Antitumor and antimetastatic activity of ribozymes targeting the messenger RNA of vascular endothelial growth factor receptors

Chemically stabilized hammerhead ribozymes are nuclease-resistant, RNA-based oligonucleotides that selectively bind and cleave specific target RNAs. Due to their potential for specifically inhibiting gene expression, ribozymes are being investigated for therapeutic applications as well as for the elucidation of gene function. In particular, we have investigated ribozymes that target the mRNA of the vascular endothelial growth factor (VEGF) receptors because VEGF signaling is an important mediator of tumor angiogenesis and metastasis. Here we report pharmacodynamic studies testing anti-Flt-1 (VEGFR-1) and anti-KDR (VEGFR-2) ribozymes in animal models of solid tumor growth and metastasis. Ribozymes targeting either Flt-1 or KDR significantly inhibited primary tumor growth in a highly metastatic variant of Lewis lung carcinoma. However, only treatment with the anti-Flt-1 ribozyme resulted in a statistically significant and dose-dependent inhibition of lung metastasis in this model. The anti-Flt-1 ribozyme was then tested in a xenograft model of human metastatic colorectal cancer in which significant inhibition of liver metastasis was observed. Taken together, these data represent the first demonstration that synthetic ribozymes targeting VEGF receptor mRNA reduced the growth and metastasis of solid tumors in vivo.

Bioactivity of anti-angiogenic ribozymes targeting Flt-1 and KDR mRNA

Vascular endothelial growth factor (VEGF) and its receptors Flt-1 and KDR play important roles in physiological and pathological angiogenesis. Ribozymes that target the VEGF receptor mRNAs were developed and their biological activities in cell culture and an animal model were assessed. Ribozymes targeting Flt-1 or KDR mRNA sites reduced VEGF-induced proliferation of cultured human vascular endothelial cells and specifically lowered the level of Flt-1 or KDR mRNA present in the cells. Anti- Flt-1 and KDR ribozymes also exhibited anti-angiogenic activity in a rat corneal pocket assay of VEGF-induced angiogenesis. This report illustrates the anti-angiogenic potential of these ribozymes as well as their value in studying VEGF receptor function in normal and pathophysiologic states.

Identification of constitutive and gamma-interferon- and interleukin 4-regulated proteins in the human renal carcinoma cell line ACHN

The effects of IFN-gamma and interleukin 4 (IL-4) on cell proliferation and two-dimensional gel electrophoretic protein patterns of the human renal carcinoma cell line ACHN were studied. Treatment of the cells with IFN-gamma resulted in a 40-50% decrease in their proliferation. IL-4 treatment resulted in a 30-40% decrease. Treating cells with both cytokines had the same effect as with IFN-gamma alone, thus precluding a synergistic antiproliferative interaction of these two cytokines. To identify IL-4- and IFN-gamma-regulated proteins in ACHN, two-dimensional preparative gel electrophoresis was used, combined with either capillary electrophoresis or high-performance liquid chromatography and either Edman or mass spectrometric sequencing. The following cytokine-induced proteins were identified: tropomyosin, heat shock protein 27, manganese superoxide dismutase, glutathione S-transferase pi, and protein kinase C inhibitor I. Tropomyosin increased 2-fold when cells were treated with IFN-gamma. Levels of heat shock protein 27 increased 2-fold with IL-4, 3-fold with IFN-gamma, and 4-fold when the cytokines were used in combination. Manganese superoxide dismutase increased 3-fold with IFN-gamma but was unaffected by IL-4. Glutathione S-transferase pi increased 3-fold with IFN-gamma. Levels of protein kinase C inhibitor I increased greater than 3-fold with IL-4, 4-fold with IFN-gamma, and 7-fold when both cytokines were used. In addition, the following constitutive ACHN proteins were identified: copper zinc superoxide dismutase, 60S acidic ribosomal protein P2, and a second heat shock protein 27 isoform. These findings help define the biochemical modes of action of IFN-gamma and IL-4 and their potential in the biological therapy of renal cell carcinoma.

Immobilized pH gradient two-dimensional gel electrophoresis and mass spectrometric identification of cytokine-regulated proteins in ME-180 cervical carcinoma cells

Two-dimensional (2-D) polyacrylamide gel electrophoresis combined with mass spectrometry is a powerful combination of technologies that allows high resolution separation of proteins and their rapid identification. Immobilized pH gradient (IPG) first-dimensional gels have several advantages over carrier ampholyte isoelectric focusing, including a high degree of reproducibility, good protein spot resolution, and a selection of pH range. Here we demonstrate the utility and efficacy of combining IPG 2-D gel electrophoresis with mass spectrometry to identify interferon-gamma- (IFN) and tumor necrosis factor (TNF)-regulated proteins in ME-180 cervical carcinoma cells. Three cytokine-regulated proteins have been identified, using imidazole-zinc-stained preparative IPG 2-D gels and in-gel tryptic digestion followed by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry for determination of peptide masses and sequences: 1) triosephosphate isomerase, a glycolytic pathway enzyme, 2) proteasome subunit C3, which is important in protein degradation, and 3) Ran, a GTP-binding protein important in cell cycle regulation, protein import into the nucleus, and RNA export from the nucleus.

Rapid mass spectrometric peptide sequencing and mass matching for characterization of human melanoma proteins isolated by two-dimensional PAGE

We report a general mass spectrometric approach for the rapid identification and characterization of proteins isolated by preparative two-dimensional polyacrylamide gel electrophoresis. This method possesses the inherent power to detect and structurally characterize covalent modifications. Absolute sensitivities of matrix-assisted laser desorption ionization and high-energy collision-induced dissociation tandem mass spectrometry are exploited to determine the mass and sequence of subpicomole sample quantities of tryptic peptides. These data permit mass matching and sequence homology searching of computerized peptide mass and protein sequence data bases for known proteins and design of oligonucleotide probes for cloning unknown proteins. We have identified 11 proteins in lysates of human A375 melanoma cells, including: alpha-enolase, cytokeratin, stathmin, protein disulfide isomerase, tropomyosin, Cu/Zn superoxide dismutase, nucleoside diphosphate kinase A, galaptin, and triosephosphate isomerase. We have characterized several posttranslational modifications and chemical modifications that may result from electrophoresis or subsequent sample processing steps. Detection of comigrating and covalently modified proteins illustrates the necessity of peptide sequencing and the advantages of tandem mass spectrometry to reliably and unambiguously establish the identity of each protein. This technology paves the way for studies of cell-type dependent gene expression and studies of large suites of cellular proteins with unprecedented speed and rigor to provide information complementary to the ongoing Human Genome Project.

The "universal" leucine codon CTG in the secreted aspartyl proteinase 1 (SAP1) gene of Candida albicans encodes a serine in vivo

A number of Candida species possess a tRNA(Ser)-like species that recognizes CTG codons that normally specify leucine (Leu) in the universal code of codon usage. Mass spectrometry and Edman sequencing of peptides from the secreted aspartyl proteinase isoenzyme (Sap1) demonstrate that positions specified by the CTG codon contain a nonmodified serine (Ser) in Candida albicans.