Coexisting cancer stem cells with heterogeneous gene amplifications, transcriptional profiles, and malignancy are isolated from single glioblastomas

Glioblastoma (GBM) is known as an intractable, highly heterogeneous tumor encompassing multiple subclones, each supported by a distinct glioblastoma stem cell (GSC). The contribution of GSC genetic and transcriptional heterogeneity to tumor subclonal properties is debated. In this study, we describe the systematic derivation, propagation, and characterization of multiple distinct GSCs from single, treatment-naive GBMs (GSC families). The tumorigenic potential of each GSC better correlates with its transcriptional profile than its genetic make-up, with classical GSCs being inherently more aggressive and mesenchymal more dependent on exogenous growth factors across multiple GBMs. These GSCs can segregate and recapitulate different histopathological aspects of the same GBM, as shown in a paradigmatic tumor with two histopathologically distinct components, including a conventional GBM and a more aggressive primitive neuronal component. This study provides a resource for investigating how GSCs with distinct genetic and/or phenotypic features contribute to individual GBM heterogeneity and malignant escalation.

MicroRNA 483-3p overexpression unleashes invasive growth of metastatic colorectal cancer via NDRG1 downregulation and ensuing activation of the ERBB3/AKT axis

In colorectal cancer, the mechanisms underlying tumor aggressiveness require further elucidation. Taking advantage of a large panel of human metastatic colorectal cancer xenografts and matched stem-like cell cultures (m-colospheres), here we show that the overexpression of microRNA 483-3p (miRNA-483-3p; also known as MIR-483-3p), encoded by a frequently amplified gene locus, confers an aggressive phenotype. In m-colospheres, endogenous or ectopic miRNA-483-3p overexpression increased proliferative response, invasiveness, stem cell frequency, and resistance to differentiation. Transcriptomic analyses and functional validation found that miRNA-483-3p directly targets NDRG1, known as a metastasis suppressor involved in EGFR family downregulation. Mechanistically, miRNA-483-3p overexpression induced the signaling pathway triggered by ERBB3, including AKT and GSK3β, and led to the activation of transcription factors regulating epithelial-mesenchymal transition (EMT). Consistently, treatment with selective anti-ERBB3 antibodies counteracted the invasive growth of miRNA-483-3p-overexpressing m-colospheres. In human colorectal tumors, miRNA-483-3p expression inversely correlated with NDRG1 and directly correlated with EMT transcription factor expression and poor prognosis. These results unveil a previously unrecognized link between miRNA-483-3p, NDRG1, and ERBB3-AKT signaling that can directly support colorectal cancer invasion and is amenable to therapeutic targeting.

Abstract 942: ErbB3 overexpression unleashed by miR-205 epigenetic silencing is a therapeutic target in glioblastoma

In glioblastoma (GBM), the most frequent and lethal brain tumor, targeted therapies suppressing commonly altered signaling pathways has remained so far disappointing. However, in selected patient subsets, specific genetic alterations can confer sensitivity to targeted agents. In this study, by generating an integrated model based on patient-derived stem-like cells, faithfully recapitulating the original GBMs in vitro and in vivo, we identified a human GBM subset (around 9% of all GBMs) characterized by ERBB3 overexpression and nuclear accumulation. This was driven by inheritable epigenetic or post-transcriptional silencing of the oncosuppressor miR-205 and sustained the malignant phenotype. Unexpectedly, ERBB3, known to be devoid of autonomous signaling properties, was overexpressed in the absence of the other members of the EGFR family, but behaved as a specific signaling platform for FGFRs. ERBB3/FGFR dimerization led to hyperactivation of the PI3K/AKT/mTOR pathway and consequent upregulation of glycolysis, oxidative metabolism and de novo fatty acid biosynthesis. Treatment with a specific antibody (MM121) preventing ERBB3 association with FGFR caused metabolic shutdown and consequent proliferative arrest and apoptosis induction in vitro. Moreover, experimental tumors regenerated through ERBB3 overexpressing stem-like cell transplantation reproduced the features of the original GBMs and, upon treatment with the anti-ERBB3 antibody, significantly regressed. These findings identify a subset of GBM patients where exploitation of an ERBB3-targeted therapy could be effective.

Citation Format: Francesca De Bacco, Francesca Orzan, Jessica Erriquez, Elena Casanova, Ludovic Barault, Raffaella Albano, Antonio D'Ambrosio, Viola Bigatto, Gigliola Reato, Monica Patané, Bianca Pollo, Geoffrey Kuesters, Carmine Dell'Aglio, Laura Casorzo, Serena Pellegatta, Gaetano Finocchiaro, Paolo M. Comoglio, Carla Boccaccio. ErbB3 overexpression unleashed by miR-205 epigenetic silencing is a therapeutic target in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 942.

