Engineering mammalian cell growth dynamics for biomanufacturing

Precise control over mammalian cell growth dynamics poses a major challenge in biopharmaceutical manufacturing. Here, we present a multi-level cell engineering strategy for the tunable regulation of growth phases in mammalian cells. Initially, we engineered mammalian death phase by employing CRISPR/Cas9 to knockout pro-apoptotic proteins Bax and Bak, resulting in a substantial attenuation of apoptosis by improving cell viability and extending culture lifespan. The second phase introduced a growth acceleration system, akin to a "gas pedal", based on an abscidic acid inducible system regulating cMYC gene expression, enabling rapid cell density increase and cell cycle control. The third phase focused on a stationary phase inducing system, comparable to a "brake pedal". A tetracycline inducible genetic circuit based on BLIMP1 gene led to cell growth cessation and arrested cell cycle upon activation. Finally, we developed a dual controllable system, combining the "gas and brake pedals", enabling for dynamic and precise orchestration of mammalian cell growth dynamics. This work exemplifies the application of synthetic biology tools and combinatorial cell engineering, offering a sophisticated framework for manipulating mammalian cell growth and providing a unique paradigm for reprogramming cell behaviour for enhancing biopharmaceutical manufacturing and further biomedical applications.

Abstract 4620: Wild-type IDH1: A molecular target in IDH1 mutant cancers

Neomorphic mutations targeting R132 of the TCA cycle enzyme, IDH1, have been identified in multiple cancer types and lead to a build up of (R)-2-hydroxyglutarate ((R)-2HG). Several mechanisms have been proposed to account for mutant-IDH1-mediated transformation: due to its structure similarity with alpha-ketoglutarate (α-KG), (R)-2HG can inhibit α-KG-dependent enzymes that act as tumour suppressors such as TET2 or EGLN, (R)-2HG might inhibit electron transport chain function, or rapid (R)-2HG generation may deplete the cellular pool of α-KG leading to depletion of NADPH. Recently, it has also emerged that IDH1 may be required to catalyse a series of back reactions through TCA cycle components (reductive decarboxylation) to facilitate fatty acid synthesis from media glutamine, particularly under hypoxic conditions. According to some reports in the literature, heterodimer formation between mutant an wild-type alleles of IDH1 is important for the production of high levels of (R)-2HG.

We were interested in exploring novel ways to target tumour cells bearing mutant IDH1 alleles that were distinct from the obvious opportunity available to identify mutant-specific IDH1 inhibitors. The potential metabolic vulnerabilities of mutant IDH1 cancers raised the possibility that wild-type IDH1 might be essential for tumourigenesis or tumour maintenance in this context. We therefore employed Horizon's rAAV-mediated homologous recombination gene engineering technology to generate conditional knockouts of the IDH1+ or IDH1R132C alleles in the fibrosarcoma cell line, HT1080. Despite several attempts, we did not recover a correctly targeted conditional knock-out of the IDH1R132C allele. However, we did recover a derivative cell line where the wild-type allele had been converted into a loxP-flanked IDH1R132C allele, and two independent clones where the wild-type allele had been flanked with loxP sites. Interestingly, in these latter two clones, no expression of wild-type IDH1 was detectable.

Here we present data characterising the growth of these clones under a variety of culture conditions, including the hypoxic state where IDH1 has been proposed to be important for enabling lipid synthesis from glutamine. We also demonstrate that HT1080 cells that express no detectable levels of wild-type IDH1 retain the ability to be tumorigenic in immuno-compromised mice. These data suggest that the wild-type allele of IDH1 is dispensable for cancer formation.

