The impact of the COVID-19 pandemic on cancer care.

The COVID-19 pandemic has disrupted the spectrum of cancer care, including delaying diagnoses and treatment and halting clinical trials. In response, healthcare systems are rapidly reorganizing cancer services to ensure that patients continue to receive essential care while minimizing exposure to SARS-CoV-2 infection

Cohesin mutations alter DNA damage repair and chromatin structure and create therapeutic vulnerabilities in MDS/AML

The cohesin complex plays an essential role in chromosome maintenance and transcriptional regulation. Recurrent somatic mutations in the cohesin complex are frequent genetic drivers in cancer, including myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). Here, using genetic dependency screens of stromal antigen 2-mutant (STAG2-mutant) AML, we identified DNA damage repair and replication as genetic dependencies in cohesin-mutant cells. We demonstrated increased levels of DNA damage and sensitivity of cohesin-mutant cells to poly(ADP-ribose) polymerase (PARP) inhibition. We developed a mouse model of MDS in which Stag2 mutations arose as clonal secondary lesions in the background of clonal hematopoiesis driven by tet methylcytosine dioxygenase 2 (Tet2) mutations and demonstrated selective depletion of cohesin-mutant cells with PARP inhibition in vivo. Finally, we demonstrated a shift from STAG2- to STAG1-containing cohesin complexes in cohesin-mutant cells, which was associated with longer DNA loop extrusion, more intermixing of chromatin compartments, and increased interaction with PARP and replication protein A complex. Our findings inform the biology and therapeutic opportunities for cohesin-mutant malignancies

Utility of CRISPR/Cas9 systems in hematology research

Since the end of the 20th century, the development of novel approaches have emerged to manipulate experimental models of hematological disorders, so they would more accurately mirror what is observed in the clinic. Despite these technological advances, the characterization of crucial genes for benign or malignant hematological disorders remains challenging, mainly because of the dynamic nature of the hematopoietic system and the genetic heterogeneity of these disorders. To overcome this limitation, genome editing technologies have been developed to specifically manipulate the genome via deletion, insertion or modification of targeted loci. These technologies have swiftly progressed, allowing their common use to investigate genetic function in experimental hematology. Amongst them, homologous recombination (HR)-mediated targeting technologies have facilitated the manipulation of specific loci by generating knockout and knock-in models. Despite promoting significant advances in the understanding of the molecular mechanisms involved in hematology, these inefficient, time-consuming and labor-intensive approaches did not permit the development of cellular or animal models recapitulating the complexity of hematological disorders. In October 2016, Dr. Ben Ebert and Dr. Chad Cowan shared their knowledge and experiences with the utilization of CRISPR for models of myeloid malignancy, disease, and novel therapeutics. Here we provide an overview of the topics they covered including insights into the novel applications of the technique as well as its strengths and limitations

Identification of RPS14 as a 5q- syndrome gene by RNA interference screen

Somatic chromosomal deletions in cancer are thought to indicate the location of tumor suppressor genes, whereby complete loss of gene function occurs through biallelic deletion, point mutation, or epigenetic silencing, thus fulfilling Knudson's two-hit hypothesis.1 In many recurrent deletions, however, such biallelic inactivation has not been found. One prominent example is the 5q- syndrome, a subtype of myelodysplastic syndrome (MDS) characterized by a defect in erythroid differentiation.2 Here, we describe an RNA interference (RNAi)-based approach to discovery of the 5q- disease gene. We find that partial loss of function of the ribosomal protein RPS14 phenocopies the disease in normal hematopoietic progenitor cells, and moreover that forced expression of RPS14 rescues the disease phenotype in patient-derived bone marrow cells. In addition, we identified a block in the processing of pre-rRNA in RPS14 deficient cells that is highly analogous to the functional defect in Diamond Blackfan Anemia, linking the molecular pathophysiology of the 5q- syndrome to a congenital bone marrow failure syndrome. These results indicate that the 5q- syndrome is caused by a defect in ribosomal protein function, and suggests that RNAi screening is an effective strategy for identifying causal haploinsufficiency disease genes

An Erythroid Differentiation Signature Predicts Response to Lenalidomide in Myelodysplastic Syndrome

Background: Lenalidomide is an effective new agent for the treatment of patients with myelodysplastic syndrome (MDS), an acquired hematopoietic disorder characterized by ineffective blood cell production and a predisposition to the development of leukemia. Patients with an interstitial deletion of Chromosome 5q have a high rate of response to lenalidomide, but most MDS patients lack this deletion. Approximately 25% of patients without 5q deletions also benefit from lenalidomide therapy, but response in these patients cannot be predicted by any currently available diagnostic assays. The aim of this study was to develop a method to predict lenalidomide response in order to avoid unnecessary toxicity in patients unlikely to benefit from treatment. Methods and Findings: Using gene expression profiling, we identified a molecular signature that predicts lenalidomide response. The signature was defined in a set of 16 pretreatment bone marrow aspirates from MDS patients without 5q deletions, and validated in an independent set of 26 samples. The response signature consisted of a cohesive set of erythroid-specific genes with decreased expression in responders, suggesting that a defect in erythroid differentiation underlies lenalidomide response. Consistent with this observation, treatment with lenalidomide promoted erythroid differentiation of primary hematopoietic progenitor cells grown in vitro. Conclusions: These studies indicate that lenalidomide-responsive patients have a defect in erythroid differentiation, and suggest a strategy for a clinical test to predict patients most likely to respond to the drug. The experiments further suggest that the efficacy of lenalidomide, whose mechanism of action in MDS is unknown, may be due to its ability to induce erythroid differentiation

