Human Melanoma Growth Research Articles

Regulation of human melanoma growth and metastasis by AGE-AGE receptor interactions.

Advanced glycation end products (AGE), nonenzymatically glycated protein derivatives, have been implicated in the development and progression of diabetic angiopathies, including skin dermopathy. Nevertheless, the involvement of AGE in the development and progression of melanoma has not been fully elucidated. In this study we investigated the expression levels of their receptor for AGE (RAGE) in human melanoma and subsequently studied the effects of AGE on melanoma growth and migration. First, RAGE was detected in the cytoplasm of human melanoma cells (G361 and A375). Among the different types of AGE, glyceraldehyde- and glycolaldehyde-derived AGE significantly stimulated the growth and migration of human melanoma cells. Furthermore, tumor formation of melanoma cell xenografts in athymic mice was prevented by treatment with anti-RAGE neutralizing antibodies. In tumor-bearing mice, survival rates were prolonged, and spontaneous pulmonary metastases were inhibited by treatment using anti-RAGE neutralizing antibodies. In addition, all AGE were present in beds of human melanoma tumor, whereas they were barely detected in normal skin. These results suggest that AGE might be involved in the growth and invasion of melanoma through interactions with RAGE and represent promising candidates for assessing the future therapeutic potential of this therapy in treating patients with melanoma.

Antitumor Activity and Other Biological Actions of Oligomers of Ribonuclease A

Dimers, trimers, and tetramers of bovine ribonuclease A, obtained by lyophilization of the enzyme from 40% acetic acid solutions, were purified and isolated by cation exchange chromatography. The two conformers constituting each aggregated species were assayed for their antitumor, aspermatogenic, or embryotoxic activities in comparison with monomeric RNase A and bovine seminal RNase, which is dimeric in nature. The antitumor action was tested in vitro on ML-2 (human myeloid leukemia) and HL-60 (human myeloid cell line) cells and in vivo on the growth of human non-pigmented melanoma (line UB900518) transplanted subcutaneously in nude mice. RNase A oligomers display a definite antitumor activity that increases as a function of the size of the oligomers. On ML-2 and HL-60 cells, dimers and trimers generally show a lower activity than bovine seminal RNase; the activity of tetramers, instead, is similar to or higher than that of the seminal enzyme. The growth of human melanoma in nude mice is inhibited by RNase A oligomers in the order dimers < trimers < tetramers. The action of the two tetramers is very strong, blocking almost completely the growth of melanoma. RNase A dimers, trimers, and tetramers display aspermatogenic effects similar to those of bovine seminal RNase, but, contrarily, they do not show any embryotoxic activity.

Redirecting mouse T hybridoma against human breast and ovarian carcinomas: in vivo activity against HER-2/neu expressing cancer cells.

Chimeric receptors comprising of the T-cell receptor-ζ cytoplasmic signalling chain fused to an extracellular ligand-binding domain of a single-chain antibody (scFv) have served as effective tools for redirecting cytotoxic T lymphocytes (CTL) against tumour cells. In this report, we constructed a chimeric scFv/ζ gene composed of the variable regions of an HER-2/neu-specific monoclonal antibody (MAb) joined to the TCR-ζ chain. The scFv(anti-HER-2/neu)/ζ chimeric gene was successfully expressed as a functional surface receptor in the MD.45 CTL hybridoma (MD.45-HER/ζ). More importantly, the scFv(anti-HER-2/neu)/ζ receptor was functionally active, since it triggered cytokine secretion by the MD.45-HER/ζ cells upon recognition of HER-2/neu-positive (+) tumour cell lines, or primary tumour cells from patients with HER-2/neu+ cancers. The MD.45-HER/ζ-transduced cells also lysed HER-2/neu+ target cells in vitro with high specificity. We tested the antitumour efficacy of scFv(anti-HER-2/neu)/ζ expressing MD.45 cells in severe combined immunodeficiency disease mice/human and murine tumour models. The adoptively transferred MD.45-HER/ζ cells both slowed significantly the growth of human FM3 melanoma or murine ALC leukaemic cells both transfected to express HER-2/neu. Our data demonstrate the feasibility of redirecting MD.45 CTL with the scFv(anti-HER-2/neu)/ζ chimeric receptor to respond specifically against HER-2/neu expressing tumour cells in vitro and in vivo. Moreover, they make it likely that T cells transduced with the same chimeric gene might be utilised in the treatment of patients with HER-2/neu+ tumours.

