Role of dietary polyamines in a phase III clinical trial of difluoromethylornithine (DFMO) and sulindac for prevention of sporadic colorectal adenomas

Background:

The polyamine-inhibitory regimen difluoromethylornithine (DFMO)+sulindac has marked efficacy in preventing metachronous colorectal adenomas. Polyamines are synthesised endogenously and obtained from dietary sources. Here we investigate dietary polyamine intake and outcomes in the DFMO+sulindac colorectal adenoma prevention trial.

Methods:

Dietary polyamine data were available for 188 of 267 patients completing the study. Total dietary polyamine content was derived by the sum of dietary putrescine, spermine and spermidine values and categorised into two groups: highest (>75–100%) vs the lower three quartiles (0–25, 25–50 and 50–75%). Baseline tissue polyamine concentration and ODC1 genotype were determined. Logistic regression models were used for risk estimation.

Results:

A significant interaction was detected between dietary polyamine group and treatment with regard to adenoma recurrence (P=0.012). Significant metachronous adenoma risk reduction was observed after DFMO+sulindac treatment in dietary polyamine quartiles 1–3 (risk ratio (RR) 0.19; 95% confidence interval (CI) 0.08–0.42; P<0.0001) but not in quartile 4 (RR 1.51; 95% CI 0.53–4.29; P=0.44). However, a lower number of events in the placebo group within dietary quartile 4 confound the aforementioned risk estimates.

Conclusion:

These preliminary findings reveal complex relationships between diet and therapeutic prevention, and they support further clinical trial-based investigations where the dietary intervention itself is controlled.

Role of obesity in a randomized placebo-controlled, double-blind trial of difluoromethylornithine plus sulindac for the prevention of sporadic colorectal adenomas

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Background: Chemoprevention with difluoromethylornithine (DFMO) plus sulindac markedly reduces risk of recurrence in colorectal adenoma (CRA) patients. Obesity is associated with risk of CRA and colorectal cancer (CRC). This study investigates how obesity influences CRA characteristics at baseline and risk of recurrence after treatment with DFMO plus sulindac vs. placebo.

Methods: Our analysis included subjects enrolled in a phase III CRA prevention clinical trial investigating DFMO plus sulindac vs. placebo. Patients were classified by obesity (BMI > 30 kg/m2) status at baseline. Pearson's χ2 statistic or Fisher's exact test and Mann-Whitney U test were used to compare baseline characteristics with regard to obesity status. Log-binomial regression analysis was used to determine the relative risk of metachronous adenoma, adenoma with advanced histology, or multiple adenomas, adjusted for covariates.

Results: At baseline, obesity was associated with increased adenoma number (p =0.017), size (p =0.003), advanced histology (p =0.042), high-risk adenomas (p =0.0002), and distal adenomas (p =0.038). Obesity did not modify adenoma recurrence after treatment with DFMO plus sulindac or placebo (p =0.80).

Conclusions: Our results provide supporting evidence for the association of obesity with high-risk adenoma features at baseline; however, obesity does not substantially modify CRA risk reduction after treatment with DFMO plus sulindac vs. placebo.

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Impact of dietary amino acids and polyamines on intestinal carcinogenesis and chemoprevention in mouse models

Colon cancer in humans is influenced by both genetic and dietary risk factors. The majority of colon cancers have somatic mutations in the APC (adenomatous polyposis coli) tumour-suppressor gene. Dietary arginine enhances the risk of APC-dependent colon carcinogenesis in mouse models by a mechanism involving NOS2 (nitric oxide synthase 2), as elimination of NOS2 alleles suppresses this phenotype. DFMO (difluoromethylornithine), a specific inhibitor of polyamine synthesis, also inhibits dietary arginine-induced colon carcinogenesis in C57BL/6J-Apc(Min)/J mice. The primary consequence of dietary arginine is to increase the adenoma grade in these mice. Either loss of NOS2 alleles or inhibition of polyamine synthesis suppresses the arginine-induced increase in adenoma grade. In addition to promoting intestinal carcinogenesis, polyamines can also reduce the efficacy of certain intestinal cancer chemopreventive agents. The NSAID (non-steroidal anti-inflammatory drug) sulindac is a potent inhibitor of intestinal carcinogenesis in the C57BL/6J-Apc(Min)/J mouse model and is used to treat humans with FAP (familial adenomatous polyposis). Dietary putrescine reduces the ability of sulindac to suppress intestinal tumorigenesis in the mouse model. These data suggest that reducing polyamine metabolism and dietary polyamine levels may enhance strategies for colon cancer chemoprevention.

Rationale for, and design of, a clinical trial targeting polyamine metabolism for colon cancer chemoprevention

Polyamine metabolic genes are downstream targets of several genes commonly mutated in colon adenomas and cancers. Inhibitors of ornithine decarboxylase, such as difluoromethylornithine (DFMO), and agents that stimulate polyamine acetylation and export, such as non-steroidal anti-inflammatory drugs (NSAIDS), act at least additively to arrest growth in human cell models and suppress intestinal carcinogenesis in mice. These preclinical studies provided the rationale for colon cancer prevention trials in humans. A Phase IIb clinical study comparing the combination of DFMO and the NSAID sulindac versus placebo was conducted. Endpoints were colorectal tissue polyamine and prostaglandin E2 contents and overall toxicity to participants. Participants in the Phase IIb study served as a vanguard for a randomized, placebo-controlled prospective Phase III trial of the combination of DFMO and sulindac with the primary study endpoint the prevention of colon polyps. Seventy percent of participants will have completed the three years of treatment in December 2006.

Polyamine-dependent gene expression

The polyamines spermidine and spermine along with the diamine putrescine are involved in many cellular processes, including chromatin condensation, maintenance of DNA structure, RNA processing, translation and protein activation. The polyamines influence the formation of compacted chromatin and have a well-established role in DNA aggregation. Polyamines are used in the posttranslational modification of eukaryotic initiation factor 5A, which regulates the transport and processing of specific RNA. The polyamines also participate in a novel RNA-decoding mechanism, a translational frame-shift, of at least two known genes, the TY1 transposon and mammalian antizyme. Polyamines are crucial for their own regulation and are involved in feedback mechanisms affecting both polyamine synthesis and catabolism. Recently, it has become apparent that the polyamines are able to influence the action of the protein kinase casein kinase 2. Here we address several roles of polyamines in gene expression.

