Basic fibroblast growth factor production and growth factor receptors as potential targets for melanoma therapy

The molecular basis of melanomagenesis and the metastatic phenotype

The last two decades have seen spectacular advances in our understanding of the biology of melanoma and, in particular, have elucidated the mechanisms operative in disease initiation and progression. With respect to the former, the genetics of melanoma and in particular the impact of genetic defects on dysregulation of the cell cycle are key issues in malignant transformation and are a major focus of this review. With respect to the latter, consideration also is given to the acquisition of growth factor autonomy and the capacity for invasion and metastasis from the standpoint of cell adhesion, motility, and matrix digestion. These events have specific morphologic correlates that will be briefly addressed. Where relevant, we will address certain of the modern pharmacogenetic strategies that flow from these novel observations concerning melanoma biology.

Anti-tumor effect in an in vivo model by human-derived pancreatic RNase with basic fibroblast growth factor insertional fusion protein through antiangiogenic properties

It is thought that the export of angiogenic fibroblast growth factors (FGF) from tumors may be involved in the onset of tumor angiogenesis. To create a new active targeting drug that inhibits the tumor angiogenic process without toxicities to normal cells, human basic FGF (h-bFGF) was inserted genetically into the Gly89 position of cross-linked RNase1 (the ribonuclease inhibitor protein [RI] binding site of cross-linked human pancreatic RNase) to prevent stereospecific binding to RI. The resultant insertional-fusion protein (CL-RFN89) was active both as h-bFGF and as RNase1. Furthermore, it acquired an additional ability of evading RI through steric blockade of RI binding caused by the fused h-bFGF domain. In the present study, the effect of the resultant protein, CL-RFN89, on the antitumor response though its antiangiogenic properties was investigated in an in vivo model. Continuous systemic treatment with CL-RFN89 significantly inhibited the growth of human A431 squamous cell carcinomas in vivo. Seven days of treatment with CL-RFN89 resulted in a 58.2% inhibition of tumor growth compared with control mice (P < 0.0001). Furthermore, immunohistochemistry using a rat antimouse CD31 antibody showed that treatment with CL-RFN89 reduced tumor vascularization. These findings identify CL-RFN89 as a potent systemic inhibitor of tumor growth as a result of its antiangiogenic properties. This protein appears to be a new systemic antitumor agent.

Parallel expression of αIIbβ3 and αvβ3 integrins in human melanoma cells upregulates bFGF expression and promotes their angiogenic phenotype

Previous studies indicated that transfection of the platelet integrin alphaIIbbeta3 into human melanoma cells expressing integrin alphavbeta3 promoted their in vivo (but not in vitro) growth and cell survival. To reveal the underlying pathomechanism, we have analyzed the angiogenic phenotype of alphaIIbbeta3 integrin-transduced human melanoma cells expressing integrin alphavbeta3. Upon heterotopic or orthotopic (intracutaneous) injections into SCID mice, the alphaIIbbeta3 integrin-overexpressing clones, ESL, ESH, 19L and 19H, grew more rapidly than the mock transfectant (alphavbeta3 expressing) clone, 3.1P. Morphometry demonstrated an increased intratumoral microvessel density in 19L and 19H tumors compared to 3.1P. Immunocytochemistry and flow cytometry indicated that vascular endothelial growth factor (VEGF) is constitutively expressed in the majority of the cells of both the mock and the alphaIIbbeta3 integrin-transfected clones. However, the mock transfectant clone, 3.1P, did not express basic fibroblast growth factor (bFGF) at protein level (<1%), unlike the alphaIIbbeta3 integrin-transfected clones, 19L and 19H, (33.9 and 84.1%, respectively). Quantitative PCR analysis of 6 related human melanoma clones with various levels of alphaIIbbeta3 integrin expressions revealed a correlation between the alphaIIb protein and bFGF mRNA expressions. Furthermore, cDNA microarray analysis of the 19H cells revealed 12 downregulated and 36 upregulated genes [among them 3 upregulated vasculogenic mimicry-genes (CD34, endothelin receptor B, Prostaglandin I-2 synthase)] when compared to 3.1P cells. The altered bFGF expression may be influenced by integrin-linked signaling, since bbeta3-endonexin is upregulated in alphaIIbbeta3-transfected cells and tyrosine kinase inhibitors downregulate bFGF both at mRNA and protein levels. We propose here that the illegitimate expression of alphaIIbbeta3 integrin in human melanoma cells already expressing alphavbeta3 integrin may alter their in vivo growth properties due to the modulation of their angiogenic phenotype.

