Advances in the Raman depth profiling of polymer laminates

The use of Raman microspectroscopy to depth profile multi-layered polymer laminates is becoming increasingly popular. However, the results are generally degraded by aberrations introduced by the change in refractive index at the air/sample interface. Recent research has suggested that the use of an immersion oil and suitable objective can reduce this effect. This study evaluates this proposal by comparing depth profiling results on a multi-layer poly(styrene)/poly(methylmethacrylate) (PS/PMMA) laminate polymer from both dry metallurgical objectives and immersion objectives (used in combination with an oil of suitable refractive index). The immersion technique enabled successful depth profiling to the full working distance of the objective (100 microm), showing clear and distinct variations in 11 different layers within the laminate; a dry metallurgical objective used for comparison achieved poor resolution of only two layers. This is the first demonstration of depth profiling within a polymer laminate to this depth. The depth profiling results are compared to results obtained by sectioning the PS/PMMA sample after setting it in resin.

Reorganization of structural proteins in vascular smooth muscle cells grown in collagen gel and basement membrane matrices (Matrigel): a comparison with their in situ counterparts

When smooth muscle cells are enzyme-dispersed from tissues they lose their original filament architecture and extracellular matrix surrounds. They then reorganize their structural proteins to accommodate a 2-D growth environment when seeded onto culture dishes. The aim of the present study was to determine the expression and reorganization of the structural proteins in rabbit aortic smooth muscle cells seeded into 3-D collagen gel and Matrigel (a basement membrane matrix). It was shown that smooth muscle cells seeded in both gels gradually reorganize their structural proteins into an architecture similar to that of their in vivo counterparts. At the same time, a gradual decrease in levels of smooth muscle-specific contractile proteins (mainly smooth muscle myosin heavy chain-2) and an increase in beta-nonmuscle actin occur, independent of both cell growth and extracellular matrix components. Thus, smooth muscle cells in 3-D extracellular matrix culture and in vivo have a similar filament architecture in which the contractile proteins such as actin, myosin, and alpha-actinin are organized into longitudinally arranged "myofibrils" and the vimentin-containing intermediate filaments form a meshed cytoskeletal network. However, the myofibrils reorganized in vitro contain less smooth muscle-specific and more nonmuscle contractile proteins.

Relationship of glycosaminoglycan and matrix changes to vascular smooth muscle cell phenotype modulation in rabbit arteries after acute injury

PURPOSE

The phenotype of vascular smooth muscle cells (SMCs) is altered in several arterial pathologies, including the neointima formed after acute arterial injury. This study examined the time course of this phenotypic change in relation to changes in the amount and distribution of matrix glycosaminoglycans.

METHODS

The immunochemical staining of heparan sulphates (HS) and chondroitin sulphates (CS) in the extracellular matrix of the arterial wall was examined at early points after balloon catheter injury of the rabbit carotid artery. SMC phenotype was assessed by means of ultrastructural morphometry of the cytoplasmic volume fraction of myofilaments. The proportions of cell and matrix components in the media were analyzed with similar morphometric techniques.

RESULTS

HS and CS were shown in close association with SMCs of the uninjured arterial media as well as being more widespread within the matrix. Within 6 hours after arterial injury, there was loss of the regular pericellular distribution of both HS and CS, which was associated with a significant expansion in the extracellular space. This preceded the change in ultrastructural phenotype of the SMCs. The glycosaminoglycan loss was most exaggerated at 4 days, after which time the HS and CS reappeared around the medial SMCs. SMCs of the recovering media were able to rapidly replace their glycosaminoglycans, whereas SMCs of the developing neointima failed to produce HS as readily as they produced CS.

CONCLUSIONS

These studies indicate that changes in glycosaminoglycans of the extracellular matrix precede changes in SMC phenotype after acute arterial injury. In the recovering arterial media, SMCs replace their matrix glycosaminoglycans rapidly, whereas the newly established neointima fails to produce similar amounts of heparan sulphates.

