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  • 1
    Online Resource
    Online Resource
    Abstract 2278: CTLA-4 targeted engineered toxin bodies designed to deplete regulatory T cells (Tregs)
    American Association for Cancer Research (AACR) ; 2020
    In:  Cancer Research Vol. 80, No. 16_Supplement ( 2020-08-15), p. 2278-2278
    Details
    In: Cancer Research, American Association for Cancer Research (AACR), Vol. 80, No. 16_Supplement ( 2020-08-15), p. 2278-2278
    Abstract: Tumor resident regulatory T cells (Tregs) are important mediators of an immunosuppressive tumor microenvironment (TME) promoting tumor immune evasion. The presence of Tregs, and a higher ratio of Tregs to effector T cells in the TME, are associated with poor prognosis. The depletion of Tregs in the TME is expected to re-expose the tumor to the immune system to allow for tumor control. CLTA-4 is expressed on the cell surface of Tregs and is a clinically validated target. Better responses to CTLA-4 monoclonal antibody (mAb) treatment are correlated with stronger ADCC-mediated Treg depletion in preclinical models, and patient FcγR polymorphism has been reported to correlate with response to CTLA-4 mAb therapy. Towards improving on current therapies, many efforts to increase effective depletion of Tregs (such as by Fc effector modification) are being pursued. Engineered toxin bodies (ETBs) are comprised of a proprietarily engineered form of Shiga-like Toxin A subunit (SLT-A) genetically fused to antibody-like binding domains. ETBs work through novel mechanisms of action and are capable of forcing internalization, self-routing through intracellular compartments to the cytosol, and inducing potent cell-kill via the enzymatic and permanent inactivation of ribosomes. Targeted ETBs are being developed to specifically target and destroy CTLA-4 expressing cells. In vitro, cells expressing CTLA-4 are effectively and specifically killed by targeted ETBs. This direct cell kill activity of the ETB has the potential to deplete Tregs in the TME without a requirement for ADCC mechanisms. ETBs have been designed to bind various CTLA-4 epitopes, and to comprise of different targeting domains formats, including monomeric and diabody single chain variable fragments (scFvs) as well as single domain and biparatopic antibody fragments. The development of a CTLA-4 targeted ETB is ongoing. The entry of a protein with direct cell kill properties into the therapeutic space represents a differentiated mechanism of action to deplete Tregs for ultimate re-invigoration of the anti-tumor immune response, and has the potential to provide benefit to patients, including in the relapsed or refractory setting. Citation Format: Aimee Iberg, Edith Acquaye-Seedah, Lilia A. Rabia, Garrett L. Robinson, Hilario J. Ramos, Joseph D. Dekker, Jay Zhao, Erin K. Willert. CTLA-4 targeted engineered toxin bodies designed to deplete regulatory T cells (Tregs) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2278.
    Type of Medium: Online Resource
    ISSN: 0008-5472 , 1538-7445
    URL: Article
    DOI: 10.1158/1538-7445.AM2020-2278
    RVK:
    XA 36000
    RVK:
    XA 10000
    Language: English
    Publisher: American Association for Cancer Research (AACR)
    Publication Date: 2020
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    detail.hit.zdb_id: 410466-3
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  • 2
    Online Resource
    Online Resource
    Abstract 1627: Preclinical characterization of a novel CTLA-4-targeted ETB for direct Treg depletion
    American Association for Cancer Research (AACR) ; 2021
    In:  Cancer Research Vol. 81, No. 13_Supplement ( 2021-07-01), p. 1627-1627
    Details
    In: Cancer Research, American Association for Cancer Research (AACR), Vol. 81, No. 13_Supplement ( 2021-07-01), p. 1627-1627
    Abstract: Regulatory T cell (Treg) depletion enhances the anti-tumor efficacy of CTLA-4 targeted mAbs in preclinical models, and is a mechanism supported by retrospective clinical data analysis. In response to these findings, many next-generation CTLA-4 targeting therapeutics have been designed to increase Fc-mediated Treg depletion in the tumor microenvironment. CTLA-4-targeted engineered toxin bodies (ETBs) are designed to deplete Tregs in the tumor microenvironment (TME) directly and in a manner independent of Fc-mediated effector functions, offering a unique approach to CTLA-4 targeted therapy. ETBs, or engineered toxin bodies, are large molecule proteins consisting of an antibody fragment genetically fused to a proprietary de-immunized (DI) form of the Shiga-like toxin A subunit (SLTA). Once engaged to the specific cell surface target of interest, in this case CTLA-4, ETBs internalize, route to the cytosol, and permanently inactivate ribosomes through an irreversible enzymatic process. This results in cell death via apoptotic mechanisms.Here we describe the preclinical characterization of a lead candidate CTLA-4-targeted ETB. CTLA-4-ETB-A directly binds and specifically kills CTLA-4 positive cells in vitro and induces apoptosis of ex-vivo expanded Tregs. CTLA-4-ETB-A is designed to bind CTLA-4 in a manner unique from classic blocking antibodies and is not expected to have sustained blocking ability in vivo due to the relatively short half-life of an ETB compared to a neutralizing mAb. We predict this will allow for focused Treg depletion in the TME based on target expression levels, while sparing autoreactive T cell activation in the periphery. Utilizing human CTLA-4 knock in mouse syngeneic tumor models, we show that CTLA-4-ETB-A can reduce the % Tregs and increase the CD8/Treg ratio in the TME. Preclinical assessment of safety and pharmacodynamic signals are underway in cynomolgus studies. Citation Format: Swati Khanna, Caleigh Howard, Lilia A. Rabia, Alvaro Aldana, Jay Zhao, Betty Chang, Hilario J. Ramos, Aimee Iberg. Preclinical characterization of a novel CTLA-4-targeted ETB for direct Treg depletion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1627.
