Therapy with inhibitors of polyamine biosynthesis in refractory prostatic carcinoma. An experimental and clinical study

Transplantable prostate adenocarcinoma were treated with polyamine biosynthetic inhibitors. alpha-difluoromethylornithine (alpha-DFMO), an inhibitor of ornithine decarboxylase and by s-methylglyoxal-bisguanylhydrazone (MGBG), an inhibitor of s-adenosylmethionine decarboxylase. The therapeutic regimen of 0.8-1.11 g/kg DFMO reduced the tumor growth by 40% whilst the combination with 10.5 mg/kg MGBG completely destroyed the prostate adenocarcinomas in the tumor-bearing animals. The polyamine content of spermidine and spermine in the cancerous tissues is significantly lower whereas the putrescine levels remain unchanged. The MGBG therapy distinctly stimulates the activity of ornithine decarboxylase and increases the putrescine concentration up to toxic levels. The application of alpha-DFMO prevented the toxic accumulation of putrescine and allowed higher doses of MGBG. Clinical trials with polyamine antimetabolites appeared useful due to pathological polyamine excretion of patients with metastatic prostate cancer. The therapy with 0.2-0.3 g/kg DFMO in patients with hormone-resistent prostate cancer and metastasis displayed a moderate anti-tumor activity following 2 months additional treatment. High levels of side effects, however, were registered and were similar to those of other cytotoxic compounds. A combined therapy with DFMO/MGBG in a patient with metastatic anaplastic prostate cancer did not improve the survival rate but showed regressive effects of the histological pattern.     

Effect of intravenous alpha-difluoromethylornithine on the polyamine levels of normal tissue and a transplantable fibrosarcoma

The effect of a continuous i.v. infusion of alpha-difluoromethylornithine (DFMO) on the polyamine metabolism of tumor and normal host tissue was determined. Non-tumor-bearing Fischer 344 rats or rats bearing a transplantable fibrosarcoma received continuous infusions of DFMO through a central venous catheter at three dose levels. Treatment with DFMO resulted in a time- and dose-dependent, cytostatic effect on the growth of the tumor. In fibrosarcoma-bearing rats the tumor putrescine levels were reduced after 6 and 12 days of DFMO treatment. Tumor spermidine levels were consistently reduced after 6 and 12 days of treatment with the reduction being dose dependent. The decrease in tumor ornithine decarboxylase activity was dose dependent. Erythrocyte putrescine levels were decreased in tumor- and non-tumor-bearing rats, suggesting that DFMO reduces the tumor contribution to the erythrocyte pool. Erythrocyte spermidine levels of fibrosarcoma- and non-tumor-bearing rats were elevated at the lower DFMO doses administered for 12 days but returned to normal as the dose was increased. Erythrocyte spermine levels were elevated in both groups of rats at all DFMO doses. Although normal host tissue weights were not affected by treatment with DFMO, the putrescine and spermidine levels of liver, spleen, and kidney and ornithine decarboxylase activity of the liver and kidney were decreased. These data demonstrate that i.v. DFMO has a cytostatic effect toward a rapidly growing fibrosarcoma associated with the depletion of both tumor putrescine and spermidine levels.     

Individual and combined effects of alpha-difluoromethylornithine and ovariectomy on the growth and polyamine milieu of experimental breast cancer in rats

