FGF Trapping Inhibits Multiple Myeloma Growth through c-Myc Degradation-Induced Mitochondrial Oxidative Stress.

Multiple myeloma, the second most common hematologic malignancy, frequently relapses because of chemotherapeutic resistance. Fibroblast growth factors (FGF) act as proangiogenic and mitogenic cytokines in multiple myeloma. Here, we demonstrate that the autocrine FGF/FGFR axis is essential for multiple myeloma cell survival and progression by protecting multiple myeloma cells from oxidative stress-induced apoptosis. In keeping with the hypothesis that the intracellular redox status can be a target for cancer therapy, FGF/FGFR blockade by FGF trapping or tyrosine kinase inhibitor impaired the growth and dissemination of multiple myeloma cells by inducing mitochondrial oxidative stress, DNA damage, and apoptotic cell death that were prevented by the antioxidant vitamin E or mitochondrial catalase overexpression. In addition, mitochondrial oxidative stress occurred as a consequence of proteasomal degradation of the c-Myc oncoprotein that led to glutathione depletion. Accordingly, expression of a proteasome-nondegradable c-Myc protein mutant was sufficient to avoid glutathione depletion and rescue the proapoptotic effects due to FGF blockade. These findings were confirmed on bortezomib-resistant multiple myeloma cells as well as on bone marrow-derived primary multiple myeloma cells from newly diagnosed and relapsed/refractory patients, including plasma cells bearing the t(4;14) translocation obtained from patients with high-risk multiple myeloma. Altogether, these findings dissect the mechanism by which the FGF/FGFR system plays a nonredundant role in multiple myeloma cell survival and disease progression, and indicate that FGF targeting may represent a therapeutic approach for patients with multiple myeloma with poor prognosis and advanced disease stage. SIGNIFICANCE: This study provides new insights into the mechanisms by which FGF antagonists promote multiple myeloma cell death. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/11/2340/F1.large.jpg.

Activated d16HER2 homodimers and SRC kinase mediate optimal efficacy for trastuzumab.

A splice isoform of the HER2 receptor that lacks exon 16 (d16HER2) is expressed in many HER2-positive breast tumors, where it has been linked with resistance to the HER2-targeting antibody trastuzumab, but the impact of d16HER2 on tumor pathobiology and therapeutic response remains uncertain. Here, we provide genetic evidence in transgenic mice that expression of d16HER2 is sufficient to accelerate mammary tumorigenesis and improve the response to trastuzumab. A comparative analysis of effector signaling pathways activated by d16HER2 and wild-type HER2 revealed that d16HER2 was optimally functional through a link to SRC activation (pSRC). Clinically, HER2-positive breast cancers from patients who received trastuzumab exhibited a positive correlation in d16HER2 and pSRC abundance, consistent with the mouse genetic results. Moreover, patients expressing high pSRC or an activated "d16HER2 metagene" were found to derive the greatest benefit from trastuzumab treatment. Overall, our results establish the d16HER2 signaling axis as a signature for decreased risk of relapse after trastuzumab treatment.

Potential role of HER2-overexpressing exosomes in countering trastuzumab-based therapy.

Exosomes are endosome-derived nanovesicles actively released into the extracellular environment and biological fluids, both under physiological and pathological conditions, by different cell types. We characterized exosomes constitutively secreted by HER2-overexpressing breast carcinoma cell lines and analyzed in vitro and in vivo their potential role in interfering with the therapeutic activity of the humanized antibody Trastuzumab and the dual tyrosine kinase inhibitor (TKI) Lapatinib anti-HER2 biodrugs. We show that exosomes released by the HER2-overexpressing tumor cell lines SKBR3 and BT474 express a full-length HER2 molecule that is also activated, although to a lesser extent than in the originating cells. Release of these exosomes was significantly modulated by the growth factors EGF and heregulin, two of the known HER2 receptor-activating ligands and naturally present in the surrounding tumor microenvironment. Exosomes secreted either in HER2-positive tumor cell-conditioned supernatants or in breast cancer patients' serum bound to Trastuzumab. Functional assays revealed that both xenogeneic and autologous HER2-positive nanovesicles, but not HER2-negative ones, inhibited Trastuzumab activity on SKBR3 cell proliferation. By contrast, Lapatinib activity on SKBR3 cell proliferation was unaffected by the presence of autologous exosomes. Together, these findings point to the role of HER2-positive exosomes in modulating sensitivity to Trastuzumab, and, consequently, to HER2-driven tumor aggressiveness.

Serological identification of HSP105 as a novel non-Hodgkin lymphoma therapeutic target.