    Type of Medium: Online Resource
    ISSN: 0008-5472 , 1538-7445
    URL: Article
    DOI: 10.1158/1538-7445.AM2021-1627
    RVK:
    XA 36000
    RVK:
    XA 10000
    Language: English
    Publisher: American Association for Cancer Research (AACR)
    Publication Date: 2021
    detail.hit.zdb_id: 2036785-5
    detail.hit.zdb_id: 1432-1
    detail.hit.zdb_id: 410466-3
    Location Call Number Limitation Availability
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  • 3
    Online Resource
    Online Resource
    Abstract 3538: A CTLA-4 targeted ETB for Treg depletion shows favorable preclinical efficacy and safety
    American Association for Cancer Research (AACR) ; 2022
    In:  Cancer Research Vol. 82, No. 12_Supplement ( 2022-06-15), p. 3538-3538
    Details
    In: Cancer Research, American Association for Cancer Research (AACR), Vol. 82, No. 12_Supplement ( 2022-06-15), p. 3538-3538
    Abstract: CTLA-4-targeted engineered toxin bodies (ETBs) are designed to deplete immune-suppressive regulatory T cells (Tregs) in the tumor microenvironment (TME) directly and in a manner independent of Fc-mediated effector functions, offering a unique approach to CTLA-4 targeted therapy that may show efficacy where blocking antibodies have failed. ETBs are large molecule proteins consisting of an antibody fragment genetically fused to a proprietary de-immunized (DI) form of the Shiga-like toxin-1 subunit A (SLTA). Once engaged to the specific cell surface target of interest, ETBs internalize, route to the cytosol, and permanently inactivate ribosomes through an irreversible enzymatic process. This results in cell death via apoptotic mechanisms. Here we describe the preclinical characterization of a candidate CTLA-4-targeted ETB. The candidate ETB kills gain-of-function model cell lines that express CTLA-4 at levels observed on primary human tumor Tregs. Notably, the potency of the candidate ETB is limited when CTLA-4 is expressed at low levels, thereby allowing a mechanism to spare CD8+ cytotoxic T lymphocytes (CTLs) and effector CD4+ T cells from targeted depletion. The candidate ETB binds CTLA-4 with high affinity utilizing a unique biparatopic binding domain. Using in vitro systems, we show that the candidate ETB can block CTLA-4:B7 interactions and repress Treg-mediated T-cell suppression. In a syngeneic mouse pharmacodynamic model, the candidate ETB depletes tumor-resident Tregs and increases the CD8:Treg ratio in the TME. A toxicological study in naive NHP demonstrate that the candidate ETB, which is cross-reactive to NHP, is well-tolerated at 450 mcg/kg (highest dose tested) administered intravenously once weekly for 4-weeks and does not significantly alter the CTLA-4 low/null peripheral T cell populations. Overall, the candidate ETB is a unique CTLA-4 targeting modality that is designed to deplete Tregs selectively and directly in the tumor, spare CD8+ CTLs, and represents an alternative treatment option to traditional blocking antibodies. Development activities are underway to support the upcoming IND application. Citation Format: Asis Sarkar, Rebecca Martin, Lauren R. Byrne, Caleigh Howard, Swati Khanna, Lilia A. Rabia, Diana Adhikari, Michaela M. Sousares, Alvaro Aldana, Garrett L. Robinson, Jay Zhao, Chris B. Moore, Aimee Iberg. A CTLA-4 targeted ETB for Treg depletion shows favorable preclinical efficacy and safety [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3538.
    Type of Medium: Online Resource
    ISSN: 1538-7445
    URL: Article
    DOI: 10.1158/1538-7445.AM2022-3538
    Language: English
    Publisher: American Association for Cancer Research (AACR)
    Publication Date: 2022
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    detail.hit.zdb_id: 1432-1
    detail.hit.zdb_id: 410466-3
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