Intravenous Hydroxypropyl β-Cyclodextrin Formulation of Letermovir: A Phase I, Randomized, Single-Ascending, and Multiple-Dose Trial

Clinical Pharmacokinetics and Pharmacodynamics of Letermovir in Allogenic Hematopoietic Cell Transplantation

Letermovir is a newly developed antiviral agent used for the prophylaxis of human cytomegalovirus infections in patients undergoing allogeneic hematopoietic cell transplantation. This novel anti-cytomegalovirus drug, used for the prophylaxis of cytomegalovirus reactivation until approximately 200 days after transplantation, effectively reduces the risk of clinically significant cytomegalovirus infection. No human counterpart exists for the terminase complex; letermovir is virus specific and lacks some toxicities previously observed with other anti-cytomegalovirus drugs, such as cytopenia and nephrotoxicity. The absolute bioavailability of letermovir in healthy individuals is estimated to be 94% based on a population-pharmacokinetic analysis. In contrast, oral administration of letermovir to patients undergoing hematopoietic cell transplantation results in lower exposure than that in healthy individuals. Renal or hepatic impairment does not influence the intrinsic clearance of letermovir. Co-administration of letermovir may alter the plasma concentrations of other drugs, including itself, as it acts as a substrate and inhibitor/inducer of several drug-metabolizing enzymes and transporters. In particular, attention should be paid to the drug-drug interactions between letermovir and calcineurin inhibitors or azole antifungal agents, which are commonly used in patients undergoing hematopoietic cell transplantation. This article reviews and summarizes the clinical pharmacokinetics and pharmacodynamics of letermovir, focusing on patients undergoing hematopoietic cell transplantation, healthy individuals, and specific patient subsets.

Management of Cytomegalovirus Infections in the Era of the Novel Antiviral Players, Letermovir and Maribavir

Cytomegalovirus (CMV) infections may increase morbidity and mortality in immunocompromised patients. Until recently, standard antiviral drugs against CMV were limited to viral DNA polymerase inhibitors (val)ganciclovir, foscarnet and cidofovir with a risk for cross-resistance. These drugs may also cause serious side effects. This narrative review provides an update on new antiviral agents that were approved for the prevention and treatment of CMV infections in transplant recipients. Letermovir was approved in 2017 for CMV prophylaxis in CMV-seropositive adults who received an allogeneic hematopoietic stem cell transplant. Maribavir followed four years later, with an indication in the treatment of adult and pediatric transplant patients with refractory/resistant CMV disease. The target of letermovir is the CMV terminase complex (constituted of pUL56, pUL89 and pUL51 subunits). Letermovir prevents the cleavage of viral DNA and its packaging into capsids. Maribavir is a pUL97 kinase inhibitor, which interferes with the assembly of capsids and the egress of virions from the nucleus. Both drugs have activity against most CMV strains resistant to standard drugs and exhibit favorable safety profiles. However, high-level resistance mutations may arise more rapidly in the UL56 gene under letermovir than low-grade resistance mutations. Some mutations emerging in the UL97 gene under maribavir can be cross-resistant with ganciclovir. Thus, letermovir and maribavir now extend the drug arsenal available for the management of CMV infections and their respective niches are currently defined.

Therapeutic Drug Monitoring of Orally Administered Letermovir Prophylaxis in Allogeneic Hematopoietic Stem Cell Transplant Recipients

