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Biomedical subjects

C E Myers

Publications and source records attributed to C E Myers.

At least 19 recordsLinked to original sources
PubMed1995

Cytostatic activity of phenylacetate and derivatives against tumor cells. Correlation with lipophilicity and inhibition of protein prenylation.

The aromatic fatty acid phenylacetate, a common metabolite of phenylalanine, shows promise as a relatively non-toxic drug for cancer treatment. This slowly metabolized fatty acid alters tumor cell lipid metabolism causing, among other effects, inhibition of protein prenylation critical to malignant growth. In pursuit of more potent analogues, we have examined the activity of related compounds against tumor cell lines established from patients with advanced prostatic carcinoma, glioblastomas, and malignant melanoma. Like phenylacetate, derivatives containing alpha-carbon or ring substitutions induced cytostasis and phenotypic reversion at non-toxic concentrations. Potency was correlated with the degree of calculated lipophilicity of the aromatic fatty acid, and the extent of inhibition of protein prenylation. Remarkably, a parallel cytostatic activity was reported in embryonic plant cells, which respond to phenylacetate and its analogues in the same concentration range and the same rank order of lipophilicity. These data suggest that phenylacetate and its analogues may act through common mechanisms to inhibit the growth of vastly divergent, undifferentiated cell types, and provide a basis for the development of new agents for the treatment of human malignancies.

Antimetabolites, Antineoplastic↗
PubMed1995

Phase I study of phenylacetate administered twice daily to patients with cancer.

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 micrograms/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 micrograms/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.

Adult↗
PubMed1995

Drug-induced apoptosis is not necessarily dependent on macromolecular synthesis or proliferation in the p53-negative human prostate cancer cell line PC-3.

The propensity of a cell to undergo apoptosis has been proposed to be a determinant for chemotherapy sensitivity that is not directly dependent on specific drug-target interactions. Androgen-independent prostate cancer is typically refractory to cytotoxic drugs, and we tested whether this is due to a loss of the ability to undergo apoptosis. Exposure of the hormone-insensitive and p53-negative human prostate carcinoma cell line PC-3 to 22 microM cisplatin, 1 microM camptothecin, 10 microM tenoposide, 135 nM vincristine, or 10 microM lovastatin for 72 h caused cell death, internucleosomal DNA fragmentation, and morphological changes typical for apoptosis. One microM cycloheximide prevented anticancer drug-induced apoptosis, whereas high concentration (1 mM) of cycloheximide alone induced apoptosis, indicating that protein synthesis was not needed for these cells to undergo apoptosis. Since cycloheximide affected DNA synthesis and proliferation of PC-3 cells, we tested whether the DNA polymerase inhibitor aphidicolin could also suppress drug-induced apoptosis. In contrast to cycloheximide, aphidicolin inhibited only vincristine-induced apoptosis. Cycloheximide prevented drug-induced changes in cell cycle distribution except for vincristine, while aphidicolin led to an accumulation of cells at the G1-S border independent of the drug used. These data indicate that macromolecular synthesis, active cell cycling, and p53 expression are not required for apoptosis to proceed in this system.

Antineoplastic Agents↗
PubMed1995

Specific labeling of isoprenylated proteins: application to study inhibitors of the post-translational farnesylation and geranylgeranylation.

Specific labeling of either farnesylated or geranylgeranylated proteins in human PC-3 prostate cancer cell line was obtained by suppression of mevalonic acid biosynthesis with lovastatin, 50 microM, followed by supplementation of cell culture medium with either [3H]farnesyl- or [3H]geranylgeranyl-pyrophosphate. The immunoprecipitation of either a farnesylated (p21 ras) or geranylgeranylated (p21 rap 1) protein demonstrated that labeling was specific since proteins were detected only if the appropriate isoprenoid was added to the culture medium. TLC analysis indicated that no conversion of one isoprenoid to the other occurred in these conditions. The selective labeling of either farnesylated or geranylgeranylated proteins may be a valuable tool for the development of inhibitors of isoprenoid transferases as a potential new class of antitumor agents.

Cell Line↗
PubMed1995

Disposition of phenylbutyrate and its metabolites, phenylacetate and phenylacetylglutamine.