Effects of collagen gel configuration on behavior of vascular smooth muscle cells in vitro: association with vascular morphogenesis

The growth, behavior, and contractile protein expression of rabbit aortic smooth muscle cells (SMC) grown on, between layers, or within a collagen gel was investigated by confocal laser scanning fluorescence microscopy and Western analysis. SMC grown on collagen gel behaved similarly to those on conventional culture dishes. However, when a second layer of collagen was overlaid, cells underwent an elongated quiescent phase before onset of proliferation and a more than threefold lower logarithmic growth rate was observed. These cells self-organized into a network with ring-like structures. With increasing culture time, some of the rings developed into funnel-like, incomplete or complete tubular structures. If a tubular template preexisted within the gel, the SMC established a cylinder-shaped tube with several circularly arranged muscular layers (similar to an artery wall). This behavior mimicked endothelial cells during angiogenesis in vitro. A similar phenomenon occurred in cultures in which SMC were randomly mixed in a collagen gel, but here their behavior and morphology varied with their position within the gel. Western blot analysis showed that the SMC differentiation marker, smooth muscle myosin heavy chain-2 (SM-2), rapidly decreased, disappearing by day 10 in SMC grown on collagen, but was still detectable until day 25 in cells cultured between or within the same gel. These findings indicate that like endothelial cells, vascular SMC can display blood vessel formation behavior in vitro when an appropriate three-dimensional matrix environment is provided to keep them in a relatively higher-differentiated and low-proliferative state.

Matrix metalloproteinase can facilitate the heparanase-induced promotion of phenotype change in vascular smooth muscle cells

Previous studies from this laboratory have shown that degradation of heparan sulphate proteoglycan by both living macrophages and macrophage lysosomal heparanase induces phenotypic change of vascular smooth muscle cells (SMC) from a high volume fraction of myofilaments (V(v)myo) to a low V(v)myo [Campbell et al. Exp Cell Res 1992; 200: 156-167]. The aim of this study was to determine whether matrix metalloproteinase (MMP) activity is also involved in the induction of SMC phenotypic change by macrophages. A specific inhibitor of MMPs (BB94) was able to block macrophage-induced SMC phenotypic change and subsequent DNA synthesis in freshly dispersed SMC seeded in primary culture at confluent density. The inhibitor did not block these SMC changes when SMC were seeded at low density without macrophages nor did it block heparanase activity directly. We also determined whether heparanase and MMP activities are upregulated together in vivo. Artery homogenates were analysed in a heparanase enzyme assay and for MMPs using zymograms. Increased heparanase activity was observed 3-14 days following balloon catheter injury of rabbit carotid arteries, and returned to control levels 6 weeks after injury. Active MMP2 was induced with heparanase after injury. MMP9 induction was also apparent 6 h after injury. Immunohistology on sections of these arteries showed the presence of MMPI1, 2, 3 and 9 with these MMPs being strongly induced in the intima 7 days after balloon catheter injury. Both heparanase and MMP activities were also present in human end-stage complex lesions from coronary arteries, carotid endarterectomies and abdominal aortic aneurysms. Because MMPs and heparanase are expressed at the same time, it is possible that MMPs facilitate heparanase activity in promotion of phenotypic modulation of SMC in vivo during neointimal thickening following injury and in atherosclerotic lesions.

Arterial heparan sulfate proteoglycans inhibit vascular smooth muscle cell proliferation and phenotype change in vitro and neointimal formation in vivo

PURPOSE

The aim of this study was to determine whether heparan sulfate proteoglycans (HSPGs) from the normal arterial wall inhibit neointimal formation after injury in vivo and smooth muscle cell (SMC) phenotype change and proliferation in vitro.

METHODS

Arterial HSPGs were extracted from rabbit aortae and separated by anion-exchange chromatography. The effect of HSPGs, applied in a periadventitial gel, on neointimal formation was assessed 14 days after balloon catheter injury of rabbit carotid arteries. Their effect on SMC phenotype and proliferation was measured by point-counting morphometry of the cytoplasmic volume fraction of myofilaments (Vvmyo) and 3H-thymidine incorporation in SMCs in culture.

