H414

Ganciclovir Triphosphate Incorporation Drives Mutagenesis in Hematopoietic and Colorectal Cells

Ganciclovir (GCV) is a mainstay for cytomegalovirus management in transplant patients, yet its potential mutagenicity remains poorly defined. Clinical review of two hematopoietic stem cell transplant (HSCT) patients who developed colorectal neoplasms harboring the GCV-associated mutational signature (GCVsig) revealed prior exposure to both GCV and acyclovir (ACV). To determine the specificity of GCVsig, Fang et al. treated the H414 colorectal cancer cell line with DMSO, GCV, or ACV. While cells tolerated treatment at 100 µM, only GCV exposure induced the characteristic CA > AA mutational signature, which was absent in ACV-treated samples (Fig. 1A). This specificity was validated in HoxA9-Meis1-transformed murine myeloid cells, which were less tolerant to antivirals. Despite a 20-fold lower dose (5 µM), only GCV-treated cells acquired significant CA > AA mutations compared to ACV or controls (p< 0.01, Student's t-test) (Fig. 1B).

Mechanistically, GCV-triphosphate (GCV-TP) incorporation into DNA was confirmed by increased staining of the DNA damage marker γH2AX in H414 cells after 36 hours of GCV treatment-coinciding with DNA replication-whereas ACV-treated cells showed minimal γH2AX signal (Fig. 1C). Flow cytometry revealed no significant cell cycle arrest in either treatment group at 36 hours, indicating that GCV-induced mutagenesis occurs without overt cytotoxicity in tolerant cells.