Fluorescent location of malignant cells in fine needle aspirates

Malignant cells in fine needle aspirates possess a cell surface protease which can be targeted with fluorescent affinity probes. Cells with active GB exhibit cell surface fluorescence when stained with such affinity probes. The nuclei of all cells on the slides can be counterstained with a nuclear fluorescent stain. Malignant cells are then located by their cell surface fluorescence and their diagnosis confirmed by examining their fluorescent nuclei. Normal cells and benign cells exhibit no cell surface fluorescence and can be ignored. This technique can be used to rapidly select cells of cytological interest in FNA samples obtained routinely and might be adapted for automated screening of FNA.

Evidence for the induction of a tumour associated cell surface protease on cytologically normal epithelial cells present in the sputum of patients possessing lung tumours

Sputum obtained from healthy subjects and patients with known lung tumours has been challenged with fluorescent probes for the presence of an active cell surface protease. The mature epithelial cells from healthy patients' sputum lacked ability to bind these fluorescent probes whilst the majority of mature epithelial cells in the tumour patients' sputum bound these probes and consequently fluoresced. This demonstrable difference in the cell surface chemistry of mature epithelial cells was linked to the presence of lung tumour cells, which also possessed this cell surface protease. The mechanism of this induced cell surface enzyme appearance is not understood.

Fluorescent location of lung tumour cells

Cells were collected on glass slides by touching tumour surfaces (A) and normal regions (B) of the lung. The slides were stained with a nuclear stain and a fluorescent probe for a tumour associated cell surface protein. The (B) slides from the normal regions lacked fluorescent epithelial cells. The tumour slides (A) contained typical tumour cells and dyskaryotic cells which exhibited cell surface fluorescence.

Sputum cells from lung tumor patients carry a cell surface marker not found in normal sputum

Cells were collected from sites of known lung tumours and corresponding control areas of these lungs. Fluorescent staining demonstrated that the tumour cells and epithelial cells (cytologically these cells appeared normal) both possessed a receptor for these fluorescent probes. Fluorescent labelling of sputum cells from these tumour patients also resulted in fluorescent labelling of these "cyto logically normal" epithelial cells. No such fluorescent epithelial cells were observed in sputum samples collected from control subjects or in cells collected from the control areas of the tumour patients' lungs. We conclude that a cell surface protein receptor is expressed in lung tumour-associated epithelial cells but is absent from control sputum epithelial cells.

On the stability of a tumour cell surface protease after exposure to 6N HCl

Well defined acinar tumour cells in frozen sections were exposed to 6NHCl for 5 h at room temperature. A technique was designed to monitor the activity of the enzyme, guanidinobenzoatase (GB), on these tumour cells; this involved cross-linking the enzyme to the cell surface and challenging the active centre with known fluorescent probes which only bind to the functional enzyme. It was demonstrated that the enzymic activity can be regained by appropriate folding of the protein.

A simple clinical method for the preparation of improved cervical smears-approximating to monolayers

Conventionally prepared cervical smears contain multilayers of cells deposited within strands of mucin. The present study is concerned with chemical reduction of disulphide bonds in the mucin leading to depolymerisation prior to forming a smear in the conventional manner. The resultant distribution of cells on the slide is similar to that obtained by machines designed to produce monolayers of cells. These monolayers have been developed for use in automated analysis of cervical smears and sputum samples. This new technique does not interfere with conventional PAP analysis of dyskaryotic cells nor does it interfere with the fluorescent location of such cells of cytological interest.

Fluorescent location of cells of cytological interest in cervical smears prestained with thionin

Cervical cells of cytological interest were located in conventional smears, treated with thionin for quantitative DNA staining by subsequent treatment with fluorescent probes for a cell surface protease. Normal mature cervical epithelial cells failed to bind these fluorescent probes whilst metaplastic cells, glandular cells, and dyskaryotic cells were readily located. By this means, the nuclear staining of these fluorescent cells of cyotological interest enabled them to be classified by a cytologist.

