Treatment-emergent Resistance Research Articles

High efficacy of bictegravir/emtricitabine/tenofovir alafenamide (B/F/TAF) in Black adults in the United States, including those with pre-existing HIV resistance and suboptimal adherence.

BRAAVE (NCT03631732), a Phase 3b, multicenter, open-label US study, demonstrated the efficacy of switching to bictegravir/emtricitabine/tenofovir alafenamide (B/F/TAF) among Black individuals with suppressed HIV through 48 weeks. Here, 72-week resistance, adherence, and virologic outcomes are presented. Enrollment criteria permitted nonnucleoside reverse transcriptase inhibitor (NNRTI)-resistance (R), protease inhibitor (PI)-R, and certain nucleos(t)ide reverse transcriptase inhibitor (NRTI)-R (M184V/I allowed; ≥3 thymidine analog mutations [TAMs] excluded); but excluded primary integrase strand transfer inhibitor (INSTI)-R. Pre-existing resistance was determined using historical genotypes and retrospective baseline proviral DNA genotyping. Adherence, virologic outcomes, and viral blips were assessed. Of 489 participants receiving B/F/TAF with ≥1 post-switch HIV-1 RNA measurement: pre-existing NRTI-R (15% of participants), M184V/I (11%), ≥1 TAMs (8%), NNRTI-R (22%), and PI-R (13%) were observed; pre-existing INSTI-R substitutions (2%) were detected post-randomization; mean viral blip frequency was 0.9% across all timepoints (unassociated with virologic failure); 24% of participants had <95% adherence (98% of whom had HIV-1 RNA<50 copies/mL at last visit); none had treatment-emergent study-drug resistance. Overall, 99% of participants, including all with baseline NRTI-R/INSTI-R, had HIV-1 RNA<50 copies/mL at the last visit, demonstrating that B/F/TAF maintained virologic suppression through 72 weeks regardless of pre-existing resistance, viral blips, and suboptimal adherence.

Efficacy and safety of ZX-7101A, an inhibitor of influenza cap-dependent endonuclease, in adults with uncomplicated influenza: a randomized, double-blind, placebo-controlled phase 2/3 trial

ObjectivesTo evaluate the efficacy and safety of ZX-7101A: an inhibitor of influenza viral cap-dependent endonuclease, in adults with uncomplicated influenza and explore treatment-emergent resistance. MethodsWe conducted a randomized, double-blind, placebo-controlled, adaptive-design phase 2 and phase 3 studies (ZX-7101A-202) in adults with uncomplicated influenza. Eligible patients were randomized 1:1:1 to receive a single dose of 40 or 80 mg ZX-7101A or placebo, stratified by body weight and baseline composite symptom score. The primary efficacy endpoint was time to alleviation of influenza symptoms (TTAS) in intention-to-treat infected population. ResultsThe phase 2 trial suggested a significantly shorter TTAS for ZX-7101A compared with placebo: the median TTAS of 40 or 80 mg ZX-7101A was 34.7 hours (95% CI, 22.8–43.4; p 0.005) and 45.8 hours (95% CI, 32.0–66.3; p 0.020), compared with 63.6 hours (95% CI, 43.9–93.4) in the placebo group. In the phase 3 trial, the TTAS of both ZX-7101A dose groups was significantly shortened relative to the placebo: the median TTAS was shortened to 48.4 hours (95% CI, 40.5–55.6) for 40 mg and 39.4 hours (95% CI, 35.8–49.3) for 80 mg, compared with 62.9 hours (95% CI, 56.4–69.3) for placebo (p 0.003 and p < 0.001, respectively). In the safety population, ZX-7101A treatment was associated with fewer adverse events, with 41.8% (100/239) in the 40 mg group, 44.2% (106/240) in the 80 mg group, and 53.8% (129/240) in the placebo group. The majority of adverse events were mild or moderate. Emergence of resistance to ZX-7101A through I38T amino acid substitution was detected in 5/122 (4.1%) patients. Discussion: ZX-7101A was an effective treatment for influenza with a single dose of either 40 mg or 80 mg, with more rapid alleviation of influenza symptoms vs. placebo. No safety concerns were identified with single dose treatment of ZX-7101A.

Emerging SARS-CoV-2 Resistance After Antiviral Treatment.