With balanced safety-efficacy profile, letermovir anti-cytomegalovirus (CMV) prophylaxis is used in hematopoietic stem cell transplant recipients (HSCTR). We assessed feasibility and usefulness of letermovir therapeutic drug monitoring (TDM) in HSCTR. We performed a prospective observational study on letermovir-TDM including 40 consecutive adult CMV-seropositive allogeneic-HSCTR who received orally (PO) administered letermovir. Minimal blood concentrations of letermovir (C_trough) were measured on days 3 and 7 postletermovir initiation and weekly thereafter. Letermovir-C_trough remained stable during the first 70 days post-HSCT at a median of 286 μg/L (interquartile range, 131 to 591 μg/L), with large interpatient/intrapatient variability. No associations between breakthrough clinically significant CMV infection or detectable CMV DNAemia and letermovir-C_trough were observed. Patients with letermovir-associated adverse events had higher letermovir-C_trough than patients without (400 versus 266 μg/L, P = 0.02). Letermovir-C_trough was similar in patients with or without gastrointestinal symptoms (280 versus 300 μg/L, P = 0.49). Acute grade ≥2 GvHD was associated with higher letermovir-C_trough (479 versus 248 μg/L, P = 0.001), including gastrointestinal GvHD (499 versus 263 μg/L, P = 0.004). Concomitantly administered posaconazole and cyclosporine were associated with higher letermovir-C_trough (707 versus 259 μg/L, P < 0.001 and 437 versus 248 μg/L, P = 0.01, respectively). In multivariable analysis, both posaconazole (odds ratio [OR], 4.9; 95% confidence interval [CI], 2.4 to 9.7; P < 0.0001) and cyclosporine-adjusted letermovir dose at 240 mg daily (OR, 3.5; 95% CI, 1.4 to 9.0; P = 0.01) were independently associated with higher letermovir-C_trough. In conclusion, administration of PO letermovir led to measurable and relatively stable letermovir-C_trough, without noticeable associations with clinical efficacy. Letermovir exposure was not affected by gastrointestinal symptoms, but with posaconazole and cyclosporine administration. Associations between letermovir and concomitantly administered agents and adverse events warrant additional clinical studies.

Cyclodextrin-based delivery systems in parenteral formulations: a critical update review

Parenteral formulations are indispensable in clinical practice and often are the only option to administer drugs that cannot be administrated through other routes, such as proteins and certain anticancer drugs - which are indispensable to treat some of the most prevailing chronic diseases worldwide (like diabetes and cancer). Additionally, parenteral formulations play a relevant role in emergency care since they are the only ones that provide an immediate action of the drug after its administration. However, the development of parenteral formulations is a complex task owing to the specific quality and safety requirements set for these preparations and the intrinsic properties of the drugs. Amongst all the strategies that can be useful in the development of parenteral formulations, the formation of water-soluble host-guest inclusion complexes with cyclodextrins (CDs) has proven to be one of the most advantageous. CDs are multifunctional pharmaceutical excipients able to form water-soluble host-guest inclusion complexes with a wide variety of molecules, particularly drugs, and thus improve their apparent water-solubility, chemical stability, and bioavailability, to make them suitable for parenteral administration. Besides, CDs can be employed as building blocks of more complex injectable drug delivery systems with enhanced characteristics, such as nanoparticles and supramolecular hydrogels, that has been found particularly beneficial for the delivery of anticancer drugs. However, only a few CDs are considered safe when parenterally administered, and some of these types are already approved to be used in parenteral dosage forms. Therefore, the application of CDs in the development of parenteral formulations has been a more common practice in the last few years, due to their significant worldwide acceptance by the health authorities, promoting the development of safer and more efficient injectable drug delivery systems.

Pharmacokinetics, Safety, and Tolerability of Letermovir Following Single- and Multiple-Dose Administration in Healthy Japanese Subjects

Letermovir is a human cytomegalovirus terminase inhibitor for the prophylaxis of cytomegalovirus infection and disease in allogeneic hematopoietic stem cell transplant recipients. The pharmacokinetics, safety, and tolerability of letermovir were assessed in healthy Japanese subjects in 2 phase 1 trials: trial 1-single ascending oral doses (240, 480, and 720 mg) and intravenous (IV) doses (240, 480, and 960 mg), and trial 2-multiple oral doses (240 and 480 mg once daily for 7 days). Following administration of oral single and multiple doses, letermovir was absorbed with a median time to maximum plasma concentration of 2 to 4 hours, and concentrations declined in a biphasic manner with a terminal half-life of ≈10 to 13 hours. The post absorption plasma concentration-time profile of letermovir following oral administration was similar to the profile observed with IV dosing. There was minimal accumulation with multiple-dose administration. Letermovir exposure in healthy Japanese subjects was ≈1.5- to 2.5-fold higher than that observed in non-Japanese subjects. Based on the population pharmacokinetic analysis, weight differences primarily accounted for the higher exposures observed in Asians. Letermovir was generally well tolerated following oral and IV administration to healthy Japanese subjects.

