Photo by Larry Young
SAN FRANCISCO—MicroRNA-155 (miR-155) can act as an oncogenic driver in ALK− anaplastic large-cell lymphoma (ALCL) and may therefore be a therapeutic target for the disease, according to a presentation at the 7th Annual T-cell Lymphoma Forum.
Analyzing patient samples and cell lines, researchers discovered that miR-155 is highly expressed in ALK− ALCL but is nearly absent in ALK+ ALCL.
They also found evidence suggesting that miR-155 drives tumor growth in mouse models of ALK− ALCL.
Philipp Staber, MD, PhD, of the Medical University of Vienna in Austria, presented these findings at the meeting.
Dr Staber and his colleagues previously found (Merkel et al, PNAS 2010) that miR-155 was highly expressed in ALK− ALCL. So they decided to take a closer look at the phenomenon.
They assessed miR-155 expression in samples from patients with ALK+ or ALK− ALCL, as well as 6 ALCL cell lines.
miR-155 expression was significantly higher in the ALK− patient samples than in the ALK+ samples (P<0.001). And it was significantly higher (P<0.001) in the ALK− cell lines (DL-40, Mac1, and Mac2a) than in the ALK+ cell lines (K299, SR789, and SUP-M2).
Dr Staber and his colleagues then overexpressed miR-155 in ALK+ ALCL cell lines (K299 and SR789). And they observed a decrease in known target genes of miR-155—C/EBPβ, SOCS1, and SHIP1.
The researchers also observed an inverse correlation between miR-155 host gene promoter methylation and miR-155 expression in an ALCL+ cell line, which suggested that ALK activity has no direct effect on miR-155 levels.
The team treated the K299 cell line with the ALK inhibitor crizotinib at 100 nM, 200 nM, and 400 nM doses and found that miR-155 did not increase at any dose. Dr Staber noted, however, that the researchers were only able to treat cells for a maximum of 24 hours.
The group then discovered that anti-miR-155 mimics could reduce tumor growth in mouse models of ALK- ALCL. Mice were injected with Mac1 or Mac2a cells transfected with anti-miR-155, control RNA, or pre-miR-155 oligos.
In both Mac1 and Mac2 models, tumors were substantially smaller in the anti-mir-155 mice than in the pre-miR-155 mice (P=0.038 and P=0.006, respectively). But tumor growth was not significantly reduced compared to controls.
“Immunohistochemistry in these tumors shows quite a clear picture,” Dr Staber said. “The C/EBPβ target gene is overexpressed when using anti-miR-155, and [expression is decreased] with overexpression of miR-155. And the same is true for SOCS1. STAT3 signaling is increased through overexpression of miR-155.”
The researchers observed the same effect in ALK− ALCL patient samples.
Using ALK+ cell lines (K299 and SR789), the team went on to show that miR-155 suppresses IL-8 expression and induces IL-22 expression, a finding they verified in mice.
“IL-8 is a direct target of C/EBPβ, and C/EBPβ, as shown before, is a target of miR-155, so this makes sense,” Dr Staber said. “On the other hand, IL-22 is a strong inducer of STAT3 signaling, which is strongly induced when we increase miR-155 expression.”
Dr Staber and his colleagues concluded that these findings, when taken together, suggest that miR-155 could be a therapeutic target for ALK− ALCL.