Mechanistic insights into the inhibition of drug‐resistant cytomegalovirus by letermovir and ganciclovir

Background and Purpose Letermovir and ganciclovir are used to prevent cytomegalovirus (CMV) infection, but the generation of resistant viruses and the interactions between wild and resistant CMV have not been studied. We evaluated the effect of letermovir/ganciclovir on the release of the wild‐type and letermovir/ganciclovir‐resistant CMV in their coinfected or superinfected cells. Experimental Approach We analysed the extracellular CMV infectivity released from CMV‐infected cells treated with letermovir and ganciclovir. Subsequently, we characterized growth of letermovir/ganciclovir‐resistant viruses in wild‐type CMV‐infected cells in the presence of letermovir/ganciclovir, respectively. Key Results The number of infectious cells resuming viral replication after letermovir/ganciclovir removal decreased over time, and the CMV‐infected cells treated with letermovir or ganciclovir remained infectious for 1 month. During the treatment course, letermovir‐/ganciclovir‐resistant viruses arise from CMV infection foci, and we investigated the proliferation of resistant viruses in the presence of letermovir/ganciclovir. Letermovir inhibited superinfected CMV release by inhibiting the superinfected CMV from using the DNA terminase‐packaging complex pathway occupied by a prior infected CMV. Co‐infection and superinfection of ganciclovir‐resistant CMV in wild‐type CMV‐infected cells inhibited viral release by inhibiting DNA synthesis by ganciclovir phosphorylated by wild‐type UL97 . These results suggested that letermovir‐resistant CMV emerging in wild‐type CMV‐infected cells would not easily spread to the surrounding wild‐type CMV‐infected cells in CMV‐infected patients under letermovir. Conclusion and Implications Despite different mechanisms of action, both drugs inhibited the spread of newly emerging resistant viruses around wild‐type CMV‐infected lesions during letermovir/ganciclovir treatment, suggesting the practical use of both drugs and strategies for treating drug‐resistant CMV.