Cytotoxic sesquiterpene lactones from Centaurothamnus maximus and Vicoa pentanema.

The aerial parts of Centaurothamnus maximus yielded three cytotoxic guaianolides, chlorojanerin (1), cynaropicrin (2) and janerin (3). The structure elucidation of 1-3 was based on (1)H and (13)C NMR data, mainly 2D-NMR (1)H-(1)H COSY and (1)H-(13)C HETCOR experiments. Compounds 1-3 showed in vitro cytotoxic activity against human cancer cell lines of malignant melanoma (SK-MEL), epidermoid (KB), ductal (BT-549) and ovarian (SK-OV-3) carcinomas with IC(50) values of 2-6 microgram/mL. In addition, 12 sesquiterpene lactones (4-15), isolated previously from the aerial parts of Vicoa pentanema, were evaluated for cytotoxic and antimicrobial activities. 2alpha- Acetoxy-3beta-hydroxyalantolactone (10) and 8beta-hydroxyparthenolide (14) were found to be the main cytotoxic agents (IC(50) values of 2-6 microgram/mL against SK-MEL, BT-549 and SK-OV-3), while lactones 4, 5, 11 and 15 selectively inhibited the growth of human malignant melanoma (IC(50) value of 3.6-7.3 microgram/mL). Cell aggregation and cell adhesion assays, using HL-60 and HeLa cell lines, evaluated the effect of cytotoxic constituents 1-3, 10 and 14 on immune response and inflammation.

Role for beta3 integrins in human melanoma growth and survival.

The role of alphaIIbbeta3 integrin in regulating platelet function is well appreciated, whereas its role in tumor progression and metastasis is not. The purpose of our study was to determine a functional relevance to expression of alphaIIbbeta3 integrin in cells derived from human solid tumors. A study of human melanoma biopsies (n = 24) showed that alphaIIbbeta3 expression increased with tumor thickness, which is indicative of metastatic propensity. Expression of alphaIIbbeta3 was 8% (+/-1.8), 33% (+/-10.4) and 62% (+/-5) in melanomas ranging in thickness from 0-1.5 mm, 1.5-4.0 mm and >4 mm, respectively; alphavbeta3 was equally high all categories. To determine biological function, we stably transfected alphaIIbbeta3 into human melanoma cells that express alphavbeta3, but not alphaIIbbeta3. Surface expression of alphavbeta3 remained unaltered between alphaIIbbeta3 (+) and mock transfected counterparts. The alphaIIbbeta3 (+) cells possessed increased ability to adhere, spread and migrate on fibrinogen. They had decreased ability to attach, spread and migrate on vitronectin. Immunocytochemistry showed that expression of alphaIIbbeta3 displaced alphavbeta3 from focal contact points. When implanted subcutaneously into SCID mice, the alphaIIbbeta3 (+) cells developed approximately 4-fold larger tumors when compared to their mock counterparts and the level of apoptosis was reduced within the tumors. Results suggest that co-expression of the 2 beta3 integrins, alphavbeta3 and alphaIIbbeta3, in human melanoma cells enhanced cell survival and promoted growth in vivo.

