Matrix metalloproteinase inhibition as a novel anticancer strategy: a review with special focus on batimastat and marimastat.

Matrix metalloproteinases (MMPs) are a homologous family of enzymes that are involved in tissue remodeling and morphogenesis. Collectively, these enzymes are capable of degrading all components of the extracellular matrix, and they play an important role in normal physiologic conditions, such as wound healing and other processes involving tissue remodeling. However, increased activity of these enzymes now has been observed in a number of different pathological conditions, and it has been hypothesized that such increased activity of MMPs might play a role in the pathogenesis of these conditions. Cancer is one such condition; extracellular matrices constitute the principal barrier to tumor growth and spread, and there is growing experimental evidence that malignant tumors utilize MMPs to overcome these barriers. Consequently, inhibitors of MMPs represent an attractive target for a new class of anticancer agents. Marimastat and batimastat are potent broad-spectrum inhibitors of all major MMPs and have been shown to prevent or reduce spread and growth of a number of different malignant tumors in numerous animal models. Both agents are now in advanced clinical testing in a number of different solid tumors in North America and Europe. The purpose of this paper is to review available preclinical and emerging clinical data, using batimastat and marimastat as prototype MMP inhibitors in the cancer area.

Antihuman Immunodeficiency Virus (HIV-1) Activities of Inhibitors of Polyamine Pathways.

Four inhibitors of polyamine biosynthetic pathways were tested for their effect on HIV-1 replication in phytohemagglutinin-stimulated human peripheral blood mononuclear cells. Methyl acetylenic putrescine (MAP) and alpha-monofluoromethyldehydroornithine methyl ester, irreversible inhibitors of ornithine decarboxylase, inhibited the production of p24 antigen in phytohemagglutinin-stimulated peripheral blood mononuclear cells by clinical HIV-1 strains isolated from HIV-infected patients with IC(50) values of about 1-2 &mgr;M. 5'--5'-deoxyadenosine (MDL 73811), an enzyme-activated irreversible inhibitor of S-adenosyl-L-methionine (AdoMet) decarboxylase, also inhibited the production of p24 antigen by HIV-1 strains in peripheral blood mononuclear cells with IC(50) values of 1-2 &mgr;M. The least potent was 1-aminoxyethylamine which is another inhibitor of AdoMet decarboxylase. MAP showed the best therapeutic index of 500-1,000. Copyright 1996 S. Karger AG, Basel

S-Adenosylmethionine and methylation.

S-Adenosylmethionine (AdoMet or SAM) plays a pivotal role as a methyl donor in a myriad of biological and biochemical events. Although it has been claimed that AdoMet itself has therapeutic benefits, it remains to be established whether it can be taken up intact by cells. S-Adenosylhomocysteine (AdoHcy), formed after donation of the methyl group of AdoMet to a methyl acceptor, is then hydrolyzed to adenosine and homocysteine by AdoHcy hydrolase. This enzyme has long been a target for inhibition as its blockade can affect methylation of phospholipids, proteins, DNA, RNA, and other small molecules. Protein carboxymethylation may be involved in repair functions of aging proteins, and heat shock proteins are methylated in response to stress. Bacterial chemotaxis involves carboxymethylation and demethylation in receptor-transducer proteins, although a similar role in mammalian cells is unclear. The precise role of phospholipid methylation remains open. DNA methylation is related to mammalian gene activities, somatic inheritance, and cellular differentiation. Activation of some genes has been ascribed to the demethylation of critical mCpG loci, and silencing of some genes may be related to the methylation of specific CpG loci. Viral DNA genomes exist in cells as extrachromosomal units and are generally not methylated, although once integrated into host chromosomes, different patterns of methylation are correlated with altered paradigms of transcriptional activity. Some viral latency may be related to DNA methylation. Cellular factors have been found to interact with methylated DNA sequences. Methylation of mammalian ribosomal RNAs occurs soon after the synthesis of its 47S precursor RNA in the nucleolus before cleavage to smaller fragments. Inhibition of the methylation of rRNA affects its processing to mature 18S and 28S rRNAs. The methylation of 5'-terminal cap plays an important role in mRNA export from the nucleus, efficient translation, and protection of the integrity of mRNAs. Another important function of AdoMet is that it serves as the sole donor of an aminopropyl group that is conjugated with putrescine to form, first, the polyamine spermidine, and then spermine.

Combination chemotherapy of drug-resistant Trypanosoma brucei rhodesiense infections in mice using DL-alpha-difluoromethylornithine and standard trypanocides.

