The lipid kinase PI3Kδ is specifically over-expressed/aberrantly activated in a variety of B-cell malignances such as chronic lymphocytic leukemia and acute myelocytic leukemia. Till now, PI3Kδ has been extensively explored as a therapeutic target in hematologic malignancies. The CAL-101 is the first selective PI3Kδ inhibitor approved by US Food and Drug Administration (FDA) for the treatment of chronic lymphocytic leukemia, B-cell non-Hodgkin lymphoma and relapsed small lymphocytic lymphoma.

Based on the X-ray structure of PI3Kδ kinase, a study team in High Magnetic Field Laboratory, Chinese Academy of Sciences (CHMFL) designed a highly potent and selective ATP competitive PI3Kδ inhibitor, PI3KD-IN-015.

The ADP-glo biochemical assay demonstrated that the PI3KD-IN-015 inhibited PI3K with a IC50 of 5nM, meanwhile it exhibited 12~60 fold selectivity against PI3Ks and PI4Ks kinases. The selectivity profile of PI3KD-IN-015 in the kinome wide range displayed that the PI3KD-IN-015 did not target any other protein kinases except for a few lipid kinases, including isoforms and mutants of PI3K and PI4K at a concentration of 1μM.

The effects of PI3KD-IN-015 on PI3K mediated downstream signaling in various B-cell malignant cell lines showed that PI3KD- IN-015 potently inhibited the phosphorylation of Akt at both Thr308 and Ser473 sites, the downstream target of PI3K, among MOLM-13 , HT, Namalwa, MEC-1, MEC-2, and HS505T cells, with EC50 less than 1 μM.

The anti-proliferative activity against cancer cell lines showed that PI3KD-IN-015 exhibited moderate antiproliferative effects against most of the cell lines including AML, B-cell lymphoma and multiple myeloma cell lines with GI50 between 1-10 μM but did not exhibit apparent inhibitory activity against CLL cell lines. The PI3KD- IN-015 effectively suppressed the growth of 2 of 3 CLL primary cells and was effective against most of AML patient cells with GI50 less than 10 μM.

The study also reported that PI3KD-IN-015 induced apparent PARP cleavage in MOLM-13 cell, HT cell, but only weakly in MEC-1 cell within 12 hours. Similar trend was observed for the reported PI3Kδ inhibitor, CAL- 101 and pan-PI3K inhibitor GDC-0941. Both HT cells and MEC-1 cells, treatment of PI3KD-IN-015 significantly increased the production of LC3B II, which indicated that PI3KD-IN-015 can induce autophagy, probably through its activity against PI3Kδ.

The results were published in Oncotarget entitled Characterization of Selective and Potent PI3Kδ Inhibitor (PI3KD-IN-015) for B-Cell Malignances.

Selectivity and Activity of PI3KD-IN-015 (Image by LIANG Xiaofei)