Letermovir (formerly known as MK-8828 and AIC-246; trade name: Prevymis) is a new potent anticytomegalovirus drug in clinical development. On 11/8/2017, Letermovir was approved by FDA to prevent infection after bone marrow transplant. Despite modern prevention and treatment strategies, human cytomegalovirus (HCMV) remains a common opportunistic pathogen associated with serious morbidity and mortality in immunocompromised individuals, such as transplant recipients and AIDS patients. All drugs currently licensed for the treatment of HCMV infection target the viral DNA polymerase and are associated with severe toxicity issues and the emergence of drug resistance.

Letermovir (10-100 mg/kg/day, p.o.) leads to a dose-dependent reduction of the HCMV titer in transplanted cells compared to that of the placebo-treated control group using the mouse xenograft model

AIC246 has consistent antiviral efficacy, and there is remarkable selectivity of AIC246 for human cytomegaloviruses. AD169 mutant strains and designated rAIC246-1 and rAIC246-2 are highly resistant to Letermovir (AIC246), with EC50s of 5.6 nM, 1.24 μM, 0.37 μM, respectively. Letermovir inhibits HCMV replication through a specific antiviral mechanism that involves the viral gene product UL56. Letermovir inhibits HCMV replication in cell culture by interfering with the proper cleavage/packaging of HCMV progeny DNA[2]. Letermovir inhibits the current gold standard GCV by more than 400-fold with respect to EC50s (mean, 4.5 nM versus 2 μM) and by more than 2,000-fold with respect to EC90 values (mean, 6.1 nM versus 14.5 μM)[3]. Letermovir in conbination with anti-HCMV drugs causes additive antiviral effects, but there is no interaction between letermovir and anti-HIV drugs.

Briefly, 5×103 AD169-infected NHDF cells/well are seeded into the wells of 30 96-well microtiter plates. The infection is allowed to proceed under the exposure of 50 nM AIC246 (10×EC50) until a CPE developed in one or more of the compound-treated wells (indicative of resistant virus breakthrough). Noninfected and nontreated cells serve as controls on each plate. Mutant virus amplification is accomplwashed after cultures achieved maximum CPE by the passage of cell-free supernatant virus in the presence of 50 nM AIC246. The resultant AIC246-resistant progeny virus mutants are plaque purified three times by limiting dilutions in the presence of AIC246. The stability of resistance is tested by serially passaging plaque-purified viruses without selective pressure (8 to 10 times).

Absorption, Distribution and Excretion
Letermovir has a bioavailability of 94% in healthy subjects when administered without cyclosporin, 35% in HSCT recipients when administered without cyclosporin, and 85% in HSCT recipients when administered with cyclosporin. Letermovir's Tmax is 45 min to 2.25 hours. Time to steady state has been observed to be 9-10 days. Taking Letermovir with food increases Cmax by an average of 129.82% (range of 104.35%-161.50%). No significant effect on AUC has been observed.
Letemovir is taken up by the liver through OATP1B1/3 transporters. 93% is excreted in the feces with 70% as the parent drug. <2% is excreted in the urine.
The mean steady state volume of distribution is 45.5L.
The mean clearance is 11.25 L/h in healthy subjects.

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Metabolism / Metabolites
Letermovir undergoes a minor degree of metabolism through UGT1A1/1A3.

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Biological Half-Life
The mean terminal half-life was observed to be 12 hours following administration of Letemovir 480 mg IV once daily.

Hepatotoxicity
In large preregistration clinical trials, ALT elevations occurred in 18.5% of letermovir vs 21.9% of placebo recipients after hematopoietic cell transplantation, and levels rose to above 5 times ULN in 3.5% vs 1.6%. The ALT elevations were generally transient, mild and asymptomatic. Recurrence of serum ALT elevations on rechallenge has been reported. In prelicensure studies, 0.5% of subjects developed jaundice and liver injury, but in the setting of hematopoietic cell transplantation other more likely causes for liver injury were present in all, and none could be convincingly attributed to letermovir therapy. Since the approval of letermovir and its general availability, there have been no reported cases of clinically apparent liver injury with jaundice associated with its use; however, the total clinical experience with letermovir therapy has been limited.
Likelihood score: E (unlikely cause of clinically apparent liver injury).

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Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
No information is available on the use of letermovir during breastfeeding. Because letermovir is 99% bound to plasma proteins, the amount in milk is likely to be very low. However, an alternate drug may be preferred, especially while nursing a newborn or preterm infant.
◉ Effects in Breastfed Infants
Relevant published information was not found as of the revision date.
◉ Effects on Lactation and Breastmilk
Relevant published information was not found as of the revision date.

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Protein Binding
Letermovir has been observed to be 99% bound to plasma proteins at concentrations of 0.2-50 mg/L _in vitro_.

[1]. Antimicrob Agents Chemother. 2012 Feb;56(2):1135-7.

[2]. J Virol. 2011 Oct;85(20):10884-93.

[3]. Antimicrob Agents Chemother. 2010 Mar;54(3):1290-7.

[4]. Antimicrob Agents Chemother. 2015;59(6):3140-8.

