PHILADELPHIA—Two multikinase inhibitors (MKIs) can treat chronic myeloid leukemia (CML) that is resistant to other inhibitors, according to preclinical research.
A series of in vitro experiments showed that the MKIs, sorafenib and axitinib, can overcome treatment resistance mediated by hyperactivation of the Src kinase Lyn, overexpression of the docking protein Gab2, and the presence of the Bcr-Abl T315I mutation.
Sebastian Halbach, of the University of Freiburg in Germany, and his colleagues presented these findings in a poster at the AACR Annual Meeting 2015 (abstract 2708).
Mechanisms of resistance
Halbach noted that CML is driven by the hyperactive fusion kinase Bcr-Abl, which builds up its own signaling network with various proteins, such as Gab2 and Lyn.
Resistance to tyrosine kinase inhibitors (TKIs) and MKIs can be caused by mutations in the Bcr-Abl oncogene, such as T315I, or by aberrant activity of components of the Bcr-Abl signaling network.
“We have previously shown in our lab that overexpression of the docking protein Gab2 . . . confers resistance against imatinib and dasatinib,” Halbach said. “And another mechanism of resistance is hyperactivation of the Src kinase Lyn.”
For the current study, Halbach and his colleagues investigated the role of Lyn by introducing imatinib, dasatinib, or DMSO to K562 cells (blast-phase CML), Lyn-transformed K562 cells, and Lyn-Y508F-transformed K562 cells.
They also compared imatinib and DMSO in Ba/F3 cells (a murine pro-B cell line), Lyn-transformed Ba/F3 cells, and Lyn-Y508F-transformed Ba/F3 cells.
The results of these experiments showed that hyperactive Lyn confers resistance to imatinib but not dasatinib.
“That’s not that surprising because dasatinib is a multikinase inhibitor which targets Src kinases,” Halbach noted. “Therefore, the hyperactivity of Lyn is directly targeted.”
Identifying new drugs
Having established that TKI and MKI resistance in CML can be mediated by Lyn and Gab2, as well as T315I, Halbach and his colleagues wanted to find drugs that would overcome this problem. They screened a panel of inhibitors and identified sorafenib and axitinib.
The researchers first evaluated the effects of sorafenib and axitinib against the T315I mutation. They tested the 2 MKIs—as well as imatinib, dasatinib, nilotinib, ponatinib, and DMSO—in the KBM5 cell line (blast-phase CML) and the KBM5-T315I cell line (imatinib-resistant CML).
Sorafenib and axitinib killed KBM5-T315I cells more effectively than any of the other inhibitors. The 2 MKIs also decreased the metabolic activity of T315I-positive cells more effectively than imatinib, dasatinib, or nilotinib, but not ponatinib, which produced similar results.
Next, Halbach and his colleagues tested sorafenib, axitinib, and the aforementioned inhibitors in K562 cells overexpressing Gab2. Overexpression of Gab2 conferred resistance to imatinib, dasatinib, nilotinib, and ponatinib, but not sorafenib and axitinib.
Both sorafenib and axitinib decreased the metabolic activity of Gab2-overexpressing cells more effectively than any of the other inhibitors.
Lastly, the researchers tested all of the inhibitors in Lyn-transformed K562 cells, Lyn-Y508F-transformed K562 cells, and K562 cells. They found that sorafenib and axitinib both overcame Lyn-Y508F-mediated resistance.
Sorafenib and axitinib killed K562 cells and Lyn-transformed K562 cells more effectively than any of the other inhibitors. The 2 MKIs also killed Lyn-Y508F-transformed K562 cells more effectively than imatinib and nilotinib, but not ponatinib or dasatinib.
Sorafenib decreased the metabolic activity of Lyn-Y508F-transformed K562 cells more effectively than all of the other inhibitors. But axitinib only proved more effective than imatinib in this regard.
Halbach said he hopes sorafenib and axitinib can one day serve as alternatives to ponatinib for CML patients, especially those with T315I mutations or high Gab2 levels.
For now, his team’s next step is to further analyze the influence of axitinib and sorafenib on the Bcr-Abl—Gab2 signaling complex.
