Impact of isotype on the mechanism of action of agonist anti-OX40 antibodies in cancer: implications for therapeutic combinations.

BACKGROUND: OX40 has been widely studied as a target for immunotherapy with agonist antibodies taken forward into clinical trials for cancer where they are yet to show substantial efficacy. Here, we investigated potential mechanisms of action of anti-mouse (m) OX40 and anti-human (h) OX40 antibodies, including a clinically relevant monoclonal antibody (mAb) (GSK3174998) and evaluated how isotype can alter those mechanisms with the aim to develop improved antibodies for use in rational combination treatments for cancer. METHODS: Anti-mOX40 and anti-hOX40 mAbs were evaluated in a number of in vivo models, including an OT-I adoptive transfer immunization model in hOX40 knock-in (KI) mice and syngeneic tumor models. The impact of FcγR engagement was evaluated in hOX40 KI mice deficient for Fc gamma receptors (FcγR). Additionally, combination studies using anti-mouse programmed cell death protein-1 (mPD-1) were assessed. In vitro experiments using peripheral blood mononuclear cells (PBMCs) examining possible anti-hOX40 mAb mechanisms of action were also performed. RESULTS: Isotype variants of the clinically relevant mAb GSK3174998 showed immunomodulatory effects that differed in mechanism; mIgG1 mediated direct T-cell agonism while mIgG2a acted indirectly, likely through depletion of regulatory T cells (Tregs) via activating FcγRs. In both the OT-I and EG.7-OVA models, hIgG1 was the most effective human isotype, capable of acting both directly and through Treg depletion. The anti-hOX40 hIgG1 synergized with anti-mPD-1 to improve therapeutic outcomes in the EG.7-OVA model. Finally, in vitro assays with human peripheral blood mononuclear cells (hPBMCs), anti-hOX40 hIgG1 also showed the potential for T-cell stimulation and Treg depletion. CONCLUSIONS: These findings underline the importance of understanding the role of isotype in the mechanism of action of therapeutic mAbs. As an hIgG1, the anti-hOX40 mAb can elicit multiple mechanisms of action that could aid or hinder therapeutic outcomes, dependent on the microenvironment. This should be considered when designing potential combinatorial partners and their FcγR requirements to achieve maximal benefit and improvement of patient outcomes.

Activating Inducible T-cell Costimulator Yields Antitumor Activity Alone and in Combination with Anti-PD-1 Checkpoint Blockade.

In recent years, there has been considerable interest in mAb-based induction of costimulatory receptor signaling as an approach to combat cancer. However, promising nonclinical data have yet to translate to a meaningful clinical benefit. Inducible T-cell costimulator (ICOS) is a costimulatory receptor important for immune responses. Using a novel clinical-stage anti-ICOS immunoglobulin G4 mAb (feladilimab), which induces but does not deplete ICOS+ T cells and their rodent analogs, we provide an end-to-end evaluation of the antitumor potential of antibody-mediated ICOS costimulation alone and in combination with programmed cell death protein 1 (PD-1) blockade. We demonstrate, consistently, that ICOS is expressed in a range of cancers, and its induction can stimulate growth of antitumor reactive T cells. Furthermore, feladilimab, alone and with a PD-1 inhibitor, induced antitumor activity in mouse and humanized tumor models. In addition to nonclinical evaluation, we present three patient case studies from a first-time-in-human, phase I, open-label, dose-escalation and dose-expansion clinical trial (INDUCE-1; ClinicalTrials.gov: NCT02723955), evaluating feladilimab alone and in combination with pembrolizumab in patients with advanced solid tumors. Preliminary data showing clinical benefit in patients with cancer treated with feladilimab alone or in combination with pembrolizumab was reported previously; with example cases described here. Additional work is needed to further validate the translation to the clinic, which includes identifying select patient populations that will benefit from this therapeutic approach, and randomized data with survival endpoints to illustrate its potential, similar to that shown with CTLA-4 and PD-1 blocking antibodies. Significance: Stimulation of the T-cell activation marker ICOS with the anti-ICOS agonist mAb feladilimab, alone and in combination with PD-1 inhibition, induces antitumor activity across nonclinical models as well as select patients with advanced solid tumors.

Belantamab Mafodotin (GSK2857916) Drives Immunogenic Cell Death and Immune-mediated Antitumor Responses In Vivo.

