Proximity proteomics identifies septins and PAK2 as decisive regulators of actomyosin-mediated expulsion of von Willebrand factor

In response to tissue injury, within seconds the ultra-large glycoprotein von Willebrand factor (VWF) is released from endothelial storage organelles (Weibel-Palade bodies) into the lumen of the blood vasculature, where it leads to the recruitment of platelets. The marked size of VWF multimers represents an unprecedented burden on the secretory machinery of endothelial cells (ECs). ECs have evolved mechanisms to overcome this, most notably an actomyosin ring that forms, contracts, and squeezes out its unwieldy cargo. Inhibiting the formation or function of these structures represents a novel therapeutic target for thrombotic pathologies, although characterizing proteins associated with such a dynamic process has been challenging. We have combined APEX2 proximity labeling with an innovative dual loss-of-function screen to identify proteins associated with actomyosin ring function. We show that p21 activated kinase 2 (PAK2) recruits septin hetero-oligomers, a molecular interaction that forms a ring around exocytic sites. This cascade of events controls actomyosin ring function, aiding efficient exocytic release. Genetic or pharmacological inhibition of PAK2 or septins led to inefficient release of VWF and a failure to form platelet-catching strings. This new molecular mechanism offers additional therapeutic targets for the control of thrombotic disease and is highly relevant to other secretory systems that employ exocytic actomyosin machinery.

Structure modeling hints at a granular organization of the Golgi ribbon

BACKGROUND

In vertebrate cells, the Golgi functional subunits, mini-stacks, are linked into a tri-dimensional network. How this "ribbon" architecture relates to Golgi functions remains unclear. Are all connections between mini-stacks equal? Is the local structure of the ribbon of functional importance? These are difficult questions to address, without a quantifiable readout of the output of ribbon-embedded mini-stacks. Endothelial cells produce secretory granules, the Weibel-Palade bodies (WPB), whose von Willebrand Factor (VWF) cargo is central to hemostasis. The Golgi apparatus controls WPB size at both mini-stack and ribbon levels. Mini-stack dimensions delimit the size of VWF "boluses" whilst the ribbon architecture allows their linear co-packaging, thereby generating WPBs of different lengths. This Golgi/WPB size relationship suits mathematical analysis.

RESULTS

WPB lengths were quantized as multiples of the bolus size and mathematical modeling simulated the effects of different Golgi ribbon organizations on WPB size, to be compared with the ground truth of experimental data. An initial simple model, with the Golgi as a single long ribbon composed of linearly interlinked mini-stacks, was refined to a collection of mini-ribbons and then to a mixture of mini-stack dimers plus long ribbon segments. Complementing these models with cell culture experiments led to novel findings. Firstly, one-bolus sized WPBs are secreted faster than larger secretory granules. Secondly, microtubule depolymerization unlinks the Golgi into equal proportions of mini-stack monomers and dimers. Kinetics of binding/unbinding of mini-stack monomers underpinning the presence of stable dimers was then simulated. Assuming that stable mini-stack dimers and monomers persist within the ribbon resulted in a final model that predicts a "breathing" arrangement of the Golgi, where monomer and dimer mini-stacks within longer structures undergo continuous linking/unlinking, consistent with experimentally observed WPB size distributions.

CONCLUSIONS

Hypothetical Golgi organizations were validated against a quantifiable secretory output. The best-fitting Golgi model, accounting for stable mini-stack dimers, is consistent with a highly dynamic ribbon structure, capable of rapid rearrangement. Our modeling exercise therefore predicts that at the fine-grained level the Golgi ribbon is more complex than generally thought. Future experiments will confirm whether such a ribbon organization is endothelial-specific or a general feature of vertebrate cells.

Human endothelial cells size-select their secretory granules for exocytosis to modulate their functional output

BACKGROUND

The secretory granules of endothelial cells, Weibel-Palade bodies, are released in response to numerous extracellular signals. Their cargo is critical to many vascular functions including hemostasis and inflammation. This presents a fundamental problem: how can these cells initiate tailor-made responses from the release of a single type of organelle, each with similar cargo? Each cell contains Weibel-Palade bodies in a wide range of sizes, and we have shown that experimentally shortening these organelles disproportionately reduces their ability to initiate hemostasis in vitro, leaving leukocyte recruitment unaffected. Could the production of this range of sizes underpin differential responses?

