Abstract P4-01-19: Liquid biopsy and re-biopsy: Tracking mutational trajectories in HER2+ breast cancer patients undergoing T-DM1 treatment

Background: The antibody-drug conjugate Trastuzumab emtansine (T-DM1, Kadcyla®) is standard of care in HER2+ breast cancer patients on clinical progression after Trastuzumab/Pertuzumab and taxanes. Despite considerable clinical benefits, most patients rapidly develop progressive disease due to adaptive resistance, the molecular bases of which remain largely unknown and/or controversial. Next generation sequencing (NGS) and digital PCR (dPCR) applied to serial biological samples obtained through liquid biopsy (LB) and re-biopsy (RB) offer a unique opportunity to intercept mutational trajectories and uncover molecular patterns linked to primary as well as adaptive resistance.

Materials and methods: Tumor tissues (n=14), either from primary or metastatic lesions, and plasma samples (n=99) were collected, upon informed consent, from 9 breast cancer patients undergoing T-DM1 administration. Tissue (tDNA) and circulating tumor DNA (ctDNA) were extracted by the QIAmp DNA FFPE and CNA kits (Qiagen), respectively, and analyzed by ultra-deep sequencing and dPCR (IonTorrent S5 and QuantStudio 3D, LifeTechnologies) with commercial 400-gene panel and custom-designed dPCR assays. Genomic data were correlated with clinical imaging (CT/PET).

Results: Six out 9 (66.7%) patients experienced progression within 1 year of treatment (mean 192±97 days), whereas the remaining 3 were stable at the last follow up (> 400 days). No correlation was found between outcome and HER2, ER or PR status in the latest available (prior to T-DM1) archival tissue, in which NGS revealed several pre-existing mutations, including some associated with resistance to ERBB2 blockade. LB analysis detected increases in both baseline and de novo occurring aberrations in 5/6 (83.4%) relapsing patients. As compared to clinical imaging, progression disease was anticipated by an average lead time of 1.9 months (range 0.7-2.8). Surprisingly, the sixth relapsing patient underwent rapid progression (3 months) in spite of decreased PIK3CA p.E545K in blood, further confirmed in the re-biopsy, thus suggesting heterogeneous response to T-DM1 across multiple cancer cell populations. Of note, we observed progressive accumulation of ERBB2 p.L755S (associated with Lapatinib resistance) in multiple biopsies of serial metastatic foci from a patient over 18 years of multimodal ERBB2 blockade. However, a single administration of T-DM1 resulted in ultra-fast (within few weeks) clearance of ERBB2 p.L755S ctDNA, and stabilization of two distinct 'bystander' TP53 ctDNAs (p.R273H and p.S241T).

Conclusions: Non-invasive LB monitoring of a small cohort of T-DM1-treated patients provides proof of principle of intersecting mutational trajectories, anticipation and classification of resistance, as well as de novo appearance/clearance of resistance mutations. Thus, LB and RB may hint at disease evolution and successive lines of medical treatment.

This work was supported by AIRC (Nuvenia Fellowship to MA, IG 19052 to PG), EU commission (grant #633937 – ULTRAPLACAD), and Regina Elena National Cancer Institute intramural funding.

Citation Format: Allegretti M, Giordani E, Casini B, Romania P, Gasparro S, Russillo M, Gallo E, Buglioni S, Pescarmona E, Cognetti F, Ciliberto G, Giacomini P, Fabi A. Liquid biopsy and re-biopsy: Tracking mutational trajectories in HER2+ breast cancer patients undergoing T-DM1 treatment [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-01-19.

The Vici syndrome protein EPG5 regulates intracellular nucleic acid trafficking linking autophagy to innate and adaptive immunity

Vici syndrome is a human inherited multi-system disorder caused by recessive mutations in EPG5, encoding the EPG5 protein that mediates the fusion of autophagosomes with lysosomes. Immunodeficiency characterized by lack of memory B cells and increased susceptibility to infection is an integral part of the condition, but the role of EPG5 in the immune system remains unknown. Here we show that EPG5 is indispensable for the transport of the TLR9 ligand CpG to the late endosomal-lysosomal compartment, and for TLR9-initiated signaling, a step essential for the survival of human memory B cells and their ultimate differentiation into plasma cells. Moreover, the predicted structure of EPG5 includes a membrane remodeling domain and a karyopherin-like domain, thus explaining its function as a carrier between separate vesicular compartments. Our findings indicate that EPG5, by controlling nucleic acids intracellular trafficking, links macroautophagy/autophagy to innate and adaptive immunity.