Despite considerable evidence suggesting a critical role of polyamines in the hormonal control of breast cancer growth in vitro, their role in in vivo tumor growth is not established. In these experiments, we evaluated the individual and combined effects of the polyamine biosynthesis inhibitor alpha-difluoromethylornithine (DFMO) and ovariectomy on the growth and cellular levels of ornithine decarboxylase (ODC) and polyamines of N-nitrosomethylurea-induced rat mammary tumors. Despite a similar suppressive effect on ODC activity, the two treatments had a different effect on polyamine levels. As expected, DFMO selectively suppressed putrescine, whereas spermidine and spermine levels were minimally or not affected at all. Since quantitatively putrescine contributes the least to overall polyamine pools, the DFMO effect on this latter parameter was modest. In contrast, ovariectomy, by suppressing the more abundant spermidine and spermine, produced a more profound suppression of total polyamine pools. This finding is in agreement with the notion that hormones not only control ODC activity, but also other enzymes involved in the synthesis of the distal polyamines. Ovariectomy was also more potent than DFMO administration in inhibiting N-nitrosomethylurea-induced mammary tumor growth. No major additive/synergistic effects were observed between DFMO and ovariectomy on tumor growth and cellular levels of ODC activity and polyamines. DFMO administration lowered the tumor level of progesterone receptors and appeared to potentiate the suppressive effect of ovariectomy. In contrast, neither treatment, alone or in combination, altered tumor levels of estrogen receptors. DFMO administration did not affect circulating levels of estradiol and prolactin or uterine and ovarian weights, thus suggesting that its effects were not indirectly mediated through alterations of the endocrine milieu of the host.     

Chemoprevention of human actinic keratoses by topical 2-(difluoromethyl)-dl-ornithine.

Alpha-2-(Difluoromethyl)-dl-ornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, has been shown to suppress skin carcinogenesis in murine models after oral or topical administration. We designed a randomized, placebo-controlled study using a topical hydrophilic ointment formulation with or without 10% (w/w) DFMO. Forty-eight participants with moderate-severe actinic keratoses (AKs) on their forearms (i.e., at least 10 well-circumscribed lesions on the lateral surface) completed a 1-month run-in on placebo ointment. Before randomization, all lateral forearm AKs were circled, counted, photographed, and skin biopsies were obtained for DFMO and polyamine levels. Then participants were randomized to receive DFMO ointment on the right versus the left forearm and placebo hydrophilic ointment on the contralateral forearm twice daily for 6 months. DFMO was not detected in the blood of any subject, and there were no systemic toxicities. None of a subsample of 17 placebo forearms had measurable concentrations of DFMO, whereas 13 of the corresponding DFMO-treated forearms had high DFMO skin levels. As compared with placebo, the 6-month DFMO treatment caused a 23.5% reduction in the number of AKs (P = 0.001) as well as significant suppression of AK biopsy spermidine levels (26%; P = 0.04). Seven of the 48 (14.6%) participants experienced severe (2; 4.2%) or moderate (5; 10.4%) inflammatory reactions on their DFMO-treated arms which required dosing modification. Topical DFMO for 6 months can reduce the number of AK lesions and skin spermidine concentrations in high-risk participants and deserves additional study as a skin cancer chemopreventive agent.     

Effects of inhibitors of polyamine biosynthesis on the growth and melanogenesis of murine melanoma cells

Both 2-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (EC 4.1.1.17), and methylglyoxal bis(guanylhydrazone) (MGBG), a competitive inhibitor of S-adenosylmethionine decarboxylase (EC 4.1.1.50), strikingly stimulated melanotic expression of murine Cloudman S91 melanoma cells. The stimulation of tyrosinase (EC 1.10.3.1) activity and melanin formation by DFMO was closely associated with intracellular depletion of putrescine and spermidine developed in response to the drug. However, little or no evidence was obtained indicating that enhanced melanogenesis in response to MGBG was mediated through an inhibition of polyamine biosynthesis. Indirect inhibitors of ornithine decarboxylase, such as 1,3-diaminopropane and 1,3-diaminopropan-2-ol, but not putrescine, likewise inhibited the growth of the melanoma cells and stimulated their melanin production. The stimulation of melanogenesis by polyamine antimetabolites was not mediated by cyclic adenosine 3':5'-monophosphate, in contrast to the effect elicited by alpha-melanotropin. It is also unlikely that MGBG or the diamines acted as lysosomotropic agents capable of stimulating tyrosinase activity in situ, since the enzyme activity was stimulated by the drugs irrespective of whether assayed in cultured cells or using cell-free homogenates. None of the agents stimulated tyrosinase activity in vitro. The effect of DFMO and MGBG on melanoma cell proliferation was reversible, but the restoration of normal growth and melanin formation, especially in cells exposed to DFMO, was remarkably slow. The present results represent a further experimental model, in which the inhibition of polyamine accumulation is accompanied by signs of terminal differentiation.     

