Bushangqing Liu

Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate (ADC) targeting HER2, exhibiting significant clinical efficacy in breast cancer (BC) with varying HER2 expression, including HER2-low and HER2-ultralow. However, the precise mechanism underlying its efficacy and the contribution of immune activation in these settings remain unclear. Here, we demonstrate that T-DXd efficacy in HER2-low and HER2-negative BC is independent of HER2 engagement and ADC internalization. Instead, its activity relies on extracellular proteases, such as cathepsin L (CTSL), within the tumor microenvironment. Irrespective of their HER2 status, tumor and stromal compartments of invasive BC abundantly express CTSL, which efficiently cleaves the specialized linker of T-DXd, facilitating payload release and inducing cytotoxicity against HER2-low/negative tumors. In HER2-positive BC, the antibody backbone of T-DXd engages Fcγ-receptors and drives antibody-dependent cellular phagocytosis (ADCP). Concurrently, its cytotoxic payload (DXd) induces immunogenic cell death, further activating myeloid cells via TLR4 and STING pathways to enhance tumor antigen presentation to CD8+ T cells. Notably, T-DXd cytotoxicity also upregulates tumor CD47 expression, dampening immune activation. Combining T-DXd with CD47 checkpoint blockade significantly enhances anti-tumor immune responses in a HER2-transgenic BC mouse model, while also inducing durable CD8+ T cell memory to prevent tumor recurrence after therapy cessation. Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate targeting HER2 but paradoxically efficient even in breast cancers expressing HER2 at very low levels. Here authors show that invasive breast cancers, even if their HER2 expression is negligible, secrete extracellular proteases, such as cathepsin L, which cleave the specialized linker of T-DXd, releasing the drug in the tumour microenvironment, while in HER2 positive breast cancers, T-DXd engages Fcγ receptors to promote phagocytosis of HER2-expressing cells and triggers payload-induced immunogenic cell death.

Abstract Trastuzumab deruxtecan (T-DXd), or fam-trastuzumab-deruxtecan-nxki, is a novel antibody-drug-conjugate (ADC) targeting HER2 that has demonstrated profound clinical efficacy across HER2-positive breast cancer (BC), including in HER2-low and HER2 “ultra-low” BC. However, the precise mechanism underlying its efficacy in HER2-low BC is still poorly understood. To determine the mechanism of DXd release and cytotoxicity, we compared in vivo T-DXd treatment of human BC xenografts with varying HER2 expression profiles, coupled with in vitro bystander killing analysis of co-cultured HER2-negative cells, and liquid chromatography–mass spectrometry of DXd payload levels in the tumor microenvironment. Our findings revealed that the efficacy of T-DXd in HER2-low and HER2-negative BC is mediated by extracellular proteases, specifically cathepsin L (CTSL), but not cathepsin B, within the tumor microenvironment (TME). Unlike traditional ADCs such as trastuzumab emtansine (T-DM1), which contain a non-cleavable linker and require efficient intracellular endocytosis for payload release and cytotoxicity, HER2-low and HER2 “ultra-low” BC demonstrated limited ADC uptake. Despite this, these cancer types exhibited strong sensitivity to T-DXd in vivo, but not to T-DM1. Critically, using CTSL overexpression and knockout strategies on HER2 “ultra-low” MDA-MB-231 cells, we found that extracellular CTSL released by tumor cells mediates the proteolytic cleavage of T-DXd’s linker. This enables broader DXd payload release and cytotoxicity, bypassing traditional ADC-resistance mechanisms, including HER2 downregulation and resistance to ADC internalization. Our studies reveal a crucial payload release mechanism of T-DXd within the TME, mediated by extracellular CTSL cleavage of T-DXd’s tetrapeptide linker. This mechanism likely contributes to the broad efficacy of T-DXd in HER2-low and even HER2 “ultra-low” BC over T-DM1. Collectively, our findings suggest that CTSL and other extracellular proteases in the TME may serve as important biomarkers for predicting T-DXd efficacy. Citation Format: Li-Chung Tsao, John S. Wang, Joey Ragusa, Bushangqing Liu, Jason McBane, Ivan Spasojevic, Ping Fan, Timothy N. Trotter, Herbert Kim Lyerly, Zachary C Hartman. Uncovering Bystander Killing Mechanisms of Trastuzumab Deruxtecan (T-DXd): Effective Extracellular Payload Release via Cathepsin L in HER2-low Breast Cancer. [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr A059.

Background: Kisspeptin was identified in 1996 and it was known as a suppressor of metastatic malignant tumors. Kisspeptin and its receptor KISS1R have been identified as potential prognostic or therapeutic markers in cancers. Recent study suggested that kisspeptin plays an important role in gynecological cancer, including breast cancer, ovarian cancer, and endometrium cancer.

Abstract During initiation and progression, cancerous tissue hijacks a series of elaborate tissue homeostatic mechanisms to avoid immune surveillance, including neuro-immune interactions. Here, we show that amyloid-β precursor protein (APP) and its β-cleavage product amyloid-β1-42 (Aβ1-42), well-known in the pathogenesis of Alzheimer’s disease (AD), are expressed in multiple cancer tissues. However, the oncogenic activity of APP is due to its E1 domain, instead of Aβ1-42. Mechanistically, APP restricts immune cells influx into tumor microenvironment (TME) and impairs CD8+ T cell and NK cell-based immunity, by dampening type I interferon (IFN) response in TME. We also provide proof-of-concept that vaccination targeting APP is effective for cancer prevention. Our current study reveals a previously unrecognized role of APP in cancer immune surveillance, and provides a new strategy for cancer prevention and treatment by targeting APP.