OBJECTIVES

To determine whether different agonists drive the exocytosis of different sizes of Weibel-Palade bodies.

METHODS

We used a high-throughput automated unbiased imaging workflow to analyze the sizes of Weibel-Palade bodies within human umbilical vein endothelial cells (HUVECs) before and after agonist activation to determine changes in organelle size distributions.

RESULTS

We found that a subset of agonists differentially evoke the release of the longest, most pro-hemostatic organelles. Inhibiting the release of these longest organelles by just 15% gives a fall of 60% in an assay of secreted von Willebrand factor (vWF) function.

CONCLUSIONS

The size-selection of granules for exocytosis represents a novel layer of control, allowing endothelial cells to provide diverse responses to different signals via the release of a single type of organelle.

A GBF1-Dependent Mechanism for Environmentally Responsive Regulation of ER-Golgi Transport

How can anterograde membrane trafficking be modulated by physiological cues? A screen of Golgi-associated proteins revealed that the ARF-GEF GBF1 can selectively modulate the ER-Golgi trafficking of prohaemostatic von Willebrand factor (VWF) and extracellular matrix (ECM) proteins in human endothelial cells and in mouse fibroblasts. The relationship between levels of GBF1 and the trafficking of VWF into forming secretory granules confirmed GBF1 is a limiting factor in this process. Further, GBF1 activation by AMPK couples its control of anterograde trafficking to physiological cues; levels of glucose control GBF1 activation in turn modulating VWF trafficking into secretory granules. GBF1 modulates both ER and TGN exit, the latter dramatically affecting the size of the VWF storage organelles, thereby influencing the hemostatic capacity of the endothelium. The role of AMPK as a central integrating element of cellular pathways with intra- and extra-cellular cues can now be extended to modulation of the anterograde secretory pathway.

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The Arf-GEF GBF1 modulates anterograde trafficking of VWF and ECM proteins

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Loss of GBF1 slows ER and TGN exit, producing swollen ER and giant WPBs

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Activation of GBF1 via AMPK reduces endothelial WPB size and secretion

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Metabolic change alters anterograde trafficking and cargo secretion via AMPK-GBF1

Weibel-Palade bodies at a glance

The vascular environment can rapidly alter, and the speed with which responses to both physiological and pathological changes are required necessitates the existence of a highly responsive system. The endothelium can quickly deliver bioactive molecules by regulated exocytosis of its secretory granules, the Weibel-Palade bodies (WPBs). WPBs include proteins that initiate both haemostasis and inflammation, as well those that modulate blood pressure and angiogenesis. WPB formation is driven by von Willebrand factor, their most abundant protein, which controls both shape and size of WPBs. WPB are generated in a range of sizes, with the largest granules over ten times the size of the smallest. In this Cell Science at a Glance and the accompanying poster, we discuss the emerging mechanisms by which WPB size is controlled and how this affects the ability of this organelle to modulate haemostasis. We will also outline the different modes of exocytosis and their polarity that are currently being explored, and illustrate that these large secretory organelles provide a model for how elements of secretory granule biogenesis and exocytosis cooperate to support a complex and diverse set of functions.

The scaffold protein Ajuba suppresses CdGAP activity in epithelia to maintain stable cell-cell contacts

Levels of active Rac1 at epithelial junctions are partially modulated via interaction with Ajuba, an actin binding and scaffolding protein. Here we demonstrate that Ajuba interacts with the Cdc42 GTPase activating protein CdGAP, a GAP for Rac1 and Cdc42, at cell-cell contacts. CdGAP recruitment to junctions does not require Ajuba; rather Ajuba seems to control CdGAP residence at sites of cell-cell adhesion. CdGAP expression potently perturbs junctions and Ajuba binding inhibits CdGAP activity. Ajuba interacts with Rac1 and CdGAP via distinct domains and can potentially bring them in close proximity at junctions to facilitate activity regulation. Functionally, CdGAP-Ajuba interaction maintains junctional integrity in homeostasis and diseases: (i) gain-of-function CdGAP mutants found in Adams-Oliver Syndrome patients strongly destabilize cell-cell contacts and (ii) CdGAP mRNA levels are inversely correlated with E-cadherin protein expression in different cancers. We present conceptual insights on how Ajuba can integrate CdGAP binding and inactivation with the spatio-temporal regulation of Rac1 activity at junctions. Ajuba provides a novel mechanism due to its ability to bind to CdGAP and Rac1 via distinct domains and influence the activation status of both proteins. This functional interplay may contribute towards conserving the epithelial tissue architecture at steady-state and in different pathologies.

