12 Key pharmacokinetic and pharmacodynamic parameters that correlate with the anti-tumor activity of a bispecific PD-L1 conditional 4–1BB agonist

Background

4-1BB is a costimulatory molecule that is predominantly expressed on activated CD8+ T cells and is induced upon T cell receptor mediated activation.1 Within the tumor microenvironment, 4-1BB-expressing T cells are enriched for anti-tumor reactivity 2; thus, 4-1BB agonism provides an opportunity for selective activation of anti-cancer immune effector cells. Early efforts to develop 4-1BB targeted agonists were limited by poor tolerability (Urelumab) or insufficient efficacy (Utomilumab). INBRX-105 is a bispecific antibody that aims to overcome these prior limitations through induction of 4-1BB agonism specifically at sites of PD-L1 expression. Preclinical models have defined pharmacokinetic (PK) and pharmacodynamic (PD) parameters that are correlated with maximal INBRX-105-specific immune responses and antitumor activity.

Methods

INBRX-105 was generated by linking 2 humanized single-domain antibody binding domains targeting human PD-L1 and 4-1BB, fused to an effector-silenced human IgG1 constant domain (Fc). A bispecific, anti-mouse PD-L1x4-1BB surrogate molecule, INBRX-105-a, was engineered to match the function and target affinities of INBRX-105. This surrogate was tested for in vivo activity in non-tumor-bearing and MC-38 tumor-bearing animals, including measurements of serum exposure, PD-L1 receptor occupancy, immunophenotyping of peripheral blood and intra-tumoral immune cell populations.

Results

INBRX-105-a was shown to be an appropriate anti-mouse surrogate for INBRX-105 in a variety of in vitro assays. Comparable potencies of activity were demonstrated in a PD-L1 dependent 4-1BB reporter assay, as well as in cytokine induction through co-stimulation of primary T cells. In vivo, INBRX-105-a showed robust induction of mouse CD8+ T effector memory populations (CD8+ TEM) at dose levels that achieved ≥ 96 hours of PD-L1 receptor occupancy. A serum concentration of 800 ng/mL at 96 hours, achieved by a dose of 2 mg/kg in mice, was sufficient to provide the requisite occupancy for maximal pharmacodynamics. CD8+ TEM responses were dependent on 4-1BB agonism and were more efficiently induced by PD-L1 localization, as opposed to 4-1BB multivalent clustering alone. Optimal tumor responses, including complete responses and demonstration of immunological memory, were observed when maximal 4-1BB driven pharmacodynamics were paired with extended PD-1/PD-L1 pathway blockade, provided either by an orthogonal molecule or increased exposure of INBRX-105.

Conclusions

Preclinical receptor occupancy and pharmacokinetic determinations have defined a dose of INBRX-105-like activity that induces maximal pharmacodynamics. Additional PD-1 checkpoint inhibition does not change the pharmacodynamic profile of INBRX-105-a, but does allow for optimal efficacy. INBRX-105 is currently being evaluated in patients with advanced solid tumors in a first-in-human trial (NCT03809624).

Trial Registration

INBRX-105 is currently being evaluated in patients with advanced solid tumors in a first-in-human trial (NCT03809624).

References

Vinay DS, Kwon BS. 4-1BB (CD137), an inducible costimulatory receptor, as a specific target for cancer therapy. BMB Reports; 2014:47:122–129.

Ye Q, Song D-G, Poussin M, et al. CD137 accurately identifies and enriches for naturally occurring tumor-reactive T cells in tumor. Clin Cancer Res; 2014:20:44–55.

Ethics Approval

The care and use of all animals were reviewed and approved by Explora BioLabs’ IACUC # SP17-010-013 and conducted in accordance with AAALAC regulations.

