Product information and disease description Product description Product information Pharmacology

Mechanism of action

33 evidence topics · 23 sources

Mechanism of action: prescribing information

“HOVILPRI is an antiviral drug against HSV-1 and HSV-2 [see Microbiology (12.4)].” (opens the prescribing information at this quote)
“Pritelivir is a HSV helicase-primase inhibitor.” (opens the prescribing information at this quote)
“It is active against both HSV types, HSV-1 and HSV-2, and prevents de novo synthesis of virus deoxyribonucleic acid (DNA) through inhibition of the viral helicase-primase complex.” (opens the prescribing information at this quote)
“Kinetic analysis of the enzyme complex pUL5-pUL52-6xHis revealed the IC50 value of 30 nM.” (opens the prescribing information at this quote)

Antiviral activity in cell culture: prescribing information

“Pritelivir exhibits an apparent 50% effective concentration (EC50 value) between 0.01 μM and 0.07 μM in cell culture infected with HSV-1 or HSV-2 (laboratory strains and clinical isolates), depending on cell type, virus strain/isolate, and method used.” (opens the prescribing information at this quote)
“The median EC50 values of pritelivir were 26 nM (average 26 nM, range 10-45 nM, n=27) and 24 nM (average 30 nM, range 7-70 nM, n=32) against HSV-1 and HSV-2 clinical isolates, respectively.” (opens the prescribing information at this quote)

Resistance selected in cell culture: prescribing information

“Pritelivir-resistant HSV-1 and HSV-2 strains were isolated in cell culture with mutations in the viral helicase (UL5) and primase (UL52) genes.” (opens the prescribing information at this quote)
“In cell culture the following resistance-associated amino acid substitutions were observed (Table 5).” (opens the prescribing information at this quote)

Pritelivir resistance-associated amino acid substitutions in cell culture: prescribing information

Virus	Protein	Substitutions
HSV-1	“pUL5 helicase”	“N342K, G352R, G352C, G352V, G352N, M355T, K356N, K356T, K356Q, K356R, K356E”
HSV-1	“pUL52 primase”	“A899T”
HSV-2	“pUL5 helicase”	“N341K, G351R, M354T, K355N, K355T, K355R”
HSV-2	“pUL52 primase”	“A906T”

Resistance in clinical trials: prescribing information

“In the PRIOH-1 Phase 3 trial (NCT 03073967) in immunocompromised participants, viral sequence analysis was performed on samples obtained from pritelivir-treated participants who did not heal on pritelivir treatment and for whom on-treatment samples were available for analysis.” (opens the prescribing information at this quote)
“Paired baseline and on-treatment/end-of-treatment sequences were obtained for 8.3% (4/48) of pritelivir-treated participants who experienced treatment failure (lesions not healed by Day 28).” (opens the prescribing information at this quote)
“The pUL5 K356N (>1,000-fold reduction in susceptibility in cell culture) substitution was detected in 1 participant infected with HSV-1.” (opens the prescribing information at this quote)
“The pUL5 K355R (50-fold reduction, 2 participants) and pUL5 N341K, pUL5 G351R (distinct viral subpopulations, 33-fold reduction, 1 participant) substitutions were detected in participants infected with HSV-2.” (opens the prescribing information at this quote)
“In the PRIOH-1 Phase 2 trial (NCT 03073967), the pUL5 K355T (12-fold reduction, 1 participant) substitution was detected in a participant infected with HSV-2.” (opens the prescribing information at this quote)
“In another study, the HSV-1 pUL5 N342K (38-fold reduction) + G352C (fold reduction not available) + K356R (fold reduction not available) + pUL52 A899T (100-fold reduction) substitutions were detected in one participant one week after pritelivir discontinuation.” (opens the prescribing information at this quote)

Cross-resistance: prescribing information

“Cross resistance is not likely with acyclovir, penciclovir, or foscarnet.” (opens the prescribing information at this quote)
“Pritelivir retains activity against nucleoside analogue-resistant (e.g., acyclovir) and foscarnet-resistant HSV strains with TK or DNA polymerase substitutions.” (opens the prescribing information at this quote)
“Substitutions leading to pritelivir resistance do not affect susceptibility to nucleoside analogs and foscarnet.” (opens the prescribing information at this quote)

