Influence of cyclosporin A and alpha-difluoromethylornithine, an inhibitor of polyamine biosynthesis, on two rodent T-cell cancers in vivo

The polyamines: past, present and future

The polyamines, spermidine and spermine, were first discovered in 1678 by Antonie van Leeuwenhoek. In the early part of the 20th century their structure was determined and their pathway of biosynthesis established. The polyamines are essential elements of cells from all species. They are required for optimum cell growth, and cells where polyamine production has been prevented by mutation, or blocked by inhibitors, require exogenous provision of at least one polyamine for continued survival. Despite this critical function, the polyamines have not attracted as much attention as they deserve in the wider field of biochemistry and cell biology. They are rarely mentioned in standard textbooks, despite over 75000 research papers having been written on the subject since 1900, and more than half (54%) were published after 1990. There have been a number of books dedicated to the polyamines published and "The Guide to the Polyamines" by Seymour Cohen deserves mention as a work of outstanding scholarship describing "everything you ever wanted to know about the polyamines" in exquisite detail. The current volume of Essays in Biochemistry has a much humbler aim: to introduce the polyamines to interested researchers and students, and to describe how they are associated with, and might be utilized as a target for intervention in major diseases such as cancer.

Polyamine analogues – an update

The polyamines are growth factors in both normal and cancer cells. As the intracellular polyamine content correlates positively with the growth potential of that cell, the idea that depletion of polyamine content will result in inhibition of cell growth and, particularly tumour cell growth, has been developed over the last 15 years. The polyamine pathway is therefore a target for development of rationally designed, antiproliferative agents. Following the lessons from the single enzyme inhibitors (alpha-difluoromethylornithine DFMO), three generations of polyamine analogues have been synthesised and tested in vitro and in vivo. The analogues are multi-site inhibitors affecting multiple reactions in the pathway and thus prevent the up-regulation of compensatory reactions that have been the downfall of DFMO in anticancer chemotherapy. Although the initial concept was that the analogues may provide novel anticancer drugs, it now seems likely that the analogues will have wider applications in diseases involving hyperplasia.

Immunosuppressive drugs and their effect on experimental tumor growth

The effect of cyclosporin (CyA), FK 506, and mycophenolate mofetil (MPM) on tumor growth was investigated using syngeneic mouse colon carcinoma 38. Mice were laparotomized and the tumor cells were injected into the portal vein to establish liver metastasis. The animals were grouped as follows: groups A-1, B-1, and C-1 were given CyA [15 mg/kg body weight (BW)], FK 506 (0.15 mg/kg BW), and MPM (100 mg/kg BW), respectively, 30 min before tumor inoculation and daily for 5 days by gavage; groups A-2, B-2, and C-2 were given CyA (30 mg/kg BW), FK 506 (0.3 mg/kg BW), and MPM (200 mg/kg BW), respectively, with the same dose timing; and groups A-3, B-3, and C-3 received CyA (30 mg/kg BW), FK 506 (0.3 mg/kg BW), and MPM (200 mg/kg BW), respectively, on the 7th post-tumor inoculation day and on the following 5 days. The mean tumor diameter in groups A-1 and A-2 was greater than that in the control group and in groups C-1 and C-2 at 3 weeks (P < 0.05). The mean tumor numbers in groups A-1 and A-2 were greater than those in the control group and in groups C-1 and C-2 at 4 weeks (P < 0.05). With in vitro MTT assay, all three drugs acted cytostatically on tumor cells with a higher concentration (10(-6)-10(-4) mol/l), while no cytostatic effect was noted with CyA at a lower concentration (10(-9)-10(-7) mol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of tumor proliferation by cyclosporine A in early phase of experimental hepatic metastasis

The effect of cyclosporine A (CsA) on in vivo growth of hepatic metastasis was studied. Murine colon 38 tumor cells (1 x 10(5) were inoculated via the superior mesenteric vein. Mice were grouped depending on CsA dosage and time schedules: Group A: CsA 30 mg/kg body weight on the 7, 8 and 9th post tumor inoculation days by gavage; Group B: CsA 15 mg/kg body weight 30 min before tumor inoculation and 2 times more at 24 h intervals; Group C: CsA 30 mg/kg body weight at the same dose timing as Group B. Measurement of the diameter of the largest tumor serially by weekly laparotomy up to 4 weeks revealed that the tumor growth rates were significantly greater in Groups B and C than those in Group A or the control (without CsA). The mean tumor doubling times in the control, and Groups A, B and C were 2.2 +/- 1.3, 2.0 +/- 0.5, 1.5 +/- 0.4 and 1.3 +/- 0.8 days, respectively. The mean tumor numbers of hepatic metastasis were 13.2 +/- 8.3, 11.3 +/- 7.3, 19.4 +/- 8.7 and 19.6 +/- 6.8, respectively. Values of tumor proliferation index obtained by bromodeoxyuridine immunohistochemistry were 10.0 +/- 6.1%, 14.9 +/- 8.0%, 28.6 +/- 8.2% and 30.1 +/- 12.4%, respectively, with significant differences (Groups B and C vs. A or control, P < 0.05). In vitro MTT assay showed that cell viability rates were greater than 100% in the medium containing CsA concentrations of less than 10(-7) mol/liter. However, a cytostatic effect of CsA was apparent at higher concentrations. In contrast to the previous in vivo finding of a cytostatic effect of CsA on tumor cells, we found a cytoproliferative action when CsA was administered early in the course of metastatic tumor implantation in the liver. The mechanism of cytoproliferative effect of CsA is unknown but may involve multiple factors.