Endoplasmic reticulum aminopeptidase 1 function and its pathogenic role in regulating innate and adaptive immunity in cancer and major histocompatibility complex class I-associated autoimmune diseases

Major histocompatibility complex (MHC) class I molecules present antigenic peptides on the cell surface to alert natural killer (NK) cells and CD8(+) T cells for the presence of abnormal intracellular events, such as virus infection or malignant transformation. The generation of antigenic peptides is a multistep process that ends with the trimming of N-terminal extensions in the endoplasmic reticulum (ER) by aminopeptidases ERAP1 and ERAP2. Recent studies have highlighted the potential role of ERAP1 in reprogramming the immunogenicity of tumor cells in order to elicit innate and adaptive antitumor immune responses, and in conferring susceptibility to autoimmune diseases in predisposed individuals. In this review, we will provide an overview of the current knowledge about the role of ERAP1 in MHC class I antigen processing and how its manipulation may constitute a promising tool for cancer immunotherapy and treatment of MHC class I-associated autoimmune diseases.

Therapeutic targeting of Chk1 in NSCLC stem cells during chemotherapy

Cancer stem cell (SC) chemoresistance may be responsible for the poor clinical outcome of non-small-cell lung cancer (NSCLC) patients. In order to identify the molecular events that contribute to NSCLC chemoresistance, we investigated the DNA damage response in SCs derived from NSCLC patients. We found that after exposure to chemotherapeutic drugs NSCLC-SCs undergo cell cycle arrest, thus allowing DNA damage repair and subsequent cell survival. Activation of the DNA damage checkpoint protein kinase (Chk) 1 was the earliest and most significant event detected in NSCLC-SCs treated with chemotherapy, independently of their p53 status. In contrast, a weak Chk1 activation was found in differentiated NSCLC cells, corresponding to an increased sensitivity to chemotherapeutic drugs as compared with their undifferentiated counterparts. The use of Chk1 inhibitors in combination with chemotherapy dramatically reduced NSCLC-SC survival in vitro by inducing premature cell cycle progression and mitotic catastrophe. Consistently, the co-administration of the Chk1 inhibitor AZD7762 and chemotherapy abrogated tumor growth in vivo, whereas chemotherapy alone was scarcely effective. Such increased efficacy in the combined use of Chk1 inhibitors and chemotherapy was associated with a significant reduction of NSCLC-SCs in mouse xenografts. Taken together, these observations support the clinical evaluation of Chk1 inhibitors in combination with chemotherapy for a more effective treatment of NSCLC.

Overexpression of Ets-1 in human hematopoietic progenitor cells blocks erythroid and promotes megakaryocytic differentiation

Ets-1 is a widely expressed transcription factor implicated in development, tumorigenesis and hematopoiesis. We analyzed Ets-1 gene expression during human erythroid and megakaryocytic (MK) differentiation in unilineage cultures of CD34+ progenitor cells. During erythroid maturation, Ets-1 is downmodulated and exported from the nucleus into the cytoplasm through an active mechanism mediated by a leucine-rich nuclear export signal. In contrast, during megakaryocytopoiesis Ets-1 increases and remains localized in the nucleus up to terminal maturation. Overexpression of Ets-1 in erythroid cells blocks maturation at the polychromatophilic stage, increases GATA-2 and decreases both GATA-1 and erythropoietin receptor expression. Conversely, Ets-1 overexpressing megakaryocytes are characterized by enhanced differentiation and maturation, coupled with upmodulation of GATA-2 and megakaryocyte-specific genes. We show that Ets-1 binds to and activates the GATA-2 promoter, in vitro and in vivo, indicating that one of the pathways through which Ets-1 blocks erythroid and promotes MK differentiation is via upmodulation of GATA-2 expression.