The Effect of Oral Letermovir Administration on the Pharmacokinetics of a Single Oral Dose of P-Glycoprotein Substrate Digoxin in Healthy Volunteers

Letermovir is a human cytomegalovirus (CMV) terminase inhibitor approved in the United States, Canada, Japan, and the European Union for prophylaxis of CMV infection and disease in CMV-seropositive, allogeneic, hematopoietic stem-cell transplant recipients. In vitro, letermovir is a substrate and potential modulator of P-glycoprotein. The potential of letermovir to alter the pharmacokinetics of digoxin (a P-glycoprotein substrate) upon coadministration in healthy subjects was therefore investigated in a phase 1 trial (EudraCT: 2011-004516-39). Oral letermovir 240 mg was administered twice daily for 12 days with a single oral digoxin 0.5-mg dose on day 7; after a washout period, oral digoxin 0.5 mg was administered on day 35 (sequence 1). The period order was reversed after a 28-day washout for sequence 2. Pharmacokinetics and safety were evaluated. The presence of steady-state letermovir reduced digoxin area under the plasma concentration-time curve from administration until last quantifiable measurement by 12% and maximum plasma concentration by 22% compared with digoxin alone; digoxin half-life and elimination rate remained similar in both conditions. The between-subject variability of digoxin maximum plasma concentration was higher with letermovir than without (42% vs 31%) and similar for digoxin area under the plasma concentration-time curve in both periods. No specific safety or tolerability concerns were identified. Overall, letermovir had no clinically relevant effect on concomitant administration with digoxin.

Molecular encapsulation of andrographolide in 2-hydroxypropyl-β-cyclodextrin cavity: synthesis, characterization, pharmacokinetic and in vitro antiviral activity analysis against SARS-CoV-2

In present investigation, AND-2-HyP-β-CYD (Andrographolide-2-Hydroxypropyl-β-cyclodextrin) complex was synthesized and characterized for antiviral and pharmacokinetic profile. The linear host-guest relation suggested synthesis of a 1:1 complex of AND with 2-HyP-β-CYD by inclusion mode. The Kc, stability constant of the two phase system of AND with 2-HyP-β-CYD computed to be 38.60 x 10⁻³M. ¹H NMR spectrum of AND indicated the presence of triplet at 6.63-ppm which was up-fielded in AND-2-HyP-β-CYD complex at 6.60-ppm (doublet) confirmed the insertion of AND in cavity of 2-HyP-β-CYD through lactone ring. AND-2-HyP-β-CYD complex exhibited the IC₅₀ of 0.1-μg.mL⁻¹ (E gene) and 0.29-μg.mL⁻¹ (N gene) against SARS-CoV-2 infected Vero6 cells. Moreover, a 1.5-fold increment in extent of absorption of AND was noticed post complexation. The bioavailability was estimated to be 15.87 ± 3.84% and 23.84 ± 5.46%, respectively for AND and AND-2-HyP-β-CYD complex. AND-2-HyP-β-CYD complex may be a prospective candidate for further studies to evolve as a clinically viable formulation against SARS-CoV-2.

Population pharmacokinetics of letermovir following oral and intravenous administration in healthy participants and allogeneic hematopoietic cell transplantation recipients

Letermovir is indicated for prophylaxis of cytomegalovirus infection and disease in allogeneic hematopoietic stem cell transplant (HSCT) recipients. Two‐stage population pharmacokinetic (PK) modeling of letermovir was conducted to support dose rationale and evaluate the impact of intrinsic/extrinsic factors. Data from healthy phase I study participants over a wide dose range were modeled to evaluate the effects of selected intrinsic factors, including pharmacogenomics; next, phase III HSCT‐recipient data at steady‐state following clinical doses were modeled. The model in HSCT recipients adequately described letermovir PK following both oral or i.v. administration, and was consistent with the healthy participant model at steady‐state clinical doses. Intrinsic factor effects were not clinically meaningful. These staged analyses indicate that letermovir PK in HSCT recipients and healthy participants differ only with respect to bioavailability and absorption rate. The HSCT recipient model was suitable for predicting exposure for exposure–response analysis supporting final dose selection.