Citation Format: Julie A. Wickenden, Paul Russell, Amy Smith, Tom Henley, Jane Elliott, Dan Gitterman, Mark Stockdale, Christine Schofield, Chris Torrance, Jonathan D. Moore. Wild-type IDH1: A molecular target in IDH1 mutant cancers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4620. doi:10.1158/1538-7445.AM2014-4620

A novel cell-based, high-content assay for phosphorylation of Lats2 by Aurora A

Aurora A kinase is a key regulator of mitosis, which is upregulated in several human cancers, making it a potential target for anticancer therapeutics. Consequently, robust medium- to high-throughput cell-based assays to measure Aurora A kinase activity are critical for the development of small-molecule inhibitors. Here the authors compare measurement of the phosphorylation of two Aurora A substrates previously used in high-content screening Aurora A assays, Aurora A itself and TACC3, with a novel substrate Lats2. Using antibodies directed against phosphorylated forms of Aurora A (pThr288), P-TACC3 (pSer558), and P-Lats2 (pSer83), the authors investigate their suitability in parallel for development of a cell-based assay using several reference Aurora inhibitors: MLN8054, VX680, and AZD1152-HQPA. They validate a combined assay of target-specific phosphorylation of Lats2 at the centrosome and an increase in mitotic index as a measure of Aurora A activity. The assay is both sensitive and robust and has acceptable assay performance for high-throughput screening or potency estimation from concentration-response assays. It has the advantage that it can be carried out using a commercially available monoclonal antibody against phospho-Lats2 and the widely available Cellomics ArrayScan HCS reader and thus represents a significant addition to the tools available for the identification of Aurora A specific inhibitors.

Reduced maximal inhibition in phenotypic susceptibility assays indicates that viral strains resistant to the CCR5 antagonist maraviroc utilize inhibitor-bound receptor for entry

Maraviroc is a CCR5 antagonist in clinical development as one of a new class of antiretrovirals targeting human immunodeficiency virus type 1 (HIV-1) coreceptor binding. We investigated the mechanism of HIV resistance to maraviroc by using in vitro sequential passage and site-directed mutagenesis. Serial passage through increasing maraviroc concentrations failed to select maraviroc-resistant variants from some laboratory-adapted and clinical isolates of HIV-1. However, high-level resistance to maraviroc was selected from three of six primary isolates passaged in peripheral blood lymphocytes (PBL). The SF162 strain acquired resistance to maraviroc in both treated and control cultures; all resistant variants were able to use CXCR4 as a coreceptor. In contrast, maraviroc-resistant virus derived from isolates CC1/85 and RU570 remained CCR5 tropic, as evidenced by susceptibility to the CCR5 antagonist SCH-C, resistance to the CXCR4 antagonist AMD3100, and an inability to replicate in CCR5 Delta32/Delta32 PBL. Strain-specific mutations were identified in the V3 loop of maraviroc-resistant CC1/85 and RU570. The envelope-encoding region of maraviroc-resistant CC1/85 was inserted into an NL4-3 background. This recombinant virus was completely resistant to maraviroc but retained susceptibility to aplaviroc. Reverse mutation of gp120 residues 316 and 323 in the V3 loop (numbering from HXB2) to their original sequence restored wild-type susceptibility to maraviroc, while reversion of either mutation resulted in a partially sensitive virus with reduced maximal inhibition (plateau). The plateaus are consistent with the virus having acquired the ability to utilize maraviroc-bound receptor for entry. This hypothesis was further corroborated by the observation that a high concentration of maraviroc blocks the activity of aplaviroc against maraviroc-resistant virus.

Is the complexity of care a paradox?

This paper looks at the phenomenon known as care and the medium through which it is expressed - caring. It explores some of the meanings of these terms but focuses particularly on nursing care. Superficially, nurses and society have a broad understanding of what 'care' means but common usage of the word belies its complexity. When examined alongside the writings of scholars the inconsistent nature of care and caring emerges. We reflect on the difficulties this presents for both the nurse and the cared for when, on the one hand care is promoted as the essence of nursing, while on the other there is no acceptable definition of care on which to base this claim. Encompassed within our discussion is the underlying theme that although care is an appropriate ideal for nursing it does not capture all of the day-to-day realities and hence it is not an overriding ideal. Care in nursing in this sense is contradictory and we describe it as paradoxical.

Osteopetrosis in the Grüneberg (mi) mouse can be cured by cultured allogeneic bone marrow

H2 compatible allogeneic bone marrow cultured for four weeks was effective in inducing bone resorption when injected intravenously into osteopetrotic mi mouse. The active cell line or its progenitors can therefore be established in culture and is probably derived from a haematopoietic stem cell (HSC).