B-cell maturation antigen (BCMA) is an attractive therapeutic target highly expressed on differentiated plasma cells in multiple myeloma and other B-cell malignancies. GSK2857916 (belantamab mafodotin, BLENREP) is a BCMA-targeting antibody-drug conjugate approved for the treatment of relapsed/refractory multiple myeloma. We report that GSK2857916 induces immunogenic cell death in BCMA-expressing cancer cells and promotes dendritic cell activation in vitro and in vivo GSK2857916 treatment enhances intratumor immune cell infiltration and activation, delays tumor growth, and promotes durable complete regressions in immune-competent mice bearing EL4 lymphoma tumors expressing human BCMA (EL4-hBCMA). Responding mice are immune to rechallenge with EL4 parental and EL4-hBCMA cells, suggesting engagement of an adaptive immune response, immunologic memory, and tumor antigen spreading, which are abrogated upon depletion of endogenous CD8+ T cells. Combinations with OX40/OX86, an immune agonist antibody, significantly enhance antitumor activity and increase durable complete responses, providing a strong rationale for clinical evaluation of GSK2857916 combinations with immunotherapies targeting adaptive immune responses, including T-cell-directed checkpoint modulators.

Tumor-immune profiling of murine syngeneic tumor models as a framework to guide mechanistic studies and predict therapy response in distinct tumor microenvironments.

Mouse syngeneic tumor models are widely used tools to demonstrate activity of novel anti-cancer immunotherapies. Despite their widespread use, a comprehensive view of their tumor-immune compositions and their relevance to human tumors has only begun to emerge. We propose each model possesses a unique tumor-immune infiltrate profile that can be probed with immunotherapies to inform on anti-tumor mechanisms and treatment strategies in human tumors with similar profiles. In support of this endeavor, we characterized the tumor microenvironment of four commonly used models and demonstrate they encompass a range of immunogenicities, from highly immune infiltrated RENCA tumors to poorly infiltrated B16F10 tumors. Tumor cell lines for each model exhibit different intrinsic factors in vitro that likely influence immune infiltration upon subcutaneous implantation. Similarly, solid tumors in vivo for each model are unique, each enriched in distinct features ranging from pathogen response elements to antigen presentation machinery. As RENCA tumors progress in size, all major T cell populations diminish while myeloid-derived suppressor cells become more enriched, possibly driving immune suppression and tumor progression. In CT26 tumors, CD8 T cells paradoxically increase in density yet are restrained as tumor volume increases. Finally, immunotherapy treatment across these different tumor-immune landscapes segregate into responders and non-responders based on features partially dependent on pre-existing immune infiltrates. Overall, these studies provide an important resource to enhance our translation of syngeneic models to human tumors. Future mechanistic studies paired with this resource will help identify responsive patient populations and improve strategies where immunotherapies are predicted to be ineffective.

Evaluation of B cell maturation antigen as a target for antibody drug conjugate mediated cytotoxicity in multiple myeloma.

B-cell maturation antigen (BCMA, also termed TNFRSF17) is an attractive therapeutic target due to its restricted expression on normal and malignant plasma cells (PC). GSK2857916 (or J6M0-MMAF) is a BCMA-specific antibody conjugated to the microtubule-disrupting agent monomethyl auristatin F (MMAF) via a protease-resistant linker. To evaluate the clinical potential of this agent, tumour cells from seventy multiple myeloma (MM) patients were assessed for BCMA expression by immunohistochemistry and flow cytometry. All patients tested expressed BCMA, at varying levels, and both surface and intracellular expression were observed. BCMA expression is maintained through relapse, extramedullary spread and in residual disease post therapy. BCMA levels may also be prognostically useful as higher levels of BCMA were associated with poorer outcomes, even taking into account genetic risk. We observed rapid internalization of surface BCMA and newly expressed protein by 1 h, suggesting a mechanism for J6M0-MMAF activity even with low surface antigen. J6M0-MMAF mediated cytotoxicity of MM cells varied with dose and antigen levels, with clonogenic progenitors killed at lower doses than mature cells. In comparison, J6M0-MMAF killing of primary CD138(+) myeloma cells occurred with slower kinetics. Our observations support BCMA to be a promising therapeutic target in MM for novel therapies such as J6M0-MMAF.

The BRAF and MEK Inhibitors Dabrafenib and Trametinib: Effects on Immune Function and in Combination with Immunomodulatory Antibodies Targeting PD-1, PD-L1, and CTLA-4.