Letermovir recieved approval from the FDA on November 8th, 2017 for use in prophylaxis of cytomegalovirus (CMV) infection in allogeneic hematopoietic stem cell transplant patients. It is the first of a new class of CMV anti-infectives called DNA terminase complex inhibitors. Letermovir has recieved both priority and orphan drug status from the FDA. It is currently marketed under the brand name Prevymis.
Letermovir is a Cytomegalovirus DNA Terminase Complex Inhibitor. The mechanism of action of letermovir is as a DNA Terminase Complex Inhibitor, and Cytochrome P450 3A Inhibitor, and Organic Anion Transporting Polypeptide 1B1 Inhibitor, and Organic Anion Transporting Polypeptide 1B3 Inhibitor, and Cytochrome P450 2C8 Inhibitor, and Cytochrome P450 2C9 Inducer, and Cytochrome P450 2C19 Inducer.
Letermovir is an antiviral agent which targets the DNA terminal transferase complex of the cytomegalovirus (CMV) and which is used to prevent CMV reactivation in immunocompromised patients. Letermovir has been associated with mild-to-moderate serum aminotransferase elevations during therapy but has not been linked to cases of clinically apparent acute liver injury.
Letermovir is an orally bioavailable, non-nucleoside, 3,4-dihydroquinazolinyl acetic acid and inhibitor of the pUL56 subunit of the viral terminase complex of cytomegalovirus (CMV), with potential CMV-specific antiviral activity. Upon oral administration, letermovir binds to the pUL56 subunit of the viral terminase complex of CMV and prevents the cleavage of concatemeric DNA into monomeric genome length DNA. As this agent interferes with viral DNA processing and subsequent viral DNA packaging into procapsids, CMV replication is blocked and CMV infection is prevented.

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Drug Indication
Letermovir is indicated for prophylaxis against cytomegalovirus (CMV) infection and disease in adult recipients of an allogeneic hematopoietic stem cell transplant (HSCT) who are CMV-seropositive. It is also indicated for prophylaxis against CMV disease in adult kidney transplant recipients who are at risk (i.e. donor CMV-seropositive/recipient CMV-seronegative).
FDA Label
Prevymis is indicated for prophylaxis of cytomegalovirus (CMV) reactivation and disease in adult CMV-seropositive recipients [R+] of an allogeneic haematopoietic stem cell transplant (HSCT). Consideration should be given to official guidance on the appropriate use of antiviral agents.
Prevention of cytomegalovirus infection

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Mechanism of Action
CMV relies on a DNA terminase complex consisting of multiple subunits (pUL51, pUL56, and pUL89) for processing of viral DNA. Viral DNA is produced in a single repeating strand which is then cut by the DNA terminase complex into individual viral genomes which can then be packaged into mature viral particles. Letemovir inhibits the activity of this complex to prevent production of mature viral genomes and the production of viable viral particles. The exact nature of Letemovir's binding to this complex is not currently known. Initially, the observation of resistance-causing mutations in pUL56 suggested this subunit was the location of Letemovir binding. However, resistance mutations have now been observed in pUL51, pUL56, and pUL89. It is possible that changes in amino acid sequence in one subunit could result in conformational changes to interacting subunits affecting Letemovir binding or that Letemovir interacts with multiple subunits of the complex but evidence towards either of these distinctions has not yet been seen. pUL89 is known to contain the endonuclease activity of the complex but because all members of the complex are necessary for targeting as well as protection from proteosomal degradation, it is difficult to discern if Letemovir inhibits pUL89's activity directly.

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Pharmacodynamics
Letermovir inhibits the activity of the DNA terminase complex of CMV thereby preventing the cutting of viral DNA into mature length genomes for packaging into viral particles. Letemovir inhibits the DNA terminase complex with an EC50 of 2.1nM.

C29H28F4N4O4

572.56

572.204

C, 60.84; H, 4.93; F, 13.27; N, 9.79; O, 11.18

917389-32-3

45138674

Solid powder

1.4±0.1 g/cm3

706.5±70.0 °C at 760 mmHg

381.1±35.7 °C

0.0±2.4 mmHg at 25°C

1.601

3.47

1

10

7

41

931

1

C([C@H]1C2C=CC=C(C=2N=C(N2CCN(C3C=CC=C(OC)C=3)CC2)N1C1C=C(C(F)(F)F)C=CC=1OC)F)C(=O)O

FWYSMLBETOMXAG-QHCPKHFHSA-N

InChI=1S/C29H28F4N4O4/c1-40-20-6-3-5-19(16-20)35-11-13-36(14-12-35)28-34-27-21(7-4-8-22(27)30)23(17-26(38)39)37(28)24-15-18(29(31,32)33)9-10-25(24)41-2/h3-10,15-16,23H,11-14,17H2,1-2H3,(H,38,39)/t23-/m0/s1

(S)-2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-(4-(3-methoxyphenyl)piperazin-1-yl)-3,4-dihydroquinazolin-4-yl)acetic acid

MK-8828; MK 8828; MK8828; AIC-246; AIC 246; AIC246; Letermovir; Prevymis

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ~100 mg/mL ( ~174.65 mM )
Ethanol : ~100 mg/mL

Solubility in Formulation 1: ≥ 2.5 mg/mL (4.37 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (4.37 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (4.37 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 10% DMSO+40% PEG300+5% Tween-80+45% Saline: ≥ 2.5 mg/mL (4.37 mM)

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 (Please use freshly prepared in vivo formulations for optimal results.)