Subcellular localization of hematoporphyrin derivative in bladder tumor cells in culture

Mitochondria have been implicated as a primary subcellular site of porphyrin localization and photodestruction. However, other organelles including the cell membrane, lysosomes and nucleus have been shown to be damaged by hematoporphyrin derivative (HpD) photosensitized destruction as well. In this study we attempted to follow the translocation of the fluorescent components of HpD in human bladder tumor cells (MGH-U1) in culture to determine whether specific subcellular localization occurs over time. Following a 30 min exposure to HpD the cellular fluorescence was examined immediately and 1, 2, 4, and 24 h after HpD removal using fluorescence microscopy and an interactive laser cytometer. The in vitro translocation of dye appeared to be fairly rapid with fluorescence present at the cell membrane and later (1-2 h) within a perinuclear area of the cytoplasm. To determine whether HpD had become concentrated into a specific subcellular organelle, these fluorescence distribution patterns were compared with fluorescent marker dyes specific for mitochondria, endoplasmic reticulum and other membranous organelles. The HpD fluorescence did not appear to be as discrete as the dyes specific for mitochondria or endoplasmic reticulum but appeared similar to the diffuse cytomembrane stain. Finally, the interaction between the fluorescent components of HpD and the cellular constituents was evaluated using a "fluorescence redistribution after photobleaching" technique. The results indicated that the mean lateral diffusion for HpD in MGH-U1 cells was 1.05 x 10(-8) cm2/s, a rate closer to that of lipid diffusion (10(-8)) than that of protein diffusion (10(-10)).(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of retinoic acid receptor mRNA in hematopoietic cells

Retinoic acid (RA) has profound effects upon the proliferation and differentiation of many hematopoietic cells. The mechanism by which RA acts is unclear. Recently, several retinoic acid receptors (RAR) have been cloned. We studied expression of RAR-alpha mRNA by RNA blots in hematopoietic cells blocked at different stages of differentiation. All hematopoietic cells expressed RAR-alpha mRNA (3.4, 4.5 kb) including KG-1 (myeloblasts); HL-60 (promyelocytes); ML3, THP-1, U937 (myelomonoblasts and monoblasts); K562 (erythroblasts); and S-LB1 (T-lymphocytes). In addition, transformed cells from four non-hematopoietic tissues also expressed RAR-alpha mRNA. Steady-state levels of RAR-alpha mRNA were not affected by induction of terminal differentiation of HL-60 cells to either granulocytes or macrophages. Furthermore, both actively proliferating and resting lymphocytes from the same individuals expressed equal concentrations of RAR-alpha mRNA. Taken together, data suggest that level of expression of RAR-alpha mRNA is not related to cellular proliferation. We also showed that exposure to ligand (all-trans retinoic acid) did not change levels of RAR-alpha mRNA in three different cell types. Half-life of RAR-alpha mRNA was short (0.7 h) as determined by measuring decay of message after addition of actinomycin D. Consistent with this finding, accumulation of RAR-alpha mRNA increased in cells of three lines as their protein synthesis was inhibited. In summary, hematopoietic cells of different lineages and stages of differentiation constitutively express RAR-alpha mRNA. This expression is unaffected either by terminal differentiation or cell cycle. The RAR-alpha mRNA is short-lived and super-inducible by a protein synthesis inhibitor.

Distinct requirements for activation at CCK-A and CCK-B/gastrin receptors: studies with a C-terminal hydrazide analogue of cholecystokinin tetrapeptide (30-33)

We describe here the properties of tert-butyloxycarbonyl-Trp-Leu-Asp-Phe-NHNH2 (A-57696), a C-terminal hydrazide analogue of tert-butyloxycarbonyl-CCK4 (Boc-Trp-Met-Asp-Phe-NH2), at four cholecystokinin (CCK) receptor-bearing tissues, the guinea pig pancreas and gall bladder (Type A), guinea pig cortex (Type B), and NCI-H345 cells, a human small cell lung cancer cell line that expresses CCK-B/gastrin receptors. Using 125I-Bolton-Hunter-cholecystokinin octapeptide (26-33) (125I-Bolton-Hunter-CCK8) as the radioligand, A-57696 was found to be selective for cortical CCK-B receptors (IC50 = 25 nM), compared with pancreatic CCK-A receptors (IC50 = 15 microM). A-57696 behaved as a competitive antagonist in reversing CCK8-stimulated pancreatic amylase secretion and phosphoinositide breakdown. By Schild analysis, its Kd was determined to be 4.7 and 6.8 microM in amylase and phosphoinositide assays, respectively. A-57696 (100 microM) did not elicit gall bladder contraction, and it inhibited contractions induced by CCK8. The Kd of A-57696 at gall bladder CCK-A receptors was 19 microM. In contrast, A-57696 behaved as a partial agonist (80% of maximal CCK8 response) in stimulating calcium mobilization at CCK-B/gastrin receptors on NCI-H345 cells. A-57696 and CCK8 inhibited each other in calcium mobilization experiments utilizing the fluorescent dye Indo-1. Stimulatory actions of CCK8 and A-57696 were reversed by the CCK-B-selective (R)-L-365,260 (100 nM), whereas at the same concentration, the CCK-A-selective (S)-L-365,260 was ineffective. Binding studies using 125I-Bolton-Hunter-CCK8 and 125I-gastrin indicated that binding sites labeled by these two ligands displayed similar affinities for CCK8, desulfated CCK8, gastrin, A-57696, and both enantiomers of L-365,260. A-57696 represents a new class of CCK-A peptide antagonist at guinea pig pancreas a new class of CCK-A peptide antagonist at guinea pig pancreas and gall bladder. Its contrasting functional activities at guinea pig CCK-A and CCK-B/gastrin receptors in a human tumor cell demonstrate that, in addition to the previously described differences in binding specificity for selective agonists and antagonists, CCK-A receptors and CCK-B/gastrin receptors have different requirements for activation.