Abstract 1387: MET inhibition radiosensitizes KRAS-mutant rectal cancer

Rectal carcinoma, representing about a third of all newly diagnosed colorectal cancers, is one of the most common malignant tumors. The standard of care for locally advanced rectal cancer (LARC), consisting of neoadjuvant chemo/radiotherapy prior to surgical resection, is poorly effective, leading to complete tumor regression only in 10-30% of the cases. Approximately 40% of LARC harbor activating KRAS mutations, which have been extensively associated with primary resistance to targeted EGFR therapy and with radioresistance as well. Previous work showed that the MET receptor tyrosine kinase supports radioresistance and can be inhibited to radiosensitize tumor cell subpopulations retaining stem-like properties. Here, we show that LARC often express high levels of MET and can be successfully radiosensitized by MET inhibition. This was assessed in rectal stem-like cells isolated from human tumors (rectospheres), and transplanted in the mouse to regenerate tumors that faithfully reproduce the phenotype, the genotype and the therapeutic response of the original tumor. Mechanistically, we found that radioresistant KRAS-mutant rectospheres display significantly higher basal levels of RAD51, a master regulator of DNA homologous recombination repair, and increased RAD51 recruitment to irradiation-induced DNA double-strand breaks, as compared with KRAS-wild type rectospheres. Importantly, we showed that MET pharmacological inhibition by small-molecule kinase inhibitors, combined with radiotherapy, impairs RAD51 expression and function. This leads to DNA damage accumulation and results in effective radiosensitization of K-RAS-mutant rectal stem-like cells in vitro and in vivo, and significant inhibition of experimental tumors. Therefore, preclinical evidence is provided that MET can be exploited as a therapeutic target to radiosensitize KRAS-mutant rectal cancer at stem-like cell level.

Citation Format: Antonio D'Ambrosio, Federica Verginelli, Francesca Orzan, Raffaella Albano, Elena Casanova, Paolo Luraghi, Francesca De Bacco, Andrea Bertotti, Livio Trusolino, Rebecca Senetta, Anna Sapino, Elena Del Mastro, Marco Gatti, Paolo M. Comoglio, Carla Boccaccio. MET inhibition radiosensitizes KRAS-mutant rectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1387.

Abstract 2358: miRNA-483-3p overexpression unleashes invasiveness of metastatic colorectal cancer by NDRG1 targeting and upregulation of the HER3-AKT axis

In colorectal cancer, the genetic mechanisms underlying the metastatic switch are still poorly understood. Here we show that overexpression of miRNA-483-3p, encoded by a frequently amplified gene locus encompassing also insulin-like growth factor 2, confers an aggressive phenotype to stem-like cells derived from colorectal cancer metastases (m-colospheres). As result of miRNA-483-3p ectopic overexpression, m-colospheres displayed (i) increased proliferative response to exogenous EGFR family ligands EGF and NRG1; (ii) increased spontaneous and growth factor-induced in vitro invasiveness and epithelial-mesenchymal transition (EMT); (iii) enhanced stem-cell frequency and resistance to differentiation. By transcriptomic analyses and functional validation, we found that miRNA-483-3p targets NDRG1, a known ‘metastasis suppressor', which is responsible for degradation of EGFR family members, in particular HER3. As result, ectopic or native miRNA-483-3p overexpression was associated with hyper-activation of the signaling pathway triggered by HER3, including AKT and GSK3β, responsible for activation of EMT transcription factors. Consistently, treatment of miRNA-483-3p overexpressing m-colospheres with HER3 specific antibodies counteracted their proliferative and invasive phenotype. The pro-invasive role of miRNA-483-3p in patients was further confirmed by (i) analysis of colorectal tumors, where miRNA-483-3p expression levels directly correlated with expression of EMT transcription factors and poor-prognosis, and (ii) downregulation of naturally occurring miRNA-483-3p overexpression, which prevented invasion of tumors formed by m-colosphere transplantation. These results indicate that miRNA-483-3p can support colorectal cancer invasion through a signaling pathway amenable to targeting in human patients.

Citation Format: Ermes Candiello, Gigliola Reato, Federica Verginelli, Antonio D'Ambrosio, Gennaro Gambardella, Raffaella Albano, Paolo Luraghi, Paolo M. Comoglio, Andrea Bertotti, Livio Trusolino, Carla Boccaccio. miRNA-483-3p overexpression unleashes invasiveness of metastatic colorectal cancer by NDRG1 targeting and upregulation of the HER3-AKT axis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2358.

Activation of the MET receptor attenuates doxorubicin-induced cardiotoxicity in vivo and in vitro

Background and Purpose

Doxorubicin anti‐cancer therapy is associated with cardiotoxicity, resulting from DNA damage response (DDR). Hepatocyte growth factor (HGF) protects cardiomyocytes from injury, but its effective use is compromised by low biodistribution. In this study, we have investigated whether the activation of the HGF receptor—encoded by the Met gene—by an agonist monoclonal antibody (mAb) could protect against doxorubicin‐induced cardiotoxicity.

Experimental Approach

The mAb (5 mg·kg⁻¹) was injected in vivo into C57BL/6J mice, before doxorubicin (three doses of 7 mg·kg⁻¹). Cardiac functions were evaluated through MRI after treatment termination. Heart histological staining and mRNA levels of genes associated with heart failure (Acta1 and Nppa), inflammation (IL‐6), and fibrosis (Ctgf, Col1a2, Timp1, and Mmp9) were assessed. MAb (100 nM) was administered in vitro to H9c2 cardiomyoblasts before addition of doxorubicin (25 μM). DDR and apoptosis markers were evaluated by quantitative western blotting, flow cytometry, and immunofluorescence. Stattic was used for pharmacological inactivation of STAT3.

