Antiglioma effects of N6‐isopentenyladenosine, an endogenous isoprenoid end product, through the downregulation of epidermal growth factor receptor

Abstract

Malignant gliomas are highly dependent on the isoprenoid pathway for the synthesis of lipid moieties critical for cell proliferation. 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 inhibited 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 inhibition 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 levels 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.

The isoprenoid derivative N6‐benzyladenosine CM223 exerts antitumor effects in glioma patient‐derived primary cells through the mevalonate pathway

“…We have demonstrated that the modified adenosine compound i6A exerts cytotoxic, antiangiogenic and proapoptotic activity in different cell lines (Laezza et al, ; Spinola et al, ; Laezza et al, ; Laezza et al, ; Pisanti et al, ; Ciaglia et al, ). Earlier reports by our group highlighted the involvement of FPPS in i6A action in different physiopathological settings (Laezza et al, ; Ciaglia et al, ).…”

“…It belongs to the cytokinin family, involved in control of many processes in plants (Kersten, ; Laten and Zahareasdoktor, ; Bifulco et al, ). In humans, many biological actions, both in vitro and in vivo , including antitumour effects, have been attributed to i6A (Woo et al, ; Castiglioni et al, ; Laezza et al, ; Pisanti et al, ; Laezza et al, ; Ciaglia et al, ). Interest in the study of this compound has been reinforced by experimental observations that i6A interferes with the growth of k‐ras transformed thyroid cells (KiMol) xenograft tumours by inhibiting the expression and activity of farnesyl pyrophosphate synthase (FPPS) (Laezza et al, ).…”

Recognition by natural killer cells of N6‐isopentenyladenosine‐treated human glioma cell lines

“…We and others have previously reported cytotoxic, antiangiogenic and proapoptotic activity of iPA in different cell lines . Recently, a surprising antiglioma effect was also documented in vitro and in vivo model, where the isoprenoide derivative act through the specific degradation of EGFR and downregulation of cell signaling pathways dependent from the growth factor receptor oncogene.…”

“…The patients had been informed about the establishment of cellular models from their tumor and had given informed consent in written form. The preparation of adherent primary cultures of brain tumor cells (designated as GBMn) was conducted as reported elsewhere …”

“…iPA can act directly on cancer growth by inducing the apoptosis of several tumor cells such as colon cancer cells, sarcoma and myeloma cells . Interest in the study of this compound has been reinforced by our recent observations that iPA interferes with the growth of primary glioma cells in vitro and in vivo by selectively downregulating epidermal growth factor (EGFR) oncogene‐driven pathways . Furthermore, immunomodulatory properties have also been attributed to iPA, because of its ability to selectively expand and directly target human NK cells and to promote a direct activation of human‐resting NK cells …”