Mechanism as described in the approval announcement

“HOVILPRI is a helicase-primase inhibitor with a mechanism of action distinct from nucleoside analogue therapies.” (opens the source at this quote in a new tab)
“HOVILPRI is active against both HSV-1 and HSV-2, including strains resistant to nucleoside analogs and foscarnet.” (opens the source at this quote in a new tab)

Helicase-primase complex: subunits and position in viral DNA replication

“The heterotrimeric helicase–primase complex is formed by UL5 (the helicase subunit, which unwinds and separates the duplex DNA to form the replication fork, exposing the two individual DNA strands), UL52 (the primase, which synthesizes short RNA primers as substrates for DNA polymerase), and UL8 (noncatalytic subunit, essential for coordination between UL5 and UL52).” (opens the source at this quote in a new tab)
“Dedicated studies revealed that pritelivir, while allowing cell infection and initiation of expression of viral immediate early genes, was associated with reduction, suppression, or loss of initiation of early and late gene expression.” (opens the source at this quote in a new tab)
“showing that operation of the helicase–primase complex precedes that of the DNA polymerase, the target of nucleoside analogue drugs like acyclovir.” (opens the source at this quote in a new tab)
“Resistance mutation studies (see section 2.2.4 for more detail) suggest that pritelivir interacts with the helicase–primase complex at its DNA-binding site, binding simultaneously to the helicase and primase components, thereby stabilizing the interaction between the HSV helicase–primase complex and nucleic acid” (opens the source at this quote in a new tab)

“The HP complex acts at the viral replication fork, upstream of the viral DNA polymerase, by unwinding double-stranded DNA and depositing RNA primers on the lagging strand” (opens the source at this quote in a new tab)
“Given its critical role in viral DNA replication and the absence of an equivalent enzymatic complex in host cells, the HP complex has emerged as a promising antiviral target” (opens the source at this quote in a new tab)

“Pritelivir (also known as BAY 57–1293 and AIC316) belongs to a new class of antiviral compounds, the helicase-primase inhibitors (HPIs), that prevent the de novo synthesis of virus DNA through inhibition of the helicase-primase complex” (opens the source at this quote in a new tab)
“Functionally, both UL5 and UL52, together with the accessory protein UL8, form the helicase-primase enzyme complex, the molecular target of pritelivir” (opens the source at this quote in a new tab)

Activity without activation by viral thymidine kinase

“Unlike nucleoside analogues, which are currently the mainstay of therapy for herpes simplex virus (HSV) infections, pritelivir does not require activation by viral thymidine kinase within an HSV-infected cell.” (opens the source at this quote in a new tab)

“In contrast, there is no delay in the onset of action in the case of the helicase–primase inhibitors, which attack viral replication earlier than acyclovir-type inhibitors and do not need an activation step.” (opens the source at this quote in a new tab)
“Due to its different mode of action, the drug does not need to become activated by viral or cellular enzymes and is active against nucleoside analogue-resistant virus.” (opens the source at this quote in a new tab)

“Unlike the nucleoside analogues, pritelivir does not require activation by phosphorylation, and it is active in uninfected cells.” (opens the source at this quote in a new tab)

“In contrast to existing drugs, pritelivir does not require activation by viral thymidine kinase, thus can prevent infection of uninfected cells” (opens the source at this quote in a new tab)

“Helicase-primase (UL52/UL5) (HP) inhibitors amenamevir and pritelivir reportedly have less adverse effects.” (opens the source at this quote in a new tab)
“They do not depend on activation by enzymes like TK” (opens the source at this quote in a new tab)

First report of the helicase-primase inhibitor class

“Here we report new inhibitors of the HSV helicase-primase with potent in vitro anti-herpes activity, a novel mechanism of action, a low resistance rate and superior efficacy against HSV in animal models.” (opens the source at this quote in a new tab)
“Thus, this class of drugs has significant potential for the treatment of HSV disease in humans, including those resistant to current medications.” (opens the source at this quote in a new tab)

