Mutational Inactivation and allelic loss of the von HlppelLlndau (VHL) gene appear to be causal events for the majority of spontaneous clear-cell renal cardnomas. We now show that hypermethylatlon of a normally unmethylated CpG Island in the 5' region provides another potentially important mechanism for Inactivation of the VHL gene In a siificant portion of these cancers. This hypermethylation was found in S of 26 (19%) tumors examined. Four of these had lost one copy of VHL while one retained two heavily methylated alleles. Four of the tumors with VHL hypermethylation had no detectable mutations, whereas one had a missense mutation In addition to hypermethylation of the single retained allele. As would be predicted for the consequence of methylation in this 5' CpG island, none of the 5 tumors expressed the VHL gene.

The Epstein-Barr Virus (EBV) latency C promoter (Cp) is the origin of transcripts for six viral proteins. The promoter is active in lymphoblastoid B-cell lines but silent in many EBV-associated tumors and tumor cell lines. In these latter cell lines, the viral episome is hypermethylated in the vicinity of this promoter. We show that in such a cell line (Rael, a Burkitt's lymphoma line), 5-azacytidine inhibits DNA methyltransferase, brings about demethylation of EBV genomes, activates Cp transcription, and induces the expression of EBNA-2. Investigation of the phenomenon demonstrates the importance of the methylation status of a particular CpG site for the regulation of the Cp: (i) genomic sequencing shows that this site is methylated when the Cp is inactive and is not methylated when the promoter is active; (ii) methylation or transition mutation at this site abolishes complex formation with a cellular binding activity (CBF2) as determined by electrophoretic mobility shift analyses, competition binding analyses, and DNase I footprinting; and (iii) a single C --> T transition mutation at this site is associated with a marked reduction (> 50-fold) of transcriptional activity in a reporter plasmid. Thus, the CBF2 binding activity is shown to be methylation sensitive and crucial to EBNA-2-mediated activation of the Cp.

Cinnamic acid, a naturally occurring aromatic fatty acid of low toxicity, has a long history of human exposure. We now show that cinnamic acid induces cytostasis and a reversal of malignant properties of human tumor cells in vitro. The concentration causing a 50% reduction of cell proliferation (IC50) ranged from 1 to 4.5 mM in glioblastoma, melanoma, prostate and lung carcinoma cells. Using melanoma cells as a model, we found that cinnamic acid induces cell differentiation as evidenced by morphological changes and increased melanin production. Moreover, treated cells had reduced invasive capacity associated with modulation of expression of genes implicated in tumor metastasis (collagenase type IV, and tissue inhibitor metalloproteinase 2) and immunogenicity (HLA-A3, class-I major histocompatibility antigen). Further molecular analysis indicated that the anti-tumor activity of cinnamic acid may be due in part to the inhibition of protein isoprenylation known to block mitogenic signal transduction. The results presented here identify cinnamic acid as a new member of the aromatic fatty acid class of differentiation-inducers with potential use in cancer intervention.

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Background. The growth‐inhibiting and differentiating effects of sodium phenylacetate against hematopoietic and solid tumor cell lines has aroused clinical interest in its use as an anticancer drug. In an earlier Phase I trial of phenylacetate aimed at maintaining serum drug concentrations in the range that proved active in vitro (>250 μg/ml) for 2 consecutive weeks, infusion rates approached the maximum velocity of drug elimination and commonly resulted in drug accumulation and reversible dose‐limiting neurologic toxicity. In this study, the authors described the nonlinear pharmacokinetics, metabolism, toxicity, and clinical activity of phenylacetate. Methods. The treatment regimen of this Phase I study was designed to expose patients intermittently to drug concentrations exceeding 250 μg/ml and to allow time for drug elimination to occur between doses to minimize accumulation. Sodium phenylacetate was administered as a 1‐hour infusion twice daily (8 a.m., 5 p.m.) at two dose levels of 125 and 150 mg/kg for a 2‐week period. Therapy was repeated at 4‐week intervals for patients who did not experience dose‐limiting toxicity or disease progression. Results. Eighteen patients (4 of whom previously were treated with phenylacetate by continuous intravenous infusion) received 27 cycles of therapy. Detailed pharmacokinetic studies for eight patients indicated that phenylacetate induced its own clearance by a factor of 27% in a 2‐week period. Dose‐limiting toxicity, consisting of reversible central nervous system depression, was observed for three patients at the second dose level. One patient with refractory malignant glioma had a partial response, and one with hormone‐independent prostate cancer achieved a 50% decline in prostate specific antigen level, which was maintained for 1 month. Conclusions. Phenylacetate administered at a dose of 125 mg/kg twice daily for 2 consecutive weeks is well tolerated. High grade gliomas and advanced prostate cancer are reasonable targets for Phase II clinical trials. Cancer 1995;75:2932–8.

Alterations in ras oncogene expression have been associated with increased cellular resistance to ionizing radiation. As an extension of studies with murine cell models, we have now explored the radioresponses of human osteosarcoma (HOS) sub-clones that differ in their EJras expression. Quantitative analysis revealed a tight correlation between the amounts of ras-encoded mRNA and p21 produced, and the degree of cell radioresistance. Interestingly, treatment of the ras-transformed cells with lovastatin, an inhibitor of p21ras post-translational processing via the mevalonate pathway, markedly decreased their radioresistance. Under the experimental conditions used, lovastatin prevented the membrane association, but not the biosynthesis, of p21. The decline in radiation resistance following lovastatin treatment could not be attributed to perturbation of cholesterol metabolism or to non-specific cell-cycle effects. In agreement, lovastatin did not alter the radiation responses of control HOS cells that do not express EJras, or those with an activated met oncogene. The results indicate that elevation in ras gene expression can lead to increased radioresistance of human tumor cells. It appears, however, that p21ras membrane localization is critical for maintenance of the radioresistant phenotype, thus providing a target for pharmacological intervention.

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We conclude that decitabine is a well tolerated regimen with modest clinical activity against hormone-independent prostate cancer. Further investigations in patients of African-American origin may be warranted.