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.

Emergence of the CD226 Axis in Cancer Immunotherapy

In recent years, a set of immune receptors that interact with members of the nectin/nectin-like (necl) family has garnered significant attention as possible points of manipulation in cancer. Central to this axis, CD226, TIGIT, and CD96 represent ligand (CD155)-competitive co-stimulatory/inhibitory receptors, analogous to the CTLA-4/B7/CD28 tripartite. The identification of PVRIG (CD112R) and CD112 has introduced complexity and enabled additional nodes of therapeutic intervention. By virtue of the clinical progression of TIGIT antagonists and emergence of novel CD96- and PVRIG-based approaches, our overall understanding of the ‘CD226 axis’ in cancer immunotherapy is starting to take shape. However, several questions remain regarding the unique characteristics of, and mechanistic interplay between, each receptor-ligand pair. This review provides an overview of the CD226 axis in the context of cancer, with a focus on the status of immunotherapeutic strategies (TIGIT, CD96, and PVRIG) and their underlying biology (i.e., cis/trans interactions). We also integrate our emerging knowledge of the immune populations involved, key considerations for Fc gamma (γ) receptor biology in therapeutic activity, and a snapshot of the rapidly evolving clinical landscape.

Abstract 6268: Discovery and characterization of the CD96 antibody GSK6097608, a high-affinity, antagonistic anti-CD96 antibody for cancer immunotherapy

The overall therapeutic benefit of blocking the first generation of immune checkpoint pathways (PD-1 and CTLA-4) has been demonstrated across multiple tumor types, yielding long term protection in some patients. However, most patients do not respond to these single-agent approaches. Thus, collaborative strategies that seek to engage novel pathways and cell types may provide therapeutic options for patients wherein pre-existing host and tumor microenvironment factors do not favor current immunotherapeutic agents or in tumors where adaptive resistance has occurred.

In recent years, the CD226 (DNAX Accessory Molecule-1 [DNAM-1]) axis has emerged as a relevant regulatory node in for natural killer (NK) and T cells - particularly in the context of tumor immunology. Similar to the competitive interplay between CTLA-4/CD28 and B7 (CD80/86), inhibitory receptors within the axis (e.g., CD96 [TACTILE]) effectively compete with the co-stimulatory receptor CD226 for binding to shared ligands (e.g., CD155), thereby impairing the initiation and/or promotion of ongoing antitumor immune responses. Indeed, genetic or monoclonal antibody (mAb)-based co-inhibition of CD96 with other immune checkpoints has proven efficacious in several nonclinical tumor models.

CD96 has been shown to impact both T cell and NK cell function, offering a level of versatility as a target for cancer immunotherapy. For example, in the setting of anti-PD-1 neoadjuvant treatment, significantly improved survival of pancreatic ductal adenocarcinoma (PDAC) tumor-bearing mice was observed following enhancement of NK cell activity by CD96 antibody treatment. Equally, pronounced effects on primary tumor growth following anti-PD-1, -TIGIT, and -CD96 mAb treatment in a colorectal carcinoma tumor model (CT26) was found to be dependent on CD8+ T cells.

GSK6097608 is a clinical-stage fully-human immunoglobulin G1 (IgG1)κ mAb that targets the inhibitory immune receptor CD96. GSK6097608 was identified, in part, for its ability prevent and disrupt CD96:CD155 interactions, thereby promoting T and NK cell function. GSK6097608 demonstrated concentration-dependent rescue of human immune cell activity following exposure to plate-bound recombinant CD155 (cognate receptor/ligand); an effect that was improved with concomitant TIGIT blockade. Notably, functional activity was found to be dependent on intact Fc-FcγR co-engagement, as potentiation of primary human T and NK cell function was lost when GSK6097608 was grafted on an Fc-attenuated backbone. Here, we describe some of the biophysical and functional characteristics that support the rationale for clinical evaluation of GSK6097608.

Citation Format: Yan Degenhardt, Jun Guan, Peter Morley, David Jones, Michael Conner, Stephen Eastman, Wei Wang, Andrew Sanderson, Anand Ravindran, Julie Krueger, Iris Roth, James Smothers, Jeremy D. Waight. Discovery and characterization of the CD96 antibody GSK6097608, a high-affinity, antagonistic anti-CD96 antibody for cancer immunotherapy [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 6268.