Enzyme inhibition and cell culture potency in the first nonclinical report

“It inhibited the replication of HSV type 1 (HSV-1) and HSV-2 in Vero cells with a 50% inhibitory concentration (IC50) of 20 nM and a selectivity index of 2,500 and had about equal potencies against different strains and clinical isolates, while under the same assay conditions, acyclovir exhibited an IC50 of 1 μM and a selectivity index of 250.” (opens the source at this quote in a new tab)
“BAY 57-1293 targets the viral primase-helicase complex and inhibits its ATPase activity in a dose-dependent manner with an IC50 of 30 nM.” (opens the source at this quote in a new tab)
“Resistant viral mutants exhibited amino acid substitutions in viral UL5 and/or UL52, which code for components of the viral primase-helicase complex.” (opens the source at this quote in a new tab)
“Accordingly, BAY 57-1293 also is active against acyclovir-resistant mutant strains which carry mutations in the tk or DNA pol genes.” (opens the source at this quote in a new tab)

Selectivity for the viral helicase over human helicases

“Neither of these enzymes was inhibited by pritelivir, confirming selectivity between human and HSV helicases which is also in line with the lack of cytotoxicity on a panel of different cell types (liver, heart muscle, kidney, macrophages, monocytes, T lymphocytes, fibroblasts, and neuronal cells)” (opens the source at this quote in a new tab)
“Thus, it was a predictable outcome that pritelivir showed high specificity and failed to inhibit helicases of human origin in vitro.” (opens the source at this quote in a new tab)

Antiviral spectrum limited to HSV-1 and HSV-2

“Indeed, AMNV exhibits pan-α-herpesvirus coverage, whereas PTV antiviral activity is restricted to HSV-1 and HSV-2.” (opens the source at this quote in a new tab)

“Pritelivir has activity against both HSV-1 and HSV-2, including acyclovir-resistant HSV strains, but it does not have any activity against other herpesviruses (e.g., varicella-zoster virus [VZV], Epstein-Barr virus [EBV], cytomegalovirus [CMV], and human herpesvirus 6 [HHV-6])” (opens the source at this quote in a new tab)

“In contrast, the lack of activity of pritelivir against VZV may reflect weakened interactions elsewhere within the UL5–UL52 interface due to sequence variation in the expected drug binding site.” (opens the source at this quote in a new tab)
“UL5 residue H349 is replaced by an aspartate, and UL52 residues A899, H906, and F907, are replaced by valine, phenylalanine, and serine, respectively” (opens the source at this quote in a new tab)
“Thus, the UL52 F360R substitution that naturally occurs in the HCMV helicase homolog UL70 may explain at least in part why this β-herpesvirus is not susceptible to pritelivir.” (opens the source at this quote in a new tab)

Structural basis: binding site at the UL5 and UL52 interface

“Here, we report cryo–electron microscopy structures of HSV-1 HP bound to a forked DNA template alone and in complex with pritelivir or amenamevir.” (opens the source at this quote in a new tab)
“The pritelivir fills a partially accessible groove at the UL5-UL52 interface (Fig. 5B) and is positioned nearly 12 Å apart from the ATP-binding site of UL5.” (opens the source at this quote in a new tab)
“Pritelivir forms hydrophobic interactions with the side chains of UL5 amino acid residues N98, N342, N343, C346, M355, K356, E359, and Y360 and the α-carbon of G352 and with the side chains of UL52 amino acid residues Y356, L357, F360, A899, N902, A903, H906, and F907 (Fig. 5D).” (opens the source at this quote in a new tab)
“In addition, five potential H-bonds were observed between pritelivir and the HP complex.” (opens the source at this quote in a new tab)
“However, in each inhibitor-bound HP complex, either amenamevir or pritelivir occupies this space (Fig. 6, C and D), preventing the relative movement of domains 1A and 2A and, thus, inhibiting UL5 helicase activity.” (opens the source at this quote in a new tab)

“Pritelivir is in an extended conformation when it binds the H/P complex (Figures 3A and S1F).” (opens the source at this quote in a new tab)
“The 2-pyridyl moiety inserts into a pocket between the UL5 1A and 2A domains, while the aminosulfonyl group occupies a depression formed by α-helices from the UL52 NTD and middle domains.” (opens the source at this quote in a new tab)
“Pritelivir makes hydrophobic contacts with UL5 residues N98, M355, and Y882 and with UL52 residues Y356, F360, A899, H906, and F907.” (opens the source at this quote in a new tab)
“Pritelivir makes polar contacts with UL5 residues N343, K356, and Y882 and with UL52 residue N902 (Figure 3B).” (opens the source at this quote in a new tab)