Antigrowth effect of some inhibitors of polyamine synthesis on transplantable prostate cancer

Inhibitors of polyamine synthesis were tested for therapeutic effectiveness on transplantable prostate cancer. Inhibition of either ornithine decarboxylase or S-adenosyl-L-methionine decarboxylase (AMDC) by alpha-difluormethylornithine (DFMO) or methylglyoxal-bis[guanylhydrazone] (MGBG), respectively, was associated with significant antitumor effect. The combination of DFMO with MGBG was not only more effective but no more toxic than MGBG alone. Combination of MGBG with 9-B-D-arabinofuranosyladenine, an indirect effector of SAMDC, failed to increase therapeutic effectiveness of MGBG.     

Putrescine-dependent invasive capacity of rat ascites hepatoma cells.

The effects of inhibitors of polyamine synthesis on the invasive capacity of rat ascites hepatoma (LC-AH) cells were examined by in vitro assay of penetration of the LC-AH cells through a monolayer of calf pulmonary arterial endothelial (CPAE) cells. Pretreatment of LC-AH cells with alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, before seeding them onto a CPAE cell monolayer and culturing them for 24 h in the absence of DFMO decreased the number of penetrating tumor cells time and dose dependently (about 35% of the maximal inhibition) without affecting their viability or proliferative activity. DFMO treatment caused a marked decrease in the intracellular level of putrescine but not of spermidine or spermine. The DFMO-induced decreases in invasive capacity and putrescine level were almost completely reversed by the addition of putrescine to the medium during pretreatment with DFMO or invasion assay but were not affected by exogenous spermidine or spermine. No change in the invasive capacity was observed when the CPAE cells were treated with DFMO and the LC-AH cells with methylglyoxal-bis(guanylhydrazone), an inhibitor of S-adenosylmethionine decarboxylase, which depressed the spermidine and spermine levels but increased the putrescine level in the LC-AH cells. These results suggest that intracellular putrescine modulates the in vitro invasive capacity of LC-AH cells.     

Decreased cytotoxicity of 1-beta-D-arabinofuranosylcytosine in 9L rat brain tumor cells pretreated with alpha-difluoromethylornithine in vitro

The effect of pretreating 9L rat brain tumor cells in vitro with 10 mM alpha-difluoromethylornithine (DFMO), an enzyme-activated, irreversible inhibitor of ornithine decarboxylase, on the cytotoxicity of 1-beta-D-arabinofuranosylcytosine (ara-C) was investigated using a colony-forming assay. DFMO-mediated polyamine depletion significantly decreased the cytotoxicity of ara-C. The addition of putrescine to DFMO-pretreated cells replenishes intracellular polyamine levels and prevents the decrease in ara-C cytotoxicity. Flow cytometric analysis showed that cells treated with ara-C alone entered S phase semisynchronously within 8 hr after the end of treatment. This phenomenon was virtually eliminated by DFMO pretreatment. Addition of putrescine to DFMO-pretreated cells before treatment with ara-C prevented this DFMO-induced cell cycle kinetic effect.     

Inhibitory action of alpha-difluoromethylornithine on N-butyl-N-(4-hydroxybutyl)nitrosamine-induced rat urinary bladder carcinogenesis

