Biallelic variants in FLII cause pediatric cardiomyopathy by disrupting cardiomyocyte cell adhesion and myofibril organization

Pediatric cardiomyopathy (CM) represents a group of rare, severe disorders that affect the myocardium. To date, the etiology and mechanisms underlying pediatric CM are incompletely understood, hampering accurate diagnosis and individualized therapy development. Here, we identified biallelic variants in the highly conserved flightless-I (FLII) gene in 3 families with idiopathic, early-onset dilated CM. We demonstrated that patient-specific FLII variants, when brought into the zebrafish genome using CRISPR/Cas9 genome editing, resulted in the manifestation of key aspects of morphological and functional abnormalities of the heart, as observed in our patients. Importantly, using these genetic animal models, complemented with in-depth loss-of-function studies, we provided insights into the function of Flii during ventricular chamber morphogenesis in vivo, including myofibril organization and cardiomyocyte cell adhesion, as well as trabeculation. In addition, we identified Flii function to be important for the regulation of Notch and Hippo signaling, crucial pathways associated with cardiac morphogenesis and function. Taken together, our data provide experimental evidence for a role for FLII in the pathogenesis of pediatric CM and report biallelic variants as a genetic cause of pediatric CM.

Abstract 55: TT-702, a selective and potent A2B receptor antagonist for the treatment of cancer

Adenosine signaling via the A2A and A2B receptors is emerging as an important regulatory mechanism of immune responses. While A2AR has high affinity for adenosine, A2BR is a low-affinity receptor that becomes activated only under pathological conditions when adenosine concentration reaches micromolar ranges. Besides high levels of adenosine (up to 100 μM), the tumor microenvironment (TME) is characterized by hypoxia. Hypoxia upregulates A2BR on tumors and on immune cells. TT-702 is a novel, selective and highly potent, orally active A2BR antagonist. Here we show that TT-702 inhibits tumor growth through multiple mechanisms including enhancement of dendritic cell (DC) function and T-cell activation, reduction of MDSCs and Tregs, and suppression of cancer cell growth, fibrosis and angiogenesis. The cellular potency of TT-702 was assessed in NECA induced cAMP production. The ability of TT-702 to reverse NECA-mediated immune suppression was evaluated using standard human DC differentiation and MLR assays. The effects of TT-702 on tumor growth were determined in B16F10 melanoma and MC38 and CT26 colorectal cancers in mice treated with TT-702 at 0.3, 1, 3 or 10 mg/kg (BID), anti-PD-1 (RMP1-14, 5 mg/kg, Q2D) or TT-702+RMP1-14 intraperitoneally. TT-702 binds to human A2BR with Ki value of 8.3 nM and exhibits greater than 100x selectivity for A1, A2A and A3 receptors. It potently inhibited NECA-stimulated cAMP production (IC50=2.8 nM). TT-702 dose-dependently inhibited the growth of human prostate cancer cells LNCaP and PC-3 (IC50=1.4 μM). Combination of TT-702 with enzalutamide showed an additive and synergistic effects to inhibit LNCaP and PC-3 growth, respectively. TT-702 prevented NECA-induced suppression of human DC differentiation and completely reversed NECA-induced T cell inactivation (EC50=0.45 μM). By contrast, preladenant, an A2AR antagonist, had no effect on cancer cell growth and DC differentiation. Moreover, TT-702 increased MC38 tumor-infiltrating immune stimulatory cells (DCs, CD4+ and CD8+ T cells) and reduced immunosuppressive cells (MDSCs and Tregs). TT-702 dose-dependently inhibited the growth of mouse MC38 and CT26 colorectal cancers. Interestingly, TT-702 also inhibited the growth of mouse B16F10 melanoma cold tumor. Furthermore, combination of TT-702 with anti-PD-1 synergistically inhibited both B16F10 and CT26 tumor growth. Most importantly, TT-702 significantly reduced tumor fibrosis and angiogenesis, suggesting that TT-702 may improve the TME for T cell penetration, cancer killing and prevention of metastasis. TT-702, a novel, selective and potent A2B receptor antagonist, has the potential to treat a diverse range of hard-to-treat and aggressive tumors (including cold ones) as a monotherapy, and in combination with anti-PD-1, enzalutamide and other anticancer therapies. TT-702 exhibits excellent safety and PK profiles in animals and is slated to enter clinical development in 2021.

Citation Format: Peidong Fan, Filomena Housley, Helena Haberstock, Ken Horne, Jim Liu, Elfatih Elzein, Lina Yao. TT-702, a selective and potent A2B receptor antagonist for the treatment of cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 55.

Abstract GS1-08: The MYC oncogene suppresses tumor immune infiltration and function which is reversible with combinatorial immunotherapies

Immunotherapy has great potential to improve outcomes for breast cancer patients. Yet, deciding on how to rationally combine therapeutic agents and predict patient populations who would benefit remains challenging. Less than 20% of patients with metastatic breast cancer respond to current immunotherapy regiments, further demonstrating the need for research in this area. We postulate that oncogene activation leads to immune-related vulnerabilities which can be exploited to discover new immunotherapy combinations with improved efficacy. MYC is an oncogene that is frequently overexpressed in the majority of triple negative breast cancers (TNBCs), and is frequently found in disease recurrence, metastasis, and chemotherapy resistance. Despite the association of MYC with poor patient outcome, little is known about how MYC facilitates immune evasion in TNBC. Using TNBC patient datasets from the TCGA, we discovered that the MYC gene signature is anti-correlated with T-cell activation signatures and a subset of genes that regulate antigen processing and presentation with MHC-I. We further examined the effects of MYC using a MYC-driven mammary tumor mouse model (MTB-TOM). MYC activation leads to downregulation of MHC-I expression on tumor cells, poor CD8+ T cell infiltration and consequently poor response to anti-PD-L1 monotherapy. We demonstrate three methods to improve response to immunotherapy—by inactivation of MYC, by inducing an interferon response within the breast tumor, or by inducing MYC tumor synthetic lethality with a small molecule inhibitor of PIM kinases. Using these combination immunotherapy strategies, we observed that a majority of animals eradicated their breast tumors and demonstrated a durable anti-tumor response following subsequent tumor re-challenge. Our data suggest MYC is an indicator of whether a breast cancer patient will respond to immunotherapy. Analysis of the MYC gene signature as a predictor of patient response to pembrolizumab in combination with paclitaxel followed by AC in the neoadjuvant I-SPY 2 trial is on-going and will be presented. Our study is the first to describe oncogenic MYC downregulation of MHC-I in a TNBC model of breast cancer and to demonstrate translatable approaches to overcome MYC orchestrated immune evasion.

Citation Format: Joyce V Lee, Filomena Housley, Christina Yau, Golzar Hemmati, Yibing Zhang, Susan Samson, Carole Baas, Hope Rugo, Mehrdad Matloubian, Andrei Goga. The MYC oncogene suppresses tumor immune infiltration and function which is reversible with combinatorial immunotherapies [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr GS1-08.