Previous studies have identified mutations in SARS-CoV-2 strains that confer resistance to nirmatrelvir, yet how often this resistance arises and its association with posttreatment virologic rebound is not well understood. To examine the prevalence of emergent antiviral resistance after nirmatrelvir treatment and its association with virologic rebound. This cohort study enrolled outpatient adults with acute COVID-19 infection from May 2021 to October 2023. Participants were divided into those who received antiviral therapy and those who did not. The study was conducted at a multicenter health care system in Boston, Massachusetts. Treatment regimen, including none, nirmatrelvir, and remdesivir. The primary outcome was emergent SARS-CoV-2 antiviral resistance, defined as the detection of antiviral resistance mutations, which were not present at baseline, were previously associated with decreased antiviral efficacy, and emerged during or after completion of a participant's treatment. Next-generation sequencing was used to detect low frequency mutations down to 1% of the total viral population. Overall, 156 participants (114 female [73.1%]; median [IQR] age, 56 [38-69] years) were included. Compared with 63 untreated individuals, the 79 who received nirmatrelvir were older and more commonly immunosuppressed. After sequencing viral RNA from participants' anterior nasal swabs, nirmatrelvir resistance mutations were detected in 9 individuals who received nirmatrelvir (11.4%) compared with 2 of those who did not (3.2%) (P = .09). Among the individuals treated with nirmatrelvir, those who were immunosuppressed had the highest frequency of resistance emergence (5 of 22 [22.7%]), significantly greater than untreated individuals (2 of 63 [3.1%]) (P = .01). Similar rates of nirmatrelvir resistance were found in those who had virologic rebound (3 of 23 [13.0%]) vs those who did not (6 of 56 [10.7%]) (P = .86). Most of these mutations (10 of 11 [90.9%]) were detected at low frequencies (<20% of viral population) and reverted to the wild type at subsequent time points. Emerging remdesivir resistance mutations were only detected in immunosuppressed individuals (2 of 14 [14.3%]) but were similarly low frequency and transient. Global Initiative on Sharing All Influenza Data analysis showed no evidence of increased nirmatrelvir resistance in the United States after the authorization of nirmatrelvir. In this cohort study of 156 participants, treatment-emergent nirmatrelvir resistance mutations were commonly detected, especially in individuals who were immunosuppressed. However, these mutations were generally present at low frequencies and were transient in nature, suggesting a low risk for the spread of nirmatrelvir resistance in the community with the current variants and drug usage patterns.

Rapid Emergence of Resistance to Broad-Spectrum Direct Antimicrobial Activity of Avibactam.

Avibactam (AVI) is a diazabicyclooctane (DBO) β-lactamase inhibitor used clinically in combination with ceftazidime. At concentrations higher than those typically achieved in vivo , it also has broad-spectrum direct antibacterial activity against Enterobacterales strains, including metallo-β-lactamase-producing isolates, mediated by inhibition of penicillin-binding protein 2 (PBP2). This activity is mechanistically similar to that of more potent novel DBOs (zidebactam, nacubactam) in late clinical development. We found that resistance to AVI emerged readily, with a mutation frequency of 2×10 -6 to 8×10 -5 . Whole genome sequencing of resistant isolates revealed a heterogeneous mutational target that permitted bacterial survival and replication despite PBP2 inhibition, in line with prior studies of PBP2-targeting drugs. While such mutations are believed to act by upregulating the bacterial stringent response, we found a similarly high mutation frequency in bacteria deficient in components of the stringent response, although we observed a different set of mutations in these strains. Although avibactam-resistant strains had increased lag time, suggesting a fitness cost that might render them less problematic in clinical infections, there was no statistically significant difference in growth rates between susceptible and resistant strains. The finding of rapid emergence of resistance to avibactam as the result of a large mutational target has important implications for novel DBOs with potent direct antibacterial activity, which are being developed with the goal of expanding cell wall-active treatment options for multidrug-resistant gram-negative infections but may be vulnerable to treatment-emergent resistance.

Efficacy and Safety of Long-Acting Subcutaneous Lenacapavir in Heavily Treatment-Experienced People with Multi-Drug Resistant HIV-1: Week 104 Results of a Phase 2/3 Trial.

Lenacapavir is a long-acting HIV-1 capsid inhibitor for treatment of HIV-1 infection. We evaluated the efficacy and safety of lenacapavir in combination with an investigator-selected optimized background regimen (OBR) after 104 weeks in adults with multidrug-resistant HIV-1. This ongoing, international, Phase 2/3 trial at 42 sites included 72 adults living with multidrug-resistant HIV-1. Following a 2-week oral lenacapavir loading phase, participants received subcutaneous lenacapavir every 26 weeks with an OBR. HIV-1 RNA, CD4 cell counts, and adverse events were assessed over 104 weeks. One participant did not enter the extension phase. At Week 104, 44 of 71 participants (62%, 95% CI 50; 73) had HIV-1 RNA <50 copies/mL via US Food & Drug Administration (FDA) snapshot algorithm. When missing data (including discontinuations) were excluded, 44 of 54 participants (82%) had HIV-1 RNA <50 copies/mL at Week 104, mean CD4 cell count increased by 122 cells/µL (95% CI 80; 165), and the proportion of participants with CD4 cell count <200 cells/µL decreased from 64% (46 of 72) at Baseline to 29% (16 of 55). Fourteen participants had treatment-emergent lenacapavir resistance; seven resuppressed (HIV-1 RNA <50 copies/mL) while maintaining lenacapavir use. There were no Grade 4 or serious treatment-related adverse events. One participant discontinued study drug due to an injection site reaction. Treatment with subcutaneous lenacapavir in combination with an OBR was well tolerated and resulted in a high rate of virological suppression over 104 weeks. Lenacapavir represents an important treatment option in people with multidrug-resistant HIV-1.

