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Polyamines in brain tumor therapy
E S Redgate1, S Boggs, A Grudziak
1Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, USA.
Abstract:
In the search for ways to augment current brain tumor therapies many have sought to exploit the fact that adult brain tissue is virtually lacking in cell division. This endorses a special appeal to therapeutic approaches which target the dependence on cell division for brain tumor growth. Polyamines play an essential role in the proliferation of mammalian cells and depletion results in inhibition of growth. As a result, there are investigations into the feasibility of controlling tumor growth by targeting the enzymes in polyamine metabolism with specific enzyme inhibitors. DFMO, an inhibitor of putrescine synthesis, is a cytostatic agent which in combination with tritiated radioemitters or cytotoxic agents such as, MGBG or BCNU is an effective antitumor agent, but the effectiveness of DFMO in vivo is reduced by tumor cell uptake of polyamines released into the circulation by normal cells and from gut flora or dietary sources. However, DFMO therapy combined with elimination of exogenous polyamines inhibits tumor growth but also results in body weight loss, reduced protein synthesis and evidence of toxicity. Furthermore, tumor growth recurs upon termination of treatment. In contrast, competitive polyamine analogs function in the homeostatic regulation of polyamine synthesis but fail to fulfill the requirements for growth and they continue to inhibit tumor growth for several weeks after cessation of treatment. Analogs are now in clinical trials. However, their action may be highly specific and differ from one cell type to another. We suggest that the effectiveness of polyamine based therapy would be enhanced by two approaches: local delivery by intracerebral microdialysis and tumor cell killing by internal radioemitters such as tritiated putrescine or tritiated thymidine which are taken up in increased amounts by polyamine depleted tumor cells. The growth inhibition by polyamine depletion prevents the dilution of the radioactive putrescine and thymidine. The overload of radioactivity kills the growth inhibited cells so that growth cannot recur when treatment terminates.
Insights
Targeting polyamine metabolism offers a novel brain tumor therapy. Combining polyamine depletion with targeted radioemitters may enhance treatment efficacy and prevent tumor recurrence.
Area of Science:
- Neuro-oncology
- Molecular Biology
- Cancer Therapeutics
Background:
- Adult brain tissue exhibits limited cell division, making cell division-dependent tumor growth a therapeutic target.
- Polyamines are crucial for mammalian cell proliferation; their depletion inhibits growth, presenting a strategy for controlling brain tumors.
- Enzyme inhibitors targeting polyamine metabolism are being investigated for cancer therapy.
Purpose of the Study:
- To explore novel strategies for enhancing polyamine-based brain tumor therapies.
- To investigate methods for overcoming limitations of current polyamine-targeting agents like DFMO.
- To propose a combination therapy for sustained tumor growth inhibition and prevention of recurrence.
Main Methods:
- Investigating the use of difluoromethylornithine (DFMO) as a polyamine synthesis inhibitor.
- Evaluating the efficacy of polyamine analogs in regulating polyamine synthesis and inhibiting tumor growth.
- Proposing local delivery via intracerebral microdialysis and internal radioemitters (tritiated putrescine/thymidine) for enhanced therapy.
Main Results:
- DFMO combined with cytotoxic agents shows antitumor effects but faces challenges with exogenous polyamine uptake and toxicity.
- DFMO therapy with exogenous polyamine elimination inhibits growth but causes toxicity and tumor recurrence.
- Polyamine analogs show sustained tumor inhibition after treatment cessation and are in clinical trials.
Conclusions:
- Polyamine-based therapies hold promise for brain tumor treatment by targeting cell proliferation.
- Combining polyamine depletion with targeted internal radioemitters offers a potential strategy to enhance efficacy and prevent recurrence.
- Local delivery and specific radioisotope targeting may overcome limitations of systemic polyamine-based treatments.