Increased thioredoxin-1 inhibits SSAT expression in MCF-7 human breast cancer cells

Spermidine/spermine N(1)-acetyltransferase (SSAT) regulates polyamine catabolism. Thioredoxin-1 (Trx-1) is a redox protein that is overexpressed in human cancer leading to increased cell proliferation, decreased apoptosis, and decreased patient survival. We report that SSAT mRNA expression is decreased in Trx-1 transfected MCF-7 human breast cancer cells. There is also a decrease in SSAT enzyme activity and lower putrescine levels but no change in spermine or spermidine levels. The expression of SSAT is regulated by the NF-E2-related factor 2 (Nrf-2) and polyamine modulated factor-1 (PMF-1) transcription factor complex. Trx-1 transfected MCF-7 cells showed decreased Nrf-2/PMF-1 DNA binding without a change in Nrf-2 or PMF-1 protein expression. The results suggest that Trx-1 may play a role in the redox regulation of SSAT expression and polyamine homeostasis that could contribute to the biological effects of Trx-1.

Polyamines as modifiers of genetic risk factors in human intestinal cancers

Polyamines are downstream mediators of genetic risk factors in human intestinal cancers. The adenomatous polyposis coli (APC) tumour-suppressor gene, which is mutated in essentially all human colon cancers, regulates the expression of several e-box transcription factors. These factors, in turn, regulate the transcription of ornithine decarboxylase (ODC), the first enzyme in polyamine synthesis. The Kirsten ras ( K-ras ) oncogene regulates the expression of several genes, including suppressing the expression of peroxisomal proliferator-activated receptor gamma (PPARgamma). This PPAR, in turn, activates the expression of the spermidine/spermine-N(1)-acetyltransferase (SSAT), the first enzyme in polyamine catabolism. The non-steroidal anti-inflammatory drug (NSAID) sulindac induces the transcription of SSAT via activation of PPARgamma. Inactivation of the APC tumour-suppressor gene, and the activation of K-ras, have a combined effect on increasing tissue polyamine contents due to increased synthesis and decreased catabolism of the polyamines. Pharmacological strategies for suppressing ODC (e.g. the enzyme-activated inhibitor alpha-difluoromethylornithine) and activating SSAT (e.g. NSAIDs) are potent inhibitors of intestinal carcinogenesis in rodent models. Clinical trials combining these classes of agent in humans with risk factors for colon cancer are in progress.

Chemoprevention by difluoromethylornithine: correlation of an in vitro human cell assay with human clinical data for biomarker modulation

The efficacy of difluoromethylornithine (DFMO) as a chemopreventive agent has been tested in vitro using a human epidermal cell (HEC) assay with growth inhibition and involucrin induction as endpoints. Suppression of polyamine content is currently being utilized as a biomarker in clinical trials for the chemopreventive efficacy of DFMO against colon cancer formation. We have now examined the effects of DFMO on suppression of polyamine content in the HEC assay. The findings indicate 1) the % change in spermidine to spermine ratio and the depletion of putrescine show excellent correlation with chemopreventive efficacy in vitro; 2) the effective concentrations in vitro overlap the plasma concentrations in the clinical trial. These observations serve as further validation of the usefulness of the HEC assay as a screen for chemopreventive efficacy.

Sulindac sulfone inhibits K-ras-dependent cyclooxygenase-2 expression in human colon cancer cells

Both the sulfide and sulfone metabolites of sulindac, a nonsteroidal anti-inflammatory drug, display anticarcinogenic effects in experimental models. Sulindac sulfide inhibits cyclooxygenase (COX) enzyme activities and has been reported to suppress ras-dependent signaling. However, the mechanisms by which sulindac sulfone suppresses cancer growth are not as defined. We studied the effects of these sulindac metabolites in human colon cancer-derived Caco-2 cells that have been transfected with an activated K-ras oncogene. Stable transfected clones expressed high levels of COX-2 mRNA and protein, compared with parental cells. K-ras-transfected cells formed tumors more quickly when injected into severe combined immunodeficiency disease mice than parental cells, and this tumorigenesis was suppressed by treatment with sulindac. Sulindac sulfone inhibited COX-2 protein expression, which resulted in a decrease in prostaglandin synthase E2 production. Sulindac sulfide had little effect on COX-2 in this model, but did suppress prostaglandin synthase E2 production, presumably by inhibiting COX enzyme activity. These data indicate that the sulfide and sulfone derivatives of sulindac exert COX-dependent effects by distinct mechanisms.

Influence of K-ras activation on the survival responses of Caco-2 cells to the chemopreventive agents sulindac and difluoromethylornithine

The nonsteroidal anti-inflammatory drug sulindac and the ornithine decarboxylase inhibitor difluoromethylornithine (DFMO) are both potent inhibitors of colon carcinogenesis in experimental models of this disease. The combination of these two agents is undergoing evaluation as a strategy for colon cancer chemoprevention in humans with resected colon polyps. We evaluated the effects of the major sulfide and sulfone metabolites of sulindac and DFMO alone, or in combinations, on the growth and survival of Caco-2 colon cancer-derived cells and in clones of these cells transfected with an activated K-ras oncogene. Both the sulfide and sulfone metabolites of sulindac reduced cell viability, measured by colony-forming assays, primarily by inducing apoptosis. Expression of an activated K-ras oncogene caused cells treated with either sulindac sulfide or sulfone to undergo apoptosis earlier than nontransfected controls. However, clonogenic survival, measured 2 weeks after drug treatment, was the same in both Caco-2 and ras-transfected Caco-2 cells treated with sulindac metabolites. A 24-h treatment with DFMO caused a dose-dependent decrease in the colony-forming ability of cells expressing an activated K-ras but had no effect on the viability of the parental Caco-2 cells. The DFMO-dependent decrease in colony formation in K-ras-activated cells occurred in the absence of apoptosis. Assessment of cell survival by colony-forming assays indicated that these two agents acted in an additive manner when combined. These data indicate that K-ras can influence the kinetics of apoptosis induction by sulindac metabolites and cell survival in response to DFMO. However, cytotoxicity induced by these agents occurs via unique mechanisms. These studies suggest that the combination of DFMO and sulindac may be useful in human cancer prevention strategies.

Increased susceptibility of cells to inducible apoptosis during growth from early to late log phase: an important caveat for in vitro apoptosis research

The physiologic mode of cell death known as apoptosis has become a major focus of scientific research due to its biologic importance. Much of this research involves cells grown in culture, where induction of apoptosis is achieved through a variety of agents. We report that cell cultures in late log growth phase exhibit an increased susceptibility to apoptosis compared with cultures in early log growth phase when apoptosis is induced by sodium deoxycholate (NaDOC), anti-Fas antibody and cytosine-b-D-arabino-furanoside (Ara-C), three agents which induce apoptosis through different upstream mechanisms. We show that this phenomenon occurs in Jurkat lymphocytes, HT-29 and HCT-116 colon epithelial cells. We also present evidence that cell density alone does not affect NaDOC-induced apoptosis, but rather that the growth media plays a key role in increased susceptibility of cells in late log growth phase to NaDOC-induced apoptosis. These results indicate that growth phase is a variable that must be controlled in order to obtain reliable apoptosis data.