We previously have shown that urine components capable of stimulating ornithine decarboxylase activity of urothelium can enhance rat urinary bladder carcinogenesis, and that alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, suppresses carcinogen-initiated rat urinary bladder carcinogenesis. The present investigation was conducted to determine whether DFMO's suppressive effect is stage specific during carcinogenesis and whether the suppressive effect lasts with its continued use. Following initiation with 0.05% N-butyl-N-(4-hydroxybutyl)-nitrosamine in drinking water for 6 wk, male Fischer 344 rats initially weighing 125 to 150 g were randomly divided into two groups, the first receiving 0.2% DFMO in drinking water ad libitum and the second receiving tap water only. Groups of animals were killed at regular intervals until the completion of the experiment at 75 wk. The effect of DFMO was evaluated by monitoring the incidence of tumors, the mean number of tumors per rat, the mean volume of individual tumors, and the mean total tumor volume per rat. The results showed that continuous treatment with DFMO significantly reduced tumor formation until 60 wk (P less than 0.017). The effect was only of borderline significance (0.017 less than P less than 0.035) at 75 wk. Discontinuation of DFMO treatment at 40 wk resulted in the loss of protective effect in all comparisons except for the borderline effect on the tumor number and total tumor volume per rat. DFMO had no significant effect on the incidence or development of preneoplastic early lesions. Mucosal polyamine (spermidine and spermine) levels were reduced and correlated well with the reduction in tumor growth, suggesting that the reduction in tumor growth rate by DFMO may be due to its ability to reduce polyamine levels in urothelium. There were no side effects attributable to DFMO treatment. DFMO may be a useful chemopreventive agent to retard the recurrence of human superficial bladder cancer.     

Microbial flora in the gastrointestinal tract abolishes cytostatic effects of alpha-difluoromethylornithine in vivo

Although treatment with the ornithine decarboxylase inhibitor alpha-difluoromethylornithine (DFMO) leads to depletion of intracellular polyamines and to related growth inhibition in vitro, its cytostatic effects in vivo are disappointing. This may be due to abolition of DFMO-induced growth inhibition by polyamines released during normal body cell turnover, to dietary polyamines, or to putrescine synthesized by the microbial flora in the GI tract. We studied selectively (aerobic) and totally (aerobic + anaerobic) GI tract-decontaminated LI210-bearing mice fed with 3 types of diet differing in their polyamine and carbohydrate residue contents and treated with combinations of intraperitoneal DFMO and oral deuterium-labelled putrescine. Our data show that, irrespective of diet type, total decontamination markedly potentiates the moderate tumor growth inhibition that is caused by DFMO alone. During total decontamination, growth-inhibited L1210 cells accumulate in the G0/G1 phase of the cell cycle. Although orally administered deuterium-labelled putrescine gave rise to deuterium labelling of L1210 putrescine, spermidine and spermine, the polyamine levels in our diets played only a minor role.     

Phospho-sulindac (OXT-328) combined with difluoromethylornithine prevents colon cancer in mice

The nonsteroidal anti-inflammatory drug (NSAID) sulindac and the ornithine decarboxylase (ODC) antagonist difluoromethylornithine (DFMO), individually and together, are effective inhibitors of colon carcinogenesis. However, chronic use of sulindac is associated with significant side effects. We evaluated the chemopreventive efficacy of phospho-sulindac (P-S, OXT-328), an apparently safe derivative of sulindac, together with DFMO, in HT-29 human colon cancer xenografts. Nude mice were divided into four groups as follows: group 1 received vehicle (corn oil); group 2 received P-S (100 mg/kg/d) by oral gavage; group 3 received DFMO (2% in drinking water); and group 4 received P-S (100 mg/kg/d) by gavage plus DFMO (2% in drinking water; P-S/DFMO). Eighteen days after implantation, compared with controls, tumor volume was inhibited 65.9% by P-S, 52.9% by DFMO, and 70.9% by P-S/DFMO (P < 0.01 for all). P-S/DFMO reduced cell proliferation 27.1% and increased apoptosis 38.9% compared with controls (P < 0.05 for both). Compared with controls, P-S reduced the levels of thioredoxin-1 (Trx-1) and thioredoxin reductase (TrxR), whereas DFMO reduced polyamine content (putrescine and spermidine) and TrxR levels. Importantly, P-S/DFMO decreased putrescine and spermidine levels and the expression of Trx-1, TrxR, and cyclooxygenase (COX) 2. Of these molecular targets, TrxR most consistently correlated with tumor growth. Study results show that P-S/DFMO is an efficacious drug combination for colon cancer prevention and also show the safety of P-S, which may overcome the limiting side effects of conventional sulindac. P-S/DFMO has an intricate mechanism of action extending beyond polyamines and including the thioredoxin system, an emerging regulator of chemoprevention. P-S/DFMO merits further evaluation.     