Phenylacetate, an inducer of tumor cytostasis and differentiation, shows promise as a relatively nontoxic antineoplastic agent. Phenylacetate, however, has an unpleasant odor that might limit patient acceptability. Phenylbutyrate, an odorless compound that also has activity in tumor models, is known to undergo rapid conversion to phenylacetate by beta-oxidation in vivo. This phase I study examined the pharmacokinetics of phenylbutyrate and characterized the disposition of the two metabolites, phenylacetate and phenylacetylglutamine. Fourteen patients with cancer (aged 51.8 +/- 13.8 years) received a 30-minute infusion of phenylbutyrate at 3 dose levels (600, 1200, and 2000 mg/m2). Serial blood samples and 24-hour urine collections were obtained. Samples were assayed by high-performance liquid chromatography. A model to simultaneously describe the pharmacokinetics of all three compounds was developed using ADAPT II. Data were modeled as molar equivalents. The model fit the data well as shown by mean (+/- SD) coefficients of determination (r2) for phenylbutyrate, phenylacetate, and phenylacetylglutamine, which were 0.96 +/- 0.07, 0.88 +/- 0.10, and 0.92 +/- 0.06, respectively. The intrapatient coefficient of variation percentage (CV%) around the parameter estimates were small (range 7.2-33.5%). Phenylbutyrate achieved peak concentrations in the range of in vitro tumor activity (500-2000 mumol/L) and exhibited saturable elimination (Km = 34.1 +/- 18.1 micrograms/mL and Vmax = 18.1 +/- 18 mg/h/kg). Metabolism was rapid; the times to maximum concentration for phenylacetate and phenylacetylglutamine were 1 and 2 hours, respectively. The conversion of phenylbutyrate to phenylacetate was extensive (80 +/- 12.6%), but serum concentrations of phenylacetate were low owing to rapid, subsequent conversion to phenylacetylglutamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Pharmacologic variables associated with the development of neurologic toxicity in patients treated with suramin.

PURPOSE: To describe pharmacologic variables correlated with the development of neurologic toxicity in patients treated with suramin. METHODS: Eighty-one patients were treated with suramin in a phase I study. The rate of drug infusion was continuously adjusted to maintain a preassigned plasma suramin concentration (175, 215, or 275 micrograms/mL) for a fixed duration (2 to 8 weeks). RESULTS: Eight patients developed grade III/IV neurologic motor impairment (predominantly motor axonal polyneuropathy). All were treated at the 275-micrograms/mL concentration. One patient treated at the 215-micrograms/mL concentration developed grade II motor dysfunction. In addition, seven of nine patients had sensory symptoms. Pharmacologic variables associated with the development of polyneuropathy included total cumulative suramin dose, duration of exposure to plasma concentrations greater than 200 micrograms/mL, and area under the curve (AUC) greater than 200 micrograms/mL. CONCLUSION: Significant neurologic toxicity can result from therapy with suramin, even when dosing is designed to avoid exposure to plasma concentrations greater than 350 micrograms/mL. Future clinical trials of suramin should be designed in such a way as to limit the total cumulative dose to < or = 157 mg/kg given over a period of > or = 8 weeks, limit the period of exposure to plasma suramin concentrations greater than 200 micrograms/mL to < or = 25 days, and limit the AUC greater than 200 micrograms/mL to < or = 48,000 mg.h/AL.

Adult↗
PubMed1995

Paclitaxel (taxol) inhibits protein isoprenylation and induces apoptosis in PC-3 human prostate cancer cells.

Paclitaxel was examined for its effects on cell survival, internucleosomal DNA fragmentation, and protein isoprenylation in the human prostate cancer cell line PC-3. Treatment of cells with paclitaxel at 5-60 nM for 24 hr resulted in a dose-dependent inhibition of cell viability (IC50, 31.2 nM), which was partially prevented by supplementing the cell culture medium with two nonsterol polyisoprenyl compounds, farnesyl-pyrophosphate (-PP) and geranylgeranyl-PP (3 microM each). Furthermore, agarose gel electrophoresis of DNA extracted from cells treated with paclitaxel (15-60 nM) for 24 hr showed DNA laddering with production of fragments of 180-base pair multiples, indicating the occurrence of apoptotic cell death. Internucleosomal DNA fragmentation by paclitaxel was also detected by a photometric enzyme immunoassay using antihistone antibodies; if culture medium was supplemented with farnesyl-PP and geranylgeranyl-PP (3 microM each), a reduction in mono- and oligonucleosome production was observed. The post-translational incorporation of metabolites of (RS)-[5-3H]mevalonolactone (100 microCi/ml) into prenylated proteins of PC-3 cells was inhibited by paclitaxel at 30 and 60 nM. In addition, the immunoprecipitation of p21ras and p21rap-1 proteins from PC-3 cells exposed to paclitaxel (30 and 60 nM) and labeled with (RS)-[5-3H]mevalonolactone showed a substantial inhibition of the incorporation of farnesyl and geranylgeranyl prenoid groups, respectively, into the aforementioned proteins. These results indicate that the inhibition of protein isoprenylation is a novel component of the complex biochemical effects of the drug and plays an important role in the mechanism of paclitaxel cytotoxicity in PC-3 cells.

Apoptosis↗
PubMed1994

The detergent Triton X-100 induces a death pattern in human carcinoma cell lines that resembles cytotoxic lymphocyte-induced apoptosis.

