Boosting Natural Killer Cell-Mediated Targeting of Sarcoma Through DNAM-1 and NKG2D

Sarcomas are malignancies of mesenchymal origin that occur in bone and soft tissues. Many are chemo- and radiotherapy resistant, thus conventional treatments fail to increase overall survival. Natural Killer (NK) cells exert anti-tumor activity upon detection of a complex array of tumor ligands, but this has not been thoroughly explored in the context of sarcoma immunotherapy. In this study, we investigated the NK cell receptor/ligand immune profile of primary human sarcoma explants. Analysis of tumors from 32 sarcoma patients identified the proliferative marker PCNA and DNAM-1 ligands CD112 and/or CD155 as commonly expressed antigens that could be efficiently targeted by genetically modified (GM) NK cells. Despite the strong expression of CD112 and CD155 on sarcoma cells, characterization of freshly dissociated sarcomas revealed a general decrease in tumor-infiltrating NK cells compared to the periphery, suggesting a defect in the endogenous NK cell response. We also applied a functional screening approach to identify relevant NK cell receptor/ligand interactions that induce efficient anti-tumor responses using a panel NK-92 cell lines GM to over-express 12 different activating receptors. Using GM NK-92 cells against primary sarcoma explants (n = 12) revealed that DNAM-1 over-expression on NK-92 cells led to efficient degranulation against all tested explants (n = 12). Additionally, NKG2D over-expression showed enhanced responses against 10 out of 12 explants. These results show that DNAM-1⁺ or NKG2D⁺ GM NK-92 cells may be an efficient approach in targeting sarcomas. The degranulation capacity of GM NK-92 cell lines was also tested against various established tumor cell lines, including neuroblastoma, Schwannoma, melanoma, myeloma, leukemia, prostate, pancreatic, colon, and lung cancer. Enhanced degranulation of DNAM-1⁺ or NKG2D⁺ GM NK-92 cells was observed against the majority of tumor cell lines tested. In conclusion, DNAM-1 or NKG2D over-expression elicited a dynamic increase in NK cell degranulation against all sarcoma explants and cancer cell lines tested, including those that failed to induce a notable response in WT NK-92 cells. These results support the broad therapeutic potential of DNAM-1⁺ or NKG2D⁺ GM NK-92 cells and GM human NK cells for the treatment of sarcomas and other malignancies.

Imaging CAR T cell therapy with PSMA-targeted positron emission tomography

Chimeric antigen receptor (CAR) T cell therapy for hematologic malignancies is fraught with several unknowns, including number of functional T cells that engage target tumor, durability and subsequent expansion and contraction of that engagement, and whether toxicity can be managed. Non-invasive, serial imaging of CAR T cell therapy using a reporter transgene can address those issues quantitatively. We have transduced anti-CD19 CAR T cells with the prostate-specific membrane antigen (PSMA) because it is a human protein with restricted normal tissue expression and has an expanding array of positron emission tomography (PET) and therapeutic radioligands. We demonstrate that CD19-tPSMA^(N9del) CAR T cells can be tracked with [¹⁸F]DCFPyL PET in a Nalm6 model of acute lymphoblastic leukemia. Divergence between the number of CD19-tPSMA^(N9del) CAR T cells in peripheral blood and bone marrow and those in tumor was evident. These findings underscore the need for non-invasive repeatable monitoring of CAR T cell disposition clinically.

An engineered, quantifiable in vitro model for analysing the effect of proteostasis-targeting drugs on tissue physical properties

