Browsing by Author "Keir, Stephen T"

Now showing 1 - 5 of 5
  • Thumbnail Image
    ItemOpen Access
    A Therapeutic Antibody for Cancer, Derived from Single Human B Cells.
    (Cell Rep, 2016-05-17) Bushey, Ryan T; Moody, M Anthony; Nicely, Nathan L; Haynes, Barton F; Alam, S Munir; Keir, Stephen T; Bentley, Rex C; Roy Choudhury, Kingshuk; Gottlin, Elizabeth B; Campa, Michael J; Liao, Hua-Xin; Patz, Edward F
    Some patients with cancer never develop metastasis, and their host response might provide cues for innovative treatment strategies. We previously reported an association between autoantibodies against complement factor H (CFH) and early-stage lung cancer. CFH prevents complement-mediated cytotoxicity (CDC) by inhibiting formation of cell-lytic membrane attack complexes on self-surfaces. In an effort to translate these findings into a biologic therapy for cancer, we isolated and expressed DNA sequences encoding high-affinity human CFH antibodies directly from single, sorted B cells obtained from patients with the antibody. The co-crystal structure of a CFH antibody-target complex shows a conformational change in the target relative to the native structure. This recombinant CFH antibody causes complement activation and release of anaphylatoxins, promotes CDC of tumor cell lines, and inhibits tumor growth in vivo. The isolation of anti-tumor antibodies derived from single human B cells represents an alternative paradigm in antibody drug discovery.
  • Thumbnail Image
    ItemOpen Access
    MiR-215 Is Induced Post-transcriptionally via HIF-Drosha Complex and Mediates Glioma-Initiating Cell Adaptation to Hypoxia by Targeting KDM1B.
    (Cancer Cell, 2016-01-11) Hu, Jing; Sun, Tao; Wang, Hui; Chen, Zhengxin; Wang, Shuai; Yuan, Lifeng; Liu, Tingyu; Li, Hai-Ri; Wang, Pingping; Feng, Yukuan; Wang, Qinhong; McLendon, Roger E; Friedman, Allan H; Keir, Stephen T; Bigner, Darell D; Rathmell, Jeff; Fu, Xiang-Dong; Li, Qi-Jing; Wang, Huibo; Wang, Xiao-Fan
    The hypoxic tumor microenvironment serves as a niche for maintaining the glioma-initiating cells (GICs) that are critical for glioblastoma (GBM) occurrence and recurrence. Here, we report that hypoxia-induced miR-215 is vital for reprograming GICs to fit the hypoxic microenvironment via suppressing the expression of an epigenetic regulator KDM1B and modulating activities of multiple pathways. Interestingly, biogenesis of miR-215 and several miRNAs is accelerated post-transcriptionally by hypoxia-inducible factors (HIFs) through HIF-Drosha interaction. Moreover, miR-215 expression correlates inversely with KDM1B while correlating positively with HIF1α and GBM progression in patients. These findings reveal a direct role of HIF in regulating miRNA biogenesis and consequently activating the miR-215-KDM1B-mediated signaling required for GIC adaptation to hypoxia.
  • Thumbnail Image
    ItemOpen Access
    Mutations in IDH1, IDH2, and in the TERT promoter define clinically distinct subgroups of adult malignant gliomas.
    (Oncotarget, 2014-03-30) Killela, Patrick J; Pirozzi, Christopher J; Healy, Patrick; Reitman, Zachary J; Lipp, Eric; Rasheed, B Ahmed; Yang, Rui; Diplas, Bill H; Wang, Zhaohui; Greer, Paula K; Zhu, Huishan; Wang, Catherine Y; Carpenter, Austin B; Friedman, Henry; Friedman, Allan H; Keir, Stephen T; He, Jie; He, Yiping; McLendon, Roger E; Herndon, James E; Yan, Hai; Bigner, Darell D
    Frequent mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) and the promoter of telomerase reverse transcriptase (TERT) represent two significant discoveries in glioma genomics. Understanding the degree to which these two mutations co-occur or occur exclusively of one another in glioma subtypes presents a unique opportunity to guide glioma classification and prognosis. We analyzed the relationship between overall survival (OS) and the presence of IDH1/2 and TERT promoter mutations in a panel of 473 adult gliomas. We hypothesized and show that genetic signatures capable of distinguishing among several types of gliomas could be established providing clinically relevant information that can serve as an adjunct to histopathological diagnosis. We found that mutations in the TERT promoter occurred in 74.2% of glioblastomas (GBM), but occurred in a minority of Grade II-III astrocytomas (18.2%). In contrast, IDH1/2 mutations were observed in 78.4% of Grade II-III astrocytomas, but were uncommon in primary GBM. In oligodendrogliomas, TERT promoter and IDH1/2 mutations co-occurred in 79% of cases. Patients whose Grade III-IV gliomas exhibit TERT promoter mutations alone predominately have primary GBMs associated with poor median OS (11.5 months). Patients whose Grade III-IV gliomas exhibit IDH1/2 mutations alone predominately have astrocytic morphologies and exhibit a median OS of 57 months while patients whose tumors exhibit both TERT promoter and IDH1/2 mutations predominately exhibit oligodendroglial morphologies and exhibit median OS of 125 months. Analyzing gliomas based on their genetic signatures allows for the stratification of these patients into distinct cohorts, with unique prognosis and survival.
  • Thumbnail Image
    ItemOpen Access
    Sym004-induced EGFR elimination is associated with profound anti-tumor activity in EGFRvIII patient-derived glioblastoma models.
    (Journal of neuro-oncology, 2018-07) Keir, Stephen T; Chandramohan, Vidyalakshmi; Hemphill, Carlee D; Grandal, Michael M; Melander, Maria Carlsen; Pedersen, Mikkel W; Horak, Ivan D; Kragh, Michael; Desjardins, Annick; Friedman, Henry S; Bigner, Darell D