Brief Report: HIV-1 Resistance Analysis of Participants With HIV-1 and Hepatitis B Initiating Therapy With Bictegravir/Emtricitabine/Tenofovir Alafenamide or Dolutegravir Plus Emtricitabine/Tenofovir Disoproxil Fumarate: A Subanalysis of ALLIANCE Data

Background: In the phase 3 ALLIANCE study, both bictegravir/emtricitabine/tenofovir alafenamide (B/F/TAF) and dolutegravir plus emtricitabine/tenofovir disoproxil fumarate (DTG + F/TDF) achieved high rates of HIV-1 RNA suppression through week 96 in adults with HIV-1 and hepatitis B virus initiating treatment (NCT03547908). In this study, we quantify preexisting HIV-1 resistance, evaluate its effect on HIV-1 virologic suppression, and describe postbaseline HIV-1 resistance through week 96. Methods: Preexisting HIV-1 resistance was assessed by historical and/or screening genotyping. HIV-1 RNA suppression to &lt;50 copies (c)/mL at week 96 was assessed by the preexisting resistance category. Postbaseline resistance was assessed in participants with HIV-1 RNA ≥200 c/mL through week 96. Results: Primary nucleoside/nucleotide reverse transcriptase inhibitor, nonnucleoside reverse transcriptase inhibitor, and protease inhibitor resistance substitutions were present at baseline in 4 (1.7%), 19 (7.9%), and 5 (2.1%) of 241 participants, respectively. Virologic suppression rates were high, irrespective of preexisting primary resistance substitutions, including M184I. Six participants (3 per group) had confirmed HIV-1 RNA ≥200 c/mL and did not resuppress to &lt;50 c/mL while on study drugs; none of the 5 with postbaseline resistance data had treatment-emergent primary resistance substitutions. One participant on DTG + F/TDF with multiple virologic failures and documented nonadherence by pill count had treatment-emergent K70E and M184V/I, and subsequently resuppressed. Conclusion: In people with HIV-1 and hepatitis B virus treated with first-line B/F/TAF or DTG + F/TDF, preexisting HIV-1 resistance was uncommon and did not affect virologic suppression. No treatment-emergent HIV-1 resistance occurred with B/F/TAF, further supporting the high barrier to resistance of this regimen.

Real-World Experience With Maribavir for Treatment of Cytomegalovirus Infection in High-Risk Solid Organ Transplant Recipients.

We evaluated use of maribavir (MBV) for treatment of 15 episodes of refractory/resistant cytomegalovirus infection in 13 solid organ transplant recipients. Treatment failure due to treatment-emergent MBV resistance or early virological recurrence after MBV discontinuation occurred in 7 (47%) episodes. Sustained viral clearance was achieved in 6 (40%) episodes.

Treatment-emergent cefiderocol resistance in carbapenem-resistant Acinetobacter baumannii is associated with insertion sequence ISAba36 in the siderophore receptor pirA.

We report the emergence of cefiderocol resistance in a blaOXA-72 carbapenem-resistant Acinetobacter baumannii isolate from a sacral decubitus ulcer. Cefiderocol was initially used; however, a newly approved sulbactam-durlobactam therapy with source control and flap coverage was successful in treating the infection. Laboratory investigation revealed cefiderocol resistance mediated by ISAba36 insertion into the siderophore receptor pirA.

Characterization of Treatment Resistance and Viral Kinetics in the Setting of Single-Active Versus Dual-Active Monoclonal Antibodies Against Severe Acute Respiratory Syndrome Coronavirus 2.

Monoclonal antibodies (mAbs) represent a crucial antiviral strategy for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, but it is unclear whether combination mAbs offer a benefit over single-active mAb treatment. Amubarvimab and romlusevimab significantly reduced the risk of hospitalizations or death in the ACTIV-2/A5401 trial. Certain SARS-CoV-2 variants are intrinsically resistant against romlusevimab, leading to only single-active mAb therapy with amubarvimab in these variants. We evaluated virologic outcomes in individuals treated with single- versus dual-active mAbs. Participants were nonhospitalized adults at higher risk of clinical progression randomized to amubarvimab plus romlusevimab or placebo. Quantitative SARS-CoV-2 RNA levels and targeted S-gene next-generation sequencing was performed on anterior nasal samples. We compared viral load kinetics and resistance emergence between individuals treated with effective single- versus dual-active mAbs depending on the infecting variant. Study participants receiving single- or dual-active mAbs had similar demographics, baseline nasal viral load, symptom score, and symptom duration. Compared with single-active mAb treatment, treatment with dual-active mAbs led to faster viral load decline at study days 3 (P < .001) and 7 (P < .01). Treatment-emergent resistance mutations were more likely to be detected after amubarvimab plus romlusevimab treatment than with placebo (2.6% vs 0%; P < .001) and were more frequently detected in the setting of single-active compared with dual-active mAb treatment (7.3% vs 1.1%; P < .01). Single-active and dual-active mAb treatment resulted in similar decrease in rates of hospitalizations or death. Compared with single-active mAb therapy, dual-active mAbs led to similar clinical outcomes but significantly faster viral load decline and a lower risk of emergent resistance.