Antitumor Activity and Bystander Effect of Adenovirally Delivered Tissue Inhibitor of Metalloproteinases-3

We have studied the effect of a newly identified tumor suppressor tissue inhibitor of metalloproteinases- 3 (TIMP-3) on the growth of human melanoma and squamous-cell carcinoma (SCC). Adenoviral delivery of the TIMP-3 gene to human melanoma (A2058) and SCC (UT-SCC-7) cells ex vivo inhibited tumorigenesis after subcutaneous (s.c.) injection of the infected cells into SCID/SCID mice. Three daily consecutive intratumoral injections of 1.4x10(9) plaque-forming units (pfu) of TIMP-3 adenovirus (RAdTIMP-3) inhibited the growth of preestablished melanoma and SCC xenografts in SCID/SCID mice, whereas growth of control virus-injected tumors was not affected. The antitumor effect of RAdTIMP-3 was obtained with in vivo adenoviral transduction efficiency of 8-10%, and it was more potent than that of adenovirally delivered p53. Adenovirusmediated expression of TIMP-3 potently reduced gelatinolytic activity, increased the number of apoptotic cells, and inhibited vascularization of melanomas. Escalation of the adenoviral dose to three rounds of three daily consecutive injections with 1.4x10(9) pfu of RAdTIMP-3 every 6 days entirely inhibited growth of injected melanomas for 32 days. Mixing RAdTIMP-3-infected A2058 cells with uninfected cells in 1:1 ratio in culture resulted in death of all cells in 96 hours. Adenovirally delivered TIMP-3 was also expressed by A2058 cells in soluble form into the culture medium, where it exerted a cytotoxic effect on uninfected A2058 cell cultures after relocating to the cell layer. These results identify TIMP-3 as a novel type of secreted tumor suppressor, which has antiinvasive, antiangiogenic, and proapoptotic effects in vivo, and which displays a potent bystander effect validating further exploration of its applicability in human cancer gene therapy.

Poly [N -(2-hydroxypropyl)methacrylamide] Conjugates of Bovine Pancreatic Ribonuclease (RNase A) Inhibit Growth of Human Melanoma in Nude Mice

Recently hydrophilic poly [N -(2-hydroxypropyl)methacrylamide] (PHPMA) was used for BS-RNase modification to prevent its degradation in bloodstream or fast elimination. Polymer-conjugated BS-RNase preparations proved to be cytotoxic after intravenous or intraperitoneal application, whereas native BS-RNase was ineffective. Here RNase A unimer was conjugated with two HPMA polymers (classic and star) and their antitumor effects both in vitro and in vivo were compared with those of BS-RNase polymers. Surprisingly, the antitumor effect of RNase A conjugates was also pronounced. The RNase A conjugates (classic and star) injected intravenously to mice bearing melanoma tumor caused a significant reduction in tumor volume following ten doses of 5 and 1 mg/kg, respectively. Despite the antitumor activity observed in vivo, the in vitro tested cytotoxic activity of RNase A did not differ from that caused by native RNase A while native BS-RNase (50 μ g/ml) totally inhibited DNA synthesis in treated cells. The experiments with 125 I-labeled preparations demonstrated concentration-dependent internalization of native BS-RNase by tumor cells within an hour, whereas the polymer conjugate (S-BS) was not internalized. On the contrary, the in vivo experiments showed that whereas 40% of S-BS conjugate persisted in bloodstream for 24 h after administration, 98% of the native BS-RNase was already eliminated. Improved antitumor activities of PHPMA-modified RNases in vivo might be ascribed to their prolonged retention in bloodstream, better proteolytic stability and resistance to the action of the ribonuclease inhibitor.

17β-estradiol, Progesterone, and Dihydrotestosterone Suppress the Growth of Human Melanoma by Inhibiting Interleukin-8 Production