Cellular function depends on the maintenance of protein homeostasis (proteostasis) by regulated protein degradation. Chronic dysregulation of proteostasis is associated with neurodegenerative and age-related diseases, and drugs targeting components of the protein degradation apparatus are increasingly used in cancer therapies. However, as chronic imbalances rather than loss of function mediate their pathogenesis, research models that allow for the study of the complex effects of drugs on tissue properties in proteostasis-associated diseases are almost completely lacking. Here, to determine the functional effects of impaired proteostatic fine-tuning, we applied a combination of materials science characterisation techniques to a cell-derived, in vitro model of bone-like tissue formation in which we pharmacologically perturbed protein degradation. We show that low-level inhibition of VCP/p97 and the proteasome, two major components of the degradation machinery, have remarkably different effects on the bone-like material that human bone-marrow derived mesenchymal stromal cells (hMSC) form in vitro. Specifically, whilst proteasome inhibition mildly enhances tissue formation, Raman spectroscopic, atomic force microscopy-based indentation, and electron microscopy imaging reveal that VCP/p97 inhibition induces the formation of bone-like tissue that is softer, contains less protein, appears to have more crystalline mineral, and may involve aberrant micro- and ultra-structural tissue organisation. These observations contrast with findings from conventional osteogenic assays that failed to identify any effect on mineralisation. Taken together, these data suggest that mild proteostatic impairment in hMSC alters the bone-like material they form in ways that could explain some pathologies associated with VCP/p97-related diseases. They also demonstrate the utility of quantitative materials science approaches for tackling long-standing questions in biology and medicine, and could form the basis for preclinical drug testing platforms to develop therapies for diseases stemming from perturbed proteostasis or for cancer therapies targeting protein degradation. Our findings may also have important implications for the field of tissue engineering, as the manufacture of cell-derived biomaterial scaffolds may need to consider proteostasis to effectively replicate native tissues.

Inadequate fine-tuning of protein synthesis and failure of amino acid homeostasis following inhibition of the ATPase VCP/p97

The cellular mechanisms that control protein degradation may constitute a non-oncogenic cancer cell vulnerability and, therefore, a therapeutic target. Although this proposition is supported by the clinical success of proteasome inhibitors in some malignancies, most cancers are resistant to proteasome inhibition. The ATPase valosin-containing protein (VCP; p97) is an essential regulator of protein degradation in multiple pathways and has emerged as a target for cancer therapy. We found that pharmacological depletion of VCP enzymatic activity with mechanistically different inhibitors robustly induced proteotoxic stress in solid cancer and multiple myeloma cells, including cells that were insensitive, adapted, or clinically resistant to proteasome inhibition. VCP inhibition had an impact on two key regulators of protein synthesis, eukaryotic initiation factor 2α (eIF2α) and mechanistic target of rapamycin complex 1 (mTORC1), and attenuated global protein synthesis. However, a block on protein translation that was itself cytotoxic alleviated stress signaling and reduced cell death triggered by VCP inhibition. Some of the proteotoxic effects of VCP depletion depended on the eIF2α phosphatase, protein phosphatase 1 regulatory subunit 15A (PPP1R15A)/PP1c, but not on mTORC1, although there appeared to be cross-talk between them. Thus, cancer cell death following VCP inhibition was linked to inadequate fine-tuning of protein synthesis and activity of PPP1R15A/PP1c. VCP inhibitors also perturbed intracellular amino acid levels, activated eukaryotic translation initiation factor 2α kinase 4 (EIF2AK4), and enhanced cellular dependence on amino acid supplies, consistent with a failure of amino acid homeostasis. Many of the observed effects of VCP inhibition differed from the effects triggered by proteasome inhibition or by protein misfolding. Thus, depletion of VCP enzymatic activity triggers cancer cell death in part through inadequate regulation of protein synthesis and amino acid metabolism. The data provide novel insights into the maintenance of intracellular proteostasis by VCP and may have implications for the development of anti-cancer therapies.

