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G Jansen

Publications and source records attributed to G Jansen.

At least 73 records · Page 4Linked to original sources
PubMed1997

Endolymphatic sac tumor: a case report and review of the literature.

BACKGROUND: Papillary tumors of the temporal bone are very rare but aggressive neoplasms. In the past, a middle-ear origin was presumed. Only recently convincing evidence exists that these tumors in fact arise from the endolymphatic sac. METHODS: We present a case of an endolymphatic sac tumor (ELST) with detailed clinical, imaging, operative, and pathologic data. The literature on this rare tumor type is reviewed. RESULTS: This 63-year-old woman had a progressive mass lesion in the temporal bone for a period of more than 35 years, resulting in unilateral fifth to eleventh cranial nerve palsy, progressive ataxia, and a pyramidal and pseudobulbar syndrome. Computerized tomography (CT) and magnetic resonance imaging (MRI) showed a tumor invading the pars squamosa and petrosa of the temporal bone, and extending into the middle and posterior fossa. Angiography demonstrated a hypervascular tumor mass. The patient underwent surgery, with nonradical removal of a tumor. Histologic examination demonstrated a papillary ELST. A search through the literature revealed 36 patients with ELST, based on convincing anatomic and histologic considerations. CONCLUSIONS: It is important to make a distinction between ELST and the more benign middle-ear adenomas, since this leads to a different treatment and prognosis. ELST frequently invades the surrounding structures and extends intracranially. The treatment of choice is a radical resection, although complete resection is impossible in most of the cases. The value of adjunctive radiation therapy remains controversial.

Adenoma↗
PubMed1997

Reverse genetics by chemical mutagenesis in Caenorhabditis elegans.

Traditional reverse genetics on yeast, mice and other organisms uses homologous recombination with transgenic DNA to interrupt a target gene. Here we report that target-selected gene inactivation can be be achieved in Caenorhabditis elegans with the use of chemical mutagens. We use PCR to selectively visualize deletions in genes of interest; the method is sensitive enough to permit detection of a single mutant among more than 15,000 wild types. A permanent frozen mutant collection of more than a million mutagenized animals has been established, and deletion mutants of several G-protein genes were isolated from it. The approach is suitable to be scaled up for systematic inactivation of all 17,000 C. elegans genes. Because it requires no transgenesis or cell culturing, it may also be applicable to small organisms usually considered to be outside the realm of reverse genetics (for example, other nematodes and insects). Any sequenced gene in any organism that can be handled in very large numbers can possibly be targeted in this way.

Animals↗
PubMed1997

The perception of aggression.

Several academic and clinical disciplines are involved in clarifying the concept of aggression by formulating operational and descriptive definitions. In the present paper the validity of the definitions of aggression, reported by nurses in an earlier qualitative study, is examined, using a survey approach among nurses of five general psychiatric hospitals in the Netherlands. Three dimensions of aggression were found; aggression as a normal, adaptive reaction, aggression as a violent reaction and aggression as a functional reaction. These findings match the results of the qualitative study. It was investigated whether there was a relation between personal and environmental characteristics of the nurses and the way they perceive aggression. The gender of the respondents, the setting in which they were working, the degree to which they used constraint measures and whether patients were voluntarily admitted or not, were related to the perception of aggression. The study points out that different instruments are needed to measure the prevalence or incidence of aggression and to diagnose or to intervene on aggression in clinical practice.

Adult↗
PubMed1997

Relationship between allergic manifestations and Toxocara seropositivity: a cross-sectional study among elementary school children.

Toxocara (the cause of visceral larva migrans in humans) and allergy have in common both elevated immunoglobulin E (IgE) levels and eosinophilia. In the present study, we investigated: 1) associations between Toxocara seropositivity and allergic manifestations; 2) risk factors for Toxocara infection; and 3) differences in Toxocara seroprevalence, allergic manifestations and the associations between these two, in children from urban and rural environments. Blood samples from 1,379 Dutch urban and rural elementary schoolchildren, were examined for Toxocara antibodies, eosinophil numbers, total IgE concentrations, and the occurrence of inhaled allergen-specific IgE. Questionnaires investigating respiratory health and putative risk factors for infection were completed. It was found that 8% of the children had Toxocara antibodies, occurring significantly less often in females than in males. The means of total serum IgE levels and blood eosinophils were significantly higher in the Toxocara-seropositive than in the seronegative group. Allergic asthma/recurrent bronchitis was found in 7% of the children, allergic reaction on animal contact in 4%, and IgE to at least one inhaled allergen in 16%. These variables were associated with Toxocara seroprevalence. Inhaled allergen-specific IgE and asthma/recurrent bronchitis occurred significantly less often in rural than in urban areas, and significantly less often among girls than among boys. Furthermore, occurrence of allergen-specific IgE increased significantly with age. No association existed between Toxocara seroprevalence and assumed risks, i.e. contact with pet animals and public playgrounds. In conclusion, our results indicate that allergic manifestations occur more often in Toxocara-seropositive children. A relationship with an already existing allergic condition is plausible.

