Abstract 6331: The anti-tumor activity of HSP-90 therapeutic cancer vaccine (AST-021p) combine with TLR2/3 agonist in a MMTV-neu transgenic model

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Abstract Background: AST-021p, which is derived from HLA class II binding epitopes of human HSP90 protein, is an investigational therapeutic cancer vaccine for the malignant neoplasms. AST-021p is designed to demonstrate the immunologic efficacy by activating antigen-specific CD4+ Th1 cell in humans. Due to their ability to link the innate with the adaptive immune response, Toll-like receptor (TLR) agonists are highly promising as adjuvants in vaccines against life-threatening and complex diseases such as cancer, AIDS and malaria. In this study, AST-021p was investigated to evaluate the immunogenicity and tumor growth inhibitory effect under the condition of combining with various immune adjuvants derived from TLR agonists, using in-vivo model. Methods: Three different agonists of TLR (TLR-4, TLR-2/3, TLR-7/8) were assigned to investigate the immunogenicity in each group (4 FVB/N mice/group, total 4 groups). AST-021p was intradermally injected 3 times with different TLR-agonists and the immunogenicity was assessed from mouse splenocyte by HSP90-specific IFN-γ ELISpot method. We also examined the efficacy of AST-021p and selected TLR-agonist in MMTV/neu Tg mice (4 mice/group, conducted twice and A total 8 mice was assigned to each group). The combination of AST-021p and TLR-2/3 agonist (AST-021p plus TLR-2/3 agonist) was injected 3 times every 10 days to mice followed by inoculated mouse mammary cancer cell line. The tumor volume change and immunogenicity were evaluated. Results: The most effective TLR-agonist as a potent immune adjuvant was a TLR-2/3 agonist (L-pampoTM, supplied by CHA Vaccine Institute). AST-021p (100 μg) plus TLR-2/3 agonist significantly improved immunogenicity by increasing HSP-90 epitope-specific T cells up to 130±10 per 1x105 spleen cell of FVB/N mice (P<0.001). AST-021p plus TLR-2/3 agonist also showed higher tumor growth inhibitory effect (170±108 mm3) on post-implantation 35th day by suppressing mouse mammary cancer cell line (5x105)-derived tumor growth, compared with a TLR-2/3 agonist alone (1031±450 mm3). Conclusions: Combination regimen of AST-021p and TLR-2/3 agonist (as immune adjuvant) demonstrated significant immunogenicity and tumor prevention effect in in-vivo study. These data supported the clinical study of AST-021p combined with TLR-2/3 agonist as active immune adjuvant in certain tumor types, and phase 1/2 clinical program would be expected to be initiated. Citation Format: JinHo Kang, Jee Hyun Choi, Min Ji Seo, Eunjung Jung, Byung cheol Ahn, Jinback Lim, Hyo-Hyun Park, Hyunwon Shin, Eunkyo Joung, Hun Jung, Kyong Hwa Park. The anti-tumor activity of HSP-90 therapeutic cancer vaccine (AST-021p) combine with TLR2/3 agonist in a MMTV-neu transgenic model [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 6331.

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