Considerations for an In Vitro, Cell-Based Testing Platform for Detection of Drug-Induced Inotropic Effects in Early Drug Development. Part 2: Designing and Fabricating Microsystems for Assaying Cardiac Contractility With Physiological Relevance Using Human iPSC-Cardiomyocytes

Contractility of the myocardium engines the pumping function of the heart and is enabled by the collective contractile activity of its muscle cells: cardiomyocytes. The effects of drugs on the contractility of human cardiomyocytes in vitro can provide mechanistic insight that can support the prediction of clinical cardiac drug effects early in drug development. Cardiomyocytes differentiated from human-induced pluripotent stem cells have high potential for overcoming the current limitations of contractility assays because they attach easily to extracellular materials and last long in culture, while having human- and patient-specific properties. Under these conditions, contractility measurements can be non-destructive and minimally invasive, which allow assaying sub-chronic effects of drugs. For this purpose, the function of cardiomyocytes in vitro must reflect physiological settings, which is not observed in cultured cardiomyocytes derived from induced pluripotent stem cells because of the fetal-like properties of their contractile machinery. Primary cardiomyocytes or tissues of human origin fully represent physiological cellular properties, but are not easily available, do not last long in culture, and do not attach easily to force sensors or mechanical actuators. Microengineered cellular systems with a more mature contractile function have been developed in the last 5 years to overcome this limitation of stem cell-derived cardiomyocytes, while simultaneously measuring contractile endpoints with integrated force sensors/actuators and image-based techniques. Known effects of engineered microenvironments on the maturity of cardiomyocyte contractility have also been discovered in the development of these systems. Based on these discoveries, we review here design criteria of microengineered platforms of cardiomyocytes derived from pluripotent stem cells for measuring contractility with higher physiological relevance. These criteria involve the use of electromechanical, chemical and morphological cues, co-culture of different cell types, and three-dimensional cellular microenvironments. We further discuss the use and the current challenges for developing and improving these novel technologies for predicting clinical effects of drugs based on contractility measurements with cardiomyocytes differentiated from induced pluripotent stem cells. Future research should establish contexts of use in drug development for novel contractility assays with stem cell-derived cardiomyocytes.

Considerations for an In Vitro, Cell-Based Testing Platform for Detection of Adverse Drug-Induced Inotropic Effects in Early Drug Development. Part 1: General Considerations for Development of Novel Testing Platforms

Drug-induced effects on cardiac contractility can be assessed through the measurement of the maximal rate of pressure increase in the left ventricle (LVdP/dt_max) in conscious animals, and such studies are often conducted at the late stage of preclinical drug development. Detection of such effects earlier in drug research using simpler, in vitro test systems would be a valuable addition to our strategies for identifying the best possible drug development candidates. Thus, testing platforms with reasonably high throughput, and affordable costs would be helpful for early screening purposes. There may also be utility for testing platforms that provide mechanistic information about how a given drug affects cardiac contractility. Finally, there could be in vitro testing platforms that could ultimately contribute to the regulatory safety package of a new drug. The characteristics needed for a successful cell or tissue-based testing platform for cardiac contractility will be dictated by its intended use. In this article, general considerations are presented with the intent of guiding the development of new testing platforms that will find utility in drug research and development. In the following article (part 2), specific aspects of using human-induced stem cell-derived cardiomyocytes for this purpose are addressed.

Abstract 1815: Efficacy of FASN-selective small molecule inhibitors in preclinical tumor models

Fatty acid synthase (FASN) expression increases with tumor progression and is associated with impaired response to chemotherapy and diminished patient survival in many solid and hematopoietic tumor types. Palmitate, the product of FASN enzymatic activity, functions in vital cellular processes including energy metabolism and cell growth, cellular membrane biosynthesis and architecture, and protein localization and function. 3-V Biosciences has discovered and developed a series of potent, selective, orally available, and reversible FASN inhibitors with excellent pharmaceutical properties. Single agent FASN inhibition has been shown to cause anti-tumor activities in preclinical models of human cancer, including inhibition of AKT and mTOR signal transduction, induction of tumor cell apoptosis, and tumor growth inhibition and regression in pancreatic, ovarian, and lung cancer xenograft tumor models of human cancer. Current studies are supporting the active clinical development of TVB-2640, 3-V Biosciences' first-in-class FASN inhibitor, as an oncology therapeutic. These studies have multiple objectives: (1) characterizing a wide range of tumor types for responsiveness to FASN inhibition using tumor cell line and Champions TumorGraftTM efficacy models; (2) investigating the benefit of FASN combination therapy with chemotherapeutic or targeted anti-cancer agents; (3) developing biomarkers that characterize efficacy response; and (4) further elucidating the mechanisms of action that emanate from the inhibition of palmitate synthesis and lead to tumor cell apoptosis and in vivo anti-tumor efficacy. The results of these investigations show that FASN inhibition causes tumor growth inhibition or regression in diverse tumor types; and moreover, that tumor growth inhibition additivity or synergy is observed when FASN inhibition is combined with chemotherapy agents. Genomics and directed analysis of mRNA, proteins, and lipids following FASN inhibition have identified biomarker candidates and provided insights into the tumor growth inhibition mechanisms of action. For example, genome-wide gene expression analysis shows FASN inhibition to significantly increase the expression of many genes in biosynthetic (sterol, lipid, etc.) and apoptosis pathways while significantly reducing the expression of many genes in cell growth and proliferation pathways (DNA replication, cell cycle progression, mitosis, etc.). These data strongly support the clinical development of TVB-2640 as a first-in-class single and combination oncology therapeutic and are advancing the discovery and validation of biomarkers to inform clinical utility and response.