Heat-inducible vectors for use in gene therapy

The objectives of this study were to quantity and compare the activities of a minimal heat shock (HS) promoter and other promoters used in gene therapy applications, and to identify strategies to amplify the heat inducibility of therapeutic genes. Human tumour cells were transiently or stably transfected with the HS promoter driving expression of reporter genes. HS promoter activity was induced transiently, with maximum activity 16-24 h after HS, and was dependent on temperature. The activity of the minimal HS promoter was similar, after 42 degrees C HS for 1 h, to that of the cytomegalovirus (CMV) promoter. To determine if the HS promoter could be used to activate a second conditional promoter, cells were transiently transfected with vectors containing both the HS and human immunodeficiency virus type 1 (HIV1) promoters. When the IL-2 gene was placed downstream of the HIV1 promoter. IL-2 production was temperature-independent. The addition of the HIV tat gene downstream of the HS promoter caused IL-2 to be induced more than 3 fold after a single 42 degrees C HS. These data indicate that the minimal HS promoter, following activation by clinically attainable temperatures (< or = 42 degrees C), can drive expression of therapeutic genes at levels comparable to the CMV promoter and be used in conjunction with a second conditional promoter to drive temperature-dependent, gene expression.

APC-dependent changes in expression of genes influencing polyamine metabolism, and consequences for gastrointestinal carcinogenesis, in the Min mouse

The colorectal mucosa of pre-symptomatic individuals with familial adenomatous polyposis (FAP) contains elevated levels of the proliferation-associated polyamines. The Min mouse, like humans with FAP, expresses an abnormal genotype for the APC tumor suppressor gene. In order to determine how APC mutation influences intestinal tissue polyamine content, we measured steady-state RNA levels of ornithine decarboxylase (ODC), the first enzyme in polyamine synthesis, antizyme (AZ), a protein which negatively regulates ODC, and the spermidine/spermine N(1)-acetyltransferase (SSAT), the first enzyme in polyamine catabolism. RNA content was increased 6- to 8-fold in both the small intestine and colon for ODC, decreased significantly in the small intestine but not the colon for AZ and was not statistically different in either intestinal tissue for SSAT in Min mice compared with normal littermates. Consistent with the changes in ODC and AZ gene expression, small intestinal, but not colonic, polyamine content was elevated in Min mice compared with normal littermates. Treatment of Min mice with the specific ODC inhibitor difluoromethylornithine (DFMO) suppressed small intestinal, but not colonic, polyamine content and tumor number. These data indicate that small intestinal tissue polyamine content is elevated in Min mice by a mechanism involving APC-dependent changes in ODC and AZ RNA. Further, ODC enzyme activity, which is influenced by both ODC and AZ RNA levels and inhibited by DFMO, is consequential for small intestinal tumorigenesis in this model. In the FAP population, DFMO may be of value in the chemoprevention of small intestinal adenocarcinoma that remains a risk following colectomy.

Characterization of a novel spermidine/spermine acetyltransferase, BltD, from Bacillus subtilis

Overexpression of the BltD gene in Bacillus subtilis causes acetylation of the polyamines spermidine and spermine. BltD is co-regulated with another gene, Blt, which encodes a multidrug export protein whose overexpression facilitates spermidine export [Woolridge, Vazquez-Laslop, Markham, Chevalier, Gerner and Neyfakh (1997) J. Biol. Chem. 272, 8864-8866]. Here we show that BltD acetylates both spermidine and spermine at primary propyl amine moieties, with spermine being the preferred substrate. In the presence of saturating concentrations of acetyl CoA, BltD rapidly acetylates spermine at both the N1 and N12 positions. The Km (app) values for spermine, spermidine and N1-acetylspermine are </=67, 200 and 1200 microM, respectively. Diamines ranging from 1, 3-diaminopropane to 1,12-diaminododecane, monoacetylputrescine and N8-acetylspermidine were not substrates for BltD. Putrescine (1, 4-diaminobutane) and N8-acetylspermidine were competitive inhibitors of spermidine acetylation by BltD, with Ki values of 0.25 and 5.76 mM, respectively. CoA competitively inhibited both spermidine and acetyl-CoA interactions with BltD. These data and other results indicate that the mechanism of spermidine and spermine acetylation by BltD is a random-order mechanism of bi-molecular kinetics.

Development of difluoromethylornithine (DFMO) as a chemoprevention agent

D,L-alpha-difluoromethylornithine (DFMO) was synthesized over 20 years ago. It was hoped that this enzyme-activated, irreversible inhibitor of ornithine decarboxylase, the first enzyme in polyamine synthesis, would be effective as a chemotherapy for hyperproliferative diseases, including cancer and/or infectious processes. DFMO was generally found to exert cytostatic effects on mammalian cells and tissues, and its effectiveness as a therapeutic agent has been modest. DFMO was also found to cause treatment-limiting (but reversible) ototoxicity at high doses. This side effect, along with its minimal therapeutic activity, contributed to the loss of interest by many clinicians in further developing DFMO as a cancer therapeutic agent. However, DFMO was subsequently shown to inhibit carcinogen-induced cancer development in a number of rodent models, and interest in developing this compound as a preventive agent has increased. The rationale for the inhibition of ornithine decarboxylase as a cancer chemopreventive agent has been strengthened in recent years because this enzyme has been shown to be transactivated by the c-myc oncogene in certain cell/tissue types and to cooperate with the ras oncogene in malignant transformation of epithelial tissues. Recent clinical cancer chemoprevention trials, using dose de-escalation designs, indicate that DFMO can be given over long periods of time at low doses that suppress polyamine contents in gastrointestinal and other epithelial tissues but cause no detectable hearing loss or other side effects. Current clinical chemoprevention trials are investigating the efficacy of DFMO to suppress surrogate end point biomarkers (e.g., colon polyp recurrence) of carcinogenesis in patient populations at elevated risk for the development of specific epithelial cancers, including colon, esophageal, breast, cutaneous, and prostate malignancies.

Reactive nitrogen species in colon carcinogenesis

The role of reactive nitrogen species (RNS) in colon carcinogenesis is multifactorial and affects diverse processes, such as proliferation, apoptosis, differentiation, tumorigenesis, and metastases. This review describes the stages in colon carcinogenesis where nitric oxide (NO) and inducible NO synthase (NOS2) may influence the progression of a normal mucosa to overt metastatic cancer. Overexpression of NOS2 and an increase in the generation of NO and other RNS may lead to apoptosis resistance, DNA damage, mutation, up-regulation of COX-2, increased proliferation, an increase in oxidative stress and an increase in tumor vascularity and metastatic potential. Therefore, future goals are to establish mechanistically based biomarkers to assess individuals at risk for colon cancer and to implement chemopreventive and dietary strategies that reduce colon cancer risk. An understanding of NO signaling pathways in colon epithelial cells should provide the basis for novel biomarker development. Colon cancer prevention may be achieved effectively by chemically interfering with key components of the NO signaling pathways, changing dietary habits to reduce fat and increase antioxidant-containing vegetables, and dietary supplementation to increase DNA repair.