Modeling the emergence of viral resistance for SARS-CoV-2 during treatment with an anti-spike monoclonal antibody.

To mitigate the loss of lives during the COVID-19 pandemic, emergency use authorization was given to several anti-SARS-CoV-2 monoclonal antibody (mAb) therapies for the treatment of mild-to-moderate COVID-19 in patients with a high risk of progressing to severe disease. Monoclonal antibodies used to treat SARS-CoV-2 target the spike protein of the virus and block its ability to enter and infect target cells. Monoclonal antibody therapy can thus accelerate the decline in viral load and lower hospitalization rates among high-risk patients with variants susceptible to mAb therapy. However, viral resistance has been observed, in some cases leading to a transient viral rebound that can be as large as 3-4 orders of magnitude. As mAbs represent a proven treatment choice for SARS-CoV-2 and other viral infections, evaluation of treatment-emergent mAb resistance can help uncover underlying pathobiology of SARS-CoV-2 infection and may also help in the development of the next generation of mAb therapies. Although resistance can be expected, the large rebounds observed are much more difficult to explain. We hypothesize replenishment of target cells is necessary to generate the high transient viral rebound. Thus, we formulated two models with different mechanisms for target cell replenishment (homeostatic proliferation and return from an innate immune response antiviral state) and fit them to data from persons with SARS-CoV-2 treated with a mAb. We showed that both models can explain the emergence of resistant virus associated with high transient viral rebounds. We found that variations in the target cell supply rate and adaptive immunity parameters have a strong impact on the magnitude or observability of the viral rebound associated with the emergence of resistant virus. Both variations in target cell supply rate and adaptive immunity parameters may explain why only some individuals develop observable transient resistant viral rebound. Our study highlights the conditions that can lead to resistance and subsequent viral rebound in mAb treatments during acute infection.

Phage-antibiotic synergy against daptomycin-nonsusceptible MRSA in an ex vivo simulated endocardial pharmacokinetic/pharmacodynamic model.

Phage-antibiotic combinations (PAC) offer a potential solution for treating refractory daptomycin-nonsusceptible (DNS) methicillin-resistant Staphylococcus aureus (MRSA) infections. We examined PAC activity against two well-characterized DNS MRSA strains (C4 and C37) in vitro and ex vivo. PACs comprising daptomycin (DAP) ± ceftaroline (CPT) and a two-phage cocktail (Intesti13 + Sb-1) were evaluated for phage-antibiotic synergy (PAS) against high MRSA inoculum (109 CFU/mL) using (i) modified checkerboards (CB), (ii) 24-h time-kill assays (TKA), and (iii) 168-h ex vivo simulated endocardial vegetation (SEV) models. PAS was defined as a fractional inhibitory concentration ≤0.5 in CB minimum inhibitory concentration (MIC) or a ≥2 log10 CFU/mL reduction compared to the next best regimen in time-kill assays and SEV models. Significant differences between regimens were assessed by analysis of variance with Tukey's post hoc modification (α = 0.05). CB assays revealed PAS with Intesti13 + Sb-1 + DAP ± CPT. In 24-h time-kill assays against C4, Intesti13 + Sb-1 + DAP ± CPT demonstrated synergistic activity (-Δ7.21 and -Δ7.39 log10 CFU/mL, respectively) (P < 0.05 each). Against C37, Intesti13 + Sb-1 + CPT ± DAP was equally effective (-Δ7.14 log10 CFU/mL each) and not significantly different from DAP + Intesti13 + Sb-1 (-Δ6.65 log10 CFU/mL). In 168-h SEV models against C4 and C37, DAP ± CPT + the phage cocktail exerted synergistic activities, significantly reducing bio-burdens to the detection limit [2 log10 CFU/g (-Δ7.07 and -Δ7.11 log10 CFU/g, respectively)] (P < 0.001). At 168 h, both models maintained stable MICs, and no treatment-emergent phage resistance occurred with DAP or DAP + CPT regimens. The two-phage cocktail demonstrated synergistic activity against two DNS MRSA isolates in combination with DAP + CPT in vitro and ex vivo. Further in vivo PAC investigations are needed.