856 INBRX-106: a novel hexavalent anti-OX40 agonist for the treatment of solid tumors

Background

OX40 is a co-stimulatory receptor enriched on immune cells in the tumor microenvironment. OX40 agonism promotes anti-tumor responses, both singly and in combination with checkpoint inhibitors. The cognate OX40 ligand, OX40L, is a trimeric protein that activates robust signaling through clustering. INBRX-106 is a novel hexavalent OX40 agonist that has been rationally designed to optimize target clustering and provide superior agonism to previously explored bivalent entities, leading to more potent anti-tumor activity.

Methods

INBRX-106 is a homodimer, each half comprising three identical humanized, camelid single-domain antibody binding domains targeting OX40 linked end-to-end, and fused to an effector-enabled human IgG1 constant domain (Fc). Due to lack of rodent cross-reactivity, a valency, affinity and activity-matched murine surrogate, Hex-C04, was generated for the purpose of preclinical modeling. Hex-C04 contains an mIgG2a effector enabled Fc, the mouse isotype most analogous to the activity of human IgG1. The activity and potency of INBRX-106 and Hex-C04 were evaluated in functional in vitro T-cell assays, and the anti-tumor efficacy of Hex-C04 was evaluated alone or in combination with PD-1 blockade across a number of syngeneic tumor models.

Results

INBRX-106 binds specifically to OX40 with a sub nanomolar apparent affinity, without blocking the binding of its ligand OX40L. In vitro, cross-linking by INBRX-106 rapidly induces loss of OX40 surface expression in addition to driving receptor signaling. In primary T-cell assays, INBRX-106 is more potent than a bivalent comparator antibody, inducing greater upregulation of activation markers, cytokine production and proliferation. This costimulatory activity exhibits a bell-shaped dose-response curve, with maximal activity occurring at receptor occupancies of 30–100%. In vivo, tumor growth control by Hex-C04 also follows a bell-shaped dose response curve. Rapid loss of OX40 is observed in vivo as well, with both the degree and duration of OX40 loss dependent on Cmax and exposure. Hex-C04 demonstrated strong single-agent activity across a variety of preclinical tumor models including models that do not respond to a PD-1/PD-L1 checkpoint inhibitor, and this activity was improved in combination with a PD-1 blocking antibody.

Conclusions

Preclinically, INBRX-106 significantly outperforms bivalent antibodies in co-stimulatory capacity and anti-tumor activity. On the weight of this data, Inhibrx Inc. has initiated a first-in-human Phase 1 trial of INBRX-106 as a single agent or in combination with Keytruda® (pembrolizumab). The complex relationship between dose, OX40 target modulation and activity indicate the importance of integrating preclinical data sets with emerging clinical data to make informed decisions regarding INBRX-106 dose and schedule.

Trial Registration

NCT04198766

Ethics Approval

The care and use of all animals were reviewed and approved by the IACUC committees of Explora BioLabs and Molecular Diagnostic Services and conducted in accordance with AAALAC regulations.

722 INBRX-121 is an NKp46-targeted detuned IL-2 with antitumor activity as a monotherapy or in combination with multiple cancer immunotherapy modalities

Background

Natural Killer (NK) cells play a pivotal role in cancer immunosurveillance due to their potent cytolytic activity and NK cell-centric therapies have emerged as safer alternatives to targeting T cells.1 2 Interleukin 2 (IL-2) drives NK cell expansion and activity, but its therapeutic utility is limited by rapid clearance, expansion of immunosuppressive regulatory T cells, and by severe dose-limiting toxicities.3 INBRX-121 overcomes these liabilities through specific targeting of an affinity-detuned IL-2 variant to cells expressing NKp46.

Methods

An IL-2 variant was engineered to eliminate binding to CD25 and to have attenuated affinity for CD122. This detuned cytokine was fused to a high-affinity single-domain antibody targeting NKp46 to generate INBRX-121. The ability of INBRX-121 to target IL-2-like signaling specifically to NKp46-expressing cells was evaluated in vitro using human lymphocytes by measuring STAT5 signaling and cytotoxic activity in tumor cell co-cultures. Characterization of the pharmacokinetic/pharmacodynamic relationship of INBRX-121 was completed in non-human primates across escalating dose levels, while anti-tumor activity as a monotherapy and in combination with Rituximab or PD-1 checkpoint blockade was tested in Raji xenografts and syngeneic CT-26 mouse models, respectively.