RESULTS

Arterial HSPGs (680 microg) reduced neointimal formation by 35% at 14 days after injury (P=.029), whereas 2000 microg of the low-molecular-weight heparin Enoxaparin was ineffective. HSPGs at 34 microg/mL maintained subconfluent primary cultured SMCs with the same high Vvmyo (52.1%+/-13.8%) after 5 days in culture as did cells freshly isolated from the arterial wall (52.1%+/-15.1%). In contrast, 100 microg/mL Enoxaparin was ineffective in preventing phenotypic change over this time period (Vvmyo 38.9%+/-14.6%, controls 35.9%+/-12.8%). HSPGs also inhibited 3H-thymidine incorporation into primary cultured SMCs with an ID50 value of 0.4 microg/mL compared with a value of 14 microg/mL for Enoxaparin (P< .01).

CONCLUSION

When used periadventitially in the rabbit arterial injury model, natural arterial HSPGs are effective inhibitors of neointimal formation. In vitro, the HSPGs maintain SMCs in a quiescent state by inhibiting phenotypic change and DNA synthesis. This study suggests that HSPGs may be a natural agent for the treatment of clinical restenosis.

Inhibition of phenotype modulation, growth, and migration of vascular smooth muscle cells by a guanosine-rich 30-mer phosphorothioate oligodeoxynucleotide

The testing of a 30-mer dG-rich phosphorothioate oligodeoxynucleotide (LG4PS) for effects on the behaviour of vascular smooth muscle cells (VSMC) in vitro and in vivo is described. LG4PS at 0.3 microM inhibited significantly the phenotype modulation of freshly isolated rabbit VSMC, and cell outgrowth from pig aortic explants was inhibited approximately 80% by 5 microM LG4PS. The growth of proliferating rabbit and pig VSMC was inhibited approximately 70% by 0.3 microM and 5 microM LG4PS, respectively. Though less marked, the antiproliferative effects of LG4PS on human VSMC were comparable to those obtained with heparin. The cytotoxic effects of LG4PS on VSMC in vitro were low. Despite these promising results, adventitial application of 2-200 nmol LG4PS in pluronic gel failed to reduce vascular hyperplasia in balloon-injured rabbit carotid arteries, and the highest dose caused extensive mortality.

alpha 1-Adrenoceptors on rabbit aortic smooth muscle cells in culture and in experimental intimal thickening

1. This study has defined alpha 1-adrenoceptors and their reactivity in rabbit aorta, following removal of the endothelium and formation of a myointimal thickening, and also in smooth muscle cells (SMC) in cell culture which had undergone serial passaging and changes in phenotype. 2. [3H]-prazosin binding to SMC from control aorta, vessels 2 weeks after endothelial denudation and sub-cultured SMC (passage 3-6) was specific (displaceable with 10 mumol/L phentolamine), and of high affinity to a single class of sites (KD range: 71-114 pmol/L). The maximum binding density (Bmax) of alpha 1-adrenoceptors on SMC from the neointima (11,105 +/- 771 sites/cell) was not significantly different to that of control medial SMC (14,014 +/- 2472 sites/cell). However, SMC cultured to passage 6, showed a 2-fold increase in Bmax (30,227 +/- 4349 sites/cell). 3. The production of inositol phosphates (IP1, IP2 and IP3) by SMC following 10 mumol/L phenylephrine was assayed. Both freshly-dispersed aortic SMC and sub-cultured SMC were stimulated to produce increased inositol phosphates by the addition of phenylephrine which was completely inhibited by pre-incubation with 10 mumol/L phentolamine, suggesting that the stimulation was via alpha 1-adrenoceptors. 4. Maximal contractile responses of isolated thoracic and abdominal aortic rings to KCl (100 mmol/L), 5-HT and phenylephrine were unchanged two weeks after endothelial denudation. However, phenylephrine was significantly less potent (2.7-fold) in both areas of the aorta, while the potency of 5-HT was significantly enhanced (2.7-fold) after endothelial denudation only in the abdominal aorta. 5. The decreased sensitivity of the rabbit aorta to alpha 1-adrenoceptor agonists following endothelial denudation and the formation of a myointimal thickening is not due to changes in affinity or density of alpha 1-adrenoceptors. However multiple passaging of SMC in culture leads to an increase in alpha 1-adrenoceptor density. This change can be related to the altered cytodifferentiation of irreversible synthetic state SMC which are similar to those in atherosclerotic lesions.