Citation Format: Timothy S. Heuer, Richard Ventura, Joanna Waszczuk, Kasia Mordec, Julie Lai, Russell Johnson, Lilly Hu, Haiying Cai, Allan Wagman, Douglas Buckley, Stanley T. Parish, Elizabeth Bruckheimer, George Kemble. Efficacy of FASN-selective small molecule inhibitors in preclinical tumor models. [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 1815. doi:10.1158/1538-7445.AM2014-1815

Abstract 3657: Cross-regulation between the two subsets of NKT cells is dependent on interferon-gamma

Overcoming the suppression of tumor immunity has been a major challenge in the fight against cancer. Suppression of tumor immunity is being regulated by different kinds of suppressor cells and depleting or blocking their function has been the target of immunotherapy development. One subset of immune suppressors is type II NKT cells. We have previously shown that, upon simultaneous stimulation, type I NKT cells that can promote tumor immunity and type II NKT cells cross regulate each other in vitro as well as in vivo. In some tumor models it was found that activation of type II NKT cells by sulfatide can completely abrogate the protective affect of type I NKT cell activation by alpha-galactosylceramide, leading to tumor progression and reduced survival. However the mechanism for this suppression has not been understood. By co-stimulating NKT cells in vitro, we found that type II NKT cells can inhibit the proliferation of type I NKT cells. By blocking a variety of immunregulators, we found that this suppression is dependent on interferon-gamma (IFNg). Blocking IFNg or its receptor reversed the suppression of type I NKT cell proliferation in vitro. In addition suppression was not observed in IFNgKO C57BL/6 NKT cells. It was also found that exogenous IFNg reduces the proliferation of type I NKT cells after stimulation, suggesting that IFNg is necessary for the suppression of type I NKT cells by type II NKT cells. This was unexpected as IFNg is also an effector cytokine secreted by type I NKT cells. The mechanism is under investigation. Blocking the ability of type II NKT cells to suppress type I NKT cells could shift the balance toward immune protection leading to a better tumor outcome.

Citation Format: Liat Izhak, Shingo Kato, Stanley T. Parish, Masaki Terabe, Jay A. Berzofsky. Cross-regulation between the two subsets of NKT cells is dependent on interferon-gamma. [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 3657. doi:10.1158/1538-7445.AM2014-3657

Abstract 460: Delicate balance among three types of T cells in concurrent regulation of tumor immunity

Various immunosuppressive cells, such as Tregs and type II NKT cells, mediate the immune regulation of cancer. Many studies have demonstrated the importance of regulatory cells; however, it is still not clear why different suppressive cells play a dominant role in different models. Here, we examined the relative role of two suppressors - Tregs and type II NKT cells – in a subcutaneous CT26 tumor model in three strains of mice: wild-type, NKT cell-deficient CD1dKO mice and Jα18KO, which lack type I NKT cells but still retain type II NKT cells. Tumors grew in all three strains, but Treg blockade by anti-CD25 mAb (PC61) led to tumor rejection in WT and CD1dKO but not in Jα18KO mice, suggesting that in Jα18KO mice, Tregs are not necessary for immune suppression. We hypothesized that cross regulation between type I and type II NKT cells in wild-type mice leaves Treg cells as primary suppressors, whereas in mice lacking type I NKT cells, unopposed type II NKT cells can suppress tumor immunity even when Tregs are blocked. We confirmed this hypothesis in PC61-treated Jα18KO mice by blocking type II NKT cells using anti-CD1d mAb (1B1) or by adoptive transfer of type I NKT cells combined with Treg blockade. These results support our hypothesis that it is necessary to block both suppressors, type II NKT cells and Tregs, in order to achieve protection. Also, activation of type II NKT cells by sulfatide in PC61-treated wild-type mice abrogated the protective effect of Treg blockade, indicating that shifting the balance between the two types of NKT cells toward immunosuppressive type II NKT cell dominance suppresses tumor immunity even in the absence of Tregs. We conclude that both Tregs and type II NKT cells can concurrently suppress tumor immunity and the balance between these is controlled in part by a third T cell, the type I NKT cell, regulating the regulators. Finally as cancer patients often have deficient type I NKT cell function somewhat like the Jα18KO mice, managing this delicate balance among three T cells may be critical for the success of immunotherapy of human cancer.