Clathrin-mediated post-fusion membrane retrieval influences the exocytic mode of endothelial Weibel-Palade bodies

Weibel-Palade bodies (WPBs), the storage organelles of endothelial cells, are essential to normal haemostatic and inflammatory responses. Their major constituent protein is von Willebrand factor (VWF) which, following stimulation with secretagogues, is released into the blood vessel lumen as large platelet-catching strings. This exocytosis changes the protein composition of the cell surface and also results in a net increase in the amount of plasma membrane. Compensatory endocytosis is thought to limit changes in cell size and retrieve fusion machinery and other misplaced integral membrane proteins following exocytosis; however, little is known about the extent, timing, mechanism and precise function of compensatory endocytosis in endothelial cells. Using biochemical assays, live-cell imaging and correlative spinning-disk microscopy and transmission electron microscopy assays we provide the first in-depth high-resolution characterisation of this process. We provide a model of compensatory endocytosis based on rapid clathrin- and dynamin-mediated retrieval. Inhibition of this process results in a change of exocytic mode: WPBs then fuse with previously fused WPBs rather than the plasma membrane, leading, in turn, to the formation of structurally impaired tangled VWF strings.

This article has an associated First Person interview with the first authors of the paper.

Summary: Compensatory endocytosis plays key roles in Weibel-Palade body exocytosis. Inhibition of this process results in a change of exocytic mode and the release of von Willebrand factor as tangled strings.

Carbocyclic analogues of the potent cytidine deaminase inhibitor 1-(beta-D-ribofuranosyl)-1,2-dihydropyrimidin-2-one (zebularine)

Three carbocylic analogues of the potent cytidine deaminase inhibitor (CDA) zebularine [1-(beta-D-ribofuranosyl)-1, 2-dihydropyrimidin-2-one, 1a] were synthesized. The selected pseudosugar templates correspond, respectively, to the cyclopentenyl moiety of neplanocin A (compound 4), the cyclopentyl moiety of aristeromycin (compound 5), and a newly designed, rigid bicyclo[3.1. 0]hexane moiety (compound 6). These three carba-nucleoside versions of zebularine were fashioned to overcome the inherent instability of the parent drug. Each target compound was approached differently using either convergent or linear approaches. The immediate precursor to the cyclopentenyl analogue 4 was obtained by a Mitsunobu coupling of pseudosugar 7 with 2-hydroxypyrimidine. The cyclopentyl analogue 5 was linearly constructed from carbocyclic amine 17, and the final target 6 was similarly constructed from the carbobicyclic amine 27. Of the three target compounds, only 5 showed a significant level of inhibition against human CDA, but it was 16 times less potent than zebularine (Ki = 38 microM vs Ki(apparent) = 2.3 microM). Although these carbocyclic analogues appeared to be more stable than zebularine, replacement of the electronegative CO4' oxygen for the less electronegative carbon in 4-6 presumably reduces the capacity of the pyrimidin-2(1H)-one ring to form a covalent hydrate, a step considered crucial for the compound to function as a transition-state inhibitor of the enzyme.

