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We conducted a phase I clinical trial of H3B-8800, an oral small molecule that binds Splicing Factor 3B1 (SF3B1), in patients with MDS, CMML, or AML. Among 84 enrolled patients (42 MDS, 4 CMML and 38 AML), 62 were red blood cell (RBC) transfusion dependent at study entry. Dose escalation cohorts examined two once-daily dosing regimens: schedule I (5 days on/9 days off, range of doses studied 1-40 mg, n = 65) and schedule II (21 days on/7 days off, 7-20 mg, n = 19); 27 patients received treatment for ≥180 days. The most common treatment-related, treatment-emergent adverse events included diarrhea, nausea, fatigue, and vomiting. No complete or partial responses meeting IWG criteria were observed; however, RBC transfusion free intervals >56 days were observed in nine patients who were transfusion dependent at study entry (15%). Of 15 MDS patients with missense SF3B1 mutations, five experienced RBC transfusion independence (TI). Elevated pre-treatment expression of aberrant transcripts of Transmembrane Protein 14C (TMEM14C), an SF3B1 splicing target encoding a mitochondrial porphyrin transporter, was observed in MDS patients experiencing RBC TI. In summary, H3B-8800 treatment was associated with mostly low-grade TAEs and induced RBC TI in a biomarker-defined subset of MDS.

During development of the mammalian brain, many neural precursor cells (NPCs) undergo apoptosis. The regulation of such cell death, however, is poorly understood. We now show that the survival of mouse embryonic NPCs in vitro was increased by culture at a high cell density and that this effect was attributable to activation of Notch signaling. Expression of an active form of Notch1 thus markedly promoted NPC survival. Hes proteins, key effectors of Notch signaling in inhibition of neurogenesis, were not sufficient for the survival-promoting effect of Notch1. This effect of Notch1 required a region of the protein containing the RAM domain and was accompanied by up-regulation of the anti-apoptotic proteins Bc1-2 and Mc1-1. Moreover, knockdown of these proteins by RAM interference resulted in blockade of the Notch1-induced survival. These results reveal a new function of Notch, the promotion of NPC survival. Keywords: Notch: Hes; Neural Precursor Cell; Survival; Caspase; Bc1-2; Signaling

The extracellular signal-regulated kinase (ERK) is a component of the mitogen-activated protein kinase cascade. Exon 2 of erk2 was deleted by homologous recombination and resulted in embryonic lethality at embryonic day 6.5. erk2 mutant embryos did not form mesoderm and showed increased apoptosis but comparable levels of BrdUrd incorporation, indicating a defect in differentiation, erk2 null embryonic stem (ES) cells exhibited reduced total ERK activity upon serum stimulation, augmented ERK1 phosphorylation, and decreased downstream p90Rsk phosphorylation and activity; yet ES cell proliferation was unaffected. Mutant ES cells were capable of forming mesoderm; however, treatment of mutant ES cells with the mitogen-activated protein kinase kinase inhibitor PD184352 decreased total ERK activity and expression of the mesodermal marker brachyury, suggesting that ERK1 can compensate for ERK2 in vitro. Normal embryos at embryonic day 6.5 expressed activated ERK1/2 in the extraembryonic ectoderm, whereas erk2 mutant embryos had no detectable activated ERK1/2 in this region, suggesting that activated ERK1 was not expressed, and therefore cannot compensate for loss of ERK2 in vivo. These data indicate that ERK2 plays an essential role in mesoderm differentiation during embryonic development.

Dysregulation of apoptosis contributes to the pathogenesis of many human diseases. As effectors of the apoptotic machinery, caspases are considered potential therapeutic targets. Using an established in vivo model of Fas-mediated apoptosis, we demonstrate here that elimination of certain caspases was compensated in vivo by the activation of other caspases. Hepatocyte apoptosis and mouse death induced by the Fas agonistic antibody Jo2 required proapoptotic Bcl-2 family member Bid and used a Bid-mediated mitochondrial pathway of caspase activation; deficiency in caspases essential for this pathway, caspase-9 or caspase-3, unexpectedly resulted in rapid activation of alternate caspases after injection of Jo2, and therefore failed to protect mice against Jo2 toxicity. Moreover, both ultraviolet and gamma irradiation, two established inducers of the mitochondrial caspase-activation pathway, also elicited compensatory activation of caspases in cultured caspase-3[sup.-/-] hepatocytes, indicating that the compensatory caspase activation was mediated through the mitochondria. Our findings provide direct experimental evidence for compensatory pathways of caspase activation. This issue should therefore be considered in developing caspase inhibitors for therapeutic applications., Author(s): Timothy S. Zheng [1, 8, 9]; Stephane Hunot [1, 9]; Keisuke Kuida [2]; Takashi Momoi [3]; Anu Srinivasan [4]; Donald W. Nicholson [5]; Yuri Lazebnik [6]; Richard A. Flavell [...]

The activator of the caspase cascade in vitro is investigated using caspase 9 (Casp9)-knockout mice. These mutant mice usually die at birth because of the failure of the cellular death machinery. The caspase cascade is an important component of cellular apoptosis without which cells continue to live and organ enlargement and malformation results. The addition of exogenous Casp9 induced the expression of the other caspase gene indicating that Casp9 is an upstream activator of the cascade.

The deficiency of CPP32/yama/apopain of the interleukin-1 beta converting enzyme family leads to a decrease in brain apoptosis and premature lethality in mice. The CPP32 is the mammalian homologue of the Caenorhabditis elegans cell death gene, ced-3. CPP32 deficiency affects brain development and leads to hyperplasis. It also leads to the formation of a supernumerary cell population during development. The CPP32 also plays an important role in the morphogenetic cell death taking place early in the central nervous system.

Germ-line transmitted bcl-2 knock-out mice exhibited a system to analyze the function of Bcl-2 in the development, function and death of lymphocytes and morphogenesis of tissues. BCL-2 is essential for lymphocytes and kidney, hair and perichondrium tissues. The nervous system, intestines and skin appear normal, despite the pressure of high levels of Bcl-2.