PURPOSE: To assess the immunologic effects of dabrafenib and trametinib in vitro and to test whether trametinib potentiates or antagonizes the activity of immunomodulatory antibodies in vivo. EXPERIMENTAL DESIGN: Immune effects of dabrafenib and trametinib were evaluated in human CD4(+) and CD8(+) T cells from healthy volunteers, a panel of human tumor cell lines, and in vivo using a CT26 mouse model. RESULTS: Dabrafenib enhanced pERK expression levels and did not suppress human CD4(+) or CD8(+) T-cell function. Trametinib reduced pERK levels, and resulted in partial/transient inhibition of T-cell proliferation/expression of a cytokine and immunomodulatory gene subset, which is context dependent. Trametinib effects were partially offset by adding dabrafenib. Dabrafenib and trametinib in BRAF V600E/K, and trametinib in BRAF wild-type tumor cells induced apoptosis markers, upregulated HLA molecule expression, and downregulated certain immunosuppressive factors such as PD-L1, IL1, IL8, NT5E, and VEGFA. PD-L1 expression in tumor cells was upregulated after acquiring resistance to BRAF inhibition in vitro. Combinations of trametinib with immunomodulators targeting PD-1, PD-L1, or CTLA-4 in a CT26 model were more efficacious than any single agent. The combination of trametinib with anti-PD-1 increased tumor-infiltrating CD8(+) T cells in CT26 tumors. Concurrent or phased sequential treatment, defined as trametinib lead-in followed by trametinib plus anti-PD-1 antibody, demonstrated superior efficacy compared with anti-PD-1 antibody followed by anti-PD-1 plus trametinib. CONCLUSION: These findings support the potential for synergy between targeted therapies dabrafenib and trametinib and immunomodulatory antibodies. Clinical exploration of such combination regimens is under way.

Identification of iminooxothiazolidines as secreted frizzled related protein-1 inhibitors.

Secreted frizzled related protein-1 (sFRP-1) inhibitors have the potential to be used for the treatment of osteoporosis or other bone related disorders, since the level of sFRP-1 affects osteoblast apoptosis and proliferation. From high throughput screening, we have identified a class of iminooxothiazolidines as sFRP-1 inhibitors. Structure-activity relationships were established for various regions of the scaffold along with the biochemical characterization of this class to probe selectivity, binding and ex vivo activity.

A small molecule inhibitor of the Wnt antagonist secreted frizzled-related protein-1 stimulates bone formation.

Canonical Wnt signaling has been demonstrated to increase bone formation, and Wnt pathway components are being pursued as potential drug targets for osteoporosis and other metabolic bone diseases. Deletion of the Wnt antagonist secreted frizzled-related protein (sFRP)-1 in mice activates canonical signaling in bone and increases trabecular bone formation in aged animals. We have developed small molecules that bind to and inhibit sFRP-1 in vitro and demonstrate robust anabolic activity in an ex vivo organ culture assay. A library of over 440,000 drug-like compounds was screened for inhibitors of human sFRP-1 using a cell-based functional assay that measured activation of canonical Wnt signaling with an optimized T-cell factor (TCF)-luciferase reporter gene assay. One of the hits in this screen, a diarylsulfone sulfonamide, bound to sFRP-1 with a K(D) of 0.35 microM in a tryptophan fluorescence quenching assay. This compound also selectively inhibited sFRP-1 with an EC(50) of 3.9 microM in the cell-based functional assay. Optimization of this high throughput screening hit for binding and functional potency as well as metabolic stability and other pharmaceutical properties led to improved lead compounds. One of these leads (WAY-316606) bound to sFRP-1 with a K(D) of 0.08 microM and inhibited it with an EC(50) of 0.65 microM. Moreover, this compound increased total bone area in a murine calvarial organ culture assay at concentrations as low as 0.0001 microM. This work demonstrates the feasibility of developing small molecules that inhibit sFRP-1 and stimulate canonical Wnt signaling to increase bone formation.

Identification of diarylsulfone sulfonamides as secreted frizzled related protein-1 (sFRP-1) inhibitors.

Inhibitor of secreted frizzled related protein-1 (sFRP-1) would be a novel potential osteogenic agent, since loss of sFRP-1 affects osteoblast proliferation, differentiation, and activity, resulting in improved bone mineral density, quality, and strength. We have identified small molecule diarylsulfone sulfonamide derivatives as sFRP-1 inhibitors. Structure-activity relationship generated for various regions of the scaffold was utilized to improve the biochemical profile, resulting in the identification of potent selective analogues, such as 16 with desirable pharmaceutical profile.

The orphan receptor tyrosine kinase Ror2 promotes osteoblast differentiation and enhances ex vivo bone formation.