Switch to bictegravir/emtricitabine/tenofovir alafenamide from dolutegravir-based therapy.

To evaluate the efficacy and safety of 96 weeks of bictegravir/emtricitabine/tenofovir alafenamide (B/F/TAF) treatment in participants switching from dolutegravir (DTG)-based therapy. Studies 1489 (NCT02607930) and 1490 (NCT02607956) were phase 3 randomized, double-blind, active-controlled, first-line therapy trials in people with HIV-1. After 144 weeks of DTG-based or B/F/TAF treatment, participants could enter a 96-week open-label extension (OLE) of B/F/TAF. A pooled analysis evaluated viral suppression (HIV-1 RNA <50 copies/ml) and changes in CD4 + cell count at OLE Weeks 48 and 96, treatment-emergent resistance, safety, and tolerability after switch from a DTG-based regimen to B/F/TAF. Outcomes by prior treatment were summarized using descriptive statistics and compared by two-sided Wilcoxon rank sum test. At OLE Week 96, participants who switched to B/F/TAF ( N = 519) maintained high levels of virologic suppression (99.5 and 99.1% in those switching from DTG/abacavir/lamivudine and DTG+F/TAF, respectively) and CD4 + cell count, with no treatment-emergent resistance to B/F/TAF. Twenty-one participants experienced drug-related adverse events after switching, with diarrhea, weight gain, and headache occurring most commonly. There were no cases of proximal renal tubulopathy, drug-related Grade 4 adverse events, or serious adverse events. Two participants discontinued B/F/TAF due to treatment-related adverse events. Participants who switched from DTG/abacavir/lamivudine experienced statistically significant greater weight gain than those who switched from DTG+F/TAF; however, median weight change from the blinded phase baseline to OLE Week 96 was numerically similar across treatment groups. This medium-term analysis demonstrates the safety and efficacy of switching to B/F/TAF from a DTG-containing regimen in people with HIV-1.

Rapid Diagnosis of Drug-Resistant Tuberculosis-Opportunities and Challenges.

Global tuberculosis (TB) eradication is undermined by increasing prevalence of emerging resistance to available drugs, fuelling ongoing demand for more complex diagnostic and treatment strategies. Early detection of TB drug resistance coupled with therapeutic decision making guided by rapid characterisation of pre-treatment and treatment emergent resistance remains the most effective strategy for averting Drug-Resistant TB (DR-TB) transmission, reducing DR-TB associated mortality, and improving patient outcomes. Solid- and liquid-based mycobacterial culture methods remain the gold standard for Mycobacterium tuberculosis (MTB) detection and drug susceptibility testing (DST). Unfortunately, delays to result return, and associated technical challenges from requirements for specialised resource and capacity, have limited DST use and availability in many high TB burden resource-limited countries. There is increasing availability of a variety of rapid nucleic acid-based diagnostic assays with adequate sensitivity and specificity to detect gene mutations associated with resistance to one or more drugs. While a few of these assays produce comprehensive calls for resistance to several first- and second-line drugs, there is still no endorsed genotypic drug susceptibility test assay for bedaquiline, pretomanid, and delamanid. The global implementation of regimens comprising these novel drugs in the absence of rapid phenotypic drug resistance profiling has generated a new set of diagnostic challenges and heralded a return to culture-based phenotypic DST. In this review, we describe the available tools for rapid diagnosis of drug-resistant tuberculosis and discuss the associated opportunities and challenges.

A Comprehensive Literature Review of Treatment-Emergent Integrase Resistance with Dolutegravir-Based Regimens in Real-World Settings.

After a decade of dolutegravir (DTG) use in various antiretroviral therapy combinations and in diverse populations globally, it is critical to identify HIV strains with reduced drug susceptibility and monitor emergent resistance in people living with HIV who experience virologic failure while on DTG-based regimens. We searched the PubMed, Embase, and Cochrane databases to identify studies that reported DTG resistance-associated mutations (RAMs) emerging under selection pressure. Our review showed that RAMs conferring resistance to DTG were rare in 2-drug and 3-drug regimens used in real-world cohorts, corroborating data from clinical trials. The potency of DTG in maintaining virologic suppression was demonstrated, even in cases of pre-existing resistance to companion drugs in the regimen. Estimates of DTG RAMs depended on the population and certain risk factors, including monotherapy, baseline resistance or lack of genotypic testing, treatment history and prior virologic failure, and suboptimal treatment adherence. The RAMs detected after virologic failure, often in heavily treatment-experienced individuals with prior exposure to integrase strand transfer inhibitors, were G118R, E138K, G140A/C/R/S, Q148H/K/R, N155H, and R263K. Overall, these data highlight the durable effectiveness and high barrier to resistance of DTG as part of combination antiretroviral therapy in a wide variety of settings.

