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.     

Combined efficacy of polyamine antimetabolites and cis-diamminedichloroplatinum

The combined antitumor effects of the polyamine antimetabolites, alpha-difluoro methylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG), with CDDP were studied using human gastric cancer cells xenotransplanted into nude mice. DFMO (1000 mg/kg in two divided doses) and MGBG (50 mg/kg) were given IP for six consecutive days from the time when the xenotransplanted tumor weighted about 100 mg, and CDDP (3.0 mg/kg) was given IP every other day from the same time. Animals treated with DFMO plus MGBG with or without CDDP as well as with CDDP only displayed suppressed tumor growth, compared to untreated mice. In mice treated with these three drugs, however, tumor growth was rather rapid compared to those treated with CDDP only, although tumoral CDDP levels in animals given DFMO, MGBG and CDDP were higher than those given CDDP only. When DFMO, MGBG and CDDP or DFMO and MGBG were administered, tumoral spermidine and spermine levels decreased markedly. On the other hand, tumor DNA biosynthesis in the CDDP only group dropped markedly 24 hours after the termination of therapy. These results suggest that an alteration in the DNA structure caused by polyamine deficiency may prevent cross-link formation in DNA by CDDP.     

Antitumor effects of polyamine antimetabolites with polyamine-free diet

To evaluate the antitumor efficacy of polyamine antimetabolites such as methylglyoxal-bis-guanylhydrazone (MGBG), ethylglyoxal-bis-guanylhydrazone (EGBG), and alpha-difluoromethylornithine (DFMO), the combined therapies of polyamine antimetabolites with a polyamine-free diet were studied. The combination of EGBG plus DFMO or MGBG plus DFMO showed a marked suppression of tumor growth with a polyamine-free diet; and, when compared, EGBG was slightly superior to MGBG. The inhibition of DNA biosynthesis was also parallel to the above-mentioned results. Furthermore, from an analysis for polyamine levels in tumor tissues, it was confirmed that the polyamine depletion can be maintained by polyamine antimetabolites in combination with a polyamine-free diet in vivo. Moreover, as EGBG has lesser side effects than MGBG, EGBG might be more suitable for clinical use.     

Synergistic antileukemic effect of two polyamine synthesis inhibitors. Host survival and cell-cycle kinetic analysis

alpha-Difluoromethylornithine (DFMO), an enzyme-activated irreversible inhibitor of ornithine decarboxylase, was used alone and in combination with multiple doses of methylglyoxal-bis(guanylhydrazone) (MGBG) to treat mice with systemic L1210 leukemia. Used as a single agent (administered p.o. as a 3% solution in tap water), DFMO exerted a weak therapeutic effect against this tumor. The therapeutic effect of MGBG (administered i.p. at 50 mg/kg/day) was only slightly better. However, 1-3 days of pretreatment with DFMO strongly potentiated the effect of MGBG treatment. Thus, mice treated with the combination exhibited an increase in life span of up to 138%. The prolonged survival of leukemic mice treated with a combination of DFMO and MGBG was associated with inhibition of polyamine synthesis and a marked decrease in the spermidine and spermine content of the tumor cells as compared to untreated controls. As a consequence, there was a continuous decrease in the S- and G2-phase fractions with a concomitant increase in G1. Used singly, DFMO and MGBG had no significant effect on the cell-cycle distribution. The effects of the combination of DFMO and MGBG on the cell-cycle distribution are consistent with the contention that polyamine deficiency primarily interferes with initiation of DNA synthesis. However, the possibility that selective S-phase kill partly contributes to this change in cell-cycle distribution cannot be excluded.     

Alterations in bone marrow and blood mononuclear cell polyamine and methylglyoxal bis(guanylhydrazone) levels: phase I evaluation of alpha-difluoromethylornithine and methylglyoxal bis(guanylhydrazone) treatment of human hematological malignancies

Nine patients with hematological malignancies were treated with difluoromethylornithine and methylglyoxal bis(guanylhydrazone). The number of circulating blast cells decreased in all of the patients treated with DFMO and MGBG for longer than 1 wk. Morphological evidence of myeloid maturation was evident in four patients with leukemia and the circulating M Protein decreased in one patient with multiple myeloma. The polyamine content of the mononuclear cells in both the peripheral blood and bone marrow was transiently increased after the initial MGBG dose. During administration of DFMO decreases were achieved in the peripheral blood mononuclear cell putrescine levels in 7 patients, spermidine levels in 5 patients, and spermine levels in 4 patients. Alterations in bone marrow mononuclear cell polyamine levels were similar to those which occurred in the peripheral cells. An average of 9 days of DFMO treatment was required to lower mononuclear cell polyamine levels. Three of the 4 evaluable patients receiving multiple MGBG doses had an increased mononuclear cell content of MGBG after DFMO pretreatment. Enhancement of cellular MGBG levels was not directly correlated to the degree of cellular polyamine depletion.     

