Signaling via a CD27-TRAF2-SHP-1 axis during naive T cell activation promotes memory-associated gene regulatory networks

The interaction of the tumor necrosis factor receptor (TNFR) family member CD27 on naive CD8+ T (Tn) cells with homotrimeric CD70 on antigen-presenting cells (APCs) is necessary for T cell memory fate determination. Here, we examined CD27 signaling during Tn cell activation and differentiation. In conjunction with T cell receptor (TCR) stimulation, ligation of CD27 by a synthetic trimeric CD70 ligand triggered CD27 internalization and degradation, suggesting active regulation of this signaling axis. Internalized CD27 recruited the signaling adaptor TRAF2 and the phosphatase SHP-1, thereby modulating TCR and CD28 signals. CD27-mediated modulation of TCR signals promoted transcription factor circuits that induced memory rather than effector associated gene programs, which are induced by CD28 costimulation. CD27-costimulated chimeric antigen receptor (CAR)-engineered T cells exhibited improved tumor control compared with CD28-costimulated CAR-T cells. Thus, CD27 signaling during Tn cell activation promotes memory properties with relevance to T cell immunotherapy.

Abstract 510: Targeting metabolic vulnerabilities to reduce triple negative breast cancer health disparities

Triple negative breast cancer (TNBC) occurs in 10-15% of all breast cancer (BC) patients, yet it accounts for almost half of all BC deaths. Women of African ancestry (WAA) are twice as likely as women of European Ancestry (WEA) to be diagnosed with advanced TNBC with worse prognosis. Emerging data shows that insulin resistance and high circulating levels of insulin are more prevalent in WAA with invasive BCs than in WEA, and activation of the AKT/mTOR pathway by insulin may occur in aggressive TNBC. Reports show diabetic patients treated with metformin, a biguanide drug used to treat diabetes type 2, have reduced incidence of BC and improved survival. However, anticancer actions of metformin require use of high drug doses with limiting side effects in vivo. To address this challenge, we used a structure-activity strategy to develop biguanide analogues with more potent anticancer action and safety at lower doses in vivo. Using TNBC cell proliferation in vitro to screen analogues, promising candidates were identified that exerted dose-dependent inhibition of cell proliferation at significantly lower doses than that of parental metformin (P<0.01). As antitumor effects of metformin are attributed in part to activation of LKB1-AMPK pathways, we find that biguanide analogues also strongly induce AMPK phosphorylation on Western immunoblots and significantly reduce phosphorylation of downstream mTOR signaling pathway components including p70S6K, S6 ribosomal protein and 4E-BP1. Further, analogues induce TNBC cell apoptosis in vitro at lower doses than metformin. In vivo, analogues were more effective than metformin in stopping human TNBC xenograft progression in nude mouse models (P<0.001). Notably, analogues were also more effective than metformin at blocking lung metastases in syngeneic murine 4T1 TNBC models (P<0.05). Transcriptome analyses comparing mammary tumors and lung metastases revealed that analogue JD006 down-regulated genes related to oxidative phosphorylation in lung metastases treated with JD006 and increased expression of genes related to T-cell activation. Further, gene expression in tumors treated with JD006 showed significant down-regulation of long non-coding RNAs that associate with the up-regulation of malignant transformation and activation of M1 macrophages. Importantly, our data indicate that analogue JD006 modulates the activity/trafficking of myeloid-derived suppressor cells (MDSC) and tumor infiltrating lymphocytes (TIL) that may significantly impact TNBC responses to immune checkpoint inhibitors. Further understating of potential biologic differences between TNBC of WAA and WEA is needed to design more effective therapeutic strategies to reduce TNBC health disparities. New targeted treatments could be beneficial for patients afflicted with this deadly disease. (Funding: CBCRP B27IB3869, 4IB-0058; NCI U54 CA143930; JCCC BC Award, Team Research Grant; UCLA TDG).

Citation Format: Diana C. Márquez-Garban, Gang Deng, Lorena P. Burton, Gaoyuan Ma, Vishaka Muhunthan, Begonya Comin-Anduix, Gabriela Llarena, Neda Moatamed, Jennifer Murphy, Nalo Hamilton, Daivd Shackelford, Michael E. Jung, Richard J. Pietras. Targeting metabolic vulnerabilities to reduce triple negative breast cancer health disparities [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 510.

Comparative analysis of TCR and CAR signaling informs CAR designs with superior antigen sensitivity and in vivo function

Chimeric antigen receptor (CAR)-modified T cell therapy is effective in treating lymphomas, leukemias, and multiple myeloma in which the tumor cells express high amounts of target antigen. However, achieving durable remission for these hematological malignancies and extending CAR T cell therapy to patients with solid tumors will require receptors that can recognize and eliminate tumor cells with a low density of target antigen. Although CARs were designed to mimic T cell receptor (TCR) signaling, TCRs are at least 100-fold more sensitive to antigen. To design a CAR with improved antigen sensitivity, we directly compared TCR and CAR signaling in primary human T cells. Global phosphoproteomic analysis revealed that key T cell signaling proteins-such as CD3δ, CD3ε, and CD3γ, which comprise a portion of the T cell co-receptor, as well as the TCR adaptor protein LAT-were either not phosphorylated or were only weakly phosphorylated by CAR stimulation. Modifying a commonplace 4-1BB/CD3ζ CAR sequence to better engage CD3ε and LAT using embedded CD3ε or GRB2 domains resulted in enhanced T cell activation in vitro in settings of a low density of antigen, and improved efficacy in in vivo models of lymphoma, leukemia, and breast cancer. These CARs represent examples of alterations in receptor design that were guided by in-depth interrogation of T cell signaling.

