Abstract PD2-03: Targeting TGF-β and over-expressing GM-CSF in the Tumor Microenvironment (TME) with AMUN-003 Inhibits Tumor Growth and Metastases and Augments Immune Checkpoint Inhibitor (ICI) Response in Triple Negative Breast Cancer (TNBC)
Authors: Shin Sooncheon , Filimon Beniamin , Yang Yuefeng , Hu Zebin , Seth Prem , Gadi Vijayakrishna K. , Xu Weidong 
Published: March 2023

Introduction: Despite several therapeutic advancements, metastatic TNBC remains incurable for nearly all patients and is a frequent cause of cancer-related deaths worldwide. We tested the hypothesis that inhibiting suppressive signals sustained by TGF-β and concurrently stimulating recruitment of inflammatory cells with GM-CSF within the TME would result in improved anti-tumor responses. We report here pre-clinical single agent and ICI combination data for a newly developed oncolytic adenovirus rAd.sT.GM (AMUN-003) that expresses both sTGFβRIIFc (a TGF-β protein decoy), and GM-CSF tested in an immunocompetent mouse model. Methods: In addition to manufacturing Amun-003 which is a replication competent adenovirus encoding both sTGFβRIIFc and GM-CSF transgenes, we generated multiple replication competent control viruses coding for sTGFβRIIFc alone, GM-CSF alone or no transgene. We implanted 4T1 cells in the flanks of BALB/c mice, a syngeneic tumor model that is immune competent. On day 7 and day 10 post tumor cell inoculation, we performed saline or single agent virus injections into the tumor. We monitored the health of the animals, performed periodic tumor caliper measurements and collected sera for analysis of cytokines and markers of tissue injury. Animals were sacrificed on Day 25 and tissues collected. Similarly, with the same animal model and using reduced dose Amun-003, we tested combinations with systemic anti-CTLA-4, anti-PD-1 monoclonal antibodies, or both. Animals were sacrificed on Day 25 with specimens collected as above but also to report the metastatic burden in distant tissues. Results: In single agent experiments, all adenovirus constructs were similarly tolerated by the animals with no notable differences in animal weights. General safety as assessed by serum LDH and IL-6 demonstrated no difference between animal groups treated with the different virus constructs. All adenovirus resulted in delay of cancer growth and on day 25, excised tumors from sacrificed animals weighed less than tumors from animals treated with buffer. However, a single dose of Amun-003 was the most effective at delaying tumor progression than any other tested constructs (Day 21 and Day 25: P &lt; 0.0001 vs the buffer group by two-way ANOVA analysis). Next, we conducted experiments evaluating a single dose of Amun-003 alone or in combination with anti-CTLA4, anti-PD1 or both ICI. Combinations of Amun-003 with ICI delayed progression better than ICI treatments alone or Amun-003 alone. Moreover, the combination with both ICI and Amun-003 was most effective at delay of tumor progression (Day 22 and Day 25: P &lt; 0.0001 vs the buffer group; D25: P=0.0119 vs dual ICI therapy). Lung surface metastatic nodule counts and lung tissue luciferase assay for 4T1-luc2 cells both showed treatment consisted of Amun003 and both ICI was most potent in inhibiting lung metastasis (Lung nodules: P &lt; 0.0001 vs the buffer group; Relative luminescence: P=0.0036 vs the buffer group, both by one-way ANOVA analysis). Finally, the metastatic burden in the lung was least in animals treated with Amun-003 and both ICI (42% metastases free) (P = 0.0373 vs the buffer group by fisher’s exact test). Conclusions: In syngeneic immune competent animals harboring an aggressive TNBC tumor, single agent Amun-003 appeared safe and was more effective at controlling tumor progression following an intratumoral injection when compared to other tested adenovirus constructs. In the same model, combinations of ICI with Amun-003 resulted in delayed tumor growth and control of metastatic spread. These results with Amun-003 support advancement to human clinical testing.

Citation Format: Sooncheon Shin, Beniamin Filimon, Yuefeng Yang, Zebin Hu, Prem Seth, Vijayakrishna K. Gadi, Weidong Xu. Targeting TGF-β and over-expressing GM-CSF in the Tumor Microenvironment (TME) with AMUN-003 Inhibits Tumor Growth and Metastases and Augments Immune Checkpoint Inhibitor (ICI) Response in Triple Negative Breast Cancer (TNBC) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD2-03.