Results

INBRX-121 induces a STAT5 signal equal to that of wild-type IL-2 in human lymphocytes but shows an NK cell-centric activity profile. Cells targeted by INBRX-121 have increased proliferative capacity and improved cytotoxicity in antibody-dependent and -independent tumor cell killing assays. INBRX-121 shows prolonged pharmacokinetic exposure in vivo and is well-tolerated in mice and cynomolgus monkeys. The NKp46-specific IL-2 stimulus in these models results in a robust, dose-dependent NK cell expansion. As predicted by its in vitro activity, INBRX-121 also enhances the cytotoxic capacity of NK cells in vivo measured via elevated intracellular levels of Granzyme B. In a Raji xenograft model, INBRX-121 slows tumor growth as a single agent and synergizes with Rituximab to induce complete tumor regression. Similarly, co-treatment with INBRX-121 improves the incomplete suppression of CT-26 tumor growth by a PD-1 blocking antibody to yield complete responses that show immunological memory upon re-challenge.

Conclusions

INBRX-121 offers a unique approach to overcoming the limitations of current IL-2 therapeutics. NKp46-targeting of a detuned IL-2 variant helps to avoid IL-2-mediated toxicity while enhancing the antitumor activities of NK cells. Through its novel therapeutic concept INBRX-121 provides a promising treatment option for multiple cancer indications both as a monotherapy and in combination with a variety of frontline agents.

References

Shimasaki N, Jain A, Campana D. NK cells for cancer immunotherapy. Nat Rev Drug Discov 2020;19:200–218.

Liu S, Galat V, Galat Y, Lee Y, Wainwright D, Wu J. NK cell-based cancer immunotherapy: from basic biology to clinical development. J Hematol Oncol 2021;14:7.

Overwijk W, Tagliaferri M, Zalevsky J. Engineering IL-2 to give new life to T Cell immunotherapy. Annu Rev Med 2021;72:281–311.

Ethics Approval

All animal studies were conducted in accordance with AAALAC regulations and were approved by the IACUC for Explora BioLabs (#SP17-010-013) and BTS Research (20-015 Enrollment 05).

Role of in silico structural modeling in predicting immunogenic neoepitopes for cancer vaccine development

In prior studies, we delineated the landscape of neoantigens arising from nonsynonymous point mutations in a murine pancreatic cancer model, Panc02. We developed a peptide vaccine by targeting neoantigens predicted using a pipeline that incorporates the MHC binding algorithm NetMHC. The vaccine, when combined with immune checkpoint modulators, elicited a robust neoepitope-specific antitumor immune response and led to tumor clearance. However, only a small fraction of the predicted neoepitopes induced T cell immunity, similarly to that reported for neoantigen vaccines tested in clinical studies. While these studies have used binding affinities to MHC I as surrogates for T cell immunity, this approach does not include spatial information on the mutated residue that is crucial for TCR activation. Here, we investigate conformational alterations in and around the MHC binding groove induced by selected minimal neoepitopes, and we examine the influence of a given mutated residue as a function of its spatial position. We found that structural parameters, including the solvent-accessible surface area (SASA) of the neoepitope and the position and spatial configuration of the mutated residue within the sequence, can be used to improve the prediction of immunogenic neoepitopes for inclusion in cancer vaccines.

Structural parameters, including the solvent exposed surface area of the neoepitope and the position and spatial configuration of the mutated residue can be used to improve the prediction of immunogenic neoepitopes for inclusion in cancer vaccines.

