Antiglioma effects of N6-isopentenyladenosine, an endogenous isoprenoid end product, through the downregulation of epidermal growth factor receptor Elena Ciaglia 1 , Mario Abate 1 , Chiara Laezza 2,3 , Simona Pisanti 1 , Mario Vitale 1 , Vincenzo Seneca 4 , Giovanni Torelli 5 , Silvia Franceschelli 6 , Giuseppe Catapano 4 , Patrizia Gazzerro 6 and Maurizio Bifulco 1 1 Department of Medicine, Surgery and Dentistry “Scuola Medica Salernitana”, University of Salerno, Salerno, Italy 2 Institute of Endocrinology and Experimental Oncology, IEOS CNR, Naples, Italy 3 Department of Biology and Cellular and Molecular Pathology, University of Naples Federico II, Naples, Italy 4 Department of Neurosurgery, “G.Rummo” Medical Hospital, Benevento, Italy 5 Department of Neurosurgery, “San Giovanni di Dio e Ruggi d’Aragona University Hospital”, Salerno’s School of Medicine, Salerno, Italy 6 Department of Pharmacy, University of Salerno, Salerno, Italy Malignant gliomas are highly dependent on the isoprenoid pathway for the synthesis of lipid moieties critical for cell prolifera- tion. The isoprenoid derivative N6-isopentenyladenosine (iPA) displays pleiotropic biological effects, including a direct anti- tumor activity in several tumor models. The antiglioma effects of iPA was then explored in U87MG cells both in vitro and grafted in mice and the related molecular mechanism confirmed in primary derived patients’ glioma cells. iPA powerfully inhib- ited tumor cell growth and induced caspase-dependent apoptosis through a mechanism involving a marked accumulation of the pro-apoptotic BIM protein and inhibition of EGFR. Indeed, activating AMPK following conversion into its iPAMP active form, iPA stimulated EGFR phosphorylation and ubiquitination along a proteasome-mediated pathway which was responsible for receptor degradation and its downstream signaling pathways inhibition, including the STAT3, ERK and AKT cascade. The inhi- bition of AMPK by compound C prevented iPA-mediated phosphorylation of EGFR, known to precede receptor loss. As expected the block of EGFR degradation, by exposure to the proteasome inhibitor MG132, significantly reduced iPA-induced cell death. Given the importance of receptor degradation in iPA-mediated cytotoxicity, we also documented that the EGFR expression lev- els in a panel of primary glioma cells confers them a high sensitivity to iPA treatment. In conclusion our study provides the first evidence of iPA antiglioma effect. Indeed, as glioma is driven by aberrant signaling of growth factor receptors, particularly the EGFR, iPA, alone or in association with EGFR targeted therapies, might be a promising therapeutic tool to achieve a potent anti-tumoral effect. Malignant glioma of astrocytic origin (astrocytoma) or glio- blastoma multiforme (GBM) constitutes the most frequent and malignant primary brain tumour. Current standard ther- apeutic strategies for their treatment are only palliative and survival after diagnosis is normally 6 to 14 months, 1 which is mainly due to the high invasiveness and proliferation rate of GBM. 2 In addition, the high frequency of molecular altera- tions (p53, IDH1 and IDH2 genes, RB, PTEN, unmethylated MGMT) renders GBM cells poorly sensitive to cytotoxic therapies and highly resistant to standard chemotherapy and radiotherapy. Among them, the most common genetic alter- ation associated with malignant glioma is the over-activation and/or overexpression of the epidermal growth factor receptor (EGFR, also referred to as ERBB1 or HER1), a well- known oncoprotein belonging to HER superfamily of recep- tor tyrosine kinases together with ERBB2, ERBB3, and ERBB4 which transduce signaling through phosphatidylinosi- tol 3-kinase (PI3K)/Akt and the ras- raf-mitogen-activated protein kinase (MAPK) pathways to control pleiotropic cellu- lar processes, including cell differentiation, metabolism, pro- liferation, and survival. 3 When aberrant, these signaling leads to impaired apoptosis, and/or enhanced proliferation, angio- genesis, necrosis, and treatment refractoriness, suggesting a causative relationship between receptor dysregulation and the pathobiology of GBM. Among the many EGFR mutants Key words: isoprenoids, GBM, EGFR, AMPK, signaling Additional Supporting Information may be found in the online version of this article. Grant sponsor: Associazione Italiana Ricerca sul Cancro (AIRC); Grant number: IG 13312 DOI: 10.1002/ijc.30505 History: Received 28 June 2016; Accepted 25 Oct 2016; Online 3 Nov 2016 Correspondence to: Maurizio Bifulco, Department of Medicine, Surgery and Dentistry “Scuola Medica Salernitana”, University of Salerno, Via Salvatore Allende, 84081 Baronissi Salerno, Italy, Tel.: 139089965217, Fax: 139089969602, E-mail: maubiful@unisa.it or Elena Ciaglia, Department of Medicine, Surgery and Dentistry “Scuola Medica Salernitana”, University of Salerno, Via Salvatore Allende, 84081 Baronissi Salerno, Italy, Tel.: 139089965115, Fax: 139089969602, E-mail: eciaglia@unisa.it Cancer Therapy and Prevention Int. J. Cancer: 140, 959–972 (2017) V C 2016 UICC International Journal of Cancer IJC