Animals↗
PubMed1997

Cellular pharmacology and in vivo activity of a new anticancer agent, ZD9331: a water-soluble, nonpolyglutamatable, quinazoline-based inhibitor of thymidylate synthase.

ZD9331 is a drug that was developed from a potent class of water-soluble, C7-methyl-substituted, quinazoline-based inhibitors of thymidylate synthase (TS) that are transported into cells via a saturable, carrier-mediated system (reduced folate carrier, or RFC) but are not substrates for folylpolyglutamate synthetase. ZD9331 is the gamma-tetrazole analogue of 2-desamino-2, 7-dimethyl-N10-propargyl-2'fluoro-5,8-dideaza folate (ZM214888), with a TS Ki of approximately 0.4 nM. ZD9331 exhibits potent growth inhibitory and cytotoxic activity; e.g., IC50 for the inhibition of human W1L2 lymphoblastoid cell line was 7 nM. The addition of thymidine to the culture medium increased the IC50 in W1L2 cells >10, 000-fold, demonstrating the high specificity of the drug for TS. ZD9331 is transported into cells predominantly via the RFC. Accordingly, it competes with methotrexate (MTX) and folinic acid for cellular uptake and has reduced activity against two cell lines with low expression of the RFC (L1210:1565 and CEM/MTX). In addition, a cell line with acquired resistance to ZD9331 displays reduced uptake of both ZD9331 and MTX. A mouse cell line (L1210:RD1694), with acquired resistance to ZD1694 due to reduced folylpolyglutamate synthetase activity, was not significantly cross-resistant to ZD9331. The flux through TS, as measured by 3H release from 5-[3H]deoxyuridine, was rapidly inhibited when cells were incubated with ZD9331. However, because ZD9331 cannot form polyglutamates, TS activity recovered rapidly once cells were placed in drug-free medium. The minimum curative dose of ZD9331 in the i.m. L5178Y TK-/- tumor model was approximately 3 mg/kg when given by 24-h continuous infusion, and it was 25-50 mg/kg when given by a single i.p. or i.v. injection. ZD9331 had antitumor activity against the L5178Y TK+/- tumor when administered by 7-day continuous infusion; growth delays of more than 5 days (and some cures) were seen at doses of 25-50 mg/kg/day. At higher doses, significant weight loss (gastrointestinal toxicity) and myelosuppression (neutropenia and thrombocytopenia) were observed, suggesting that these may be dose-limiting toxicities in the Phase I clinical studies.

Animals↗
PubMed1996

Metabolic aspects of peroxisomal disorders.

In recent years an increasing number of inherited diseases in man have been identified in which there is an impairment in one or more peroxisomal functions. This paper discusses the current state of knowledge on these disorders with particular emphasis on the metabolic abnormalities in these diseases.

Cholesterol↗
PubMed1996

Variant GPI structure in relation to membrane-associated functions of a murine folate receptor.