    Background

    Sym004 is a mixture of two monoclonal antibodies (mAbs), futuximab and modotuximab, targeting non-overlapping epitopes on the epidermal growth factor receptor (EGFR). Previous studies have shown that Sym004 is more efficient at inducing internalization and degradation of EGFR than individual components, which translates into superior cancer cell inhibition. We investigated whether Sym004 induces removal of EGFRvIII and if this removal translates into tumor growth inhibition in hard-to-treat glioblastomas (GBMs) harboring the mutated, constitutively active EGFR variant III (EGFRvIII).

    Methods

    To address this question, we tested the effect of Sym004 versus cetuximab in eight patient-derived GBM xenograft models expressing either wild-type EGFR (EGFRwt) and/or mutant EGFRvIII. All models were tested as both subcutaneous and orthotopic intracranial xenograft models.

    Results

    In vitro studies demonstrated that Sym004 internalized and removed EGFRvIII more efficiently than mAbs, futuximab, modotuximab, and cetuximab. Removal of EGFRvIII by Sym004 translated into significant in vivo anti-tumor activity in all six EGFRvIII xenograft models. Furthermore, the anti-tumor activity of Sym004 in vivo was superior to that of its individual components, futuximab and modotuximab, suggesting a clear synergistic effect of the mAbs in the mixture.

    Conclusion

    These results demonstrate the broad activity of Sym004 in patient-derived EGFRvIII-expressing GBM xenograft models and provide a clear rationale for clinical evaluation of Sym004 in EGFRvIII-positive adult GBM patients.
  • Thumbnail Image
    ItemOpen Access
    Synergistic antitumor effects of 9.2.27-PE38KDEL and ABT-737 in primary and metastatic brain tumors.
    (PloS one, 2019-01-09) Yu, Xin; Dobrikov, Mikhail; Keir, Stephen T; Gromeier, Matthias; Pastan, Ira H; Reisfeld, Ralph; Bigner, Darell D; Chandramohan, Vidyalakshmi
    Standard treatment, unfortunately, yields a poor prognosis for patients with primary or metastatic cancers in the central nervous system, indicating a necessity for novel therapeutic agents. Immunotoxins (ITs) are a class of promising therapeutic candidates produced by fusing antibody fragments with toxin moieties. In this study, we investigated if inherent resistance to IT cytotoxicity can be overcome by rational combination with pro-apoptotic enhancers. Therefore, we combined ITs (9.2.27-PE38KDEL or Mel-14-PE38KDEL) targeting chondroitin sulfate proteoglycan 4 (CSPG4) with a panel of Bcl-2 family inhibitors (ABT-737, ABT-263, ABT-199 [Venetoclax], A-1155463, and S63845) against patient-derived glioblastoma, melanoma, and breast cancer cells/cell lines. In vitro cytotoxicity assays demonstrated that the addition of the ABT compounds, specifically ABT-737, sensitized the different tumors to IT treatment, and improved the IC50 values of 9.2.27-PE38KDEL up to >1,000-fold. Mechanistic studies using 9.2.27-PE38KDEL and ABT-737 revealed that increased levels of intracellular IT, processed (active) exotoxin, and PARP cleavage correlated with the enhanced sensitivity to the combination treatment. Furthermore, we confirmed the synergistic effect of 9.2.27-PE38KDEL and ABT-737 combination therapy in orthotopic GBM xenograft and cerebral melanoma metastasis models in nude mice. Our study defines strategies for overcoming IT resistance and enhancing specific antitumor cytotoxicity in primary and metastatic brain tumors.