Different bile acids exhibit distinct biological effects: the tumor promoter deoxycholic acid induces apoptosis and the chemopreventive agent ursodeoxycholic acid inhibits cell proliferation

Epidemiological studies have suggested that the concentration and composition of fecal bile acids are important determining factors in the etiology of colon cancer. However, the mechanism by which these compounds influence tumor development is not understood. To begin to elucidate their mechanism of action, four bile acids, cholic acid, chenodeoxycholic acid, deoxycholic acid (DCA), and ursodeoxycholic acid, were examined for their effects on the growth of several different tumor cell lines. We found that incubating cells with chenodeoxycholic acid or DCA caused morphological changes, seen by electron and light microscopy, that were characteristic of apoptosis, whereas incubating cells with ursodeoxycholic acid inhibited cell proliferation but did not induce apoptosis. Cholic acid had no discernible effect on cells. Notably, the apoptosis induced by DCA could be suppressed by inhibiting protein kinase C activity with calphostin C. These results indicate that different bile acids exhibit distinct biological activities and suggest that the cytotoxicity reported for DCA may be due to its capacity to induce apoptosis via a protein kinase C-dependent signaling pathway.

Effect of alpha-difluoromethylornithine on rectal mucosal levels of polyamines in a randomized, double-blinded trial for colon cancer prevention

BACKGROUND

Polyamines (e.g., putrescine, spermidine, and spermine) are required for optimal cell growth. Inhibition of polyamine synthesis suppresses carcinogen-induced epithelial cancers, including colon cancer, in animal models. In a short-term phase IIa trial, we determined that low doses of alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (an enzyme involved in polyamine synthesis), reduced the polyamine content of normal-appearing rectal mucosa of subjects with a prior history of resected colon polyps. In a follow-up study, we have attempted to determine the lowest dose of DFMO that can suppress the polyamine content of rectal mucosa over a course of 1 year with no or minimal side effects.

METHODS

Participants were randomly assigned to daily oral treatment with a placebo or one of three doses (0.075, 0.20, or 0.40 g/m2) of DFMO. Baseline and serial determinations of polyamine levels in rectal mucosa and extensive symptom monitoring (including audiometric measurements, since DFMO causes some reversible hearing loss at higher doses) were performed over a 15-month period.

RESULTS

DFMO treatment reduced putrescine levels in a dose-dependent manner. Following 6 months of treatment, doses of 0.20 and 0.40 g/m2 per day reduced putrescine levels to approximately 34% and 10%, respectively, of those observed in the placebo group. Smaller decreases were seen in spermidine levels and spermidine:spermine ratios. Polyamine levels increased toward baseline values after discontinuation of DFMO. Although there were no statistically significant differences among the dose groups with respect to clinically important shifts in audiometric thresholds and nonaudiologic side effects, statistically significant higher dropout and discontinuation rates were observed in the highest dose group.

CONCLUSIONS

Polyamine levels in rectal mucosa can be continuously suppressed by daily oral doses of DFMO that produce few or no side effects. A dose of 0.20 g/m2 can be used safely in combination phase IIb or single-agent phase III chemoprevention trials.

Excess putrescine accumulation inhibits the formation of modified eukaryotic initiation factor 5A (eIF-5A) and induces apoptosis

DH23A cells, an alpha-difluoromethylornithine-resistant variant of the parental hepatoma tissue culture cells, express high levels of stable ornithine decarboxylase. Aberrantly high expression of ornithine decarboxylase results in a large accumulation of endogenous putrescine and increased apoptosis in DH23A cells when alpha-difluoromethylornithine is removed from the culture. Treatment of DH23A cells with exogenous putrescine in the presence of alpha-difluoromethylornithine mimics the effect of drug removal, suggesting that putrescine is a causative agent or trigger of apoptosis. Accumulation of excess intracellular putrescine inhibits the formation of hypusine in vivo, a reaction that proceeds by the transfer of the butylamine moiety of spermidine to a lysine residue in eukaryotic initiation factor 5A (eIF-5A). Treatment of DH23A cells with diaminoheptane, a competitive inhibitor of the post-translational modification of eIF-5A, causes both the suppression of eIF-5A modification in vivo and induction of apoptosis. These data support the hypothesis that rapid degradation of ornithine decarboxylase is a protective mechanism to avoid cell toxicity from putrescine accumulation. Further, these data suggest that suppression of modified eIF-5A formation is one mechanism by which cells may be induced to undergo apoptosis.

Characterization of a diamine exporter in Chinese hamster ovary cells and identification of specific polyamine substrates

Export of the diamine putrescine was studied using inside-out plasma membrane vesicles prepared from Chinese hamster cells. Putrescine uptake into vesicles was a saturable and an ATP- and antizyme-independent process. Excess amounts of a series of diamines or monoacetyl spermidine, but not monoacetyl putrescine, spermidine, or spermine, inhibited putrescine transport. Putrescine uptake into vesicles prepared at pH 7.4 was suppressed at pH 5, compared with pH 7.4; was stimulated approximately 2.5-fold at pH 7.4 in vesicles prepared at pH 6.25, compared with vesicles prepared at pH 7.4; and was not inhibited by valinomycin in the presence of potassium ions. Reserpine and verapamil blocked [3H]putrescine uptake into inverted vesicles. Verapamil treatment caused an increase in intracellular contents of putrescine, cadaverine, and N8-acetylspermidine, in unstressed proliferating cells, or of N1-acetylspermidine, in cells subjected to heat shock to induce acetylation of spermidine at N1. These data indicate that putrescine export in Chinese hamster cells is mediated by a non-electrogenic antiporter capable of using protons as the counter ion. Physiological substrates for this exporter include putrescine, cadaverine, and monoacetyl spermidine and have the general structure NH3+-(CH2)n-NH2 + R at acidic or neutral pH.

Assessment of mutations in Ki-ras and p53 in colon cancers from azoxymethane- and dimethylhydrazine-treated rats

Mutations in the Ki-ras oncogene and the p53 tumor suppressor gene are known to occur at high frequencies in human colon cancers. We measured the frequency of mutations in these two genes in colon adenocarcinomas obtained from a widely used experimental model of human colon carcinogenesis: F344 rats treated with the carcinogens azoxymethane (AOM) or dimethylhydrazine (DMH). We detected codon 12 mutations in Ki-ras in approximately 60% of colon adenocarcinomas induced by either carcinogen. We characterized the rat p53 intron-exon junctions to construct primers for polymerase chain reaction amplification of this gene. We discovered that the rat p53 gene was structurally different from the human p53 gene, as the rat gene was missing one intron between exons 6 and 7. Both single-stranded DNA conformational polymorphism analysis and direct DNA sequencing of the highly conserved regions of rat exons 5-7 were conducted because the corresponding human regions (exons 5-8) have been reported as being mutated most frequently in human colon cancers. Using these methods, we were unable to identify any p53 mutations in the highly conserved regions of exons 5-7 in either AOM- or DMH-induced colon adenocarcinomas. These data confirm that Ki-ras was mutated in most colon cancers in AOM- or DMH-treated rats but indicate that molecular alterations in the p53 gene, if they occur in this animal model, are different from most p53 mutations in human colon cancers.