Combinations of DL-alpha-difluoromethylornithine (DFMO; eflornithine; Ornidyl) with either suramin or melarsen oxide were found to be effective against acute laboratory model infections with Trypanosoma brucei rhodesiense. We used clinical isolates known to be resistant to these drugs when used singly. An infection with a melarsen oxide-refractory isolate was cured by a combination of low-dose DFMO (0.5% in the drinking water) plus low-dose suramin (1 mg/kg of body weight given intraperitoneally). Another strain, moderately resistant to arsenical drugs, was cured with combinations of 4% DFMO with 5 mg of melarsen oxide per kg. Furthermore, a combination of DFMO (2% in the drinking water) and suramin (20 mg/kg) provided a 100% cure rate in a central nervous system model, although the same doses of these drugs used singly were completely ineffective. The synergism of DFMO and suramin against an acute infection was improved when suramin was given at the end of the DFMO administration. No adverse interactions were observed when high doses of DFMO combined with high doses of suramin were administered to uninfected mice. These results suggest that combinations of DFMO and suramin should be examined clinically for activity in arsenical-drug-refractory cases of East African sleeping sickness.

Altered intracellular polyamines in bloodstream form Trypanosoma brucei brucei: transformation to procyclic trypomastigotes.

A monomorphic strain of Trypanosoma brucei brucei (EATRO 110) was cultured as long slender bloodstream forms in vitro for 24 h with 100 microM Eflornithine HCl. This resulted in depletion of intracellular putrescine, a greater than 50% decrease in spermidine, and a cessation of cell division. These Eflornithine treated trypanosomes were stimulated to synchronously transform to procyclic trypomastigotes by transfer into SDM-79 medium containing the citric acid cycle intermediates citrate and cis-aconitate (CCA). Within 48 h morphological transformation was complete and occurred without any increase in cell numbers. The coadministration of 100 microM putrescine with Eflornithine prevented the depletion of putrescine and abrogated the cytostatic effect of Eflornithine alone, but did not prevent the transformation to procyclic trypomastigotes. Eflornithine-induced short stumpy form trypanosomes resulting from 4 days of culture with 100 microM Eflornithine did not transform to procyclic trypomastigotes in SDM-79 medium unless it contained CCA. We conclude that the high concentration of CCA can trigger transformation in all morphological types of bloodstream form trypanosomes, regardless of their threshold of sensitivity for the stimulus. Furthermore, the CCA-stimulated transformation is not dependent on putrescine and can occur independently of cell division.

Resistance to DL-alpha-difluoromethylornithine by clinical isolates of Trypanosoma brucei rhodesiense. Role of S-adenosylmethionine.

The ornithine decarboxylase (ODC) inhibitor DL-alpha-difluoromethylornithine (DFMO) has emerged as a new treatment for West African sleeping sickness but is less effective against East African sleeping sickness. We examined uncloned clinical isolates of Trypanosoma brucei rhodesiense, agent of the disease in East Africa, which were refractory to DFMO in laboratory infections, for characteristics that would explain their resistance. None of the isolates were from patients treated with DFMO. Two isolates took up [3H]DFMO at 50-70% lower rates than drug-sensitive strains but ODC activities, Ki values for DFMO, spermidine and spermine uptake rates, polyamine content and inhibition of polyamine metabolism by DFMO were statistically (P < 0.05) similar between sensitive and refractory isolates. One cloned strain, continuously passaged in vivo under DFMO pressure and included for comparison, had > 85% lower ODC activity and up to 14-fold higher putrescine uptake rates than sensitive controls. A statistically important trend was the metabolism of S-adenosylmethionine (AdoMet): activities of AdoMet synthetase and AdoMet decarboxylase were 2- to 5-fold and 3- to 40-fold lower in resistant strains, respectively, while intracellular AdoMet pools (AdoMet + decarboxylated AdoMet) that were > 60-fold elevated in sensitive strains during DFMO treatment, increased only 9-fold in refractory isolates. The extreme elevation of the AdoMet pool in sensitive isolates from 0.7 to 44 nmol/mg protein and an intracellular pool concentration of approximately 5 mM may lead to an imbalance in methylation of proteins or other cell constituents as a consequence of DFMO action. These studies indicate that the metabolism of AdoMet is altered significantly in DFMO refractory isolates and suggest that differences in AdoMet metabolism may be responsible for increased tolerance to DFMO.

S-adenosylmethionine decarboxylase as an enzyme target for therapy.

