Synthesis and evaluation of tofacitinib analogs designed to mitigate metabolic activation

Area of Science:

• Medicinal Chemistry
• Pharmacology
• Drug Metabolism

Background:

• Tofacitinib (TFT), a Janus kinase (JAK) inhibitor, is effective for rheumatoid arthritis but linked to severe liver injury.
• This hepatotoxicity is hypothesized to stem from reactive aldehyde or epoxide metabolites of TFT.
• Developing safer TFT analogs with reduced reactive metabolite formation is crucial for improving patient safety.

Purpose of the Study:

• To design and synthesize novel tofacitinib analogs aimed at preventing the formation of reactive metabolites.
• To evaluate the JAK3 inhibitory activity, metabolic stability, CYP3A inhibition, and cytotoxicity of these analogs.
• To investigate the role of TFT metabolites in mechanism-based CYP3A4 inhibition and hepatotoxicity.

Main Methods:

• Synthesis of six tofacitinib analogs designed to mitigate reactive metabolite generation.
• In vitro evaluation of JAK3 inhibitory potency (nanomolar range).
• Assessment of metabolic stability, CYP3A time-dependent inhibition, and cytotoxicity (e.g., HepG2 cells).
• Bioactivation studies using TFT and its analogs to elucidate metabolite-mediated toxicity mechanisms.

Main Results:

• Purine analog 3 demonstrated potent JAK3 inhibition in the nanomolar range.
• Analog 3 exhibited minimal CYP3A inhibition and low cytotoxicity compared to tofacitinib.
• Bioactivation studies suggest TFT's epoxide metabolite may contribute to CYP3A4 mechanism-based inhibition and hepatotoxicity.

Conclusions:

• Purine analog 3 represents a potential safer drug candidate than tofacitinib for treating inflammatory diseases.
• The findings highlight the importance of metabolite profiling in the development of safer JAK inhibitors.
• Targeting reactive metabolite formation is a viable strategy to reduce drug-induced liver injury.