Stefanie Mullins

Identification and Characterization of MEDI4736, an Antagonistic Anti–PD-L1 Monoclonal Antibody

A human antibody to PD-L1, engineered to eliminate Fc effector functions, which potently inhibits PD-L1 function, is in phase III clinical trials. Its characterization here provides clinicians and researchers with a basis for understanding and interpreting clinical trial results. Programmed cell-death 1 ligand 1 (PD-L1) is a member of the B7/CD28 family of proteins that control T-cell activation. Many tumors can upregulate expression of PD-L1, inhibiting antitumor T-cell responses and avoiding immune surveillance and elimination. We have identified and characterized MEDI4736, a human IgG1 monoclonal antibody that binds with high affinity and specificity to PD-L1 and is uniquely engineered to prevent antibody-dependent cell-mediated cytotoxicity. In vitro assays demonstrate that MEDI4736 is a potent antagonist of PD-L1 function, blocking interaction with PD-1 and CD80 to overcome inhibition of primary human T-cell activation. In vivo MEDI4736 significantly inhibits the growth of human tumors in a novel xenograft model containing coimplanted human T cells. This activity is entirely dependent on the presence of transplanted T cells, supporting the immunological mechanism of action for MEDI4736. To further determine the utility of PD-L1 blockade, an anti-mouse PD-L1 antibody was investigated in immunocompetent mice. Here, anti-mouse PD-L1 significantly improved survival of mice implanted with CT26 colorectal cancer cells. The antitumor activity of anti–PD-L1 was enhanced by combination with oxaliplatin, which resulted in increased release of HMGB1 within CT26 tumors. Taken together, our results demonstrate that inhibition of PD-L1 function can have potent antitumor activity when used as monotherapy or in combination in preclinical models, and suggest it may be a promising therapeutic approach for the treatment of cancer. MEDI4736 is currently in several clinical trials both alone and in combination with other agents, including anti–CTLA-4, anti–PD-1, and inhibitors of IDO, MEK, BRAF, and EGFR. Cancer Immunol Res; 3(9); 1052–62. ©2015 AACR.

Rational selection of syngeneic preclinical tumor models for immunotherapeutic drug discovery

Murine syngeneic tumor models are used to study responses to antitumor immunotherapies. To rationalize model selection, the underlying genetic and immunologic biology of the models was analyzed, allowing parallels to be drawn between models and human disease phenotypes. Murine syngeneic tumor models are critical to novel immuno-based therapy development, but the molecular and immunologic features of these models are still not clearly defined. The translational relevance of differences between the models is not fully understood, impeding appropriate preclinical model selection for target validation, and ultimately hindering drug development. Across a panel of commonly used murine syngeneic tumor models, we showed variable responsiveness to immunotherapies. We used array comparative genomic hybridization, whole-exome sequencing, exon microarray analysis, and flow cytometry to extensively characterize these models, which revealed striking differences that may underlie these contrasting response profiles. We identified strong differential gene expression in immune-related pathways and changes in immune cell–specific genes that suggested differences in tumor immune infiltrates between models. Further investigation using flow cytometry showed differences in both the composition and magnitude of the tumor immune infiltrates, identifying models that harbor “inflamed” and “non-inflamed” tumor immune infiltrate phenotypes. We also found that immunosuppressive cell types predominated in syngeneic mouse tumor models that did not respond to immune-checkpoint blockade, whereas cytotoxic effector immune cells were enriched in responsive models. A cytotoxic cell–rich tumor immune infiltrate has been correlated with increased efficacy of immunotherapies in the clinic, and these differences could underlie the varying response profiles to immunotherapy between the syngeneic models. This characterization highlighted the importance of extensive profiling and will enable investigators to select appropriate models to interrogate the activity of immunotherapies as well as combinations with targeted therapies in vivo. Cancer Immunol Res; 5(1); 29–41. ©2016 AACR.

Transformation of the tumour microenvironment by a CD40 agonist antibody correlates with improved responses to PD-L1 blockade in a mouse orthotopic pancreatic tumour model.