Key Results

In vivo, administration of the mAb alleviated doxorubicin‐induced cardiac dysfunction and fibrosis. In vitro, mAb mimicked the response to HGF by (a) inhibiting histone H2AX phosphorylation at S139, (b) quenching the expression of the DNA repair enzyme PARP1, and (c) reducing the proteolytic activation of caspase 3. The MET‐driven cardioprotection involved, at least in vitro, the phosphorylation of STAT3.

Conclusion and Implications

The MET agonist mAb provides a new tool for cardioprotection against anthracycline cardiotoxicity.

MET inhibition overcomes radiation resistance of glioblastoma stem-like cells

Glioblastoma (GBM) contains stem‐like cells (GSCs) known to be resistant to ionizing radiation and thus responsible for therapeutic failure and rapidly lethal tumor recurrence. It is known that GSC radioresistance relies on efficient activation of the DNA damage response, but the mechanisms linking this response with the stem status are still unclear. Here, we show that the MET receptor kinase, a functional marker of GSCs, is specifically expressed in a subset of radioresistant GSCs and overexpressed in human GBM recurring after radiotherapy. We elucidate that MET promotes GSC radioresistance through a novel mechanism, relying on AKT activity and leading to (i) sustained activation of Aurora kinase A, ATM kinase, and the downstream effectors of DNA repair, and (ii) phosphorylation and cytoplasmic retention of p21, which is associated with anti‐apoptotic functions. We show that MET pharmacological inhibition causes DNA damage accumulation in irradiated GSCs and their depletion in vitro and in GBMs generated by GSC xenotransplantation. Preclinical evidence is thus provided that MET inhibitors can radiosensitize tumors and convert GSC‐positive selection, induced by radiotherapy, into GSC eradication.

Agonist antibodies activating the Met receptor protect cardiomyoblasts from cobalt chloride-induced apoptosis and autophagy

Met, the tyrosine kinase receptor for hepatocyte growth factor (HGF), mainly activates prosurvival pathways, including protection from apoptosis. In this work, we investigated the cardioprotective mechanisms of Met activation by agonist monoclonal antibodies (mAbs). Cobalt chloride (CoCl₂), a chemical mimetic of hypoxia, was used to induce cardiac damage in H9c2 cardiomyoblasts, which resulted in reduction of cell viability by (i) caspase-dependent apoptosis and (ii) – surprisingly – autophagy. Blocking either apoptosis with the caspase inhibitor benzyloxycarbonyl-VAD-fluoromethylketone or autophagosome formation with 3-methyladenine prevented loss of cell viability, which suggests that both processes contribute to cardiomyoblast injury. Concomitant treatment with Met-activating antibodies or HGF prevented apoptosis and autophagy. Pro-autophagic Redd1, Bnip3 and phospho-AMPK proteins, which are known to promote autophagy through inactivation of the mTOR pathway, were induced by CoCl₂. Mechanistically, Met agonist antibodies or HGF prevented the inhibition of mTOR and reduced the flux of autophagosome formation. Accordingly, their anti-autophagic function was completely blunted by Temsirolimus, a specific mTOR inhibitor. Targeted Met activation was successful also in the setting of low oxygen conditions, in which Met agonist antibodies or HGF demonstrated anti-apoptotic and anti-autophagic effects. Activation of the Met pathway is thus a promising novel therapeutic tool for ischaemic injury.

BMP1-related metalloproteinases promote the development of ventral mesoderm in early Xenopus embryos

Bone morphogenetic protein 1 (BMP1) is a metalloproteinase closely related to Drosophila Tolloid (Tld). Tld regulates dorsoventral patterning in early Drosophila embryos by enhancing the activity of Dpp, a member of the TGF-beta family most closely related to BMP2 and BMP4. In Xenopus BMP4 appears to play an essential role in dorsoventral patterning, promoting the development of ventral fates during gastrula stages. To determine if BMP1 has a role in regulating the activity of BMP4, we have isolated cDNAs for Xenopus BMP1 and a novel closely related gene that we have called xolloid (xld). Whereas xbmp1 is uniformly expressed at all stages tested, the initial uniform expression of xld becomes localized to two posterior ectodermal patches flanking the neural plate and later to the inner ectoderm of the developing tailbud. xld is also expressed in dorsal regions of the brain during tailbud stages and is especially abundant in the ventricular layer of the dorsal hindbrain caudal to the otic vesicle. Overexpression of either gene inhibits the development of dorsoanterior structures in whole embryos and ventralizes activin-induced dorsal mesoderm in animal caps. Since ventralization of activin-induced animal caps can be blocked by coinjecting a dominant-inhibitory receptor for BMP2 and BMP4, we suggest a role for BMP1 and Xld in regulating the ventralizing activity of these molecules.