Inhibition of in vitro and in vivo HIV replication by a distamycin analogue that interferes with chemokine receptor function: a candidate for chemotherapeutic and microbicidal application

Select chemokine receptors act as coreceptors for HIV-1 entry into human cells and represent targets for antiviral therapy. In this report we describe a distamycin analogue, 2,2'-[4, 4'-[[aminocarbonyl]amino]bis[N,4'-di[pryrrole-2-carboxamide- 1, 1'-dimethyl]]-6,8-naphthalenedisulfonic acid]hexasodium salt (NSC 651016), that selectively inhibited chemokine binding to CCR5, CCR3, CCR1, and CXCR4, but not to CXCR2 or CCR2b, and blocked chemokine-induced calcium flux. Inhibition was not due to nonspecific charge interactions at the cell surface, but was based on a specific competition for the ligand receptor interaction sites since the inhibitory effect was specific for some but not all chemoattractant receptors. NSC 651016 inhibited in vitro replication of a wide range of HIV-1 isolates, as well as HIV-2 and SIV, and exhibited in vivo anti-HIV-1 activity in a murine model. In contrast, a distamycin analogue with similar structure and charge and the monomeric form of NSC 651016 demonstrated no inhibitory effects. These data demonstrate that molecules which interfere with HIV-1 entry into cells by targeting specific chemokine coreceptors can provide a viable approach to anti-HIV-1 therapy. NSC 651016 represents an attractive candidate for the chemotherapeutic treatment of HIV-1 infection and as a microbicide to prevent the sexual transmisssion of HIV-1. Moreover, NSC 651016 can serve as a template for medicinal chemical modifications leading to more effective antivirals.

Amplification of antibody production by phosphorothioate oligodeoxynucleotides

A phosphorothioate oligodeoxynucleotide that is complementary (antisense) to the initiation region of the rev gene of HIV-1 causes hypergammaglobulinemia and splenomegaly in mice, and it induces B cell proliferation and differentiation in mouse spleen mononuclear cells (SMNCs) and human peripheral blood mononuclear cells in vitro. The current studies were performed to investigate the specificity of these immunomodulatory effects. Both the sense and antisense rev oligomers stimulated tritiated thymidine incorporation and secretion of immunoglobulin M (IgM) and immunoglobulin G (IgG) by mouse SMNCs in a concentration-dependent fashion, but the antisense oligomer produced greater immune effects. Studies comparing phosphorothioate oligomers (anti-rev, c-myc, and c-myb) either methylated or unmethylated at CpG dinucleotides showed that methylation effectively abrogated the proliferative effect and tended to reduce the immunoglobulin secretory activity, but the latter was not statistically significant except in the case of IgG in anti-rev oligomer-treated cultures. Mice were injected with the sense or antisense rev oligomers singly or in combination. The animals then were immunized with tetanus toxoid and received a booster 21 days later. Oligodeoxynucleotide-treated mice had significantly higher levels of IgM antibodies on days 28 and 35 and of IgG antibodies on days 14 and 35 as compared with mice that were immunized but received vehicle alone. There was no evidence for additive, synergistic, or antagonistic interactions of the sense and antisense rev oligomers. These results indicate that the unmethylated anti-rev oligomer is the most potent of the phosphorothioate oligomers tested at activating lymphocyte proliferation and differentiation and that a single intravenous injection of this oligodeoxynucleotide augments antibody production to a specific antigen as long as 35 days later.

B-cell proliferation and differentiation in common variable immunodeficiency patients produced by an antisense oligomer to the rev gene of HIV-1

The immunostimulatory activity of a phosphorothioate oligodeoxynucleotide (27 mer) that is antisense to the rev gene of HIV-1 was studied on normal human lymphocytes and on cells from patients with common variable immunodeficiency (CVI). For peripheral blood mononuclear cells from nine normal individuals, the proliferation index (16.8 +/- 12.5) after anti-rev oligomer exposure was proportional to the percentage of peripheral B-cells (r = 0.76, P = 0.02). In five experiments, enriched B- or T-cell populations had proliferation indices of 47.2 +/- 32.9 and 2.4 +/- 1.9, respectively. The addition of T-cells to anti-rev oligomer treated B-cells had no effect (proliferation index = 47.5 +/- 38.1). After anti-rev oligomer stimulation, autoradiography, and counterstaining for B- and T-cell markers, all detectable [3H]thymidine uptake was by CD19-positive cells. Eight of the 14 CVI patients had a proliferation index and secreted levels of IgM and IgG comparable to cells from normal individuals. In contrast to normal cells, the direct correlation between proliferation of peripheral blood mononuclear cells and the percentage of peripheral B-cells was weak in samples from 13 CVI patients (r = 0.4, P = 0.2). These findings indicate that peripheral blood B-cells from about half of CVI patients proliferate and produce immunoglobulin after exposure to anti-rev oligomer. These data demonstrate that under the appropriate circumstances, B-cells of some CVI patients can proliferate and differentiate normally.

