Poster Number-60 - A Systematic Chemical Design Strategy Leads to NTM-004/005, an Acetaminophen Structural Analog with Minimal Liver Histopathology

A Systematic Chemical Design Strategy Leads to NTM-004/005, an Acetaminophen Structural Analog with Minimal Liver Histopathology

Purpose:

In accidental or intentional overdose acetaminophen (paracetamol) is metabolized by cytochrome P450 isozymes (mainly 2E1, 1A2, 3A4, and 2A6) to generate sufficient amounts of the reactive metabolite N-acetyl-p-benzoquinone imine to covalently bind to cysteine groups on proteins and produce hepatotoxicity.  Separation between the therapeutic and toxic effects is a desirable goal. Unfortunately, standard drug discovery strategies to date have not been successful when applied to finding efficacious analogs of acetaminophen that have reduced hepatotoxicity, because the mechanism of action of acetaminophen is not known. Therefore, strategies such as recombinant protein expression, assay development, High-Throughput Screening (HTS), and structure-based drug discovery have thus far not led to the elucidation of a molecular target for acetaminophen. Our hypothesis is that, by using knowledge of the mechanism of toxicity of acetaminophen, and through iterative chemical modification and synthesis of analogs, that an agent with significantly less hepatotoxicity compared to acetaminophen can be developed.

Methods: We sought to undertake development of a systematic chemical design strategy that results in modification of the structure of acetaminophen that was predicted to result in the maintenance of antinociceptive efficacy, but with dramatic decrease in in vivo measures of hepatotoxicity. The design process undertaken was to test substituted, cyclized analogs of acetaminophen that were predicted to be less prone to producing reactive quinone intermediates. A U.S. Patent (#10,537,552, 2020) has been issued that covers this work. The chemical entity 5-hydroxyoxindole, which differs from acetaminophen by a single chemical bond was identified and in preliminary studies showed antinociceptive activity in the mouse acetic acid induced abdominal constriction behavior test. Subsequently, a series of analogs (currently numbering around 50) were synthesized and tested by standard techniques for antinociceptive efficacy and safety (hepatotoxicity).

Results: Our hypothesis, that by using knowledge of the mechanism of toxicity of the widely used pain reliever acetaminophen, and through iterative chemical modification and synthesis of analogs, that a compound with a superior therapeutic index compared to acetaminophen can be developed, was confirmed. The lead compound JC-29 was shown to be effective in a standard pain model and demonstrated an apparent significant safety advantage over acetaminophen when assessed for liver toxicity.

Conclusion: A systematic chemical design strategy was developed that results in modifications of the template structure of acetaminophen that, in selective compounds, results in maintenance of antinociception, but a significant decrease in in vivo measure of hepatotoxicity. NTM-004/005 currently is undergoing testing for development as a substitute for acetaminophen for a variety of therapeutic uses.

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