High potency STING agonists engage unique myeloid pathways to reverse pancreatic cancer immune privilege

BACKGROUND

Intratumoral injection of cyclic dinucleotide (CDN) agonists of the stimulator of interferon genes (STING) pathway engages innate immune activation and priming of adaptive immune effectors to foster local and distal tumor clearance. Despite proven therapeutic efficacy in preclinical models, a thorough understanding of how CDNs reprogram suppressive myeloid stroma in mouse and man is lacking.

METHODS

Here, we perform deep transcript-level and protein-level profiling of myeloid-derived suppressor cells and M2 macrophages following stimulation with CDNs of ascending potency. Additionally, we leverage orthotopic Kras^+/G12DTP53^+/R172HPdx1-Cre (KPC) derived models of pancreatic adenocarcinoma (PDAC) to determine the capacity for locally administered CDNs to sensitize PDAC to immune checkpoint blockade. We use bioluminescent in vivo imaging and 30-parameter flow cytometry to profile growth kinetics and remodeling of the tumor stroma post-therapy.

RESULTS

Highly potent synthetic STING agonists repolarize suppressive myeloid populations of human and murine origin in part through inhibition of Myc signaling, metabolic modulation, and antagonism of cell cycle. Surprisingly, high-potency synthetic agonists engage qualitatively unique pathways as compared with natural CDNs. Consistent with our mechanistic observations, we find that intratumoral injection of the highest activity STING agonist, IACS-8803, into orthotopic pancreatic adenocarcinoma lesions unmasks sensitivity to checkpoint blockade immunotherapy. Dimensionality reduction analyses of high parameter flow cytometry data reveals substantial contributions of both myeloid repolarization and T cell activation underlying the in vivo therapeutic benefit of this approach.

CONCLUSIONS

This study defines the molecular basis of STING-mediated myeloid reprogramming, revealing previously unappreciated and qualitatively unique pathways engaged by CDNs of ascending potency during functional repolarization. Furthermore, we demonstrate the potential for high potency CDNs to overcome immunotherapy resistance in an orthotopic, multifocal model of PDAC.

Abstract A23: Effects of anti-CTLA-4 and anti-PD-1 on memory T-cell differentiation and resistance to tumor relapse

Both anti-CTLA-4 and anti-PD-1 mediate significant response rates in cancer patients. As a hallmark of successful immunotherapies, they also mediate durable responses that last for years. For example, anti-CTLA-4 mediates a 22% 10-year overall survival rate, while anti-PD-1 mediates a 34% 5-year overall survival rate. Because of the broader uses of immunotherapies, the number of patients who have tumor relapse also increases. About 25% of patients who initially responded to anti-PD-1 have tumor relapse within 24 months. However, the relationship between tumor relapse and long-term effect of immunotherapies is still not clear. The goal of this study is to understand the differential effect of anti-CTLA-4 and anti-PD-1 on memory T-cell differentiation in murine tumor models. By rechallenging mice with tumor cells that have had tumors previously eradicated by either treatment, our results have shown that anti-CTLA-4 induces a more durable memory antitumor response compared to that treated with anti-PD-1. By tracing the antigen-specific CD8 T-cells throughout the memory phase, anti-CTLA-4 increases the frequency and cytokine production of antigen-specific T cells compared with anti-PD-1. We have also found that anti-CTLA-4 induces the population of KLRG1+ effector CD8 T cells among the effectors compared with anti-PD-1 during rechallenge, despite the ratio between central memory and effectors remaining the same. Our studies enable us to identify the long-term effect of immunotherapies on immune system.

Citation Format: Stephen Mok, Colm R. Duffy, Nana-Ama A. Anang, James P. Allison. Effects of anti-CTLA-4 and anti-PD-1 on memory T-cell differentiation and resistance to tumor relapse [abstract]. In: Proceedings of the AACR Special Conference on Melanoma: From Biology to Target; 2019 Jan 15-18; Houston, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(19 Suppl):Abstract nr A23.

Abstract A205: Effects of anti-CTLA-4 and anti-PD-1 on memory T-cell differentiation and resistance to tumor relapse

