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Effects of carbamoylating agents on tumor metabolism
1Department of Biochemistry, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark.
Abstract:
Carbamoylation of macromolecules occurs by the displacement of hydrogen on several groups, but the most stable addition at neutral pH is on amino groups. This reaction occurs predominantly with proteins and results from the administration in vivo of inorganic cyanate or organic isocyanates. The latter act more rapidly, but also are more rapidly hydrolyzed in aqueous solution. This instability has been a factor limiting study of the pharmacological properties of organic isocyanates. However, organic isocyanates are released from some nitrosoureas of value in cancer therapy such as 1,3-bis(2-chlorethyl)-1-nitrosourea (BCNU) and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU). The carbamoylating activities of BCNU and CCNU are generally considered less significant than their alkylating activity in the action of these drugs on tumors, but carbamoylation may serve to inhibit DNA repair. There is evidence that carbamoylating agents can exert selective inhibitory effects on metabolite uptake and macromolecular synthesis in neoplastic tissues. Such selectivity is much more notable in vivo than in vitro. In the case of cyanate, the selectivity in vivo has been variously attributed to a requirement for metabolic activation, to selective effects on circulation in solid tumors, and to diminished pH in tumors. It is the distinction between such factors and the identification of critical cellular targets which provide major challenges in present studies on the effects of carbamoylating agents on tumor metabolism.
Insights
Carbamoylation, a reaction involving proteins, is explored for its role in cancer therapy. While less significant than alkylation for drugs like BCNU and CCNU, it may inhibit DNA repair and selectively impact tumor metabolism.
Area of Science:
- Biochemistry
- Pharmacology
- Oncology
Background:
- Carbamoylation involves the stable addition of isocyanates to amino groups, primarily in proteins.
- Organic isocyanates, though unstable, are released from cancer therapeutics like BCNU and CCNU.
- The carbamoylating activity of these drugs is secondary to their alkylating effects but may influence DNA repair.
Purpose of the Study:
- To investigate the pharmacological properties and therapeutic potential of carbamoylating agents.
- To understand the selective effects of carbamoylation on neoplastic tissues in vivo.
- To differentiate between metabolic activation, altered tumor circulation, and tumor pH as causes of in vivo selectivity.
Main Methods:
- Review of existing literature on carbamoylation reactions and their relevance to cancer therapy.
- Analysis of the mechanisms by which organic isocyanates and cyanate affect cellular processes.
- Comparison of in vitro and in vivo effects of carbamoylating agents on tumor metabolism.
Main Results:
- Carbamoylation by BCNU and CCNU may inhibit DNA repair, contributing to their anti-cancer effects.
- Carbamoylating agents demonstrate selective inhibition of metabolite uptake and macromolecular synthesis in tumors, particularly in vivo.
- In vivo selectivity of cyanate is attributed to potential metabolic activation, altered tumor blood flow, or tumor acidosis.
Conclusions:
- Carbamoylation represents a potential, albeit secondary, mechanism in the action of certain cancer drugs.
- Understanding the selective in vivo effects of carbamoylation is crucial for optimizing cancer therapy.
- Identifying critical cellular targets for carbamoylating agents remains a significant challenge in current research.