Despite the availability of recently developed chemotherapy regimens, survival times for pancreatic cancer patients remain poor. These patients also respond poorly to immune checkpoint blockade therapies (anti-CTLA-4, anti-PD-L1, anti-PD-1), which suggests the presence of additional immunosuppressive mechanisms in the pancreatic tumour microenvironment (TME). CD40 agonist antibodies (αCD40) promote antigen presenting cell (APC) maturation and enhance macrophage tumouricidal activity, and may therefore alter the pancreatic TME to increase sensitivity to immune checkpoint blockade. Here, we test whether αCD40 transforms the TME in a mouse syngeneic orthotopic model of pancreatic cancer, to increase sensitivity to PD-L1 blockade. We found that whilst mice bearing orthotopic Pan02 tumours responded poorly to PD-L1 blockade, αCD40 improved overall survival. αCD40 transformed the TME, upregulating Th1 chemokines, increasing cytotoxic T cell infiltration and promoting formation of an immune cell-rich capsule separating the tumour from the normal pancreas. Furthermore, αCD40 drove systemic APC maturation, memory T cell expansion, and upregulated tumour and systemic PD-L1 expression. Combining αCD40 with PD-L1 blockade enhanced anti-tumour immunity and improved overall survival versus either monotherapy. These data provide further support for the potential of combining αCD40 with immune checkpoint blockade to promote anti-tumour immunity in pancreatic cancer.

A Novel Murine GITR Ligand Fusion Protein Induces Antitumor Activity as a Monotherapy That Is Further Enhanced in Combination with an OX40 Agonist

Purpose: To generate and characterize a murine GITR ligand fusion protein (mGITRL-FP) designed to maximize valency and the potential to agonize the GITR receptor for cancer immunotherapy. Experimental Design: The EC50 value of the mGITRL-FP was compared with an anti-GITR antibody in an in vitro agonistic cell–based reporter assay. We assessed the impact of dose, schedule, and Fc isotype on antitumor activity and T-cell modulation in the CT26 tumor model. The activity of the mGITRL-FP was compared with an agonistic murine OX40L-FP targeting OX40, in CT26 and B16F10-Luc2 tumor models. Combination of the mGITRL-FP with antibodies targeting PD-L1, PD-1, or CTLA-4 was analyzed in mice bearing CT26 tumors. Results: The mGITRL-FP had an almost 50-fold higher EC50 value compared with an anti-murine GITR antibody. Treatment of CT26 tumor-bearing mice with mGITRL-FP–mediated significant antitumor activity that was dependent on isotype, dose, and duration of exposure. The antitumor activity could be correlated with the increased proliferation of peripheral CD8+ and CD4+ T cells and a significant decrease in the frequency of intratumoral Tregs. The combination of mGITRL-FP with mOX40L-FP or checkpoint inhibitor antagonists enhanced antitumor immunity above that of monotherapy treatment. Conclusions: These results suggest that therapeutically targeting GITR represents a unique approach to cancer immunotherapy and suggests that a multimeric fusion protein may provide increased agonistic potential versus an antibody. In addition, these data provide, for the first time, early proof of concept for the potential combination of GITR targeting agents with OX40 agonists and PD-L1 antagonists. Clin Cancer Res; 23(13); 3416–27. ©2017 AACR.

The MEK inhibitor selumetinib complements CTLA-4 blockade by reprogramming the tumor immune microenvironment