Ethanol induces transforming growth factor-alpha expression in hepatocytes, leading to stimulation of collagen synthesis by hepatic stellate cells

BACKGROUND

Liver fibrosis often develops in alcoholic liver diseases without accompanying inflammation; however, the underlying mechanism is unclear. Using ethanol-exposed human HepG2 hepatoblastoma cells as a model for alcoholic liver diseases, we previously found that ethanol exposure causes HepG2 cells to secrete an approximately 6,000 Da nonheparin-binding polypeptide that stimulates collagen synthesis in human IMR-90 fibroblasts. The aim of the current study was to characterize and identify this factor.

METHODS

Concentration of type I procollagen peptide and transforming growth factor (TGF)-alpha was assessed by enzyme-linked immunosorbent assay. TGF-alpha protein expression was examined by Western blot. Type I collagen messenger RNA expression in rat hepatic stellate cells was assessed by reverse transcription-polymerase chain reaction.

RESULTS

The collagen-stimulating activity in conditioned media from ethanol-exposed HepG2 cells to stimulate type I procollagen peptide synthesis of IMR-90 cells was specifically inhibited by addition of anti-TGF-alpha antibodies. Western blot analysis showed increased TGF-alpha protein expression in ethanol-treated HepG2 cells. TGF-alpha in conditioned medium from ethanol-exposed HepG2 cells stimulated type-I collagen messenger RNA expression in rat hepatic stellate cells.

CONCLUSIONS

These results suggest that TGF-alpha derived from ethanol-exposed hepatocytes may contribute to the development of hepatic fibrosis in alcoholic liver diseases.

Kinase inhibitors in cancer therapy: a look ahead

The most essential kinases involved in cell membrane receptor activation, signal transduction and cell cycle control or programmed cell death and their interconnections are reviewed. In tumours, the genes of many of those kinases are mutated or amplified or the proteins are overexpressed. The use of key kinases offers the possibility to screen in vitro for synthetic small molecule kinase inhibitors. In view of the many interconnections of cellular kinases, their role in preventing or inducing programmed cell death and the possibility that a considerable number of signal transducing proteins are still unknown, cellular test systems are recommended in which the respective key kinase or one of its main partner molecules are overexpressed.

Inhibition of cell growth by a fused protein of human ribonuclease 1 and human basic fibroblast growth factor

Pancreatic-type RNases are considered to have cytotoxic potential due to their ability to degrade RNA molecules when they enter the cytosol. However, most of these RNases show little cytotoxicity because cells have no active uptake mechanism for these RNases and because the ubiquitous cytoplasmic RNase inhibitor is considered to play a protective role against the endocytotic leak of RNases from the outside of cells. To study the cytotoxic potential of RNase toward malignant cells targeting growth factor receptors, the C-terminus of human RNase 1 was fused to the N-terminus of human basic fibroblast growth factor (bFGF). This RNase-FGF fused protein effectively inhibited the growth of mouse melanoma cell line B16/BL6 with high levels of cell surface FGF receptor. This effect appeared to result from prolongation of the overall cell cycle rather than the killing of cells or specific arrest in a particular phase of the cell cycle. Thus, human RNase 1 fused to a ligand of cell surface molecules, such as the FGF receptor, is shown to be an effective candidate for a selective cell targeting agent with low toxic effects on normal cell types.