We studied the effects of 17beta-estradiol, progesterone, and dihydrotestosterone on in vitro growth of human metastatic melanoma. Each sex hormone inhibited the growth of melanoma receptor-dependently; 17beta-estradiol inhibited 3H-thymidine uptake of estrogen receptor-positive WM266-4 and NM26, but not that of the receptor-negative HS15. Progesterone inhibited 3H-thymidine uptake of progesterone receptor-positive WM266-4 and HS15, but not that of the receptor-negative NM26. Dihydrotestosterone inhibited 3H-thymidine uptake of androgen receptor-positive HS15 and NM26, but not that of the receptor-negative WM266-4. The growth inhibition by each hormone was counteracted by the respective hormone receptor antagonist. The combination of more than two hormones neither gave additive nor synergistic growth inhibition. The growth inhibition by each sex hormone was counteracted by interleukin-8 but not by the other growth factors. Each sex hormone reduced the constitutive interleukin-8 secretion and mRNA levels in the respective receptor-positive melanoma but not in the receptor-negative melanoma. Transient transfection showed that each sex hormone inhibited the constitutive chloramphenicol acetyltransferase expression driven by interleukin-8 promoter in the respective receptor-positive melanoma but not in the receptor-negative melanoma. Transfection with a series of 5'-deleted interleukin-8 promoter/chloramphenicol acetyltransferase reporter constructs demonstrated that the sequences between -98 and -63 bp on interleukin-8 promoter may be involved in the transcriptional repression. These data suggest that 17beta-estradiol, progesterone, and dihydrotestosterone suppress the growth of melanoma by inhibiting interleukin-8 production in a receptor-dependent manner.

Gangliosides GD1b, GT1b, and GQ1b Suppress the Growth of Human Melanoma by Inhibiting Interleukin-8 Production: the Inhibition of Adenylate Cyclase

We studied the effects of various gangliosides on in vitro growth of human metastatic melanoma WM266-4. GD1b, GT1b, and GQ1b inhibited 3H-thymidine uptake and growth rate of WM266-4 whereas the other gangliosides were ineffective. The growth inhibition by GD1b, GT1b, and GQ1b was counteracted by interleukin-8 but not by the other growth factors. The growth inhibition by gangliosides was not detected in the presence of anti-interleukin-8 antibody. GD1b, GT1b, and GQ1b reduced the constitutive interleukin-8 secretion and mRNA levels in WM266-4. Transient transfection showed that GD1b, GT1b, and GQ1b inhibited the constitutive chloramphenicol acetyltransferase expression driven by interleukin-8 promoter in WM266-4. Transfection with a series of 5'-deleted mutants demonstrated that the sequences between -98 and -62 bp on interleukin-8 promoter may be involved in the transcriptional repression by these gangliosides. Cyclic AMP analog dibutyryl cAMP counteracted GD1b, GT1b, and GQ1b-induced inhibition of interleukin-8 production at the levels of protein secretion, mRNA expression, and promoter activity. GD1b, GT1b, and GQ1b reduced cAMP level and protein kinase A activity in WM266-4. These gangliosides suppressed adenylate cyclase activity without altering that of cyclic nucleotide phosphodiesterase in WM266-4. The data indicate that GD1b, GT1b, and GQ1b may suppress the growth of melanoma by inhibiting interleukin-8 production via the inhibition of adenylate cyclase.

Growth of human melanoma xenografts is suppressed by systemic angiostatin gene therapy.

The effect of local and systemic delivery of the angiostatin gene on human melanoma growth was studied in nude mice. Liposome-coated plasmids carrying the cDNA coding for murine and human angiostatin (CMVang and BSHang) were injected weekly, locally or systemically, in mice transplanted with melanoma cells. The treatment reduced melanoma growth by 50% to 90% compared to that occurring in control animals treated with liposome-coated plasmid carrying the lacZ gene or in untreated controls. The growth of both locally injected and controlateral uninjected tumors in mice bearing two melanoma grafts was significantly suppressed after intratumoral treatment. Tumor growth inhibition was also observed in mice treated by intraperitoneal delivery, suggesting that angiostatin gene therapy acts through a systemic effect. Both melanoma growth suppression and delay in the onset of tumor growth were observed in treated mice. PCR performed on tumors and normal tissues showed that the lipofected DNA was present in tissues from treated mice, and angiostatin expression was demonstrated by RT-PCR. Histopathological analysis of melanoma nodules revealed an increase in apoptotic cells and a reduction in vessel density in tumors from treated mice. Our results suggest that systemic, liposome-mediated administration of genes coding for antiangiogenic factors represents a promising strategy for melanoma treatment in humans.