Cellular eukaryotic initiation factor 5A content as a mediator of polyamine effects on growth and apoptosis

The polyamines are essential for eukaryotic cell growth. One of the most critical effects of polyamines on cell growth is the availability of spermidine for the post-translational modification of eIF-5A. Because hypusine-containing eIF-5A is necessary for cell proliferation, depletion of cellular polyamines suppresses growth by depleting cellular modified eIF-5A content. Excess putrescine accumulations in DH23A/b cells induces apoptosis and suppresses the formation of hypusine-containing eIF-5A. Treatment of DH23A/b cells with diaminoheptane also suppresses modified eIF-5A formation and induces apoptosis. These data suggest that suppression of modified eIF-5A formation may play a role in putrescine-induced apoptosis as well.

Efflux of the natural polyamine spermidine facilitated by the Bacillus subtilis multidrug transporter Blt

Multidrug transporters pump structurally dissimilar toxic molecules out of cells. It is not known, however, if detoxification is the primary physiological function of these transporters. The chromosomal organization of the gene encoding the Bacillus subtilis multidrug transporter Blt suggests a specific function for this protein; it forms a single operon with another gene, bltD, whose protein product is identified here as a spermine/spermidine acetyltransferase, an enzyme catalyzing a key step in spermidine degradation. Overexpression of the Blt transporter in B. subtilis leads not only to the multidrug-resistance phenotype but also to the efflux of large amounts of spermidine into the medium; this efflux is supressed by an inhibitor of Blt, reserpine. Taken together, these results strongly suggest that the natural function of the Blt transporter is the efflux of spermidine, whereas multiple drugs may be recognized by Blt merely opportunistically.

Loss of intracellular putrescine pool-size regulation induces apoptosis

Synthesis and uptake are two important regulated mechanisms by which eukaryotic cells maintain polyamine levels. The role that loss of synthesis and/or uptake regulation plays in mediating putrescine toxicity was investigated by comparing toxicity in an ornithine decarboxylase (ODC)-deficient Chinese hamster ovary cell line (C55.7) with a functional putrescine transport system and an ODC-overproducing rat hepatoma cell line (DH23b), which are transport regulation deficient. When C55.7 cells were transfected with either mouse ODC (M) or trypanosome ODC (Tb), intracellular putrescine content increased slightly in C55.7(Tb-ODC), compared to C55.7(M-ODC), due to the lack of response of Tb-ODC to polyamine regulation. The increase in putrescine content resulting from loss of ODC regulation had no impact on cell growth and viability. When the feedback repression of polyamine uptake was blocked with cycloheximide, C55.7 cells transfected with either ODC construct accumulated very high levels of putrescine from the medium, and underwent apoptosis in a putrescine dose-dependent manner. A similar correlation of deregulated putrescine uptake and increased apoptotic cells was observed in DH23b cells. These data demonstrate that loss of feedback regulation on the polyamine transport system, but not ODC activity, is sufficient to induce apoptosis. Thus, downregulation of the transport system is necessary to prevent accumulation of cytotoxic putrescine levels in rodent cells.

Surrogate end-point biomarkers as measures of colon cancer risk and their use in cancer chemoprevention trials

Surrogate end-point biomarkers (SEBs) have become widely used in short-term cancer chemoprevention trials in place of cancer end points. This paper discusses criteria relevant to the selection and validation of SEBs for colon cancer risk and the use of SEBs in colon cancer chemoprevention trials. As with a number of other cancers, colon carcinogenesis is the result of a multistep process in which an increasing number of alterations, including specific gene mutations, occur as cells progress from normal to precancerous states of increasing size and dysplasia to cancer and finally to metastatic disease. Ideally, a SEB would show differential expression between the various phases of colon carcinogenesis (i.e., normal, premalignant, and malignant tissues) and be associated with risk of colon cancer. Some SEBs that do not meet these criteria may still be useful for demonstrating the effect of a particular agent. It is also necessary that a SEB be measured in tissues (or other sample material) accessible for multiple and sequential sampling and allow for development of appropriate quality control procedures. Some SEBs must have the potential for modulation by chemopreventive agents. Validation of SEBs for use in chemoprevention studies requires that a relationship between the marker and subsequent risk of cancer be established. Also, the assay reliability and accuracy for each SEB must be determined adequately in well-designed prospective studies.

Hypusine modification in eukaryotic initiation factor 5A in rodent cells selected for resistance to growth inhibition by ornithine decarboxylase-inhibiting drugs

Selection of HTC cells in drugs that inhibit ornithine decarboxylase (ODC) has produced two cell lines, HMOA and DH23A/b, that contain increased amounts of more stable ODC. In addition to alterations in ODC, these cells appear to produce modified eukaryotic initiation factor 5A (eIF-5A) at different rates, a reaction that both requires spermidine and is essential for proliferation. Alterations to the modification of eIF-5A by spermidine cannot be accounted for by changes in eIF-5A protein or modified eIF-5A turnover. Deoxyhypusine synthetase activity is similar in the parental and variant cell lines and is unaltered by growth into plateau phase or by spermidine depletion. The increased rate of eIF-5A modification in DH23A/b cells is due to an increased accumulation of the unmodified eIF-5A precursor. Increased precursor accumulation is not due to increased eIF-5A transcription, but rather it can be attributed to a metabolic accumulation caused by growth under conditions of chronically limiting spermidine. Selection using drugs that inhibit ODC apparently does not cause alterations in the eIF-5A modification pathway. These data support the hypothesis that one of the main effects of spermidine depletion is depletion of the modified eIF-5A pool, and that this is a critical factor in the cytostasis often observed after depletion of cellular polyamines.