Antiviral Drugs Against Herpesviruses

The discovery of the nucleoside analogue, acyclovir, represented a milestone in the management of infections caused by herpes simplex virus and varicella-zoster virus. Ganciclovir, another nucleoside analogue, was then used for the management of systemic and organ-specific human cytomegalovirus diseases. The pyrophosphate analogue, foscarnet, and the nucleotide analogue, cidofovir, have been approved subsequently and constitute the second-line antiviral drugs. However, the viral DNA polymerase is the ultimate target of all these antiviral agents with a possible emergence of cross-resistance between these drugs. Recently, letermovir that targets the viral terminase complex was approved for the prophylaxis of human cytomegalovirus infections in hematopoietic stem cell transplant recipients. Other viral targets such as the protein kinase and the helicase-primase complex are also evaluated for the development of novel potent inhibitors against herpesviruses.

The Lord of the NanoRings: Cyclodextrins and the battle against SARS-CoV-2

A handful of singular structures and laws can be observed in nature. They are not always evident but, once discovered, it seems obvious how to take advantage of them. In chemistry, the discovery of reproducible patterns stimulates the imagination to develop new functional materials and technological or medical applications. Two clear examples are helical structures at different levels in biological polymers as well as ring and spherical structures of different size and composition. Rings are intuitively observed as holes able to thread elongated structures. A large number of real and fictional stories have rings as inanimate protagonists. The design, development or just discovering of a special ring has often been taken as a symbol of power or success. Several examples are the Piscatory Ring wore by the Pope of the Catholic Church, the NBA Championship ring and the One Ring created by the Dark Lord Sauron in the epic story The Lord of the Rings. In this work, we reveal the power of another extremely powerful kind of rings to fight against the pandemic which is currently affecting the whole world. These rings are as small as ~1 nm of diameter and so versatile that they are able to participate in the attack of viruses, and specifically SARS-CoV-2, in a large range of different ways. This includes the encapsulation and transport of specific drugs, as adjuvants to stabilize proteins, vaccines or other molecules involved in the infection, as cholesterol trappers to destabilize the virus envelope, as carriers for RNA therapies, as direct antiviral drugs and even to rescue blood coagulation upon heparin treatment.

“One ring to rule them all. One ring to find them. One ring to bring them all and in the darkness bind them.” J. R. R. Tolkien.

Assessment of Pharmacokinetic Interaction Between Letermovir and Fluconazole in Healthy Participants

Letermovir is a prophylactic agent for cytomegalovirus infection and disease in adult cytomegalovirus-seropositive recipients of allogeneic hematopoietic stem cell transplant. As the antifungal agent fluconazole is administered frequently in transplant recipients, a drug-drug interaction study was conducted between oral letermovir and oral fluconazole. A phase 1 open-label, fixed-sequence study was performed in healthy females (N = 14, 19-55 years). In Period 1, a single dose of fluconazole 400 mg was administered. Following a 14-day washout, a single dose of letermovir 480 mg was administered (Period 2), and after a 7-day washout, single doses of fluconazole 400 mg and letermovir 480 mg were coadministered in Period 3. Pharmacokinetics and safety were evaluated. The pharmacokinetics of fluconazole and letermovir were not meaningfully changed following coadministration. Fluconazole geometric mean ratio (GMR; 90% confidence interval [CI]) with letermovir for area under the concentration-versus-time curve from time 0 to infinity (AUC_0-∞ ) was 1.03 (0.99-1.08); maximum concentration (C_max ) was 0.95 (0.92-0.99). Letermovir AUC_0-∞ GMR (90%CI) was 1.11 (1.01-1.23), and C_max was 1.06 (0.93-1.21) following coadministration with fluconazole. Coadministration of fluconazole and letermovir was generally well tolerated.

Letermovir and its role in the prevention of cytomegalovirus infection in seropositive patients receiving an allogeneic hematopoietic cell transplant

Cytomegalovirus (CMV) reactivation is one of the most common infections affecting allogeneic hematopoietic cell transplant recipients. Although available anti-CMV therapies have been evaluated for the prevention of CMV reactivation, their toxicity profile makes them unfavorable for use as primary prophylaxis; thus, they are routinely reserved for the treatment of CMV viremia or CMV end-organ disease. Pre-emptive CMV monitoring strategies have been widely accepted, and although they have been helpful in early detection, they have not affected the overall morbidity and mortality associated with CMV. Letermovir is a novel agent that was approved for primary prophylaxis in CMV-seropositive adult allogeneic hematopoietic cell transplant recipients. This review focuses on letermovir's novel mechanism; clinical trials supporting its United States Food and Drug Administration (FDA) approval and subsequent follow-up analyses; clinical considerations, with an emphasis on pharmacology; and lessons learned from solid organ transplant recipients, as well as potential future directions.