Multimodal single-cell analysis of human TILs across multiple tumor types reveals heterogeneity and potential opportunities for personalized immunotherapy

Immune checkpoint blockade (ICB) efficacy varies among tumor types likely due to differences in tumor infiltrating lymphocyte (TIL) composition and function within the tumor microenvironment (TME). To help understand these differences, we conducted multimodal single-cell analysis of TILs including single-cell RNA sequencing (scRNA-seq), CITE-seq (oligo-tagged antibodies), and scTCR-seq (10× Genomics) in (non-small cell lung cancer: NSCLC; head and neck squamous cell carcinoma: HNSCC; renal cell carcinoma: RCC; and breast cancer: BrCa; n=48). We found that regulatory T cell (Treg) frequency was higher in HNSCC, whereas exhausted T cells (Tex) were higher in NSCLC and RCC. In contrast to other tumor types, Tex in RCC lacked the expression of CD103, a hallmark of tissue-resident T cells. On the other hand, expression of PD-1, TIM-3, and LAG-3 were more prominent in Tex in RCC. Interestingly, Tex in HNSCC showed higher expression of TIGIT than other tumor types. Previous work has demonstrated an increased presence of CD4+CD8+ double-positive T cells (DPT) in RCC, which was associated with better overall survival. Therefore, we used CITE-seq to identify DPT and then compared the composition of DPT among different tumor types. DPT were CD39+, a marker for tumor-reactive T cells, and the vast majority were transcriptionally categorized as CD8+ T cells in RCC, whereas DPT in other tumor types are mixture of CD4+ or CD8+ T cell subsets. We also found overlap of TCR profiles between DPT and CD8+ T cell subsets (Tex, ZNF683-CD8, and GZMK-CD8) in RCC. Together, multimodal single-cell analysis of TILs highlighted heterogeneity among tumor types that may provide insight into novel strategies to treat cancer.

Supported by a research grant from GlaxoSmithKline and the Providence Portland Medical Foundation.

Supported by a research grant from GlaxoSmithKline and the Providence Portland Medical Foundation.

Immunological profiling of tumor-infiltrating CD8+ T lymphocytes in non-small cell lung cancer, head and neck squamous cell carcinoma, breast cancer, and renal cell cancer

To explore whether the variation in clinical response to immune checkpoint blockade (ICB) reflects intrinsic characteristics of tumor-infiltrating lymphocytes (TIL), TILs from multiple tumor types were analyzed by multiparameter flow cytometry. Recent work identified CD39+CD103+ double positive (DP) CD8 TIL as tumor-reactive, therefore we assessed this phenotype in primary NSCLC (n=28), BCa (n=23), HNSCC (n=23), and RCC (n=23) specimens. TILs from NSCLC and HNSCC had significantly higher frequencies of DP T cells than BCa and RCC (NSCLC: median=34.2, IQR=15.0–53.8%; HNSCC: median=28.6%, IQR=13.5–44.5%), while TILs from BCa and RCC had low frequencies of DP T cells (BCa: median=2.4%, IQR=1.1–3.9%; RCC: median=4.2%, IQR=1.5–16.6%). Additionally, DP cells in NSCLC and HNSCC were co-expressed immune checkpoint markers PD-1, TIM-3, and LAG-3 at a higher frequency than RCC or BCa (P<0.05). DP CD8 T cells in NSCLC and HNSCC also exhibited increased effector potential (granzyme B+) as compared to BCa and RCC, suggesting functional differences. Expression of the transcription factor Eomesodermin, associated with T cell exhaustion, was higher in effector CD8 T cells from RCC (median=84.5%, IQR=44.9–97.4%) as compared to NSCLC (median=28.7%, IQR=20.7–61.4%), BCa (median=30.1%, IQR=0–50%), and HNSCC (median=40.3%, IQR=20.1–61.2%). Additionally, 4-1BB, an indicator of TCR engagement, trended higher in RCC (mean=8.6%, IQR=1.4–46.7%) as compared to BCa (median=1.9%, IQR=0.4–8.6%). These data highlight the heterogeneity of human TILs isolated from distinct tumor types and provide insight into the basal expression of actionable therapeutic targets.

