Indeno[1,2-c]isoquinolines as enhancing agents on all-trans retinoic acid-mediated differentiation of human myeloid leukemia cells

Induction of differentiation is a new and promising approach to cancer therapy, well illustrated by the treatment of acute myeloid leukemia with all-trans retinoic acid (ATRA). Using combination of ATRA and chemotherapy, adverse effects such as retinoic acid syndrome have decreased, and long-term survival has improved. In this study, we demonstrated that the indeno1,2-c]isoquinolines markedly enhanced differentiation of human myeloid leukemia HL-60 and NB4 cells when simultaneously combined with a low dose of ATRA. Of the tested compounds, 6-(4-methoxybenzyl)-2,11-dimethyl-6H,11H-indeno1,2-c]isoquinolin-5-one (IIQ-16), an indeno1,2-c]isoquinoline derivative, showed the highest differentiation-enhancing activity via a pathway involved with protein kinase C, extracellular signal-regulated kinase, and c-Jun N-terminal kinase. The ability to enhance the differentiation potential of ATRA by IIQ-16 may improve outcomes in the therapy of acute promyelocytic leukemia.