Background T-cell checkpoint blockade and MEK inhibitor combinations are under clinical investigation. Despite progress elucidating the immuno-modulatory effects of MEK inhibitors as standalone therapies, the impact of MEK inhibition on the activity of T-cell checkpoint inhibitors remains incompletely understood. Here we sought to characterize the combined effects of MEK inhibition and anti-CTLA-4 mAb (anti-CTLA-4) therapy, examining effects on both T-cells and tumor microenvironment (TME). Methods In mice, the effects of MEK inhibition, via selumetinib, and anti-CTLA-4 on immune responses to keyhole limpet haemocyanin (KLH) immunization were monitored using ex vivo functional assays with splenocytes. In a KRAS-mutant CT26 mouse colorectal cancer model, the impact on the tumor microenvironment (TME) and the spleen were evaluated by flow cytometry. The TME was further examined by gene expression and immunohistochemical analyses. The combination and sequencing of selumetinib and anti-CTLA-4 were also evaluated in efficacy studies using the CT26 mouse syngeneic model. Results Anti-CTLA-4 enhanced the generation of KLH specific immunity following KLH immunization in vivo; selumetinib was found to reduce, but did not prevent, this enhancement of immune response by anti-CTLA-4 in vivo. In the CT26 mouse model, anti-CTLA-4 treatment led to higher expression levels of the immunosuppressive mediators, Cox-2 and Arg1 in the TME. Combination of anti-CTLA-4 with selumetinib negated this up-regulation of Cox-2 and Arg1, reduced the frequency of CD11+ Ly6G+ myeloid cells, and led to the accumulation of differentiating monocytes at the Ly6C+ MHC+ intermediate state in the tumor. We also report that MEK inhibition had limited impact on anti-CTLA-4-mediated increases in T-cell infiltration and T-cell activation in CT26 tumors. Finally, we show that pre-treatment, but not concurrent treatment, with selumetinib enhanced the anti-tumor activity of anti-CTLA-4 in the CT26 model. Conclusion These data provide evidence that MEK inhibition can lead to changes in myeloid cells and immunosuppressive factors in the tumor, thus potentially conditioning the TME to facilitate improved response to anti-CTLA-4 treatment. In summary, the use of MEK inhibitors to alter the TME as an approach to enhance the activities of immune checkpoint inhibitors warrants further investigation in clinical trials. Electronic supplementary material The online version of this article (doi:10.1186/s40425-017-0268-8) contains supplementary material, which is available to authorized users.BackgroundT-cell checkpoint blockade and MEK inhibitor combinations are under clinical investigation. Despite progress elucidating the immuno-modulatory effects of MEK inhibitors as standalone therapies, the impact of MEK inhibition on the activity of T-cell checkpoint inhibitors remains incompletely understood. Here we sought to characterize the combined effects of MEK inhibition and anti-CTLA-4 mAb (anti-CTLA-4) therapy, examining effects on both T-cells and tumor microenvironment (TME).MethodsIn mice, the effects of MEK inhibition, via selumetinib, and anti-CTLA-4 on immune responses to keyhole limpet haemocyanin (KLH) immunization were monitored using ex vivo functional assays with splenocytes. In a KRAS-mutant CT26 mouse colorectal cancer model, the impact on the tumor microenvironment (TME) and the spleen were evaluated by flow cytometry. The TME was further examined by gene expression and immunohistochemical analyses. The combination and sequencing of selumetinib and anti-CTLA-4 were also evaluated in efficacy studies using the CT26 mouse syngeneic model.ResultsAnti-CTLA-4 enhanced the generation of KLH specific immunity following KLH immunization in vivo; selumetinib was found to reduce, but did not prevent, this enhancement of immune response by anti-CTLA-4 in vivo. In the CT26 mouse model, anti-CTLA-4 treatment led to higher expression levels of the immunosuppressive mediators, Cox-2 and Arg1 in the TME. Combination of anti-CTLA-4 with selumetinib negated this up-regulation of Cox-2 and Arg1, reduced the frequency of CD11+ Ly6G+ myeloid cells, and led to the accumulation of differentiating monocytes at the Ly6C+ MHC+ intermediate state in the tumor. We also report that MEK inhibition had limited impact on anti-CTLA-4-mediated increases in T-cell infiltration and T-cell activation in CT26 tumors. Finally, we show that pre-treatment, but not concurrent treatment, with selumetinib enhanced the anti-tumor activity of anti-CTLA-4 in the CT26 model.ConclusionThese data provide evidence that MEK inhibition can lead to changes in myeloid cells and immunosuppressive factors in the tumor, thus potentially conditioning the TME to facilitate improved response to anti-CTLA-4 treatment. In summary, the use of MEK inhibitors to alter the TME as an approach to enhance the activities of immune checkpoint inhibitors warrants further investigation in clinical trials.