Activation of platelet heparitinase by vascular cell lysates

Tumour cells have been reported to contain an activator of platelet heparitinase which is absent from normal cells. Using an assay which measures the degradation of radiolabelled heparin, we observed that lysates of metastatic melanoma cells did activate platelet radiolabelled heparin, we observed that lysates of metastatic melanoma cells did activate platelet heparitinase but that lysates of arterial endothelial and smooth muscle cells did likewise, with the latter being particularly effective. The activator largely survived a 10 min preincubation of the cell lysates at 70 degrees C, but not at 100 degrees C. Experimental results indicated that the contents of 10(5) vascular smooth muscle cells could increase platelet heparitinase activity in vitro to 6 times its initial value. We suggest such activation may have physiological relevance and may even assist the development of certain cardiovascular diseases in man.

Effect of extracellular matrix proteins on vascular smooth muscle cell phenotype

The effect on phenotypic expression of rabbit vascular smooth muscle cells (SMC) of the interstitial matrix proteins collagen I and fibronectin, the basal lamina proteins collagen IV and laminin, and the serum adhesion protein vitronectin was examined in culture. Experiments were performed in foetal calf serum stripped of fibronectin and vitronectin to eliminate their confounding effects. All the proteins promoted adhesion to the plastic culture dish (in a concentration dependent manner) of SMC freshly isolated from the artery wall. These cells had a high volume density of myofilaments (Vvmyo) in their cytoplasm. Laminin was best at maintaining SMC with a high Vvmyo (Vvmyo = 49.8%) followed by collagen IV (41.7%). Cells plated on vitronectin showed the lowest Vvmyo (31.3%). The results support the concept that the SMC basal lamina has a role in maintaining cells in the high Vvmyo phenotype.

Effect of extracellular matrix proteins on vascular smooth muscle cell phenotype

The effect on phenotypic expression of rabbit vascular smooth muscle cells (SMC) of the interstitial matrix proteins collagen I and fibronectin, the basal lamina proteins collagen IV and laminin, and the serum adhesion protein vitronectin was examined in culture. Experiments were performed in foetal calf serum stripped of fibronectin and vitronectin to eliminate their confounding effects. All the proteins promoted adhesion to the plastic culture dish (in a concentration dependent manner) of SMC freshly isolated from the artery wall. These cells had a high volume density of myofilaments (Vvmyo) in their cytoplasm. Laminin was best at maintaining SMC with a high Vvmyo (Vvmyo = 49.8%) followed by collagen IV (41.7%). Cells plated on vitronectin showed the lowest Vvmyo (31.3%). The results support the concept that the SMC basal lamina has a role in maintaining cells in the high Vvmyo phenotype.

Effect of TGF-beta on differentiated organoids of the colon carcinoma cell line LIM 1863

The LIM 1863 colon carcinoma cell line grows in suspension as morphologically and functionally organized organoids in serum-containing medium. Addition of TGF-beta caused the organoids to adhere and inhibited DNA synthesis. A 20 min incubation with TGF-beta was sufficient to induce adherence and this could be inhibited by cycloheximide. The adhesion and DNA synthesis inhibition were demonstrated to be separate events. We were not able to detect any changes in matrix or cell membrane antigens. Similarly there were no changes in synthesized proteins (by two-dimensional gel electrophoresis), and no upregulation of proteoglycan. When adhered organoids were lysed from the tissue culture plastic surface, untreated organoids adhered to this surface. This 'conditioned' surface was destroyed by trypsin but not collagenase or medium from normal LIM 1863 cultures. However, the adherent phenotype was prevented when organoids were treated with transforming growth factor-beta (TGF-beta) in the presence of medium conditioned by normal LIM 1863 cultures rather than in fresh medium. The adhesion process was inhibited by an antibody (QE2E5) against beta 1 integrin although no quantitative changes in integrins were observed (by immunoprecipitation or RNA analysis). A second anti-beta 1 integrin antibody (61.2C4) inhibited LIM 1863 adhesion to collagen but not TGF-beta induced adhesion, implying that TGF-beta induced a specific conformational change or interaction of a beta 1 integrin. In this morphologically structured system TGF-beta induced a number of subtle effects including formation of new extracellular matrix and conformational change of a beta 1 integrin, rather than the major quantitative changes in cell/matrix molecules reported previously.