Modulation of biologic endpoints by topical difluoromethylornithine (DFMO), in subjects at high-risk for nonmelanoma skin cancer.

More than one million new skin cancers are diagnosed yearly in the United States creating the need for effective primary and chemopreventive strategies to reduce the incidence, morbidity, and mortality associated with skin cancer. Skin chemoprevention trials often focus on subjects at high risk of nonmelanoma skin cancers and include biological endpoints like number of actinic keratoses (AK) and measures of cell proliferation, apoptosis, and p53 expression and/or mutation. Difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, suppresses increased polyamine synthesis and inhibits tumors in models of skin carcinogenesis. Thus, DFMO is a good candidate chemopreventive agent in humans at increased risk of NMSC. We reported previously results of a randomized, placebo-controlled trial of topical DFMO in 48 participants with AK. In this study there was a significant reduction in the number of AK (23.5%; P = 0.001) and the polyamine, spermidine (26%, P = 0.04; Alberts, D. S. et al. Cancer Epidemiol. Biomark. Prev., 9: 1281-2186, 2000). In skin biopsies from the same study, we demonstrate that topical DFMO significantly reduces the percentage of p53-positive cells (22%; P = 0.04); however, there were no significant changes in proliferating cell nuclear antigen or apoptotic indices, or in the frequency of p53 mutations (25% at baseline, 21% after placebo, and 26% after DFMO). We conclude that inhibition of the premalignant AK lesions as well as a reduction in the expression of p53 and in spermidine concentrations may serve as surrogate endpoint biomarkers of DFMO and possibly other topically administered skin cancer chemopreventive agents.     

Differential effects of polyamine homologues on the prevention of DL-alpha-difluoromethylornithine-mediated inhibition of malignant cell growth and normal immune response.

Natural polyamines (putrescine, spermidine, and spermine) are ubiquitous cellular cations that play an important role in cell proliferation and differentiation. Ornithine decarboxylase is the first and a rate-limiting enzyme in the biosynthesis of polyamines. Polyamine depletion using DL-alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, has been shown to suppress cell growth in a variety of settings, including those of tumor and lymphocyte proliferation. The objective of the present investigation was to examine the inhibitory effects of DFMO on a variety of murine in vitro immune responses, including lymphocyte proliferation in response to T-cell mitogen (concanavalin A), B-cell mitogen (lipopolysaccharide), and alloantigen as well as cytotoxicity. DFMO-mediated inhibition of cell proliferation in these cases correlated with depletion of intracellular polyamines. The inhibitory effects of DFMO were reversed by polyamine repletion with putrescine. Putrescine also reversed the growth-inhibitory effects of DFMO on 4 tumor cell lines that we tested: 28-13-3S, YAC-1, P-815, and K562. However, putrescine homologues exhibited a differential effect in preventing DFMO-mediated inhibition of cell growth in normal lymphocytes and cancer cell lines. Only putrescine homologues containing a shorter methylene chain were effective in preventing the growth-inhibitory action of DFMO on normal immune response. In contrast, only the longer chain homologue 1,5-diaminopentane overcame the effect of DFMO on tumor cell growth. These findings suggest that supplementation with selected polyamine homologues may sustain normal immune response in DFMO-treated individuals while effectively suppressing malignant cell growth. The potential clinical relevance of these observations is discussed.     