Immunochemical and biochemical characterizations of two monoclonal antibody-reacting antigens associated with human bladder carcinoma

Two murine monoclonal antibodies (Mabs), 3G2-C6 and C3, which react to surface components on human bladder carcinoma cells, were produced using cultured human bladder tumor cells as immunogens. The expression of these antigens is highly restricted to malignant cells, and as such these Mabs are potentially useful for cancer diagnosis and treatment. We report here the immunochemical characterizations and molecular size determinations of these two Mab-reacting bladder tumor-associated antigens. The 3G2-C6 antigen has a molecular weight of 92,000, while the C3 antigen is a macromolecule with a molecular weight of about 600,000, consisting of 4 subunits of identical size, as determined by high pressure liquid chromatography gel filtration and sodium dodecyl sulfate and gradient-gel electrophoresis. The apparent affinity constants for the binding of these two Mabs and the number of antigenic determinants per cell were determined in 4 human bladder tumor cell lines (MGH-U1 through MGH-U4) with different degrees of malignancy. The apparent affinity constants for 3G2-C6 ranged from 1.8 x 10(-10) to 1.7 x 10(-8) M, while those for C3 ranged from 1.9 x 10(-9) to 4.4 x 10(-8) M. The number of antigenic determinants per cell ranged from 3 x 10(5) to 2.9 x 10(3) for 3G2-C6 and from 2 x 10(6) to 1.2 x 10(5) for C3. This coincides with our earlier observation that bladder tumor cells of higher malignancy tend to express higher numbers of determinants of these antigens, particularly of 3G2-C6. Very low levels of both of the antigens were released from the cells; less than 10% of the antigens could be detected in 3-day spent culture medium. Radioactively labeled Mabs were used to assess the stability of the antibody bound to MGH-U1 cells. More than 70% of 3G2-C6 remained bound to the cell after 24 h, whereas more than 60% of C3 was lost from the cell and recovered in the culture medium as small fragments. This information may be useful for the clinical applications of these Mabs, including the improvement of in vitro detection of bladder cancer through identification of exfoliated tumor cells and determining the potential utilities of these Mabs in in vivo localization of in situ and metastatic bladder tumors.

Chondrocyte activation by interleukin-1: analysis of the synergistic properties of fibroblast growth factor and phorbol myristate acetate

Following activation, monolayers of lapine articular chondrocytes secreted into their culture media large amounts of prostaglandin E2 (PGE2) and the neutral metalloproteinases collagenase and gelatinase. Partially purified preparations of synovial "chondrocyte activating factors" (CAF), which contain interleukin-1 (IL-1), generally proved stronger activators of chondrocytes than recombinant, human, IL-1 alpha (rHIL-1 alpha) or IL-1 beta (rHIL-1 beta). The presence of synergistic cytokines within the synovial material provides one possible explanation of this discrepancy. As first reported by K. Phadke (1987, Biochem. Biophys. Res. Commun. 142, 448-453) fibroblast growth factor (FGF) synergized with rHIL-1 in promoting the synthesis of neutral metalloproteinases. In our hands FGF alone did not induce neutral metalloproteinases and increased PGE2 synthesis only modestly. However, at doses from 1 ng/ml to 1 microgram/ml, FGF progressively enhanced the synthesis of PGE2, collagenase, and gelatinase by chondrocytes responding to rHIL-1. Acidic and basic FGF synergized equally well with both rHIL-1 alpha and rHIL-1 beta. Phorbol myristate acetate (PMA), but not the Ca2+-ionophore A23187, could substitute for FGF as a synergist. PMA alone was a poor inducer of collagenase or gelatinase but, unlike FGF, it greatly enhanced the synthesis of PGE2 by chondrocytes. Dot-blot analyses with a cDNA probe to collagenase mRNA confirmed that partially purified synovial CAF induced collagenase mRNA more effectively than rHIL-1, with rHIL-1 alpha being superior to rHIL-1 beta in this regard. The synergistic effects of both FGF and PMA upon IL-1-mediated collagenase induction were associated with increased abundance of collagenase mRNA.

Chondrocyte activation by interleukin-1: synergism with fibroblast growth factor and phorbol myristate acetate

Exposure to synovial factors or purified interleukin-1 (IL-1) induces the production of prostaglandin E2 (PGE2) and the neutral proteinases (NP) collagenase, gelatinase and stromelysin by lapine articular chondrocytes. Having frequently found our partially purified synovial preparations to elicit this process of chondrocyte activation more strongly than recombinant IL-1, Phadke's report of synergism between IL-1 and fibroblast growth factor (FGF) intrigued us. In our hands, basic FGF (1 ng/ml-1 micrograms/ml) did not activate chondrocytes but, in a dose-dependent manner, enhanced the production of PGE2 and NP by chondrocytes exposed to IL-1 alpha or IL-1 beta (1-10 U/ml). Further examination determined that the basic FGF was a better synergist than acidic FGF. In view of reports that FGF activates protein kinase C, we tested whether phorbol myristate acetate (PMA) could substitute for FGF as a synergist. Not only did it do so, but PMA alone (0.1 ng/ml-100 ng/ml), unlike FGF, provoked the production of PGE2 by chondrocytes. The Ca2+ ionophore A23187 could not substitute for FGF in enhancing induction of the NP. Using a cDNA probe, we confirmed that the synergistic effects of both FGF and PMA upon IL-1 mediated collagenase induction, were associated with an increased abundance of collagenase mRNA.

Cycloheximide inhibits the induction of collagenase mRNA in chondrocytes exposed to synovial factors or recombinant interleukin-1

Synoviocytes secrete "chondrocyte activating factors" (CAF) which, like recombinant interleukin-1 (IL-1), induce the synthesis of collagenase by cultures of articular chondrocytes. Enzyme synthesis is preceded by the appearance of collagenase mRNA some 3-5 hours after exposure of the chondrocytes to CAF or IL-1. Cycloheximide (CX) inhibits the appearance of this message in a dose-dependent manner. At a concentration of 5 micrograms/ml inhibition by CX is completely reversible, with superinduction being observed in certain experiments. Identification of the newly synthesised proteins which are required for collagenase mRNA induction would greatly advance our understanding of collagenase gene expression.

Photodynamic effect in an experimental bladder tumor treated with intratumor injection of hematoporphyrin derivative

Photodynamic therapy (PDT) is an experimental treatment modality for malignant tumors. It is based on the principle that a photosensitizer, such as hematoporphyrin derivative (HPD), is retained in higher concentrations in tumors than in surrounding nonmalignant tissues and that photoactivation of the sensitizer can be used to evoke tumor destruction. However, retention of the systemic injection of HPD is not limited to malignant tissues. This lack of specific tumor localization thus reduces the therapeutic ratio of the treatment and causes skin photosensitivity and possible systemic toxicity. Injection of HPD directly into the tumor, on the other hand, has been shown to yield higher levels of the drug in the tumor and lower levels in normal tissues, in comparison with systemic administration. In this study, we examined the photodynamic effect on s.c. implanted mouse bladder tumors subjected to intratumor (i.t.) and i.p. HPD injections. Tumor cell killing, measured by cell survival, was observed in both the it. and i.p. groups and was dependent on fluence and HPD dosage. However, no significant enhancement of cell killing was observed in the i.t. injected tumors, despite the higher porphyrin levels in these tumors. Histological examination of the effect of PDT on the blood vessels indicated that while cell death accompanied severe hemorrhage in the i.p. injected tumors, in the i.t. tumors there was much less hemorrhage and intact blood vessels remained. This observation suggests that with i.t. administration, direct photodynamic action may play a significant role in the tumor cell killing, in contrast to systemic administration, in which destruction of the blood vessels is believed to be the main cause of tumor destruction.