The polyamine biosynthetic pathway has attracted much interest as a therapeutic target. Many studies have shown the potential value of inhibitors of the first enzyme in the biosynthetic pathway, ornithine decarboxylase, which forms putrescine. In order to convert putrescine into the polyamines, spermidine and spermine, the aminopropyl donor, decarboxylated S-adenosylmethionine, is needed. Therefore, S-adenosylmethionine decarboxylase (AdoMetDC, EC 4.1.1.50) is essential for polyamine synthesis. Early studies of the inhibition of this enzyme were carried out with compounds such as methylglyoxal bis(guanylhydrazone) that lack specificity and also lack potency since they are competitive inhibitors whose effects are overcome by a compensatory increase in the amount of the target enzyme. Recently, powerful irreversible inhibitors of AdoMetDC have become available including 5'-([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxyadenosine, an enzyme activated inhibitor and 5'-deoxy-5'-[(3-hydrazinopropyl)methylamino]adenosine which binds to the active site and forms a covalent bond with the pyruvate prosthetic group. This review describes the current state of knowledge of the structure and properties of AdoMetDC, the available inhibitors of this enzyme, their mechanism of action and their effects on polyamines and on the growth of tumors and protozoan parasites. These effects indicate that AdoMetDC inhibitors may be of therapeutic value either alone or in combination with ornithine decarboxylase inhibitors and that further trials of these compounds should be considered.

Cure of murine Trypanosoma brucei rhodesiense infections with an S-adenosylmethionine decarboxylase inhibitor.

The compound 5'-([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxyadenosine (MDL73811), a potent inhibitor of S-adenosylmethionine decarboxylase, was effective in mice against six of eight clinical isolates of Trypanosoma brucei rhodesiense, the causative agent of East African sleeping sickness. In combination with the ornithine decarboxylase inhibitor DL-alpha-difluoromethylornithine (DFMO; Ornidyl), MDL73811 acted synergistically to cure seven of eight infections. MDL73811 was effective when given singly at 50 to 100 mg/kg of body weight per day for 7 days (osmotic pumps). In combination with subcurative DFMO levels (0.25 to 1.0% in drinking water for 7 days), the curative MDL73811 dose could be lowered to 25 or 50 mg/kg, depending on the isolate. Oral administration of the MDL73811-DFMO combination was also effective in an acute infection and in a long-term central nervous system model of Trypansoma brucei brucei infection. These data indicate that MDL73811 may be effective therapeutically in drug-refractory and late-stage East African trypanosomiasis.

Biochemical evidence for the presence of arginine decarboxylase activity in Trypanosoma cruzi.

Trypanosoma cruzi was found to release 14CO2 from radiolabeled arginine, and this effect was inhibited by either DL-alpha-difluoromethylarginine or monofluoromethylagmatine, both specific inhibitors of arginine decarboxylase (ADC). Furthermore, agmatine, which can be derived metabolically only by ADC-mediated arginine decarboxylation, was produced when T. cruzi was incubated with radiolabeled arginine, and agmatine production was inhibited in the presence of DL-alpha-difluoromethylarginine. These results constitute direct biochemical evidence for the presence in T. cruzi of ADC, an enzyme that does not occur in mammalian cells.

Ornithine decarboxylase as an enzyme target for therapy.

Interest in ornithine decarboxylase (ODC) and the therapeutic effects of its inhibition with the consequent depletion of polyamine biosynthesis has been widespread since the late 1970s and 1980s. This review covers new information about the properties of ODC, recent findings with ODC inhibitors and a discussion of the mechanism of inactivation of ODC by eflornithine. Recent in vivo therapeutic approaches of ODC inhibition are also discussed including: cancer and cancer chemoprevention; autoimmune diseases; polyamines and the blood-brain barrier, ischemia and hyperplasia; the NMDA receptor and modulation by polyamines; hearing loss; African trypanosomiasis; Pneumocystis carinii pneumonia and Cryptosporidium in AIDS; and other infectious diseases/organisms.

Suppression of Leishmania donovani by oral administration of a bis(benzyl)polyamine analog.