Ror2 is a receptor tyrosine kinase, the expression of which increases during differentiation of pluripotent stem cells to osteoblasts and then declines as cells progress to osteocytes. To test whether Ror2 plays a role in osteoblastogenesis, we investigated the effects of Ror2 overexpression and down-regulation on osteoblastic lineage commitment and differentiation. Expression of Ror2 in pluripotent human mesenchymal stem cells (hMSCs) by adenoviral infection caused formation of mineralized extracellular matrix, which is the ultimate phenotype of an osteogenic tissue. Concomitantly, Ror2 over-expression inhibited adipogenic differentiation of hMSCs as monitored by lipid formation. Ror2 shifted hMSC fate toward osteoblastogenesis by inducing osteogenic transcription factor osterix and suppressing adipogenic transcription factors CCAAT/enhancer-binding protein alpha and peroxisome proliferator activated receptor gamma. Infection with Ror2 virus also strongly promoted matrix mineralization in committed osteoblast-like MC3T3-E1 cells. Expression of Ror2 in a human preosteocytic cell line by stable transfection also promoted further differentiation, as judged by inhibited alkaline phosphatase activity, potentiated osteocalcin secretion, and increased cellular apoptosis. In contrast, down-regulation of Ror2 expression by short hairpin RNA essentially abrogated dexamethasone-induced mineralization of hMSCs. Furthermore, down-regulation of Ror2 expression in fully differentiated SaOS-2 osteosarcoma cells inhibited alkaline phosphatase activity. We conclude that Ror2 initiates commitment of MSCs to osteoblastic lineage and promotes differentiation at early and late stages of osteoblastogenesis. Finally, using a mouse calvariae ex vivo organ culture model, we demonstrate that these effects of Ror2 result in increased bone formation, suggesting that it may also activate mature osteoblasts.

Bone anabolic effects of parathyroid hormone are blunted by deletion of the Wnt antagonist secreted frizzled-related protein-1.

Secreted frizzled-related protein (sFRP)-1 is a Wnt antagonist that when deleted in mice leads to increased trabecular bone formation in adult animals after 13 weeks of age. Treatment of mice with parathyroid hormone (PTH) also increases trabecular bone formation, and some of the anabolic actions of this hormone may result from altered expression of Wnt pathway components. To test this hypothesis, we treated +/+ and -/- female sFRP-1 mice with PTH 1-34 for 30 days and measured distal femur trabecular bone parameters by peripheral quantitative computed tomography (pQCT) and high-resolution micro-computed tomography. During the course of the 32-week study, volumetric bone mineral density (vBMD) declined 41% in vehicle-treated +/+ mice, but increased 24% in vehicle-treated -/- animals. At 8 weeks of age when vBMD was not altered by deletion of sFRP-1, treatment of +/+ and -/- mice with PTH increased vBMD by 147 and 163%, respectively. In contrast, at 24 weeks of age when vBMD was 75% higher in -/- mice than in +/+ controls, treatment with PTH increased vBMD 164% in +/+ animals, but only 58% in -/- mice. Furthermore, at 36 weeks of age when vBMD was 117% higher in -/- mice than in +/+ controls, treatment with PTH increased vBMD 74% in +/+ animals, while no increase was observed in -/- mice. At each of these time points, PTH treatment increased vBMD to a similar level in +/+ and -/- mice, and this level declined with age. In addition, at 36 weeks of age, the vBMD level reached by PTH treatment of +/+ mice was the same as that achieved solely by deletion of sFRP-1. These results indicate that loss of sFRP-1 and PTH treatment increase vBMD to a similar extent. Moreover, as the effects of sFRP-1 deletion on vBMD increase, the ability of PTH to enhance vBMD declines suggesting that there are overlapping mechanisms of action.

The orphan receptor tyrosine kinase Ror2 modulates canonical Wnt signaling in osteoblastic cells.

Ror2 is an orphan receptor tyrosine kinase that plays crucial roles in developmental morphogenesis, particularly of the skeleton. We have identified human Ror2 as a novel regulator of canonical Wnt signaling in osteoblastic (bone-forming) cells with selective activities, enhancing Wnt1 but antagonizing Wnt3. Immunoprecipitation studies demonstrated physical interactions between human Ror2 and mammalian Wnt1 and Wnt3. Functionally, Ror2 antagonized Wnt1- and Wnt3-mediated stabilization of cytosolic beta-catenin in osteoblastic cells. However, Ror2 had opposing effects on a more distal step of canonical Wnt signaling: it potentiated Wnt1 activity but inhibited Wnt3 function as assessed by changes in Wnt-responsive reporter gene activity. Despite binding to Ror2, neither Wnt1 nor Wnt3 altered receptor activity as assessed by levels of Ror2 autophosphorylation. The ability of Ror2 to regulate canonical Wnt signaling in osteoblastic cells should have physiological consequences in bone, because Wnt signaling is known to modulate osteoblast survival and differentiation. Expression of Ror2 mRNA was highly regulated in a biphasic manner during human osteoblast differentiation, being virtually undetectable in pluripotent stem cells, increasing 300-fold in committed preosteoblasts, and disappearing again in osteocytes. Furthermore, Ror2 expression in osteoblasts was suppressed by the Wnt antagonist, secreted frizzled-related protein 1. The regulated expression of Ror2 during osteoblast differentiation, its inverse expression pattern with secreted frizzled-related protein 1, and its ability to modulate Wnt signaling in osteoblastic cells suggest that Ror2 may regulate bone formation.