Expression of the human spermidine/spermine N1-acetyltransferase in spermidine acetylation-deficient Escherichia coli

A cDNA encoding the human spermidine/spermine N1-acetyltransferase (N1SSAT) was conditionally expressed in a strain of Escherichia coli deficient in spermidine-acetylating activity. Conditional expression of this cDNA was performed under the control of the lac promoter, by addition of the non-hydrolysable lactose analogue isopropyl beta-D-thiogalactoside. Expression of the N1SSAT cDNA oriented in the sense direction resulted in the acetylation of spermidine at the N1 but not the N8 position and a decrease in endogenous spermidine contents and growth rates in these bacteria. When this cDNA was expressed in the antisense orientation, spermidine acetylation was not detected and endogenous spermidine contents and growth rates were unaffected. Increasing the endogenous N1-acetylspermidine concentration by addition of this amine to the culture medium did not suppress growth, and increasing endogenous spermidine pools by exogenous addition was not sufficient to restore optimal growth in cells expressing the human N1SSAT. Exogenous spermidine, but neither N1- nor N8-acetylspermidine, stimulated cell growth in strains unable to synthesize spermidine. These results suggest that one physiological consequence of spermidine acetylation in E. coli is growth inhibition. The mechanism of this inhibition seems to involve the formation of acetylspermidine, and is not simply due to a decrease in the intracellular concentration of non-acetylated spermidine.

Bile acid activation of the gadd153 promoter and of p53-independent apoptosis: relevance to colon cancer

Bile acids are strongly implicated in the etiology of colon cancer. Bile acids also induce apoptosis, and this action may be a key to understanding their role in colon cancer. However the mechanism of bile acid induction of apoptosis is not known. We present evidence of bile acid activation of the gadd153 promoter (a promoter activated by DNA damaging agents). We also show that bile acid induction of apoptosis is p53-independent. In addition, bile salts were found to induce blebbing preceding the actual morphological onset of apoptosis, which indicates early cytoskeletal alterations.

Growth arrest- and polyamine-dependent expression of spermidine/spermine N1-acetyltransferase in human tumor cells

Polyamines are essential for optimal cell growth. The regulation of polyamine biosynthetic, but not catabolic, enzymes has been studied in detail. Because intracellular polyamine contents depend on both synthesis and catabolism, we studied the regulation of spermidine/spermine N1-acetyltransferase (N1SSAT), the first enzyme in polyamine catabolism. Steady-state RNA levels of N1SSAT increased 3-5 fold as human colon tumor-derived HCT116 cells traversed the log phase and entered the plateau phase. Depletion of cellular polyamines, using alpha-difluoromethylornithine, caused a decrease in the steady-state levels of both the 1.3-kb N1SSAT transcript and its 3.5-kb precursor, without affecting the stability of either RNA. N1SSAT enzyme activity was low in cells with normal polyamine contents but could be induced by heat shock. The level of induction of N1SSAT enzyme activity by heat shock on different days of growth correlated with N1SSAT RNA levels prior to heat shock and occurred without changes in levels of message after heat shock. Although non-heat-shocked cells containing normal polyamine contents expressed N1SSAT RNA but not enzyme activity, exogenous spermidine restored both RNA levels and enzyme activity in polyamine-depleted cells. This result suggests that the expression of N1SSAT enzyme activity, but not RNA, requires a change in the intracellular compartmentalization of spermidine. These data demonstrate that N1SSAT is regulated at both the transcriptional and posttranscriptional levels by conditions that arrest growth in HCT116 cells, and that both of these mechanisms are affected by endogenous polyamine contents.

Development of difluoromethylornithine as a chemoprevention agent for the management of colon cancer

Experimental studies have demonstrated that carcinogenesis is a multistep process in which inappropriate proliferation of cells is a critical determinant. Polyamines support sustained growth and are highly regulated in all cells. The rate limiting enzyme for this pathway is ornithine decarboxylase (ODC), an enzyme that exhibits rapid turnover, and converts the amino acid ornithine to putrescine, which in turn is converted to the longer chain amines spermidine and spermine. In animal models of colon carcinogenesis, inhibition of ODC by difluoromethylornithine (DFMO), an enzyme-activated irreversible inhibitor, reduces the number and size of colon adenomas and carcinomas. DFMO was first ineffective when used clinically to treat acute leukemia or melanoma and caused clinically significant but reversible ototoxicity. Subsequently, we performed a series of analyses demonstrating that hearing loss was rare below a total cumulative dose of 150 gm/m2 and increased with total cumulative dose of DFMO. The hearing loss was reversible with rapid reversion to baseline hearing. We and others have conducted Phase IIa trials to determine the lowest dose at which DFMO can decrease colon mucosa polyamine content, and found that an oral dose as low as 0.25 gm/m2 per day (perhaps lower) decreases colon tissue putrescine content and lowers the spermidine/spermine ratio. We are currently conducting a long-term randomized Phase IIb trial which serially measures the long-term effect of several low doses (and placebo) of DFMO on sustaining polyamine depletion in colon mucosa, as well as carefully monitoring hearing by audiometry and other sophisticated tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Polyamine-dependent expression of the matrix metalloproteinase matrilysin in a human colon cancer-derived cell line

Matrilysin, which is a member of the matrix metalloproteinase family and is implicated in colon cancer invasion, is expressed in human colon adenocarcinoma-derived SW1116 cells. We investigated the effect of alpha-difluoromethylornithine (DFMO) on matrilysin expression in this cell line because others have shown that DFMO can inhibit invasion and carcinogenesis in epithelial tissues, including the colon, in experimental models. DFMO reduced extracellular levels of matrilysin protein after 4 d of treatment. Intracellular levels of matrilysin protein were minimally affected by DFMO treatment. The decrease in extracellular matrilysin protein levels caused by DFMO was not a consequence of lowered steady-state levels of matrilysin mRNA. After 4 d of exposure, the amount of this transcript was higher in DFMO-treated cells than in untreated cultures, whereas the mRNA stabilities were similar. These data show that polyamine depletion by DFMO can suppress the expression of matrilysin, a gene product thought to be involved in tumor invasion. The decrease in extracellular matrilysin protein caused by DFMO treatment appears to be due to a posttranscriptional mechanism, although transcription of this gene also seems to be affected by polyamines in SW1116 cells.

Dose de-escalation chemoprevention trial of alpha-difluoromethylornithine in patients with colon polyps

BACKGROUND

alpha-Difluoromethylornithine (DFMO) is a potent inhibitor of carcinogenesis in experimental animal models. In these animal models, DFMO has been especially active in preventing carcinogen-induced epithelial cancers, including those of the skin, colon, breast, and urinary bladder. Although DFMO is known to exert its diverse biological effects by suppressing intracellular pools of the polyamines putrescine and spermidine, the precise mechanism by which polyamine depletion, induced by DFMO, suppresses carcinogenesis is unknown.

PURPOSE

The specific aim of our study was to determine the lowest dose of DFMO that would deplete target tissue (colorectal mucosa) levels of these polyamines in humans who had undergone prior removal of colon polyps while producing minimal toxic effects.