Correlation of cell surface fluorescence with conventional PAP analysis of cells of cytological interest obtained from cervical scrapes

Archival PAP stained cervical smears were destained and treated with a fluorescent probe for a cell surface enzyme (GB). Cells which exhibited cell surface fluorescence were demonstrated to be cells of cytological interest in the analysis of cervical smears. These cells could be directly related to PAP and reclassified by subsequent restaining with PAP. Fluorescent cell surface technology was shown to be compatible with conventional PAP staining.

Selectivity of the plasminogen activator inhibitor (PAI-1) for the iso enzyme of guanidinobenzoatase on the surface of colonic carcinoma cells

The interaction of plasminogen activator-inhibitor (PAI-1) with a cell surface protease, guanidinobenzoatase (GB), has been studied in free solution and on the surface of colonic epithelial cells. It has been demonstrated that PAI-1 recognises and inhibits the iso enzymic form of GB associated with colonic carcinoma cells but fails to bind to the iso enzymic form of GB associated with normal donor colonic epithelial cells. This interaction is mediated by a lysyl binding site on the GB: complex formation prevents GB binding to fibrin fibrils which also involves lysyl binding sites.

The fluorescent location of abnormal cervical cells employing the principle of differential competitive inhibition

The screening of cervical smears is concerned with the detection of abnormal epithelial cells which may be indicative of cervical intraepithelial neoplasia (CIN). Several types of cells in cervical smears possess a cell surface protease where isoenzymic forms of this enzyme can be differentially inhibited. Using this phenomenon a simple fluorescent technique has been developed in conjunction with differential competitive inhibition which enables abnormal cervical epithelial cells to bind the fluorescent probe whilst other cells do not bind the probe. The abnormal cells can then be located by fluorescence microscopy and their co-ordinates recorded for subsequent characterisation of these cells by nuclear analysis employing haematoxylin to stain the nuclei.

Differential competitive inhibition of a cell surface protease on normal epithelial cells and carcinoma cells of the colon

The cell surfaces of normal colonic epithelial cells and colonic carcinoma cells both possess a protease referred to as guanidinobenzoatase (GB). Previous studies have shown that these cells possess two distinct isoenzymic forms of GB which could be distinguished by their selective recognition of cytoplasmic protein inhibitors of GB. In the present study we have used competitive inhibitors of GB to demonstrate the differential inhibition of the GB on normal colonic epithelial cells whilst the GB on colonic carcinoma cell surfaces remains active. The enzymic status of GB on these cells has been determined by challenging the treated cells in frozen sections with a second fluorescent inhibitor, followed by fluorescence microscopic analysis.

Differential competitive inhibition: the theory of a concept

The concept of differential competitive inhibition of cell surface isoenzymes is discussed. If the isoenzymes have different structures and functions it is likely that they will handle active site directed molecules at different rates. This could be tested by employing two competitive inhibitors in sequence and exploited if the second inhibitor is fluorescent. Two practical examples of this technique will be presented in the following manuscripts.

Fluorescent location of malignant cells in smears obtained from sputum

A fluorescent probe (rhodamine a-N-agmatine) has been used to locate cells possessing a surface protease in sputum smears. Malignant epithelial cells possess this protease and can be quickly located by this technique. These results have been confirmed by using a second fluorescent probe (9-animo acridine) for this same cell surface protease.

Retinoic acid inhibition of a tumour protease immobilised on cell surfaces and in free solution

Retinoids are inhibitors of tumour cell proliferation in culture and have been shown to suppress carcinogenesis and decrease the levels of proteases. The present study has demonstrated that retinoic acid is a potential non-competitive inhibitor of a protease (GB) immobilised on the surfaces of tumour cells in thin sections and free GB in solution. The enzymic status of GB on the cell surfaces in sections has been determined by challenging the retinoic acid-treated cells with a second fluorescent inhibitor (9-AA), followed by fluorescence microscopic analysis. The inhibition of cell surface GB by retinoic acid was demonstrated to be reversible. The activity of soluble GB has been measured by the MUGB assay in the presence and absence of retinoic acid. It is suggested that retinoic acid acts on GB by interacting with a binding site, different from the active site, and causes major conformational changes, resulting in enzyme inhibition. It is possible that the modulation of GB activity by retinoic acid may play a role in the control of cell migration and metastasis.