Abstract C141: Targeting SHP2-dependent adaptive resistance to BRAF and MEK inhibition in gliomas

Abstract Introduction: BRAF-mutant gliomas, common in children, are sensitive to MEK and/or BRAF inhibitors. However, responses are incomplete and can be short-lived, due to poorly understood mechanisms of resistance that are likely to involve kinome re-programming, treatment-emergent resistance mutations, and adaptive resistance, by which upstream signaling components become activated due to release of negative feedback. Based on the critical role of SHP2 upstream of RAS pathway, we postulated that the combination of SHP2i and BRAFi/MEKi would maintain superior ERK pathway inhibition in gliomas. Here, we demonstrate that combined SHP2i+BRAFi can be efficacious in BRAFV600E mutant gliomas, potentially without the toxicity posed by SHP2i+MEKi in human participants. Methods: Using a panel of BRAFV600E mutant and wild-type glioma cell lines, we examined cell growth with Incucyte live-cell imaging, RAS activity with pull-down assay, and immunoblots of ERK signaling activity in response to MEKi (Trametinib), BRAFi (Dabrafenib), and/or SHP2i (TNO155). NSG immune-deficient mice were implanted subcutaneously with human-derived glioma lines and patient-derived xenografts (PDXs), then treated via oral gavage for ≤28 days while recording tumor volume and weight. Results: In BRAFV600E glioma cells, we observed ERK reactivation and increased RAS activity in response to BRAFi or MEKi. SHP2 knockdown using PTPN11 pooled siRNA partially inhibited cell growth, while the addition of BRAFi/MEKi enhanced growth inhibition compared with either intervention alone. BRAFV600E cells showed insensitivity to small molecule SHP2i monotherapy, but augmented growth inhibition upon the combination with either BRAFi or MEKi due to prolonged ERK pathway suppression. BRAF wt glioma cell lines exhibit sensitivity to TNO155 monotherapy, and combination with MEKi demonstrates sustained pERK suppression in NF1-mut and NF1 wt cell lines. Additionally, we evaluated the effect of combined BRAFi+SHP2i in heterotopic xenografts using human-derived glioma lines and PDXs. In both models, tumor growth was significantly slower in the combined treatment group than either monotherapy. Moreover, mice tolerated the combination well with no weight loss or lethargy. Conclusion. Combined MEKi and SHP2i attenuate RAS reactivation in response to MEKi and demonstrates additive effects in glioma cell lines that are resistant to MEKi monotherapy. Moreover, SHP2i in combination with BRAFi in BRAFV600E mutant glioma cells synergistically attenuated tumor growth in vitro and shows superior preclinical activity to BRAFi or SHP2i alone in BRAFV600E models of gliomas. Citation Format: Abiola Abdulrahman Ayanlaja, Kriti Lalwani, Maria Ioannou, Christine Pratilas, Karisa Schreck. Targeting SHP2-dependent adaptive resistance to BRAF and MEK inhibition in gliomas [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C141.

512. Interim Results of a Prospective Cohort Study to Monitor the Emergence of Resistance in Immunocompromised Non-Hospitalized Patients With COVID-19 Who Were Treated with Sotrovimab in Great Britain: LUNAR Study