Combined therapy of polyamine antimetabolite and nitrosourea in human gastric cancer

Antitumor therapy using the polyamine antimetabolites, alpha-difluoromethylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG), combined with ACNU was studied in human gastric cancer xenotransplanted into nude mice. DFMO 1,000 mg/kg (in two divided doses) and MGBG 50 mg/kg were given i.p. for 6 successive days from the time when the xenotransplanted tumor weighed about 100 mg, and ACNU 20 mg/kg was given i.p. every other day from the same time. Antitumor efficacy was assessed by the time course of tumor weight as well as of DNA biosynthesis and polyamine levels in tumor tissue. Tumor weight was estimated using Battelle's Columbus Institute protocol and DNA biosynthesis was assayed biochemically by 3H-TdR injection at a prescribed interval after termination of therapy. Furthermore, tumoral polyamine levels were assayed by HPLC. This three-drug regimen showed a favorable antitumor effect, compared to those of the other two therapies with DFMO plus MGBG as well as ACNU only. These data suggest that this combined regimen may have a synergistic efficacy judging from the action mechanisms of these three drugs.     

Anticancer treatment with a combination of antimetabolites of polyamine and pyrimidine

A combined efficacy of the polyamine antimetabolites, alpha-difluoromethylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG) with two fluorinated pyrimidines was studied. DFMO, MGBG, 5-FU and 5'-deoxy-5-fluorouridine (5'-DFUR) were administered intraperitoneally to BALB/c nu/nu mice bearing xenotransplanted human gastric cancer for 5 consecutive days. Similar antitumor efficacies were observed in 3 groups treated with DFMO plus MGBG, DFMO, MGBG plus 5-FU as well as DFMO, MGBG plus 5'-DFUR. The two groups on 5-FU or 5'-DFUR alone did not differ in antitumor effects from the control, although reasonable levels of 5-FU were involved in tumor tissues. Hepatic and splenic 5-FU levels after 5-FU administration were significantly higher than those after 5'-DFUR, and marked decrease in mouse body weight was caused by 5-FU alone as well as 5-FU plus polyamine antimetabolites for 5 consecutive days. DNA biosynthesis and spermine levels in the tumor tissues on day 2 after cessation of the treatments dropped in 3 groups with DFMO plus MGBG, DFMO, MGBG plus 5'-DFUR as well as DFMO, MGBG plus 5-FU, while on day 6 there was little difference between the control and treated groups. These data suggest that combination with 5-FU or 5'-DFUR does not enhance the antitumor activity of polyamine antimetabolites by this experimental regimen.     

MGBG: Teaching an old drug new tricks

Methylglyoxalbisguanylhydrazone or MGBG is an agent with a uniquemechanism of action (polyamine biosynthesis inhibition). MGBGwas discarded in the 1960s because of severe mucositis and othertoxicities. New clinical trials in the late 1970s and early1980s utilized weekly administration and indicated MGBG hadsignificant activity in patients with chemotherapy-refractoryHodgkin's and non-Hodgkin's lymphoma. In addition, some activitywas noted in patients with head and neck, prostate, esophageal,and endometrial cancer. The toxicities on the weekly schedulewere minimal and no myelosuppression was noted. Based on MGBG'sspectrum of antitumor activity and its activity in severelydebilitated patients, we hypothesize that MGBG may have greaterantitumor activity in patients who are malnourished (possiblybased on polyamine depletion). MGBG is a good candidate fortreatment of AIDS-associated NHL because it has proven activityin patients with NHL which is not associated with AIDS, crossesthe blood brain barrier, is non-myelosuppressive, and appearsto work in patients with inanition (no polyamines availableto reverse MGBG's antitumor effects). Clinical trials are ongoingto determine the activity of MGBG in AIDS-associated NHL andother diseases. Based on encouraging initial results, it appearsMGBG may become part of our therapeutic armamentarium. MGBG, polyamine, AIDS, Hodgkin's lymphoma, non-Hodgkin's lymphoma     