Supported by GlaxoSmithKline and the Providence Portland Medical Foundation

Response to anti-PD-1 and anti-LAG-3 immune checkpoint blockade is associated with induction of pro-inflammatory Tregs

Only a subset of patients durable clinical responses to aPD-1 and/or aCTLA-4 immunotherapies, thus, developing new therapeutic agents to increase the proportion of responding patients is a priority. Combining aPD-1 with aLAG-3 has shown promising results; however, lack of mechanistic understanding of aPD-1/aLAG-3 synergy remains a barrier for its optimal clinical use. Here, we examined the mechanism of aPD-1/aLAG-3 synergy in multiple mouse models using flow cytometry and single cell RNA sequencing. Combined aPD-1/aLAG-3 immunotherapy significantly improved the survival of CT26 (BALB/c; colon carcinoma) and MCA-205 (C57BL/6; sarcoma) tumor-bearing mice compared to monotherapy. Regulatory T cells (Tregs) suppressed response to this therapy, as in the absence of CD4+ T cells, 100% of mice responded. To understand how responders overcome Treg suppression, we performed an in-depth analysis of tumor-infiltrating lymphocytes (TIL) comparing mice that responded to treatment (decreased tumor size post-treatment) to non-responders (same tumor growth trajectory as control). Responders had reduced Foxp3+ CD4+ Tregs in comparison to non-responders and, in addition, those Tregs had a ‘fragile’ phenotype, including a pro-inflammatory cytokine profile (TNF-a; IFN-g), increased LAG-3, and decreased NRP1 expression. Within responders, CD8+ TIL exhibited increased frequency, effector cytokine production (TNF-a; IFN-g), and LAG-3 expression as compared to non-responders. Together, these data suggest that aPD-1/aLAG-3 can reduce Treg frequency and function leading to expansion of active tumor-specific CD8+ T cells capable of supporting tumor regression and improved survival.

Supported by the Providence Portland Medical Foundation and GlaxoSmithKline

662 Dissecting the CD226 immune axis in the tumor microenvironment using CyTOF-based high-dimensional immunophenotyping

Background

In recent years, a regulatory network involving nectin/nectin-like immune receptors has emerged as a potential point of manipulation for cancer immunotherapy. Central to this axis, CD226 (DNAM-1) is a T and NK cell co-stimulatory receptor that competes for ligand (CD155 and CD112) binding with multiple inhibitory receptors (TIGIT, CD96, and PVRIG [CD112R]). Despite a large body of literature for TIGIT, detailed cellular characterization of the entire axis is still lacking. Therefore, we used mass cytometry (CyTOF) to systematically evaluate expression of the CD226 axis in tumors from a range of indications.

Methods

To thoroughly characterize the CD226 axis in the tumor microenvironment, we immunophenotyped approximately 100 tumor samples derived from a variety of cancer types using a bespoke 46-parameter CyTOF panel. Human biological samples were sourced ethically and their research use was in accord with the terms of the informed consents under an IRB/EC approved protocol. Using a suite of high-dimensional analytical tools, including FlowSOM, UMAP, and tSNE, we revealed distinct expression profiles for each receptor; a finding that was previously obscured due to a lack of sufficient resolution.

Results

We observed a notable divergence in expression profiles between the CD226 axis members across tumor indications. For example, TIGIT expression was found to be highest on activated CD4+ regulatory T (Treg) cells, where its expression correlated strongly with ICOS, FoxP3, CD25, and CCR8. By contrast, CD96 and PVRIG exhibited broad expression across intratumoral T and NK cell populations. Other receptors (e.g., CD226) demonstrated variegated expression profiles across T and NK cell subsets. Finally, despite relatively consistent expression profiles of certain CD226 axis (i.e., TIGIT on Treg cells) across tumors, we also found several cell subsets/clusters unique to specific indications.

Conclusions

Using high-parameter CyTOF analysis, we were able to thoroughly characterize the CD226 axis (CD226, TIGIT, CD96, PVRIG) and related immune receptors across a range of tumor indications. These analyses revealed divergent expression profiles for each CD226 axis member, suggesting distinct/contextual biological role(s) for each receptor. However, future studies will need to dissect the importance of the distinct cellular representation for each CD226 axis member.

Ethics Approval

All samples were purchased from Discovery Life Sciences (DLS). DLS represents and warrants that it has ownership of all Products available for sale and has properly obtained, where required under HHS/OHRP 45 CFR 46.102 (d) (f), IRB approval (or appropriate research approval for institutions outside the U.S.) for study protocols and informed consent documents for all human subject derived biological materials.