Abstract Background Immunocompromised (IC) patients are at risk of adverse COVID-19 outcomes. The risk of treatment emergent resistance may be high in this population. This study investigated clinical and virological outcomes in sotrovimab-treated IC patients in Great Britain while the Omicron variant was predominant. Methods IC, non-hospitalized patients aged ≥ 18 years who were infected with SARS-CoV-2 and received early treatment with sotrovimab 500 mg IV for COVID-19 as per standard of care were included in this multicenter, single arm, observational prospective cohort study. Nasal/oropharyngeal samples were collected at baseline, Day (D) 7, 14, and 28 (+/-2 days) for viral load and sequencing analyses. Clinical (hospitalization, respiratory support, intensive care unit [ICU] admission and death) and safety outcomes were assessed through D28. This interim analysis included patients enrolled from 1 July 2022–31 January 2023. Results Among 195 patients (median age: 58 years), 56% were female, 86% were white, and 98.5% had ≥ 1 COVID-19 vaccine dose prior to enrollment. All patients received sotrovimab within 8 (median: 2) days of diagnosis. Absolute median viral load declined from 7.46 log10 copies/mL at baseline to 0.55 log10 copies/mL at D28 (Table 1). Of 189 patients with spike consensus sequencing data, all harbored the Omicron variant, with 32 sublineages identified. Omicron BA.4, BQ.1, BE.9, BA.5.1.18, and BN.1 were most common in this data cut. We also plan to present interim data on treatment emergent substitutions. No patients were hospitalized due to COVID-19. Six (1.3%) patients had all-cause hospitalizations; none were admitted to ICU. One patient (0.5%; infected with Omicron CH.1.1) with progressive neuromuscular disease needed high flow oxygen/non-invasive mechanical intervention and died on D18 (death deemed not COVID-19 related by investigator) (Table 2). Three mild sotrovimab-related adverse events were reported.Table 1:Summary of absolute viral load (log10 copies/mL) through Day 28, as measured by qRT-PCR from nasal/oropharyngeal swabsNote: Baseline log10 viral load was defined as the non-missing assessment taken at Day 0, excluding the negative viral load results. The post-baseline viral load values with Ct value &amp;gt; 38 were imputed as half the lower limit of detection (i.e. 453 copies/mL*0.5=226.5). Negative viral loads were defined as Ct ≥ 45 and were imputed as 3.57 copies/mL. These imputed values were used to derive log10 viral loads. Ct, cycle threshold; IV, intravenous; qRT-PCR, quantitative real-time reverse transcriptase polymerase chain reactionTable 2:Summary of clinical outcomes through Day 28Notes: N = Number of participants in Completer population (defined as all participants who were enrolled, exposed to study intervention [sotrovimab], and who had been followed for 30 days or discontinued from the study early); n = Number of participants with data available. ECMO, extracorporeal membrane oxygenation; ICU, intensive care unit; IV, intravenous Conclusion Sotrovimab-treated patients had reduced viral load by D7 which further decreased through D28, despite being IC and infected with Omicron subvariants (reduced in vitro neutralization has been reported for some of the subvariants). Few severe clinical outcomes were reported (all unrelated to COVID-19). Disclosures Judith Breuer, MD, GSK: Funding to conduct study|MRC/UKRI: Grant/Research Support|National Institutes of Health: Grant/Research Support|NIHR: Senior investigator|UKNIHR: Grant/Research Support|Vir Biotechnology, Inc: Funding to conduct study|Wellcome Trust: Grant/Research Support Myriam Drysdale, PhD, GSK: Employee|GSK: Stocks/Bonds Jill Walker, PhD, GSK: Employee|GSK: Stocks/Bonds Jennifer Han, MD, GSK: Employment|GSK: Stocks/Bonds Magdalena Gorczycka, MSc, GSK: Employee|GSK: Stocks/Bonds Alicia Aylott, MSc, GSK: Employee|GSK: Stocks/Bonds Melissa K. Van Dyke, PhD, GSK: Employee|GSK: Stocks/Bonds Helen Birch, PhD, GSK: Employee|GSK: Stocks/Bonds Elizabeth McKie, PhD, GSK: Employee|GSK: Stocks/Bonds David M. Lowe, FRCP, PhD, Biotest: Speaker fees|Blood Cancer UK: Grant/Research Support|Bristol Myers Squibb: Grant/Research Support|British Society of Antimicrobial Chemotherapy: Grant/Research Support|Gilead: Speaker fees (educational video)|GSK: Funding to conduct study|Langland: Speaker fees|LifeArc: Grant/Research Support|Merck: Personal fees for a round-table discussion|National Institute of Health Research: Grant/Research Support|Octapharma: Travel, accommodation and conference fees|UK Medical Research Council: Grant/Research Support|Vir Biotechnology, Inc: Funding to conduct study

Baseline and treatment-emergent bedaquiline resistance in drug-resistant tuberculosis: a systematic review and meta-analysis.

Baseline and treatment-emergent bedaquiline resistance in drug-resistant tuberculosis: a systematic review and meta-analysis.

Treatment-Emergent Cilgavimab Resistance Was Uncommon in Vaccinated Omicron BA.4/5 Outpatients.

Mutations in the SARS-CoV-2 Spike glycoprotein can affect monoclonal antibody efficacy. Recent findings report the occurrence of resistant mutations in immunocompromised patients after tixagevimab/cilgavimab treatment. More recently, the Food and Drug Agency revoked the authorization for tixagevimab/cilgavimab, while this monoclonal antibody cocktail is currently recommended by the European Medical Agency. We retrospectively reviewed 22 immunocompetent patients at high risk for disease progression who received intramuscular tixagevimab/cilgavimab as early COVID-19 treatment and presented a prolonged high viral load. Complete SARS-CoV-2 genome sequences were obtained for a deep investigation of mutation frequencies in Spike protein before and during treatment. At seven days, only one patient showed evidence of treatment-emergent cilgavimab resistance. Quasispecies analysis revealed two different deletions on the Spike protein (S:del138-144 or S:del141-145) in combination with the resistance S:K444N mutation. The structural and dynamic impact of the two quasispecies was characterized by using molecular dynamics simulations, showing the conservation of the principal functional movements in the mutated systems and their capabilities to alter the structure and dynamics of the RBD, responsible for the interaction with the ACE2 human receptor. Our study underlines the importance of prompting an early virological investigation to prevent drug resistance or clinical failures in immunocompetent patients.

In vitro activity of cefiderocol against Pseudomonas aeruginosa demonstrating evolved resistance to novel β-lactam/β-lactamase inhibitors.