Structural basis: allosteric inhibition that does not compete with DNA or ATP

“Here we present the cryogenic electron microscopy structure of the HSV-1 HP apo-complex (3.8 Å), along with structures bound to pritelivir (3.2 Å) and amenamevir (3.2 Å)” (opens the source at this quote in a new tab)
“The purified complex was functional in unwinding double-stranded DNA, and could be inhibited by PTV and AMNV, with 50% inhibitory concentration (IC50) values of 11.1 nM and 3.5 nM, respectively (Extended Data Fig. 2d–f).” (opens the source at this quote in a new tab)
“The density maps revealed that despite their chemical divergence, PTV and AMNV bind to the same pocket within the complex.” (opens the source at this quote in a new tab)
“The dual interactions of the UL5 motif IV loop suggest a non-competitive allosteric inhibition mechanism” (opens the source at this quote in a new tab)
“Indeed, PTV disrupted the ATP-driven DNA unwinding activity of HSV-1 HP without competing with DNA or ATP (Extended Data Fig. 7).” (opens the source at this quote in a new tab)
“Both function as molecular clogs by binding to the same allosteric site, obstructing the movement of the UL5 four motor domains that translocate and unwind double-stranded DNA, thereby inhibiting helicase activity” (opens the source at this quote in a new tab)

Structural basis: helicase locked in an open, inactive conformation

“Here, we report cryo-EM structures of the herpes simplex virus 1 H/P complex bound to HPIs, showing that these lock the helicase-primase complex in an inactive state.” (opens the source at this quote in a new tab)
“Single-molecule assays reveal that HPIs cause helicase-primase complexes to pause on DNA.” (opens the source at this quote in a new tab)
“In the pritelivir-bound structure, α13 and α29 are shifted away from their ATP-bound positions by 2.8 Å and 3.6 Å, respectively (Figure 4A).” (opens the source at this quote in a new tab)
“The structures thus suggest that HPIs allosterically inhibit helicase activity by locking UL5 in an open conformation and preventing ATP-induced closure of the RecA-like domains required for translocation on DNA.” (opens the source at this quote in a new tab)

“Here, cryo-EM structures of the HHV1 (α-subfamily) HPC bound to single-stranded DNA and two clinical inhibitors, amenamevir and pritelivir, are reported.” (opens the source at this quote in a new tab)
“The HPC features flexible helicase and primase modules, with both inhibitors binding a shared allosteric pocket in the helicase module.” (opens the source at this quote in a new tab)
“Structural, biochemical, and molecular dynamics analyses indicate that these inhibitors lock the helicase in an open, inactive conformation.” (opens the source at this quote in a new tab)
“Combined molecular dynamics and fragment molecular orbital analyses explain the α-subfamily selectivity and distinct antiviral spectra of these drugs.” (opens the source at this quote in a new tab)

Concentration-dependent slowing and pausing of DNA unwinding by the purified enzyme

“In the presence of the wild-type (WT) HSV-1 H/P complex alone, we observed robust and continuous DNA unwinding, with no detectable pausing, at an average rate of 33 nt s−1 (n = 41).” (opens the source at this quote in a new tab)
“At 100 nM pritelivir, the average unwinding rate decreased to 25 nt s−1 (n = 38), with a corresponding pause fraction of 17.9% (n = 11).” (opens the source at this quote in a new tab)
“At 200 nM, the rate further declined to 17 nt s−1 (n = 37), and the pause fraction increased to 25.6% (n = 15).” (opens the source at this quote in a new tab)
“At the highest concentration tested, 500 nM, unwinding activity was severely impaired, with an average rate of only 9.5 nt s−1 (n = 51) and a pause fraction of 51.5% (n = 16).” (opens the source at this quote in a new tab)
“These results indicate that pritelivir slows the helicase translocation rate and promotes pausing in a dose-dependent manner, consistent with stabilization of an inactive conformation of the H/P complex.” (opens the source at this quote in a new tab)

Inhibition of ATP hydrolysis, primer synthesis, and replication fork activity in vitro