Inhibition of ornithine decarboxylase with 2-difluoromethylornithine: reduced incidence of dimethylhydrazine-induced colon tumors in mice

2-Difluoromethylornithine (DFMO) was administered to 1,2-dimethylhydrazine (DMH)-treated mice to reduce colonic polyamine levels and mucosal hyperplasia. Mice received 1% DFMO in drinking water throughout the experiment and were given injections of DMH (20 mg/kg) weekly for 28 weeks. DFMO inactivated 93% of colonic ornithine decarboxylase activity. Although DMH treatment did not induce colonic ornithine decarboxylase activity by Week 28, the putrescine content was increased 31% in DMH-treated mice (p less than 0.01). Concurrent treatment with DFMO depressed putrescine content (42 to 63%) and spermidine content (27 to 38%), but it increased spermine content (18 to 22%). At Week 28 of treatment with DMH alone, RNA content was increased 8.6% (p less than 0.01), DNA content 10% (p less than 0.01), DNA specific activity 24% (p less than 0.01), and crypt depth 20% (p less than 0.01), but not in mice receiving DMH and DFMO. At 28 weeks, 13 of 17 mice (76%) treated with DMH alone had histologically confirmed colon cancers; of mice treated with DMH and DFMO, two of 18 (11%) had colonic tumors. Throughout the experiment, 50 colon cancers developed in 16 DMH-treated mice (mean, 3.12 tumors/mouse); three mice treated with DMH and DFMO developed three colon cancers total (p less than 0.001). Reduction of colonic polyamine levels after DFMO treatment prevents proliferative changes induced by DMH and reduces the incidence of tumors.     

Inhibition of the growth of U-251 human glioblastoma in nude mice by polyamine deprivation

An almost complete prevention of tumor growth was achieved in U-251 human glioblastoma xenografted nude mice, by partial decontamination of the gastrointestinal tract and feeding of a polyamine-free diet containing inhibitors of ornithine decarboxylase (DFMO) and of polyamine oxidase (MDL 72527). After one week of polyamine deprivation, spermidine concentrations were lowered, and spermine levels were increased in all tissues. In contrast, putrescine concentrations were only reduced in tumor and in brain. Erythrocyte polyamine determinations revealed differences similar to those observed in tissues: spermidine concentration was lowered by 50% and spermine level was 3-fold increased. If this or related treatments should become of therapeutic importance in the future, then the determination of erythrocyte polyamine levels might be of diagnostic value.     

Chemoprevention of prostate carcinogenesis by DFMO and/or finasteride treatment in male Wistar rats

In the present study the chemopreventive activities of DFMO, the irreversible inhibitor of ornithine decarboxylase, and finasteride, the inhibitor of prostatic 5a-reductase, against the development of chemically induced prostate adenocarcinoma by methylnitrosourea/testosterone propionate in male Wistar rats were investigated. According to histological examination, oral administration of DFMO and finasteride, either alone or combined, for two months to MNU/TP-inoculated rats reduced the tumor incidence to 11.11%, 10% and 10%, respectively, compared to tumored controls (64.3%). DFMO and/or finasteride treatment resulted in significant reductions in the wet weight of the prostate gland and seminal vesicles and its ratio relative to the total body weight, as well as the levels of prostate total protein, DNA, RNA and DNA/RNA ratio, compared to tumored controls. However, the effect of the combined treatment was of no statistical significance compared to single DFMO or finasteride treatment, as demonstrated by the non-significant differences between the mean values of most of the studied parameters. The tumor chemopreventive activity and the prostate growth inhibitory effect of DFMO and finasteride were due to suppression of prostate polyamine synthesis. ANOVA test revealed that the relative weight of the prostate as well as blood and tissue polyamine levels could be used as significant endpoint biomarkers for DFMO and finasteride as cancer chemopreventive agents.     

