Relapse and refractory T cell acute lymphoblastic leukemia (T-ALL) has a poor prognosis and new combination therapies are sorely needed. Here, we used an ex vivo high-throughput screening platform to identify drug combinations that kill zebrafish T-ALL and then validated top drug combinations for preclinical efficacy in human disease. This work uncovered potent drug synergies between AKT/mTORC1 inhibitors and the general tyrosine kinase-inhibitor, dasatinib. Importantly, these same drug combinations effectively killed a subset of relapse and dexamethasone-resistant zebrafish T-ALL. Clinical trials are currently underway using the combination of mTORC1 inhibitor temsirolimus and dasatinib in other pediatric cancer indications, leading us to prioritize this therapy for preclinical testing. This combination effectively curbed T-ALL growth in human cell lines and primary human T-ALL and was well tolerated and effective in suppressing leukemia growth in patient-derived xenografts grown in mice. Mechanistically, dasatinib inhibited phosphorylation and activation of the lymphocyte-specific protein tyrosine kinase (LCK) to blunt the T-cell receptor (TCR) signaling pathway and when complexed with mTORC1 inhibition, induced potent T-ALL cell killing through reducing MCL-1 protein expression. In total, our work uncovered unexpected roles for the LCK kinase and its regulation of downstream TCR signaling in suppressing apoptosis and driving continued leukemia growth. Analysis of a wide array of primary human T-ALLs and PDXs grown in mice suggest that combination of temsirolimus and dasatinib treatment will be efficacious for a large fraction of human T-ALLs.
Antibody–peptide epitope conjugates (APEC) are a new class of modified antibody–drug conjugates that redirect T-cell viral immunity against tumor cells. APECs contain a tumor-specific protease cleavage site linked to a patient-specific viral epitope, resulting in presentation of viral epitopes on cancer cells and subsequent recruitment and killing by CD8+ T cells. Here we developed an experimental pipeline to create patient-specific APECs and identified new preclinical therapies for ovarian carcinoma. Using functional assessment of viral peptide antigen responses to common viruses like cytomegalovirus (CMV) in patients with ovarian cancer, a library of 192 APECs with distinct protease cleavage sequences was created using the anti-epithelial cell adhesion molecule (EpCAM) antibody. Each APEC was tested for in vitro cancer cell killing, and top candidates were screened for killing xenograft tumors grown in zebrafish and mice. These preclinical modeling studies identified EpCAM-MMP7-CMV APEC (EpCAM-MC) as a potential new immunotherapy for ovarian carcinoma. Importantly, EpCAM-MC also demonstrated robust T-cell responses in primary ovarian carcinoma patient ascites samples. This work highlights a robust, customizable platform to rapidly develop patient-specific APECs. Significance: This study develops a high-throughput preclinical platform to identify patient-specific antibody–peptide epitope conjugates that target cancer cells and demonstrates the potential of this immunotherapy approach for treating ovarian carcinoma.
Rhabdomyosarcoma (RMS) accounts for 50% of all soft-tissue childhood sarcomas and is characterized by tumor cells that molecularly and morphologically resemble undifferentiated skeletal muscle. Treatment involves an aggressive regimen of chemotherapy followed by surgical resection and/or radiation therapy. Although survival rates can be as high as 70-90% in low-risk or localized disease, patients with oligoclonal or relapsed disease have extremely poor prognoses. Thus, there is a clinical imperative to identify novel therapeutic targets, particularly ones that could reduce clonality and suppress cancer stem cell self-renewal. Our lab has recently shown that fusion-negative (FN-)RMS contain four dominant tumor cell states: proliferative, ground, mesenchymal cancer stem cells (mCSCs) and differentiated muscle. Importantly, the mCSCs are largely quiescent under normal growth conditions but re-enter the cell cycle to promote tumor growth following stress. This suggests that mCSCs are likely responsible for driving therapy resistance and relapse. Building on our previous successes in live imaging cancer stem cells using transgenic zebrafish models that express fluorophores under control of developmentally restricted muscle promoters, we are now developing similar approaches to drive fluorescent protein expression in human FN-RMS cell lines to trace lineage fate and to witness the division history of mCSCs in real time. Using a combination of CRISPR/Cas9 gene inactivation and these newly developed tools, we are poised to identify new self-renewal pathways by the direct, live-cell imaging of FN-RMS engrafted into optically clear, immune-deficient zebrafish. In addition, we are also using tumor clonality as a surrogate of increased tumor aggression and cancer stem cell potential in the zebrafish RAS-induced RMS model. We have adapted the transgenic zebrafish model of kRASG12D-induced RMS to analyze tumor clonality using multispectral Zebrabow and GESTALT, a CRISPR barcoding technique that tracks cell fate. Using RMS-specific gene expression datasets that are associated with cancer stem cells, we are now screening for genes that elevate tumor clonality, increase tumor penetrance and accelerate tumor growth. Ultimately, by developing these lineage tracing tools in both human RMS cell lines and our transgenic Zebrafish RMS model, we will identify new modulators of the mCSC transcriptional cell states and possible therapeutic targets. Citation Format: Tiffany Eng, Yun Wei, Qian Qin, Chuan Yan, Qiqi Yang, Alexandra Veloso, Karin McCarthy, David Langenau. Dynamic single cell imaging of cancer stem cells and clonality in fusion-negative rhabdomyosarcoma [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr A002.
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