Chromosome fusions triggered by noncoding RNA.

Chromosomal fusions are common in normal and cancer cells and can produce aberrant gene products that promote transformation. The mechanisms driving these fusions are poorly understood, but recurrent fusions are widespread. This suggests an underlying mechanism, and some authors have proposed a possible role for RNA in this process. The unicellular eukaryote Oxytricha trifallax displays an exorbitant capacity for natural genome editing, when it rewrites its germline genome to form a somatic epigenome. This developmental process provides a powerful model system to directly test the influence of small noncoding RNAs on chromosome fusion events during somatic differentiation. Here we show that small RNAs are capable of inducing chromosome fusions in 4 distinct cases (out of 4 tested), including one fusion of 3 chromosomes. We further show that these RNA-mediated chromosome fusions are heritable over multiple sexual generations and that transmission of the acquired fusion is associated with endogenous production of novel piRNA molecules that target the fused junction. We also demonstrate the capacity of a long noncoding RNA (lncRNA) to induce chromosome fusion of 2 distal germline loci. These results underscore the ability of short-lived, aberrant RNAs to act as drivers of chromosome fusion events that can be stably transmitted to future generations.

HPN328, a Trispecific T Cell-Activating Protein Construct Targeting DLL3-Expressing Solid Tumors.

Delta-like ligand 3 (DLL3) is expressed in more than 70% of small cell lung cancers (SCLCs) and other neuroendocrine-derived tumor types. SCLC is highly aggressive, and limited therapeutic options lead to poor prognosis for patients. HPN328 is a trispecific T cell-activating construct (TriTAC) consisting of three binding domains: a CD3 binder for T-cell engagement, an albumin binder for half-life extension, and a DLL3 binder for tumor cell engagement. In vitro assays, rodent models, and non-human primates were used to assess the activity of HPN328. HPN328 induces potent dose-dependent killing of DLL3-expressing SCLC cell lines in vitro, concomitant with T-cell activation and cytokine release. In an NCI-H82 xenograft model with established tumors, HPN328 treatment led to T-cell recruitment and anti-tumor activity. In an immunocompetent mouse model expressing a human CD3ε epitope, mice previously treated with HPN328 withstood tumor rechallenge, demonstrating long-term anti-tumor immunity. When repeat doses were administered to cynomolgus monkeys, HPN328 was well tolerated up to 10 mg/kg. Pharmacodynamic changes, such as transient cytokine elevation, were observed, consistent with the expected mechanism of action of T-cell engagers. HPN328 exhibited linear pharmacokinetics in the given dose range with a serum half-life of 78 to 187 hours, supporting weekly or less frequent administration of HPN328 in humans. Preclinical and nonclinical characterization suggests that HPN328 is a highly efficacious, safe, and novel therapeutic candidate. A phase 1/2 clinical trial is currently underway testing safety and efficacy in patients with DLL3-expressing malignancies.

Epigenetic Regulation of Neuregulin-1 Tunes White Adipose Stem Cell Differentiation.

Expansion of subcutaneous adipose tissue by differentiation of new adipocytes has been linked to improvements in metabolic health. However, an expandability limit has been observed wherein new adipocytes cannot be produced, the existing adipocytes become enlarged (hypertrophic) and lipids spill over into ectopic sites. Inappropriate ectopic storage of these surplus lipids in liver, muscle, and visceral depots has been linked with metabolic dysfunction. Here we show that Neuregulin-1 (NRG1) serves as a regulator of adipogenic differentiation in subcutaneous primary human stem cells. We further demonstrate that DNA methylation modulates NRG1 expression in these cells, and a 3-day exposure of stem cells to a recombinant NRG1 peptide fragment is sufficient to reprogram adipogenic cellular differentiation to higher levels. These results define a novel molecular adipogenic rheostat with potential implications for the expansion of adipose tissue in vivo.

Discovery of a stem-like multipotent cell fate.

Adipose derived stem cells (ASCs) can be obtained from lipoaspirates and induced in vitro to differentiate into bone, cartilage, and fat. Using this powerful model system we show that after in vitro adipose differentiation a population of cells retain stem-like qualities including multipotency. They are lipid (-), retain the ability to propagate, express two known stem cell markers, and maintain the capacity for trilineage differentiation into chondrocytes, adipocytes, and osteoblasts. However, these cells are not traditional stem cells because gene expression analysis showed an overall expression profile similar to that of adipocytes. In addition to broadening our understanding of cellular multipotency, our work may be particularly relevant to obesity-associated metabolic disorders. The adipose expandability hypothesis proposes that inability to differentiate new adipocytes is a primary cause of metabolic syndrome in obesity, including diabetes and cardiovascular disease. Here we have defined a differentiation-resistant stem-like multipotent cell population that may be involved in regulation of adipose expandability in vivo and may therefore play key roles in the comorbidities of obesity.