Functional screening in human HSPCs identifies optimized protein-based enhancers of Homology Directed Repair

Homology Directed Repair (HDR) enables precise genome editing, but the implementation of HDR-based therapies is hindered by limited efficiency in comparison to methods that exploit alternative DNA repair routes, such as Non-Homologous End Joining (NHEJ). In this study, we develop a functional, pooled screening platform to identify protein-based reagents that improve HDR in human hematopoietic stem and progenitor cells (HSPCs). We leverage this screening platform to explore sequence diversity at the binding interface of the NHEJ inhibitor i53 and its target, 53BP1, identifying optimized variants that enable new intermolecular bonds and robustly increase HDR. We show that these variants specifically reduce insertion-deletion outcomes without increasing off-target editing, synergize with a DNAPK inhibitor molecule, and can be applied at manufacturing scale to increase the fraction of cells bearing repaired alleles. This screening platform can enable the discovery of future gene editing reagents that improve HDR outcomes.

Abstract A19: Transformation of primary neural crest cells to model pediatric cancers

Neural crest cells (NCCs) are a multipotent, highly migratory cell population specified from the neural tube during embryonic development. NCCs undergo EMT (epithelial to mesenchymal transition) then migrate throughout the body forming diverse lineages including neurons, Schwann cells, melanocytes, and osteoblasts. Precursor cells from NCC lineages are thought to be the cell of origin for several pediatric and adult cancers including neuroblastoma, peripheral primitive neuroectodermal tumors (pPNET), malignant peripheral nerve sheath tumors (MPNST), cranial-facial osteosarcoma, and melanoma.

The most common pediatric cancer in infants is neuroblastoma, which arises from the sypathoadrenal lineage of trunk NCCs. To study early events in neuroblastoma oncogenesis we established a system based on transformation of primary mouse NCCs. Trunk NCCs were isolated from day E9.5 embryos, and resulted in a population that was >95% positive for the NCC markers Sox10, p75, and Ascl1 (MASH1) by immunofluorescence. Culturing primary NCCs in neurogenic differentiation media resulted in neurons positive for Tuj1, Map2, and tyrosine hydroxylase (TH).

Since a prominent category of high-risk neuroblastoma involves amplification of MYCN, we next determined whether MYCN overexpression was sufficient to transform wild-type NCCs in our assay. NCCs were isolated from C57Black6 mice and infected with MYCN retrovirus within 48hr of isolation, and then 10,000 cells/mouse were injected subcutaneously. MYCN overexpression alone generated a single tumor in 1 out of 12 mice, and the resulting tumor expressed the neuronal markers synaptophysin and tyrosine hydroxylase (TH) by immunohistochemistry (IHC).

To determine whether loss of p53 could increase the transformation efficiency, NCCs from p53-compromised mice were infected with MYCN. These tumors had increased penetrance with 19 out of 19 mice developing tumors whether cells were injected into nude mice or into syngeneic C57Black6 mice with an intact immune system. Based on pathological analysis, these tumors were classified as primitive neuroectodermal tumors with divergent differentiation. Tumor regions which were diffusely positive for neuronal markers appeared neuroblastoma-like or PNET-like. Osteosarcoma was also a prominent feature in tumors with loss of p53. We also observed an additional tumor type which was negative by IHC for neuronal, Schwannian, and melanoma markers, and is not yet fully characterized. In general, mice with the fastest onset of tumor growth displayed micrometastases to the lung and liver, while mice with slower tumor growth had macrometastases to these organs. Injection of cell lines derived from the primary tumors also lead to aggressive metastasis to the lung and liver. Although metastasis from subcutaneous tumors is generally rare, it was a recurrent feature in our model which recapitulates the highly metastatic nature of human cancers derived from NCCs like neuroblastoma and melanoma.

Lastly, we determined whether NCCs were sensitive to the BET bromodomain inhibitor JQ1. JQ1 treatment significantly inhibited growth of both primary NCCs and cell lines derived from NCC tumors, while having minimal effect on NIH-3T3 fibroblasts. Furthermore, our results imply that JQ1 sensitivity in these cells is independent of MYCN expression levels.

Using primary mouse NCCs, we found that MYCN overexpression is capable of initiating cell transformation and formed a single tumor with characteristics of neuroblastoma. Additional loss of p53 resulted in a more diverse panel of tumor types, which emphasizes the ability of NCCs to contribute to multiple lineages. Our results suggest that studies utilizing primary NCCs may be beneficial to identify initiating oncogenic events in neuroblastoma and perhaps other pediatric cancers.

Citation Format: Rachelle R. Olsen, Joel H. Otero, Jesus Garcia-Lopez, Kirby A. Wallace, Zhirong Yin, Kevin W. Freeman. Transformation of primary neural crest cells to model pediatric cancers. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr A19.