Abstract 1261: Comprehensive failure of intracellular protein homeostasis kills myeloma and solid cancer cells following VCP/p97 inhibition

Introduction: Intracellular protein homeostasis requires a well-controlled protein degradation machinery to clear damaged and old proteins and to replenish intracellular amino acid pools. Cancer cells may be particularly susceptible to agents that disrupt protein degradation because of unbalanced protein levels related to gain or loss of genetic material, high protein turnover, or high-level production of specific proteins such as Ig in multiple myeloma (MM). The AAA ATPase VCP (p97) is a master regulator of protein degradation that has been implicated in oncogenesis. Small molecule VCP inhibition (VCP-i) rapidly activates caspases in cancer cells, induces endoplasmic reticulum (ER) stress, and has anti-tumor activity in murine xenograft models. A phase 1 trial of VCP-i in relapsed MM has recently opened. Methods: We investigated the cellular mechanisms that govern VCP-i mediated cancer cell death in MM cell lines including bortezomib-adapted AMO1 cells, MM cells from patients with bortezomib-resistant MM, as well as lung cancer (A549) and osteosarcoma (Saos2) cells. Results: The ATP-competitive inhibitor DBeQ and the allosteric inhibitor NMS873 induced cell line as well as primary MM cell death at similar low micromolar concentrations independently of bortezomib sensitivity. DBeQ and NMS873 caused phosphorylation of eIF2alpha in a time- and dose-dependent manner and resulted in strong transcriptional and translational up-regulation of ATF4, CHOP and GADD34. VCP-i also increased expression of ER chaperones BiP and p58IPK. Inhibition of eIF2alpha de-phosphorylation with guanabenz reduced S6 phosphorylation, a marker of protein translation, and increased A549 and OPM2 cell survival early (8h) after VCP-i. Direct inhibition of protein translation with cycloheximide also decreased early VCP-i mediated cell death. Using MEFs deficient in eIF2alpha kinases we show that eIF2alpha phosphorylation following VCP-i depends on both the unfolded protein response mediator PERK and the nutrient sensor GCN2. We found that DBeQ induces GCN2 phosphorylation in parallel with loss of mTORC1 signalling, induction of the key autophagy factor p62, and accumulation of LC3-II. DBeQ also induced a rapid decrease in free intracellular L-amino acids. Depletion of selected amino acids in the cell culture medium increased cell death and mRNA levels of CHOP and GADD34 following VCP-i with DBeQ or NMS873, but not following induction of ER stress with tunicamycin. Conclusion: Collectively, these data show that both ATP-competitive and allosteric VCP-i effectively kills cancer cells independently of bortezomib sensitivity. Disrupting VCP function induces early cell death via inappropriate eIF2alpha-regulated protein translation downstream of GADD34. VCP-i also depletes the intracellular free amino acid pool, resulting in cell death despite compensatory catabolic processes.

Citation Format: Katarzyna Parzych, Sandra Loaiza, Tamara M. Chinn, Philippa May, Florentina Porsch, Anastasios Karadimitris, Christoph Driessen, Heather P. Harding, David Ron, Holger W. Auner. Comprehensive failure of intracellular protein homeostasis kills myeloma and solid cancer cells following VCP/p97 inhibition. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1261. doi:10.1158/1538-7445.AM2015-1261

Reexamining Michaelis-Menten enzyme kinetics for xanthine oxidase

Abbreviated expressions for enzyme kinetic expressions, such as the Michaelis-Menten (M-M) equations, are based on the premise that enzyme concentrations are low compared with those of the substrate and product. When one does progress experiments, where the solute is consumed during conversion to form a series of products, the idealized conditions are violated. Here, we analyzed data of xanthine oxidase in vitro from Escribano et al. (Biochem J 254: 829, 1988) on two conversions in series, hypoxanthine to xanthine to uric acid. Analyses were done using four models: standard irreversible M-M reactions (model 1), Escribano et al.'s M-M forward reaction expressions with product inhibition (model 2), fully reversible M-M equations (model 3), and standard differential equations allowing forward and backward reactions with mass balance accounting for binding (model 4). The results showed that the need for invoking product inhibition vanishes with more complete analyses. The reactions were not quite irreversible, so the backward reaction had a small effect. Even though the enzyme concentration was only 1-2% of the initial substrate concentrations, accounting for the fraction of solutes bound to the enzyme did influence the parameter estimates, but in this case, the M-M model overestimated Michaelis constant values by only about one-third. This article also presents the research and models in a reproducible and publicly available form.