Inhibition of a tumour protease with 3,4-dichloroisocoumarin, pentamidine-isethionate and guanidino derivatives

Guanidinobenzoatase (GB) is a cell surface proteolytic enzyme capable of degrading fibronectin, and is associated with tumour cells and cells capable of migration. The location of active GB in sections has been demonstrated with 9-aminoacridine (9-AA), a competitive inhibitor of GB. 3,4-Dichloroisocoumarin (3,4-DCI) and pentamidine isethionate (PI) are inhibitors of trypsin-like enzymes. It has now been demonstrated that 3,4-DCI, PI, and guanidino derivative compounds are significant inhibitors of GB, on the surfaces of lung squamous cell carcinoma cells in frozen sections and free GB in solution. Dexamethasone acetate (DMA) and medroxy-progesterone (MP) did not show any significant inhibition of GB activity. These molecules lack a reactive chloride or guanidino groups and are thought to react at the nuclear level, rather than directly on this cell surface protease. Kinetic studies have shown that 3,4-DCI, PI and guanidino derivatives are reversible competitive inhibitors of GB, as determined in vitro on the purified enzyme. The inhibition resulting with 3,4-DCI was a time-dependent process. It is suggested that these inhibitors interact with GB by binding to its active site, resulting in the formation of enzyme-inhibiter complexes (GB-I). The GB-I complexes can be dissociated with SDS treatment, resulting in the regain of GB activity.

The interactions of protein inhibitors with tumour proteases studied in solution and immobilised on cell surfaces in frozen sections

The cell surface protease guanidinobenzoatase (GB) has been purified from human colonic and lung carcinoma tissue by an affinity step involving the binding of the enzyme either onto fibrin fibrils or onto agmatine-sepharose. The inhibitor protein (I) was extracted from the cytoplasm of tumour cells and isolated by an affinity step involving the binding of I to GB on the surface of cultured carcinoma cells. The interaction of GB and I in solution was followed by kinetic studies employing the release of the fluorescent 4-methylumbelliferone (MU) from the synthetic substrate 4-methylumbelliferyl-p-guanidinobenzoate (MUGB). The interaction of soluble I with membrane bound GB was followed by using the yellow fluorescent probe 9-aminoacridine (9AA) which binds to active GB but not to GB-I. The results of these studies demonstrated the presence of isoenzymic froms of GB which were recognized specifically by their appropriate isoinhibitor, isolated from the appropriate cell type. This high degree of selectivity suggests a cell specific regulatory role for the inhibitors and the possibility that they might be used for the delivery of cytotoxic molecules to the surface of specific types of tumour cells.

A protein inhibitor, extracted from Hela cells, which recognises a cell surface protease on preneoplastic cells obtained from cervical smears

Hela cells originate from a clone of cervical carcinoma cells. The cytoplasm of Hela cells contains a protein which recognises and inhibits a proteolytic enzyme (guanidino-benzoatase) on the surface of Hela cells. This same protease is present on the surface of abnormal epithelial cells obtained from cervical smears, enabling a rhodamine labelled inhibitor extracted from Hela cells to locate abnormal cervical cells in monolayer spreads.

Association and dissociation of a protease and its inhibitor on the surface of lung squamous cell carcinoma cells

Squamous cell carcinoma cells possess a cell surface protease, referred to as guanidinobenzoatase (GB). GB is a plasminogen-activator-like enzyme which can be located by the fluorescent probe 9-amino acridine in frozen sections. Fluorescence microscopy has been used to study the inhibition of this GB, the displacement of inhibitor from GB, the displacement of GB from the cell surface receptor and the preparation of both active GB and inhibitor, obtained from these frozen sections of tumour tissue.

