The key nuclear export protein CRM1/XPO1 may represent a promising novel therapeutic target in human multiple myeloma (MM). Here we showed that chromosome region maintenance 1 (CRM1) is highly expressed in patients with MM, plasma cell leukemia cells and increased in patient cells resistant to bortezomib treatment. CRM1 expression also correlates with increased lytic bone and shorter survival. Importantly, CRM1 knockdown inhibits MM cell viability. Novel, oral, irreversible selective inhibitors of nuclear export (SINEs) targeting CRM1 (KPT-185, KPT-330) induce cytotoxicity against MM cells (ED50<200 nM), alone and cocultured with bone marrow stromal cells (BMSCs) or osteoclasts (OC). SINEs trigger nuclear accumulation of multiple CRM1 cargo tumor suppressor proteins followed by growth arrest and apoptosis in MM cells. They further block c-myc, Mcl-1, and nuclear factor κB (NF-κB) activity. SINEs induce proteasome-dependent CRM1 protein degradation; concurrently, they upregulate CRM1, p53-targeted, apoptosis-related, anti-inflammatory and stress-related gene transcripts in MM cells. In SCID mice with diffuse human MM bone lesions, SINEs show strong anti-MM activity, inhibit MM-induced bone lysis and prolong survival. Moreover, SINEs directly impair osteoclastogenesis and bone resorption via blockade of RANKL-induced NF-κB and NFATc1, with minimal impact on osteoblasts and BMSCs. These results support clinical development of SINE CRM1 antagonists to improve patient outcome in MM.

Key Points• SIRT6 is highly expressed in multiple myeloma cells and blocks expression of ERKregulated genes.• Targeting SIRT6 enzymatic activity sensitizes multiple myeloma cells to DNAdamaging agents.Multiple myeloma (MM) is characterized by a highly unstable genome, with aneuploidy observed in nearly all patients. The mechanism causing this karyotypic instability is largely unknown, but recent observations have correlated these abnormalities with dysfunctional DNA damage response. Here, we show that the NAD 1 -dependent deacetylase SIRT6 is highly expressed in MM cells, as an adaptive response to genomic stability, and that high SIRT6 levels are associated with adverse prognosis. Mechanistically, SIRT6 interacts with the transcription factor ELK1 and with the ERK signaling-related gene. By binding to their promoters and deacetylating H3K9 at these sites, SIRT6 downregulates the expression of mitogen-activated protein kinase (MAPK) pathway genes, MAPK signaling, and proliferation. In addition, inactivation of ERK2/p90RSK signaling triggered by high SIRT6 levels increases DNA repair via Chk1 and confers resistance to DNA damage. Using genetic and biochemical studies in vitro and in human MM xenograft models, we show that SIRT6 depletion both enhances proliferation and confers sensitization to DNA-damaging agents. Our findings therefore provide insights into the functional interplay between SIRT6 and DNA repair mechanisms, with implications for both tumorigenesis and the treatment of MM. (Blood. 2016;127(9):1138-1150 IntroductionGenomic instability is a common feature of monoclonal gammopathies, resulting in complex genetic changes associated with disease progression from monoclonal gammopathy of undetermined significance to active multiple myeloma (MM) to plasma cell leukemia.1,2 Although alterations in DNA damage checkpoint proteins are less common (10% to 15%) in blood cancers compared with solid tumors, [3][4][5] MM cells do manifest a dysfunctional DNA-damage response (DDR), a key determinant of their genomic instability. [6][7][8] Identifying proteins and signaling pathways that protect MM cells from cumulative genomic instability may therefore lead to innovative therapeutic opportunities, as exemplified by the clinical efficacy of PARP inhibitors in the context of breast and ovarian tumors lacking functional BRCA1 or BRCA2. 9,10 In MM cells, direct evidence of homozygous loss or mutations in BRCA1/2 or other DDR genes is lacking, but increased DNA repair activity has been reported. 11,12 Thus, identification of adaptive pathways for coping with genomic instability in MM may similarly provide the framework for new therapeutic strategies. Sirtuins (SIRTs) are NAD1 -degrading enzymes involved in a variety of biological processes, ranging from metabolism to lifespan regulation. 13,14 Of the 7 sirtuin family members, only SIRT6 clearly contributes to DNA repair. [15][16][17][18] Consistently, murine SIRT6 knockout cells exhibit genomic instability and hypersensitivity to DNA-damaging agents. 15,17,19 Moreover...