Two variant sublines of murine L1210 leukemia cells (L1210A and L1210JF) overexpress the cell surface folate receptor (FR). The membrane bound FR in L1210A cells exhibited significantly (up to 17-fold) greater relative affinities for (6S)-N5-methyltetrahydrofolate, (6S)-N5-formyltetrahydrofolate and methotrexate compared to the FR in L1210JF cells. Furthermore, receptor-mediated transport of [3H]-(6S)-N5-methyltetrahydrofolate was much more efficient in L1210A cells compared to L1210JF cells. When solubilized with Triton X-100, the ligand binding characteristics of FR from both sublines resembled those of the receptor associated with L1210 JF cell membranes. N-terminal amino acid sequence analysis as well as RT-PCR analysis of the entire coding region revealed a single species of FR in both cells, identical to murine FR-alpha. The FR in L1210JF cells was sensitive to phosphatidylinositol specific phospholipase C (PI-PLC) indicating the presence of a glycosyl-phosphatidylinositol (GPI) membrane anchor while the FR in L1210A cells was resistant to PI-PLC; however, the FR in L1210A cells was released from plasma membranes by nitrous acid, as expected for GPI and its PI-PLC resistant structural variants. Treatment of L1210A cell membranes with mild base rendered the protein PI-PLC sensitive as expected for GPI anchors acylated in the inositol ring and also decreased the affinities of the membrane associated FR for reduced folates. When the cDNA for murine FR-alpha was expressed in parental L1210 cells the protein was PI-PLC resistant but was sensitive to PI-PLC when the cDNA was expressed in human 293 fibroblasts. In L1210JF, L1210A, and parental L1210 cells, several cell surface proteins, including FR, incorporated [3H]ethanolamine, a component of the GPI membrane anchor; however, the labeled proteins were released by PI-PLC only in L1210JF cells. The above results preclude any peculiarity of the FR polypeptide in either L1210 subline as the basis for the observed differences in PI-PLC sensitivity and membrane-associated functions of FR. Partial deglycosylation of membrane associated FR from either cell with N-glycanase did not influence its ligand binding characteristics. The results of this study lead to the hypothesis that variant GPI structures may modulate the function of a protein by influencing its conformation/topography in the membrane. Such effects may be identified by their disappearance/reduction upon detergent solubilization or mild base treatment of the membrane.

Amino Acid Sequence↗
PubMed1996

Functional aspects of membrane folate receptors in human breast cancer cells with transport-related resistance to methotrexate.

Two methotrexate (MTX)-resistant human breast-cancer cell lines with impaired transport via the reduced folate carrier (RFC), one established in vitro (MTX(R)-ZR-75-1) and another inherently resistant (MDA-231), were adapted to grow in medium containing 2 nM folic acid. This induced the expression of previously undetectable membrane folate receptors (MFR) to levels of 8.2 and 2.3 pmol/10(7) cells, respectively. Polymerase chain reaction (PCR) quantitation revealed that MFR messenger-RNA levels of the isoform first described in human nasopharyngeal carcinoma KB cells (MFR-alpha) were increased in low-folate-adapted MTX(R)-ZR-75-1 cells, whereas placental transcripts (MFR-beta) coincided with MFR-alpha expression in low-folate (LF)-adapted MDA-231 cells. These cell lines were used to study the role of MFR in the uptake and growth-inhibitory effects of five different antifolates with varying affinities for MFR: N10-propargyl-5, 8-dideazafolic acid (CB3717) > 5,10-dideazatetra-hydrofolic acid (DDATHF) > N-5-[N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6-methyl) -N-methyl-amino]-2-theonyl}-glutamic acid (ZD1694) >> MTX > edatrexate (EDX). Expression of MFR only slightly decreased the resistant phenotype for MTX, EDX, and ZD1694, suggesting that these drugs are not transported intracellularly to cytotoxic concentrations at these levels of MFR expression. On the other hand, both cell lines became from at least 180- to 400-fold more sensitive to growth inhibition by CB3717 and DDATHF, which may be correlated with their high affinity for MFR. These sensitivity/resistance profiles were largely similar following cell culture in medium containing 1 nM L-leucovorin, a folate with an affinity for MFR 10-fold lower than that of folic acid, the one exception being the increased sensitivity for ZD1694 seen in the LF-adapted cells with the highest level of MFR expression (MTX(R)-ZR-75-1). These results illustrate that the efficacy of MFR in mediating antifolate transport and cytotoxicity depends on their affinity for the folate antagonist, their degree of expression, and the levels of competing folates.

Aminopterin↗
PubMed1996

Abnormal myotonic dystrophy protein kinase levels produce only mild myopathy in mice.

Myotonic dystrophy (DM) is commonly associated with CTG repeat expansions within the gene for DM-protein kinase (DMPK). The effect of altered expression levels of DMPK, which is ubiquitously expressed in all muscle cell lineages during development, was examined by disrupting the endogenous Dmpk gene and overexpressing a normal human DMPK transgene in mice. Nullizygous (-/-) mice showed only inconsistent and minor size changes in head and neck muscle fibres at older age, animals with the highest DMPK transgene expression showed hypertrophic cardiomyopathy and enhanced neonatal mortality. However, both models lack other frequent DM symptoms including the fibre-type dependent atrophy, myotonia, cataract and male-infertility. These results strengthen the contention that simple loss- or gain-of-expression of DMPK is not the only crucial requirement for development of the disease.

Animals↗
PubMed1996

Endocytosis of GPI-linked membrane folate receptor-alpha.