Both anti-CTLA-4 and anti-PD-1 mediate significant response rates in cancer patients. As a hallmark of successful immunotherapies, they also mediate durable responses that last for years. For example, anti-CTLA-4 mediates a 22% 10-year overall survival rate, while anti-PD-1 mediates a 34% 5-year overall survival rate. Because of the broader uses of immunotherapies, the number of patients who have tumor relapse also increases. About 25% of patients who initially responded to anti-PD-1 have tumor relapse within 24 months. However, the relationship between tumor relapse and long-term effect of immunotherapies is still not clear. The goal of this study is to understand the differential effect of anti-CTLA-4 and anti-PD-1 on memory T-cell differentiation in murine tumor models. By rechallenging mice with tumor cells that have had tumors previously eradicated by either treatment, our results have shown that anti-CTLA-4 induces a more durable memory antitumor response compared to that treated with anti-PD-1. By tracing the antigen-specific CD8 T-cells throughout the memory phase, anti-CTLA-4 increases the frequency and cytokine production of antigen-specific T-cells compared with anti-PD-1. We have also found that anti-CTLA-4 induces the population of KLRG1+ effector CD8 T-cells among the effectors compared with anti-PD-1 during rechallenge, despite the ratio between central memory and effectors remaining the same. Our studies enable us to identify the long-term effect of immunotherapies on immune system.

Citation Format: Stephen Mok, Colm R. Duffy, Nana-Ama A.S. Anang, James P. Allison. Effects of anti-CTLA-4 and anti-PD-1 on memory T-cell differentiation and resistance to tumor relapse [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A205.

Fundamental Mechanisms of Immune Checkpoint Blockade Therapy

Immune checkpoint blockade is able to induce durable responses across multiple types of cancer, which has enabled the oncology community to begin to envision potentially curative therapeutic approaches. However, the remarkable responses to immunotherapies are currently limited to a minority of patients and indications, highlighting the need for more effective and novel approaches. Indeed, an extraordinary amount of preclinical and clinical investigation is exploring the therapeutic potential of negative and positive costimulatory molecules. Insights into the underlying biological mechanisms and functions of these molecules have, however, lagged significantly behind. Such understanding will be essential for the rational design of next-generation immunotherapies. Here, we review the current state of our understanding of T-cell costimulatory mechanisms and checkpoint blockade, primarily of CTLA4 and PD-1, and highlight conceptual gaps in knowledge.Significance: This review provides an overview of immune checkpoint blockade therapy from a basic biology and immunologic perspective for the cancer research community. Cancer Discov; 8(9); 1069-86. ©2018 AACR.

Blocking colony stimulating factor 1 receptor (CSF-1R) and tropomyosin receptor kinase A (TrkA) improves the antitumor efficacy of immune checkpoint blockade

Established tumors can escape immune responses by secreting the cytokine colony stimulating factor 1 (CSF-1), stimulating the proliferation and recruitment of immunosuppressive myeloid cells to the tumor microenvironment by binding to colony stimulating factor-1 receptor (CSF-1R). Additionally, the neurotrophin nerve growth factor (NGF) is a ligand for tropomyosin receptor kinase A (TrkA), which is over-expressed on multiple tumor types. Signaling through TrkA via the Akt and MAPK pathways regulates survival, proliferation and invasion of tumor cells. This invasion can occur around nerves, and perineural invasion (PNI) has emerged as a critical pathological feature of multiple malignancies, resulting in poor prognosis.

PLX7486 is a novel orally bioavailable small molecule Trk and CSF-1R dual-inhibitor that is now being studied in Phase I clinical trials. We hypothesized that PLX7486 would synergize with immune checkpoint blockade to result in a greater antitumor effect, by targeting Trk signaling directly on cancer cells and by inhibiting the recruitment of immunosuppressive myeloid cells through CSF-1R, thus enabling an improved antitumor T cell response.

We confirmed the expression of TrkA receptor on multiple murine cancer cell lines in vitro and exposed them to PLX7486, showing a direct cytotoxic effect with an IC50 of 5–8μM on most of the cell lines and an inhibition of AKT pathway signaling in MC38 cells. PLX7486 also had a direct cytotoxic effect on bone marrow-derived macrophages and the murine macrophage cell line RAW264.7 with an IC50 <1μM, while it had no effect on activated T cells in vitro. Combining PLX7486 and anti-CTLA-4 or anti-PD-1 in vivo in MC38 and B16F10 tumor models resulted in increased antitumor effects.

Effects of anti-CTLA-4 and anti-PD-1 on memory T-cell differentiation and resistance to tumor relapse

Clinical studies have shown that αPD-1 therapy mediates a greater response rate compared to αCTLA-4 according to RECIST criteria. However, it may not be as durable as αCTLA-4. 25% of patients who initially responded to αPD-1 have tumor relapse within 24 months. In contrast, the 10-year survival rate of patients treated with αCTLA-4 is at least ~25% suggesting a durable response. The goal of this study is to understand the relationship between memory T-cell formation in tumor models mediated by checkpoint antibodies and tumor relapse.