Common morality and moral reform

The idea of moral reform requires that morality be more than a description of what people do value, for there has to be some measure against which to assess progress. Otherwise, any change is not reform, but simply difference. Therefore, I discuss moral reform in relation to two prescriptive approaches to common morality, which I distinguish as the foundational and the pragmatic. A foundational approach to common morality (e.g., Bernard Gert's) suggests that there is no reform of morality, but of beliefs, values, customs, and practices so as to conform with an unchanging, foundational morality. If, however, there were revision in its foundation (e.g., in rationality), then reform in morality itself would be possible. On a pragmatic view, on the other hand, common morality is relative to human flourishing, and its justification consists in its effectiveness in promoting flourishing. Morality is dependent on what in fact does promote human flourishing and therefore, could be reformed. However, a pragmatic approach, which appears more open to the possibility of moral reform, would need a more robust account of norms by which reform is measured.

A feminist challenge to practices of medicine

Susan Sherwin's No Longer Patient: Feminist Ethics and Health Care is a readable book that is accessible to a wide range of medical practitioners. It presupposes no prior training in ethics or feminism (and for just this reason, it may be somewhat less satisfying, although not necessarily less useful, for philosophers). The book is a feminist bioethics primer that introduces medical practitioners to issues that feminist theory makes prominent and that illuminate tensions in the structure and practice of medicine.

Control and the elderly: "goodness-of-fit"

The present study is an investigation of the effects of person-environment fit on control in an elderly population. Person-environment fit theory predicts that a fit or a match between the characteristics of the person and the characteristic of the environment is important in determining positive outcomes. In the present study, a measure of the misfit (i.e., the mismatch) between an individual's perceptions of control and that individual's desire for control was used to predict life satisfaction, depression, and self-reported health. The misfit between these constructs was found to be a significant predictor of depression, suggesting that a person-environment fit model may be important in explaining this outcome variable. In contrast to the hypothesis, misfit did not significantly predict life satisfaction, and only approached significance in the physical health model. Possible interpretations and implications of these findings were discussed, and potential future research directions were suggested.

Ethanol inhibition of NMDA currents in acutely dissociated medial septum/diagonal band neurons from ethanol dependent rats

The effect of acutely applied ethanol and the impact of chronic ethanol treatment, sufficient to induce tolerance and physical dependence, on N-methyl-D-aspartate (NMDA) receptor function were studied in acutely isolated neurons from the medial septum/diagonal band (MS/DB) of adult rats using whole cell, patch-clamp electrophysiology. There was a small positive correlation for capacitance and current amplitude activated by 100 microM NMDA for all groups. Also, cell membrane capacitance was significantly smaller for Ethanol Dependent (approximately 80-84%) than either Naive or Control cells. Therefore NMDA-activated responses were normalized for capacitance (current density, pA/pF) across all three groups. NMDA-activated (30-1000 microM) responses were significantly larger in cells from Control and Ethanol Dependent rats relative to those from Naives. In addition, estimated maximal responses were significantly larger for Ethanol Dependent cells, compared to either Control or Naive, respectively, while EC50s and slopes were not significantly different. Acute 60 mM ethanol significantly inhibited responses to 100 microM NMDA in all three groups, however, mean ethanol inhibition was 12-25% smaller after ethanol dependence. There was no evidence of acute tolerance to ethanol inhibition for any group, but examination of patterns of inhibition for individual neurons showed a few cells were resistant to ethanol or exhibited progressive loss of ethanol inhibition. These results suggest that NMDA receptor function in acutely isolated MS/DB neurons is increased following in vivo chronic ethanol treatment, and shows resistance to acute ethanol inhibition suggesting NMDA receptor-mediated cellular tolerance.

Diet and exercise patterns in pet dogs

A study was conducted to provide baseline data on pet dog diet and exercise patterns. In addition, the repeatability of a telephone questionnaire to determine these patterns was evaluated. Dogs seen at the Texas Veterinary Medical Center that were less than 3 years old and of medium, large, or giant purebreeds or mixed-breeds were included. Information was collected about background variables, brands, quantities, and types of foods fed, and types and frequency of exercise. Daily intake of metabolizable energy, calcium, fat, and protein were calculated from the diet. Sixty-nine dog owners completed the study. Most dogs were kept as pets in an urban/suburban environment. Most were also fed dry food. About 60% were fed dog biscuits or some other dog snack or treat, and about half of the dogs in the study were fed twice daily. Meat scraps and bones were the table foods most commonly fed. Most owners considered their dogs to be moderately or very active. Greater than 70% of the dogs were confined to a fenced yard. About 65% of the owners took their dogs for walks. Forty percent of dogs in the study exercised with other dogs daily. More than half of the owners reported playing retrieving games with their dogs, including playing with a flying disk. The questionnaire was shown to be repeatable.