GPI-linked membrane folate receptors (MFRs) have been implicated in the receptor-mediated uptake of reduced folate cofactors and folate-based chemotherapeutic drugs. We have studied the biosynthetic transport to and internalization of MFR isoform alpha in KB-cells. MFR-alpha was synthesized as a 32-kD protein and converted in a maturely glycosylated 36-38-kD protein 1 h after synthesis. 32-kD MFR-alpha was completely soluble in Triton X-100 at 0 degree C. In contrast, only 33% of the 36-38-kD species could be solubilized at these conditions whereas complete solubilization was obtained in Triton X-100 at 37 degrees C or in the presence of saponin at 0 degree C. Similar solubilization characteristics were found when MFR-alpha at the plasma membrane was labeled with a crosslinkable 125I-labeled photoaffinity-analog of folic acid as a ligand. Triton X-100-insoluble membrane domains containing MFR-alpha could be separated from soluble MFR-alpha on sucrose flotation gradients. Only Triton X-100 soluble MFR-alpha was internalized from the plasma membrane. The reduced-folate-carrier, an integral membrane protein capable of translocating (anti-)folates across membranes, was completely excluded from the Triton X-100-resistant membrane domains. Internalized MFR-alpha recycled slowly to the cell surface during which it remained soluble in Triton X-100 at 0 degree C. Using immunoelectron microscopy, we found MFR-alpha along the entire endocytic pathway: in clathrin-coated buds and vesicles, and in small and large endosomal vacuoles. In conclusion, our data indicate that a large fraction, if not all, of internalizing MFR-alpha bypasses caveolae.

Biological Transport↗
PubMed1996

Ste50p sustains mating pheromone-induced signal transduction in the yeast Saccharomyces cerevisiae.

In the yeast Saccharomyces cerevisiae, the heterotrimeric G protein transduces the mating pheromone signal from a cell-surface receptor. Free G beta gamma then activates a mitogen-activated protein (MAP) kinase cascade. STE50 has been shown to be involved in this pheromone signal-transduction pathway. In this study, we present a functional characterization of Ste50p, a protein that is required to sustain the pheromone-induced signal which leads cells to hormone-induced differentiation. Inactivation of STE50 leads to the attenuation of mating pheromone-induced signal transduction, and overexpression of STE50 intensifies the pheromone-induced signalling. By genetic analysis we have positioned the action of Ste50p downstream of the alpha-pheromone receptor (STE2), at the level of the heterotrimeric G protein, and upstream of STE5 and the kinase cascade of STE11 and STE7. In a two-hybrid assay Ste50p interacts weakly with the G protein and strongly with the MAPKKK Ste11p. The latter interaction is absent in the constitutive mutant Ste11pP279S. These data show that a new component, Ste50p, determines the extent and the duration of signal transduction by acting between the G protein and the MAP kinase complex in S. cerevisiae.

Alleles↗
PubMed1995

Functional activity of the reduced folate carrier in KB, MA104, and IGROV-I cells expressing folate-binding protein.

The role of a membrane-associated folate binding protein (mFBP) in transport of folate analogues was investigated in three epithelial cell lines that were grown in high folate medium and folate-conditioned medium and express different levels of mFBP: human nasopharyngeal KB cells, monkey kidney MA104 cells, and IGROV-I ovarian carcinoma cells. Folate analogues were selected for which mFBP exhibits a low affinity, i.e., methotrexate (MTX) and 10-ethyl-10-deazaaminopterin (10-EdAM) or a (moderately) high affinity as compared to folic acid, i.e., N-(5[N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6-ylmethyl(-N-m ethylamino]-2-theonyl)-L-glutamic acid (ZD1694), N10-propargyl-5,8-dideazafolic acid (CB3717), and 5,10-dideazatetrahydrofolic acid. Regardless of the medium folate status, growth inhibition studies with IGROV-I and MA104 cells demonstrated a lack of correlation between the affinity of mFBP for the antifolate drugs and their sensitivity profile; both cell lines were highly sensitive to growth inhibition by MTX, 10-EdAM, ZD1694 and 5,10-dideazatetrahydrofolic acid, but were insensitive for CB3717. The same drug sensitivity profile was observed for KB cells, with the exception that these cells were also sensitive to growth inhibition by CB3717 but only in folate-conditioned medium. This overall drug sensitivity profile appeared to correlate with the differential efficiency of drug transport via the "classical" reduced folate/MTX carrier (RFC), rather than by mFBP. Characteristics that further supported functional RFC activity in KB, IGROV-I, and MA104 cells included: (a) the growth inhibitory effects of the drugs could be prevented by the reduced folate leucovorin rather than by folic acid; (b) rates for uptake of [3H]10-EdAM were 2-4-fold higher than for [3H]MTX at 1 microM extracellular concentrations and coincided with the affinity of the RFC for these drugs, rather than those of the mFBP; (c) uptake of [3H]10-EdAM and [3H]leucovorin was markedly inhibited by leucovorin and 10-EdAM, respectively, or by an N-hydroxysuccinimide ester of MTX (irreversibly labeling RFC) but only to a minor extent by folic acid or an N-hydroxysuccinimide ester of folic acid (irreversibly labeling mFBP); and, finally, (d) labeling with an N-hydroxysuccinimide ester of [3H]MTX identified a protein with a molecular weight within the range of that reported for the RFC in human leukemic cells. Altogether, these results indicate that both RFC and mFBP are coexpressed in three epithelial cell lines and that RFC is the preferential route of entry for antifolate compounds, even when mFBP is expressed to very high levels.