Abstract 1695: Exploiting the pancreatic cancer mutome for immune interception

This study aims to translate tumor-specific mutations identified by next-generation sequencing techniques into an effective anti-tumor vaccine for a classically non-immunogenic tumor, pancreatic ductal adenocarcinoma (PDA). Pancreatic ductal adenocarcinomas develop an average of 63 mutations during tumorigenesis, collectively referred to as the “mutome.” Of these, approximately 45 are amino acid point mutations. These mutations are not present in normal cells and provide a source of tumor-specific neoepitopes for targeted immunotherapy. Next-generation sequencing technologies allow for rapid identification of mutations present in patient tumors; however, methods for rapid identification of immunogenic neoepitopes which can be effectively targeted for tumor clearance, and optimized vaccination strategies for targeting them, still need to be developed.

In this study, we are using a transplantable murine PDA model, Panc02, to develop vaccination strategies for inducing neoepitope-specific T cell antitumor responses, and to define parameters for selecting appropriate targets. Exome sequencing identified 878 nonsynonymous mutations in the Panc02 cell line. Three immunological epitope prediction servers identified 878 potentially immunogenic peptides in the Panc02 model, 29 of which were strong candidates (scores <50) and another 240 candidate epitopes within the limits of prediction (scores <1000). Panc02 neoepitope peptide vaccinations in mice confirmed 14% of the predicted epitopes to be immunogenic by IFNγ ELISPOT, which may include both CD8+ and CD4+ T cell responses. Tumor transplant experiments demonstrate that therapeutic vaccination against neoepitopes in combination with a human STING-activating cyclic dinucleotide adjuvant is capable of inducing a temporary regression of implanted tumors. After tumor escape and regrowth, flow cytometry reveals a large population of infiltrating lymphocytes, the majority of which are co-expressing the checkpoint molecules PD-1, Tim3, and Lag3, indicating that treatment of vaccinated animals with checkpoint blockade therapy may potentiate infiltrating lymphocytes and ultimately result in permanent tumor regression. Thus, a broad and unbiased approach for screening vaccine targets will allow for the evaluation of predictive algorithms and ultimately the development of more effective vaccination approaches for targeting the tumor mutome.

Citation Format: Heather Kinkead, Eric Lutz, Thomas W. Dubensky, Elizabeth Jaffee. Exploiting the pancreatic cancer mutome for immune interception [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1695. doi:10.1158/1538-7445.AM2017-1695

Priming the pancreatic cancer tumor microenvironment for checkpoint-inhibitor immunotherapy

Single agent immunotherapy is effective against several cancers, but has failed against poorly immunogenic cancers, including pancreatic cancer. Evaluation of pancreatic tumors following treatment with an experimental vaccine (Lutz et al. Cancer Immunology Research 2014) suggests that vaccination primes the tumor microenvironment (TME) for checkpoint-inhibitor immunotherapy, and supports a new platform for evaluating checkpoint-inhibitors in poorly immunogenic cancers.

Functional stability of unliganded envelope glycoprotein spikes among isolates of human immunodeficiency virus type 1 (HIV-1)

The HIV-1 envelope glycoprotein (Env) spike is challenging to study at the molecular level, due in part to its genetic variability, structural heterogeneity and lability. However, the extent of lability in Env function, particularly for primary isolates across clades, has not been explored. Here, we probe stability of function for variant Envs of a range of isolates from chronic and acute infection, and from clades A, B and C, all on a constant virus backbone. Stability is elucidated in terms of the sensitivity of isolate infectivity to destabilizing conditions. A heat-gradient assay was used to determine T₉₀ values, the temperature at which HIV-1 infectivity is decreased by 90% in 1 h, which ranged between ∼40 to 49°C (n = 34). For select Envs (n = 10), the half-lives of infectivity decay at 37°C were also determined and these correlated significantly with the T₉₀ (p = 0.029), though two ‘outliers’ were identified. Specificity in functional Env stability was also evident. For example, Env variant HIV-1_ADA was found to be labile to heat, 37°C decay, and guanidinium hydrochloride but not to urea or extremes of pH, when compared to its thermostable counterpart, HIV-1_JR-CSF. Blue native PAGE analyses revealed that Env-dependent viral inactivation preceded complete dissociation of Env trimers. The viral membrane and membrane-proximal external region (MPER) of gp41 were also shown to be important for maintaining trimer stability at physiological temperature. Overall, our results indicate that primary HIV-1 Envs can have diverse sensitivities to functional inactivation in vitro, including at physiological temperature, and suggest that parameters of functional Env stability may be helpful in the study and optimization of native Env mimetics and vaccines.