Citation Format: Liat Izhak, Elena Ambrosino, Jessica J. O'Konek, Shingo Kato, Stanley T. Parish, Zheng Xia, David Venzon, Jay A. Berzofsky, Masaki Terabe. Delicate balance among three types of T cells in concurrent regulation of tumor immunity. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 460. doi:10.1158/1538-7445.AM2013-460

Delicate balance among three types of T cells in concurrent regulation of tumor immunity

The nature of the regulatory cell types that dominate in any given tumor is not understood at present. Here, we addressed this question for regulatory T cells (Treg) and type II natural killer T (NKT) cells in syngeneic models of colorectal and renal cancer. In mice with both type I and II NKT cells, or in mice with neither type of NKT cell, Treg depletion was sufficient to protect against tumor outgrowth. Surprisingly, in mice lacking only type I NKT cells, Treg blockade was insufficient for protection. Thus, we hypothesized that type II NKT cells may be neutralized by type I NKT cells, leaving Tregs as the primary suppressor, whereas in mice lacking type I NKT cells, unopposed type II NKT cells could suppress tumor immunity even when Tregs were blocked. We confirmed this hypothesis in 3 ways by reconstituting type I NKT cells as well as selectively blocking or activating type II NKT cells with antibody or the agonist sulfatide, respectively. In this manner, we showed that blockade of both type II NKT cells and Tregs is necessary to abrogate suppression of tumor immunity, but a third cell, the type I NKT cell, determines the balance between these regulatory mechanisms. As patients with cancer often have deficient type I NKT cell function, managing this delicate balance among 3 T-cell subsets may be critical for the success of immunotherapy for human cancer.

Sustained CD28 expression delays multiple features of replicative senescence in human CD8 T lymphocytes

CD28 costimulatory signal transduction in T lymphocytes is essential for optimal telomerase activity, stabilization of cytokine mRNAs, and glucose metabolism. During aging and chronic infection with HIV-1, there are increased proportions of CD8 T lymphocytes that lack CD28 expression and show additional features of replicative senescence. Moreover, the abundance of these cells correlates with decreased vaccine responsiveness, early mortality in the very old, and accelerated HIV disease progression. Here, we show that sustained expression of CD28, via gene transduction, retards the process of replicative senescence, as evidenced by enhanced telomerase activity, increased overall proliferative potential, and reduced secretion of pro-inflammatory cytokines. Nevertheless, the transduced cultures eventually do reach senescence, which is associated with increased CTLA-4 gene expression and a loss of CD28 cell surface expression. These findings further elucidate the central role of CD28 in the replicative senescence program, and may ultimately lead to novel therapies for diseases associated with replicative senescence.

Adenosine deaminase modulation of telomerase activity and replicative senescence in human CD8 T lymphocytes

Increased proportions of CD8 T lymphocytes lacking expression of the CD28 costimulatory receptor have been documented during both aging and chronic infection with HIV-1, and their abundance correlates with numerous deleterious clinical outcomes. CD28-negative cells also arise in cell cultures of CD8(+)CD28(+) following multiple rounds of Ag-driven proliferation, reaching the end stage of replicative senescence. The present study investigates the role of a second T cell costimulatory receptor component, adenosine deaminase (ADA), on the process of replicative senescence. We had previously reported that CD28 signaling is required for optimal telomerase upregulation. In this study, we show that the CD8(+)CD28(+) T lymphocytes that are ADA(+) have significantly greater telomerase activity than those that do not express ADA and that ADA is progressively lost as cultures progress to senescence. Because ADA converts adenosine to inosine, cells lacking this enzyme might be subject to prolonged exposure to adenosine, which has immunosuppressive effects. Indeed, we show that chronic exposure of CD8 T lymphocytes to exogenous adenosine accelerates the process of replicative senescence, causing a reduction in overall proliferative potential, reduced telomerase activity, and blunted IL-2 gene transcription. The loss of CD28 expression was accelerated, in part due to adenosine-induced increases in constitutive caspase-3, known to act on the CD28 promoter. These findings provide the first evidence for a role of ADA in modulating the process of replicative senescence and suggest that strategies to enhance this enzyme may lead to novel therapeutic approaches for pathologies associated with increases in senescent CD8 T lymphocytes.

