Related Experiment Videos
Nitro reduction as an electronic switch for bioreductive drug activation
B G Siim1, W A Denny, W R Wilson
1Department of Pathology, University of Auckland, New Zealand. b.siim@auckland.ac.nz
Abstract:
It is well known that the reduction of aromatic nitro groups can give rise to toxic species, and that net nitro reduction by one-electron reductases can usually be inhibited by oxygen. There has been much interest in utilizing this biotransformation to activate drugs in hypoxic regions of tumors, but no clinically useful compound has yet resulted. Nitroreductive activation of prodrugs by oxygen-insensitive (and oxygen-sensitive) reductases is also of current interest because of new methods for introducing specific nitroreductases into tumors (e.g., as antibody-enzyme conjugates or by gene therapy). In most of the compounds investigated previously, cytotoxicity appears to be due to reactive nitroso or hydroxylamine reduction products arising from the nitro group itself. It is argued that there is greater scope for designing potent and selective nitro compounds by using the nitro group as an electronic switch to activate a latent reactive moiety elsewhere in the molecule. Examples of this approach include the nitro(hetero)aromatic mustards (e.g., SN 23816, NSC 646394) in which the nitro group controls the reactivity of a nitrogen mustard to which it is directly conjugated, and the nitro(hetero)aromatic methylquaternary (NMQ) mustards (e.g., SN 25341, NSC 658926) in which reduction of the nitro group triggers fragmentation of the molecule to release a reactive aliphatic nitrogen mustard. Many of these compounds show very high selectivity for hypoxic cells in culture. Some are also active against hypoxic cells in tumors, and provide large tumor growth delays when combined with tumor blood flow inhibitors such as 5,6-dimethylxanthenone-4-acetic acid (DMXAA). These prodrug designs also have potential for releasing effectors other than nitrogen mustards, which opens up many possibilities for use of nitro compounds as tumor-selective prodrugs.
Insights
Nitroaromatic compounds can be activated in hypoxic tumors. New prodrug designs use the nitro group as a switch to release potent cytotoxic agents, showing high selectivity for cancer cells.
Area of Science:
- Medicinal Chemistry
- Tumor Biology
- Drug Discovery
Background:
- Nitro group reduction can yield toxic byproducts, often inhibited by oxygen.
- Tumor hypoxia presents a target for bioreductive drug activation, but clinical success has been limited.
- Novel methods for delivering nitroreductases to tumors are emerging, increasing interest in nitroreductive prodrugs.
Purpose of the Study:
- To explore the design of potent and selective nitroaromatic prodrugs for cancer therapy.
- To investigate prodrugs where the nitro group acts as an electronic switch to activate a latent cytotoxic moiety.
- To evaluate the efficacy of these novel prodrugs against hypoxic tumor cells.
Main Methods:
- Design and synthesis of nitro(hetero)aromatic mustards and nitro(hetero)aromatic methylquaternary (NMQ) mustards.
- In vitro testing for cytotoxicity against hypoxic cancer cells.
- In vivo studies assessing tumor growth delay in combination with tumor blood flow inhibitors like DMXAA.
Main Results:
- Nitroaromatic mustards and NMQ mustards demonstrated high selectivity for hypoxic cells in culture.
- Some compounds showed significant activity against hypoxic tumor cells in vivo.
- Combination therapy with DMXAA resulted in substantial tumor growth delays.
Conclusions:
- Nitroaromatic compounds can be effectively designed as prodrugs by using the nitro group to control the release of cytotoxic agents.
- This approach offers a promising strategy for developing tumor-selective therapies targeting hypoxic regions.
- The prodrug design has potential for releasing various effector molecules, expanding therapeutic possibilities.