The 90-kDa heat shock protein (Hsp90) has become an important therapeutic target with ongoing evaluation in a number of malignancies. Although Hsp90 inhibitors have a high therapeutic index with limited effects on normal cells, they have been described to inhibit dendritic cell function. However, its effect on human immune effector cells may have significant clinical implications, but remains unexplored. In this study, we have evaluated the effects of Hsp90 inhibition on human T lymphocyte and NK cells, including their Ag expression, activation, proliferation, and functional activities. These studies demonstrate that Hsp90 inhibition irreversibly downregulates cell surface expression of critical Ags (CD3, CD4, CD8), the costimulatory molecule (CD28, CD40L), and αβ receptors on T lymphocytes, as well as activating receptors (CD2, CD11a, CD94, NKp30, NKp44, NKp46, KARp50.3) on NK cells. Hsp90 inhibition significantly reduced CD4 protein expression on T lymphocytes at both the cell surface and intracellular level, which was shown to be associated with aberrant regulation of Src-kinase p56Lck. Downregulation of the Ags triggered by Hsp90 inhibition on CD3+ T lymphocytes, both in CD4+ and CD8+ T cell subsets, was associated with a disruption in their cellular activation, proliferation, and/or IFN-γ production, when the inhibition occurred either in activated or inactivated cells. In addition, downregulation of key activating receptors on NK cells following Hsp90 inhibition resulted in decreased cytotoxicity against tumor cells. Therefore, these observations demonstrate the need to closely monitor immune function in patients being treated with a Hsp90 inhibitor and may provide a potential therapeutic application in autoimmune diseases.

Keywords: breast / colon / pancreatic cancer, cancer vaccine, heteroclitic peptides, XBP1XBP1 is a critical transcriptional activator of the unfolded protein response (UPR), which increases tumor cell survival under prolonged endoplasmic reticulum (ER) stress and hypoxic conditions.This study was designed to evaluate the immunogenicity of heteroclitic XBP1 unspliced (US) [184][185][186][187][188][189][190][191][192] (YISPWILAV) and heteroclictic XBP1 spliced (SP) [367][368][369][370][371][372][373][374][375] (YLFPQLISV) HLA-A2 peptides, and to characterize the specific activities of XBP1 peptides-specific cytotoxic T lymphocytes (XBP1-CTL) against breast cancer, colon cancer, and pancreatic cancer cells.The XBP1-CTL had upregulated expression of critical T cell markers and displayed HLA-A2-restricted and antigen-specific activities against breast cancer, colon cancer and pancreatic cancer cells. XBP1-CTL were enriched withCD45RO C memory CTL, which showed high expression of critical T cell markers (CD28, ICOS, CD69, CD40L), cell proliferation and antitumor activities as compared to CD45RO ¡ non-memory CTL. The effector memory (EM: CD45RO C CCR7 ¡ ) subset had the highest level of cell proliferation while the central memory (CM: CD45ROC CCR7 C ) subset demonstrated enhanced functional activities (CD107a degranulation, IFNg/IL-2 production) upon recognition of the respective tumor cells. Furthermore, both the EM and CM XBP1-CTL subsets expressed high levels of Th1 transcription regulators Tbet and Eomes. The highest frequencies of IFNg or granzyme B producing cells were detected within CM XBP1-CTL subset that were either Tbet C or Eomes C in responding to the tumor cells.These results demonstrate the immunotherapeutic potential of a cocktail of immunogenic HLA-A2 specific heteroclitic XBP1 US [184][185][186][187][188][189][190][191][192] and heteroclictic XBP1 SP 367-375 peptides to induce CD3 C CD8C CTL enriched for CM and EM cells with specific antitumor activities against a variety of solid tumors.