Ganciclovir (GCV) is the cornerstone of cytomegalovirus prevention and treatment in transplant patients. It is associated with problematic adverse hematological effects in this population of immunosuppressed patients, which may lead to dose reduction thus favoring resistance. GCV crosses the membranes of cells, is activated by phosphorylation, and then stops the replication of viral DNA. Its intracellular accumulation might favor host DNA polymerase inhibition, hence toxicity. Following this hypothesis, we investigated the association between a selected panel of membrane transporter polymorphisms and the evolution of neutrophil counts in n = 174 renal transplant recipients. An independent population of n = 96 renal transplants served as a replication and experiments using HEK293T-transfected cells were performed to validate the clinical findings.
In both cohorts, we found a variant in ABCC4 (rs11568658) associated with decreased neutrophil counts following valganciclovir (GCV prodrug) administration (exploratory cohort: β ± SD = −0.68 ± 0.28, p = 0.029; replication cohort: β ± SD = −0.84 ± 0.29, p = 0.0078). MRP4-expressing cells showed decreased GCV accumulation as compared to negative control cells (transfected with an empty vector) (−61%; p < 0.0001). The efflux process was almost abolished in cells expressing MRP4 rs11568658 variant protein. Molecular dynamic simulations of GCV membrane crossing showed a preferred location of the drug just beneath the polar head group region, which supports its interaction with efflux transporters.