Cefiderocol demonstrates excellent activity against MDR Pseudomonas aeruginosa; however, the activity against isolates from patients previously treated with β-lactam agents is unknown. We aimed to determine the activity of cefiderocol against P. aeruginosa collected before and after treatment with traditional β-lactams and new β-lactam/β-lactamase inhibitors. Cefiderocol MICs were determined in triplicate in iron-depleted cation-adjusted Mueller-Hinton broth and compared with β-lactam MICs tested by standard methods. All isolates underwent WGS analysis to identify mutations associated with resistance. One hundred and seventy-eight P. aeruginosa isolates were evaluated; 48% (86/178) were non-susceptible to ceftazidime/avibactam, ceftolozane/tazobactam and/or imipenem/relebactam. The cefiderocol MIC50 and MIC90 were 0.12 and 1 mg/L, respectively. Median cefiderocol MICs did not vary against isolates classified as MDR, XDR, or those non-susceptible to ceftazidime/avibactam, ceftolozane/tazobactam and/or imipenem/relebactam when compared with non-MDR isolates. Against isolates collected from patients previously treated with ceftolozane/tazobactam, cefiderocol MICs were increased 4-fold compared with baseline. Cross-resistance to cefiderocol was identified in 21% (3/14) of patients who developed treatment-emergent resistance to ceftolozane/tazobactam. Overall, 6% (11/178) of isolates demonstrated cefiderocol MICs ≥2 mg/L, which were disproportionately collected from patients previously treated with ceftolozane/tazobactam (73%; 8/11). Isolates with reduced cefiderocol susceptibility harboured mutations in ampC, tonB-dependent receptors, the response regulator pirR and ftsI. Cefiderocol demonstrates excellent in vitro activity against P. aeruginosa isolates exposed to other novel β-lactam agents; however, some exceptions were identified. Cross-resistance between cefiderocol and ceftolozane/tazobactam was evident, but not with ceftazidime/avibactam or imipenem/relebactam. Reduced cefiderocol susceptibility was mediated by mutations in ampC and tonB-dependent receptors.

Impact of Baloxavir Resistance-Associated Substitutions on Influenza Virus Growth and Drug Susceptibility.

Baloxavir marboxil (baloxavir) is a recently FDA-approved influenza virus polymerase acidic (PA) endonuclease inhibitor. Several PA substitutions have been demonstrated to confer reduced susceptibility to baloxavir; however, their impacts on measurements of antiviral drug susceptibility and replication capacity when present as a fraction of the viral population have not been established. We generated recombinant A/California/04/09 (H1N1)-like viruses (IAV) with PA I38L, I38T, or E199D substitutions and B/Victoria/504/2000-like virus (IBV) with PA I38T. These substitutions reduced baloxavir susceptibility by 15.3-, 72.3-, 5.4-, and 54.5-fold, respectively, when tested in normal human bronchial epithelial (NHBE) cells. We then assessed the replication kinetics, polymerase activity, and baloxavir susceptibility of the wild-type:mutant (WT:MUT) virus mixtures in NHBE cells. The percentage of MUT relative to WT virus necessary to detect reduced baloxavir susceptibility in phenotypic assays ranged from 10% (IBV I38T) to 92% (IAV E199D). While I38T did not alter IAV replication kinetics or polymerase activity, IAV PA I38L and E199D MUTs and the IBV PA I38T MUT exhibited reduced replication levels and significantly altered polymerase activity. Differences in replication were detectable when the MUTs comprised ≥90%, ≥90%, or ≥75% of the population, respectively. Droplet digital PCR (ddPCR) and next-generation sequencing (NGS) analyses showed that WT viruses generally outcompeted the respective MUTs after multiple replication cycles and serial passaging in NHBE cells when initial mixtures contained ≥50% of the WT viruses; however, we also identified potential compensatory substitutions (IAV PA D394N and IBV PA E329G) that emerged and appeared to improve the replication capacity of baloxavir-resistant virus in cell culture. IMPORTANCE Baloxavir marboxil, an influenza virus polymerase acidic endonuclease inhibitor, represents a recently approved new class of influenza antivirals. Treatment-emergent resistance to baloxavir has been observed in clinical trials, and the potential spread of resistant variants could diminish baloxavir effectiveness. Here, we report the impact of the proportion of drug-resistant subpopulations on the ability to detect resistance in clinical isolates and the impact of substitutions on viral replication of mixtures containing both drug-sensitive and drug-resistant variants. We also show that ddPCR and NGS methods can be successfully used for detection of resistant subpopulations in clinical isolates and to quantify their relative abundance. Taken together, our data shed light on the potential impact of baloxavir-resistant I38T/L and E199D substitutions on baloxavir susceptibility and other biological properties of influenza virus and the ability to detect resistance in phenotypic and genotypic assays.