Mesenchymal stromal cells (MSCs), also called mesenchymal stem cells, migrate and function as stromal cells in tumor tissues. The effects of MSCs on tumor growth are controversial. In this study, we showed that MSCs increase proliferation of tumor cells in vitro and promote tumor growth in vivo. We also further analyzed the mechanisms that underlie these effects. For use in in vitro and in vivo experiments, we established a bone marrow-derived mesenchymal stromal cell line from cells isolated in C57BL/6 mice. Effects of murine MSCs on tumor cell proliferation in vitro were analyzed in a coculture model with B16-LacZ cells. Both coculture with MSCs and treatment with MSC-conditioned media led to enhanced growth of B16-LacZ cells, although the magnitude of growth stimulation in cocultured cells was greater than that of cells treated with conditioned media. Co-injection of B16-LacZ cells and MSCs into syngeneic mice led to increased tumor size compared with injection of B16-LacZ cells alone. Identical experiments using Lewis lung carcinoma (LLC) cells instead of B16-LacZ cells yielded similar results. Consistent with a role for neovascularization in MSC-mediated tumor growth, tumor vessel area was greater in tumors resulting from co-injection of B16-LacZ cells or LLCs with MSCs than in tumors induced by injection of cancer cells alone. Co-injected MSCs directly supported the tumor vasculature by localizing close to vascular walls and by expressing an endothelial marker. Furthermore, secretion of leukemia inhibitory factor, macrophage colony-stimulating factor, macrophage inflammatory protein-2 and vascular endothelial growth factor was increased in cocultures of MSCs and B16-LacZ cells compared with B16-LacZ cells alone. Together, these results indicate that MSCs promote tumor growth both in vitro and in vivo and suggest that tumor promotion in vivo may be attributable in part to enhanced angiogenesis.

Background Wilms' tumor 1 (WT1) is overexpressed in various malignancies. DSP-7888 Dosing Emulsion, also known as ombipepimut-S (United States Adopted Name; International Nonproprietary Name: adegramotide/nelatimotide), is an investigational therapeutic cancer vaccine comprising two synthetic peptides derived from WT1 to promote both cytotoxic T-lymphocyte (CTL) and helper T-lymphocyte-mediated immune responses against WT1-expressing tumors. Objective The aim of this study was to report the results from a phase I dose-escalation study (NCT02498665) that evaluated DSP-7888, administered either intradermally (ID) or subcutaneously (SC), in patients with recurrent or advanced malignancies associated with overexpression of WT1. Patients and Methods In this phase I dose-escalation study, patients with recurrent or advanced malignancies associated with overexpression of WT1 who progressed on, were intolerant to, or not a candidate for standard therapy or who presented with a malignancy that had no definite standard therapy received escalating doses of ID or SC DSP-7888 in a rolling-six study design. DSP-7888 3.5, 10.5, or 17.5 (ID only) mg was administered until disease progression or other discontinuation event. Primary objectives were safety, tolerability, and identification of the recommended phase II dose (RP2D). Overall survival (OS) and WT1-specific CTL induction were included as secondary and exploratory objectives, respectively. Results Twenty-four patients received either ID (3.5 mg, n = 4; 10.5 mg, n = 3; 17.5 mg, n = 3) or SC DSP-7888 (3.5 mg, n = 9; 10.5 mg, n = 5). No dose-limiting toxicity was observed. The most frequent treatment-emergent adverse event was injection site reactions (ID, 100% [10/10]; SC, 35.7% [5/14]); all were grade 1 or 2. Four patients (ID 17.5 mg, n = 1; SC 3.5 mg, n = 1; SC 10.5 mg, n = 2) had stable disease, 16 had progressive disease, and four were not evaluable. Median (95% confidence interval) OS duration was 180.0 (136.0-494.0) days. Among evaluable patients, WT1-specific CTL induction was observed in 66.7% (6/9) and 41.7% (5/12) of those administered ID and SC DSP-7888, respectively. Conclusions DSP-7888 Dosing Emulsion was well tolerated, with no dose-limiting toxicities, in patients with recurrent or advanced malignancies. Higher WT1-specific CTL induction activity was noted with ID compared with SC administration; because of this, the ID route was selected for further evaluation in the clinical program. Trial registration ClinicalTrials.gov identifier: NCT02498665.