Immunogenic Chemotherapy Enhances Recruitment of CAR-T Cells to Lung Tumors and Improves Antitumor Efficacy when Combined with Checkpoint Blockade

Adoptive therapy using chimeric antigen receptor-modified T cells (CAR-T cells) is effective in hematologic but not epithelial malignancies, which cause the greatest mortality. In breast and lung cancer patients, CAR-T cells targeting the tumor-associated antigen receptor tyrosine kinase-like orphan receptor 1 (ROR1) infiltrate tumors poorly and become dysfunctional. To test strategies for enhancing efficacy, we adapted the Kras^LSL-G12D/+;p53^f/f autochthonous model of lung adenocarcinoma to express the CAR target ROR1. Murine ROR1 CAR-T cells transferred after lymphodepletion with cyclophosphamide (Cy) transiently control tumor growth but infiltrate tumors poorly and lose function, similar to what is seen in patients. Adding oxaliplatin (Ox) to the lymphodepletion regimen activates tumor macrophages to express T-cell-recruiting chemokines, resulting in improved CAR-T cell infiltration, remodeling of the tumor microenvironment, and increased tumor sensitivity to anti-PD-L1. Combination therapy with Ox/Cy and anti-PD-L1 synergistically improves CAR-T cell-mediated tumor control and survival, providing a strategy to improve CAR-T cell efficacy in the clinic.

Designed protein logic to target cells with precise combinations of surface antigens

Precise cell targeting is challenging because most mammalian cell types lack a single surface marker that distinguishes them from other cells. A solution would be to target cells using specific combinations of proteins present on their surfaces. In this study, we design colocalization-dependent protein switches (Co-LOCKR) that perform AND, OR, and NOT Boolean logic operations. These switches activate through a conformational change only when all conditions are met, generating rapid, transcription-independent responses at single-cell resolution within complex cell populations. We implement AND gates to redirect T cell specificity against tumor cells expressing two surface antigens while avoiding off-target recognition of single-antigen cells, and three-input switches that add NOT or OR logic to avoid or include cells expressing a third antigen. Thus, de novo designed proteins can perform computations on the surface of cells, integrating multiple distinct binding interactions into a single output.

Abstract 692: Discovery of novel metformin derivatives with potent antitumor activity in combination with immunotherapy for treatment of triple-negative breast cancer

Triple negative breast cancer (TNBC) occurs in about 15% of breast cancer (BC) patients, yet it accounts for almost 50% of all BC deaths. TNBC is characterized by lack of expression of estrogen, progesterone and HER2 receptors, and it cannot be treated with current targeted therapies. TNBCs are heterogeneous and occur often in younger and African American women. Although initially responsive to some chemotherapies, TNBCs tend to relapse early and metastasize, leading to poor survival. Development of new therapeutic approaches for clinical translation is a high priority. Emerging evidence from epidemiologic and preclinical work suggests that metformin, the most widely used drug to treat type 2 diabetes mellitus, exerts anticancer activity in BC. Diabetic patients treated with metformin have a reduced incidence and better survival from BC. Moreover, TNBC cells are reported to be uniquely sensitive to metformin in vitro, but strong antitumor effects require relatively high metformin doses in vivo. To address this challenge, we used a structure-activity strategy to develop metformin analogues with more potent anticancer action and safety at lower doses in vivo. Using TNBC cell proliferation in vitro to screen drug candidates, selected new metformin analogues were identified that exerted dose-dependent inhibition of cell proliferation at significantly lower concentrations than that of parental metformin (P<0.01). As antitumor effects of metformin are attributed in part to activation of the LKB1-AMPK pathway, we find that metformin analogues also strongly induced phosphorylation of AMPK by Western blot assays and significantly reduced phosphorylation of mTOR downstream signaling pathway components (p70S6K, S6 ribosomal protein, 4E-BP1). Analogues also induced TNBC cell apoptosis at lower doses than metformin. In vivo, metformin analogues were more effective at lower doses given by oral gavage than metformin in suppressing TNBC human tumor xenograft progression in nude mouse models (P<0.001). It is notable that data from clinical trials with immune checkpoint inhibitors (ICI) indicate that TNBCs are susceptible to immunotherapy, but only a minority of patients to date have had clinical benefit. Importantly, our studies indicate that metformin analogues modulate the activity and trafficking of myeloid-derived suppressor cells (MDSC) and tumor infiltrating lymphocytes (TIL) that may significantly impact TNBC responses to ICIs. Thus, combination therapy with metformin analogues and anti-PD-L1 antibodies was more effective at blocking tumor growth in vivo than either treatment given alone using murine 4T1 TNBC implants in syngeneic, immune-competent BALB/C mouse models. In the TNBC microenvironment, analogue treatment with ICIs elicited significant infiltration of predominantly effector T-cells, increased populations of tissue-resident memory T-cells, and a reduction of exhausted T-cells as compared to controls (P<0.01). Moreover, MDSC were significantly decreased after combination therapy as compared to appropriate controls (P<0.05). Since there are currently no specific treatments for TNBC, identification of a new targeted therapeutic approach could ultimately be beneficial for managing patients afflicted with this deadly disease. Funding by California BC RP, NCI U54 CA143930.

Citation Format: Diana C. Márquez-Garban, Gang Deng, Begonya Comin-Anduix, Vishaka Muhunthan, Gaoyuan Ma, Jennifer Murphy, Alejandro J. Garcia, Cristian D. Yanes, Lorena R. Burton, Nalo Hamilton, David Shackelford, Michael E. Jung, Richard J. Pietras. Discovery of novel metformin derivatives with potent antitumor activity in combination with immunotherapy for treatment of triple-negative breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 692.