Polyamines: from molecular biology to clinical applications

The polyamines putrescine, spermidine and spermine represent a group of naturally occurring compounds exerting a bewildering number of biological effects, yet despite several decades of intensive research work, their exact physiological function remains obscure. Chemically these compounds are organic aliphatic cations with two (putrescine), three (spermidine) or four (spermine) amino or amino groups that are fully protonated at physiological pH values. Early studies showed that the polyamines are closely connected to the proliferation of animal cells. Their biosynthesis is accomplished by a concerted action of four different enzymes: ornithine decarboxylase, adenosylmethionine decarboxylase, spermidine synthase and spermine synthase. Out of these four enzyme, the two decarboxylases represent unique mammalian enzymes with an extremely short half life and dramatic inducibility in response to growth promoting stimuli. The regulation of ornithine decarboxylase, and to some extent also that of adenosylmethionine decarboxylase, is complex, showing features that do not always fit into the generally accepted rules of molecular biology. The development and introduction of specific inhibitors to the biosynthetic enzymes of the polyamines have revealed that an undisturbed synthesis of the polyamines is a prerequisite for animal cell proliferation to occur. The biosynthesis of the polyamines thus offers a meaningful target for the treatment of certain hyperproliferative diseases, most notably cancer. Although most experimental cancer models responds strikingly to treatment with polyamine antimetabolites--namely, inhibitors of various polyamine synthesizing enzymes--a real breakthrough in the treatment of human cancer has not yet occurred. It is, however, highly likely that the concept is viable. An especially interesting approach is the chemoprevention of cancer with polyamine antimetabolites, a process that appears to work in many experimental animal models. Meanwhile, the inhibition of polyamine accumulation has shown great promise in the treatment of human parasitic diseases, such as African trypanosomiasis.

Effects of cyclosporin A on growth and polyamine metabolism of MOLT-4 T-lymphoblastic leukaemia cells

We have examined the effects of Cyclosporin A (CsA) on growth and polyamine metabolism of MOLT-4, human T lymphoblastic leukaemia cells to ascertain the role of the polyamine biosynthetic pathway in the antitumour action of CsA. We observed that CsA had a dose-dependent inhibitory effect on growth of the cells in vitro, decreasing protein content, cell number and the rate of incorporation of 3H-thymidine into the cells. However, CsA treatment had no significant effect on intracellular polyamine levels in the cells. Contrary to previous reports, simultaneous addition of the diamine, putrescine, with CsA did not block or lessen the growth inhibitory effects of CsA. On the other hand, ornithine decarboxylase activity, the rate limiting enzyme of polyamine biosynthesis which converts ornithine to putrescine, was decreased by CsA treatment. This decrease appeared to be reversible and contrasts with the inhibition by alpha-difluoromethyl-ornithine, which is irreversible and can be overcome by addition of putrescine. This suppression of ornithine decarboxylase by CsA is more likely to occur by indirect effects on translation and/or transcription rather than a direct effect on the enzyme. It may be a contributory factor in the overall antiproliferative effects of CsA but is more likely to be a response to these growth inhibitory effects rather than a direct effect of the drug.

The potential of cyclosporin A as an anti-tumour agent

Cyclosporin A (CsA) has become established as the agent of choice for the prevention of organ allograft rejection and has shown considerable promise in the clinical management of certain autoimmune disorders. The impact of CsA as an immunotherapeutic agent of major importance is attributable to its powerful, selective inhibitory action on T-lymphocyte activation and proliferation. Moreover, CsA lacks the myelotoxic and other major side effects associated with cytotoxic immunosuppressive agents, such as cyclophosphamide or azathioprine. It is now clear that CsA has a potential therapeutic role in the treatment of malignancies, especially T-cell cancers. Recent studies suggest that there may be several areas of application for CsA, either as a direct antiproliferative agent or in combination with other drugs, including inhibitors of polyamine biosynthesis or cytotoxic anti-tumour agents, including vincristine and adriamycin. In addition, CsA and non-immunosuppressive analogues have been shown to restore multi-drug sensitivity in cancer cells with acquired drug resistance. A further application of CsA may be to prevent the induction of human immune responses to therapeutic mouse monoclonal antibodies directed against tumour antigens, thereby enhancing the efficiency and safety of this form of cancer immunotherapy. Due to our incomplete understanding of the antiproliferative properties of CsA, further exploration of its potential as an anti-tumour agent must be accompanied by detailed studies aimed at elucidating its action on subcellular molecular events in both normal and malignant cells.