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.

Anti-OX40 Antibody Directly Enhances The Function of Tumor-Reactive CD8+ T Cells and Synergizes with PI3Kβ Inhibition in PTEN Loss Melanoma

PURPOSE

OX40 agonist-based combinations are emerging as a novel avenue to improve the effectiveness of cancer immunotherapy. To better guide its clinical development, we characterized the role of the OX40 pathway in tumor-reactive immune cells. We also evaluated combining OX40 agonists with targeted therapy to combat resistance to cancer immunotherapy.Experimental Design: We utilized patient-derived tumor-infiltrating lymphocytes (TILs) and multiple preclinical models to determine the direct effect of anti-OX40 agonistic antibodies on tumor-reactive CD8⁺ T cells. We also evaluated the antitumor activity of an anti-OX40 antibody plus PI3Kβ inhibition in a transgenic murine melanoma model (Braf mutant, PTEN null), which spontaneously develops immunotherapy-resistant melanomas.

RESULTS

We observed elevated expression of OX40 in tumor-reactive CD8⁺ TILs upon encountering tumors; activation of OX40 signaling enhanced their cytotoxic function. OX40 agonist antibody improved the antitumor activity of CD8⁺ T cells and the generation of tumor-specific T-cell memory in vivo. Furthermore, combining anti-OX40 with GSK2636771, a PI3Kβ-selective inhibitor, delayed tumor growth and extended the survival of mice with PTEN-null melanomas. This combination treatment did not increase the number of TILs, but it instead significantly enhanced proliferation of CD8⁺ TILs and elevated the serum levels of CCL4, CXCL10, and IFNγ, which are mainly produced by memory and/or effector T cells.

CONCLUSIONS

These results highlight a critical role of OX40 activation in potentiating the effector function of tumor-reactive CD8⁺ T cells and suggest further evaluation of OX40 agonist-based combinations in patients with immune-resistant tumors.

Author Correction: Design of amidobenzimidazole STING receptor agonists with systemic activity

Change history: In this Letter, author Ana Puhl was inadvertently omitted; this error has been corrected online.An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Abstract A054: In vivo characterization of Ipilimumab T cell modulation and antitumor activity in a tumor bearing humanized NSG mouse model

The purpose of these studies was to determine the effect of Ipilimumab treatment on T cell expansion, activation, cytokine production, tumor infiltration, and expression level of co-stimulatory and co-inhibitory receptors in a tumor bearing humanized NSG mouse model. Antibody therapies for immune modulation are proving to be effective in the oncology setting, as demonstrated by anti-CTLA-4 Ipilimumab and anti-PD-1 Pembrolizumab clinical activity. In order to assess efficacy of new therapies in the context of immune activation and tumor response, there is a need for suitable preclinical in vivo models. One approach to study immune cell function is to inject human peripheral blood mononuclear cells (PBMCs) into adult immunodeficient NSG (NOD/SCID/IL-2Rγnull) mice. This model, known as Hu-PBMC NSG, induces a Graft-versus-Host Disease (GvHD) state and has been used to study effector and memory T cell activity. Here we utilized the Hu-PBMC NSG model implanted with human cancer cell lines to investigate the effect of Ipilimumab on T cells and tumor growth in vivo. All studies were conducted in accordance with the GSK Policy on the Care, Welfare and Treatment of Laboratory Animals and were reviewed the Institutional Animal Care and Use Committee at GSK. The human biological samples were sourced ethically and their research use was in accord with the terms of the informed consents. We confirmed human PBMC engraftment in NSG mice, validated tumor growth of human A2058 melanoma and 786-O renal adenocarcinoma cell lines, and dosed Ipilimumab in tumor bearing NSG mice with different human PBMC donors. Naïve NSG mice were intravenously injected with 20x106 human PBMCs and the kinetics of human cell engraftment was monitored weekly. For studies including Ipilimumab dosing, mice were inoculated with a subcutaneous injection of 2.5x106 A2058 or 1x106 786-O tumor cells. As tumor size reached 100 mm3, mice were randomized and injected with 20x106 human PBMCs. Two days later, mice were intraperitoneally treated with Ipilimumab or human IgG1 isotype control twice weekly for 6 doses total. Tumor growth and body weight was evaluated over time. Peripheral blood was collected weekly for analysis of T cell activation, receptor expression levels, and human cytokine production until mice developed GvHD or tumor volume reached 2,000 mm3. Select tumors were also harvested for tumor infiltrating lymphocyte (TIL) analysis by flow cytometry. Our studies showed NSG mice demonstrated similar human CD45+ cell engraftment in blood with various PBMC donors. The frequency of circulating human CD45+ lymphocytes in mouse peripheral blood increased to 50% or greater until week 4. 95% of the CD45+ cells were CD3+ T cells, containing both CD4+ and CD8+ subsets. Signs of GvHD were observed at week 4, and serum cytokine analysis showed high levels of GvHD markers e.g. IL5, IL10, and TNF-alpha. Ipilimumab treatment delayed tumor growth, increased the expansion of human CD45+ cells, and induced higher levels of TNF-alpha, IL-12p70, IL-13, and IL-5 cytokines compared to isotype control. Ipilimumab also increased the surface expression level of CD69, PD-1, OX40, ICOS, CD137, TIM3, and LAG3 on circulating T cells, and increased the number of A2058 tumor infiltrating lymphocytes. TIL analysis showed that compared to isotype control, Ipilimumab increased expression of CD69, PD-1, OX40, and ICOS on tumor infiltrating lymphocytes. In conclusion, Ipilimumab treatment increased T cell expansion, activation, expression of co-stimulatory and co-inhibitory receptors, and cytokine production in this tumor-bearing Hu-PBMC NSG model. It also increased the number of tumor infiltrating lymphocytes with a corresponding tumor growth delay. Based on Ipilimumab activity, this model can be utilized to assess pre-clinical efficacy of novel immunotherapies.