Optoacoustic detection of early therapy-induced tumor cell death using a targeted imaging agent

Purpose: The development of new treatments and their deployment in the clinic may be assisted by imaging methods that allow an early assessment of treatment response in individual patients. The C2A domain of Synaptotagmin-I (C2Am), which binds to the phosphatidylserine (PS) exposed by apoptotic and necrotic cells, has been developed as an imaging probe for detecting cell death. Multispectral optoacoustic tomography (MSOT) is a real-time and clinically applicable imaging modality that was used here with a near infrared (NIR) fluorophore-labeled C2Am to image tumor cell death in mice treated with a TNF-related apoptosis-inducing ligand receptor 2 (TRAILR2) agonist and with 5-fluorouracil (5-FU). Experimental Design: C2Am was labeled with a NIR fluorophore and injected intravenously into mice bearing human colorectal TRAIL-sensitive Colo205 and TRAIL-resistant HT-29 xenografts that had been treated with a potent agonist of TRAILR2 and in Colo205 tumors treated with 5-FU. Results: Three-dimensional (3D) MSOT images of probe distribution showed development of tumor contrast within 3 hours of probe administration and a signal-to-background ratio in regions containing dead cells of >10 after 24 hours. A site-directed mutant of C2Am that is inactive in PS binding showed negligible binding. Tumor retention of the active probe was strongly correlated (R2 = 0.97, P value < 0.01) with a marker of apoptotic cell death measured in histologic sections obtained post mortem. Conclusions: The rapid development of relatively high levels of contrast suggests that NIR fluorophore-labeled C2Am could be a useful optoacoustic imaging probe for detecting early therapy-induced tumor cell death in the clinic. Clin Cancer Res; 23(22); 6893–903. ©2017 AACR.

Abstract 1475: Local immune activation resulting in tumor growth inhibition with MEDI9197 - an intratumorally administered TLR7/8 agonist

MEDI9197 (formerly 3M-052) is a sustained-release imidazoquinoline toll like receptor (TLR) TLR7/8 agonist designed with a lipid tail that, when injected, is retained within the tumor. This has been shown in pharmacokinetic studies in mice and rats injected with MEDI9197 via the subcutaneous (SC) or intratumoral (IT, mouse only) routes. Stimulation of TLR7 and TLR8 in primary human dendritic cells induces the release of interferon-alpha (IFN-a) from plasmacytoid dendritic cells (pDCs) and interleukin 12 (IL-12) from myeloid dendritic cells (mDCs). Intratumoral administration of MEDI9197 induces a local immune response characterized by upregulation of genes involved in activation of innate and adaptive immunity both from the injected tumor and tumor draining lymph node. Furthermore, flow cytometric analysis of tumor infiltrating lymphocytes (TILs) show increased expression of activation markers, such as CD69, on natural killer (NK) cells and CD8 cytotoxic T cells. This local stimulation of immune cells with MEDI9197 results in tumor growth inhibition as shown in the B16F10 luc syngeneic mouse tumor model using in vivo imaging system (IVIS) equipment. Additionally, combination of MEDI9197 with immune checkpoint inhibitors enhances the efficacy observed in syngeneic mouse tumor models. The data presented shows intratumoral administration of MEDI9197 induces local immune activation leading to tumor growth inhibition in preclinical models of cancer. MEDI9197 is currently being evaluated as a monotherapy for safety and efficacy in human clinical trials. Citation Format: Stefanie Mullins, Iwen Grigsby, Lester I. Harrison, Song Ren, Serguei Soukharev, Lesley Young, James M. Elvecrog, Robert W. Wilkinson, Mark A. Tomai, Ronald Herbst, John P. Vasilakos, Andrew J. Leishman. Local immune activation resulting in tumor growth inhibition with MEDI9197 - an intratumorally administered TLR7/8 agonist. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1475.