MPLW515L Is a Novel Somatic Activating Mutation in Myelofibrosis with Myeloid Metaplasia

BACKGROUND: The JAK2V617F allele has recently been identified in patients with polycythemia vera (PV), essential thrombocytosis (ET), and myelofibrosis with myeloid metaplasia (MF). Subsequent analysis has shown that constitutive activation of the JAK-STAT signal transduction pathway is an important pathogenetic event in these patients, and that enzymatic inhibition of JAK2V617F may be of therapeutic benefit in this context. However, a significant proportion of patients with ET or MF are JAK2V617F-negative. We hypothesized that activation of the JAK-STAT pathway might also occur as a consequence of activating mutations in certain hematopoietic-specific cytokine receptors, including the erythropoietin receptor (EPOR), the thrombopoietin receptor (MPL), or the granulocyte-colony stimulating factor receptor (GCSFR). METHODS AND FINDINGS: DNA sequence analysis of the exons encoding the transmembrane and juxtamembrane domains of EPOR, MPL, and GCSFR, and comparison with germline DNA derived from buccal swabs, identified a somatic activating mutation in the transmembrane domain of MPL (W515L) in 9% (4/45) of JAKV617F-negative MF. Expression of MPLW515L in 32D, UT7, or Ba/F3 cells conferred cytokine-independent growth and thrombopoietin hypersensitivity, and resulted in constitutive phosphorylation of JAK2, STAT3, STAT5, AKT, and ERK. Furthermore, a small molecule JAK kinase inhibitor inhibited MPLW515L-mediated proliferation and JAK-STAT signaling in vitro. In a murine bone marrow transplant assay, expression of MPLW515L, but not wild-type MPL, resulted in a fully penetrant myeloproliferative disorder characterized by marked thrombocytosis (Plt count 1.9–4.0 × 10 (12)/L), marked splenomegaly due to extramedullary hematopoiesis, and increased reticulin fibrosis. CONCLUSIONS: Activation of JAK-STAT signaling via MPLW515L is an important pathogenetic event in patients with JAK2V617F-negative MF. The bone marrow transplant model of MPLW515L-mediated myeloproliferative disorders (MPD) exhibits certain features of human MF, including extramedullary hematopoiesis, splenomegaly, and megakaryocytic proliferation. Further analysis of positive and negative regulators of the JAK-STAT pathway is warranted in JAK2V617F-negative MPD

Musashi-2 controls cell fate, lineage bias, and TGF-β signaling in HSCs

Hematopoietic stem cells (HSCs) are maintained through the regulation of symmetric and asymmetric cell division. We report that conditional ablation of the RNA-binding protein Msi2 results in a failure of HSC maintenance and engraftment caused by a loss of quiescence and increased commitment divisions. Contrary to previous studies, we found that these phenotypes were independent of Numb. Global transcriptome profiling and RNA target analysis uncovered Msi2 interactions at multiple nodes within pathways that govern RNA translation, stem cell function, and TGF-β signaling. Msi2-null HSCs are insensitive to TGF-β–mediated expansion and have decreased signaling output, resulting in a loss of myeloid-restricted HSCs and myeloid reconstitution. Thus, Msi2 is an important regulator of the HSC translatome and balances HSC homeostasis and lineage bias

Human tumors instigate granulin-expressing hematopoietic cells that promote malignancy by activating stromal fibroblasts in mice

Systemic instigation is a process by which endocrine signals sent from certain tumors (instigators) stimulate BM cells (BMCs), which are mobilized into the circulation and subsequently foster the growth of otherwise indolent carcinoma cells (responders) residing at distant anatomical sites. The identity of the BMCs and their specific contribution or contributions to responder tumor growth have been elusive. Here, we have demonstrated that Scal(+)cKit(-) hematopoietic BMCs of mouse hosts bearing instigating tumors promote the growth of responding tumors that form with a myofibroblast-rich, desmoplastic stroma. Such stroma is almost always observed in malignant human adenocarcinomas and is an indicator of poor prognosis. We then identified granulin (GRN) as the most upregulated gene in instigating Scal(+)cKit(-) BMCs relative to counterpart control cells. The GRN(+) BMCs that were recruited to the responding tumors induced resident tissue fibroblasts to express genes that promoted malignant tumor progression; indeed, treatment with recombinant GRN alone was sufficient to promote desmoplastic responding tumor growth. Further, analysis of tumor tissues from a cohort of breast cancer patients revealed that high GRN expression correlated with the most aggressive triple-negative, basal-like tumor subtype and reduced patient survival. Our data suggest that GRN and the unique hematopoietic BMCs that produce it might serve as novel therapeutic targets

Macrophages support pathological erythropoiesis in Polycythemia Vera and Beta-Thalassemia

Regulation of erythropoiesis is achieved by integration of distinct signals. Among these, macrophages are emerging as erythropoietin-complementary regulators of erythroid development, particularly under stress conditions. We investigated the contribution of macrophages for physiological and pathological conditions of enhanced erythropoiesis. We utilized mouse models of induced anemia, Polycythemia vera and β-thalassemia in which macrophages were chemically depleted. Our data indicate that macrophages contribute decisively for recovery from induced anemia as well as the pathological progression of Polycythemia vera and β-thalassemia by modulating erythroid proliferation and differentiation. We validated these observations in primary human cultures, showing a critical direct impact of macrophages on proliferation and enucleation of erythroblasts from healthy individuals and Polycythemia vera or β-thalassemic patients. In summary, we identify a new mechanism that we named “Stress Erythropoiesis Macrophage-supporting Activity” (SEMA) that contributes to the pathophysiology of these disorders and will have critical scientific and therapeutic implications in the near future