Aminopterin↗
PubMed1995

Structural organization and developmental expression pattern of the mouse WD-repeat gene DMR-N9 immediately upstream of the myotonic dystrophy locus.

The diverse biological consequences of size-expansion of the unstable (CTG)n repeat in the myotonic dystrophy protein kinase (DM-PK) gene at chromosome region 19q13.3, are still poorly understood. Abnormal (CTG)n length may affect either DM-PK mRNA fate or function, or alternatively, compromise gene transcription by distortion of chromatin configuration. In the latter model involvement of neighbouring genes in DM upon extreme expansion of the repeat cannot be discarded as a possibility and should be studied further. Here we report on the elucidation of the complete genomic structure and expression pattern of the mouse DMR-N9 gene (called 59 gene in humans), which is at 1.1 kbp upstream of the DM-PK gene. This gene contains five exons spanning 7 kbp and codes for a protein of 650 amino acids. Two regions of the predicted protein show significant homology to WD repeats, highly conserved amino acid sequences found in a family of proteins engaged in signal transduction or cell regulatory functions. The start site of transcription has been determined and we have identified putative transcription factor binding sequences in a 400 bp putative promoter area immediately upstream of the transcribed unit. Northern blotting analysis and RNA in situ hybridization revealed ubiquitous low expression in all tissues of the mouse embryo and enhanced expression in adult brain and testis. The onset of transcription is phased early in mouse embryogenesis, before or at day 9.5 of gestation. From day 14.5 onwards DMR-N9 mRNAs were detected in all neural tissues, especially in the telencephalon and mesencephalon. Later, mRNA presence is evident in distinct tubules of the mature testis, restricted to secondary spermatocytes of stages VIII to XII of the spermatogenic proliferation cycle. We conclude that the DMR-N9 gene is a candidate for being involved in the manifestation of mental and testicular symptoms in severe cases of DM.

Amino Acid Sequence↗
PubMed1994

Isochromosome 12p-positive pineal germ cell tumor.

We report the chromosomal characteristics of a recurrent pineal non-seminomatous germ cell tumor in a 16-year-old male patient. This non-seminomatous tumor had the following components: embryonal carcinoma, teratoma, yolk sac tumor, and trophoblastic giant cells. Chromosome analysis showed a near-triploid karyotype (64 chromosomes), including two copies of an isochromosome 12p. This latter finding could be confirmed using 12p-specific competitive in situ hybridization techniques applied to cultured cells (T2219-P6 cell line) derived from the tumor. The present findings are in keeping with the hypothesis that isochromosome 12p formation is associated with the development of malignant extragonadal germ cell tumors.

Adolescent↗
PubMed1994

Leucovorin rescue of human cancer and bone marrow cells following edatrexate or methotrexate.

We have examined the cytotoxic activities of edatrexate (EDX) and methotrexate (MTX) and their reversal by leucovorin in nine human cancer cell lines and in human bone marrow CFU-GM cells. EDX was 3.7- to 123-fold more toxic than MTX against the cancer cell lines and 25-fold against the bone marrow cells. Lower EDX concentrates generally were needed to inhibit cancer cell growth relative to bone marrow cells, however, whereas bone marrow and cancer cell growth were more often susceptible to the same MTX concentrations. The new antifolate was metabolized to long-chain polyglutamates to a greater extent than MTX in seven cell lines. Leucovorin at 0.2 microM rescued two breast cancer and two non-small cell lung cancer cell lines to a lesser extent following EDX than MTX, but significant rescue was observed in two head and neck cancer cell lines that formed large amounts of polyglutamates. These cell lines also accumulated reduced folates to a greater extent than the other cell lines following leucovorin exposure. Leucovorin rescued bone marrow cells following MTX but only partially following the highest EDX concentrations. EDX may enjoy a better therapeutic index than MTX against some cancer cell lines relative to bone marrow precursor cells, especially after leucovorin rescue.

