Abstract LB532: Bifidobacterium longum RAPO alleviates the risk of immune-related adverse events of anti-PD-1 immunotherapy in a mouse model of triple-negative breast cancer

Abstract Background: Triple negative breast cancer (TNBC) has higher risk of early metastasis and recurrence compared with other types of breast cancer. Although immune checkpoint inhibitors (ICIs) have emerged as a feasible strategy for the treatment of TNBC, its use causes various side effects known as immune-related adverse events (irAEs) including pneumonitis, myocarditis, colitis, hepatitis, and nephritis. Considering severe irAEs could lead to ICIs termination and fatal outcomes, studies into immunotherapy that increases anti-tumor efficacy while reducing side effects are needed. We have previously reported that combination therapy of Bifidobacterium longum RAPO and anti-PD-1 shows a better efficacy compared with monotherapy in mice with TNBC. In the present study, we further investigated whether this combination therapy with probiotics would affect the risk of irAEs induced by anti-PD-1 therapy against TNBC. Methods: BALB/c mice bearing the 4T1 murine metastatic breast cancer cells were randomly assigned to tumor control, Bifidobacterium longum RAPO (RAPO), Anti-PD-1, or Anti-PD-1+RAPO group. Tumor tissues were analyzed by Affymetrix Mouse Gene 2.0 ST Array, and functional analysis of microarray data was performed using Ingenuity Pathway Analysis (IPA®, QIAGEN). Lung, heart, colon, liver, and kidney tissues were analyzed by qRT-PCR to determine expression of pro- and anti-inflammatory cytokines. Colon and liver tissues were also analyzed by a Western blot and immunohistochemistry (IHC), respectively. Results: Functional analysis revealed that inflammation in lung and cardiac lesion was predicted to be reduced in Anti-PD-1+RAPO group compared with Anti-PD-1 group. Indeed, expression of pro-inflammatory cytokines including IL1β, IL6, and TNFα was significantly decreased, while anti-inflammatory cytokine IL10 expression was increased in the lung, liver, and kidney tissues of Anti-PD-1+RAPO group compared with Anti-PD-1 group. Similarly, in the heart tissue, TNFα expression was decreased, whereas IL10 was significantly increased in Anti-PD-1+RAPO group than monotherapy group. In the colon tissue, combination therapy of Anti-PD-1 with RAPO significantly enhanced expression of IL10 and tight junction proteins such as occludin and ZO-1 compared with Anti-PD-1 treatment alone. Colonic expression of pro-inflammatory cytokines tended to be reduced in combination therapy group than Anti-PD-1 group. Furthermore, Anti-PD-1+RAPO group was associated with lower level of myeloperoxidase, a pro-inflammatory enzyme released by activated neutrophils, in the liver than Anti-PD-1 group. Conclusions: Collectively, in addition to the effects on anti-tumor efficacy, combination therapy of anti-PD-1 with B. longum RAPO alleviates the risk of irAEs in mice with TNBC. This study provides evidence that B. longum RAPO supplementation might be a novel therapeutic approach in cancer immunotherapy. [This work was supported by BIFIDO Co. and NRF (2020R1C1C1007553 to S-EK).] Citation Format: Hyeyoon Kim, Rira Oh, Ji-Won Heo, Geun Eog Ji, Myeong Soo Park, Sung-Eun Kim. Bifidobacterium longum RAPO alleviates the risk of immune-related adverse events of anti-PD-1 immunotherapy in a mouse model of triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB532.