The detergent Triton X-100 (TX100) was used with the intention to establish a model for necrotic cell death. However, TX100 was found to induce apoptotic and necrotic death in prostate and colon cancer cell lines. Apoptosis was characterized by the typical morphological features and internucleosomal DNA fragmentation. The rapid onset within 60 min and the lack of inhibition by cycloheximide indicated that apoptosis induced by TX100 was not dependent on protein synthesis. Removal of extracellular calcium blocked internucleosomal DNA fragmentation. This pattern of cell death shows a striking similarity to the effect of cytotoxic lymphocytes on their target cells.

Apoptosis↗
PubMed1994

Inhibition of heat shock protein HSP90-pp60v-src heteroprotein complex formation by benzoquinone ansamycins: essential role for stress proteins in oncogenic transformation.

The molecular mechanisms by which oncogenic tyrosine kinases induce cellular transformation are unclear. Herbimycin A, geldanamycin, and certain other benzoquinone ansamycins display an unusual capacity to revert tyrosine kinase-induced oncogenic transformation. As an approach to the study of v-src-mediated transformation, we examined ansamycin action in transformed cells and found that drug-induced reversion could be achieved without direct inhibition of src phosphorylating activity. To identify mechanisms other than kinase inhibition for drug-mediated reversion, we prepared a solid phase-immobilized geldanamycin derivative and affinity precipitated the molecular targets with which the drug interacted. In a range of cell lines, immobilized geldanamycin bound elements of a major class of heat shock protein (HSP90) in a stable and pharmacologically specific manner. Consistent with these binding data, we found that soluble geldanamycin and herbimycin A inhibited specifically the formation of a previously described src-HSP90 heteroprotein complex. A related benzoquinone ansamycin that failed to revert transformed cells did not inhibit the formation of this complex. These results demonstrate that HSP participation in multimolecular complex formation is required for src-mediated transformation and can provide a target for drug modulation.

3T3 Cells↗
PubMed1994

Terminal neuroendocrine differentiation of human prostate carcinoma cells in response to increased intracellular cyclic AMP.

Recent clinicopathologic studies have shown that many prostatic adenocarcinomas express focal neuroendocrine differentiation and that neuroendocrine differentiation is most apparent in advanced anaplastic tumors. While studying growth-regulatory signal transduction events in human prostate carcinoma cell lines, we found that in two of four cell lines, the androgen-sensitive line LNCaP and the highly metastatic androgen-independent line PC-3-M, elevation of cAMP through addition of cAMP analogues or phosphodiesterase inhibitors induced a markedly neuronal morphology. Also in LNCaP cells ultrastructural analysis showed that cAMP induced the appearance of neurosecretory cell-like dense-core granules. Phenotypic analysis of untreated LNCaP and PC-3-M cells showed that both cell lines express markers of the neural crest including S-100, chromogranin A, pp60c-src, and neuron-specific enolase as well as the epithelial marker KS1/4 and stage-specific embryonic antigen 4. In PC-3-M cells, cAMP markedly elevated neuron-specific enolase protein and caused an increase in the specific activity of the neuroendocrine marker pp60c-src, and in both cell lines expression of KS1/4 and stage-specific embryonic antigen 4 was down-regulated. In addition to effects on lineage markers, cAMP treatment induced G1 synchronization, growth arrest, and loss of clonogenicity, indicating terminal differentiation. Our data provide direct evidence of plasticity in the lineage commitment of adenocarcinoma of the prostate. We have shown that cell-permeant cAMP analogues can induce terminal differentiation, suggesting that hydrolysis-resistant cyclic nucleotides may present an additional approach to the treatment of advanced prostate cancer.

Adenocarcinoma↗
PubMed1994

Growth inhibition, tumor maturation, and extended survival in experimental brain tumors in rats treated with phenylacetate.

Phenylacetate is a naturally occurring plasma component that suppresses the growth of tumor cells and induces differentiation in vitro. To evaluate the in vivo potential and preventive and therapeutic antitumor efficacy of sodium phenylacetate against malignant brain tumors, Fischer 344 rats (n = 50) bearing cerebral 9L gliosarcomas received phenylacetate by continuous s.c. release starting on the day of tumor inoculation (n = 10) using s.c. osmotic minipumps (550 mg/kg/day for 28 days). Rats with established brain tumors (n = 12) received continuous s.c. phenylacetate supplemented with additional daily i.p. dose (300 mg/kg). Control rats (n = 25) were treated in a similar way with saline. Rats were sacrificed during treatment for electron microscopic studies of their tumors, in vivo proliferation assays, and measurement of phenylacetate levels in the serum and cerebrospinal fluid. Treatment with phenylacetate extended survival when started on the day of tumor inoculation (P < 0.01) or 7 days after inoculation (P < 0.03) without any associated adverse effects. In the latter group, phenylacetate levels in pooled serum and cerebrospinal fluid samples after 7 days of treatment were in the therapeutic range as determined in vitro (2.45 mM in serum and 3.1 mM in cerebrospinal fluid). Electron microscopy of treated tumors demonstrated marked hypertrophy and organization of the rough endoplasmic reticulum, indicating cell differentiation, in contrast to the scant and randomly distributed endoplasmic reticulum in tumors from untreated animals. In addition, in vitro studies demonstrated dose-dependent inhibition of the rate of tumor proliferation and restoration of anchorage dependency, a marker of phenotypic reversion. Phenylacetate, used at clinically achievable concentrations, prolongs survival of rats with malignant brain tumors through induction of tumor differentiation. Its role in the treatment of brain tumors and other cancers should be explored further.