Detection of tumor cells in bladder washings by a monoclonal antibody to human bladder tumor-associated antigen

We have conducted two studies to evaluate the efficacy of using a specific monoclonal antibody (McAb) to detect exfoliated tumor cells in bladder washings. This is a preliminary step toward the development of immunological methods to improve the cytologic detection of bladder carcinoma. In this study, McAb 3G2-C6 was used. The McAb reacts to a bladder tumor-associated cell-surface antigen expressed in bladder tumors of various grades. Bladder washings from patients with and without carcinoma were stained with the McAb using two different indirect immunofluorescence methods (Methods A and B). The results of the immunological studies were compared with those obtained from the cytology laboratory and these in turn, were evaluated against the histopathological diagnosis of respective patients at the time the samples were taken. Immunofluorescence method A detected positive cells in 87% (56/64) of specimens from bladder cancer patients, including 18 of 19 from patients with grade 1 tumor. This method also had a low false-positive rate; only one of 17 specimens from patients with other urinary disorders had positively reacting cells. Immunofluorescence method B, evaluating a second group of specimens, detected positive cells in 68% (15/22) of specimens from patients with carcinoma, and in only one of 17 controls. However, it also identified positive cells in specimens from patients with chronic cystitis and urinary calculi. Overall the results of these studies indicate that the McAb method is superior to the routine cytology in detecting tumor cells in bladder washing specimens. More work must be done, however, to improve the specificity of the method before it can be used as an aid for routine tumor detection.

Establishment and characterization of a doxorubicin-resistant human bladder cancer cell line (MGH-U1R)

A doxorubicin-resistant bladder cancer cell line has been established. This was accomplished by exposing an established human bladder tumor cell line, MGH-U1, to progressively higher concentrations of doxorubicin over a period of 12 months. The resistant cells, MGH-U1R, are nine times more resistant to doxorubicin and 30 times more resistant to daunorubicin than the parent cells. The MGH-U1R and the MGH-U1 cells have identical isozyme phenotypes. Compared to the parent cells, the resistant cells have a slower growth rate, lower confluent density, are more heterogeneous morphologically, and exhibit more chromosomal aberrations and rearrangements. The resistant cells may now be used as an experimental system for the search of means to overcome drug resistance in human bladder cancer.

Induction of collagenase mRNA in lapine articular chondrocytes by synovial factors and interleukin-1

The cDNA probe H-9, originally constructed to recognize a portion of the mRNA for lapine synovial collagenase, also hybridized with a RNA of the same size (approximately 2.0 kb) isolated from activated lapine articular chondrocytes. Primary, monolayer cultures of lapine articular chondrocytes did not contain detectable amounts of this RNA, nor did they secrete measurable amounts of collagenase into their culture media. Following exposure to synovial factors, the chondrocytes contained high levels of collagenase mRNA, while their conditioned media had considerable collagenolytic activity. Collagenase mRNA started to appear in chondrocytes 3-5 h after treatment with the synovial material. Maximum levels occurred after 12-24 h. Recombinant human interleukin-1 also induced the appearance of this mRNA. We conclude that chondrocyte collagenase is likely to be the same gene product as synovial collagenase, and that its regulation by lapine articular chondrocytes probably occurs at a pretranslational level.

Intratumor injection as a more effective means of porphyrin administration for photodynamic therapy

Photodynamic therapy (PDT) with hematoporphyrin derivative (HpD) as the photosensitizer is a promising new cancer treatment. The major drawback of this procedure is the resulting skin photosensitivity. Patients must remain in subdued light for four to six weeks to avoid cutaneous phototoxicity. In this study, we examine the possibility of reducing the skin photosensitization while maintaining the tumor phototoxic effect by administering the drug directly into the tumor. A subcutaneously implanted mouse bladder tumor (MBT-2) was used. HpD was administered either intraperitoneally (I.P.; 20 mg./kg. b.w.) or by intratumor injection (I.T.; 0.4 mg./cc tumor). The concentrations of HpD in tumor and various tissues (skin, muscle, liver, spleen, kidney, bladder and whole blood) were analyzed at various times after the injection, by 3H-HpD method and by a fluorometric method. Results indicated that at three to 96 hours after the administration, porphyrin levels in tumor were about three to 15 times higher by I.T. than by I.P. injection, while the concentrations in skin and other tissues were 1.3 to 10 times lower. Consequently, at 24 hours after injection ratios between tumor to skin porphyrin were 14 to 92 times higher for I.T. than I.P. injection. Higher porphyrin levels in tumor and lower in normal tissues would indicate lower skin photosensitivity, systemic cytotoxicity and possible greater tumor photosensitivity. This method of porphyrin administration may be useful for the PDT of certain single lesions that are accessible for direct injection.

Photodynamic therapy with hematoporphyrin derivative in the treatment of superficial transitional-cell carcinoma of the bladder

Photodynamic therapy involves light-induced destruction of tumors containing a photosensitizer such as hematoporphyrin derivative. We conducted a collaborative study to evaluate the efficacy of this form of therapy in treating superficial transitional-cell carcinoma of the bladder. Thirty-seven patients were evaluated and 20 were selected for treatment. A total of 50 papillary tumors and 3 areas of carcinoma in situ were treated. All except two tumors were smaller than 2.5 cm. Assessments for treatment response and toxicity were carried out three months after treatment. The initial diagnosis of one patient was revised after the biopsy material was reviewed, and this patient was not included in the analysis. Complete eradication of all tumors was observed in 9 of 19 patients (47 percent), including those with carcinoma in situ. In the remaining 10 of these 19 patients, 13 tumors could not be eradicated (the overall eradication rate was 37 of 50 tumors [74 percent]), but 9 of the 10 patients had a reduction in tumor size, number, or both of 50 percent or more. We conclude that photodynamic therapy is useful in the treatment of superficial transitional-cell carcinoma of the bladder, but controlled trials will be required to define its place in the treatment of cancer.