The application of double fluorescence to the rapid selection of atypical cervical epithelial cells spread in monolayers

Monolayer spreads of cervical cells were prepared and reacted in sequence with two fluorescent probes. The nuclei were reacted with 4,6-Diamidino-2-phenylindole (DAPI), resulting in white fluorescence of all cell nuclei. Those cells possessing active guanidinobenzoatase (GB) bound the second probe, rhodamine-alpha-N-agmatine (Rh-Agm), resulting in orange cell surface fluorescence. Atypical epithelial cells possessed both active GB and enlarged nuclei; such cells could easily be recognised by their cytological appearance. We illustrate our results in the form of colour prints which are representative of our observations of cells in both normal and abnormal cervical spreads.

The status of the surface enzyme guanidinobenzoatase on mature epithelial cells in sputum cell monolayers

Mature epithelial cells derived from the sputum of normal healthy adults lack GB, while the epithelial cells of sputum collected from patients with lung tumours contain a spectrum of epithelial cells with active GB, some of which are clearly tumour cells, based upon their morphology. The presence of abnormal epithelial cells was confirmed by the cytologist whilst observing the fluorescent stained cells and later by independent cytological analysis of these same cells employing conventional stains.

Affinity preparation of a protein inhibitor recognising a cell surface protease

Epithelial cell surfaces possess a trypsin-like protease, referred to as guanidinobenzoatase (GB). The cytoplasm of these cells contains an extractable protein (I) which recognises the cell surface GB by forming an enzyme-inhibitor complex (GB-I). Rhodamine-agmatine (Rh-Agm) was designed as a red fluorescent probe, directed to the active centre of GB, which can be used to locate cells with GB, employing fluorescence microscopy. Rh-Agm has a high affinity for GB and will displace I from GB-I on the surfaces of cells in frozen sections. Rh-Agm has been used to displace I from immobilised GB-I complexes on the surface of cultured colonic carcinoma cells in an affinity procedure aimed at purifying the inhibitors of GB obtained from cultured carcinoma cells. These inhibitors have been tested on protected frozen sections of normal colon and carcinoma of the colon, the formation of GB-I complexes being followed by a second yellow fluorescent probe which competes for the active centre of GB. The study of the protein-protein interactions to form GB-I has been facilitated by employing two synthetic fluorescent inhibitors of GB with differing affinities for GB and different fluorescent properties. The use of sections of tissue in this study has enabled a sequence of reactions to be carried out on the same cell surface GB, such that reversible inhibition reactions can be quickly demonstrated and recorded by fluorescence microscopy.

Observations on the inhibition of serum and cell surface enzymes by eicosapentaenoic acid

The relationship between serum and tumour cell surface proteolytic enzymes and the development of muscle breakdown in cancer cachexia has been studied in a murine model of the condition (MAC16). The surface of the MAC16 tumour cells carried a proteolytic enzyme referred to as guanidinobenzoatase (GB). Serum from mice also contained an enzyme (referred to as MSE) which cleaved the trypsin inhibitor 4-methylumbelliferyl-p-guanidinobenzoate as a true substrate, but there was no relationship with weight loss or the presence or absence of tumour and the level of this serum enzyme. Polyunsaturated fatty acids (PUFAs) were shown to be inhibitors of MSE at microM concentrations and one PUFA, eicosapentaenoic acid (EPA) was found to be a non-competitive inhibitor of both MSE and GB. The effect of EPA was specific since other proteolytic enzymes, trypsin, esterase and tissue plasminogen activator were unaffected by concentrations inhibiting GB and MSE. MSE and GB are two different enzymes which possess some common properties. However, GB is likely to be significant for tumour development since MSE is also found in normal mouse serum.