Abstract 4697: Intratumoral immunotherapy with TLR7/8 agonist MEDI9197 modulates the tumor microenvironment and holds potential for combination with immune checkpoint inhibitors

Recent successes in immuno-oncology have focussed primarily on the T-cell synapse, targeting co-activatory /inhibitory pathways to modulate T cell function. However, strategies that target tumor-resident myeloid cells may be required to fully exploit the therapeutic potential of the anti-cancer immune response. TOLL-like receptors (TLRs) are expressed on a broad range of myeloid cells and function to recognise highly evolutionarily conserved pathogen-associated molecular patterns. Signalling through TLRs leads to the activation of antigen-presenting cells (APCs) and to expression of inflammatory cytokines. However, whilst topical application of TLR agonists have proved successful in the treatment of dermatological tumors, systemic administration have proved to be poorly tolerated. MEDI9197 (formerly 3M-052), is a novel lipophilic TLR7/8 agonist designed with a lipid tail to facilitate retention at the site of injection, limiting systemic exposure. These properties make MEDI9197 ideal for intratumoral (IT) administration. We have demonstrated that MEDI9197 is a potent TLR7 and TLR8 agonist and induces pro-inflammatory cytokines through activation of a diverse range of myeloid and lymphoid cells. In mice bearing established tumors, IT injection of MEDI9197 induces a local inflammatory response, characterized by upregulation of genes associated with the activation of innate and adaptive immunity in the injected tumor and tumor draining lymph nodes. Moreover, treatment leads to an increase in the frequency of tumor infiltrating lymphocytes (TILs), such as CD8+ cytotoxic T cells and increased expression of activation markers, such as CD69. Cellular depletion studies reveal that CD8+ T cells are required for therapeutic activity. Furthermore, using in vitro co-cultures we demonstrate that MEDI9197 is able to enhance cytotoxic activity of NK cell and T cells. Importantly, in models that respond poorly to mAbs targeting either PD-L1 or CTLA-4, combination with MEDI9197 significantly improved anti-tumor activity when compared to either monotherapy alone. These preclinical data demonstrate that MEDI9197 can modulate both the myeloid and lymphoid immune compartments to mediate anti-tumor activity and combines productively with immune checkpoint blockade. MEDI9197 is currently being evaluated as a monotherapy for safety and efficacy in human clinical trials (NCT02556463). Citation Format: Stefanie R. Mullins, Katharina Vogel, John Vasilakos, Iwen Grigsby, Simon Dovedi, Ryan Patricia, Zachary Cooper, Ronald Herbst, Rakesh Kumar, Mark Tomai, Robert W. Wilkinson. Intratumoral immunotherapy with TLR7/8 agonist MEDI9197 modulates the tumor microenvironment and holds potential for combination with immune checkpoint inhibitors [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 4697. doi:10.1158/1538-7445.AM2017-4697

Abstract 4203: Non-invasive imaging of tumor cell death induced by a TRAILR2 agonist