“Consistent with this notion, ATPase assays performed in the presence of HPIs and ssDNA showed that pritelivir and amenamevir reduce HSV-1 H/P ATP hydrolysis in a dose-dependent manner (Figure S5E).” (opens the source at this quote in a new tab)
“Pritelivir and amenamevir suppressed primer synthesis in a dose-dependent manner (Figures S3F and S3G).” (opens the source at this quote in a new tab)
“After adding these inhibitors, the amounts of long DNA products were reduced in a dose-dependent manner, indicating inhibition of the HSV-1 replication fork complex (Figures 5E and 5F).” (opens the source at this quote in a new tab)
“Importantly, the synthesis of the 7 kb product, which is primarily generated by DNA polymerase holoenzyme in the absence of helicase activity, remained unaffected.” (opens the source at this quote in a new tab)

Baseline susceptibility of clinical isolates and activity against acyclovir-resistant strains

“Fifty-nine US isolates of HSV-1 and HSV-2 obtained between 1998 and 2004 were tested for sensitivity to the helicase-primase inhibitor, pritelivir (AIC316, BAY 57-1293) by plaque-reduction assay.” (opens the source at this quote in a new tab)
“All isolates, which were collected prior to any clinical use of primase-helicase inhibitors, were sensitive and showed mean EC50 values of 0.026 and 0.029μM for HSV-1 and HSV-2, respectively.” (opens the source at this quote in a new tab)
“Furthermore, several laboratory-selected acyclovir-resistant HSV mutants were also sensitive to pritelivir.” (opens the source at this quote in a new tab)
“The data also validate pritelivir as an appropriate therapy for nucleoside-resistant HSV infections.” (opens the source at this quote in a new tab)

“These changes, however, are not relevant to the action of helicase–primase inhibitors.” (opens the source at this quote in a new tab)
“It is also important to note that resistance to foscarnet, which plays a role as emergency medication in particular in immunocompromised patients with acyclovir-resistant HSV strains, can also be overcome by treatment with pritelivir” (opens the source at this quote in a new tab)
“Since pritelivir-resistance and acyclovir-resistance mediating mutations are located in different genes in different genomic loci (cf. section 2.1.4), the anti-HSV potency of pritelivir is independent of the resistance status to acyclovir (Figure 8).” (opens the source at this quote in a new tab)

“Pritelivir is active against HSV-1 and HSV-2 isolates including nucleos(t)ide analog- and foscarnet-resistant isolates in vitro” (opens the source at this quote in a new tab)

Location of resistance mutations in the UL5 helicase and UL52 primase genes

“Such resistances are mostly based on single amino acid exchanges.” (opens the source at this quote in a new tab)
“To date, all mutations in the HSV genome conferring resistance to pritelivir (and other helicase–primase inhibitors) are located in the UL5 gene that codes for the helicase and/or at a single locus in the UL52 gene coding for the primase gene (A899 for HSV-1, A905 for HSV-2).” (opens the source at this quote in a new tab)
“No virus isolate or strain has been identified so far, for which resistance to pritelivir was mediated by an amino acid change in the noncatalytic subunit, UL8.” (opens the source at this quote in a new tab)

“In preclinical work, resistance-mediating mutations were identified in the HSV-2 genome at 3 loci in the UL5 gene and 1 locus in UL52.” (opens the source at this quote in a new tab)
“All resistance-mediating mutations to pritelivir identified so far in vitro are located either at a single amino acid position in the viral UL52 primase (amino acid 906) or within/downstream of the fourth functional motif of the viral UL5 helicase (the conserved helicase motif; amino acids 341–355; Figure 1)” (opens the source at this quote in a new tab)
“For comparison, the known HPI resistance–mediating mutations C1023A (N341K), G1051C (G351R), and G1065T (K355N) in UL5 and G2716A (A906T) in UL52 are included in red.” (opens the source at this quote in a new tab)

Resistance substitutions mapped onto the inhibitor binding pocket

“It is not unexpected that all the residues associated with the observed pritelivir-resistant mutations (N342K, G352C, G352R, M355T, K356N, K356T, and K356Q in UL5 and A899T in UL52) are interacting with it.” (opens the source at this quote in a new tab)
“Amenamevir and pritelivir share some resistant mutations in UL5 (G352V and M355I), while the positions of the amino acids with the amenamevir-resistant mutations in UL52 (S364G and R367H) are different” (opens the source at this quote in a new tab)

