp- and Vp-induced stimulation of Dx accumulation was observed in AUXB1, but not in A2780 cells. Bp effected a dose-dependent inhibition of Dx efflux from preloaded 2780AD cells, but not from A2780 cells. We conclude that Bp is more effective than Vp in reversing resistance when both compounds are used in vitro at concentrations which are clinically achievable in plasma.

Bepridil↗
PubMed1987

Daunomycin accumulation in resistant tumor cells as a screening model for resistance modifying drugs: role of protein binding.

A potential screening system for drugs that modify anthracycline resistance was investigated. The effect of the calcium antagonistic agents verapamil, diltiazem, bepridil and Ro 11-2933/001 on daunorubicin (DNR) accumulation in the doxorubicin resistant cell line 2780AD was measured. For this purpose cells were suspended in medium with varying concentrations of bovine serum albumin (BSA) and in human plasma to establish the influence of protein binding on DNR accumulation. Increase of protein concentration did not affect DNR accumulation when no calcium antagonists were present but caused an increase in concentrations of calcium antagonists needed to promote DNR accumulation. It appeared that DNR accumulation in suspended cells correlated well with cytotoxicity assays, performed on cells growing in monolayer in 96-well microtiter plates, when accumulation was measured in medium with the same protein constitution as in growth medium (10% fetal calf serum). It is concluded that protein binding effects should be taken into account in the screening of compounds for the circumvention of multidrug resistance.

Antibiotics, Antineoplastic↗
PubMed1985

Binding of [3H]flunitrazepam and [3H]spiperone to melanoma cell membrane preparations.

Binding of [3H]flunitrazepam and [3H]spiperone to membrane preparations isolated by high speed centrifugation of hamster, rabbit and human melanoma cell homogenates was analyzed. All melanoma cell types expressed a high density of specific binding sites for [3H]flunitrazepam (3-4 pmol/mg protein) with a high affinity (Kd about 30 nM). This binding was independent of melanin content of cells and could be classified, based on competition experiments, as a Ro 5-4864-like binding type. Specific [3H]spiperone binding to these cell lines clearly revealed at least two types of binding sites: a low affinity, high capacity type of binding site (Kd greater than 100 nM, Bmax about 50 pmol/mg protein) and a high affinity, low capacity binding site (Kd less than 1 nm, Bmax 30 fmol/mg protein). Binding of spiperone to the low affinity, high capacity site appeared displaceable by NM 113 and dependent on melanin content of the cells and probably represents binding to melanin. Analysis of drug binding to melanoma membrane cell preparations and correlation with drug effects should include the possible involvement of binding to melanin.

Animals↗
PubMed1983

Potential radiopharmaceuticals for the detection of ocular melanoma. Part I. 5-iodo-2-thiouracil derivatives.

The tissue distribution of a number of 5-[131I]-iodo-2-thiouracil derivatives was measured in Syrian golden hamsters with Greene melanoma. These compounds were rapidly (in less than 1 h) distributed in all tissues, while in most tissues fast elimination (T1/2 1-3 h) was observed. Because of retention of the 131I activity in the tumour, high tumour/non-tumour tissue ratios were found (e.g. tumour/eye 2.3-10, tumour/skin 1.5-3) suggesting that some of these compounds might be used as melanoma delineating agents, when labelled with 123I.

Animals↗
PubMed1983

Incorporation of [125I]-5-iodo-2-thiouracil in cultured hamster, rabbit, and human melanoma cells.

The incorporation of [2-14C]-2-thiouracil and a series of [125I]-5-iodo-2-thiouracils ([125I]ISUra(s)) into cultured Greene hamster melanoma cells was determined in order to establish their properties as false precursors in the melanin-biosynthetic pathway. The cold trichloroacetic acid-precipitable incorporation of [2-14C]-2-thiouracil as well as [125I]ISUra into melanoma cells after a 24- to 48-hr labeling period proved to be completely tyrosinase dependent (more than 99.5% inhibition could be achieved by 0.5 mM phenylthiourea). [125I]ISUra incorporation was 3-fold higher than was [2-14C]-2-thiouracil incorporation and was enhanced by 1 mM theophylline treatment. [125I]ISUra incorporation into hamster, rabbit, and human melanoma cells showed a linear relationship with cell melanin content. Methylation of the sulfur completely prevented the incorporation, while propylation but not methylation at position 6 resulted in lower incorporation. [125I]ISUra proved to be a marker for melanogenesis and may be useful in studies on the differentiation of cultured melanoma cells.

Animals↗
PubMed1980

Assay of HA-966 in rat plasma by capillary gas-liquid chromatography with nitrogen-selective detection.

A gas-liquid chromatographic method for the determination of the gamma-aminobutyric acid-like drug 1-hydroxy-3-aminopyrrolidone-2 (HA-966) in plasma is described. HA-966 was converted into its diacetyl derivative AC2HA-966 with acetic anhydride. This compound could be suitable eluted from a capillary OV-17 support-coated open tubular column. A sensitive detection method was achieved by making use of nitrogen-phosphorus-selective flame ionization.

Animals↗
PubMed1979

Differential effects of acute and subacute HA-966 treatment on storage and release of striatal dopamine.

Acute injections of HA-966 (100 mg/kg) into rats caused a rapid elevation of dopamine (DA) content in the striatum. 3,4-Dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels increased after a latency period of 0.5 h and 1 h respectively. Repeated ("subacute") HA-966 treatment produced a smaller DA increase than did single administration, while DOPAC and HVA rose at the same rate after both treatments. In HA-966-pretreated rats no tolerance for DA increase followed a lesion of the dopaminergic fibres. Acute as well as subacute HA-966 prevented the disappearance of DA after alpha-methyl-p-tyrosine for about 3 h. In both cases DOPAC and HVA levels dropped sharply after HA-966. HA-966 had no influence on the decline of DOPAC and HVA levels after monoamine oxidase inhibition. It is concluded that the rises of DOPAC and HVA after HA-966 did not occur because the capacity of the vesicular DA stores was exceeded. Instead, HA-966 affects the storage mechanism for newly formed DA. Possible explanations for the observed tolerance to DA accumulation after HA-966 are discussed.

3,4-Dihydroxyphenylacetic Acid↗