Feedforward regulatory logic controls the specification-to-differentiation transition and terminal cell fate during Caenorhabditis elegans endoderm development.

The architecture of gene regulatory networks determines the specificity and fidelity of developmental outcomes. We report that the core regulatory circuitry for endoderm development in Caenorhabditis elegans operates through a transcriptional cascade consisting of six sequentially expressed GATA-type factors that act in a recursive series of interlocked feedforward modules. This structure results in sequential redundancy, in which removal of a single factor or multiple alternate factors in the cascade leads to a mild or no effect on gut development, whereas elimination of any two sequential factors invariably causes a strong phenotype. The phenotypic strength is successfully predicted with a computational model based on the timing and levels of transcriptional states. We found that one factor in the middle of the cascade, END-1, which straddles the distinct events of specification and differentiation, functions in both processes. Finally, we reveal roles for key GATA factors in establishing spatial regulatory state domains by repressing other fates, thereby defining boundaries in the digestive tract. Our findings provide a paradigm that could account for the genetic redundancy observed in many developmental regulatory systems.

Pharmacy Operationalization of the Intralesional Oncolytic Immunotherapy Talimogene Laherparepvec.

Objective: Oncolytic immunotherapy involves the use of viruses to target and destroy cancer cells and to induce immune responses for an enhanced antitumor effect. Talimogene laherparepvec, a genetically modified herpes simplex virus type 1 (HSV-1) that selectively replicates in tumors to induce lytic cell death, tumor antigen release, and the local production of granulocyte-macrophage colony-stimulating factor (GM-CSF), has been approved for the treatment of a defined population of patients with metastatic melanoma. Talimogene laherparepvec is administered as a series of intralesional injections, and specific procedures are implemented to minimize the risk of viral exposure. Because talimogene laherparepvec represents a novel therapeutic modality, its preparation, administration, and handling requirements differ from current therapies; pharmacists have an important role in developing new procedures to incorporate it into clinical practice. Methods: In this review, pharmacists with experience dispensing talimogene laherparepvec, in the clinical trial setting and/or as a commercially available product at US academic institutions, synthesized their personal experiences through group discussions to provide insights on the ordering, receipt, storage, preparation, administration, and handling of talimogene laherparepvec. Results: Suggestions for patient education and practical guidance to assist hospital pharmacists and decision makers with implementing talimogene laherparepvec at their institutions are provided. Conclusion: These insights may further inform the development of policies or procedures to incorporate talimogene laherparepvec into clinical settings and improve patient outcomes.

Phase 1b Trial of Biweekly Intravenous Pexa-Vec (JX-594), an Oncolytic and Immunotherapeutic Vaccinia Virus in Colorectal Cancer.

Fifteen patients with treatment-refractory colorectal cancer were enrolled on a phase 1b study of Pexa-Vec (pexastimogene devacirepvec; JX-594), an oncolytic and immunotherapeutic vaccinia designed to selectively replicate in cancer cells. Pexa-Vec was administered intravenously every 14 days, at dose levels of 1 × 10(6), 1 × 10(7), or 3 × 10(7) plaque-forming units (pfu)/kg. The primary endpoint was to determine the maximum tolerated dose. Secondary endpoints were pharmacokinetics and pharmacodynamics as well as antitumor activity. Patients were heavily pretreated (mean 4.5 lines of therapy). All patients received at least two Pexa-Vec doses (median = 4; range = 2-4). No dose-limiting toxicities were reported, and the maximum tolerated dose was not reached. The most common adverse events were grade 1/2 flu-like symptoms, generally lasting <24 hours. During the first and last cycles, genome pharmacokinetics were unchanged. Infectious pfu could be detected in plasma up to 2 hours after cycle 1 and up to 30 minutes after cycle 4 (when antivaccinia antibody titers are known to have peaked). Ten patients (67%) had radiographically stable disease. Given the acceptable safety profile of multiple intravenous Pexa-Vec infusions in patients with treatment-refractory colorectal cancer, further trials evaluating efficacy of intravenous Pexa-Vec, as monotherapy or in combination with chemotherapeutic agents, is warranted in this patient population.

Essential role for Notch signaling in restricting developmental plasticity.

We report that Notch signaling is essential for the switch from developmental plasticity to commitment during Caenorhabditis elegans embryogenesis. The GLP-1 and LIN-12 Notch receptors act to set a memory state that affects commitment of cells arising from the major ectodermal progenitor (AB blastomere) several cell divisions later, thereby preventing their forced reprogramming by an endoderm-determining transcription factor. In contrast to Notch-dependent cell fate induction, this activity is autonomous to the AB lineage, is independent of the known cell fate-inducing Notch ligands, and requires a putative secreted Notch ligand, Delta Serrate Lag-3 (DSL-3). Thus, Notch signaling promotes developmental commitment by a mechanism that is distinct from that involved in specifying cell fates.

Endoderm development in Caenorhabditis elegans: the synergistic action of ELT-2 and -7 mediates the specification→differentiation transition.

The transition from specification of cell identity to the differentiation of cells into an appropriate and enduring state is critical to the development of embryos. Transcriptional profiling in Caenorhabditis elegans has revealed a large number of genes that are expressed in the fully differentiated intestine; however, no regulatory factor has been found to be essential to initiate their expression once the endoderm has been specified. These gut-expressed genes possess a preponderance of GATA factor binding sites and one GATA factor, ELT-2, fulfills the expected characteristics of a key regulator of these genes based on its persistent expression exclusively in the developing and differentiated intestine and its ability to bind these regulatory sites. However, a striking characteristic of elt-2(0) knockout mutants is that while they die shortly after hatching owing to an obstructed gut passage, they nevertheless contain a gut that has undergone complete morphological differentiation. We have discovered a second gut-specific GATA factor, ELT-7, that profoundly synergizes with ELT-2 to create a transcriptional switch essential for gut cell differentiation. ELT-7 is first expressed in the early endoderm lineage and, when expressed ectopically, is sufficient to activate gut differentiation in nonendodermal progenitors. elt-7 is transcriptionally activated by the redundant endoderm-specifying factors END-1 and -3, and its product in turn activates both its own expression and that of elt-2, constituting an apparent positive feedback system. While elt-7 loss-of-function mutants lack a discernible phenotype, simultaneous loss of both elt-7 and elt-2 results in a striking all-or-none block to morphological differentiation of groups of gut cells with a region-specific bias, as well as reduced or abolished gut-specific expression of a number of terminal differentiation genes. ELT-2 and -7 synergize not only in activation of gene expression but also in repression of a gene that is normally expressed in the valve cells, which immediately flank the termini of the gut tube. Our results point to a developmental strategy whereby positive feedback and cross-regulatory interactions between two synergistically acting regulatory factors promote a decisive and persistent transition of specified endoderm progenitors into the program of intestinal differentiation.