Citation Format: Meixia Bi, Chris Hopson, Tianqian Zhang, James Smothers, Axel Hoos. In vivo characterization of Ipilimumab T cell modulation and antitumor activity in a tumor bearing humanized NSG mouse model. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A054.

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.

Abstract 5031: Effects of BRAF and MEK inhibitors, dabrafenib and trametinib, on the immune system and in combination with immunomodulatory antibodies targeting PD1, PD-L1 and CTLA-4

The immunological effects of dabrafenib and trametinib and whether they potentiate or antagonize the activity of immunomodulatory antibodies are not well understood. We assessed the immunological effects of dabrafenib and trametinib at clinically relevant exposure concentrations on both immune and tumor cells in vitro and in vivo, and tested their anti-tumor efficacy in combination with immunomodulatory antibodies in immune-competent syngeneic mouse models. Human CD4+ and CD8+ T cells isolated from healthy volunteers were treated with trametinib and dabrafenib either alone or in combination, and with or without anti-CD3/anti-CD28 bead activation (concurrently or sequentially). Dabrafenib alone enhanced pERK expression levels with no changes of pAKT and pS6 proteins, and had no suppressive impact on human CD4+ or CD8+ T cell proliferation, apoptosis and cytokine production in response to T cell activation. Trametinib alone reduced the pERK levels with no changes in pAKT and apoptosis. However trametinib resulted in partial inhibitory effects on T cell proliferation, pS6 proteins and cytokine expression. These inhibitory effects were transient and only observed if cells were treated with trametinib prior to or simultaneously with T cell activation, while trametinib had little or no suppressive effects on activated T cells. Adding dabrafenib partially offset the transient inhibitory effects caused by trametinib alone. Similarly, gene expression profiling showed that trametinib partially decreased the expression levels of a subset of cytokines and chemokines (e.g. IL1, IL2, IL8, IL10, TNFa, CCL2) and activation/regulation markers (e.g. CD69, CD25, PD1, CTLA4) when trametinib was added prior to or simultaneously with T cell activators. Multi-color flow cytometry confirmed cell surface changes in the expression of CD69, CD25, PD1, OX40 and CTLA4. However, the expression levels of CD69 and OX40 were still well above non-activated T cells. On tumor cells, dabrafenib and trametinib up-regulated HLA molecules and melanoma antigen MART1 expression, and down regulated immune-suppressive factors such as PD-L1, VEGF and IL8 etc in BRAFV600E melanoma cells. Combinations of trametinib with immunomodulators targeting PD1, PD-L1 or CTLA4 in murine syngeneic tumor models are underway and will be presented at the meeting. These findings to date support clinical exploration of dabrafenib and/or trametinib in combination with specific immunomodulatory antibodies.