A New Cytotoxic Saponin from Pulsatilla patens var. multifida

A new oleanane-type glycoside was isolated from the methanolic extract of the roots of Pulsatilla patens var. multifida (Ranunculaceae). Its structure was identified as 3- O -ß-D-glucopyranosyl-(1 ? 2)-ß-D-galactopyranosyl hederagenin 28- O -a-L-rhamnopyranosyl-(1 ? 4)-ß-D-glucopyranosyl-(1 ? 6)-ß-D-glucopyranosyl ester by interpretation of the spectroscopic data and partial hydrolysis. The saponin inhibited the growth of human melanoma A 375 cells.

In vivo therapy of malignant melanoma by means of antagonists of αv integrins

Integrin αvβ3 (vitronectin receptor) has been implicated in human malignant melanoma progression and angiogenesis as a receptor that provides survival signals. However, little is known about the therapeutic potential of antagonists of αvβ3. In this report, we characterize the activities of 2 antagonists of αvβ3 integrins: a human specific monoclonal antibody (MAb), 17E6, and a cyclic RGD peptide that blocked cell adhesion and induced detachment of previously substrate-attached cells in vitro. In vivo, αvβ3 antagonists behaved as anti-tumor drugs in a dose- and time-dependent manner. Moreover, different therapeutic treatments proved to be effective even in the therapy of established macroscopic tumor masses, thus supporting the use of these antagonists in clinical therapy. Using a panel of 6 human melanomas and 5 carcinomas, MAb 17E6 efficiently blocked the in vivo tumor growth of melanomas expressing αvβ3 as xenografts but did not affect the αvβ3-negative (although αv integrin-positive) tumors. This demonstrated that αvβ3 is a pivotal integrin for the growth of human melanomas. Furthermore, since MAb 17E6 does not recognize murine αvβ3, the effect is due only to the direct anti-tumor activity and not to the well-known anti-angiogenic activity of αv-integrin antagonists. Taken together, our results confirm the essential role of αvβ3 integrin in the growth of human malignant melanoma in vivo and provide strong evidence of the therapeutic potential of αv-integrin antagonists for the treatment of such tumors. Int. J. Cancer 87:716–723, 2000. © 2000 Wiley-Liss, Inc.

Inhibition of tumor growth and metastasis of human melanoma by intracellular anti-ATF-1 single chain Fv fragment.

Activating transcription factor-1 (ATF-1) and cAMP-responsive element (CRE)-binding protein (CREB) have been implicated in cAMP and Ca2+-induced transcriptional activation. The expression of the transcription factors CREB and ATF-1 is upregulated in metastatic melanoma cells. However, how overexpression of ATF-1/CREB contributes to the acquisition of the metastatic phenotype remains unclear. Here, the effect of disrupting ATF-1 activity was investigated using intracellular expression of an inhibitory anti-ATF-1 single chain antibody fragment (ScFv). Intracellular expression of ScFv anti-ATF-1 in MeWo melanoma cells caused significant reduction in CRE-dependent promoter activation. In addition, expression of ScFv anti-ATF-1 in melanoma cells suppressed their tumorigenicity and metastatic potential in nude mice. ScFv anti-ATF-1 rendered the melanoma cells susceptible to thapsigargin-induced apoptosis in vitro and caused massive apoptosis in tumors transplanted subcutaneously into nude mice, suggesting that ATF-1 and its associated proteins act as survival factor for human melanoma cells. This is the first report to demonstrate the potential of ScFv anti-ATF-1 as an inhibitor of tumor growth and metastasis of solid tumor in vivo. Oncogene (2000).