Our results have shown that αCTLA-4 could induce a superior memory antitumor response during tumor rechallenge on mice compared to that treated with αPD-1 after 80 days. We also showed that this memory antitumor response was antigen-specific. These antigen-specific memory T-cells in mice that were treated with αCTLA-4 had better proliferative potential with cytokine producing function and more CD62L+CD44+ memory T-cells were converted back to CD62L-CD44+ effectors during rechallenge. We found that αCTLA-4 and αPD-1 facilitated the development of CD4 and CD8 memory T-cells respectively. We also demonstrated that the memory antitumor activity mediated by the combination of αCTLA-4 and αPD-1 overlapped with αCTLA-4 alone suggesting the effect of the combined treatment is dominated by αCTLA-4.

Abstract 1685: Effects of anti-ctla-4 and anti-pd-1 on memory T-cell differentiation and resistance to tumor relapse

The FDA has begun to expand the approved uses of immune checkpoint blockade antibodies targeting CTLA-4 and PD-1. Blocking either checkpoint relieves the negative regulation of T-cells resulting in significant responses in patients with cancer. Data has now begun to emerge regarding differences between these two therapies. While αPD-1 therapy has a greater response rate (~30% vs. 11%) according to RECIST criteria, recent reports have suggested responses to αPD-1 may not be as durable as αCTLA-4. 25% of patients who initially responded to αPD-1 have tumor relapse within 24 months. In contrast, the 3-year survival rate of patients treated with αCTLA-4 is at least ~25% suggesting a durable response. Previous studies in bacterial or chronic LCMV infectious models have shown that αCTLA-4 can increase CD8+ memory T-cell formation, whereas genetic ablation of PD-1 on T-cells often promotes the terminally differentiated exhausted CD8+ T-cell phenotype, while attenuating memory T-cell formation. However, the mechanism which leads to relapse following αPD-1 treatment in tumor models is not clear. The goal of this project is to understand how immunotherapies shape memory T-cell formation and how that relates to the mechanism of tumor relapse.

To test whether αCTLA-4 or αPD-1 can induce a better memory T-cell response, mice were vaccinated with irradiated B16F10 murine melanoma cells and treated αCTLA-4 or αPD-1. Mice were re-challenged with B16F10 80 days after vaccination. Although both αCTLA-4 and αPD-1 improved tumor rejection compared with controls, αCTLA-4 treated mice exhibited superior tumor control compared to αPD-1 (p<0.0005) suggesting the memory T-cell response mediated by αCTLA-4 is more durable. In order to test whether this memory T-cell response is antigen-specific, mice were re-challenged with unrelated MC38 or 3LL cancer cells. The antibody treated groups did not show improved antitumor effect compared with vaccine control (p>0.5). To test whether the frequency of memory T-cells recruited to the re-challenged tumor could affect memory T-cell response, antigen-specific pmel-1 T-cells were infused to mice following vaccination with αCTLA-4 or αPD-1. Our result suggested that there were more tumor-infiltrating pmel-1 T-cells in the αCTLA-4 treated group compared to the αPD-1 treated group (p<0.05). In order to augment the durability of αPD-1 treatment, αPD-1 was combined with αCTLA-4 following vaccination. The combined treatment group has superior antitumor response compared to that with αPD-1 (p<0.000003) and overlapped with the αCTLA-4 treated group (P>0.05) during re-challenge, indicating that the effect of the combined treatment is dominated by αCTLA-4.

Collectively, our studies facilitate the design of combination immunotherapy treatments that enhance both response rates and generation of memory T-cells to prevent relapse.

Citation Format: Stephen Mok, Colm R. Duffy, James P. Allison. Effects of anti-ctla-4 and anti-pd-1 on memory T-cell differentiation and resistance to tumor relapse [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 1685. doi:10.1158/1538-7445.AM2017-1685

Identification of bacterial proteins observed in MALDI TOF mass spectra from whole cells

Characteristic ions in the MALDI TOF mass spectra from bacterial cells have been associated with four known proteins. The proteins, observed both from cells and in filtered cellular suspensions, were isolated by HPLC and identified on the basis of their mass spectra and their partial amino acid sequence, determined using the Edman method (10-15 residues). The acid resistance proteins HdeA and HdeB give rise to ions near m/z 9735 and 9060 in MALDI TOF mass spectra from cells and from extracts of both Escherichia coli 1090 and Shigella flexneri PHS-1059. However, the proteins associated with proteolytic cleavage by the peptidase Lep, rather than the precursor proteins, were observed, both using cells and from cellular extracts. A cold-shock protein, CspA, was associated with the ion near m/z 7643 from Pseudomonas aeruginosa. Similarly, a cold-acclimation protein, CapB, was identified as the source of the ion near m/z 7684 in P. putida. This last protein was homologous with a known CapB from P. fragi. While these experiments involved the detection of known or homologous proteins from typical bacteria, this same approach could also be applied to the detection of unique proteins or biomarker proteins associated with other bacteria of public health significance.