We reported previously that intraperitoneal administration of a bis(benzyl)polyamine analog, MDL 27,695, suppressed both pentavalent antimony (Sbv)-susceptible and -resistant Leishmania donovani in vivo. The present studies were performed to optimize parasite suppression by parenteral administration and to evaluate the efficacy of oral treatment with MDL 27,695. L. donovani infections in BALB/c mice were suppressed greater than 99% after intraperitoneal dosing for 20 days with a total dose of 150 mg of MDL 27,695 per kg of body weight or 560 mg of Sbv per kg. Suppression was not increased by a total dose of 400 mg of MDL 27,695 per kg given for 20 days. In mice treated for 2, 4, or 7 days with either MDL 27,695 or Sbv (total doses of 60, 120, and 210 mg/kg, respectively), more liver parasites were killed with MDL 27,695 than with Sbv. Assessment of livers posttreatment showed that parasite killing continued for at least 3 days in MDL 27,695-treated mice but not for longer than 1 day in Sbv-treated mice. Intramuscular administration of drugs resulted in 92% parasite suppression by MDL 27,695 (15 mg/kg three times per day for 5 days) and 64% suppression by Sbv (60 mg/kg once per day for 5 days). Dosing of mice by oral gavage with 100 mg of MDL 27,695 per kg twice per day for 14 days resulted in 99.7% parasite suppression, and the 50% effective dose was approximately 11 mg of MDL 27,695 per kg. MDL 27,695 represents an effective new drug potentially useful for oral or parenteral treatment of visceral leishmaniasis.

Irreversible inhibition of S-adenosylmethionine decarboxylase in Plasmodium falciparum-infected erythrocytes: growth inhibition in vitro.

Blocking spermidine and spermine synthesis in Plasmodium falciparum-infected erythrocytes with irreversible inhibitors of S-adenosylmethionine decarboxylase (AdoMet DC; EC 4.1.1.50), prevented the growth of the parasite in vitro. The most potent of these compounds, MDL 73811, inhibited growth of chloroquine-sensitive and -resistant strains of P. falciparum equally, with an IC50 of 2-3 microM. Other structurally related compounds also inhibited parasite proliferation, but to a lesser degree, determined apparently by their potency for inhibition of AdoMet DC. The growth inhibition by MDL 73811 could be alleviated by incubating infected erythrocytes with spermidine and spermine, but not putrescine. Parasites treated with the drug were arrested at the trophozoite stage of the erythrocytic cycle and had putrescine levels which were elevated by about 3- to 4-fold. Treatment of crude extracts of purified parasites with 1 microM MDL 73811 inhibited AdoMet DC activity by greater than 90%. These biochemical changes in P. falciparum-infected cells were consistent with AdoMet DC inhibition being the primary effect of MDL 73811 treatment.

Disruption of Plasmodium falciparum-infected erythrocyte cytoadherence to human melanoma cells with inhibitors of glycoprotein processing.

Adherence of Plasmodium falciparum-infected erythrocytes (IE) to the venular endothelium in brain and other organs is characteristic of cerebral malaria, an often fatal complication in infected individuals. It has been shown that cytoadherence may be mediated through interaction of IE with glycoproteins on host target cell surfaces, including CD36 (GPIV), intercellular adhesion molecule-1 (ICAM-1), and thrombospondin. Inhibitors of glycoprotein synthesis and processing were tested for their abilities to decrease IE adherence to C32 human melanoma cells. The alpha-glucosidase inhibitor, castanospermine, was effective in disrupting cytoadherence in vitro when incubated with C32 cells (IC50 = 600-700 microM). Castanospermine-6-butyrate was even more effective than the parent compound (IC50 = 9 microM) in disrupting cytoadherence. The mannosidase inhibitors, swainsonine and deoxymannojirimycin, had no effect on cytoadherence at concentrations up to 2 mM. No effect on cytoadherence was observed when the glucosidase and mannosidase inhibitors were incubated with IE rather than the C32 cell cultures. The level of CD36 on the C32 cell surface was decreased as measured by fluorescence-activated cell sorting (FACS) analysis with the same inhibitors which inhibited cytoadherence. Cells labeled with fluorescein isothiocyanate (FITC) OKM5 monoclonal antibody, which recognizes CD36 and disrupts cytoadherence, showed decreased fluorescence when treated with tunicamycin and castanospermine-6-butyrate but not when treated with swainsonine or deoxymannojirimycin. ICAM-1 levels, as measured by surface labeling of C32 cells with FITC CD54 monoclonal antibody, were decreased in cells treated with tunicamycin. However, incubation of cells with castanospermine-6-butyrate or deoxymannojirimycin decreased cell surface ICAM-1 levels only slightly. These findings suggest that (1) in C32 cells, levels of cell surface CD36, and not ICAM-1, change proportionally to the level of cytoadherence; (2) drugs which can affect the carbohydrate moiety of cellular glycoproteins decrease cytoadherence of IE to C32 cells; and (3) protection against the development of cerebral malaria may be possible with inhibitors of glycoprotein biosynthesis.