Further evidence for different isoenzymic forms of a cell surface protease, guanidinobenzoatase, associated with tumours

Normal colonic epithelial cells possess a cell surface protease referred to as guanidinobenzoatase (GB) and a corresponding cytoplasmic protein inhibitor of GB. Colonic carcinoma cells possess two isoenzymic forms of GB, the normal and the carcinoma specific form, each of which is recognised by the corresponding inhibitors present in the cytoplasm of colonic carcinoma cells. An affinity-purified inhibitor preparation obtained from the cytoplasm of cultured colonic carcinoma cells inhibited these two colonic carcinoma isoenzymic forms of GB but not the GB associated with other forms of tumour. The data suggest that each cell type possessing isoenzymic forms of cell surface GB also possesses the corresponding cell-specific inhibitors of GB.

A simple fluorescent technique for screening cervical cells prior to nuclear analysis

Monolayer spreads of cervical cells were prepared and stained with haematoxylin and rhodamine-alpha-N-agmatine, a fluorescent marker for a cell surface protease. Mature epithelial cells from normal cervices lacked this cell surface enzyme and did not fluoresce. The abnormal cells possessed the cell surface enzyme, bound the probe and were quickly detected by fluorescence microscopy. The degree of abnormality of these fluorescent cells was determined by examination of their nuclear details, with the result that mild, moderate and severe dyskaryotic cells could be defined.

Fluorescent location of brain tumour cells in wax embedded sections

Tumour cells and certain normal cells in wax embedded brain sections possess active isoenzymic forms of a cell surface protease. The normal isoenzymic forms are recognised by protease inhibitors present in normal serum; the tumour isoenzyme remains active after exposure to serum. Fluorescent location of cells possessing active isoenzyme after serum treatment reveals the tumour cells in these sections.

Fluorescent location of abnormal cells in cell smears obtained from the lungs of patients with lung cancer

A bronchoscope fitted with a brush was used to collect cells from patients with lung tumours. The cells were either made into smears or deposited as monolayers on microscope slides. Using a fluorescent probe for the cell surface enzyme, referred to as guanidinobenzoatase, abnormal cells were readily distinguished from normal cells which lacked this enzyme.

GB (guanidinobenzoatase) cell surface protease and serum inhibitors in colorectal neoplasia

Cell surface proteases and their inhibitors are functionally related to the invasive properties and metastatic potential of tumour cells. Epithelial cells of the colorectal mucosa possess a cell surface protease referred to as guanidinobenzoatase (GB), which is similar, if not identical, to plasminogen activator. GB exists in isoenzymatic forms, one of which is associated with epithelial cells of normal colorectal mucosa and of adenomatous polyps, whilst another isoenzymatic form is associated with colorectal adenocarcinoma cells. Normal serum contains inhibitor proteins which recognize the isoenzymatic form of GB found on normal and adenomatous polyp epithelial cells but this inhibitor does not recognize the isoenzymatic form of GB associated with adenocarcinoma cells. The fluorescent probe 9-amino-acridine locates cells possessing active GB in frozen sections of colorectal mucosa. A technique is described which enables colorectal carcinoma cells to be highlighted by fluorescence microscopy whilst normal epithelial cells are distinguished by their lack of fluorescence. This is of biological and possibly diagnostic significance.

Differential inhibition of a cell surface protease on normal and tumour cells

This report is concerned with a cell surface protease which may be important for cell migration. We investigated the molecular recognition of this protease on pancreatic carcinoma cells by proteins (a) extractable from the cells of normal pancreas, and (b) present in normal serum. We then compared these data with results obtained from studies on lung carcinoma cells.

Observations on the conformational changes in the structure of a cell surface protease, followed by its ability to be recognised by competitive and non-competitive inhibitors

Lung tumour cells possess a cell surface protease which can be inhibited by a cytoplasmic protein inhibitor extracted from these cells. The dissociation of this enzyme-inhibitor complex on the surface of tumour cells in sections treated with 10(-4) M sodium dodecyl sulphate has been studied. The dissociation of the inhibitor and regain of enzymic activity was followed by the use of a fluorescent probe which binds to the active centre of the cell surface enzyme in a competitive manner.

