Faculty Bibliography

Intratumoral heterogeneity and subclonal diversity, characterized by the coexistence of genetically and functionally distinct leukemic cell populations within a single patient, have long been recognized as major contributors to chemotherapy resistance and disease relapse in acute myeloid leukemia. In this issue of Blood Cancer Discovery, Karigane and colleagues delve into the mechanisms that underlie the interactions between distinct leukemic subpopulations and identify IFN signaling as a critical regulator that determines clonal dominance and expansion. See related article by Karigane et al., p. XX .

Dysregulation of RNA binding proteins (RBPs) is a hallmark in cancerous cells. In acute myeloid leukaemia (AML) RBPs are key regulators of tumour proliferation. While classical RBPs have defined RNA binding domains, RNA recognition and function in AML by non-canonical RBPs (ncRBPs) remain unclear. Given the inherent complexity of targeting AML broadly, our goal was to uncover potential ncRBP candidates critical for AML survival using a CRISPR/Cas-based screening. We identified the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a pro-proliferative factor in AML cells. Based on cross-linking and immunoprecipitation (CLIP), we are defining the global targetome, detecting novel RNA targets mainly located within 5'UTRs, including GAPDH, RPL13a, and PKM. The knockdown of GAPDH unveiled genetic pathways related to ribosome biogenesis, translation initiation, and regulation. Moreover, we demonstrated a stabilizing effect through GAPDH binding to target transcripts including its own mRNA. The present findings provide new insights on the RNA functions and characteristics of GAPDH in AML.

Chimeric antigen receptor (CAR) T cell immunotherapy is promising for treatment of blood cancers; however, clinical benefits remain unpredictable, necessitating development of optimal CAR T cell products. Unfortunately, current preclinical evaluation platforms are inadequate owing to their limited physiological relevance to humans. Here we engineer an organotypic immunocompetent chip that recapitulates microarchitectural and pathophysiological characteristics of human leukaemia bone marrow stromal and immune niches for CAR T cell therapy modelling. This leukaemia chip empowers real-time spatiotemporal monitoring of CAR T cell functionality, including T cell extravasation, recognition of leukaemia, immune activation, cytotoxicity and killing. We use our chip to model clinically observed heterogeneous responses such as remission, resistance and relapse under CAR T cell therapy and map factors that drive therapeutic success or failure. Finally, we demarcate functional performance of CAR T cells produced from different healthy donors and patients with cancer, with various CAR designs and protocols, systematically and multidimensionally. Together, our chip introduces an enabling '(pre-)clinical-trial-on-chip' tool for CAR T cell development, which may translate to personalized therapies and improved clinical decision-making.

Acute myeloid leukemia (AML) is the most prevalent and deadliest adult leukemia. Its frontline treatment uses the BH3 mimetic venetoclax to trigger mitochondria-dependent apoptosis. However, drug resistance nearly always develops, calling for therapies to circumvent it. Advanced microscopy and genome-wide CRISPRi screen analyses pinpointed mitochondrial adaptations primarily mediated by the master regulator of cristae shape optic atrophy 1 (OPA1) as critical for BH3 mimetics resistance. Resistant AML cells up-regulate OPA1 to modify their mitochondrial structure and evade apoptosis. MYLS22 and Opitor-0, two specific and nontoxic OPA1 inhibitors, promote apoptotic cristae remodeling and cytochrome c release, synergizing with venetoclax in AML cells and xenografts derived from AML patients ex vivo and in vivo. Mechanistically, OPA1 loss renders AML cells dependent on glutamine and sensitizes them to ferroptosis by activating ATF4-regulated integrated stress responses. Overall, our data clarify how OPA1 up-regulation allows AML cells' metabolic flexibility and survival and nominates specific OPA1 inhibitors as efficacious tools to overcome venetoclax resistance in leukemia.

Inflammation has enduring impacts on organismal immunity. However, the precise mechanisms by which tissue-restricted inflammation conditions systemic responses are poorly understood. Here, we leveraged a highly compartmentalized model of skin inflammation and identified a surprising type I interferon (IFN)-mediated activation of hematopoietic stem/progenitor cells (HSPCs) that results in profound changes to systemic host responses. Post-inflamed mice were protected from atherosclerosis and had worse outcomes following influenza virus infection. This IFN-mediated HSPC modulation was dependent on IFNAR signaling and could be recapitulated with the administration of recombinant IFN-α. Importantly, the transfer of post-inflamed HSPCs was sufficient to transmit the immune suppression phenotype. IFN modulation of HSPCs was rooted both in long-term changes in chromatin accessibility and the emergence of an IFN-responsive functional state from multiple progenitor populations. Collectively, our data reveal the profound and enduring effect of transient inflammation and more specifically type I IFN signaling and set the stage for a more nuanced understanding of HSPC functional modulation by peripheral immune signals.

