Retinoblastoma cells activate the AKT pathway and are vulnerable to the PI3K/mTOR inhibitor NVP-BEZ235

Abstract

Retinoblastoma is a pediatric cancer of the retina most often caused by inactivation of the retinoblastoma (RB1) tumor suppressor gene. We previously showed that Rb1 loss cooperates with either co-activating the phosphatidylinositol 3-kinase (PI3K)/AKT pathway, or co-deleting Pten, to initiate retinoblastoma tumors in mice. The objectives of this study were to determine if the AKT pathway is activated in human retinoblastomas and the extent that anti-PI3K therapy induces apoptosis in retinoblastoma cells, alone or in combination with the DNA damaging drugs carboplatin and topotecan. Serial sections from human retinoblastoma tissue microarrays containing 27 tumors were stained with antibodies specific to p-AKT, Ki-67, forkhead box O1 (p-FOXO1), and ribosomal protein S6 (p-S6) using immunohistochemistry and each tumor sample scored for intensity. Human retinoblastoma tumors displayed significant correlation between p-AKT intensity with highly proliferative tumors (p = 0.008) that were also highly positive for p-FOXO1 (p = 0.002). Treatment with BEZ235, a dual PI3K/mTOR inhibitor, reduced phosphorylation levels of the AKT targets p-FOXO and p-S6 and effectively induced apoptosis the Y79 and Weri-1 human retinoblastoma cell lines and in vivo in our retinoblastoma mouse model. Long-term treatment with BEZ235 in vivo using our retinoblastoma-bearing mice induced apoptosis but did not significantly extend the lifespan of the mice. We then co-administered BEZ235 with topotecan and carboplatin chemotherapeutics in vivo, which more effectively induced apoptosis of retinoblastoma, but not normal retinal cells than either treatment alone. Our study has increased the variety of potentially effective targeted treatments that can be considered for human retinoblastoma.

LncRNA HOTAIR facilitates proliferation and represses apoptosis of retinoblastoma cells through the miR-20b-5p/RRM2/PI3K/AKT axis

“…Both in vivo and ex vivo assays unraveled the inhibitory functions of HOTAIR silencing on the phosphorylation levels of PI3K and AKT. Rb1 deletion and PI3K/AKT activation synergistically provoke RB in mice [ 42 ]. Repression of the PI3K/AKT contributes to retarding RB progression [ 43 ].…”

Identification of Epigenetically Modified Hub Genes and Altered Pathways Associated With Retinoblastoma

“…In Rb −/- cells, Rb loss accompanied by the co-activation of PI3K/Akt pathway is found to be crucially involved in the initiation of Rb tumor development ( Chakraborty et al, 2007 ; Cohen et al, 2009 ). Indeed, the immunohistochemical analysis of 27 human Rb tissue microarrays shows that p-Akt overexpression in highly proliferative tumors which in turn is indicative of its role in Rb progression ( Xie et al, 2017 ). Hence, the identification of PI3K as hub gene in Rb tumors is evidential of the role of PI3K/Akt/mTOR signaling pathway in Rb tumor progression.…”

Pharmacologic inhibition of Akt in combination with chemotherapeutic agents effectively induces apoptosis in ovarian and endometrial cancer cell lines

“…In that case, the use of PI3K inhibitors would have the unwanted effect of stimulating alternate pathways, an effect that would be mitigated in the case of AZD5363, which disables solely Akt signaling, possibly preventing unwanted balancing effects. Also, the failure of NVP-BEZ235 to inhibit BAD phosphorylation, one of the most striking effects of AZD5363, could explain the higher efficacy of the latter in inducing apoptosis, especially considering that abnormal Akt activation, and thus substrate phosphorylation, is one of the most well recognized molecular process of chemoresistance [2,4,67,68]. Alternatively, as seen in Fig.3A, some level of cleaved caspase-3 can be observed without an increase in PARP cleavage; it is highly plausible that the combination of NVP-BEZ235 and cisplatin is capable of activating the intrinsic pathway of apoptosis but fails to reduce downstream inhibitors of apoptosis such as XIAP, which could explain this discrepancy.…”

“…In that case, the use of PI3K inhibitors would have the unwanted effect of stimulating alternate pathways, an effect that would be mitigated in the case of AZD5363, which disables solely Akt signaling, possibly preventing unwanted balancing effects. Also, the failure of NVP-BEZ235 to inhibit BAD phosphorylation, one of the most striking effects of AZD5363, could explain the higher efficacy of the latter in inducing apoptosis, especially considering that abnormal Akt activation, and thus substrate phosphorylation, is one of the most well-recognized molecular process of chemoresistance [2,4,67,68]. Alternatively, as seen in Fig.…”