Background: Hypomethylating agents (HMA), including azacitidine (AZA) are currently the first-line treatment option for higher-risk myelodysplastic syndrome (MDS). However, the prognosis of patients after AZA failure is poor with a median overall survival of 5.6 months from the treatment failure (J Clin Onclol 2011;29:3322-7 Prébet T et al.), and currently there are no approved therapeutic options for such patients. Suzuki et al. reported that WT4869, one of the HLA-A*24;02-restricted synthetic peptide vaccine derived from Wilms' tumor 1 (WT1) protein, demonstrated the sign of prolongation of overall survival (OS) with a median OS of 13.0 months in AZA failure higher-risk population, in the phase 1/2 study with MDS patients (Blood 126:2868, 2015;Suzuki et al.). DSP-7888 is a novel WT1-based peptide vaccine which induces the CTLs that recognize WT1 antigens in HLA-A*02:01/06 and HLA-A*24:02 restricted manner, and also includes a WT1-derived helper peptide applicable for various subtypes of HLA-DRB1. DSP-7888 is currently being investigated in a phase 1/2 study to evaluate the safety and efficacy in HLA-A*24:02+ and/or HLA-A*02:01/:06+ MDS patients, with some exploratory biomarker analyses. Methods: The objectives of this study were to assess the tolerability of DSP-7888 treatment in MDS patients in the phase 1 portion and to evaluate preliminary clinical activity of DSP-7888 in higher-risk MDS patients after AZA failure in the study. In phase 1 portion, higher-risk or transfusion-dependent lower-risk MDS patients including the AZA failure population were enrolled, and DSP-7888 was administered at doses of 3.5 to 10.5 mg/body by intradermal injections every two to four weeks in dose-escalation cohorts according to the 3 + 3 design until discontinuation criteria were met. Overall survival was evaluated for primarily clinical activity and hematological response and time to AML were also examined. Delayed type hypersensitivity (DTH), WT1-specific CTL induction and expression of WT1 mRNA in peripheral blood and bone marrow cells were also evaluated as exploratory biomarkers. The clinical data in phase 1 portion as of May 25th 2016 was presented in this report. Results: In phase 1 portion, enrollment of patients and dose-limiting toxicities (DLTs) evaluation were completed. Twelve patients including 7 higher- and 5 lower-risk patients were enrolled in 3.5 and 10.5 mg/body cohorts of 6 patients each, and safety profiles were evaluated. DLTs were not observed in either cohorts and the most common adverse drug reaction (ADR) was injection site reaction (ISR). ISR in 6 patients worsened to grade 3 with continuous treatment of DSP-7888 (2 patients at 3.5 mg/body, and 4 patients at 10.5 mg/body). Five serious ADR including 3 ISR, 1 pyrexia and 1 myocarditis were reported and dose-dependent toxicity was not observed except for ISR. All 12 patients were analyzed for preliminary clinical activity. Eight patients remained in stable disease (SD) with 2 hematological improvements (HI), and disease control rate (SD + any HI) was 66.6 %. Seven high risk AZA failure patients were enrolled, and the current survival time in this population is 7.3-10.8 months. Though preliminary, CTL induction was observed in 6 patients, and a trend of higher CTL induction was observed in patients with grade 3 ISR. DTH response was observed in 10 patients. Conclusions: In the phase 1 portion, DSP-7888 was well-tolerated in MDS patients although ISR was observed in all patients. CTL induction was detected with clinically observed reactions that may suggest preliminary signs of clinical activity. Further evaluation is needed to confirm the clinical potential of DSP-7888, and phase 2 portion is currently ongoing to evaluate the efficacy of DSP-7888 in higher-risk MDS patients after AZA failure. Disclosures Usuki: Nippon Shinyaku: Honoraria; MSD: Honoraria; Kyouwa-Kirin: Honoraria; Novartis: Honoraria; Bristol-Myer-Squibb: Honoraria; Sumitomo Dainippon Pharma: Honoraria; SymBio Pharmaceuticals: Research Funding. Matsumura:Bristol-Myers Squibb Company: Honoraria; Novartis Pharma K.K: Honoraria; Otsuka Pharmaceutical Co., Ltd.: Consultancy, Honoraria; Pfizer Japan Inc.: Honoraria. Ueda:Alexion Pharmaceuticals Inc.: Membership on an entity's Board of Directors or advisory committees. Origuchi:Sumitomo Dainippon Pharma Co.,Ltd.: Employment. Tagashira:Sumitomo Dainippon Pharma Co.,Ltd.: Employment. Naoi:Sumitomo Dainippon Pharma Co.,Ltd.: Employment. Naoe:Bristol-Myers Squibb: Honoraria; Sumitomo Dainippon Pharma Co.,Ltd.: Honoraria, Research Funding; Pfizer Inc.: Research Funding; Astellas Pharma Inc.: Research Funding; Kyowa-Hakko Kirin Co.,Ltd.: Honoraria, Patents & Royalties, Research Funding; Amgen Astellas BioPharma K.K.: Honoraria; Otsuka Pharmaceutical Co.,Ltd.: Honoraria, Research Funding; CMIC Co., Ltd.: Research Funding; Celgene K.K.: Honoraria, Research Funding; TOYAMA CHEMICAL CO.,LTD.: Research Funding; Chugai Pharmaceutical Co.,LTD.: Honoraria, Patents & Royalties; Nippon Boehringer Ingelheim Co., Ltd.: Honoraria, Research Funding; Fujifilm Corporation: Honoraria, Patents & Royalties, Research Funding. Heike:Sumitomo Dainippon Pharma: Consultancy; Chugai Pharma: Consultancy; Otsuka Pharma: Consultancy. Miyazaki:Kyowa Kirin: Honoraria; Nihonshinyaku: Honoraria; Celgene Japan: Honoraria; Sumitomo Dainippon Pharma Co.,Ltd.: Honoraria.

