Disease relapse and resistance to chemotherapy represent challenging issues for Hodgkin Lymphoma (HL) patients. PI3K/AKT and RAF/MEK/ERK pathways are constitutively activated in the majority of HL patients, thus representing attractive therapeutic targets. Previous results from our phase II study indicate that combining the PI3K/AKT inhibitor perifosine with the RAF/MEK/ERK inhibitor sorafenib can achieve significant clinical responses in relapsed/refractory HL. The present study was therefore aimed at characterizing the in vitro and in vivo activity and mechanism(s) of action of a novel PI3K/ERK dual inhibitor AEZS-136 (Æterna Zentaris GmbH, Germany, EU).
Four HL cell lines (L-540, SUP-HD1, KM-H2 and L-428) were used to investigate the in vitro effects of AEZS-136 on cell growth, cell cycle distribution, gene expression profiling (GEP), and apoptosis. Live cell imaging experiments were performed to asses the production of reactive oxygen species (ROS). Western blotting (WB) was used to assess the effects of AEZS-136 on MAPK and PI3K/AKT pathways as well as apoptosis. The antitumor efficacy of AEZS-136 was investigated in vivo in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice.
Exposure of L-540, SUP-HD1, KM-H2 and L-428 cell lines to AEZS-136 induced a marked, early and time-dependent dephosphorylation of PI3K/Akt and MAPK pathways that was associated with a significant time and dose-dependent cell growth inhibition [80 ± 3% (mean ±SEM) in the L-540 and SUP-HD1 responsive cell lines] and S phase cell cycle arrest. Indeed, upon AEZS-136 treatment the mean (±SEM) percentages of cells in S phase were reduced by 3-fold (13 ± 1%) as compared to control (33 ± 2%). Significant levels of cell death, as assessed by AnnexinV/PI staining, were only observed in L-540 (62 ± 9 vs 14 ± 3%, P ≤.0001) and SUP-HD1 (46 ± 2% vs 15 ± 2%, P ≤.0001) cell lines and were associated with severe mitochondrial dysfunction (up to 40%, P ≤.001). While no activation of caspase-3 and PARP cleavage were observed in L-540 and SUP-HD1 cells treated with AEZS-136, a potent generation of reactive oxygen species (ROS) was observed upon AEZS-136 treatment (up to 90%, P≤.0001). Pretreating cells with the ROS inhibitor YCG063 strongly inhibited AEZS-136-induced ROS generation, mitochondrial dysfunction and cell death, whereas the pan-caspase inhibitor Z-VADfmk did not. Since ROS generation has been implicated in mediating necroptosis, we tested if blocking programmed necrosis with Necrostatin-1 could prevent AEZS-136-induced cytotoxicity. When L-540 cells were treated with AEZS-136 in the presence of Necrostatin-1, cell death and ROS generation were completely prevented, suggesting that cell death was mechanistically related to necroptosis. Additionally, HL cells responsive to AEZS-136-induced cell death showed a pronounced JNK activation whose inhibition by the JNK inhibitor SP600125 reduced cell death and ROS generation. Furthermore, AEZS-136-increased JNK phosphorylation was inhibited by Necrostatin-1 or YCG063, suggesting that ROS-dependent necroptosis was linked to JNK. Interestingly, GEP analysis of L-540 and SUP-HD1 cell lines, but not KM-H2 and L-428 cells, indicated that AEZS-136 treatment induced upregulation of genes involved in positive regulation of cell death. In addition, in KM-H2 and L-428 cells, AEZS-136 strikingly induced the expression of the immediate early response 3 (IER3). Silencing of IER3 restored sensitivity of KM-H2 and L-428 cells to AEZS-136-induced necroptotic cell death, suggesting that IER3 acts as the signaling molecule that mediated AEZS-136-resistance to oxidative cell death. Finally, in vivo experiments were conducted to investigate the antitumor activity of AEZS-136. Treatment of NOD/SCID mice bearing L540 tumor nodules with increasing dose of AEZS-136 (30 – 60 mg/Kg body weight, PO, 5 days/2 weeks) resulted in a dose-dependent reduction of tumor growth (mean TGI of 70%, P ≤.0001) compared to vehicle-treated controls. No mice experienced any apparent treatment-related toxicity.
The PI3K/ERK dual inhibitor AEZS-136 demonstrates a potent antitumor activity against HL cell lines by targeting aberrant expression of MAPK and PI3K/Akt pathways. These data support further clinical evaluation of AEZS-136 in refractory/relapsed HL patients.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.