Abstract 6524: A novel HER2/4-1BB bispecific antibody, YH32367 (ABL105) shows potent anti-tumor effect through tumor-directed T cell activation

4-1BB (TNFSF9, CD137) is a member of the tumor necrosis factor receptor superfamily that functions as a potent costimulator to immune cells, especially T-cell. Although current 4-1BB-targeted strong agonistic antibody exhibit a considerable anti-tumor effect through T cell activation, it has a limitation of liver toxicity. To overcome the challenges of targeting the 4-1BB, we developed a bispecific antibody that can induce tumor-directed T cell activation.

A novel HER2/4-1BB bispecific antibody, YH32367 (ABL105) targets human epidermal growth factor receptor 2 (HER2) and 4-1BB simultaneously and binds to both targets with high affinity. YH32367 (ABL105) exhibited a strong activation of 4-1BB signal in tumor cells expressing HER2 such as NCI-N87, BT474 and HCC1954 cell lines. In co-culture assay using human peripheral blood mononuclear cell (hPBMC) and HER2-expressing tumor cells, YH32367 (ABL105) stimulated IFN-γ secretion from hPBMC and thereby induced tumor cell lysis. The anti-tumor efficacy of YH32367 (ABL105) was evaluated in HCC1954-bearing hPBMC engrafted humanized mice and MC38/hHER2-bearing h4-1BB knock-in mice. YH32367 (ABL105) had more potent efficacy on tumor growth inhibition in both mouse models compared to the equimolar dosing of trastuzumab. Peripheral T cell increase was not observed in these studies. In particular, YH32367 (ABL105) showed a tumor regression in MC38/hHER2-bearing h4-1BB knock-in mice.

In conclusion, YH32367 (ABL105) significantly inhibited tumor growth in a HER2 expression dependent manner and showed potent in vivo efficacy through tumor-directed T cell activation without non-specific systemic T-cell activation.

Citation Format: Moo Young Song, Eun-Jung Lee, Hyejin Chung, Yangsoon Lee, Young Bong Park, Min Hyeok Jee, KyeongBae Kim, Mikyeong Ju, Jun Kyung Lee, Byung Hyun Choi, Ju Young Park, DaeWon Kim, Junhwan Kim, Sujin Ahn, Kyoung Kyu Ahn, Kyeongsu Park, Uijung Jung, Wonjun Son, Jaehyun Eom, Eunjung Kim, Donghoon Yeom, Jinhyung Ahn, Daehae Song, Byungje Sung, Weon-kyoo You, Jong Gyun Kim, Se-Woong Oh, Jaeho Jung. A novel HER2/4-1BB bispecific antibody, YH32367 (ABL105) shows potent anti-tumor effect through tumor-directed T cell activation [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6524.

RACK1 mediates rewiring of intracellular networks induced by hepatitis C virus infection

Hepatitis C virus (HCV) is a positive-strand RNA virus replicating in a membranous replication organelle composed primarily of double-membrane vesicles (DMVs) having morphological resemblance to autophagosomes. To define the mechanism of DMV formation and the possible link to autophagy, we conducted a yeast two-hybrid screening revealing 32 cellular proteins potentially interacting with HCV proteins. Among these was the Receptor for Activated Protein C Kinase 1 (RACK1), a scaffolding protein involved in many cellular processes, including autophagy. Depletion of RACK1 strongly inhibits HCV RNA replication without affecting HCV internal ribosome entry site (IRES) activity. RACK1 is required for the rewiring of subcellular membranous structures and for the induction of autophagy. RACK1 binds to HCV nonstructural protein 5A (NS5A), which induces DMV formation. NS5A interacts with ATG14L in a RACK1 dependent manner, and with the ATG14L-Beclin1-Vps34-Vps15 complex that is required for autophagosome formation. Both RACK1 and ATG14L are required for HCV DMV formation and viral RNA replication. These results indicate that NS5A participates in the formation of the HCV replication organelle through interactions with RACK1 and ATG14L.

All positive-strand RNA viruses replicate their genomes in distinct membrane-associated compartments designated replication organelles. The compartmentalization of viral replication machinery allows the enrichment and coordination of cellular and viral factors required for RNA replication and the evasion from innate host defense systems. Hepatitis C virus (HCV), a prototype member of the Flaviviridae family, rearranges intracellular membranes to construct replication organelles composed primarily of double-membrane vesicles (DMVs) which are morphologically similar to autophagosomes. Nonstructural protein 5A (NS5A), which is essential for HCV replication, induces DMV formation. Here, we report that NS5A triggers DMV formation through interactions with RACK1 and components of the vesicle nucleation complex acting at the early stage of autophagy. These results illustrate how a virus skews cellular machineries to utilize them for its replication by hijacking cellular proteins through protein-protein interactions. This research sheds light on the molecular basis of replication organelle formation by HCV and possibly other viruses employing organelles with DMV morphology.

New potent biaryl sulfate-based hepatitis C virus inhibitors

The discovery of a new series of potent hepatitis C virus (HCV) NS5A inhibitors containing biaryl sulfone or sulfate cores is reported. Structure-activity relationship (SAR) studies on inhibitors containing various substitution patterns of the sulfate or sulfone core structure established that m-,m'- substituted biaryl sulfate core-based inhibitors containing an amide moiety (compound 20) or an imidazole moiety (compound 24) showed extremely high potency. Compound 20 demonstrated double-digit pM potencies against both genotype 1b (GT-1b) and 2a (GT-2a). Compound 24 also exhibited double-digit pM potencies against GT-1b and sub nM potencies against GT-2a. Furthermore, compounds 20 and 24 exhibited no cardiotoxicity in an hERG ligand binding assay and showed acceptable plasma stability and no mutagenic potential in the Ames test. In addition, these compounds showed distinctive additive effects in combination treatment with the NS5B targeting drug sofosbuvir (Sovaldi^®). The results of this study showed that the compounds 20 and 24 could be effective HCV inhibitors.

Infectivity of hepatitis C virus correlates with the amount of envelope protein E2: development of a new aptamer-based assay system suitable for measuring the infectious titer of HCV

Various forms of hepatitis C virus (HCV)-related particles are produced from HCV-infected cells. Measuring infectivity of a HCV sample with the conventional 'foci counting method' is laborious and time-consuming. Moreover, the infectivity of a HCV sample does not correlate with the amount of viral RNA that can be measured by real-time RT-PCR. Here we report a new assay suitable for quantifying infectious HCV particles using aptamers against HCV E2, which is named 'Enzyme Linked Apto-Sorbent Assay (ELASA)'. The readout value of HCV ELASA linearly correlates with the infectious dose of an HCV sample, but not with the amount of HCV RNA. We also demonstrated that the activities of anti-HCV drugs can be monitored by HCV ELASA. Therefore, HCV ELASA is a quick-and-easy method to quantify infectious units of HCV stocks and to monitor efficacies of potential anti-HCV drugs.