Biomedical subjects
Publications and source records attributed to I R Hart.
The expression of the c-fos gene in murine cells of melanocyte origin in response to cAMP-elevating agents has been examined. Accumulation of c-fos mRNA at a high level as a consequence of these treatments precedes both proliferative and cytodifferentiative changes in non-tumorigenic or tumorigenic cell lines.
A nontumorigenic line of murine melanocytes, Mel-ab, has been transfected with the v-Ha-ras gene under transcriptional control of the Moloney murine leukemia virus long terminal repeat. Transfectants produced rapidly growing undifferentiated melanomas in recipient mice. The inhibition of melanin production in transformed cells, observable both in vitro and in vivo, suggests that ras may affect melanocyte cytodifferentiation. Mel-ab cells require the continual presence of 12-O-tetradecanoylphorbol-13-acetate, or other activators of protein kinase C, for in vitro growth. Transfectants expressing v-Ha-ras no longer manifested this requirement and were actually growth inhibited by the addition of protein kinase C activators. These results are consistent with the notion that ras acts via the protein kinase C pathway in conferring autonomous growth on Mel-ab cells.
A new quantitative assay for measuring angiogenesis in a s.c. located sponge implant in rats is described. Using this model, which detects neovascularization by measuring alterations in 133Xe clearance, it has been shown that the known angiogenic factors, transforming growth factor alpha and tumor necrosis factor alpha, cause maximum vascularization of the sponge to occur by Day 11 postimplantation compared with Days 15 to 17 in control animals. The monokine interleukin 1 alpha is shown to be strongly angiogenic, suggesting that more than one macrophage-derived cytokine may be the active mediator in macrophage-induced angiogenesis. Extracellular matrix proteins appear to play a role in regulating the angiogenic response such that presoaking sponges in laminin (40 micrograms/ml) or fibrinogen (500 micrograms/ml) solutions induced a significant reduction in the time taken to achieve maximum 133Xe clearance values; no such enhancement of neovascularization was observed when sponges were presoaked in type IV collagen (100 micrograms/ml) solution. The assay described here, which is reproducible, objective, and quantitative, should be of considerable use in elucidating the molecular basis of angiogenesis regulation.
The effect of anatomical site of tumour growth on selective uptake and retention of chloro-aluminium sulphonated phthalocyanine (ClAlSPc) was determined using the murine colorectal carcinoma (Colo 26). Tumours were established in the liver, spleen, kidney, lung, thoracic cavity and s.c. flank region of syngeneic BALB/c mice and animals received 10 mg/kg ClAlSPc by i.v. injection. Colo 26 growths at s.c., intra-pulmonary, intra-thoracic or intra-renal sites took up and retained greater amounts of ClAlSPc than did adjacent normal tissues. Such selective retention of ClAlSPc by neoplastic tissue was not observed when Colo 26 was grown in the spleen, where tumour and normal tissue took up about the same amounts, or the liver, where normal tissue took up more ClAlSPc than either directly implanted or metastatic tumours. ClAlSPc ratios found in tumour/adjacent tissue may vary for a single tumour growing at different anatomical sites and such variability could have a distinct effect on the efficacy of photodynamic therapy of cancer.
Using eight different physical examination or technical stations, 400 examinations were conducted to evaluate the effectiveness of immediate feedback during the Objective Structured Clinical Examination (OSCE). The test group comprised 50 medical students who underwent a standard 4-minute examination followed by 2 minutes of feedback. Immediately following feedback the students repeated an identical 4-minute examination scored by the same examiners. The control group consisted of 50 students from the same class who underwent an identical testing sequence, but instead of receiving feedback, they were instructed to continue their examinations for an additional 2 minutes before repeating the stations. Simple repetition of the task did not significantly improve score (mean increase 2.0%, NS). Extending the testing period from 4 to 6 minutes resulted in a small but significant increase in score (mean 6.7%, P less than 0.001). However, there was a much larger increase in the scores obtained following 2 minutes of immediate feedback compared to pre-feedback performance (mean 26.3%, P less than 0.0001). The majority of students and examiners felt that feedback, as administered in this study, was valuable both as a learning and teaching experience. Short periods of immediate feedback during an OSCE are practical and can improve competency in the performance of criterion-based tasks, at least over the short term. In addition, such feedback provides students with valuable self-assessment that may stimulate further learning.