In-solution virus capture assay helps deconstruct heterogeneous antibody recognition of human immunodeficiency virus type 1

Human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) on whole virions is heterogeneous, so molecular analysis of Env with monoclonal antibodies (MAbs) is challenging. Virus capture assays (VCAs) involving immobilized MAbs are typically used, but these assays suffer from immobilization artifacts and do not provide binding constants. Furthermore, we show here that certain HIV-1 neutralizing MAbs, including 2G12, 4E10, 2F5, Z13e1, and D5, will capture virion particles completely devoid of Env. We modified the VCA such that MAbs and virions are incubated in solution, and unbound MAbs are removed prior to the capture step. This modification nearly eliminated evidence of Env-independent binding by MAbs to virions and allowed determination of apparent affinity constants in solution. Three important qualitative observations were further revealed. First, neutralizing MAbs 2F5, 4E10, and Z13e1 against the membrane-proximal external region (MPER) of HIV-1 gp41 were found to capture virions efficiently only if a significant amount of uncleaved gp160 or synthetic MPER peptide was present. Second, we show how non-native forms of Env vary by Env genotype and that Env from HIV-1(JR-FL) is more homogeneously trimeric than that from HIV-1(JR-CSF). Third, we determined that Env containing all or parts of gp41, including uncleaved gp160, binds spontaneously to free virions. This exogenous Env is an indiscriminate molecular "bridge" between Env-specific Ab and virions and can affect VCA analyses, particularly using pseudotyped virions. Heterogeneity in Env from endogenous and exogenous sources might also subvert humoral immunity to HIV-1, so in-solution VCAs may help to dissect this heterogeneity for vaccine design purposes.

Antibody elicited against the gp41 N-heptad repeat (NHR) coiled-coil can neutralize HIV-1 with modest potency but non-neutralizing antibodies also bind to NHR mimetics

Following CD4 receptor binding to the HIV-1 envelope spike (Env), the conserved N-heptad repeat (NHR) region of gp41 forms a coiled-coil that is a precursor to the fusion reaction. Although it has been a target of drug and vaccine design, there are few monoclonal antibody (mAb) tools with which to probe the antigenicity and immunogenicity specifically of the NHR coiled-coil. Here, we have rescued HIV-1-neutralizing anti-NHR mAbs from immune phage display libraries that were prepared (i) from b9 rabbits immunized with a previously described mimetic of the NHR coiled-coil, N35(CCG)-N13, and (ii) from an HIV-1 infected individual. We describe a rabbit single-chain Fv fragment (scFv), 8K8, and a human Fab, DN9, which specifically recognize NHR coiled-coils that are unoccupied by peptide corresponding to the C-heptad repeat or CHR region of gp41 (e.g. C34). The epitopes of 8K8 and DN9 were found to partially overlap with that of a previously described anti-NHR mAb, IgG D5; however, 8K8 and DN9 were much more specific than D5 for unoccupied NHR trimers. The mAbs, including a whole IgG 8K8 molecule, neutralized primary HIV-1 of clades B and C in a pseudotyped virus assay with comparable, albeit relatively modest potency. Finally, a human Fab T3 and a rabbit serum (both non-neutralizing) were able to block binding of D5 and 8K8 to a gp41 NHR mimetic, respectively, but not the neutralizing activity of these mAbs. We conclude from these results that NHR coiled-coil analogs of HIV-1 gp41 elicit many Abs during natural infection and through immunization, but that due to limited accessibility to the corresponding region on fusogenic gp41 few can neutralize. Caution is therefore required in targeting the NHR for vaccine design. Nevertheless, the mAb panel may be useful as tools for elucidating access restrictions to the NHR of gp41 and in designing potential improvements to mimetics of receptor-activated Env.