Studies on the interaction and exchange of inhibitors and proteases on the surface of tumour cells in frozen sections

We have used frozen sections of squamous cell carcinoma as a convenient source of a cell surface protease associated with tumour cells. This protease has been referred to as guanidinobenzoatase (GB) and is now known to be functionally identical to tissue plasminogen activator (t-PA). The use of a fluorescent competitive inhibitor of GB enabled the enzymic status of GB to be determined, i.e. was the enzyme active, latent or removed from our test system. The cell surface GB was then demonstrated to interact with extractable cytoplasmic inhibitors obtained from these sections. We then used a protected form of the GB in the absence of these internal inhibitors; such sections were used to transfer the GB to fibrin fibrils, thus exposing the presumptive receptor on the tumour cell surfaces. Texas red labelled t-PA was then shown to bind to the tumour cells in these pretreated sections from which the GB had previously been removed. We believe that the surface of tumour cells can be used to study the interaction of the naturally occurring inhibitors with GB and also that the cell surface receptors for GB can be used to study the binding of t-PA to cell surfaces.

Fluorescent location of tumour cells in fine needle aspirates

Cells obtained by fine needle aspiration of breast lumps were spread onto microscope slides, defatted with xylene and stained with a fluorescent probe for a cell surface protease. In these aspirates, carcinoma cells possess an active cell surface protease, guanidinobenzoatase (GB), very similar to plasminogen activator (1), which binds the fluorescent probe as a competitive inhibitor. Cells obtained from benign and normal breast lack this active GB and can be distinguished easily from the carcinoma cells by fluorescent microscopy. We use this simple technique to examine breast lumps containing carcinoma cells and to demonstrate the similarity of GB on these carcinoma cells to tissue type plasminogen activator (t-PA).

A simple fluorescent technique for the location of tumour cells in frozen sections of the head and neck region

Tumour cells possess cell surface proteases referred to as guanidinobenzoatase (GB) which are closely similar to plasminogen activator. Previous studies have demonstrated different isoenzymic forms of GB on tumour cells and normal cells which can be recognised by cytoplasmic protein inhibitors extracted from frozen sections of appropriate tissues. We now show that normal human serum possesses inhibitors which selectively recognise the isoenzymic forms of GB associated with normal cell surfaces but do not recognise the GB on tumour cell surfaces in frozen sections of tissue obtained from the head and neck regions.

Evidence for the functional similarity between tumour cell surface guanidinobenzoatase and tissue type plasminogen activator

Tumour cells possess a cell surface protease referred to as guanidinobenzoatase (GB). The active centre of GB binds the fluorescent probe 9-amino acridine (9-AA) and this binding enables cells possessing active GB to be located by fluorescent microscopy. GB binding of 9-AA was inhibited by prior treatment of sections of tumour tissue with a specific polyclonal antibody recognising the tumour associated protease tissue plasminogen activator (t-PA). GB binding of 9-AA was also inhibited by prior treatment of sections of tumour tissues with PAI-I, a protein inhibitor of plasminogen activatory. We conclude from these studies and kinetic analyses that GB and t-PA are very similar both in structure and function.

Evidence for distinct isoenzymic forms of a cell surface protease on normal colonic cells and on carcinoma cells from the same colon

Both normal and carcinoma cells of the colon possess the cell surface protease guanidinobenzoatase (GB). GB is similar to plasminogen activator. In fixed sections, the insolubilised GB can be located by the fluorescent probe 9-amino acridine (9-AA) which binds to the active centre of GB, causing cells possessing active GB to fluoresce yellow. Both cell types possess cytoplasmic proteins which can be extracted in isotonic saline and were shown to inhibit their respective cell surface GB. The formation of an enzyme-inhibitor complex was demonstrated by the failure of 9-AA to react with the cell surface GB inhibitor complex. The data presented indicate that the colonic carcinoma cells possess an isoenzymic form of GB not recognised by the inhibitors of GB extracted from normal colonic cells.