Effects of Betulinic Acid Alone and in Combination with Irradiation in Human Melanoma Cells

Recently, betulinic acid was identified as a highly selective inhibitor of human melanoma growth and was reported to induce apoptosis in these cells. We have investigated the growth-inhibitory properties of this compound alone and in combination with ionizing radiation in a panel of established human melanoma cell lines as well as in normal human melanocytes. Betulinic acid strongly and consistently suppressed the growth and colony-forming ability of all human melanoma cell lines investigated. In combination with ionizing radiation the effect of betulinic acid on growth inhibition was additive in colony-forming assays. Betulinic acid also induced apoptosis in human melanoma cells as demonstrated by Annexin V binding and by the emergence of cells with apoptotic morphology. The growth-inhibitory action of betulinic acid was more pronounced in human melanoma cell lines than in normal human melanocytes. Notably, despite the induction of apoptosis, analysis of the expression of Bcl-2 family members in betulinic-acid-treated cells revealed that expression of the anti-apoptotic protein Mcl-1 was induced. Furthermore, the antiproliferative action of betulinic acid seemed to be independent of the p53 status. The properties of betulinic acid make it an interesting candidate, not only as a single agent but also in combination with radiotherapy. We conclude that the strictly additive mode of growth inhibition in combination with irradiation suggests that the two treatment modalities may function by inducing different cell death pathways or by affecting different target cell populations.

In vivo therapy of malignant melanoma by means of antagonists of αv integrins

Integrin alphavbeta3 (vitronectin receptor) has been implicated in human malignant melanoma progression and angiogenesis as a receptor that provides survival signals. However, little is known about the therapeutic potential of antagonists of alphavbeta3. In this report, we characterize the activities of 2 antagonists of alphavbeta3 integrins: a human specific monoclonal antibody (MAb), 17E6, and a cyclic RGD peptide that blocked cell adhesion and induced detachment of previously substrate-attached cells in vitro. In vivo, alphavbeta3 antagonists behaved as anti-tumor drugs in a dose- and time-dependent manner. Moreover, different therapeutic treatments proved to be effective even in the therapy of established macroscopic tumor masses, thus supporting the use of these antagonists in clinical therapy. Using a panel of 6 human melanomas and 5 carcinomas, MAb 17E6 efficiently blocked the in vivo tumor growth of melanomas expressing alphavbeta3 as xenografts but did not affect the alphavbeta3-negative (although alphav integrin-positive) tumors. This demonstrated that alphavbeta3 is a pivotal integrin for the growth of human melanomas. Furthermore, since MAb 17E6 does not recognize murine alphavbeta3, the effect is due only to the direct anti-tumor activity and not to the well-known anti-angiogenic activity of alphav-integrin antagonists. Taken together, our results confirm the essential role of alphavbeta3 integrin in the growth of human malignant melanoma in vivo and provide strong evidence of the therapeutic potential of alphav-integrin antagonists for the treatment of such tumors.

Novel Ras antagonist blocks human melanoma growth.

During past decades, knowledge of melanoma biology has increased considerably. Numerous therapeutic modalities based on this knowledge are currently under investigation. Advanced melanoma, nevertheless, remains a prime example of poor treatment response that may, in part, be the consequence of activated N-Ras oncoproteins. Besides oncogenic Ras, wild-type Ras gene products also play a key role in receptor tyrosine kinase growth factor signaling, known to be of importance in oncogenesis and tumor progression of a variety of human neoplasms, including malignant melanoma; therefore, it is reasonable to speculate that a pharmacological approach that curtails Ras activity may represent a sensible approach to inhibit melanoma growth. To test this concept, the antitumor activity of S-trans, trans-farnesylthiosalicylic acid (FTS), a recently discovered Ras antagonist that dislodges Ras from its membrane-anchoring sites, was evaluated. The antitumor activity of FTS was assessed both in vitro and in vivo in two independent SCID mouse xenotransplantation models of human melanoma expressing either wild-type Ras (cell line 518A2) or activated Ras (cell line 607B). We show that FTS (5-50 microM) reduces the amounts of activated N-Ras and wild-type Ras isoforms both in human melanoma cells and Rat-1 fibroblasts, interrupts the Ras-dependent extracellular signal-regulated kinase in melanoma cells, inhibits the growth of N-Ras-transformed fibroblasts and human melanoma cells in vitro and reverses their transformed phenotype. FTS also causes a profound and statistically significant inhibition of 518A2 (82%) and 607B (90%) human melanoma growth in SCID mice without evidence of drug-related toxicity. Our findings stress the notion that FTS may qualify as a novel and rational treatment approach for human melanoma and possibly other tumors that either carry activated ras genes or rely on Ras signal transduction more heavily than nonmalignant cells.