2,4-Diaminothieno[2,3-d]pyrimidine analogues of trimetrexate and piritrexim as potential inhibitors of Pneumocystis carinii and Toxoplasma gondii dihydrofolate reductase

A series of eight previously undescribed 2,4-diaminothieno[2,3-d]pyrimidine analogues of the potent dihydrofolate reductase (DHFR) inhibitors trimetrexate (TMQ) and piritrexim (PTX) were synthesized as potential drugs against Pneumocystis carinii and Toxoplasma gondii, which are major causes of severe opportunistic infections in AIDS patients. 2,4-Diamino-5-methyl-6-(aryl/aralkyl)thieno[2,3-d]pyrimidines with 3,4,5-trimethoxy or 2,5-dimethoxy substitution in the aryl/aralkyl moiety and 2,4-diamino-5-(aryl/aralkyl)thieno[2,3-d]pyrimidines with 2,5-dimethoxy substitution in the aryl/aralkyl moiety were obtained by reaction of the corresponding 2-amino-3-cyanothiophenes with chloroformamidine hydrochloride. The aryl group in the 5,6-disubstituted analogues was either attached directly to the hetero ring or was separated from it by one or two carbons, whereas the aryl group in the 5-monosubstituted analogues was separated from the hetero ring by two or three carbons. 2-Amino-3-cyano-5-methyl-6-(aryl/alkyl)thiophene intermediates for the preparation of the 5,6-disubstituted analogues were prepared from omega-aryl-2-alkylidene-malononitriles and sulfur in the presence of a secondary amine, and 2-amino-3-cyano-4-(aryl/aralkyl)thiophene intermediates for the preparation of the 5-monosubstituted analogues were obtained from omega-aryl-1-chloro-2-alkylidenemalononitriles and sodium hydrosulfide. Synthetic routes to the heretofore unknown ylidenemalononitriles, and the ketone precursors thereof, were developed. The final products were tested in vitro as inhibitors of DHFR from Pneumocystis carinii, Toxoplasma gondii, rat liver, beef liver, and Lactobacillus casei. A selected number of previously known 2,4-diaminothieno[2,3-d]pyrimidines lacking the 3,4,5-trimethoxyphenyl and 2,5-dimethoxyphenyl substitution pattern of TMQ and PTX, respectively, were also tested for comparison. None of the compounds was as potent as TMQ or PTX, and while some of them showed some selectivity in their binding to Pneumocystis carinii and Toxoplasma gondii versus rat liver DHFR, this effect was not deemed large enough to warrant further preclinical evaluation.

Immune stimulation by an antisense oligomer complementary to the rev gene of HIV-1

Mice developed massive splenomegaly and polyclonal hypergammaglobulinemia within 2 days after intravenous injection of a phosphorothioate oligomer that is antisense to a portion of the rev region of the HIV-1 genome. Histologic examination of spleens from injected animals showed marked expansion of a uniform-appearing population of small lymphocytes and many mitoses. Spleen mononuclear cells (SMNCs) from injected animals showed approximately a 10-fold-increased uptake of [3H]thymidine and production of IgM and IgG. Flow cytometry analysis indicated that the responding cells were predominantly B-lymphocytes. The anti-rev oligomer also was mitogenic in vitro and stimulated immunoglobulin production by normal mouse SMNCs and human peripheral blood mononuclear cells. Similar immunologic effects were observed with an anti-rev 21-mer phosphorothioate, truncated at the 3' end, but not with a 20-mer human p53 antisense phosphorothioate or a 28-mer anti-rev phosphodiester. These observations are consistent with the possibility that DNA sequences homologous to the rev gene participate in the regulation of mammalian lymphocyte activation, proliferation and maturation.