A highly sensitive charge-coupled device (CCD) camera, linked to a computerized image processor, has been used to obtain fluorescence images of chloro-aluminum sulfonated phthalocyanine (ClAlSPc), and its mono- to tetra-sulfonated constituents, in cells recovered from the peritoneal cavity of dye-treated mice. Immunofluorescence and cytochemistry showed that cells which preferentially took up ClAlSPc and its sulfonated species were predominantly of the monocyte-macrophage series. While this technique may be of use in determining the nature of those cells capable of taking up light sensitive dyes and, perhaps, the intracellular location of such agents, the possibility that photoinactivation by dye aggregation could reduce the sensitivity of this procedure is discussed.
The effects of the two photosensitizers chloroaluminum sulfonated phthalocyanine (ClAlSPc) and hematoporphyrin derivative (HpD) on the functional activities of macrophages and natural killer (NK) cells, two immunocyte populations implicated in the control of tumor development and spread, have been investigated. Murine peritoneal macrophages treated in vivo with ClAlSPc or HpD at 10 mg/kg body weight showed no impairment of Fc-mediated phagocytic capacity and only minor disturbances of in vitro tumoricidal/tumoristatic function. The NK cell activity of splenocytes obtained from photosensitizer-treated mice, assayed 24 or 48 h after i.v. injection of ClAlSPc or HpD at 10 mg/kg was unaffected compared to controls. However significant inhibition of NK activity was observed when splenocytes obtained from mice with or without subcutaneous Colo 26 tumors, treated with ClAlSPc plus laser therapy (675 nm) were used as effector cells. The results show that impairment of some anti-tumor activity can be observed in phthalocyanine treated or phthalocyanine + laser-treated animals but this relatively minor impairment may augur well for the use of systemic phthalocyanine administration in photodynamic therapy.
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The potency of chloroaluminum sulfonated phthalocyanine (ClAlSPc) as a photosensitizing agent for photodynamic therapy of cancer was evaluated in vivo by its ability to be taken up and retained by murine tumors of diverse histological origin. Antitumor effects following laser irradiation were evaluated by measurement of the tumor weights of dissected-out tumor masses. Three tumors (Colo 26, a colorectal carcinoma; M5076, a reticulum cell sarcoma; and UV-2237, a fibrosarcoma) growing s.c. in the flank region retained substantially greater quantities of ClAlSPc than did adjacent skin and muscle achieving peak values 24-48 h after the i.v. administration of ClAlSPc (10 mg/kg). The relative magnitude of ClAlSPc retention by these tumors was Colo 26 greater than M5076 greater than UV-2237. However, normal liver and spleen were organs which retained the greatest amounts of ClAlSPc even compared to the s.c. grown tumors and other normal tissues examined. Flow cytometric analysis of tumor cell suspensions obtained from collagenase-digested tumors showed that individual neoplastic cells were capable of taking up and retaining ClAlSPc. Photodynamic therapy, undertaken by i.v. administration of dye (5 mg/kg) followed 24 h later by local laser light irradiation (675 nm, 100 J), brought about significant (Colo 26, M5076, and 3LL tumors) and obvious but nonsignificant (UV-2237 tumor) reductions in tumor weights, as assessed 5 days later. Thus, selective tumor retention of ClAlSPc coupled with a significant response to red light produced dramatic alterations in cancer growth.
Histamine induced a concentration-dependent increase in intracellular cyclic-AMP of the two human melanoma cell lines SK23 and DX3.LT5.1; maximal stimulation was obtained with 17.8 microM histamine which consistently produced greater than 50-fold increases in the cyclic AMP content of both cell lines. The dose-response curve for histamine in each culture was progressively displaced to the right with increasing concentrations of the histamine H2 receptor antagonist cimetidine. Ranitidine, another H2 receptor antagonist also prevented the histamine-induced cyclic AMP elevation, but the H1 receptor antagonists mepyramine and tripelennamine had no significant effect. These findings indicate that human melanoma cells express histamine H2 receptors, stimulation of which activates adenylate cyclase with a subsequent rise in intracellular cyclic AMP. Mast cell:melanoma interactions mediated by histamine in vivo might therefore be expected to modify some aspects of melanoma cell behaviour.