Role of AP-2 in tumor growth and metastasis of human melanoma.

We previously demonstrated that expression of the cell surface adhesion molecule MCAM/MUC18 correlates directly with the metastatic potential of human melanoma cells. In addition, the progression of human melanoma towards the metastatic phenotype is associated with loss of expression of the tyrosine-kinase receptor c-KIT. This review summarizes our recent data demonstrating that the expression of both genes is regulated by the AP-2 transcription factor. Moreover, we have observed a loss of AP-2 expression in metastatic melanoma cells. Re-expression of AP-2 in the highly metastatic A375SM cells decreased their tumorigenicity and inhibited their metastatic potential in nude mice. MCAM/MUC18 mRNA and protein expression was significantly downregulated while c-KIT expression was upregulated in the AP-2 transfected cells. Since AP-2 also regulates other genes that are involved in the progression of human melanoma such as E-cadherin, MMP-2, p21WAF-1, HER-2, BCL-2, and insulin like growth factor receptor-1, we propose that loss of AP-2 is a crucial event in the development of malignant melanoma.

Blocking of Ras function by a competitive Ras antagonist inhibits human melanoma growth

Blocking of Ras function by a competitive Ras antagonist inhibits human melanoma growth

Dominant-negative CREB inhibits tumor growth and metastasis of human melanoma cells.

The ATF/CREB family of eukaryotic transcription factors contain the bZIP structural motif and mediate their transcriptional activities via heterodimerization with ATF and AP-1 family members. Quenching of CREB-associated proteins by a dominant-negative CREB (KCREB) that is mutated within its DNA-binding domain decreases radiation resistance of human melanoma cells. The purpose of this study was to determine the role of CREB in tumor growth and metastasis of human melanoma using KCREB. Highly metastatic MeWo human melanoma cells were transfected with the KCREB expression vector and subsequently analysed for changes in their tumorigenic and metastatic potential. Expression of KCREB in MeWo human cells decreased their tumorigenic and metastatic potential in nude mice compared with parental and control transfected cells. The KCREB-transfected cells displayed downregulation of 72 kDa collagenase type IV (MMP-2) mRNA expression and activity and decreased invasiveness through Matrigel-coated filters. Moreover, transcriptional activities mediated by the CAT gene driven by the MMP-2 promoter were decreased by 14-45-fold in KCREB-transfected cells. In addition, the cell-surface adhesion molecule MCAM/MUC18 that is involved in metastasis of human melanoma was downregulated in the KCREB-transfected cells. These data indicate that, through their transcriptional activities, CREB and its associated proteins play an important role in the acquisition of the metastatic phenotype of human melanoma cells.

Bioorganometallic chemistry--synthesis and antitumor activity of cobalt carbonyl complexes.

The interaction of organometallic compounds with biological systems, generally called bioorganometallic chemistry, is receiving increasing interest. We present the first part of our studies concerning the biological activity of organometallic compounds. Several alkyne-cobalt carbonyl complexes inhibited the growth of human melanoma and lung carcinoma cell lines. They are more active than uncomplexed dicobalt octacarbonyl, cobalt chloride, or the free ligand. A significant difference in potency towards the lung carcinoma cell line was observed among the cobalt complexes, indicating that the complexed ligand may influence cytotoxic activity. These results suggest that further exploratory work with such cobalt-alkyne complexes is warranted.