Moving Past Ganciclovir and Foscarnet: Advances in CMV Therapy

PURPOSE OF REVIEW

CMV DNA polymerase inhibitors such as ganciclovir and foscarnet have dramatically reduced the burden of CMV infection in the HCT recipient. However, their use is often limited by toxicities and resistance. Agents with novel mechanisms and favorable toxicity profiles are critically needed. We review recent developments in CMV antivirals and immune-based approaches to mitigating CMV infection.

RECENT FINDINGS

Letermovir, an inhibitor of the CMV terminase complex, was approved in 2017 for primary CMV prophylaxis in adult seropositive allogeneic HCT recipients. Maribavir, an inhibitor of the CMV UL97 kinase, is currently in two phase 3 treatment studies. Adoptive immunotherapy using third-party T cells has proven safe and effective in preliminary studies. Vaccine development continues, with several promising candidates currently under study. No longer limited to DNA polymerase inhibitors, the prevention and treatment of CMV infections in the HCT recipient is a rapidly evolving field which should translate into improvements in CMV-related outcomes.

Compassionate Use of Letermovir in a 2-Year-Old Immunocompromised Child With Resistant Cytomegalovirus Disease

Little information on the efficacy and pharmacokinetics of letermovir among immunocompromised children is currently available. We describe here the use of letermovir in a 2-year-old immunocompromised child with ganciclovir-resistant cytomegalovirus disease who required extracorporeal membrane oxygenation. Detailed information on therapeutic-drug-monitoring measures and dosage adjustments for letermovir is provided.

Cyclodextrin Based Nanoparticles for Drug Delivery and Theranostics

Colloidal nanoparticulate technology has been described in the literature as a versatile drug delivery system. But it possesses some inherent lacunae in their formulation. Cyclodextrins (CDs) have been extensively reported for the solubility enhancement of poorly water-soluble drugs. The CDs can cause intervention in aspects related to nanoparticles (NPs) that include improving drug loading in nano-system, improving stability, site-specific/targeted drug delivery, improving solubility profile and absorption of the drug in nanosystem with consequent improvement in bioavailability, with the possibility of controlled release, safety and efficacy. They find application in for simultaneous diagnosis and therapeutics for better treatment procedures. The current communication is focused on the application of CDs to overcome troubles in nanoparticulate formulation and enhancement of their performance. It also envisages the theranostic aspects of CDs.

An overview of letermovir: a cytomegalovirus prophylactic option

Introduction: Human cytomegalovirus (HCMV) or human herpesvirus 5 (HHV-5) is a β-herpesvirus that causes widespread infection in nearly all members of the human population worldwide. Its persistence in humans after primary infection in a latent phase as well as a partial non-protective immune response is the basis for repeated re-activation/re-infection episodes occurring both in immunocompetent and immunocompromised subjects. In the latter patient populations, which include hematopoietic stem cell transplant (HSCT) recipients, HCMV reactivation episodes may be particularly severe, leading to both systemic and end-organ diseases. Since the 90s, at least four antiviral drugs targeting the DNA polymerase complex have been developed for the prevention and treatment of HCMV infections in transplant recipients, used as first-line (ganciclovir and valganciclovir) and second-line therapy (foscarnet and cidofovir). However, due to their toxicity and drug-resistance induction, new drugs with different targets were needed. Areas covered: In 2017, a new drug named letermovir (LTV), which targets the HCMV DNA terminase complex, was licensed for prophylaxis of HCMV infections in HSCT recipients. This is the focus of this review. Expert opinion: LTV safety and efficacy are promising. However, long-term adverse events and the emergence of drug-resistant HCMV strains must be investigated in extended clinical trials prior to drawing final conclusions.