Imaging tumour cell death can give an early indication of treatment efficacy. Tumour necrosis factor (TNF)-related apoptosis-inducing ligand receptor2 (TRAILR2) is a member of the TNF receptor superfamily, which interacts with death receptors (DRs) and induces apoptosis in a broad range of cancer cells but not normal cells[1]. MEDI3039, a newly described agonist of TRAILR2, was used to induce tumour cell death. A NIRF fluorophore-labelled phosphatidylserine (PS)-binding protein (∼15kDa), the C2A domain of Synaptotagmin-I (C2Am-750), which binds to the PS exposed by apoptotic and necrotic cells, was used to image MEDI3039-induced cell death[2]. Non-specific binding was assessed using a site-directed mutant that is inactive in PS binding, which was conjugated to a different fluorophore (iC2Am-680). Binding of C2Am-750 to MEDI3039-treated human colon and breast adenocarcinoma cells in vitro (Colo205 and MDA-Dual respectively) was assessed by flow cytometry and confocal microscopy. Both methods showed that C2Am-750 labelled MEDI3039-treated Colo205 cells, while the inactive iC2Am-680 showed only low non-specific binding. C2Am-750 and iC2Am-680 were also used to monitor the effect of treatment in a Colo205 xenograft model. One cohort of mice (n = 5) received a single dose of MEDI3039 (0.4 mg/kg), while another untreated cohort (n = 5) served as a control group. All mice received a single i.v. injection of a 1:1 mixture of 0.1 μmole/kg C2Am-750 and iC2Am-680 at 16 h after drug treatment, followed by whole body fluorescence imaging (FLI) measurements using an IVIS200 camera at 0 and 3 h post probe injection. FLI measurements in MEDI3039-treated Colo205 tumours showed significant increases in the uptake of C2Am-750 relative to iC2Am-680, both in vivo (4-9 fold, P value NIRF fluorophore-labelled C2Am showed a favourable biodistribution profile, with good tumour penetration and quick clearance of unbound material in vivo. The probe can be used to investigate the efficacy of targeted therapy, or other anti-tumour therapies, at an early stage following treatment. 1. Prasad, S., Kim, J.H., Gupta, S.C. & Aggarwal, B.B. Targeting death receptors for TRAIL by agents designed by Mother Nature. Trends in pharmacological sciences 35, 520-536 (2014). 2. Alam, I.S., Neves, A.A., Witney, T.H., Boren, J. & Brindle, K.M. Comparison of the C2A domain of synaptotagmin-I and annexin-V as probes for detecting cell death. Bioconjugate chemistry 21, 884-891 (2010). Citation Format: Bangwen Xie, Andre Neves, Stefanie R. Mullins, David Tice, Danielle Carroll, Robert W. Wilkinson, Kevin M. Brindle. Non-invasive imaging of tumor cell death induced by a TRAILR2 agonist. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4203.

Abstract 270: Preclinical assessment of combination therapy with selumetinib and CTLA-4 for cancer

Immune mediated therapies for Cancer (IMT-C), such as anti-CTLA-4 and anti-PD-1/PD-L1 monoclonal antibodies (mAb), are showing promise in the treatment of solid tumors. However, although these treatments demonstrate clinical activity in a range of tumors, the durable benefit of these agents appears to be limited to a subset of patients. One hypothesis is that activity in these patients is limited by a lack of immune priming or by additional immunosuppressive pathways. Combination with molecular targeted therapies offers the potential to explore additional treatment strategies for patients. However, in order to select the best combination partners, a greater understanding is needed as to how each therapy affects the immune system both directly, through effects on leukocytes, and indirectly, through effects on tumor immunogenicity and the microenvironment. Selumetinib is a potent inhibitor of the mitogen-activated protein kinase (MAPK) kinase 1/2 (MEK1/2), involved in the activation of signaling pathways which regulates cellular growth, proliferation and survival. Given that these pathways are often found aberrantly activated in human tumors, and also play key roles in the regulation of immunological processes, it is difficult to predict the combinatorial effect of MEK1/2 inhibition and IMT in cancer treatment. To assess the effect of selumetinib in a tumor model with an intact immune system, we have characterized the impact of dosing selumetinib with or without anti-CTLA-4 mAb on the immune system in the CT26 syngeneic tumor model. Flow cytometric analysis showed that this combination reduced T-cell proliferation and memory T-cell generation, but increased the frequency of splenic T cells. Selumetinib treatment decreased PD-L1 expression and increased MHC class II expression on the tumor cells, whilst decreasing myeloid-derived suppressor cell (MDSC)-like cells in the tumor. Despite the apparent ability of selumetinib to have both positive and negative effects on immune responses in vivo, the combination of selumetinib and anti-CTLA4 mAb was found to show anti-tumor activity in the CT26 colorectal tumor mouse model. These studies highlight the potential for enhancing anti-tumor immune response through combinations of molecular targeted therapies and IMT-Cs. Citation Format: Stefanie R. Mullins, Edmund Poon, Amanda Watkins, Paul D. Smith, Andrew Leishman, Ross Stewart, Robert Wilkinson. Preclinical assessment of combination therapy with selumetinib and CTLA-4 for cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 270. doi:10.1158/1538-7445.AM2015-270