Distribution, retention, and phototoxicity of hematoporphyrin derivative in a rat glioma. Intraneoplastic versus intraperitoneal injection

The distribution, retention, and phototoxicity of the sensitizer hematoporphyrin derivative (HPD) were studied following intraperitoneal and direct intraneoplastic injections of the agent into subcutaneous or intracerebral gliosarcomas in rats. Forty-eight hours after intraperitoneal injection, the ratio of tritiated (3H) HPD in subcutaneous tumor: adjacent normal skin was about 1.4:1 and the ratio in tumor: normal brain was 3:1. In contrast, direct injection of 3H-HPD into subcutaneous tumors resulted in tumor: adjacent normal skin concentration ratios of approximately 44:1 and tumor: normal brain ratios of about 61:1. For rats bearing intracerebral gliosarcomas, intraperitoneal administration of 3H-HPD resulted in approximately 1.3-fold sensitization in tumor tissue relative to adjacent edematous brain. In contrast, after direct injection into intracerebral tumors, the tumor: adjacent edematous brain and tumor: skin 3H-HPD ratios were 3:1 and 32:1, respectively. In all cases, 3H-HPD was found in every portion of the tumor, even at a distance from the injection site. For the 3H-HPD doses used in this study, after direct injection both subcutaneous and intracerebral tumor tissue contained about three to four times more 3H-HPD than tumors in rats receiving intraperitoneal 3H-HPD. Both in vitro and in vivo clonogenic assays demonstrated that the photodynamic inactivation of the tumors was significantly greater after direct injection than after intraperitoneal injection.

Cholecystokinin receptors: relationships among phosphoinositide breakdown, amylase release and receptor affinity in pancreas

The gut hormone cholecystokinin (CCK) octapeptide stimulates the release of amylase from exocrine pancreas, a process believed to be the result of the breakdown of phosphatidylinositol lipids. To examine further the relationship between phosphoinositide (PI) breakdown and amylase release, we have investigated the effect of N-terminally protected CCK C-terminal fragments in these systems using guinea-pig pancreatic lobules. There was a good correlation between the ability of these fragments to elicit amylase release and their potency in enhancing PI breakdown. In general, the EC50 for amylase release is 10-fold lower than the EC50 for PI breakdown. In addition, a good correlation existed between amylase release and the affinity of CCK fragments for [125I]Bolton Hunter-CCK octapeptide binding sites in pancreatic membranes. We also discovered that N-carbobenzyloxy-CCK tetrapeptide was relatively inefficient in causing PI breakdown, but it caused a near maximal stimulation in amylase release. These findings might reflect an amplification mechanism between PI breakdown and amylase release or that N-carbobenzyloxy-CCK tetrapeptide-induced amylase release is independent of PI breakdown.

Vascular invasion as a prognosticator of metastatic disease in nonseminomatous germ cell tumors of the testis. Importance in "surveillance only" protocols

Forty-five nonseminomatous germ cell carcinomas of the testis were evaluated retrospectively to define the biologic features associated with the occurrence of metastatic disease. A statistical analysis of several pertinent clinical and pathologic factors was performed. The factors evaluated included: duration of symptoms before diagnosis, serum level of alpha-fetoprotein, serum or urinary level of human chorionic gonadotropin, testicular weight, extent of local tumor (pathologic T stage), and vascular invasion at the primary site. In each case, metastases were documented by a retroperitoneal node dissection, other biopsies, or by chest films. In 29 tumors with vascular invasion, 25 patients were seen with metastatic disease. In 16 tumors without vascular invasion, 3 patients demonstrated metastasis. The presence or absence of vascular invasion was strongly correlated with concomitant lymph node involvement or subsequent appearance of other metastatic disease (chi-square = 17.19). Additionally, vascular invasion in bifactoral++ analysis with tumor size and pathologic T stage proved a significant prognosticator even in low-staged (chi-square = 8.48) and small tumors (chi-square = 8.13). The implications of these findings, both as an adjunct to the staging of nonseminomatous germ cell tumors and in the management of clinical Stage I lesions, are discussed.

Establishment and characterization of four human bladder tumor cell lines and sublines with different degrees of malignancy

We have established four human bladder tumor cultures, designated MGH-U1 to -U4 (also known as EJ, HM, RN, and RB in some previous reports). All have been grown in culture for over 30 passages and were free of Mycoplasma contamination. Characterizations of these cell lines were performed. These include isozyme profile, morphology with light and scanning electron microscopes, karyotype, growth rate, DNA content by flow cytometry, presence of cell surface ABH isoantigens, tumorigenicity in nude mice, lactic acid dehydrogenase isozymes, and colony formation in soft agar. Results obtained from these characterizations confirm that MGH-U1 and -U2 are sublines of a previously established bladder tumor cell line, T-24. These results also show that MGH-U3 and -U4, derived respectively from a grade 1 tumor and an urothelium biopsy with severe atypia, are likely to be independent human bladder cell lines and different from other transitional cell bladder carcinoma cell lines reported. The study further demonstrates that these four cell lines/sublines have different degrees of malignancy and a close correlation, in biological and malignant characteristics, between the cells in culture and those in the original tumors. Therefore these cultures may represent cells at different stages of malignant progression. These can be useful models for studies of the development and progression of bladder tumors and detection and treatment of bladder tumors of different grades and stages.

