Abstract
The PI3K/AKT pathway acts as a critical regulator of cell survival by stimulating cell proliferation and inhibiting apoptosis and has been implicated in the pathogenesis of lymphoproliferative disorders. Therefore, inhibition of AKT seems to be a highly attractive new approach for the treatment of lymphoma.
We treated 9 cell lines with AKT-nhibitor (1, 10, 20 μM) over 24h and 48h respectively: EHEB (B-CLL), GRANTA-519 (MCL), JURKAT (T-ALL) BL-60, NAMALWA and BJAB (all Burkitt’s lymphoma), L363, OPM-2 and RPMI-8226 (all multiple myeloma). To determine the rates and type of AKT-inhibitor induced cell death, FACS analyses for CD19, 7AAD, active caspase-3, cytochrome c were performed. The phosphorylation status of AKT and its downstream proteins GSK3β, p70S6k and S6 was studied by Western blotting after 5–120 minutes.
In addition, 11 primary CLL samples with either del 13q (n=3), del 11q (n=2), del 17p (n=3) or a normal karyotype (n=3) were treated with AKT inhibitor (10 μM; 2.5μM; 0.625 μM; 0.156 μM). CLL samples were cultured in both standard medium as well as in HS5-(human stromal cells) conditioned medium to reduce spontaneous apoptosis of CLL in-vitro. 6 out of 11 patients had unmutated VH genes. 8 Patients were untreated, 3 were previously treated. Fludarabine (0.1 μM) was added to AKT-inhibitor in 11 cases to test for synergistic effects. CLL cells were harvested after 48 hours and 5 days to measure cell viability using Celltiter-GLO-Assay.
Treatment of cell lines lead to significant rates of AKT-inhibitor induced cell death (table 1), to hyperphosphorylation of AKT and to inhibition of phosphorylation of GSK3β (after 5 min) and S6 (after 20 min) in all cell lines and of p70S6k (after 120 min) in GRANTA, JURKAT, NAMALWA and BJAB. Cell death did not depend on functional p53 gene. Treatment of primary CLL samples with AKT-inhibitor alone was followed by a decrease of cell viability in a time and concentration dependent manner regardless of the medium used (table 2). Only with the lowest concentration and when cultured in HS5-conditioned medium, no further reduction of viable cells was seen between 48h and 5d. Treatment with AKT-inhibitor as a single agent seemed to be at least as effective as treatment with fludarabine. Response was independent of the genetic subgroup, VH mutation status or prior treatment. High risk cases with del 17p responded worse to fludarabine alone when compared to cases without del 17p (i.e. 75% of viable cells after 5d at 10000 μM in cases with del 17p vs. 25% in cases without del 17p). The same fludarabine resistant cases showed good responses to treatment with AKT-inhibitor (9% of viable cells after 5d at 10000 μM in cases with del 17p). A synergistic effect was not achieved by combining AKT-inhibitor and fludarabine. Culture of CLL cells in HS5-conditioned medium resulted in lower rates of spontaneous apoptosis, but also in lower rates of AKT-inhibitor induced cell death.
In conclusion, in-vitro treatment with AKT-inhibitor resulted in significant rates of cell death in cell lines and primary CLL cells, even in patients with del 17p or resistance to fludarabine. In cell lines, treatment with AKT-inhibitor was followed by typical features of apoptosis such as activation of caspase-3 and cytochrome c release. In CLL samples, prior treatment did not affect in-vitro response rates. These data underline the involvement of the PI3K/Akt pathway in the pathogenesis of lymphoma and point to an efficacy of the AKT-inhibitor in the treatment of lymphoma, multiple myeloma and CLL in-vivo. Concerning CLL, the AKT-inhibitor seems to be an attractive new treatment option even for cases with high risk cytogenetics. Using HS5-conditioned medium seems to be a well functioning method to reduce spontaneous apoptosis of CLL cells in-vitro.
Table 1: rates of cell death, caspase-3 activation and cytochrome c release after treatment of cell lines with AKT inhibitor (1μM, 48h)
7AAD-positive cells active caspase-3 cytochrome c release EHEB 15% − + GRANTA-519 15% + + JURKAT 17% + + BL60 24% + + NAMALWA 25% − (+) BJAB 30% + (+) L363 15% + − OPM-2 41% + + RPMI-8226 32% + (+)
Table 2: mean percentage of viable cells after treatment with AKT-Inhibitor (A), fludarabine (F; 0,1μM) and their combination (A + F) measured by Celltiter-GLO-Assay
10000 nM 2500 nM 625 nM 156,25 nM 48h 5d 48h 5d 48h 5d 48h 5d A F A + F A F A + F A A F A+ F A F A+ F A HS5 + (n=8) 94 84 (n=5) 75 (n=5) 45 22 (n=5) 25 (n=5) 88 52 91 84 80 69 22 18 76 85 HS5 − (n=11) 60 79 59 8 39 21 77 27 80 79 76 28 39 34 82 (n=10) 21
A caspase-3-dependent pathway is predominantly activated by the excitotoxin pregnenolone sulfate and requires early and late cytochrome c release and cell-specific caspase-2 activation in the retinal cell death