Combined Use of α-Difluoromethylornithine and an Inhibitor of S-Adenosylmethionine Decarboxylase in Mice Bearing P388 Leukemia or Lewis Lung Carcinoma

The antitumor and antimetastatic effects of α-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, combined with an inhibitor of S-adenosylmethionine decarboxylase, either methylglyoxal bis(guanylhydrazone) (MGBG) or ethylglyoxal bis(guanylhydrazone) (EGBG), were studied in mice bearing P388 leukemia or Lewis lung carcinoma. Although EGBG is a more specific inhibitor of polyamine biosynthesis than the widely used MGBG, the antitumor effect of the DFMO-EGBG combination on P388 leukemia-bearing mice was less than that of the DFMO-MGBG combination. The prolongation of survival time by the DFMOC1000 mg/kg)-MGBG(25 mg/kg) combination was 2.65-fold, while that of the DFMO(1000 mg/kg)-EGBG(50 mg/kg) combination was 1.34-fold. When mice were fed a polyamine-deficient diet, stronger antitumor effects were exerted; the prolongation of survival time by the DFMO-MGBG and the DFMO-EGBG combinations was 2.89-fold and 2.03-fold, respectively. The antitumor effect of combined use of the two polyamine antimetabolites with mice on normal and polyamine-deficient diets correlated with a decrease of polyamine charge contents in the tumor cells. The above in vivo results were confirmed clearly in the KB cell culture system. The antimetastatic activity of DFMO on Lewis lung carcinoma-bearing mice was strengthened by the addition of MGBG or EGBG. The antimetastatic activity of the DFMO-MGBG or DFMO-EGBG combination did not parallel the polyamine charge contents in the primary tumor and blood.     

Combined use of alpha-difluoromethylornithine and an inhibitor of S-adenosylmethionine decarboxylase in mice bearing P388 leukemia or Lewis lung carcinoma

The antitumor and antimetastatic effects of alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, combined with an inhibitor of S-adenosylmethionine decarboxylase, either methylglyoxal bis(guanylhydrazone) (MGBG) or ethylglyoxal bis(guanylhydrazone) (EGBG), were studied in mice bearing P388 leukemia or Lewis lung carcinoma. Although EGBG is a more specific inhibitor of polyamine biosynthesis than the widely used MGBG, the antitumor effect of the DFMO-EGBG combination on P388 leukemia-bearing mice was less than that of the DFMO-MGBG combination. The prolongation of survival time by the DFMO(1000 mg/kg)-MGBG(25 mg/kg) combination was 2.65-fold, while that of the DFMO(1000 mg/kg)-EGBG(50 mg/kg) combination was 1.34-fold. When mice were fed a polyamine-deficient diet, stronger antitumor effects were exerted; the prolongation of survival time by the DFMO-MGBG and the DFMO-EGBG combinations was 2.89-fold and 2.03-fold, respectively. The antitumor effect of combined use of the two polyamine antimetabolites with mice on normal and polyamine-deficient diets correlated with a decrease of polyamine charge contents in the tumor cells. The above in vivo results were confirmed clearly in the KB cell culture system. The antimetastatic activity of DFMO on Lewis lung carcinoma-bearing mice was strengthened by the addition of MGBG or EGBG. The antimetastatic activity of the DFMO-MGBG or DFMO-EGBG combination did not parallel the polyamine charge contents in the primary tumor and blood.     

Potentiation of methylglyoxal-bis-guanylhydrazone by alpha-difluoromethylornithine in rat prostate cancer