Production and characterization of mouse monoclonal antibodies to human bladder tumor-associated antigens

Monoclonal antibodies (McAbs) to human bladder carcinoma were generated by fusion of NS-1 mouse myeloma cells with spleen cells from BALB/c mice immunized with either cultured human bladder cancer cells or cells obtained from a fresh surgically removed bladder tumor. Four hybridomas which reacted strongly with bladder tumor cells and not to normal skin fibroblasts or urothelial cells were identified and cloned by limiting dilution to obtain monoclonality. One McAb, 3G2-C6, raised with cultured tumor bladder cells MGH-U1 (EJ) as the immunogen reacted more strongly to the bladder tumor lines tested than any of the other McAbs resulting from various fusion experiments. Hybridoma 3G2-C6 was found to secrete murine immunoglobulin G1 and to produce high titer ascites fluid when grown in BALB/c mice. Results from quantitative enzyme-linked immunosorbent assays on a panel of more than 35 cell lines demonstrated that McAb 3G2-C6 reacted with several bladder tumor cell lines 50 to 90 times more than with normal transitional urothelium. Two kidney and two testicular tumor lines also bound 10 times more 3G2-C6 than with normal cells. The 3G2-C6 antigen was only marginally detected on a number of other cancer and noncancerous cells tested such as breast and lung tumor cells, melanoma, fetal cells, and peripheral blood lymphocytes. To identify the antigen 125I-labeled membrane components from MGH-U1 cells were extracted with detergent, immunoprecipitated with Protein-A bound 3G2-C6, and analyzed by sodium dodecyl sulfate-gel electrophoresis. This revealed that McAb 3G2-C6 binds to a Mr 90,000 cell surface component. Indirect immunofluorescence microscopy with fluorescein isothiocyanate-anti-mouse immunoglobulin G also identified the antigen on the surface of cultured and fresh tumor cells and detected the antigen on 16 of 17 Grade 3 bladder tumor specimens as well as on some kidney and testicular tumor cells. This study confirms the potential of the hybridoma technique for producing McAbs capable of identifying tumor associated antigens which may be useful in the diagnosis and treatment of bladder cancer.

Photosensitization and split-dose recovery in cultured human urinary bladder carcinoma cells containing nonexchangeable hematoporphyrin derivative

The photosensitization and survival recovery of cultured EJ human urinary bladder carcinoma cells containing nonexchangeable hematoporphyrin derivative (HPD) were studied. Cultures were incubated at 37 degrees C in growth medium supplemented with HPD (50 micrograms/ml) and 5% fetal bovine serum for 12 h followed by incubation in HPD-free medium containing 5% fetal bovine serum for 9 or 18 h. The levels of porphyrin remaining in the cells (termed the "nonexchangeable" intracellular porphyrin component) were not significantly different at these times, and as a result sensitivities to broad-band red light (greater than 580 nm) were also identical. Shouldered survival curves were obtained in each case, indicating the ability to accumulate sublethal photodamage. Recovery from photosensitized damage using a split-dose technique was examined. Single, attached, asynchronously growing cells containing nonexchangeable HPD (12 h HPD uptake plus 9 h in porphyrin-free medium) were exposed to red light (1.2 kJ/sq m) and, after various intervals at 37 degrees C in the dark, a second dose of 1.2 kJ/sq m. Survival rapidly increased and reached a maximum at about 9 h between light doses. Analysis of dose-response curves revealed a partial reappearance of the curve shoulder (Dq = 0.22 kJ/sq m) and a markedly reduced curve slope (D0 = 0.82 kJ/sq m) for fractionated irradiations with a 9-h interval in comparison with graded, single light exposures (Dq = 0.48 kJ/sq m; D0 = 0.41 kJ/sq m). These observations suggest that the cells developed an increased tolerance to photosensitized damage after prior HPD-light treatment. No significant change in intracellular HPD levels between irradiations was detected, indicating that the increased survival was not due to a loss of sensitizer from inside the cells. These results demonstrate that EJ cells accumulate and recover from HPD-sensitized photodamage; analogous to the accumulation and recovery from sublethal damage (Elkind recovery) in other mammalian cultures treated with ionizing radiation.

Characterization of cholecystokinin receptor sites in guinea-pig cortical membranes using [125I]Bolton Hunter-cholecystokinin octapeptide

[125I]Bolton Hunter-cholecystokinin octapeptide (BH-CCK8) has been prepared using a modified method and was used to study putative cholecystokinin (CCK) receptor sites in the guinea-pig cerebral cortex. Specific binding of [125I]BH-CCK8, defined as the difference in binding in the absence and presence of 10(-6) M CCK8, was 70% of total binding. In saturation experiments, the apparent dissociation constant (Kd) was 1 nM and total binding capacity was 28 fmol/mg of protein. In association experiments, conducted at 30 degrees C, binding of [125I]BH-CCIK8 reached equilibrium in approximately 150 min. Binding was stable for 4 hr and was reversed by the addition of unlabeled CCK8-sulfated. Dissociation of bound ligand was biphasic and the apparent T1/2 was 45 min. Analyses of kinetic experiments yielded an association rate constant of 0.58 X 10(8) min-1 M-1 and a dissociation rate constant for the slower component of 0.012 min-1. Dithiothreitol increased and N-ethylmaleimide decreased specific binding of [125I]BH-CCK8, indicating that CCK receptor sites involve sulfhydryl groups. In competition experiments, the potency of CCK4 was enhanced 50-fold with addition of protease inhibitors. The rank order of CCK-related peptides was CCK8-sulfated greater than or equal to Gastrin 17 greater than or equal to CCK33 greater than CCK4 greater than or equal to CCK8-desulfated. Proglumide, a proposed CCK antagonist in the periphery and brain, was inactive at 10(-3) M. The specificity of [125I]BH-CCK8 binding sites are similar to that reported for [125I]BH-CCK33.

Effect of 514.5-nm argon ion laser radiation on hematoporphyrin derivative-treated bladder tumor cells in vitro and in vivo

The therapeutic effect of hematoporphyrin derivative (HpD) plus 514.5-nm argon ion laser radiation was compared to HpD plus 630-nm argon ion laser-pumped dye laser radiation in experimental urinary bladder transitional cell carcinoma models. Cultured human bladder cancer cells (EJ) containing HpD were 2.8-fold more sensitive to 514.5-nm radiation than to 630-nm radiation as measured by clonogenic capacity. The relative effectiveness of 514.5-nm versus 630-nm light was approximately proportional to the spectral absorbance for cell-bound HpD at these wavelengths. HpD-sensitized photoirradiation was studied in solid tumors produced by a) the subcutaneous inoculation of cells from murine bladder tumors induced by N-[4-(5-nitro-2-furyl)-2-thiazoyl]formamide (CAS: 24554-26-5) into female C3H mice (MBT-2 tumor) and b) the intravesical instillation of N-methyl-N-nitrosourea (CAS: 684-93-5) into the urinary bladders of female Wistar rats. The tumors were exposed to 144 J/cm2 laser light 24-48 hours following ip injection of 20 mg HpD/kg body weight. By 24-48 hours, animals that received HpD and light of either wavelength had partially or completely necrosed tumors. Control groups showed no necrotic changes. Regression of MBT-2 tumors was also investigated. Seven of 14 and 6 of 12 animals had nonpalpable tumors 1 week after treatment with 514.5-nm and 630-nm light, respectively. Tumors in control groups demonstrated no regression. Spectral transmittance from 630 nm to 514.5 nm decreased by about 4% for 130- to 160-micron-thick sections of canine urothelium and bladder submucosa-muscularis. The results of this study indicate that HpD plus 514.5-nm laser radiation may be an effective treatment for small or superficial malignant lesions of the urinary bladder.