Antitrypanosomal effects of polyamine biosynthesis inhibitors correlate with increases in Trypanosoma brucei brucei S-adenosyl-L-methionine.

We reported recently that administration of ([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxyadenosine (MDL 73811), an enzyme-activated irreversible inhibitor of S-adenosyl-L-methionine decarboxylase (AdoMetDC; EC 4.1.1.50), a key enzyme in the synthesis of spermidine, cures African trypanosome infections in mice. The precise mechanism of action of MDL 73811 was not clear because a rapid disappearance of trypanosomes from the bloodstream of treated rats occurred before significant depletion of spermidine. Administration of MDL 73811 to Trypanosoma brucei brucei-infected rats resulted in a 70% decrease in parasitaemia within 1 h and a complete disappearance of parasites by 5 h. The reduction in parasitaemia was accompanied by complete inhibition of AdoMetDC activity by 10 min after injection of MDL 73811; inhibition was sustained for at least 4 h. Polyamine levels in trypanosomes were unaffected during the first 1 h in which the marked decrease in parasitaemia was observed, but parasite AdoMet levels increased 20-fold within this time. In contrast, exposure of cultured mammalian cells to MDL 73811 resulted in only a 1.5-2-fold increase in AdoMet levels over a 6 h time course. Experiments with inhibitors of ornithine decarboxylase (ODC) also suggested that the increased AdoMet levels might be an important factor for antitrypanosomal efficacy. Trypanosomes taken from rats treated for 36 h with eflornithine, an inhibitor of ODC, were depleted of putrescine and had markedly decreased spermidine levels. These organisms also had less than 10% of control AdoMetDC activity, and had elevated decarboxy AdoMet (greater than 4000-fold) and AdoMet (up to 50-fold) levels. The methyl ester of alpha-monofluromethyl-3,4-dehydro-ornithine (delta-MFMO-CH3), which cures murine T. b. brucei infections, and the ethyl ester analogue of this compound (delta-MFMO-C2H5), which does not cure this infection, become ODC inhibitors upon hydrolysis and thus were tested for their effects on trypanosomal polyamines, AdoMet and decarboxy AdoMet levels. Although both esters of delta-MFMO depleted trypanosomal polyamines, AdoMet and decarboxy AdoMet levels were elevated in T. b. brucei from infected mice treated with delta-MFMO-CH3 but not in parasites from mice treated with the delta-MFMO-C2H5. These data suggest that inhibition of AdoMetDC, either directly with MDL 73811 or indirectly with inhibitors of ODC, apparently leads to a trypanosome-specific elevation of AdoMet. It is possible that major changes in AdoMet, rather than changes in polyamines, may be responsible for the antitrypanosomal effects of these drugs.

Antimalarial polyamine analogues.

A series of novel tetraamines of the general formula RNH(CH2)xNH(CH2)yNH(CH2)xNHR was synthesized and examined for activity against growth of Plasmodium falciparum in vitro. Within the series, dibenzyl analogues (R = benzyl) were found to be the most effective growth inhibitors, with IC50 values of about 10(-6) M. Further modifications of the tetraamine provided the optimum chain length for antimalarial activity of y = 7, x = 3. Compound 8 (MDL 27,695) with the structure y = 7, x = 3, R = benzyl, in combination with the ornithine decarboxylase inhibitor alpha-(difluoromethyl)ornithine, resulted in radical cures when tested against experimental Plasmodium berghei infections in mice. The structure-activity relationships of the series are discussed.

Effect of bis(benzyl)polyamine derivatives on polyamine transport and survival of Brugia pahangi.

A potent filaricidal effect of bis(benzyl)polyamine derivatives is reported; the addition of 1 microM MDL 27695 to Brugia pahangi maintained in vitro killed the worms within 1 week. Using the labelled derivative, MDL 27391 uptake was demonstrated and evidence was provided for an uptake system that is independent of and clearly distinguishable from those for polyamines. The Km value for the uptake of MDL 27391 was determined to be 2 microM, and that for putrescine, spermidine, and spermine was 4.9, 1.7, and 4.8 microM, respectively. The uptake of MDL 27391 was not affected by polyamines. In contrast, bis(benzyl)polyamines were shown to be strong inhibitors of both the putrescine and the spermidine/spermine uptake system. As shown for MDL 27391, bis(benzyl)polyamines are not metabolized after uptake by Brugia worms; therefore, it is expected that the filaricidal effect of the drug depends on its interaction with potential polyamine-binding sites.