“These include M355I/T and K356N/T/Q in the UL5 2A domain, F360C/V in the UL52 NTD, and A899T and N902T in the UL52 middle domain.” (opens the source at this quote in a new tab)
“Additionally, UL5 2A domain substitutions N342K and G352C/V/R, although they do not directly affect HPI contact residues, are adjacent to the HPI binding site and may cause steric hindrance or reorganization of pocket residues, thereby impairing inhibitor binding (Figure S5C).” (opens the source at this quote in a new tab)
“Consistent with drug resistance, H/P complexes containing either the UL5 K356N or UL52 F360R mutant subunits had robust helicase activity in the presence of 500 nM pritelivir” (opens the source at this quote in a new tab)
“When tested in the absence of pritelivir, both mutants had unwinding kinetics comparable to the WT H/P complexes, indicating that these substitutions do not intrinsically impair helicase function.” (opens the source at this quote in a new tab)

Interaction with both the helicase and the primase inferred from a UL52 mutation

“A single mutation (UL52: A899T) confers 43-fold resistance to BAY 57-1293, but does not confer any resistance to BILS 22 BS.” (opens the source at this quote in a new tab)
“A double mutant (UL52: A899T and UL5: K356T) is 2500-fold resistant to BAY 57-1293, which is more than 17 times the sum of fold-resistance due to the individual mutations, UL52: A899T (43-fold) and UL5: K356T (100-fold).” (opens the source at this quote in a new tab)
“Furthermore, our observations suggest that BAY 57-1293 interacts simultaneously with UL5 and UL52.” (opens the source at this quote in a new tab)

Reduction in susceptibility by substitution: recombinant virus and dose-escalation studies

“Substitutions such as HSV-1 UL5 K356N, HSV-2 UL5 K355N and VZV K350N (equivalent positions) reduced sensitivity to PTV and/or AMNV by 200 to >2,000-fold” (opens the source at this quote in a new tab)
“Interestingly, an N342K substitution reduces the potency of PTV (≈40-fold)” (opens the source at this quote in a new tab)
“In the HSV-1 dose-escalation study, emergence of the UL5 K356N variant was observed (Extended Data Fig. 5a).” (opens the source at this quote in a new tab)
“This substitution conferred a substantial loss of sensitivity to PTV (210-fold) when introduced into a recombinant HSV-2 virus (UL5 K355N; Extended Data Fig. 5b and Extended Data Table 2).” (opens the source at this quote in a new tab)
“In the HSV-2 dose-escalation studies, a UL5 K355R variant was detected, either alone or paired with two additional substitutions, UL5 L805I and UL52 A906V (Extended Data Fig. 5a).” (opens the source at this quote in a new tab)
“By contrast, UL52 A906 (equivalent to HSV-1 A899) stabilizes the PTV sulfonamide head (Fig. 2b), and an A-to-V substitution was associated with a 17-fold decrease in sensitivity to PTV (Fig. 2f).” (opens the source at this quote in a new tab)
“Strikingly, a recombinant HSV-2 virus bearing all three substitutions (UL5 K355R, L805I and UL52 A906V) was virtually insensitive to PTV (EC50 change >1,300-fold) (Extended Data Fig. 5b and Extended Data Table 2).” (opens the source at this quote in a new tab)
“Our study emphasizes that the acetamide carboxyl oxygen present in all known HPIs is crucial for interacting with HSV-2 UL5 K355, rendering them susceptible to the emergence of resistant variants at this position.” (opens the source at this quote in a new tab)

Reduction in susceptibility by substitution: HSV-1 clones selected under drug pressure

“Both the K356N and K356Q mutations in the helicase were associated with high-level (>30-fold) PTV and AMV resistance.” (opens the source at this quote in a new tab)
“Resistance to PTV and AMV was also observed in clones bearing the helicase mutations G352C (29- and 13-fold), M355I (6.8- and 7.0-fold), and E400A (4.5- and 2.1-fold).” (opens the source at this quote in a new tab)
“The UL5 S866R mutant clone was resistant to PTV (6.6-fold) but not to AMV (1.8-fold), whereas two clones harboring the S364G mutation in the primase gene revealed low-level AMV resistance (2.0- and 2.2-fold) but remained susceptible to PTV (1.6- and 1.5-fold).” (opens the source at this quote in a new tab)

Selection of resistance in cell culture under pritelivir alone and combined with acyclovir or foscarnet