Immunosuppressive properties of chloroquinoxaline sulfonamide

Chloroquinoxaline sulfonamide (CQS), a sulfanilamide derivative with antitumor activity, was found to be toxic to lymphoid tissue during preclinical studies. The mechanism of this toxicity appears to involve profound inhibition of lymphocyte activation. Incubation of human peripheral blood mononuclear cells (PBMNCs) with CQS decreased cellular incorporation of thymidine and deoxyuridine in a dose-dependent manner. Analysis of cell cycle distribution by flow cytometry indicated that CQS blocked movement out of the G0/G1 phase. Drug-treated cells were smaller and expressed fewer receptors for interleukin-2 (IL-2) and transferrin than untreated mitogen-stimulated lymphocytes. These observations support the notion that CQS has cell cycle specificity in regulating lymphocyte proliferation. As little as 10 microM CQS markedly inhibited both human lymphocyte and murine CTLL cell replication in response to IL-2 containing growth factors. However, CQS did not block secretion of IL-2 into culture supernatant fractions by human PBMNCs. Finally, CQS inhibited in vitro production of immunoglobulins G and M by mitogen-stimulated lymphocytes, primarily by causing cytotoxicity. In all of these drug effects, CQS was approximately one to two logs more potent than the parent compound, sulfaquinoxaline (SQ). These studies indicate that CQS inhibits essential basic processes in human lymphocytes. This agent may find use as an immunosuppressive drug.

Synthesis and antitumor activity of a series of (aminoethylpyrrolidine) platinum complexes

A series of aminoethylpyrrolidine-platinum complexes were synthesized and partially characterized for chemical structure. The leaving groups in this series of complexes were varied in an attempt to identify cytotoxic, water-soluble aminoethylpyrrolidine-platinum complexes. The cytotoxic activity was tested in vitro against L1210 cells sensitive to cis-diamminedichloroplatinum(II) (L1210/0), L1210 cells resistant to cis-diamminedichloroplatinum(II) (L1210/DDP), and L1210 cells resistant to 1,2-diaminocyclohexane platinum (L1210/DACH). The complexes were also tested for in vivo antitumor activity against L1210/0 cells injected i.p. The results of these studies indicate that the aminoethylpyrrolidine-platinum complexes have moderate antitumor activity but are cross-resistant in L1210/DDP cells. The degree of antitumor activity was dependent on the characteristic leaving group of a given complex.

Cellular pharmacology of chloroquinoxaline sulfonamide and a related compound in murine B16 melanoma cells

Chloroquinoxaline sulfonamide (CQS), a chlorinated derivative of sulfaquinoxaline (SQ), inhibited proliferation of murine B16 melanoma cells, but only when relatively high drug concentrations (1 mM) were used. The inhibition of cell growth by CQS was at least partially reversible by incubation in drug-free medium. Incubation of melanoma cells with CQS was associated with an arrest of the cell cycle in G0/G1 as measured by flow cytometry. The drug slightly decreased uptake of radiolabeled deoxyuridine and thymidine after 24- and 48-hr incubation periods but increased nucleoside incorporation at 72 hr. No evidence of intercalation with DNA was found. Because SQ previously was reported to inhibit an aspect of folate metabolism, we investigated the possibility that CQS limits tumor cell growth by altering folate homeostasis. This appears unlikely, however, in view of the following observations: (1) the cytotoxic effects of CQS could not be reversed by folinic acid; (2) deoxyuridine suppression of thymidine incorporation was not affected by CQS treatment; (3) CQS did not inhibit dihydrofolate reductase from mammalian or bacterial sources; and (4) CQS toxicity in mice was not reduced by folinic acid. Experiments performed with analogues modified in the quinoxaline and para-amino phenyl functions indicated that tumor cell inhibition did not require preservation of the conventional sulfonamide structure.