Aminopterin↗
PubMed1994

Gonosomal mosaicism in myotonic dystrophy patients: involvement of mitotic events in (CTG)n repeat variation and selection against extreme expansion in sperm.

Myotonic dystrophy (DM) is caused by abnormal expansion of a polymorphic (CTG)n repeat, located in the DM protein kinase gene. We determined the (CTG)n repeat lengths in a broad range of tissue DNAs from patients with mild, classical, or congenital manifestation of DM. Differences in the repeat length were seen in somatic tissues from single DM individuals and twins. Repeats appeared to expand to a similar extent in tissues originating from the same embryonal origin. In most male patients carrying intermediate- or small-sized expansions in blood, the repeat lengths covered a markedly wider range in sperm. In contrast, male patients with large allele expansions in blood (> 700 CTGs) had similar or smaller repeats in sperm, when detectable. Sperm alleles with > 1,000 CTGs were not seen. We conclude that DM patients can be considered gonosomal mosaics, i.e., combined somatic and germ-line tissue mosaics. Most remarkably, we observed multiple cases where the length distributions of intermediate- or small-sized alleles in fathers' sperm were significantly different from that in their offspring's blood. Our combined findings indicate that intergenerational length changes in the unstable CTG repeat are most likely to occur during early embryonic mitotic divisions in both somatic and germ-line tissue formation. Both the initial CTG length, the overall number of cell divisions involved in tissue formation, and perhaps a specific selection process in spermatogenesis may influence the dynamics of this process. A model explaining mitotic instability and sex-dependent segregation phenomena in DM manifestation is discussed.

Aged↗
PubMed1993

Importance of pharmacodynamics in the in vitro antiproliferative activity of the antifolates methotrexate and 10-ethyl-10-deazaaminopterin against human head and neck squamous cell carcinoma.

The pharmacodynamic profiles of methotrexate (MTX) and 10-ethyl-10-deazaaminopterin (10-EdAM) were determined in three head and neck squamous cell carcinoma (HNSCC) cell lines. Cell growth inhibition was tested using a semi-automated 96-well based proliferation assay, the sulforhodamine B (SRB) assay. Drug concentrations ranged from 10(-5) to 10(-9) M, with exposure periods of 4, 24, 48, 72 and 96 hr. The SRB-test was performed after each of these periods of continuous exposure and after an additional period of 24 and 48 hr in drug-free medium. Without a drug-free period the IC50 values strongly depended on the time of exposure. For example, with respect to MTX, IC50 values at 24 hr ranged from 2.9 (UM-SCC-14C) to over 10 microM (UM-SCC-22B and -11B), but when exposed continuously for 96 hr, IC50 values varied between 0.039 and 0.1 microM. 10-EdAM followed a similar sensitivity pattern with 5-20-fold lower IC50 values. The minimal time to achieve significant growth inhibition varied between the cell lines, < 24 hr for UM-SCC-14C, > 24 and > 48 hr for UM-SCC-11B and -22B, respectively. The cell lines also varied with respect to growth behaviour when placed in drug-free medium for an additional period. Growth of UM-SCC-14C cells was recovered significantly after removing the drug, whereas UM-SCC-22B showed a different pattern: when cultured for over 48 hr, cell growth was strongly inhibited, independent of the drug being removed. This variable pattern of sensitivity could be correlated with the capacity of the cells to form polyglutamate derivatives. After 24 hr, drug accumulation was at least three times lower in UM-SCC-14C than in both other cell lines. The low level of antifolate accumulation in UM-SCC-14C is in line with the recovery from growth inhibition at culture in drug-free medium, while the persistent growth inhibition observed in UM-SCC-22B agrees with the intracellular accumulation of higher polyglutamates. In conclusion, these experiments show that the pharmacodynamic profile varies between HNSCC cell lines and plays an important role in the growth inhibition by antifolates. Both exposure time and the intrinsic capacity to synthesize polyglutamates are important factors in the sensitivity of HNSCC to antifolate drugs.

Aminopterin↗