Long noncoding RNAs (lncRNAs) are a significant yet largely uncharted component of the cancer transcriptome, with their isoform-specific functions remaining poorly understood. In this study, we employed RNA-targeting CRISPR-Cas13d to uncover and characterize hundreds of tumor-essential (te)-lncRNA isoforms with clinical relevance. Focusing on multiple myeloma (MM), we targeted the lncRNA transcriptome expressed in tumor cells from MM patients and revealed both MM-specific and pan-cancer dependencies across diverse cancer cell lines, which we further validated in animal models. Additionally, we mapped the subcellular localization of these te-lncRNAs, identifying over 30 cytosolic isoforms that proved essential when targeted by cytosol-localized Cas13d. Notably, a specific isoform of SNHG6, enriched in the endoplasmic reticulum, interacts with heat shock proteins to maintain cellular proteostasis. We also integrated functional and clinical data into the publicly accessible LongDEP Portal, providing a valuable resource for the research community. Our study offers a comprehensive characterization of te-lncRNAs, underscoring their oncogenic roles and therapeutic potential.

Isocitrate dehydrogenase 1/2 (IDH) mutations are early initiating events in acute myeloid leukemia (AML). The complex clonal architecture and cellular heterogeneity in IDH-mutant AML underlies the heterogeneous clinical presentation and outcomes. Integrating single-cell genotyping and transcriptomics, we demonstrate a stem-like and inflammatory phenotype of IDH-mutant AML and identify clone-specific programs associated with NPM1, NRAS, and SRSF2 co-mutations. Furthermore, these clones had distinct responses to treatment with combination IDH inhibitors and chemotherapy, including elimination, reconstitution of myeloid differentiation, or retention within progenitor populations. At relapse after IDH inhibitor monotherapy, we identify upregulated stemness, inflammation, mitochondrial metabolism, and anti-apoptotic factors, as well as downregulated major histocompatibility complex (MHC) class II antigen presentation. At the pre-leukemic stage, we observe upregulation of IDH2-associated pathways, including inflammation. We deliver a detailed phenotyping of IDH-mutant AML and a framework for dissecting contributions of recurrently mutated genes in AML at diagnosis and following therapy, with implications for precision medicine.

UNLABELLED:Melanoma being one of the most common and deadliest skin cancers has been increasing since the past decade. Patients at advanced stages of the disease have very poor prognoses, as opposed to at the earlier stages. Nowadays, the standard of care of advanced melanoma is resection, followed by immune checkpoint inhibition-based immunotherapy. However, a substantial proportion of patients either do not respond or develop resistance. This underscores a need for novel approaches and therapeutic targets as well as a better understanding of the mechanisms of melanoma pathogenesis. Long noncoding RNAs (lncRNA) comprise a poorly characterized class of functional players and promising targets in promoting malignancy. Certain lncRNAs have been identified to play integral roles in melanoma progression and drug resistance; however, systematic screens to uncover novel functional lncRNAs are scarce. In this study, we profile differentially expressed lncRNAs in patient-derived short-term metastatic cultures and BRAF-MEK inhibition-resistant cells. We conduct a focused growth-related CRISPR inhibition screen of overexpressed lncRNAs, validate, and functionally characterize lncRNA hits with respect to cellular growth, invasive capacities, and apoptosis in vitro as well as the transcriptomic impact of our lead candidate the novel lncRNA XLOC_030781. In sum, we extend the current knowledge of ncRNAs and their potential relevance in melanoma. SIGNIFICANCE/UNASSIGNED:LncRNAs have emerged as novel players in regulating many cellular aspects also in melanoma. The number of functional significances of most lncRNAs remains elusive. We provide a comprehensive strategy to identify functionally relevant lncRNAs in melanoma by combining expression profiling with CRISPR inhibition growths screens. Our results broaden the characterized lncRNAs as potential targets for future therapeutic applications.

Leukemia-driving mutations are thought to arise in hematopoietic stem cells (HSC), yet the natural history of their spread is poorly understood. We genetically induced mutations within endogenous murine HSC and traced them in unmanipulated animals. In contrast to mutations associated with clonal hematopoiesis (such as Tet2 deletion), the leukemogenic KrasG12D mutation dramatically accelerated HSC contribution to all hematopoietic lineages. The acceleration was mediated by KrasG12D-expressing multipotent progenitors (MPP) that lacked self-renewal but showed increased proliferation and aberrant transcriptome. The deletion of osteopontin, a secreted negative regulator of stem/progenitor cells, delayed the early expansion of mutant progenitors. KrasG12D-carrying cells showed increased CXCR4-driven motility in the bone marrow, and the blockade of CXCR4 reduced the expansion of MPP in vivo. Finally, therapeutic blockade of KRASG12D spared mutant HSC but reduced the expansion of mutant MPP and their mature progeny. Thus, transforming mutations facilitate their own spread from stem cells by reprogramming MPP, creating a preleukemic state via a two-component stem/progenitor circuit.