Phase I clinical and pharmacokinetic study of trimetrexate using a daily x5 schedule

Trimetrexate (TMQ; NSC 352122) is a potent inhibitor of dihydrofolate reductase with good activity against murine i.p.-implanted B16 melanoma and colon 26 tumors. Preclinical antineoplastic activity, demonstrated schedule dependency, and data suggesting effectiveness against methotrexate-resistant cells prompted a Phase I clinical and pharmacokinetic study of trimetrexate using an i.v. daily x5 schedule. Forty-three good performance status patients were treated with 12 dose levels using daily doses varying from 0.5 to 15 mg/m2/d. Plasma and urine samples were obtained for pharmacokinetic analysis using a high-performance liquid chromatographic method. Myelosuppression was dose limiting and 15 mg/m2/d x5 was the maximum tolerated dose. White blood cell (WBC) and platelet toxicity were noted at doses of 1.6 mg/m2 and above. Median WBC and platelet nadirs occurred on approximately Days 11-12 with recovery by Days 15-18. Nonhematological toxicity included mucositis, nausea and vomiting, stomatitis, diarrhea, and rash. Evidence for antitumor activity was seen in seven patients. Trimetrexate elimination from plasma could be represented as either a bi- or triexponential process. Terminal elimination half-lives were in the range of 5-14 h in patients represented by a triexponential model. Approximately 10-20% of the dose administered was excreted in urine over a 24-h period. The recommended starting dose for patients in Phase II trials using the d x5 i.v. schedule is 8.0 mg/m2/d repeated every 21 days. Dose escalations may be possible depending on the extent of prior therapy and individual tolerance of the drug.

Effects of folate deficiency on the metastatic potential of murine melanoma cells

Experiments were designed to measure the effect of folic acid deficiency on a major determinant of cancer lethality, the propensity to form metastases. Murine B16 melanoma cells (F10 strain) were grown in folate-deficient and -supplemented media. After 3 days, cells in the deficient medium had restricted proliferative capacity, low folate levels by bioassay, increased cell volume, abnormal deoxyuridine suppression tests, accumulation of cells in S phase by flow cytometry, and increased numbers of DNA strand breaks. These folate-deficient cells consistently initiated more pulmonary metastases than control cells when injected into host mice. Cell size did not appear to be a major factor in pulmonary metastasis formation. In vitro growth rates and cloning efficiencies were comparable for cells in both types of medium as was subcutaneous growth of tumors. We conclude that folate deficiency increases the metastatic potential of cultured melanoma cells.

Local collaboration needed for long-term care insurance

Private insurance may be the most viable approach to financing long-term care for middle- and upper-income elderly, but many issues must be considered. Should public policy favor service-oriented or indemnity plans? Should states require companies to offer a minimum plan benefit to sell policies? Should companies try to design integrated plans that presume future Medicaid eligibility for some private-plan enrollees? Should states and private businesses require professional quality review, utilization control, and cost management features? One policy direction would encourage local management of insured individuals' long-term care, but such a strategy should be tested for structural, technical, administrative, and financial feasibility. A local management structure for long-term care insurance would have four functions: expenditure control, utilization control, quality control, and service development.

Effect of trimethoprim, paracetamol and cimetidine on trimetrexate metabolism by rat perfused isolated livers

Trimetrexate (TMTX), a non-classical antifolate, is currently in clinical trial as an antineoplastic drug. In the rat perfused isolated liver, it undergoes extensive metabolism to two metabolites, M1 and M2, which are excreted primarily in the bile. The metabolites result from demethylation, and M1 is also glucuronidated. We examined the effects of three commonly used drugs on the elimination of 1 mg of TMTX by the rat perfused isolated liver (perfusate volume was 100 mL). Co-administration of either 1 or 5 mg cimetidine, a well-known inhibitor of microsomal oxidation, caused an increase in TMTX terminal elimination half-life (69 and 100% at 1 and 5 mg, respectively) and a decrease in clearance (40 and 46% at 1 and 5 mg, respectively). Paracetamol (acetaminophen) was chosen for a possible interaction with TMTX because its major metabolic pathway is glucuronidation. Five mg paracetamol resulted in no change in TMTX pharmacokinetics, but M1 concentrations were increased by 72% in bile, and M2 was not present in perfusate. The third drug tested was trimethoprim, which has some structural similarities to TMTX; however, no effects were noted on the levels of TMTX, M1 or M2 after 1 mg trimethoprim. These results indicate that TMTX elimination can be inhibited by cimetidine, probably due to competition for microsomal enzymes, and that paracetamol may alter the metabolite profiles; trimethoprim had no effect on TMTX disposition under the conditions employed.