Modulation of T lymphocyte replicative senescence via TNF-{alpha} inhibition: role of caspase-3

Expanded populations of CD8(+) T lymphocytes lacking CD28 expression are associated with a variety of deleterious clinical outcomes, including early mortality in the elderly, more rapid progression to AIDS, cardiovascular disease, and enhanced tumor cell growth. In cell culture, irreversible loss of CD28 expression correlates with increased production of TNF-alpha as CD8(+) T cells are driven to the nonproliferative end stage of replicative senescence by multiple rounds of Ag-driven cell division. Interestingly, in patients with rheumatoid arthritis, inhibition or neutralization of TNF-alpha reduces the proportion of T cells lacking CD28 in the disease joints, consistent with studies showing a direct involvement of this cytokine in CD28 gene transcription. Here, we show that modulation of TNF-alpha levels in long-term cultures of human CD8(+) T lymphocytes, by chronic exposure either to a neutralizing Ab or to an inhibitor of the TNF-alpha receptor-1, increases proliferative potential, delays loss of CD28 expression, retards cytokine profile changes, and enhances telomerase activity. We also show that constitutive caspase-3, one of the downstream effectors of TNF-alphaR1 binding, increases in parallel with the loss of CD28 in long-term cultures, but this effect is blunted in the presence of the TNF-alpha inhibitors. Consistent with the in vitro culture data, CD8(+)CD28(-) T lymphocytes tested immediately ex vivo also show significantly higher levels of caspase-3 compared with their CD28(+) counterparts. These findings help elucidate the complex nature of CD28 gene regulation, and may ultimately lead to novel therapeutic approaches for diseases associated with increased proportions of CD28(-) T lymphocytes.

Loss of CD28 expression in human T cells: possible causes and downstream effects (33.24)

High proportions of CD8+CD28- T cells are present during HIV infection and aging. These cells, which have features of replicative senescence, are associated with decreased vaccine responses, early mortality, and progression to AIDS. To identify the underlying mechanisms for CD28 downregulation, we first analyzed caspase-3, which inhibits the CD28 promoter. Both CD28- T cells tested immediately ex vivo and cells that reached replicative senescence in vitro have significantly greater caspase-3 levels than their CD28+ counterparts. This increase is reversed in cultures in which CD28 expression is maintained by inhibiting TNFα. We next addressed the possible role of adenosine, which is released from metabolically active cells, and which, when added to long-term cultures, downregulates CD28. We showed that adenosine deaminase (ADA), which converts adenosine to inosine, is more highly expressed on CD28+ vs. CD28- T cells. These data suggest multiple regulatory pathways for CD28 gene suppression. Irrespective of the precise mechanism, once cells lose CD28 expression, they show decreased transcription of numerous glycolysis pathway enzymes, consistent observations on ex vivo T cells from older persons. Our data, which help elucidate the complexity of CD28 downregulation and its downstream consequences, may lead to therapeutic strategies to prevent accumulation of senescent T cells in vivo. (NIH AG023720).

Manipulaion of TNFalpha delays loss of CD28 expression in human CD8 T cells (96.19)

The CD28 costimulatory receptor is essential for T cell activation, glucose metabolism, and optimal telomerase activity. Increased proportions of CD8+CD28 T cells, seen in HIV infection and aging, correlate with decreased vaccine responsiveness and early mortality. CD28 expression is also lost in chronically stimulated cultures of CD8 T cells as they approach replicative senescence, a state of irreversible cell cycle arrest, associated with shortened telomeres and increased levels of TNFα. Based on the link between TNFα and the CD28 gene promoter, we sought to investigate the effects of manipulating TNFα on replicative senescence. Human T cells were repeatedly stimulated with an allogeneic cell line in the presence of either a neutralizing antibody (anti-TNFα) or a TNFα receptor 1 inhibitor (rhuTNFR:Fc). CD28 expression and gene transcription were monitored by flow cytometry and RT-PCR, respectively. Chronic exposure of antigen-stimulated CD8 T cells to rhuTNFR:Fc or anti-TNFα delayed the loss of CD28 expression. Even after completing 17 population doublings, the treated cultures contained >20% more CD28+ cells; CD28 gene transcription was similarly elevated. Finally, telomerase activity was increased by as much as 6-fold in the treated cultures. Manipulation of TNFα, therefore, may be a useful clinical approach to delay accumulation of senescent CD8 T cell in vivo.

Supported by NIH AI060362 and AG023720