TPS6099 Background: DSP-7888 is a therapeutic cancer vaccine composed of two synthetic peptides derived from Wilms’ tumor 1 (WT1) to promote both cytotoxic and helper T-lymphocyte-mediated immune responses against WT1-expressing tumors. WT1 is overexpressed in various solid tumors, including ovarian cancer. Combining cancer vaccines like DSP-7888 with a CPI may reduce resistance to immunomodulators and improve clinical benefit. A phase Ib/II study is being conducted to evaluate DSP-7888 in combination with a CPI in pts with advanced solid tumors, including PROC (NCT03311334). Methods: This phase Ib/II, open-label, multicenter, two-part dose-search/dose-expansion study investigates DSP-7888 + nivolumab or pembrolizumab in pts with advanced solid tumors (phase Ib), including PROC (phase II). The phase Ib primary objectives are safety, tolerability, and identification of the recommended phase II dose (RP2D). The phase II primary objective is evaluation of objective response rate (ORR); secondary objectives are clinical activity, safety, and tolerability. Pts aged ≥18 years with unresectable, metastatic cancer approved for treatment with nivolumab (phase Ib, Arm 1, n=6–12, 7 enrolled) or pembrolizumab (phase Ib, Arm 2, n=6–12, 6 enrolled), or with PROC (phase II) are eligible. Phase II will enroll ~40 pts into two groups based on programmed death-ligand 1 status (combined positive score of ≥10 [Group 1] or <10 [Group 2]). Clinical activity will be assessed continuously using Bayesian analysis and actual enrollment may increase by ~20 pts/group based on this analysis. Pts in phase II will receive DSP-7888 intradermally (RP2D from phase Ib) once a week (wk) for 6 wks in the induction phase then every 3 wks in the maintenance phase. Beginning Day 1, pembrolizumab will be administered intravenously every 3 wks. In phase II, objective disease will be assessed every 6 wks for 24 wks, then every 12 wks until progression. Endpoints include ORR (per RECIST v1.1) (primary), duration of response, disease control rate (DCR), progression-free survival (PFS), 6-month PFS rate (per RECIST v1.1), and overall survival, immune (i)ORR, iDCR, and iPFS (per iRECIST) (secondary). Exploratory endpoints include blood and tumor tissue biomarkers. Safety and tolerability, assessed by adverse events, will be evaluated throughout the duration of the study and follow-up. This study is currently recruiting patients. Clinical trial information: NCT03311334.

[Background] Mesenchymal stromal cells (MSCs), also referred as mesenchymal stem cells are pluripotent progenitor cells that differentiate into chondrocytes, adipocytes, osteoblasts and other types of cell. Although MSCs are resident mainly in bone marrow, MSCs are found in adipose tissue, lung, and many other organs where MSCs maintain and regenerate the connective tissues of organs. Recent report proposed that MSCs also migrate and function as stromal cells in the tumor tissues. Effects of MSCs on tumor growth in vitro and in vivo are still unclear. In this study, we verified tumor promotion by MSCs and analyzed mechanisms. [Method] B16-LacZ, a melanoma cell line expressing β-galactosidase protein, was tested for their growth rate by X-gal colorizing assay in the presence or absence of mouse bone marrow MSCs in vitro. Growth of B16-LacZ was also examined in the detached condition using cell disk or conditioned medium from MSCs. Next, B16-LacZ and Lewis Lung Carcinoma (LLC) cells were mixed with MSCs at 1/1 and 1/5 ratios and subcutaneously inoculated into mice. Tumor sizes were measured and immunostaining of CD31 was performed to evaluate angiogenesis. We also determine the secretion of soluble factors associated with angiogenesis in cultured medium from B16-LacZ alone, MSCs alone, or B16-LacZ and MSCs ELISA. [Result] Proliferation of B16-LacZ co-cultured with MSCs exhibited 5.8 times greater than that of B16-LacZ alone in vitro (P&lt;0.01). In detached condition, using cell disk or conditioned medium from MSCs, the growth rate was only 1.6 times (P&lt;0.01) in cell disk, and 1.4 times (P&lt;0.05) in conditioned medium at 60-hour incubation. Mixed group of B16-LacZ and MSCs at 1/1 and 1/5 ratios developed 2.3 times (P&lt;0.05) and 4.3 times (P&lt;0.01) grater tumor compared to B16-LacZ alone in vivo. MSCs alone did not develop a tumor. Results of LLC experiments were similar to B16-LacZ experiments. Tumor vessel area of mixture of B16-LacZ and MSCs was 2.4 times (P&lt;0.05) at 1/1 and 4.2 times (P&lt;0.01) at 1/5 ratio lager than B16-LacZ alone. The amount of the secretion of LIF, M-CSF, MIP-2 and VEGF factors from MSCs were significantly larger compared with B16-LacZ. The amount of the secretion from co-culture of B16-LacZ and MSCs was almost the same as the MSCs alone group. [Conclusion] MSCs promoted tumor growth both in vitro and in vivo, and promotion of tumor growth by MSCs can be at least in part attributed to the tumor angiogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 536.