A phase I study of trimetrexate, an analog of methotrexate, administered monthly in the form of nine consecutive daily bolus injections

Trimetrexate glucuronate (TMTX) is a methotrexate (MTX) analog that is active against transport-deficient MTX-resistant tumor cells. We performed a phase I study of TMTX administered by daily bolus for 9 consecutive days since this schedule is one of the most active in experimental murine tumor models. The drug was administered in this fashion every 4 weeks for at least two cycles. Fifteen patients with refractory metastatic cancers were studied and all had received prior chemotherapy. The dose-limiting toxicity was a rapidly reversible thrombocytopenia first seen at a daily dose of 4.0 mg/m2 which occurred 7 days after the end of TMTX administration. There was great inter- and intrapatient variability in the platelet nadirs observed in the six patients treated at 4.0 mg/m2. One patient died of massive hemoptysis during a platelet nadir at that dose level. Granulocyte counts never dropped below 1500/mm3. Only one patient had significant non-hematological toxicity: a radiation recall skin toxicity along with a self-limited maculopapular rash. One patient with melanoma and lung metastases treated at 4.0 mg/m2 had a partial response. TMTX plasma levels were measured by HPLC every 3 days prior to daily dosing in patients receiving 4 mg/m2 to determine whether drug accumulation occurred during this prolonged administration schedule. Nadir drug levels varied from less than 0.02 to 0.35 microM and did not seem to increase during the 9-day schedule in individual patients. By comparison with other phase I trials, the hematologic toxicity of TMTX seems to be schedule-dependent, with less drug being tolerated and more severe thrombocytopenia observed with more protracted treatment protocols. A firm phase II starting dose for daily bolus X 9 schedules is difficult to recommend in view of the variable toxicity observed in the patients treated at 4.0 mg/m2 daily, who, in addition, had all been extensively pretreated. A reasonable starting dose might be 3.0 mg/m2 daily with built-in dosage increases or decreases.

Inhibition of lymphocyte nucleic acid metabolism and antibody production by trimetrexate

Trimetrexate is a lipid soluble dihydrofolate reductase inhibitor which, unlike methotrexate, does not depend upon the membrane folate transport system for cell entry. We investigated the possibility that trimetrexate (but not methotrexate) might permeate intermitotic lymphocytes and, following stimulation, impair only the responding cells, rather than all dividing cells, as is the case with methotrexate. Peripheral blood mononuclear cells from normal individuals were incubated for 1 hr in three moderate to high concentrations (1, 10 and 100 microM) of methotrexate or trimetrexate, washed, and incubated with phytohemagglutinin. Intracellular folate activity, as assessed by the deoxyuridine suppression test, was abnormal at all three concentrations of trimetrexate but only at the highest concentration of methotrexate. Similarly, incorporation of [3H]deoxyuridine was depressed profoundly in trimetrexate-treated cells (2% of control) but unaffected by methotrexate. Analysis of cell cycle distribution by flow cytometry confirmed G0 + G1 arrest in trimetrexate but not methotrexate-treated cells. Neither drug altered morphologic transformation, Tac antigen expression, or incorporation of [3H]thymidine by the "salvage" pathway. Therefore, brief exposure to methotrexate has little effect on intermitotic lymphocytes, whereas trimetrexate very specifically inhibits the conversion of deoxyuridine to thymidine in these cells and leads to the arrest of DNA synthesis in the G0 + G1 phase. This metabolic abnormality markedly reduces in vitro antibody synthesis: a 1-hr treatment of lymphocytes with 10 or 100 microM trimetrexate prior to incubation with pokeweed mitogen on four occasions completely inhibited both IgG and IgM secretion. Similar treatment with methotrexate had no effect until the highest concentration (100 microM) was used. We conclude that brief exposure of peripheral blood mononuclear cells to the nonclassical dihydrofolate reductase inhibitor, trimetrexate, results in inhibition of nucleic acid synthesis and impairment of antibody production. This drug effect may permit more incisive modulation of immune responses.