Effects of cholera toxin on human colon carcinoma cell lines

This study reports on changes in morphology and membrane transport in 5 human colon carcinoma cell lines treated with cholera toxin (CT). Three of the cell lines that grew as monolayers (LIM 1215, LIM 1899, LIM 2099) and 1 that grew as floating clumps (LIM 2408) did not show morphological changes after CT treatment. However, cell line LIM 1863 that grows as floating "crypt-like" organoids showed rapid and distinctive changes in morphology and membrane transport after CT treatment. At 1 and 6 hrs after CT treatment, light and transmission electron microscopy revealed rapid dilatation of the central lumen of organoids and the appearance of 2 populations of apical vesicular inclusions. The first population was unusual in being non-membrane bound and limited by fuzzy filamentous material. The second population was membrane bound. Scanning electron microscopy at 1-6 hr after CT treatment showed swelling and loss of surface microvilli on some, but not all, cells. At 24 hr after CT treatment the majority of organoids showed evidence of fluid accumulation and small apical vesicles coalesced to form large single vacuoles that obliterated normal cell morphology. By 48 hr, continued swelling produced extreme attenuation of the plasma membrane with cells taking on an "endothelial cell-like" appearance. The response to CT was dose-dependent. Uptake studies using 86Rubidium and blocking studies using ouabain and amiloride indicated that CT is acting on the Na+/K+ ATPase membrane pump to cause the increased fluid uptake by LIM 1863 cells. This study is the first to report specific morphological changes in intestine-derived cells in response to CT.(ABSTRACT TRUNCATED AT 250 WORDS)

Retention of tissue-specific phenotype in a panel of colon carcinoma cell lines: relationship to clinical correlates

A panel of eight cell lines has been derived from colon carcinomas. These cell lines have both been characterized according to standard criteria of growth rate, response to mitogens (epidermal growth factor and basic fibroblast growth factor), xenograft growth and growth in soft agar, and according to the ability of the cells to express epitopes known to be expressed by cells in the normal intestinal mucosa. The expression of epitopes present in columnar (absorptive) cells has been assessed using a panel of monoclonal antibodies to brush border peptidases and disaccharidases, villin and brush border-specific peptides. Goblet cell epitopes have been determined by monoclonal antibodies to mucin and carcinoembryonic antigen. An antibody to chromogranin was used to identify endocrine cells. Using these antibodies we found that all the cell lines reacted with at least one of the antibodies to columnar cells. Similarly, varying proportions of cells in six of the eight cell lines stained with antibodies to mucin. None of the cells expressed chromogranin. Expression of a differentiated colonic phenotype, as measured from antibody staining, did not correlate with measurements of malignancy, such as the ability of the cells to grow in soft agar or as xenografts. Similarly, there was no correlation between retention of a colonic phenotype and the initial pathological stage of the tumour from which the cell lines were derived.

Combination chemotherapy tested in a short-term thymidine incorporation assay in primary cultures of ovarian adenocarcinomas

Fifty-six tumor specimens from patients with ovarian adenocarcinoma were tested for sensitivity to single and combination drug regimens in a short-term antimetabolic assay measuring inhibition of thymidine incorporation. Response in primary cultures to drug combinations was compared with response to each component drug: cisplatinum, chlorambucil, adriamycin, etoposide and activated cyclophosphamide. Using cut-off criteria previously shown to correlate with "sensitive" and "resistant" tumors for single drugs, 11% of tumors showed increased sensitivity to a combination compared with the single drugs, but 10% showed decreased sensitivity to a combination. The majority of tumors remained in the same "sensitive" or "resistant" categories obtained with the single drugs. Analysis by isobolograms demonstrated synergy, addition or antagonism with the same combination on different tumors. No significant difference between combinations and the best single drug used alone was found in 70% of assays. Overall thymidine incorporation inhibition by the combination and by the best single drug was highly correlated. It is suggested that the best single drug predicts the effectiveness of its combination regimens.