Design, synthesis, and evaluation of mitomycin-tethered phosphorothioate oligodeoxynucleotides

Mitomycin C (1) is the prototypical bioreductive alkylating agent. Studies have shown that mitomycin C and its derivatives selectively alkylate guanine residues within di- and trinucleotide DNA sequences. This investigation sought to improve the selective DNA bonding properties of the mitomycins by coupling them with antisense oligodeoxynucleotides. Two procedures were developed that allowed the attachment of a phosphorothioate oligodeoxynucleotide containing a hexylamino spacer at the 5' terminus with a C(10)-activated mitomycin. In the first procedure, decarbamoylation of 1 (NaOCH3/ benzene) afforded 10-decarbamoylmitomycin C (10), which was treated with either dimethyl sulfate or methylthiochloroformate and base to yield 10-decarbamoylporfiromycin (11) and N(1a)-[(methylthio)-carbonyl]-10-decarbamoylmitomycin C (12), respectively. Activation of the C(10) site in 11 and 12 with 1,1'-carbonyldiimidazole or with 1,1'-thiocarbonyldiimidazole provided the N(1a)-substituted mitomycin 10-decarbamoyl-10-O-carbonylimidazoles (5, 7) and 10-decarbamoyl-10-O-thiocarbonylimidazoles (6, 8), respectively. Compounds 5-8 were reacted with glycine methyl ester hydrochloride (17) and base in both methylene chloride and aqueous buffered solutions to determine the ease and efficiency in which these C(10)-activated mitomycin derivatives coupled to amines. It was found that 5-8 all reacted with 17 in methylene chloride to give the coupled products 18-21 but that improved amine coupling yields in water were observed for the 10-decarbamoyl-10-O-thiocarbonylimidazoles 6 and 8 as compared with the 10-decarbamoyl-10-O-carbonylimidazoles 5 and 7. This finding led to the coupling of the phosphorothioate oligodeoxynucleotide, H2N(CH2)6-P(S)(OH)-GGCCCCGTG-GTGGCTCCAT (22) to 8. Compound 22 complemented a 19-base sequence in the translation initiation region of the human A-raf-1 gene. Use of excess 8 (28 equiv) with 22 gave only a 36% yield of the coupled product 23, which proved difficult to separate from 22. In the second procedure, phosphorothioate oligodexynucleotides that contained a hexylamino spacer at the 5'termini were coupled to 10-des(carbamoyloxy)-10-isothiocyanatoporfiromycin (9). Compound 9 was prepared in four steps from 11. Mesylation (methanesulfonyl chloride/pyridine) of 11 gave the C(10) mesylate 13, which was then treated with NaN3 (dimethylformamide, 90 degrees C) to give 10-des(carbamoyloxy)-10-azidoporfiromycin (14). Catalytic reduction (PtO2, H2) of 14 in pyridine afforded C(10) amine 15. Treatment of 15 with di-2-pyridyl thionocarbonate provided the desired 10-des(carbamoyloxy)-10-isothiocyanatoporfiromycin (9). Compound 9 readily coupled with 17 and base in both methylene chloride and aqueous buffered solutions to give 25. Use of the 5'hexylaminophosphorothioate oligodeoxynucleotides 32-35 in place of 17 gave the conjugated adducts 28-31, respectively, in a 12% to near-quantitative yield. The products were purified by semipreparative HPLC. Antisense agents 28-31 were designed to target a 30-base-long region from the coding region of the human FGFR1 gene. One adduct, 29, reduced the number of FGFR1 receptors in human aortic smooth cells for bFGF on the cell surface, which suggested down-regulation of FGFR1 gene expression. Further, 29 inhibited cultured human aortic smooth muscle cell proliferation and was less cytotoxic than porfiromycin (2). The biological assay data suggest that the phosphorothioate oligodexynucleotide porfiromycin conjugates may be more target selective and less toxic than either mitomycin or porfiromycin and thus be promising therapeutic agents.

Adenovirus-mediated gene transfer of wild-type p53 results in melanoma cell apoptosis in vitro and in vivo