Antimalarial activity of a 4',5'-unsaturated 5'-fluoroadenosine mechanism-based inhibitor of S-adenosyl-L-homocysteine hydrolase.

A 4',5'-unsaturated 5'-fluoroadenosine inhibitor of S-adenosyl-L-homocysteine hydrolase (SAH hydrolase; EC 3.3.1.1), MDL 28842, was found to inhibit markedly the growth of Plasmodium falciparum in vitro and Plasmodium berghei in mice. Inhibition of P. berghei growth was associated with a large increase in the concentration of S-adenosyl-L-homocysteine (SAH) in the erythrocytes of the mice treated with MDL 28842. This increase in SAH was due apparently to inhibition of the mouse erythrocyte SAH hydrolase activity, because SAH hydrolase activity was undetectable in either P. berghei or P. falciparum isolated from infected erythrocytes, although enzyme activity was readily detected in mouse erythrocyte extracts. Therefore, MDL 28842 probably inhibits plasmodial growth indirectly by adversely changing the milieu of the host erythrocyte. SAH hydrolase represents a worthwhile target for the future development of potent inhibitors for the chemotherapy of malaria.

Cure of Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense infections in mice with an irreversible inhibitor of S-adenosylmethionine decarboxylase.

A structural analog, 5'-([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxy adenosine (MDL 73811), of decarboxy S-adenosyl-L-methionine, the product of the reaction catalyzed by S-adenosyl-L-methionine (AdoMet) decarboxylase (DC), was found to inhibit Trypanosoma brucei brucei AdoMet DC. The inhibition was time dependent (tau 50, 0.3 min), exhibited pseudo-first-order kinetics (Ki, 1.5 microM), and was apparently irreversible. The natural substrate of the reaction, AdoMet, protected the enzyme from inactivation, suggesting that MDL 73811 was directed at the enzyme active site and was probably catalytically activated. Administration of MDL 73811 to T. b. brucei-infected rats resulted in rapid inhibition of AdoMet DC activity, a decrease in spermidine, and an increase in putrescine in the trypanosomes isolated from treated rats. Treatment of T. b. brucei-infected mice with MDL 73811 (20 mg/kg of body weight intraperitoneally twice daily for 4 days) resulted in cures of the trypanosome infections. Additionally, drug-resistant T. brucei rhodesiense infections in mice were cured by either a combination of MDL 73811 (50 mg/kg intraperitoneally three times per day for 5 days) and relatively low oral doses of alpha-difluoromethylornithine or MDL 73811 (50 mg/kg per day for 7 days) administered alone in implanted miniosmotic pumps. These data suggest that MDL 73811 and, perhaps, other inhibitors of AdoMet DC have potential for therapeutic use in various forms of African trypanosomiasis.

bis(benzyl)polyamine analogues are substrates for a mammalian cell-transport system which is distinct from the polyamine-transport system.

Bis(benzyl)polyamine analogues (e.g. NN'-bis(3-[(phenylmethyl)amino]propyl)-1,8-diamino-octane [C6H5CH2NH-(CH2)3NH(CH2)8NH(CH2)3NHCH2C6H5]) have previously been shown to regulate polyamine biosynthesis and growth of rat hepatoma (HTC) cells. Saturable uptake of the analogues, the ability of other bis(benzyl)polyamine analogues to compete for this uptake and the trans-acceleration of this uptake in pre-loaded cells indicate that these novel compounds are accumulated through the action of a transport system in HTC cells. A mutant Chinese-hamster-ovary (CHO) cell line, CHOMG, which lacks a functional polyamine-transport system, exhibited saturable bis(benzyl)polyamine uptake identical with that observed in the parental CHO cells, which have normal polyamine transport. The uptake of the analogue by both CHOMG and CHO cells was competitively inhibited by other bis(benzyl)polyamine analogues, but was insensitive to excess spermine. Treatment with alpha-difluoromethylornithine, an inhibitor of polyamine biosynthesis, resulted in the enhancement of spermine uptake in CHO cells but did not alter the uptake of a bis(benzyl)polyamine analogue by either CHO or CHOMG cells. Thus it appears that bis(benzyl)polyamine analogues are substrates for a mammalian-cell-transport system distinct from the polyamine-transport system.