Citation Format: Li Liu, Patrick Mayes, Stephen Eastman, Hong Shi, Sapna Yadavilli, Xiaoyu Pan, Jingsong Yang, Laura Seestaller-Wehr, Shu-Yun Zhang, Chris Hopson, Lyuben Tsvetkov, Junping Jing, James Smothers, Drew M. Pardoll, Axel Hoos. Effects of BRAF and MEK inhibitors, dabrafenib and trametinib, on the immune system and in combination with immunomodulatory antibodies targeting PD1, PD-L1 and CTLA-4. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5031. doi:10.1158/1538-7445.AM2014-5031

Abstract 644: Novel anti-B cell maturation antigen-monomethyl auristatin F antibody-drug conjugate (GSK2857916) induces potent and selective anti-multiple myeloma activity via enhanced effector function and direct tumor cell killing

B cell maturation antigen (BCMA), highly expressed on malignant plasma cells in human multiple myeloma (MM), has not been effectively targeted with therapeutic monoclonal antibodies (mAbs). We here investigated the anti-MM activity of J6M0-mcMMAF (GSK2857916), a humanized and afucosylated anti-BCMA antibody-drug conjugate (ADC) via uncleavable linker. This novel antagonist anti-BCMA antibody shows binding against all CD138-expressing MM cell lines and patient MM cells, confirming universal BCMA expression on the surface of myeloma cells. Real-time qRT-PCR also showed significantly upregulated BCMA mRNA in CD138+ cells purified from MM patients vs. normal donors (p < 0.03). In contrast, BCMA is undetectable in CD138-negative cells from MM patients. J6M0-mcMMAF inhibits cell growth and induces caspase 3-dependent apoptosis in both drug-sensitive and -resistant MM cell lines and patient CD138+ MM cells, alone and in co-culture with BMSCs. It strongly blocks colony formation of MM cell lines (ED50 ∼6-70 ng/ml) via induction of G2/M arrest, followed by apoptosis. This ADC does not affect viability of BCMA-negative NK, PBMC, and BMSCs, cultured alone or together, confirming its specific targeting of BCMA-positive MM cells. J6M0-mcMMAF, which has enhanced Fc-receptor binding due to afucosylation, significantly improved autologous antibody-dependent cellular cytotoxicity (ADCC) potency and maximum MM cell lysis against MM patient cells (n=5), when compared to J6M0 with normal Fc. The in vivo efficacy of J6M0-mcMMAF was evaluated in murine subcutaneous xenograft models using NCI-H929 and OPM2 cells, as well as in NK-deficient SCID-beige mice with diffuse human MM bone lesions using MM1Sluc cells. Administration of J6M0-mcMMAF at 4 mg/kg (q3d x 4, ip) completely eliminated NCI-H929 and OPM2 xenograft tumors in all mice which remained tumor-free until the termination of studies at 60 and 100 days, respectively. In the MM1Sluc bone marrow dissemination model, J6M0-mcMMAF eradicates detectable tumors after 2 doses at 0.4 mg/kg (q3d x 9, ip), which resulted in extended survival (p<0.0001) and no weight loss of mice following 120 days. J6M0 treatment, although less effective than J6M0-mcMMAF, also had significantly prolonged survival (p<0.03) and diminished tumor burden when compared with control vehicle and isotype-treated groups, indicating a potential role of macrophage-mediated phagocytosis. Indeed, J6M0-mcMMAF recruits macrophage and mediates phagocytosis of target MM cells. Taken together, our studies show that J6M0-mcMMAF potently and selectively induce direct and indirect killing of MM tumor cells both in vitro and in vivo, providing a very promising next-generation immunotherapeutic in this cancer.

Note: This abstract was not presented at the meeting.

Citation Format: Yu-Tzu Tai, Chirag Acharya, Mike Y. Zhong, Michele Cea, Antonia Cagnetta, Patrick A. Mayes, Jenny Craigen, Louise Gliddon, James Smothers, Amanda L. Christie, Andrew L. Kung, Paul Richardson, Nikhil C. Munshi, Kenneth C. Anderson. Novel anti-B cell maturation antigen-monomethyl auristatin F antibody-drug conjugate (GSK2857916) induces potent and selective anti-multiple myeloma activity via enhanced effector function and direct tumor cell killing. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 644. doi:10.1158/1538-7445.AM2014-644