암 치료 효과 극대화를 위한 신규 HER2 항체-약물 결합체 개발 및 면역반응성 기전을 응용한 면역치료-방사선치료 병용요법의 항암 효능 증진

Abstract

PART I An elaborate new linker system significantly enhances the efficacy of a HER2-antibody-drug conjugate against refractory HER2-positive cancers. Despite promising efficacy in cancer cell lines and xenograft models, development of targeted anti-cancer drugs has frequently been staying in clinical trials. To improve clinical relevance of preclinical studies, patient-derived xenograft (PDX) models were generated and characterized reflecting HER2-positive gastric cancer (HER2+ GC) patients to aim successful development of targeted therapies for HER2+ GC. GC tissues from surgery of GC patients were implanted into immune-deficient mice and selected HER2+ PDXs from GC PDXs according to the histopathological diagnosis of patients. The HER2+ PDXs were verified of the patient-mimic HER2 expressing by immunohistochemistry (IHC) and explored for the feasibility by testing with Herceptin, commercialized therapeutics and novel HER2 antibody therapeutics being developed. I obtained 5 cases of HER2+ GC PDX models reflecting patient’s GC tumor, consisting of 2 cases of HER2 3+ and 2 cases of HER2 2+. Novel HER2 antibody displayed improved anti-cancer efficacy in combination with Herceptin. The PDX models were successfully established to be utilized for preclinical evaluation of HER2-targeting drugs and combined therapies for GC treatment, as an ideal platform of personalized tools for precision therapy. HER2 is amplified and overexpressed in breast and gastric cancers, and this causes poor clinical outcomes. Although T-DM1 and Enhertu have both been approved as a HER2-targeting antibody drug conjugate (ADC), the effects of these drugs are still not satisfactory to eradicate diverse tumors expressing HER2. To address this shortfall in HER2-targeted therapeutics, a novel HER2-targeting ADC composed with trastuzumab and MMAF were created an elaborate cleavable linker and manufactured, which is being investigated in a phase 1 clinical trial and is referred to as LCB-ADC in this study. LCB-ADC displayed a higher cytotoxic potency than T-DM1, and it also had a higher G2/M arrest ratio in a dose-dependent manner. In animal studies, LCB-ADC produced noticeable tumor growth inhibition compared with trastuzumab or T-DM1 in a HER2 high-expressing N87 xenograft tumor. Of particular note, LCB-ADC showed good efficacy in terms of suppressing tumor growth in a patient-derived xenograft (PDX) model of HER2-positive gastric cancer, as well as in T-DM1-resistant models such as HER2 low-expressing JIMT-1 and PDX. Collectively, the results of this research demonstrate that LCB-ADC with elaborate linker has a higher efficacy and greater biostability than its ADC counterparts and may successfully treat cancers that are non-responsive to previous therapeutics.|PART II Mechanistic investigation of antitumor immune responses following combined treatment with radiotherapy and immunotherapy One of the basic mechanisms by which radiation therapy kills cancer cells is DNA damage-induced apoptosis. Radiation therapy can be curative, palliative, or serving as an adjuvant therapy after the main treatment to lower cancer risk. Recently, it has been discovered that radiation therapy shows an abscopal effect by activating target host immune cells, and not by DNA damage in cancer cells, thereby causing a general anticancer effect in addition to the localized treatment. Radiotherapy is known to affect the immune system in a variety of ways, including 1) surface MHC class I and calreticulin upregulation, and HMGB1 secretion 2) increase in the number of activated dendritic cells and antigen cross-presentation of tumors, 3) increase in tumor-infiltrating lymphocyte (TIL) density, 4) change of immune checkpoint substances, and 5) the regulation of regulatory T cells (Tregs). Radiotherapy has been shown to increase the diversity of the T-cell receptor repertoire—a protein complex found on the surface of T cells—within the tumor. Therefore, many researchers expect to further improve the anticancer effect of radiation therapy via its enhancement of the immune response. Immunotherapy has recently emerged as a promising alternative to chemotherapy, and immune checkpoint blockade (ICB) has shown impressive therapeutic response in the treatment of some solid cancers, such as lung, head, and neck cancer and metastatic malignant melanoma. This anticancer effect is mediated by immune checkpoint inhibitors, such as anti-CTLA4 and anti-PD-1, which block on the surface of T cells. The abscopal effect has been reported in patients treated with radiotherapy and ICB in clinical and preclinical studies; however, its mechanism of occurrence is still unclear. Although it is difficult to observe the effect in both clinical and preclinical studies, an optimized combination therapy comprising irradiation (IR) therapy and ICB could simultaneously reactivate exhausted T cells. In this study, tumor growth was inhibited in MC-38 allograft tumor model mice through combined treatment with IR and anti-PD-L1. Compared to that in other single treatment groups, the anti-tumor effect was enhanced in the radiation and drug-treated group in a dose-dependent manner. Moreover, all the implanted MC-38 tumor models treated with combination therapy showed a complete remission of the irradiated tumor (primary tumor). Two mice showed tumor-free as well as contralateral tumors that were not irradiated. The distribution of the immune cells at the tumor site was confirmed by testing for the levels of TILs and peripheral blood mononuclear cells (PBMC); moreover, the frequency of CD8+ T cells in the tumor was increased following combination therapy. Taken together, these observations indicate that treating patients with a combination therapy of high-dose radiation and ICB could induce the abscopal effect of radiation therapy and enhance its antitumor activity through its effect on the systemic immune system, which could induce a long-term immune response by increasing the levels of effector memory T cells (TEM) in the whole body.