“In this study, we assessed whether combining antivirals with different targets affects drug resistance emergence by passaging wild-type HSV-1 under increasing concentrations of acyclovir (ACV), foscarnet (phosphonoformic acid, PFA), or the helicase–primase inhibitor pritelivir (PTV), individually or in combination (ACV + PTV or PFA + PTV).” (opens the source at this quote in a new tab)
“Deep sequencing and subsequent phenotyping showed the rapid acquisition of resistance mutations under monotherapy pressure, whereas combination therapy resulted in either no mutations or mutations conferring ACV and/or PFA resistance.” (opens the source at this quote in a new tab)
“Notably, mutations associated with PTV resistance were not detected after five passages under combination pressure.” (opens the source at this quote in a new tab)
“Strains resistant to both ACV and PTV were eventually obtained upon further passaging under ACV + PTV pressure initiated from lower drug concentrations.” (opens the source at this quote in a new tab)
“PFA + PTV dual treatment induced PFA resistance mutations in the DP, but PTV resistance mutations were not acquired, even after 15 passages.” (opens the source at this quote in a new tab)
“Three mutations were detected at frequencies >10% in the helicase (K356N and K356Q) and primase (S364G) genes of the PTVL viral culture at Passage 5, while in the case of PTVH, the K356N (91.8%) mutation was the only mutation detected at a frequency >10%.” (opens the source at this quote in a new tab)

Replication capacity and pathogenicity of pritelivir-resistant virus

“The K356N mutation confers the highest level of PTV resistance of all helicase mutations described to date, is frequently selected under antiviral pressure in vitro, and shows near wild-type growth properties” (opens the source at this quote in a new tab)
“Most resistance mutations in the helicase, including the G352C mutation, show reduced growth in cell culture and reduced pathogenicity in mice” (opens the source at this quote in a new tab)

“As shown in Fig. 8, wild-type HSV-1F and the BAY 57-1293-resistant mutant exhibited almost equal pathogenicities, while the acyclovir-resistant mutant was nonpathogenic, as judged by animal survival after infection.” (opens the source at this quote in a new tab)
“Other BAY 57-1293-resistant mutants might behave differently.” (opens the source at this quote in a new tab)

Frequency of pre-existing resistant variants in laboratory and clinical isolates

“In vitro, the frequency of pritelivir-resistant HSV mutants among plaque-purified virus was determined to be 0.5 to 4.5 × 10–6.” (opens the source at this quote in a new tab)
“This is at least 1 order of magnitude lower than that for acyclovir, for which a resistance frequency of 10–3–10–4 was reported.” (opens the source at this quote in a new tab)

“Resistant mutants with point mutations in the helicase (UL5) were reported to be present in laboratory isolates at a low frequency of approximately 10(-6).” (opens the source at this quote in a new tab)
“Therefore, we screened 10 recent clinical isolates of HSV-1 for BAY 57-1293-resistant virions.” (opens the source at this quote in a new tab)
“One isolate contained highly resistant variants at 10(-4) and another at 10(-5).” (opens the source at this quote in a new tab)
“Both variants contained a previously reported BAY 57-1293 resistance mutation (K356N) in UL5 and were >5000-fold resistant.” (opens the source at this quote in a new tab)
“These results have important implications for HPI drug-resistance monitoring during subsequent clinical trials.” (opens the source at this quote in a new tab)

Natural polymorphism of UL5 and UL52 among clinical isolates

“In this study, we describe the low natural polymorphism (interstrain identity >99.1% at both nucleotide and amino acid levels) of HSV HP complex subunits pUL5 and pUL52 among 64 HSV (32 HSV-1 and 32 HSV-2) clinical isolates, and we show that the HSV resistance profile to the first-line antiviral drug acyclovir (ACV) does not impact on the natural polymorphism of HSV HP complex.” (opens the source at this quote in a new tab)
“Genotypic tools and polymorphism data concerning HSV HP complex provided herein will be useful to detect drug resistance mutations in a relevant time frame when HP inhibitors (HPIs), i.e., amenamevir and pritelivir, will be available in medical practice.” (opens the source at this quote in a new tab)

“We characterized mutations from 32 cultivated HSV-2 isolates previously found to be susceptible to pritelivir in vitro and identified several novel mutations that most likely reflect preexisting variation in circulating HSV-2.” (opens the source at this quote in a new tab)