Patterns of growth and differentiation in the colon carcinoma cell line LIM 1863

The LIM 1863 colon carcinoma cell line grows in the form of morphologically and functionally organized organoids. Cells are arranged around a central lumen with a brush border and nuclei are polarized to the periphery. The organoids contain 3 morphological cell types (columnar, goblet and caveolated cells). By agar cloning it has been possible to isolate 29 subclones of the cell line, all of which display the same phenotype and percentage of morphological cell types as the parent line. Cell-sorting experiments showed that precursor cells of LIM 1863 cultures could express either mucin (large-intestinal-mucus antigen) or a brush-border enzyme (sucrase-isomaltase). Proliferating cells were predominantly found near the outer periphery of organoids with cell maturation towards the internal lumen. Dead cells were continuously shed from the organoids but terminal non-cycling cells were not observed within the organoids. The organoid structure was calcium-dependent and promoted cell survival. Suspension cultures of disaggregated cells could be grown in medium containing less than 100 microM calcium. No decrease in differentiation antigens was observed in the low-calcium cultures, although polarization of the cells was lost. The organoid cultures formed by this cell line represent a unique in vitro model for colonic crypt growth and organization.

Characterization and properties of nine human ovarian adenocarcinoma cell lines

Four series of cell lines have been derived from patients with ovarian adenocarcinoma. Nine cell lines have been established at one from a solid metastasis. Six lines were derived from the ascites or pleural effusion of patients with poorly differentiated adenocarcinoma: PEO1, PEO4, and PEO6 from one patient, PEA1 and PEA2 from a second, and PEO16 from a third. Three lines (PEO14 and PEO23 from ascites and TO14 from a solid metastasis) were derived from a patient with a well-differentiated serous adenocarcinoma. Each set of cell lines was morphologically distinct. The five cell lines PEO1, PEO4, PEO6, PEA1, and PEA2 had cloning efficiencies on plastic of 1-2% and only a few cells in these lines expressed alkaline phosphatase or vimentin. Only a low percentage of these cells reacted with the monoclonal antibodies 123C3 and 123A8 but most reacted with OC125. Conversely the cell lines PEO14, TO14, PEO23, and PEO16 were characterized by low cloning efficiency values (less than 0.05%), marked expression of alkaline phosphatase and vimentin, and good reaction with 123C3 and 123A8 but not OC125. These four cell lines also exhibited dome formation. Four of the cell lines, PEO1, PEO4, PEO6, and PEO16, have been xenografted into immune-deprived mice and found to be tumorigenic.

Cellular heterogeneity and drug resistance in two ovarian adenocarcinoma cell lines derived from a single patient

Two ovarian cell lines were derived from the ascites of a patient before and after the onset of resistance to chemotherapy involving cis-platinum, chlorambucil and 5-fluorouracil. Characterization of these lines shows them to have various features in common and some significant differences. Cytologically the lines cannot be distinguished and they both contain high concentrations of oestrogen receptor. However, they do differ with respect to their growth characteristics, karyotype, glutathione content and sensitivity to cis-platinum. The karyotypes of the 2 lines show several marker chromosomes in common but the resistant line contained a chromosome 8 and a 17 which were absent from the earlier sensitive line. This suggests a clonal origin with subsequent divergence to a heterogeneous population.

Human melanoma cells sensitive to deoxyadenosine and deoxyinosine

In an in vitro study conducted without the use of adenosine/deoxyadenosine deaminase inhibitors, two human melanoma cell lines, MM96L and MM127, were found to be highly sensitive to killing by continuous treatment with deoxyadenosine (dAdo) (D37 47 microM and 68 microM respectively) compared with fibroblasts (D37 440 microM), Hela cells (D37 1.1 mM) and other melanoma cell lines (D37 0.8 to 2.5 mM). Cross-sensitivity was found to deoxyinosine (dIno) and in part to adenosine but not to related metabolites such as inosine or hypoxanthine. Hypersensitivity to dAdo was associated with deficiency in cell membrane 5'-deoxynucleotidase but not in deaminase activity. dAdo toxicity could be prevented in MM96L by addition of the other three deoxynucleosides together but not by removing dAdo after a brief (2 hr) treatment. Resistant melanoma cells, however, required more than 24 hr dAdo treatment to produce toxicity. DNA synthesis in MM96L cells was reversibly inhibited, and cells tended to accumulate in G1/S. No DNA strand breaks were detected. These results showed that in contrast to the resistant cell line, asynchronous MM96L cells are highly sensitivity to brief treatment, toxicity resulting from an effect associated with inhibition of DNA synthesis. dAdo and dIno, either combined with a deaminase inhibitor or as deaminase-resistant derivatives, may have a favourable therapeutic index for some melanomas in vivo.