Visualization of urothelial blood group isoantigens A and B using direct biotin-labeled antibodies and avidin-biotin-peroxidase complex

The loss of blood group isoantigens from the surface of bladder tumor cells has been correlated with the potential invasiveness of the tumor. Development of simple and reliable methods for detection of these isoantigens should facilitate the general clinical use of this test for predicting malignant potential in low grade, low stage cancer of the bladder. We now report a direct peroxidase technique for the detection of isoantigens A and B by utilizing the specific interaction between biotin and avidin, and the capability of labeling a single antibody with multiple biotin molecules. Antibodies specific to the isoantigens A and B were purified from human antisera by affinity chromatography using an immunoabsorbent containing chemically synthesized antigenic determinants. The purified antibodies were directly labeled with biotin. An avidin-biotin-peroxidase complex was used to bind the biotinylated antibody for the peroxidase staining reaction of the isoantigens on tissue section. Application of this technique to formalin-fixed, paraffin-embedded bladder tissue and tumor sections yielded specific and strong stainings of the isoantigens with low background staining. The potential clinical application of this method requires further evaluation.

Correlation of vascular invasion and metastasis in germ cell tumors of testis--a preliminary report

A preliminary study was conducted to correlate vascular invasion with metastasis in testicular tumors. A lectin-immunoperoxidase procedure was used to identify the vessels. Together with standard hematoxylin and eosin staining, the presence of tumor cells in vessels was detected. Primary tumor specimens from 37 cases and retroperitoneal lymph nodes from 10 cases of germ cell tumors were studied. The results showed good correlations between vascular invasion in primary tumors and metastasis to lymph nodes in nonseminomatous germ cell tumors, and between vascular invasion in retroperitoneal lymph nodes and the presence of other metastases. Eight of the 9 nonseminomatous germ cell tumor patients with vascular invasion had metastases, and all 4 patients that had vascular invasion in the lymph nodes had other metastases. However, there seemed to be no correlation between vascular invasion and clinical staging in cases with seminoma in which retroperitoneal lymph node dissection was not performed. These observations, although based on a limited number of cases, warrant more extensive investigations.

Identification of vessels by lectin-immunoperoxidase staining of endothelium: possible applications in urogenital malignancies

Ulex europaeus agglutinin I binds specifically to vascular endothelium of various human tissues irrespective of the blood group type or secretive status of the tissue. Using this property, we have developed an immunoperoxidase technique to identify vessel structures in urogenital tissues. Most vessels in malignant and nonmalignant tissues of bladder, prostate and testis of different blood types (A, B, AB and O) can be readily identified by this method. This technique has potential application in detecting tumor cell invasion of vessels and in studying distribution of vessels in relation to various normal and pathological events.

Cystoscopic fluorescence detector for photodetection of bladder carcinoma with hematoporphyrin derivative

Hematoporphyrin derivative, a fluorogenic substance, tends to accumulate at higher levels in most tumor tissues after intravenous injection. These properties provide a potential application for the detection of malignant tumors. We report the development and in vitro evaluation of an instrument designed to excite and detect low levels of hematoporphyrin derivative fluorescence emitted by tumor cells in the bladder after hematoporphyrin derivative administration. The light source of the instrument for specific hematoporphyrin derivative excitation is at a wavelength of 405 nanometers. Optical fibers for both the excitation and detection of fluorescence were bundled in a single 7 French ureteral catheter which can be inserted into a standard cystoscope. The fluorescence is initially detected as an electrical signal which is amplified and then converted into an audio signal. The interference of the cystoscope illuminating white light to the fluorescence signal is eliminated by a phase-sensitive electronic circuit. The instrument thus allows simultaneous viewing of the bladder and detection of hematoporphyrin derivative fluorescence produced from tumor tissues. In vitro testings using hematoporphyrin derivative solutions on filter paper indicated that the instrument detects as little as 30 nanograms per milliliter of hematoporphyrin derivative and has relatively low noise levels from normal tissues. The utility of this instrument for hematoporphyrin derivative photodetection of small tumors and carcinoma in situ in bladder is currently under clinical evaluation.

The determination of dissociation constants for substance P and substance P analogues in the guinea pig ileum by pharmacological procedures

The dissociation constants (Kd values) of substance P (SP), physalaemin, kassinin, and SP analogues acting on SP receptors in guinea pig ileal longitudinal muscle strips were determined by the pharmacological procedures of Furchgott [Adv. Drug Res. 3:21-55 (1966)]. This method involves analysis of the concentration-response data before and after fractional inactivation of receptors with phenoxybenzamine (2 X 10(-5) M). Estimations of the Kd values for SP were similar when phenoxybenzamine was incubated for 10, 13, or 15 min. Coincubation with high concentrations of SP protected against receptor inactivation with phenoxybenzamine, but bradykinin and serotonin did not cross-protect SP receptors. Kd values for SP were similar when trypsin was substituted for phenoxybenzamine [Kd = 8.1 +/- 4 nM (n = 9) versus 10 +/- 6 nM (n = 5)]. In atropinized preparations the Kd values obtained for physalaemin were similar to those obtained for untreated preparations [Kd = 8.0 +/- 3.6 nM (n = 5) and 12.6 +/- 3 nM (n = 4), respectively]. The effects of phenoxybenzamine on concentration-response curves for kassinin showed greater shifts to the right with phenoxybenzamine. This indicated that kassinin may interact with another population of receptors, in addition to the sites that SP and other analogues bind. A direct correlation was found between EC50 values and Kd values and Kd values for SP and SP analogues. It was estimated that, for SP, a 20% receptor occupancy is required to elicit a 50% response.