The polyamines, putrescine, spermidine, and spermine, are fundamentally related to both normal and neoplastic cell proliferation. The prostate gland and prostatic tumors in man and rodents contain large amounts of polyamines. This suggests that inhibition of polyamine biosynthetic enzymes, ornithine decarboxylase (ODC) and S-adenosyl-methionine decarboxylase (SAMDC) may retard the growth of prostatic cancer. Since alpha-difluoromethylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG) are irreversible and competitive inhibitors of ODC and SAMDC, respectively, they were tested as single agents and in combination on a transplantable rapidly growing and hormone-resistant G subline of the Dunning R-3327 rat prostatic adenocarcinoma. Groups of rats bearing tumors were treated with various regimens of DFMO, MGBG, and DFMO plus MGBG, daily for 21 days. Analysis of differences in tumor growth between treatment groups and controls showed DFMO had no antitumor effect but was well tolerated, MGBG retarded growth rate significantly but resulted in drug deaths in over 50% of the animals, and the combination of DFMO and MGBG resulted in rapid decline in tumor growth rates after 5 to 9 days of treatment with reduced toxicity. At 21 days, or death, 38 of 60 (63%) rats had no viable tumor on histologic study, whereas tumor was present in each of the animals in the other groups. Alpha-difluoromethylornithine increased the intracellular uptake of MGBG and potentiated the antigrowth activity of MGBG on a hormone refractory rat prostatic tumor with less toxicity than MGBG alone.     

Effect of pretreatment with alpha-difluoromethylornithine on the selectivity of methylglyoxal bis(guanylhydrazone) for tumor tissue in L1210 leukemic mice

A number of studies have demonstrated that pretreatment of tumor-bearing animals with the inhibitor of polyamine biosynthesis, alpha-difluoromethylornithine (DFMO), potentiates the antitumor activity of methylglyoxal bis(guanylhydrazone) (MGBG). The present study examines whether this phenomenon is related to a DFMO-mediated increase in the selectivity of MGBG for tumor tissue. Specifically, the effect of DFMO pretreatment on the tissue distribution and content of MGBG was investigated in mice bearing ascites L1210 leukemia. At 3 and 18 h following a single i.v. injection of [14C]MGBG (50 mg/kg), L1210 cells and seven tissues from nonpretreated (control) and DFMO-pretreated (3% by drinking water for 3 days) animals were compared for their [14C]MGBG content. In control mice, the greatest amount of drug was found in L1210 cells, small intestine, and kidney (in decreasing order of magnitude) at both 3 and 18 h. This distribution was not altered following DFMO pretreatment, but the relative MGBG content of other tissues was shifted. On an average, DFMO pretreatment increased the accumulation of MGBG by 30% in normal tissues and 32% in tumor tissues at 3 h and 56% and 69%, respectively, at 18 h. Thus, pretreatment of leukemic mice with DFMO fails to improve the selectivity of MGBG for L1210 cells. It is possible that other tumor systems might demonstrate sufficient DFMO-mediated increases in MGBG uptake to enhance drug selectivity but not without significantly increasing MGBG uptake (and hence toxicity) in normal tissues.     

Phase II trial of methylglyoxal bis (guanylhydrazone) (MGBG) in advanced head and neck cancer

Methylglyoxal bis (guanylhydrazone) (MGBG) is an inhibitor of polyamine synthesis. In vitro studies demonstrate the accumulation of some tumor cells in S and G2 phases of the cell cycle. Nineteen patients with advanced head and neck cancer were entered in a Phase II trial of MGBG. MGBG, 500 mg/M2, was administered as a brief intravenous infusion weekly for 4 weeks, then every 2 weeks. Dose modifications were based on cumulative toxicity after 2 weekly treatments. All but three patients had prior exposure to chemotherapy for disease recurrence. Of 17 patients evaluable for response and toxicity, one brief partial response was observed. The most common toxicities were mild to moderate nausea, vomiting, diarrhea, and stomatitis. Myelosuppression occurred in three patients. Dose modifications were required in four patients; a maximum dose of 700 mg/M2 was tolerated. The results of four other Phase II single and combination chemotherapy trials of MGBG in head and neck cancer are reviewed. The single agent response rate in 59 patients was 22% (range, 6%-41%). The poor response rate observed in this trial was similar to that in other trials in which a heavily pretreated group of patients was evaluated. It is concluded that single agent MGBG is not a useful drug in heavily pretreated recurrent disease patients. However, because of its biochemical effects, further testing in combination with cycle specific agents and in larger numbers of patients with minimal prior treatment may be warranted.     