Tumor angiogenesis and polyamines: alpha-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, inhibits B16 melanoma-induced angiogenesis in ovo and the proliferation of vascular endothelial cells in vitro.

alpha-Difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, inhibited B16 melanoma-induced angiogenesis in chick embryo chorioallantoic membrane and subsequently the growth of the tumor on the chorioallantoic membrane. These inhibitions were reversed by exogenous putrescine and spermidine. DFMO also inhibited rapid neovascularization in yolk sac membrane of 4-day-old chick embryos and the inhibition was reversed by exogenous putrescine and spermidine. DFMO strongly inhibited DNA synthesis and proliferation of bovine pulmonary artery endothelial (BPAE) cells in culture and decreased their ornithine decarboxylase activity and intracellular polyamine concentrations. Addition of putrescine to the culture medium of DFMO-treated BPAE cells restored their intracellular putrescine and spermidine concentrations and their DNA synthesis and proliferation. Addition of spermidine to cultures of DFMO-treated BPAE cells restored their intracellular spermidine concentration and their DNA synthesis and proliferation. DFMO inhibited the proliferation of B16 melanoma cells in culture but the inhibitory effect was much less than that on BPAE cells. When one-half the monolayer of confluent cultures of BPAE cells had been peeled off, addition of DFMO to the cultures inhibited the proliferation and extension of the BPAE cells into the vacant area but had no effect on stationary cells in the remaining half of the monolayer, suggesting that it inhibited induction of proliferation of endothelial cells. These findings suggest that the antitumor activity of DFMO against solid tumors is probably due more to its inhibition of tumor-induced angiogenesis by inhibition of proliferation of endothelial cells induced by polyamine depletion than to a direct effect on tumor cell proliferation.     

Selectivity of polyamine involvement in hormone action on normal and neoplastic target tissues of the rat

The present experiments were designed to evaluate the polyamine involvement in hormonal actions on proliferation and receptor content of neoplastic tissue (hormone-responsive breast cancer) as well as on growth of normal endocrine target tissue (uterus) in the same animals. Administration of estradiol and perphenazine (to stimulate endogenous prolactin release) stimulated N-nitrosomethyl-urea (NMU)-induced rat mammary tumor growth following ovariectomy-induced tumor regression. Such hormonal activation of breast cancer growth was completely abolished by treatment with -difluoromethyl-ornithine (DFMO), a specific irreversible inhibitor of ornithine decarboxylase, which lowered tumor content of polyamines. The growth inhibitory effect of DFMO was partially reversible by exogenous putrescine administration. In contrast, the rise in cytosolic content of progesterone receptors induced by hormonal treatment was not affected by suppression of tumor polyamine levels by DFMO. Similarly, DFMO administration failed to influence the hormone-induced increase in uterine weight in the same animals. Thus, our data suggest selectivity of polyamine involvement in hormone actions, which, in our experimental system, seems to be restricted to the endocrine control of neoplastic cell proliferation.     

Inhibition of the development of metastatic squamous cell carcinoma in protein kinase C epsilon transgenic mice by alpha-difluoromethylornithine accompanied by marked hair follicle degeneration and hair loss

The role of 12-O-tetradecanoylphorbol-13-acetate (TPA)-stimulated polyamine biosynthesis in the development of metastatic squamous cell carcinoma (mSCC) in protein kinase C epsilon (PKC epsilon) transgenic mice was determined. TPA treatment induced epidermal ornithine decarboxylase (ODC) activity and putrescine levels approximately 3-4-fold more in PKC epsilon transgenic mice than their wild-type littermates. Development of mSCC by the 7,12-dimethylbenz(a)anthracene (100 nmol)-TPA (5 nmol) protocol in PKC epsilon transgenic mice was completely prevented by administration of the suicide inhibitor of ODC alpha-difluoromethylornithine (DFMO, 0.5% w/v) in the drinking water during TPA promotion. However, DFMO treatment led to marked hair loss in PKC epsilon transgenic mice. DFMO treatment-associated hair loss in PKC epsilon transgenic mice was accompanied by a decrease in the number of intact hair follicles. These results indicate that TPA-induced ODC activity and the resultant accumulation of putrescine in PKC epsilon transgenic mice are linked to growth and maintenance of hair follicles, and the development of mSCC. Severe hair loss observed in PKC epsilon transgenic mice on DFMO during skin tumor promotion has not been reported before in the prevention of cancer in other animal models or in human cancer prevention trials.     

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.