Abstract PD2-08: Targeting of eIF4A1 along with anti-PD-L1 therapy limits lung metastases efficaciously in triple-negative breast cancer
Authors: Dulal Dharmindra , Boring Andrew , Raman Dayanidhi 
Published: March 2023

Abstract
Background: Triple-negative breast cancer (TNBC) is the most aggressive subtype of metastatic breast cancer with poor clinical prognosis. Currently used neoadjuvant chemotherapy for TNBC, such as taxanes, and/or anthracyclines demonstrate an initial treatment response but is often followed by drug resistance, tumor relapse, and high proclivity to develop metastases. There is an unmet need to develop effective combination therapies against metastatic TNBC (mTNBC). eIF4A1 is an mRNA helicase that help translate many oncogenic mRNAs including PD-L1 (through STAT1 translational regulation) that are involved in tumor growth, chemoresistance and metastases. Our prior studies pointed out that eIF4A1 is intricately linked to cancer stemness and drug resistance in TNBC. Emerging evidence has revealed that the tumor immune microenvironment (TIME) of TNBC do consist of mononuclear cells and lymphocytes. Combining chemotherapy with immune checkpoint inhibition had demonstrated a significant benefit for high-risk TNBC patients. In this study, we examine the efficacy of targeting eIF4A1 along with anti-PD-L1 therapy as an effective therapeutic strategy to limit cancer stemness, primary tumor progression and metastasis in an immunocompetent murine model of TNBC. Approach: Initially, we examined the human TNBC biospecimens and found that eIF4A1 protein level is upregulated in drug-resistant cases. STAT1 is an upstream regulator of PD-L1 and a downstream effector of eIF4A1. The protein level of STAT1 was significantly elevated as assessed by immunoblotting of human tumor lysates. In human TNBC cells, when eIF4A1 is pharmacologically or genetically targeted, PD-L1 was downregulated at the protein level. Based on this premise, we targeted eIF4A1 with the small molecule inhibitor, Rocaglamide A (RocA), along with anti-PD-L1 immunotherapy in orthotopically implanted 4T1 mouse TNBC tumors in BALB/c mice. The treatment arms were 1) Control (vehicle for RocA + control IgG) 2) RocA 3) RocA + anti-PD-L1 antibodies 4) Control IgG only 5) Anti-PD-L1 antibodies only with 10 mice in each group. Results: The combination treatment comprising of RocA and anti-PD-L1 antibodies worked out efficaciously as the primary tumor volume, wet tumor weight, bioluminescent tumor imaging and quantitation were significantly lower than the combination vehicle control. Furthermore, metastasis to the lungs were significantly impaired (1 out of 10 mice only had metastasis and that too it was small). On the contrary, ‘RocA single arm’ group had 6 out of 10 mice with lung metastasis. The lung metastases were observed in 4 out of 10 mice in the PD-L1 single arm and 6 out of 10 mice in control IgG single arm group. The RocA was tolerated well at 0.6 mg/kg with no significant change in the body weight and the liver and kidney function test values were within the normal range. Importantly, the combination treatment with RocA and PD-L1 was also tolerated well. Conclusions: The combination therapy involving RocA and PD-L1 had the significant impact in reducing lung metastases and may pave the way for phase I/II clinical trials.
Citation Format: Dharmindra Dulal, Andrew Boring, Dayanidhi Raman. Targeting of eIF4A1 along with anti-PD-L1 therapy limits lung metastases efficaciously in triple-negative breast cancer [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 PD2-08.