Evaluation of prostate specific acid phosphatase and prostate specific antigen in identification of prostatic cancer

The peroxidase-anti-peroxidase technique was used to stain for prostate specific acid phosphatase and prostate specific antigen in 12 patients with primary tumors and in 12 patients with metastases in whom the nature of the tumor was in doubt after routine histopathological studies. Nine of the primary tumors were positive for both markers and an additional 2 tumors stained for prostate specific antigen only. Six metastatic lesions stained for both markers and a seventh for prostate specific antigen alone. Thus, 11 of 12 primary tumors and 7 of 12 metastases studied were proved to be of prostatic orgin. While the peroxidase staining was sometimes weak and uneven this method, using prostate specific antigen and prostate specific acid phosphatase, allowed for ready identification of metastases. The heterogeneity of the tumors in regard to these 2 prostate markers is demonstrated, and the value of staining for prostate specific acid phosphatase and prostate specific antigen is emphasized.

Rat bladder isograft model for focal carcinoma

A model for focal bladder carcinoma in rats was developed with the use of an isograft technique. Bladder tumors developed by carcinogen induction with FANFT or MNU were grafted to bladders of syngeneic rats. Ninety-six per cent (56 our of 58) of the grafts were taken and 83 per cent (34 out of 41) of the grafted tumors remained neoplastic. Most of the grafts from FANFT-induced tumor remained localized at the original site whereas many from the MNU-induced tumor spread beyond the original graft area. The model system may be useful for the evaluation of chemotherapeutic agents as well as for the studies of basic mechanisms of tumor growth and spreading.

Immunohistochemical identification of prostatic acid phosphatase: correlation of tumor grade with acid phosphatase distribution

The localization and distribution of prostatic specific acid phosphatase (PSAP) in normal, hyperplastic and neoplastic prostates were studied by specific immunohistochemical of normal and hyperplastic prostates. In adenocarcinoma of the prostate, a correlation of the PSAP staining with the degree of differentiation and the ability of the tumor to form a gland was observed: more intense and uniform staining in well differentiated tumors and less intense and more variable stains in poorly differentiated tumors. The same correlation was also observed in tumors metastasized to lymph nodes and other organs.

The effect of typical and atypical neuroleptics on binding of [3H]spiroperidol in calf caudate

The effect of typical and atypical neuroleptics on the binding of [3H]spiroperidol to calf caudate membranes was studied. Saturable or specific binding was defined as the difference between binding in the absence and in the presence of 1 microM d-butaclamol. Scatchard analysis revealed nonhomogeneity of the saturable sites. Inhibition constants (Ki) and IC50 values for various typical and atypical neuroleptics and for two clinically inactive butyrophenones were determined. The Ki and IC50 values of typical neuroleptics paralleled their potencies in vivo. By contrast, the binding potencies of atypical neuroleptics did not correlate with their effects in vivo. For example, the clinically active drug clozapine has an IC50 value similar to the clinically inactive butyrophenone AHR-1900. U-25, 927, another clinically inactive butyrophenone that does not increase dopamine turnover is more potent in the binding assay than perlapine, a drug that increases dopamine turnover and elevates serum prolactin levels. The most striking discrepancy between binding and properties in vivo was found for the benzamide derivatives, sulpiride and metoclopramide. These clinically active agents, which increase dopamine turnover, have much higher Ki values than the clinically inactive butyrophenones. It is concluded that binding assays with [3H]spiroperidol in calf caudate cannot account for the antidopamine effects in vivo of atypical neuroleptics.

Immunofluorescent staining of histaminase (diamine oxidase) in human placenta

An immunofluorescent procedure for the localization of histaminase in human tissue sections has been developed by using a specific antiserum against human placental histaminase. For localization of this enzyme in placental sections, fixation in equal volumes mixture of absolute ethanol and acetone provided the optimum visualization of this enzyme in both frozen sections and paraffin-embedded sections. The immunofluorescent staining of this enzyme in placenta is found to be localized in areas within the maternal decidua, both within the cytoplasm of the decidual cells and in tissue space between the cells. The chorionic villi are completely void of the immunofluorescent stain. Variations in patterns of histaminase localization have been found between term and premature placentas, with the former showing a predominantly intercellular localization and the latter a predominantly intracellular localization. The intercellular localization of this enzyme in the decidua may represent a nonspecific diffusion of the enzyme associated with delivery of the placenta or may reflex a specific functional role of the enzyme in the intercellular space during pregnancy.

Plasma membrane localization of alkaline phosphatase in HeLa cells

The localization of alkaline phosphatase in HeLa cells was examined by electron microscopic histochemistry and subcellular fractionation techniques. Two monophenotypic sublines of HeLa cells which respectively produced Regan and non-Regan isoenzymes of alkaline phosphatase were used for this study. The electron microscopic histochemical results showed that in both sublines the major location of alkaline phosphatase is in the plasma membrane. The enzyme reaction was occasionally observed in some of the dense body lysosomes. This result was supported by data obtained from a subcellular fractionation study which showed that the microsomal fraction rich in plasma membrane fragments had the highest activity of alkaline phosphatase. The distribution of this enzyme among the subcellular fractions closely paralleled that of the 5'-nucleotidase, a plasma membrane marker enzyme. Characterization of the alkaline phosphatase present in each subcellular fraction showed identical enzyme properties, which suggests that a single isoenzyme exists among fractions obtained from each cell line. The results, therefore, confirm the reports suggesting that plasma membrane is the major site of alkaline phosphatase localization in HeLa cells. The absence of any enzyme reaction in the perimitochondrial space in these cultured tumor cells also indicates that the mitochondrial localization of the Regan isoenzyme reported in ovarian cancer may not be a common phenomenon in Regan-producing cancer cells.

Elevation of histaminase and its concurrence with Regan isoenzyme in ovarian cancer

Histaminase has been shown to be associated with several types of human cancer. In the present study, we examined the activity of histaminase and its relationship with Regan isoenzyme of alkaline phosphatase in ascitic fluids obtained from patients with ovarian and several other types of cancer. We have found that about 44% of the ovarian cancer patients had elevated levels of histaminase in the ascitic fluid, whereas a less frequent incidence was observed in fluids obtained from other types of cancer. There was concurrence in the elevation of histaminase activity with the appearance of Regan isoenzyme in most of the samples examined. Of the 10 patients who showed elevated histaminase, 9 had high Regan isoenzyme activity; whereas in 9 patients with normal levels of histaminase, all except 1 had low or moderate levels of Regan isoenzyme activity. These results, therefore, confirm the observation of an association of histaminase with human cancer and suggest the possibility for the utilization of histaminase, in conjunction with Regan isoenzyme and cancer-associated proteins, for cancer diagnosis and clinical evaluation of tumor progression and regression during therapy.

