# Diverse Inhibitors of De Novo Purine Synthesis Promote AICAR‐Induced AMPK Activation and Glucose Uptake in L6 Myotubes

## TL;DR

This study shows that several drugs inhibit purine synthesis, which activates AMPK and increases glucose uptake in muscle cells.

## Contribution

The study identifies multiple drugs that enhance AICAR-induced AMPK activation and glucose uptake through inhibition of purine synthesis.

## Key findings

- Methotrexate and other drugs inhibit purine synthesis to activate AMPK and increase glucose uptake in L6 myotubes.
- Inhibitors of IMP metabolism, like mycophenolate mofetil and alanosine, enhance AICAR-induced AMPK activation.
- These drugs do not suppress mitochondrial function, as shown by oxygen consumption rate measurements.

## Abstract

Methotrexate, an immunosuppressant and anticancer drug, promotes glucose uptake and lipid oxidation in skeletal muscle via activation of AMP‐activated protein kinase (AMPK). Methotrexate promotes AMPK activation by inhibiting 5‐aminoimidazole‐4‐carboxamide ribonucleotide (ZMP) formyltransferase/inosine monophosphate (IMP) cyclohydrolase (ATIC), which converts ZMP, an endogenous purine precursor and an active form of the pharmacological AMPK activator AICAR, to IMP during de novo purine synthesis. In addition to methotrexate, inhibition of purine synthesis underpins the therapeutic effects of a number of commonly used immunosuppressive, anticancer, and antimicrobial drugs, raising the question of whether activation of AMPK in skeletal muscle could be a recurrent feature of these drugs. Using L6 myotubes, we found that AICAR‐induced AMPK activation and glucose uptake were enhanced by inhibitors of the conversion of IMP to GMP (mycophenolate mofetil) or of IMP to AMP (alanosine) as well as by indirect inhibitors of human (trimetrexate) and bacterial ATIC (sulfamethoxazole). 6‐Mercaptopurine, which inhibits the conversion of IMP to GMP and AMP, activated AMPK, increased glucose uptake, and suppressed insulin signaling, but did not enhance the effect of AICAR. As determined by measuring oxygen consumption rate, none of these agents suppressed mitochondrial function. Overall, our results indicate that IMP metabolism is a gateway for the modulation of AMPK and its metabolic effects in skeletal muscle cells.

Mycophenolate mofetil, alanosine, trimetrexate, and sulfamethoxazole mimic methotrexate's effects by enhancing AICAR‐induced AMPK activation and glucose uptake in L6 myotubes. Collectively, our results suggest that IMP metabolism may serve as a gateway for the modulation of AMPK and its metabolic effects in skeletal muscle cells.