Antiviral prophylaxis for cytomegalovirus infection in allogeneic hematopoietic cell transplantation

Patients treated with allogeneic hematopoietic cell transplantation (HCT) are at risk of cytomegalovirus (CMV) reactivation and disease, which results in increased morbidity and mortality. Although universal antiviral prophylaxis against CMV improves outcomes in solid organ transplant recipients, data have been conflicting regarding such prophylaxis in patients undergoing allogeneic HCT. We conducted a systematic review of randomized trials of prophylactic antivirals against CMV after allogeneic HCT to summarize the evolution of the field over the last 35 years and evaluate the prophylactic potential of antiviral agents against CMV after allogeneic HCT. Electronic databases were queried from database inception through 31 December 2017. For included studies, incidence of CMV infection and all-cause mortality were collected as primary outcomes; CMV disease incidence, use of preemptive therapy, and drug toxicities were collected as secondary outcomes. Nineteen clinical trials conducted between 1981 and 2017 involving a total of 4173 patients were included for review. Prophylactic strategies included use of acyclovir, valacyclovir, ganciclovir, maribavir, brincidofovir, and letermovir compared with placebo or a comparator antiviral. Fourteen trials that compared antiviral prophylaxis with placebo demonstrated overall effectiveness in reducing incidence of CMV infection (odds ratio [OR], 0.49; 95% confidence interval [CI], 0.42-0.58), CMV disease (OR, 0.56; 95% CI, 0.40-0.80), and use of preemptive therapy (OR, 0.51; 95% CI, 0.42-0.62; 6 trials); however, none demonstrated reduction in all-cause mortality (OR, 0.96; 95% CI, 0.78-1.18) except the phase 3 trial of letermovir (week-24 OR, 0.59; 95% CI, 0.38-0.98). Additional research is warranted to determine patient groups most likely to benefit from antiviral prophylaxis and its optimal deployment after allogeneic HCT.

Overcoming the Blood–Brain Barrier. Challenges and Tricks for CNS Drug Delivery

Treatment of certain central nervous system disorders, including different types of cerebral malignancies, is limited by traditional oral or systemic administrations of therapeutic drugs due to possible serious side effects and/or lack of the brain penetration and, therefore, the efficacy of the drugs is diminished. During the last decade, several new technologies were developed to overcome barrier properties of cerebral capillaries. This review gives a short overview of the structural elements and anatomical features of the blood–brain barrier. The various in vitro (static and dynamic), in vivo (microdialysis), and in situ (brain perfusion) blood–brain barrier models are also presented. The drug formulations and administration options to deliver molecules effectively to the central nervous system (CNS) are presented. Nanocarriers, nanoparticles (lipid, polymeric, magnetic, gold, and carbon based nanoparticles, dendrimers, etc.), viral and peptid vectors and shuttles, sonoporation and microbubbles are briefly shown. The modulation of receptors and efflux transporters in the cell membrane can also be an effective approach to enhance brain exposure to therapeutic compounds. Intranasal administration is a noninvasive delivery route to bypass the blood–brain barrier, while direct brain administration is an invasive mode to target the brain region with therapeutic drug concentrations locally. Nowadays, both technological and mechanistic tools are available to assist in overcoming the blood–brain barrier. With these techniques more effective and even safer drugs can be developed for the treatment of devastating brain disorders.

Clinical development of letermovir and maribavir: Overview of human cytomegalovirus drug resistance

The prevention and treatment of human cytomegalovirus (HCMV) infections is based on the use of antiviral agents that currently target the viral DNA polymerase and that may cause serious side effects. The search for novel inhibitors against HCMV infection led to the discovery of new molecular targets, the viral terminase complex and the viral pUL97 kinase. The most advanced compounds consist of letermovir (LMV) and maribavir (MBV). LMV inhibits the cleavage of viral DNA and its packaging into capsids by targeting the HCMV terminase complex. LMV is safe and well tolerated and exhibits pharmacokinetic properties that allow once daily dosing. LMV showed efficacy in a phase III prophylaxis study in hematopoietic stem cell transplant (HSCT) recipients seropositive for HCMV. LMV was recently approved under the trade name Prevymis^™ for prophylaxis of HCMV infection in adult seropositive recipients of an allogeneic HSCT. Amino acid substitutions conferring resistance to LMV selected in vitro map primarily to the pUL56 and rarely to the pUL89 and pUL51 subunits of the HCMV terminase complex. MBV is an inhibitor of the viral pUL97 kinase activity and interferes with the morphogenesis and nuclear egress of nascent viral particles. MBV is safe and well tolerated and has an excellent oral bioavailability. MBV was effective for the treatment of HCMV infections (including those that are refractory or drug-resistant) in transplant recipients in two phase II studies and is further evaluated in two phase III trials. Mutations conferring resistance to MBV map to the UL97 gene and can cause cross-resistance to ganciclovir. MBV-resistant mutations also emerged in the UL27 gene in vitro and could compensate for the inhibition of pUL97 kinase activity by MBV. Thus, LMV and probably MBV will broaden the armamentarium of antiviral drugs available for the prevention and treatment of HCMV infections.

