Background: Drug-induced myopathy is a serious side effect that often requires removal of
a medication from a drug regimen. For most drugs, the underlying mechanism of drug-induced myopathy
remains unclear. Monocarboxylate transporters (MCTs) mediate L-lactic acid transport, and inhibition
of MCTs may potentially lead to perturbation of L-lactic acid accumulation and muscular disorders.
Therefore, we hypothesized that L-lactic acid transport may be involved in the development of
drug-induced myopathy. The aim of this study was to assess the inhibitory potential of 24 acidic drugs
on L-lactic acid transport using breast cancer cell lines Hs578T and MDA-MB-231, which selectively
express MCT1 and MCT4, respectively.
Methods: The influx transport of L-lactic acid was minimally inhibited by all drugs tested. The efflux
transport was next examined: loratadine (IC50: 10 and 61 µM) and atorvastatin (IC50: 78 and 41 µM)
demonstrated the greatest potency for inhibition of L-lactic acid efflux by MCT1 and MCT4, respectively.
Acidic drugs including fluvastatin, cerivastatin, simvastatin acid, lovastatin acid, irbesartan and
losartan exhibited weak inhibitory potency on L-lactic acid efflux.
Results: Our results suggest that some acidic drugs, such as loratadine and atorvastatin, can inhibit the
efflux transport of L-lactic acid.
Conclusion: This inhibition may cause an accumulation of intracellular L-lactic acid leading to acidification
and muscular disorders.