Combined antitumor therapy with polyamine biosynthesis inhibitors and mitomycin C

A combined effect of the polyamine biosynthesis inhibitors, alpha-difluoromethylornithine (DFMO) and methyglyoxal-bis-guanylhydrazone (MGBG) with mitomycin C (MMC) was studied. DFMO, MGBG and MMC were given intraperitoneally to nude mice xenotransplanted human gastric cancer. This new combination of the three drugs resulted in the complete halt of the xenotransplanted tumor growth and marked decline of spermine levels in the tumor tissues. The other treatments with DFMO and MGBG as well as MMC alone were inferior to this new combined therapy in suppression in both tumor growth and tissue spermine level. These data suggest that this new combined treatment be effective against human gastric cancer.     

Effects of alpha-difluoromethylornithine and methylglyoxal bis(guanylhydrazone) on the growth of experimental renal adenocarcinoma in mice

alpha-Difluoromethylornithine (DFMO) and methylglyoxal bis-(guanylhydrazone) (MGBG) were tested against a murine renal adenocarcinoma, because polyamines are necessary for neoplastic cell growth and because human renal adenocarcinomas contain higher levels of spermidine than do normal renal cells; MGBG inhibits spermidine synthesis and has some activity against human renal tumors; DFMO irreversibly inhibits ornithine decarboxylase, the first rate-limiting enzyme controlling polyamine biosynthesis; and DFMO promotes intracellular accumulation of MGBG in experimental tumor models and human leukemia. DFMO (2%) in drinking water, MGBG (15 mg/kg i.p.), or a combination of DFMO and MGBG was administered daily to BALB/c mice (n = 80) with intrarenal transplants of renal adenocarcinoma cells. At 28 days, renal carcinomas weighed 64 and 73% less, respectively, in DFMO- and DFMO-MGBG-treated mice than in control animals (p less than 0.01). MGBG alone had no antigrowth effect. DFMO-MGBG reduced the total metastatic index (total number of metastases/total number of animals) to 1.2 versus 3.6 in control animals (p less than 0.01) and increased survival by 12.3 +/- 1.5 (S.E.) days, from 30.8 to 42.5 days (p less than 0.05). Compared with control, DFMO-, or MGBG-treated animals, DFMO-MGBG exposure reduced tumor growth and the number of metastases, prevented metastases in some animals (47%), and increased survival of mice bearing renal adenocarcinomas. DFMO also appeared to selectively increase the uptake of [14C]MGBG by tumor tissue, which may help to explain the enhanced synergistic antigrowth effect of DFMO and MGBG against this murine renal adenocarcinoma.     

Modulation of the tissue disposition of methylglyoxal bis(guanylhydrazone) in mice by polyamine depletion and by polyamine administration

Treatment of mice with DL-alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (EC 4.1.1.17), produced a significant spermidine depletion in liver, small intestine, and bone marrow among eight tissues studied. The accumulation of methylglyoxal bis(guanylhydrazone) (MGBG) was selectively enhanced in small intestine and in bone marrow cells in response to a prior DFMO treatment. In other tissues studied, i.e., brain, skeletal and cardiac muscle, liver, kidney, and spleen, a preceding treatment with DFMO had no effect on the accumulation of subsequently injected MGBG. When mice, primed with DFMO and then treated with a single injection of MGBG, were given nontoxic doses of spermidine or putrescine through a gastric tube, high concentrations of MGBG in the small intestine and in bone marrow cells were effectively reduced. In spite of the route of administration, bone marrow cells appeared to be more sensitive than intestinal tissue as regards the prevention of the tissue accumulation of MGBG by the polyamines. The different sensitivity of various tissues to the natural polyamines in this respect may offer a means to develop a tissue-specific "polyamine rescue concept" to be used in connection with MGBG treatment.     

New S-adenosylmethionine decarboxylase inhibitors with potent antitumor activity.