Letermovir for prophylaxis of cytomegalovirus manifestations in adult allogeneic hematopoietic stem cell transplant recipients

Cytomegalovirus (CMV) manifestations remain important complications after allogeneic hematopoietic stem cell transplantation (HSCT), even in the current era. Unfortunately, available anti-CMV agents, mainly viral polymerase inhibitors, have a substantial risk of myelosuppression and nephrotoxicity. Letermovir, a novel anti-CMV drug that targets the viral terminase complex, has recently been approved for the prevention of clinically significant CMV infection in adult CMV seropositive hematopoietic stem cell transplantation recipients. This molecule could become a paradigm-shifting drug in preventing CMV manifestations based on its novel mechanism of action, lack of cross-resistance with available drugs, proven efficacy in a large randomized clinical trial, and its beneficial toxicity and tolerability profile. Drug-drug interactions and the lack of any activity against other viruses are the main shortcomings of letermovir.

Treatment and Prevention of CMV Disease in Transplant Recipients: Current Knowledge and Future Perspectives

This review summarizes the significant impact of cytomegalovirus (CMV) infection on solid organ and hematopoietic stem cell transplant recipients. A discussion of the various CMV prevention and treatment strategies is provided, including a detailed description of each of the available CMV antiviral drugs.

Pharmacokinetic drug evaluation of letermovir prophylaxis for cytomegalovirus in hematopoietic stem cell transplantation

INTRODUCTION

Letermovir is a new antiviral approved to prevent cytomegalovirus infection in hematopoietic stem cell transplant recipients. It has a distinct mechanism of action as it acts as a terminase complex inhibitor, and shows some advantages compared to the current treatment options for cytomegalovirus infection. Areas covered: This review focuses on the efficacy, safety, pharmacokinetics, pharmacodynamics, and drug-drug interactions of letermovir. Expert opinion: Letermovir is a new antiviral to prevent cytomegalovirus infection. Unlike the currently used polymerase inhibitors, it has a distinct mechanism of action with better safety, limited resistance, and no cross-resistance. Although a lot of research on pharmacokinetics and drug-drug interactions has already been performed, it might be useful to clarify the effect of letermovir on voriconazole exposure, the drug-drug interaction between caspofungine and letermovir and the effect of statins on letermovir exposure. Also, the lack of an exposure-response relationship should be confirmed in large real-life post-marketing studies in order to be able to lower the intravenous dose of letermovir.

Targeting the terminase: An important step forward in the treatment and prophylaxis of human cytomegalovirus infections

A key step in the replication of human cytomegalovirus (HCMV) in the host cell is the generation and packaging of unit-length genomes into preformed capsids. Enzymes required for this process are so-called terminases, first described for double-stranded DNA bacteriophages. The HCMV terminase consists of the two subunits, the ATPase pUL56 and the nuclease pUL89, and a potential third component pUL51. The terminase subunits are essential for virus replication and are highly conserved throughout the Herpesviridae family. Together with the portal protein pUL104 they form a powerful biological nanomotor. It has been shown for tailed dsDNA bacteriophages that DNA translocation into preformed capsid needs an extraordinary amount of energy. The HCMV terminase subunit pUL56 provides the required ATP hydrolyzing activity. The necessary nuclease activity to cleave the concatemers into unit-length genomes is mediated by the terminase subunit pUL89. Whether this cleavage is mediated by site-specific duplex nicking has not been demonstrated, however, it is required for packaging. Binding to the portal is a prerequisite for DNA translocation. To date, it is a common view that during translocation the terminase moves along some domains of the DNA by a binding and release mechanism. These critical structures have proven to be outstanding targets for drugs to treat HCMV infections because corresponding structures do not exist in mammalian cells. Herein we examine the HCMV terminase as a target for drugs and review several inhibitors discovered by both lead-directed medicinal chemistry and by target-specific design. In addition to producing clinically active compounds the research also has furthered the understanding of the role and function of the terminase itself.