Gene transfer techniques may provide efficient treatment for a variety of malignant neoplasms. A replication-deficient adenovirus (Ad) vector which carries the cDNA for wild-type p53 (AdCMV.p53) was tested for its in vitro and in vivo effects on the growth of murine melanoma cell line B16-G3.26 and human melanoma cell line SK-MEL-24. The growth of B16-G3.26 cells infected with AdCMV.p53 was inhibited when compared to the uninfected cells or cells infected with the control vector AdCMV.NLS beta gal. Similarly, the growth of SK-MEL-24 cells infected with AdCMV.p53 was also below that of AdCMV.NLS beta gal-infected and uninfected controls. DNA laddering using agarose gel electrophoresis and in situ labeling of DNA fragmentation (TUNEL) showed that AdCMV.p53-infected murine and human melanoma cells underwent apoptosis. Nude mice injected s.c. either with B16-G3.26 cells or with SK-MEL-24 cells developed localized tumors. These tumors were subsequently infiltrated with either AdCMV.p53, AdCMV.NLS beta gal or saline alone. One week after infection, B16-G3.26 tumors exposed to AdCMV.p53 were 2.5 times smaller than control tumors and exhibited DNA fragmentation. A similar growth-inhibitory effect of AdCMV.p53 was observed with SK-MEL-24 tumors. Thus, Ad-mediated wild-type p53 overexpression resulted in melanoma cell apoptosis and inhibition of melanoma growth in vitro and in vivo. These gene therapy approaches may be useful in targeting rapidly growing, malignant melanomas in a clinical setting.

Autocrine down-regulation of basic fibroblast growth factor receptors causes mitotoxin resistance in a human melanoma cell line

The ability of melanoma to develop resistance to mitotoxins, growth-factor-directed anti-neoplastic agents that offer potential for the treatment of this highly refractory disease, may limit therapeutic efficacy. To address this problem, we developed a subcloned human melanoma cell line that is resistant to the mitotoxin composed of basic fibroblast growth factor conjugated to the ribosome-inactivating protein saporin. Resistance was caused by autocrine FGF ligands, which down-regulate bFGF receptors and reduce bFGF-saporin binding. Inhibiting the autocrine loop with suramin or with neutralizing antibodies to FGF up-regulated receptors and decreased resistance in vitro. Furthermore, suramin restored sensitivity in resistant tumor xenografts. These results suggest the potential of therapeutic modalities combining agents that neutralize growth factors with receptor-directed mitotoxins for targeting malignant melanoma either to prevent emergence of resistance or to circumvent resistance once it occurs.

Antisense oligodeoxynucleotides for IL-2, c-myc and transferrin receptor synchronize mitogen-activated lymphocytes in the G1 phase

In order to clarify the role and interrelationship of c-myc, interleukin-2 (IL-2), and transferrin receptor (TfR) expressions on PHA-stimulated lymphocyte proliferation, we examined the effects of antisense oligodeoxynucleotides directed against c-myc, TfR, and IL-2 mRNAs on DNA synthesis and cell-cycle phase. Exposure of PHA-stimulated lymphocytes to each antisense oligomer resulted in approximately 75-80% inhibition of DNA synthesis. TfR expression was not inhibited in PHA-stimulated lymphocytes by c-myc or IL-2 antisense oligonucleotides, suggesting that the expression of c-myc, TfR, and of IL-2 is regulated by an independent mechanism. All three antisense oligonucleotides for c-myc, TfR and IL-2 synchronized mitogen-activated lymphocytes to the G1 phase as assessed by morphologic blast formation and cell-cycle phase analysis.

Expression of growth factor receptors on human melanoma cells: comparison of modulating effects of interferons and retinoids

Autocrine and paracrine growth factors are important mediators in malignant transformation. Interferons (IFN) and retinoids (RX) are well-known differentiative and immunomodulating agents with effects on subsets of different human tumors including malignant melanoma. In this study, we examined the modulating effects of three IFN and seven different RX on human melanoma cell lines regarding growth factor receptor expression. Growth factor receptor expression, including PDGF-R, NGF-R, EGF-R, IR, IGF-I-R, TFR and c-kit, was studied by immunohistochemistry and FACSscan analysis. Both groups of substances modulated the expression of some growth factor receptors. Upregulation of PDGF-R was seen after treatment with IFN as well as with RX. In contrast, EGF-R was found to be downregulated in two EGF-R-positive cell lines by IFN and, on the other hand, induced by RX in two EGF-R-negative cell lines. The expression of NGF-R was modulated ambiguously by these substances but demonstrated a cell line specificity in the different melanoma cell lines tested. Additionally, some of the tested growth factor receptors were not markedly changed regarding their expression by treatment with IFN and RX (IR, IGF-I-R, c-kit, TFR).