RNA–protein interactions are vital throughout the HIV-1 life cycle for the successful production of infectious virus particles. One such essential RNA–protein interaction occurs between the ...full-length genomic viral RNA and the major structural protein of the virus. The initial interaction is between the Gag polyprotein and the viral RNA packaging signal (psi or Ψ), a highly conserved RNA structural element within the 5′-UTR of the HIV-1 genome, which has gained attention as a potential therapeutic target. Here, we report the application of a target-based assay to identify small molecules, which modulate the interaction between Gag and Ψ. We then demonstrate that one such molecule exhibits potent inhibitory activity in a viral replication assay. The mode of binding of the lead molecules to the RNA target was characterized by 1H NMR spectroscopy.
Retroviruses selectively encapsidate two copies of their genomic RNA, the Gag protein binding a specific RNA motif in the 5' UTR of the genome. In human immunodeficiency virus type 2 (HIV-2), the ...principal packaging signal (Psi) is upstream of the major splice donor and hence is present on all the viral RNA species. Cotranslational capture of the full length genome ensures specificity. HIV-2 RNA dimerisation is thought to occur at the dimer initiation site (DIS) located in stem-loop 1 (SL-1), downstream of the main packaging determinant. However, the HIV-2 packaging signal also contains a palindromic sequence (pal) involved in dimerisation. In this study, we analysed the role of the HIV-2 packaging signal in genomic RNA dimerisation in vivo and its implication in viral replication.
Using a series of deletion and substitution mutants in SL-1 and the Psi region, we show that in fully infectious HIV-2, genomic RNA dimerisation is mediated by the palindrome pal. Mutation of the DIS had no effect on dimerisation or viral infectivity, while mutations in the packaging signal severely reduce both processes as well as RNA encapsidation. Electron micrographs of the Psi-deleted virions revealed a significant reduction in the proportion of mature particles and an increase in that of particles containing multiple cores.
In addition to its role in RNA encapsidation, the HIV-2 packaging signal contains a palindromic sequence that is critical for genomic RNA dimerisation. Encapsidation of a dimeric genome seems required for the production of infectious mature particles, and provides a promising therapeutic target.
Abstract
Background: In the Phase 3 POSEIDON study (NCT03164616), 1L T plus D and platinum-based CT demonstrated statistically significant improvements in both PFS (HR, 0.72; 95% CI, 0.60-0.86; ...p=0.0003; data cutoff DCO July 24, 2019) and OS (HR, 0.77; 95% CI, 0.65-0.92; p=0.0030; DCO March 12, 2021) vs CT in patients (pts) with EGFR/ALK wild-type metastatic (m) NSCLC. On the basis of these results, T+D+CT was approved by the FDA in November 2022 for use in this setting. Here we report outcomes in POSEIDON pt subgroups defined by a range of bTMB values, including a pre-specified cutoff of 20 mutations/megabase (mut/Mb).
Methods: Pts were randomized 1:1:1 to 1L T+D+CT (platinum-based), D+CT or CT, with stratification by tumor cell (TC) PD-L1 expression (TC ≥50% vs <50%; VENTANA PD-L1 SP263 assay), disease stage (IVA vs IVB) and histology (squamous vs non-squamous). bTMB was assessed using the GuardantOMNI platform. OS, PFS and ORR with T+D+CT vs CT were determined for pts with bTMB ≥ vs <20 mut/Mb. Outcomes across additional bTMB cutoffs (10, 12 and 16 mut/Mb) were also explored.
Results: Plasma samples were available for 958/1013 pts from the intention-to-treat (ITT) population. Of those with available plasma samples, 81.8% (784/958) were evaluable for bTMB, including 277 in the T+D+CT arm and 241 in the CT arm. Similar demographic characteristics and OS were observed in the bTMB evaluable vs ITT populations. Consistent with previous reports, the proportion of never smokers was higher in the bTMB <20 mut/Mb subgroup than in the bTMB ≥20 mut/Mb subgroup. Across all bTMB cutoffs analyzed, OS and PFS benefit for T+D+CT vs CT were generally consistent with the ITT population in both bTMB high and bTMB low subgroups. However, at each bTMB cutoff, OS and PFS benefit appeared more prominent among pts in the bTMB high subgroups. Median OS (mOS) was longer with T+D+CT vs CT in both the bTMB ≥20 mut/Mb and <20 mut/Mb subgroups and HRs suggested more pronounced benefit in the bTMB high group. mOS was 13.5 months with T+D+CT vs 10.3 months with CT (unstratified HR, 0.61; 95% CI, 0.42-0.88) for pts with bTMB ≥20 mut/Mb and 12.6 months vs 10.9 months (unstratified HR, 0.79; 95% CI, 0.63-0.99) for pts with bTMB <20 mut/Mb. PFS and ORR showed similar trends to OS (data will be presented). In both subgroups with PD-L1 TC ≥1% or <1%, HRs suggested more pronounced OS/PFS benefit in pts with bTMB ≥20 (vs <20) mut/Mb (data will be presented).
Conclusions: In pts with mNSCLC, treatment with a limited course of T plus D (until progression) and four cycles of CT consistently improved clinical outcomes vs CT alone in both bTMB high and low subgroups, supporting the use of this regimen as a 1L treatment option for pts with mNSCLC. The clinical benefit vs CT appeared to be greater in pts with higher bTMB over a range of cutoffs, consistent with expectations based on mechanistic biology and previous clinical data.
Citation Format: Solange Peters, Hisani Madison, Kelly Oliner, Anne L’Hernault, Marianne Ratcliffe, Karen Barrett, Xiaojin Shi, Edward B. Garon, Tony Mok, Melissa L. Johnson. Tremelimumab (T) + durvalumab (D) + chemotherapy (CT) in 1L metastatic NSCLC: Outcomes by blood tumor mutational burden (bTMB) in POSEIDON abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT080.
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