Epigenetic effects of the methylating agent 5-(3-methyl-1-triazeno) imidazole-4-carboxamide in human melanoma cells

The anti-tumour methylating agent 5-(3-methyl-1-triazeno) imidazole-4-carboxamide (MTIC) increased the thymidine and deoxycytidine pools but not the deoxyguanosine pool in human melanoma cells. Incorporation of deoxyguanosine and deoxyadenosine was strongly inhibited by MTIC due to formation of the decomposition product 5-aminoimidazole-4-carboxamide (AIC). Theophylline, natural nucleosides and sulphydryl compounds did not affect the toxicity of MTIC in either MTIC-sensitive (Mer-) or autologous-resistant (Mer+) melanoma cells. 3-Aminobenzamide (3 mM for 48 h), an inhibitor of ADP-ribosyl transferase, greatly enhanced MTIC toxicity in the resistant compared with the sensitive cell line.

Comparison of virus reactivation, DNA base damage, and cell cycle effects in autologous human melanoma cells resistant to methylating agents

A human melanoma cell line (MM253c1-3D) having an induced stable resistance to the methylating agents 5-(3'-methyl-1-triazeno)imidazole-4-carboxamide, methylnitrosourea, and N-methyl-N'-nitro-N-nitrosoguanidine gave more efficient replication of 5-(3'-methyl-1-triazeno)imidazole-4-carboxamide-treated adenovirus 5 than did the methylation-sensitive parent line (MM253c1). Analysis of DNA hydrolysates from melanoma cells treated with [3H]methylnitrosourea for 1.6 hr showed similar initial levels of 7-methylguanine and 3-methyladenine in both cell lines and substantial excision of the latter lesion after 19 hr. O6-Methylguanine in the DNA of MM253c1 cells also decreased during this period, but in MM253c1-3D cells the initial yield of this lesion was too low for subsequent decrease to be detected. 5-(3'-Methyl-1-triazeno)imidazole-4-carboxamide induced a significant arrest of MM253c1 cells in the G2 phase of the cell cycle. These results show that MM253c1 is a variant of the Mer- phenotype, the resistance of MM253c1-3D cells being attributed to reversion to Mer+ and expressed as very rapid repair of O6-methylguanine lesions.

Differential effects of NAD, nicotinamide and related compounds upon growth and nucleoside incorporation in human cells

Two human melanoma cell lines, MM96 and MM127, were found to be highly sensitive to the toxicity of adenosine (D50 100-150 micrograms/ml) compared with other melanoma lines. HeLa cells and a lymphoblastoid line (D50 greater than 500 micrograms/ml). The MM127 line was also sensitive to NAD (D50 41 micrograms/ml) compared with the other lines (D50 greater than 400 micrograms/ml), and accumulated three-fold more NAD-derived isotopic label. Nicotinamide exhibited little toxicity in any cell type (D50 greater than 400 micrograms/ml); 25-100 micrograms/ml nicotinamide greatly increased the plating efficiency of melanoma cells and fibroblasts when low levels of foetal calf serum were used. The toxicity of DNA-damaging agents (alkylating agents and u.v.) in melanoma cells was not reduced in the presence of NAD, adenosine or nicotinamide. Studies of the effects of the latter compounds upon the incorporation of deoxynucleosides showed that: (a) melanoma cells have lower purine pools than fibroblasts; (b) [3H]deoxyguanosine incorporation was inhibited more than [3H]deoxyadenosine incorporation; (c) incorporation of [3H]deoxyadenosine and [3H]deoxyguanosine into RNA was inhibited by adenosine, thus providing a method for determination of guanine-specific DNA repair; and (d) NAD enhanced thymidine incorporation in intact melanoma cells but not in fibroblasts, in a pattern similar to the release from template restriction previously reported for permeabilised tumour cells.