Schürch, MD, PhD, (left)
and Adrian Ochsenbein, MD
Photo by Susi Bürki
Combining a tyrosine kinase inhibitor (TKI) with a monoclonal antibody (mAb) may circumvent TKI resistance in chronic myeloid leukemia (CML), according to preclinical research published in Science Translational Medicine.
To understand how TKI resistance develops, researchers analyzed the effect of these drugs on BCR-ABL1+ leukemia cell lines, cells from patients with newly diagnosed CML, and mouse models of CML.
The team found that TKIs induce CD70 expression in leukemic stem cells (LSCs) by downregulating microRNA-29. This results in reduced CD70 promoter DNA methylation and upregulation of the transcription factor specificity protein 1 (SP1).
The increase in CD70 triggers CD27 signaling and compensatory Wnt pathway activation. The researchers said this suggests LSCs evade TKIs by activating Wnt signaling through this route.
So the team hypothesized that combination treatment with a TKI and a mAb blocking the CD70/CD27 interaction would eradicate LSCs.
First, they tested an αCD27 mAb alone or in combination with a TKI in leukemia cell lines. Compared to either agent alone, αCD27/imatinib cotreatment significantly (P<0.001) reduced cell growth by inhibiting proliferation and enhancing apoptosis in SD-1 cells.
The researchers observed similar results when they tested the αCD27 mAb and nilotinib in SD-1 cells, as well as when they tested the αCD27 mAb with imatinib or ponatinib in KBM5 and KBM5r cells.
The team noted that αCD27/imatinib cotreatment inhibited Wnt pathway activation significantly stronger than either compound alone (P<0.001) but had little to no effect on Notch, Hedgehog, and MAP kinase pathways.
The researchers also conducted in vitro tests with an αCD70 mAb (clone 41D12-D) that was specifically designed to block the CD70/CD27 interaction without inducing effector functions such as antibody-dependent cell- or complement-mediated cytotoxicity and antibody-dependent cell-mediated phagocytosis.
They found that αCD70/imatinib cotreatment “potently reduced” CD34+ CML stem/progenitor cells in liquid cultures by inhibiting proliferation and increasing apoptosis. The combination also significantly impaired colony formation in semisolid cultures when compared to either agent alone (P<0.05).
In addition, αCD70/imatinib cotreatment eliminated human CD34+ CML stem/progenitor cells in murine xenografts. The LSCs were completely eradicated in 9 of 12 mice treated.
In a murine CML model, combination treatment with imatinib and an αCD70 mAb (clone FR70) significantly improved survival (P<0.001) compared to either agent alone. And 60% of mice (9 of 15) that received the combination were alive 90 days after transplantation.
The researchers said this suggests the LSCs were completely eradicated or at least effectively controlled long-term.