The role of fibrin fibrils in the dissociation of a cell surface protease-inhibitor complex and evidence for the recapture of the inhibitor protein

Colonic epithelial cells possess a cell surface protease referred to as guanidinobenzoatase (GB). Active GB can be located by the fluorescent active site directed competitive inhibitor 9-amino acridine (9AA) followed by fluorescence microscopy. The cell surface GB can be transferred to fibrin fibrils, which have a higher affinity for GB than the cell surface. The cytoplasm of colonic epithelial cells contains a protein which inhibits membrane bound GB, forming a latent form of GB or GB-inhibitor complex. This complex can also be dislodged from the epithelial cell surface due to the high affinity of fibrin for GB, with the consequent dissociation of the enzyme-inhibitor complex and solubilisation of the inhibitor. This use of fibrin has led to the demonstration of the transfer of a selective inhibitor protein from one cell surface (the donor) to a second cell surface (the target).

Temporary competitive inhibition of a tumour cell surface protease as a protective mechanism in the preparation of the membrane bound native enzyme in the presence of excess cytoplasmic inhibitors

Tumour cells possess a cell surface protease which is recognised and inhibited by a cytoplasmic protein extractable from frozen sections of tumour cells. In order to prepare sections with tumour cells carrying cell surface-bound native protease in the absence of this internal inhibitor we have used a reversible competitive inhibition step as a temporary measure to protect the active centre of GB whilst the cytoplasmic inhibitor is extracted from the frozen sections. These sections are described as protected in the sense that the enzyme is native and fully functional now that potential inhibitors have been extracted. The protected cell surface protease immobilised in the cell surface of squamous cell carcinoma cells has been used as the target for inhibition studies and displacement studies. The ability to follow these inhibition and exchange reactions concerning the cell surface protease has been made possible by virtue of the fluorescent probe, 9-amino acridine, which locates the active centre of the protease. Cells with active protease bind 9-amino acridine and fluoresce yellow; cells lacking this protease or having inhibited protease fail to bind 9-amino acridine and do not fluoresce.

The inhibitor reacting with a tumour cell surface protease can be exchanged with plasminogen activator inhibitor (PAI-1)

Tumour cells possess the cell surface protease guanidinobenzoatase (GB) which can be located by the fluorescent probe 9-amino acridine (9-AA). Frozen sections and formaldehyde fixed sections of tumour tissue were used to demonstrate the interactions between GB, 9-AA and two protein inhibitors of GB. A cytoplasmic extract from the tumour tissue, and a purified inhibitor of plasminogen activator (PAI-1) were shown to be exchangeable components of the enzyme-inhibitor complex on the fixed tumour cell surfaces. The evidence suggests that GB is functionally very similar to plasminogen activator and that this enzyme can be regulated by protein inhibitors in vivo and also by changes in the redox potential at the cell surface.

Labelling of tumour cells with a biotinylated inhibitor of a cell surface protease

Our objective has been to prepare a biotinylated affinity probe for the active centre of a protease associated with the surface of tumour cells. We employed three model systems in which easily recognisable tumour cells containing the active protease were used as targets for the biotinylated affinity probe. These were: squamous cell carcinoma, leukaemia cells in muscle and outgrowths of prostate carcinoma cells grown in three dimensional collagen gels. The presence of the bound biotinylated affinity probe was demonstrated by its ability to bind Texas-red labelled streptavidin with the results that the tumour cells exhibited red fluorescence. This binding was shown to be competitive with 9-amino acridine, a compound known to bind to the active centre of the target protease. This technique depends upon the affinity of the active centre of an enzyme for a competitive inhibitor and therefore should be applicable to other enzyme systems employing suitable ligands for their active centres.