Purification and characterization of mouse kidney beta-glucuronidase

Beta-Glucuronidase has been purified from mouse kidneys previously induced by gonadotrophin to a specific enzyme activity 15 times higher than the non-induced kidney. The purification procedure includes ultrasonication to solubilize the enzyme, acid and ammonium sulfate precipitations, gel filtration in Sephadex G-200, DEAE-ion exchange chromatography, and isoelectric focusing. The resulting product has a specific activity of 284,000 Fishman units/mg of protein, representing a 1,090-fold purification and is 17,000-fold higher than the level in the non-induced kidney. The purified beta-glucuronidase is apparently homogeneous by criteria of gel filtration, sodium dodecyl sulfate gel electrophoresis, and immunodiffusion. Characterization of the purified enzyme showed that it is identical with the lysosomal isoenzymic from electrophoretically, has subunit molecular weight of 74,000 (estimated by sodium dodecyl sulfate gel electrophoresis) and oligomer molecular weight of 300,000. The purified enzyme is stable at high temperature (up to 55 degrees) and at wide range of pH (from 4 to 11). It has a pH optimum for its activity at 4.7 and a Km of 1.18 times 10- minus 4 M. The purification and characterization of this enzyme from mouse kidney will have significance in the understanding of the molecular nature of the isoenzymes of beta-glucuronidase and will be useful in future studies on the mechanism of intracellular transport and distribution of this hydrolase.

Demonstration of lysosomal and extralysosomal sites for acid phosphatase in mouse kidney tubule cells with p-nitrophenylphosphate lead-salt technique

Dual localization of acid phosphatase in lysosomal and extralysosomal sites of the tubule epithelial cells of normal mouse kidney was observed at the light and electron microscope level using a modified Gomori lead-salt method with p-nitrophenylphosphate (pNPP) as substrate. Based on previous biochemical and cytochemical findings, we developed optimal conditions for the enzyme activity in extralysosomal sites. The conditions used for the light microscopic level consisted of 1.5 mM PNPP, 2.0 MM Pb(NO3)2 and 0.05 M acetate buffer (pH 5.8). Those for the electron microscopic study required 3.0 mM PNPP, 3.6 MM Pb(NO3)2 and 0.1 M acetate buffer (pH 5.8). This modified lead-salt technique was highly specific and provided a suitable method for the demonstration of nonlysosomal as well as lysosomal sites of acid phosphatase activity in the tubule epithelial cells of normal mouse kidney. As expected, the enzyme activity appeared in the lysosomes, but the prominent reaction in the brush border, the rough endoplasmic reticulum and basal infolding plasma membranes was not anticipated. We were able to demonstrate in situ organelle precursors of microsomal acid phosphatase such as endoplasmic reticulum, plasma membrane and basal infolding membranes showing the same substrate preference, which had been observed previously in biochemical studies in our laboratory. Since the possible participation of alkaline phosphatases, K+-pNPPase or Na+-K+-adenosine triphosphatase was ruled out by use of appropriate inhibitors, the enzyme-reactive sites can be interpreted as reflecting nonspecific acid phosphatase.

Golgi beta-glucuronidase of androgen-stimulated mouse kidney

Subcellular fractions were prepared from mouse kidney homogenates by differential and sucrose-gradient centrifugation. A fraction enriched in Golgi apparatus was obtained, which had considerably enriched galactosyltransferase and thiamin pyrophosphatase activities, and was morphologically typical of Golgi material. This preparation also had high beta-glucuronidase activity, which increased concomitantly with microsomal beta-glucuronidase activity during the specific stimulation of the enzyme in male mouse kidney after androgen administration. The degree of stimulation was much greater in the Golgi fraction. Gel-electrophoretic patterns of Golgi beta-glucuronidase resembled more closely those of the enzyme located within lysosomes, but contained minor bands similar to those described previously (Swank & Paigen, 1973) as characteristic of the microsomal enzyme. It was concluded that the Golgi complex is involved in the distribution of the enzyme after its synthesis to both lysosomal and microsomal fractions.

Microsomal and lysosomal acid phosphatase isoenzymes of mouse kidney. Characterization and separation

Biochemical methods have been employed to characterize and separate acid phosphatases from lysosomal and microsomal fractions in order to decide whether different isoenzymes reside in these subcellular locations. Microsomal and lysosomal fractions of mouse kidney homogenate were isolated by differential centrifugation. Acid phosphatase of lysosomal fraction goes into solution after lysosomes have been repeatedly frozen and thawed, whereas acid phosphatase of microsomal fraction is firmly bound to the membrane and is freed of contamination by lysosomal enzyme after ultrasonication and centrifugation. The membrane-bound microsomal acid phosphatase is labile at 37°C, pH 4.9, more active toward phenolic substrates (phenyl phosphate and p-nitrophenyl phosphate) than β-glycerophosphate, α-naphthol phosphate or naphthol AS-BI phosphate. It also has a higher pH optimum (6.3), is resistant to l-tartrate and oxalate inhibition and has a slower electrophoretic migration rate in Triton X-100-impregnated polyacrylamide gels. The free lysosomal acid phosphatase is relatively heat-stable, is less active against phenolic substrates, is sensitive to l-tartrate and oxalate inhibition, has a lower pH optimum (5.6) and has a faster migration rate in electrophoresis. These two acid phosphatases can also be separated by diethylaminoethyl-cellulose chromatography. This study thus demonstrated the existence of an acid phosphatase isoenzyme in the microsomal membrane with different biochemical properties from the lysosomal isoenzyme of acid phosphatase.

L-tryptophan. A non-allosteric organ-specific uncompetitive inhibitor of human placental alkaline phosphatase

l-Tryptophan, but not d-tryptophan, inhibits human placental and intestinal alkaline phosphatases, but not those of liver and bone. The nature of this stereospecific organ-specific inhibition has been elucidated. Thus, from a study of the effect of substrate concentration on inhibition in which double-reciprocal plots of 1/v versus 1/s at various inhibitor concentrations were made, this inhibition is judged to be ;uncompetitive'. That the inhibition is non-allosteric is an opinion based on (1) hyperbolic curves obtained from plotting the percentage inhibition against inhibitor concentration; (2) the independence of the inhibition to heat denaturation and urea treatment; (3) the relatively low value of entropy change; and (4) a value close to unity for n, the number of l-tryptophan molecules that combine with one molecule of enzyme. Finally, a homosteric mechanism is further postulated for the inhibition by l-tryptophan based on the increase of optimum temperature for maximum velocity and the decrease of this inhibition with increasing temperature. The mechanism of this inhibition is discussed.