Animals↗
PubMed1994

Oncogene overexpression and de novo drug-resistance in human prostate cancer cells.

We have isolated a variant [PC3(R)] of the human prostate PC3 tumor cell line which showed resistance to several anticancer drugs. Studies to evaluate the mechanisms of resistance to anticancer drugs in the PC3(R) cell line indicated that mdr1 was not overexpressed. Studies also indicated that activities of topo I and topo II were not different in these cell lines, nor was there any difference in the formation of drug-induced KCl-SDS precipitable complexes, indicating that topoisomerases were not involved in the development of resistance in PC3(R) cells. While the activity of glutathione S-transferase and total glutathione levels were also similar in these cell lines, the glutathione peroxidase activity in PC3(R) cells was 5-fold lower than in PC3 cells. Furthermore, proto-oncogene expression for c-jun, c-myc, and H-ras was significantly higher in resistant cells than in sensitive cells, indicating that the amplification of early response genes may play a role in the emergence of de novo resistance in PC3(R) cells.

Antineoplastic Agents↗
PubMed1994

Selective activity of phenylacetate against malignant gliomas: resemblance to fetal brain damage in phenylketonuria.

Phenylacetate, a deaminated metabolite of phenylalanine, has been implicated in damage to immature brain in phenylketonuria. Because primary brain tumors are highly reminiscent of the immature central nervous system, these neoplasms should be equally vulnerable. We show here that sodium phenylacetate can induce cytostasis and reversal of malignant properties of cultured human glioblastoma cells, when used at pharmacological concentrations that are well tolerated by children and adults. Treated tumor cells exhibited biochemical alterations similar to those observed in phenylketonuria-like conditions, including selective decline in de novo cholesterol synthesis from mevalonate. Because gliomas, but not mature normal brain cells, are highly dependent on mevalonate for production of sterols and isoprenoids vital for cell growth, sodium phenylacetate would be expected to affect tumor growth in vivo while sparing normal tissues. Systemic treatment of rats bearing intracranial gliomas resulted in significant tumor suppression with no apparent toxicity to the host. The data indicate that phenylacetate, acting through inhibition of protein prenylation and other mechanisms, may offer a safe and effective novel approach to treatment of malignant gliomas and perhaps other neoplasms as well.

Animals↗
PubMed1994

Surprising activity of flutamide withdrawal, when combined with aminoglutethimide, in treatment of "hormone-refractory" prostate cancer.

BACKGROUND: The best treatment for patients with "hormone-refractory" metastatic prostate cancer is unclear, particularly in patients for whom suramin and hydrocortisone have failed. PURPOSE: We investigated a combination of flutamide withdrawal and aminoglutethimide in suramin- and hydrocortisone-pretreated patients with "hormone-refractory" prostate cancer. METHODS: Twenty-nine patients with metastatic prostate cancer were treated with simultaneous flutamide withdrawal and aminoglutethimide (250 mg given orally four times daily). All patients were taking flutamide at the time of entry, and previous treatments with medical or surgical castration, flutamide, suramin, and hydrocortisone had failed in all of these patients. Because of suramin-induced adrenal insufficiency, all patients had previously received, and continued to receive, physiological doses of hydrocortisone. Treatment of all non-surgically castrated patients had previously failed; however, these patients continued to receive depot leuprolide. RESULTS: In 14 (48%) of 29 patients, the prostate-specific antigen (PSA) decreased by more than 80% for 4 or more weeks. Improvements in anemia, thrombocytopenia, soft-tissue masses, bone scans, and symptoms were also noted. Factors associated with response included prolonged flutamide pretreatment, a markedly elevated pretreatment PSA, and the absence of soft-tissue disease. CONCLUSIONS: Flutamide withdrawal, when combined with the simultaneous administration of aminoglutethimide, is a therapeutically active approach in patients with "hormone-refractory" prostate cancer. IMPLICATIONS: On the basis of these and additional data, we hypothesize that prolonged exposure to flutamide results in the selective proliferation of cancer cells containing a mutant androgen receptor that aberrantly recognizes flutamide metabolites and nonandrogenic steroids as androgenic stimuli.

Aged↗