METHODS

A dose de-escalation chemoprevention trial of DFMO was conducted in 111 patients (36 female and 75 male) who were in generally good health, aged 39-79, and who had undergone colonoscopy for surgical removal of an adenomatous colon polyp greater than 3 mm within 5 years prior to entering the study. Groups of patients (12-20 patients per group) were orally treated with single, daily doses of DFMO ranging from 3.0 to 0.1 g/m2 for 4 weeks (28 days). Prior to initiation of DFMO treatment and at the end of treatment, six colorectal biopsy specimens were collected from each patient, along with serum samples. All biopsies were performed between 9 AM and noon to avoid possible effects of diurnal variations in laboratory end points. Samples for analysis of plasma DFMO levels were also collected during this time period on the day after the last day of drug administration.

RESULTS

DFMO caused a decrease in both putrescine content and the ratio of spermidine to spermine for all dose groups down to 0.25 g/m2. Both putrescine content and the ratio of spermidine to spermine and changes in these parameters as a function of DFMO treatment decreased as a function of donor age. None of the 30 patients receiving either 0.25 or 0.5 g/m2 experienced any clinical ototoxicity in this trial.

CONCLUSIONS

DFMO is both safe and effective in reducing colorectal mucosal polyamine contents when it is administered orally to patients at doses as low as 0.25 g/m2 for 28 days. No ototoxicity was observed at doses up to twice this amount.

IMPLICATIONS

If DFMO is also found to be effective in suppressing polyamine contents in other target tissues, it may be useful in preventing a wide range of human epithelial cancers, including those of the prostate and breast.

Gastrointestinal tissue polyamine contents of patients with Barrett's esophagus treated with alpha-difluoromethylornithine

alpha-Difluoromethylornithine (DFMO), an investigational chemopreventive agent, suppresses polyamine contents and decreases epithelial carcinogenesis in experimental models. The ability of this drug to decrease polyamine contents in human esophageal tissues has not yet been determined. Eight patients with Barrett's esophagus were treated with DFMO at a dose of 1.5 g/m2/day for 12 weeks. Four sites (Barrett's lesion, adjacent normal squamous esophagus, gastric tissue, and small bowel) were biopsied in each patient before, during, and after DFMO treatment in order to assess the effects of this drug on tissue polyamine levels. Ornithine decarboxylase activities and polyamine contents varied in each site analyzed. The rank orders were Barrett's > small bowel congruent to normal esophagus > gastric tissue for ODC activities, and small bowel > or = Barrett's congruent to normal esophagus > gastric tissue for putrescine contents. Spermidine, but not spermine, contents in the Barrett's lesions and normal squamous esophageal tissue were suppressed by systemic DFMO treatment and recovered to untreated control values when DFMO therapy was discontinued. Systemic DFMO treatment did not affect the levels of either of these two amines in gastric tissue and small bowel. Since DFMO can suppress polyamine contents in several gastrointestinal tissues, including Barrett's mucosa, we conclude that it is an effective agent with which to test the hypothesis that depletion of spermidine contents may prevent the development of adenocarcinoma of the esophagus in this specific patient group.

Sources of variability in estimating ornithine decarboxylase activity and polyamine contents in human colorectal mucosa

The activity of ornithine decarboxylase (ODC), the first enzyme in polyamine synthesis, is elevated during epithelial carcinogenesis. Since this enzyme is a target for colon and other cancer chemoprevention strategies, we sought to identify sources of variability affecting the measurement of tissue ODC activities and polyamine contents. Multiple colorectal biopsies were obtained from 39 patients undergoing colonoscopy. Biopsy size affected polyamine but not ODC values. Spermidine (spd):spermine (spm) ratios varied less than the contents of the individual amines. Bowel preparation methods did not affect any of the measurements. ODC activities and spd:spm ratios did not vary with bowel location. Lab assay methods contributed to sources of error. Variability was greatest for polyamine content measurements but was reduced when polyamine contents were analyzed as spd:spm ratios. Intrapatient variability of these parameters was as great or greater than interpatient variability. When measured in apparently unaffected colorectal mucosa, none of these parameters were significantly correlated with prior polyp history, number of prevalent polyps found at current colonoscopy, or polyp size. Thus, neither ODC activity nor polyamine contents of normal mucosa appear to be discriminatory markers of colorectal carcinogenesis. However, spd:spm ratios, which show the least variability among measures of polyamine contents, should be a good marker of the consequence of polyamine synthesis inhibition in chemoprevention trials.

Combining polyamine depletion with radiation therapy for rapidly dividing head and neck tumors: strategies for improved locoregional control

PURPOSE

Locoregional control is adversely affected as clonogens from rapidly proliferating tumors repopulate during a course of radiation therapy. The cytostatic agent alpha-difluoromethylornithine (DFMO) was investigated for its capacity to slow proliferation kinetics in human squamous cell carcinomas (SCC) of the head and neck (H&N), with the ultimate objective of improving locoregional control in rapidly dividing tumors treated with radiation therapy.

METHODS AND MATERIALS

Three human SCC cell lines established from primary H&N tumors were evaluated in vitro (cell culture) and in vivo (SCC tumor xenografts in athymic mice) for the capacity of DFMO to induce growth inhibition. Flow cytometry analysis of SCC tumor growth kinetics and quantitative assessment of polyamine biosynthesis inhibition was performed to verify DFMO activity. DFMO effects on in vitro SCC radiosensitivity using clonogenic survival were also studied.

RESULTS

A noncytotoxic exposure to DFMO (5mM x 72 hours) induced pronounced growth inhibition in all three SCC cell lines (70-90% at 7 days), and induced a 2-3 fold delay in volume doubling time for SCC tumor xenografts when administered orally in the drinking water (1.5%) to athymic mice. Kinetic analysis via flow cytometry confirmed that DFMO produced a lengthening of SCC cell cycle times, but did not alter in vitro radiosensitivity. Inhibition of ornithine decarboxylase (ODC) activity and depletion of endogenous polyamines (putrescine and spermidine), were confirmed in normal tissue (mouse skin) and in human SCC tumor xenografts of athymic mice receiving continuous oral DFMO.

CONCLUSION

These data indicate that antiproliferative agents, such as DFMO, are capable of altering human SCC growth kinetics without altering intrinsic radiosensitivity. Such kinetic modulation may therefore provide a strategy to reduce the adverse impact of tumor cell proliferation during a radiotherapy treatment course for rapidly dividing tumors such as those in the H&N.

Consequences of aberrant ornithine decarboxylase regulation in rat hepatoma cells

DH23A cells, an alpha-difluoromethylornithine (DFMO)-resistant variant of rat hepatoma tissue culture cells (HTC), contain high levels of very stable ornithine decarboxylase (ODC). In the absence of DFMO, the high ODC activity results in a large accumulation of endogenous putrescine. Concomitant with the putrescine increase is a period of cytostasis and a subsequent loss of viable cells. In contrast, HTC cells with a moderate polyamine content can be maintained in exponential growth. This suggests that a moderate polyamine concentration is necessary for both optimal cell growth and survival. The cytotoxicity observed in the DH23A cells is apparently not due to byproducts of polyamine oxidation or alterations in steady state intracellular pH or free [Ca2+]. It is possible to mimic the effects of high levels of stable ODC by treatment of cells with exogenous putrescine in the presence of DFMO. This suggests that overaccumulation of putrescine is the causative agent in the observed cytotoxicity, although the mechanism is unclear. These data support the hypothesis that downregulation of ODC may be necessary to prevent accumulation of cytotoxic concentrations of the polyamines.