We reported that the clinical efficacy of dendritic cell-based vaccination is strongly associated with immunologic responses in relapsed B-cell non-Hodgkin lymphoma (B-NHL) patients. We have now investigated whether postvaccination antibodies from responders recognize novel shared NHL-restricted antigens. Immunohistochemistry and flow cytometry showed that they cross-react with allogeneic B-NHLs at significantly higher levels than their matched prevaccination samples or nonresponders' antibodies. Western blot analysis of DOHH-2 lymphoma proteome revealed a sharp band migrating at approximately 100 to 110 kDa only with postvaccine repertoires from responders. Mass spectrometry identified heat shock protein-105 (HSP105) in that molecular weight interval. Flow cytometry and immunohistochemistry disclosed HSP105 on the cell membrane and in the cytoplasm of B-NHL cell lines and 97 diagnostic specimens. A direct correlation between HSP105 expression and lymphoma aggressiveness was also apparent. Treatment of aggressive human B-NHL cell lines with an anti-HSP105 antibody had no direct effects on cell cycle or apoptosis but significantly reduced the tumor burden in xenotransplanted immunodeficient mice. In vivo antilymphoma activity of HSP105 engagement was associated with a significant local increase of Granzyme B(+) killer cells that very likely contributed to the tumor-restricted necrosis. Our study adds HSP105 to the list of nononcogenes that can be exploited as antilymphoma targets.

Improved clinical outcome in indolent B-cell lymphoma patients vaccinated with autologous tumor cells experiencing immunogenic death.

Increasing evidence argues that the success of an anticancer treatment may rely on immunoadjuvant side effects including the induction of immunogenic tumor cell death. Based on the assumption that this death mechanism is a similar prerequisite for the efficacy of an active immunotherapy using killed tumor cells, we examined a vaccination strategy using dendritic cells (DC) loaded with apoptotic and necrotic cell bodies derived from autologous tumors. Using this approach, clinical and immunologic responses were achieved in 6 of 18 patients with relapsed indolent non-Hodgkin's lymphoma (NHL). The present report illustrates an impaired ability of the neoplastic cells used to vaccinate nonresponders to undergo immunogenic death on exposure to a cell death protocol based on heat shock, γ-ray, and UVC ray. Interestingly, when compared with doxorubicin, this treatment increased surface translocation of calreticulin and cellular release of high-mobility group box 1 and ATP in histologically distinct NHL cell lines. In contrast, treated lymphoma cells from responders displayed higher amounts of calreticulin and heat shock protein 90 (HSP90) compared with those from nonresponders and boosted the production of specific antibodies when loaded into DCs for vaccination. Accordingly, the extent of calreticulin and HSP90 surface expression in the DC antigenic cargo was significantly associated with the clinical and immunologic responses achieved. Our results indicate that a positive clinical effect is obtained when immunogenically killed autologous neoplastic cells are used for the generation of a DC-based vaccine. Therapeutic improvements may thus be accomplished by circumventing the tumor-impaired ability to undergo immunogenic death and prime the antitumor immune response.

Shed HER2 extracellular domain in HER2-mediated tumor growth and in trastuzumab susceptibility.

The question of the serum HER2 extracellular domain (HER2/ECD) measurement for prediction of response to the anti-HER2 antibody Trastuzumab is still an open and current matter of clinical debate. To elucidate the involvement of shed HER2/ECD in HER2-driven tumor progression and in guiding therapy of individual patients, we examined biological effects exerted by elevated HER2/ECD in cancer growth and in response to Trastuzumab. To this purpose SKOV3 tumor cells were stably transfected to release a recombinant HER2/ECD molecule (rECD). Transfectants releasing high levels of 110-kDa rECD, identical in size to native HER2/ECD (nECD), grew significantly slower than did controls, which constitutively released only basal levels of nECD. While transmembrane HER2 and HER1 were expressed at equal levels by both controls and transfected cells, activation of these molecules and of downstream ERK2 and Akt was significantly reduced only in rECD transfectants. Surface plasmon resonance analysis revealed heterodimerization of the rECD with HER1, -2, and -3. In cell growth bioassays in vitro, shed HER2 significantly blocked HER2-driven tumor cell proliferation. In mice, high levels of circulating rECD significantly impaired HER2-driven SKOV3 tumor growth but not that of HER2-negative tumor cells. In vitro and in mice, Trastuzumab significantly inhibited tumor growth due to the rECD-facilitated accumulation of the antibody on tumor cells. Globally our findings sustain the biological relevance of elevated HER2/ECD levels in the outcome of HER2-disease and in the susceptibility to Trastuzumab-based therapy.