Resistance sequencing during 28 days of daily therapy in immunocompetent adults

“We sequenced resistance regions from 87 participants' samples, the UL5 gene in 73 samples from 44 participants, and the UL52 gene in 71 samples from 43 participants.” (opens the source at this quote in a new tab)
“We found no evidence that pritelivir induced known resistance-mediating mutations or for amino acid variation at other loci.” (opens the source at this quote in a new tab)
“Of these, 823 swab specimens (median time of collection after treatment initiation, 22 days; range, 1–44 days), collected from 87 subjects (20 in the placebo group and 67 in one of the 4 dosage groups; Supplementary Table 4), contained an HSV-2 quantity of ≥5000 copies/mL and were subjected to resistance-region sequencing.” (opens the source at this quote in a new tab)
“Of the 823 samples, 688 (84%), from 80 patients, underwent successful sequencing of the UL5 gene, and 775 (94%), from 83 patients, underwent successful sequencing of the UL52 gene (Figure 2).” (opens the source at this quote in a new tab)
“As this isolate was susceptible to pritelivir, the H334R mutation was not regarded to confer resistance (Figure 3).” (opens the source at this quote in a new tab)
“This study demonstrates evidence of retained susceptibility of HSV-2 to pritelivir in immunocompetent persons following daily therapy for up to 28 days.” (opens the source at this quote in a new tab)

Resistance sequencing in the crossover trial against valacyclovir

“Fifty-five swabs collected during pritelivir administration contained HSV DNA of more than 5000 copies/mL.” (opens the source at this quote in a new tab)
“Fifty-four were sequenced for UL5 and 55 were sequenced for UL52.” (opens the source at this quote in a new tab)

Emergent resistance in the phase 2 parts of PRIOH-1

“Resistance to trial medication (genotypic/phenotypic) was investigated in participants whose lesions did not heal within 28 days.” (opens the source at this quote in a new tab)
“Resistance to foscarnet was observed in 1 of 7 foscarnet-treated participants (E798K substitution in the HSV-2 pUL30 polymerase), and resistance to pritelivir in 1 of 15 pritelivir-treated participants (K355T substitution in the pUL5 helicase).” (opens the source at this quote in a new tab)
“No instances of resistance to pritelivir were identified in Part B.” (opens the source at this quote in a new tab)
“The HSV-2 UL5 K355T substitution, which maps to a site linked to reduced pritelivir susceptibility, emerged during treatment in this study.” (opens the source at this quote in a new tab)

Emergent resistance in the phase 3 part of PRIOH-1: congress presentation

“Resistance investigated in treatment failures with detectable HSV DNA at post-treatment visit” (opens the source at this quote in a new tab)
“UL5 helicase and UL52 primase (pritelivir), UL30 polymerase (foscarnet and cidofovir)” (opens the source at this quote in a new tab)
“One person with pritelivir resistance in an HCT patient with HSV-2” (opens the source at this quote in a new tab)
“Only 1 participant on pritelivir with failure (lesions improving but not completely healed) with detectable HSV DNA at post-treatment visit (after 42 days of treatment)” (opens the source at this quote in a new tab)
“Two pritelivir resistance-associated substitutions (UL5 N341K and G351R) detected” (opens the source at this quote in a new tab)
“Phenotypic test result: EC50 of 0.126 μM (<5x EC50 of the control of 0.129 μM)” (opens the source at this quote in a new tab)
“Both substitutions were not present at baseline and emerged on treatment day 36” (opens the source at this quote in a new tab)

Helicase-primase resistance mutations in a published resistance dataset

“AMNV and PTV bind to the viral helicase-primase complex.” (opens the source at this quote in a new tab)
“This inhibits DNA unwinding and therefore inhibits replication.” (opens the source at this quote in a new tab)
“We identified 221 novel DRMs (excluding novel polymorphisms), comprising 99 mutations in the HSV-1 TK gene, 66 in the HSV-1 POL gene, 12 in the HSV-1 HP gene, 19 in the HSV-2 TK gene, 10 in the HSV-2 POL, and 15 in the HSV-2 HP (Table S3).” (opens the source at this quote in a new tab)
“Both have inherent limitations: genotypic DST is limited by outdated datasets lacking information on new helicase-primase inhibitors and corresponding phenotypic data as well as sparse clinical correlations.” (opens the source at this quote in a new tab)