Inhibition of a cell surface protease after cisplatin chemotherapy

The epithelial cells in squamous carcinoma and leukoplakia of the oral cavity possess the cell surface protease, guanidinobenzoatase (GB), in an active form. GB is closely similar to plasminogen activator, a protease associated with both transformed cells and tumour cells. The active centre of GB binds the fluorescent probe 9-aminoacridine (9-AA) enabling cells containing active GB to be visualised by fluorescent microscopy. It was observed that chemotherapy with cisplatin resulted in a marked decrease in cell surface GB activity and this decrease was due to the formation of an enzyme-inhibitor complex. One of the results of chemotherapy was shown to be the suppression of a cell surface protease which is known to be associated with migration and malignancy of cells in vivo.

Fluorescent studies directed towards the location of abnormal epithelial cells in cervical smears

Cervical screening is concerned with the search for abnormal epithelial cells in smears prepared from scrapings from the uterine cervix. It is a highly skilled labour intensive operation and automated methods of detecting dyskariotic cells in cervical smears would be helpful. We report a fluorescence method of detecting abnormal cervical cells in smears and biopsies using a probe for guanidinobenzoatase. This approach has the potential for automation.

Evidence for cells possessing t-PA like activity in smears obtained from patients with oral squamous cell carcinoma

Squamous cell carcinoma cells possess a cell surface protease referred to as guanidinobenzoatase (GB) which is very similar to the single chain form of tissue type plasminogen activator. This enzyme binds fluorescent probes at its active center and cells possessing GB can be distinguished from those that lack this enzyme by fluorescent microscopic techniques. Normal squamous epithelial cells shed from the surface of the oral cavity lack GB and do not exhibit cell surface fluorescence when pretreated with such fluorescent probes. We have used this knowledge to design a simple technique for the rapid location of squamous cell carcinoma cells in oral smears; our results are presented in the form of colour prints in which the tumour cells can be easily distinguished from other cells by their fluorescence.

The targeting of agmatine-liganded mitomycin C to an enzyme on the surface of tumour cells

Tumour cells possess a cell surface protease referred to as guanidinobenzoatase (GB). We have synthesised a liganded form of mitomycin C which we refer to as MMC*. This MMC* has the fluorescent properties of mitomycin C and the additional ability to be directed to the active centre of GB by the agmatine moiety of the ligand. We have demonstrated the selective delivery of MMC* to the cell surface of tumour cells possessing active GB by fluorescent microscopy and competition experiments with molecules known to bind to the active centre of GB. The MMC* has a high affinity for tumour cell surface GB and we hope it may have potential in the selective delivery of mitomycin C in the chemotherapy of tumours in vivo.

Evidence for the induction of protease activity on cultured tumour cells as a consequence of implantation into nude mice

We have studied the enzymic status of a tumour associated protease on human colonic tumour cells cultured in vitro and grown in vivo in nude mice. The cultured tumour cells lack this protease. The cells of the tumour colonies in the mice possess active enzyme although the tissue contains an inhibitor capable of inactivating this tumour cell protease. The evidence indicates that the induction of this protease on the tumour cells is a consequence of implantation of the cultured cells into the nude mouse.

Direct evidence for the cell surface location of a protease-inhibitor complex on intact leukaemia cells

The interaction of a protease with two fluorescent inhibitors has been studied using intact fixed leukaemia cells as the source of the membrane bound enzyme. Fresh rat leukaemia cells were disrupted and the cytosol collected; this extract was known to contain a protein inhibitor of guanidinobenzoatase (GB) associated with leukaemia cells. All the cytosolic proteins were derivatised with Texas red acid chloride. Leukaemia cells with latent GB failed to bind the Texas red inhibitor protein but did so after activation of GB. Competition experiments with 9-amino acridine (a fluorescent marker for the active site of GB) demonstrated that the Texas red-inhibitor protein could only bind to intact leukaemia cells when the active centre of GB was not already occupied by 9-amino acridine. This competition between these two fluorescent inhibitors demonstrated their specificity for GB. The use of intact leukaemia cells and the high molecular weight of the inhibitor protein precludes the possibility of any interaction between GB and inhibitor within the cells. It is concluded that GB and the GB-inhibitor complex of latent GB are located on the external surface of intact leukaemia cells.