Letermovir for the prevention of cytomegalovirus infection in adult cytomegalovirus-seropositive hematopoietic stem cell transplant recipients

INTRODUCTION

Allogeneic hematopoietic cell transplants (allo-HCT) recipients are at the high-risk of reactivation of cytomegalovirus (CMV), and reactivation is associated with significant morbidity and mortality. Although available anti-CMV therapies may be effective for the prevention of CMV, they are plagued by unacceptable toxicities that prohibit their use in the post-transplant period. Recently studied CMV-active agents, such as maribavir and brincidofovir, failed to reduce the incidence of CMV infection in HCT recipients. Letermovir represents the first agent in the non-nucleoside 3,4 dihydro-quinazoline class of CMV viral terminase complex inhibitors, with activity solely against CMV. The positive results from the recently published Phase III study of letermovir for prevention of CMV infection in CMV-seropositive allo-HCT recipients led to its approval as a prophylactic agent for CMV in multiple countries. Areas covered: In this review, we will evaluate this novel agent with a focus on letermovir mechanism of action, pharmacokinetics and metabolism, clinical efficacy, and safety and toxicities. Expert commentary: With the introduction of letermovir, prevention of CMV infection in allo-HCT recipients may shift considerably, from a predominantly preemptive strategy to one that utilizes this novel therapy for prophylaxis.

Letermovir Prophylaxis for Cytomegalovirus in Hematopoietic-Cell Transplantation

BACKGROUND

Cytomegalovirus (CMV) infection remains a common complication after allogeneic hematopoietic-cell transplantation. Letermovir is an antiviral drug that inhibits the CMV-terminase complex.

METHODS

In this phase 3, double-blind trial, we randomly assigned CMV-seropositive transplant recipients, 18 years of age or older, in a 2:1 ratio to receive letermovir or placebo, administered orally or intravenously, through week 14 after transplantation; randomization was stratified according to trial site and CMV disease risk. Letermovir was administered at a dose of 480 mg per day (or 240 mg per day in patients taking cyclosporine). Patients in whom clinically significant CMV infection (CMV disease or CMV viremia leading to preemptive treatment) developed discontinued the trial regimen and received anti-CMV treatment. The primary end point was the proportion of patients, among patients without detectable CMV DNA at randomization, who had clinically significant CMV infection through week 24 after transplantation. Patients who discontinued the trial or had missing end-point data at week 24 were imputed as having a primary end-point event. Patients were followed through week 48 after transplantation.

RESULTS

From June 2014 to March 2016, a total of 565 patients underwent randomization and received letermovir or placebo beginning a median of 9 days after transplantation. Among 495 patients with undetectable CMV DNA at randomization, fewer patients in the letermovir group than in the placebo group had clinically significant CMV infection or were imputed as having a primary end-point event by week 24 after transplantation (122 of 325 patients [37.5%] vs. 103 of 170 [60.6%], P<0.001). The frequency and severity of adverse events were similar in the two groups overall. Vomiting was reported in 18.5% of the patients who received letermovir and in 13.5% of those who received placebo; edema in 14.5% and 9.4%, respectively; and atrial fibrillation or flutter in 4.6% and 1.0%, respectively. The rates of myelotoxic and nephrotoxic events were similar in the letermovir group and the placebo group. All-cause mortality at week 48 after transplantation was 20.9% among letermovir recipients and 25.5% among placebo recipients.

CONCLUSIONS

Letermovir prophylaxis resulted in a significantly lower risk of clinically significant CMV infection than placebo. Adverse events with letermovir were mainly of low grade. (Funded by Merck; ClinicalTrials.gov number, NCT02137772 ; EudraCT number, 2013-003831-31 .).