Heat shock-induced shedding of cell surface integrins in A549 human lung tumor cells in culture

The human lung carcinoma-derived cell line A549 attaches to plastic and vitronectin-coated substrates in a manner dependent upon the specific cell surface integrin alpha v beta 3. Exposure to hyperthermic temperatures (42-45 degrees C) causes these cells to detach from the substrates. In heat-shocked cultures, the alpha v, alpha 5, and beta 3 integrin subunits remain attached to the substrate. Analysis of individual cells by fluorescence-activated cell sorting shows that cell surface levels of alpha v beta 3 decrease by up to 10-fold in response to heat shock, while the abundance of another integrin found on the surface of A549 cells, alpha 3 beta 1, is only minimally affected by this stress. Heat shock-induced decreases in alpha v beta 3 also occur in cells growing in suspension cultures, showing that physical attachment onto an extracellular substrate is not required for the hyperthermia-induced loss of this integrin. The heat shock-induced detachment of the cells and the shedding of alpha v beta 3 from the cell surface can be inhibited by fetal bovine serum and alpha 2 macroglobulin. Reattachment of A549 cells to substrate is reduced by heat shock. These results demonstrate that heat shock can reduce the cell surface abundance of specific integrin subunits, some of which are involved at sites of cellular attachment to extracellular substrates. These findings may be relevant to the heterogeneous patterns of invasion and metastasis of human tumors following fevers or hyperthermia therapy.

Stress induction of the spermidine/spermine N1-acetyltransferase by a post-transcriptional mechanism in mammalian cells

Heat shock and diethyldithiocarbamate stimulate polyamine catabolism in animal cells by a mechanism involving the induction of spermidine/spermine N1-acetyltransferase (N1-SSAT) activity. Steady-state levels of RNA encoding this enzyme remain essentially unchanged during periods after these stresses when N1-SSAT activity is increased by 3.5-10-fold or more in three different cell lines of hamster and human origin. Depletion of intracellular spermidine pools by alpha-difluoromethylornithine (DFMO) inhibits stress induction of N1-SSAT activity. Exogenous spermidine can restore stress inducibility of N1-SSAT to DFMO-treated cells, and induce this enzyme activity in non-heat-shocked but polyamine-depleted cells. Acetylation at N1 suppresses the ability of spermidine to induce N1-SSAT activity, relative to this same modification at N8. Fluorinated spermidine analogues, which decrease the pKa values of the amine groups at positions 4 and 8, neither induce nor inhibit N1-SSAT activity in DFMO-treated cells. These data demonstrate that certain stresses induce N1-SSAT by a spermidine-dependent post-transcriptional mechanism. The mode of induction is affected by both the propyl and butyl moieties of spermidine.

Ornithine decarboxylase and polyamines in colorectal neoplasia and mucosa

Ornithine decarboxylase (ODC) and polyamines are intimately involved in normal cellular proliferation and are likely to play a role in carcinogenesis. ODC activity and polyamine content were measured in tissue samples obtained during colonoscopy from 48 benign neoplastic polyps (20 tubular adenomas; 28 villous adenomas), 18 cancers (including 5 malignant polyps), and adjacent mucosa. ODC activity in polyp and cancer tissue specimens was higher than in adjacent mucosa in 75 and 83% of pairs, respectively. Similarly, putrescine, spermidine, and spermine contents were higher in the majority of polyps and cancers compared to adjacent mucosa. ODC activity and polyamine content in colonic mucosa from 10 patients without a history of colorectal neoplasia were not different from adjacent mucosal values in the patients with neoplasia. In conclusion, ODC and polyamines are elevated in the majority of colorectal neoplasms, but amounts in normal mucosa do not differentiate between patients with cancer, benign neoplastic polyps, and normal subjects.

A DNA polymerase alpha-associated 56 kDa protein kinase

Initiation of chromosomal DNA replication must be carefully regulated during the cell cycle. We report that Drosophila embryo DNA polymerase alpha complex, isolated by immunological techniques, contains a protein kinase activity. The kinase will phosphorylate histone H1, but prefers peptides contained in the DNA polymerase alpha-kinase complex. Renaturation experiments determined that the kinase activity resides in a 56-kDa peptide.

Delta-type DNA polymerase characterized from Drosophila melanogaster embryos

Genetic and biochemical evidence suggests there are at least three DNA polymerases required for replication in eukaryotic cells. However, Drosophila embryonic cells have a very short duration S phase which is regulated differently. To address the question of whether embryos utilize different DNA polymerases, we employed Mono Q anion exchange chromatography to resolve the DNA polymerase activities. Two types of DNA polymerase, DNA polymerase delta and DNA polymerase alpha, were distinguished by: 1. copurification of DNA primase or 3'-5'exonuclease activities; 2. immunoblot analysis with alpha-specific polyclonal antisera; 3. sensitivity to aphidicolin and BuPdGTP; and 4. processivity measurements with and without Proliferating Cell Nuclear Antigen. These observations suggest that Drosophila embryos, similar to nonembryonic cells, have both alpha- and delta-type DNA polymerases.

Inhibition of DFMO-induced audiogenic seizures by chlordiazepoxide

Mice given 1% alpha-difluoromethylornithine (DFMO) in the drinking water for 5 weeks developed a hyperactive behavior characterized by uncontrolled running upon stimulation with noise. The running was followed by seizures and sometimes death. These behaviors are characteristic of audiogenic seizures. Strain differences in susceptibility to DFMO-induced audiogenic seizures were observed. The order of sensitivity to this DFMO effect was: C3HeB/FEJ = C3H/HeN > CBA/J = BALB/c. Chronic DFMO treatment was found to deplete whole brain putrescine and spermidine, but not spermine nor gamma-aminobutyric acid (GABA), in the 2 strains of mice analyzed, C3H/HeN and BALB/c. The audiogenic seizures were eliminated by pretreatment with the benzodiazepine, chlordiazepoxide (Librium) (40 mg/kg, ip) 105 minutes prior to testing for seizures.

Purtscher's retinopathy preceding acute pancreatitis

A patient with a long history of alcohol abuse had diminished vision. The clinical and angiographic findings were consistent with Purtscher's retinopathy. Subsequently, the patient was hospitalized for acute pancreatitis. To our knowledge, this is the first reported case of pancreatic retinopathy preceding the systemic findings of acute pancreatitis.