Methylglyoxal bis(guanylhydrazone) (MGBG) has been studied clinically as an antitumor and antileukemic agent and is recognized as a potent but nonspecific inhibitor of the key polyamine biosynthetic enzyme, S-adenosylmethionine decarboxylase (SAMDC). A series of four SAMDC inhibitors with structural features similar to MGBG have been found to have improved potency and specificity toward the target enzyme, SAMDC. Relative to MGBG, the new derivatives were much more effective in inhibiting partially purified preparations of SAMDC (50% inhibitory concentration, 10 to 100 nM), much less effective at inhibiting diamine oxidase, and inactive toward ornithine decarboxylase. The inhibitors varied relative to MGBG in their ability to compete with spermidine for uptake, with two being similar and two being less effective. Against L1210 leukemic cells and T24 bladder carcinoma cells, the compounds were slightly less effective than MGBG at inhibiting cell growth, with 50% inhibitory concentration values of 1 to 10 microM as compared with 0.5 and 1.1 microM, respectively, for MGBG. Under 50% growth-inhibitory conditions, the inhibitors decreased SAMDC activity, increased ornithine decarboxylase activity and putrescine pools, and markedly depleted spermidine and spermine pools of L1210 cells. At the same time, mitochondrial integrity as assessed by whole-cell pyruvate oxidation and mitochondrial DNA content was not affected as it was with MGBG. At doses less than one tenth that of the maximally tolerated dose, all of the new inhibitors strongly suppressed the growth of B16 melanoma in vivo with minimal weight loss or toxicity. At doses less than one sixth the maximally tolerated dose, they effectively inhibited the growth of T24 human bladder carcinoma xenografts. In these same systems, MGBG showed only marginal antitumor activity. These studies identify two potent and efficacious inhibitors of SAMDC as potential antitumor agents and reaffirm the importance of SAMDC as a target in anticancer drug discovery.     

Modification of uptake and antiproliferative effect of methylglyoxal bis(guanylhydrazone) by treatment with alpha-difluoromethylornithine in rodent cell lines with different sensitivities to methylglyoxal bis(guanylhydrazone)

Uptake characteristics and growth-inhibitory effects of methylglyoxal bis(guanylhydrazone) (MGBG), a competitive inhibitor of S-adenosylmethionine decarboxylase, were investigated in 9L rat brain tumor cells and in V79 hamster lung cells. Proliferation of 9L cells was only slightly inhibited by treatment with 40 microM MGBG alone, but when used in combination with 0.5 mM alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, proliferation was much more effectively inhibited. The intracellular concentration of MGBG was approximately 2-fold higher 4 days after cells were treated with both DFMO and MGBG, either simultaneously or when MGBG was added after a 48-hr DFMO pretreatment, than that in cells treated with MGBG alone. Polyamine levels in DFMO- and MGBG-treated cells correlated with the antiproliferative effects of the drugs. Used either alone or in combination with 1 mM DFMO, 0.5 microM MGBG inhibited the growth of and eventually killed V79 cells. Simultaneous or sequential treatment with DFMO and MGBG increased intracellular concentrations of MGBG at 4 days by 2- and 3-fold, respectively, compared to treatment with MGBG alone. Intracellular polyamine levels did not correlate with the antiproliferative effect of the two drugs in V79 cells. In both cell lines, polyamines and MGBG share a common transport system. The net transport of polyamines and MGBG was more temperature dependent and up to 10-fold more active in V79 cells than in 9L cells. The Km and Vmax values for spermidine and MGBG measured 10 sec after addition (initial permeation) were not affected by DFMO pretreatment in either cell line. However, 1 hr after administration, the Vmax values for spermidine and MGBG uptake were doubled in V79 cells pretreated for 48 hr with DFMO; no significant change occurred in 9L cells. Mitochondrial function, assessed by pyruvate oxidation, was substantially impaired by MGBG in V79 cells but not in 9L cells when the intracellular concentrations of MGBG were equal in each cell line. Pretreatment with DFMO did not increase MGBG-induced inhibition of pyruvate oxidation in V79 cells. These results show that, compared with V79 cells, the decreased sensitivity of 9L cells to MGBG may be related to decreased intracellular MGBG accumulation but not to cellular permeation such as carrier transport. Results of measurements of both polyamine levels and mitochondrial function indicate that V79 cells may be more susceptible to nonpolyamine-dependent effects of MGBG than are 9L cells.     

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.     

Phase II Trial of Methylglyoxal-Bis (guanylhydrazone) (MGBG) in Patients with Refractory Multiple Myeloma: An Eastern Cooperative Oncology Group (ECOG) Study

Twenty patients with refractory multiple myeloma were treated with methylglyoxalbis(guanylhydrazone) (MGBG), an inhibitor of polyamine synthesis. MGBG 500 mg/m² was administered on days 1 and 8, and then every 14 days. The dose was escalated to 600 mg/m² on day 22, as tolerated. Of 14 evaluable patients, none met ECOG criteria for an objective response. The major toxicity was hematologic and related infections. MGBG demonstrated insufficient activity in the treatment of refractory multiple myeloma to warrant further study.