The adhesive behaviour of a series of human melanoma cell lines, of varying metastatic potential, to basement membrane and stromal components was investigated in vitro. Experimental metastatic propensity was assessed from the number of pulmonary nodules formed after i.v. injection of cells into BALB/c nude mice. All cell lines showed similar kinetics of attachment when tested on plastic, type-I collagen films, type-I collagen hydrated gels, fibronectin, laminin type-IV collagen substrates and bovine aortic endothelial monolayers. Fibronectin-coated plastic compared to plastic alone produced increased cell attachment and spreading to the same extent in all the cell lines. The melanoma lines attached preferentially to cryostat sections of lung compared to other organs reflecting the pattern of organ involvement of metastasis in vivo. However, no significant quantitative differences in attachment to lung sections were seen between melanoma variants of differing metastatic capacities. Cells labelled with [125I]iododeoxyuridine to determine their initial organ distribution following i.v. injection showed that tumour-cell arrest was not significantly changed enough to explain the differing metastatic capacities. Thus it appears that adhesive properties of these melanoma cells are not correlated with their capacity to form metastases in vivo.
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We have transfected the polyoma middle T oncogene into an immortal murine melanocyte cell line, Mel-ab. This highly pigmented line is phorbol ester (TPA) dependent for in vitro growth, suggesting activation and/or down regulation of Protein Kinase C (PKC) is essential for mitogenesis. Moreover, cells of this line do not form tumours when injected subcutaneously into immunocompetent or immunoincompetent mice. Here we show that PyMT alone is sufficient to produce TPA-independence and transformation to the tumourigenic state in transfected Mel-ab cells. Western blot analysis shows that middle T overcomes the TPA requirement by a mechanism independent of PKC down regulation though this does appear to occur when Mel-ab cells are grown continuously in TPA. These results suggest that PyMT is not exerting its transforming effect by PKC down regulation, but conceivably at some later stage of second messenger signalling, possibly through PyMT-c-src protein kinase activity.
Pre-treatment of B16 melanoma cells with recombinant interferon-gamma (IFN-gamma) markedly increased their lung-colonising capacity following i.v. injection into syngeneic mice as compared with control cells. A similar enhancement was observed following the injection of treated cells into athymic nude mice but not in athymic mice carrying the beige mutation. Pre-treatment of syngeneic mice with anti-asialo GM1 antibody effectively abrogated any interferon-induced increase in experimental metastatic activity. The same IFN-gamma treatment significantly increased resistance of B16 cells to splenic natural killer (NK) cell activity as determined by in vitro assays. IFN-alpha/beta pre-treatment of B16 cells decreased sensitivity to NK-cell-mediated lysis to a lesser extent than IFN-gamma and had no detectable effect upon the subsequent metastatic activity of the tumor cells. Class-I antigen expression was altered by these IFN treatments, with IFN-gamma causing dramatic increases in expression of H-2Db antigen, in a pattern consistent with the possibility that increased H-2 antigen expression on B16 cells led to decreased NK-cell sensitivity which was reflected by an increase in experimental metastatic capacity.
An immortal line of pigmented melanocytes, "melan-a", has been derived from normal epidermal melanoblasts from embryos of inbred C57BL mice. The conditions favouring proliferation of these cells largely resemble those for normal, non-established mouse melanoblasts and melanocytes, and include a low extracellular pH and the presence of a tumour promoter, tetradecanoyl phorbol acetate (TPA) or teleocidin. Melan-a cells have the diploid chromosome number and do not form tumours in syngeneic or nude mice. They are therefore the first known line of non-tumorigenic mouse melanocytes, although an aneuploid melanocyte line of untested tumorigenicity has been reported (Sato et al., 1985). Melan-a cells are syngeneic with the B16 melanoma and its sublines, and provide an excellent parallel non-tumorigenic line for studies of the cellular and molecular basis of melanoma malignancy.