Abstract 2113: Mechanism of action of pixantrone in non-Hodgkin's lymphoma cells

Abstract Background: Pixantrone (PIX), an anthracenedione analog, has shown promising results with reduced cardiotoxicity as compared to structurally similar mitoxantrone and doxorubicin (DOX) in early phase clinical trials in patients with non-Hodgkin’s lymphoma (NHL). The exact mechanisms of action on how PIX induce cell death by targeting DNA replication through intercalating DNA and/or inhibiting Topoisomerase II has not been clearly illustrated. Methods: A short-term cell proliferation assay (3 days treatment) and a long-term clonogenic assay (cells were treated with the drugs for 24 hours and then allowed to grow into colonies for 10-14 days) were used to assess and compare the effects of PIX and DOX on cell growth in three NHL cell lines, OCI-Ly8, Z138, and Raji. Immunofluorescent assays using γH2AX antibodies, and DAPI staining were used to examine the effect of PIX and DOX on the formation of double-strand breaks and micronuclei. Results: In the short-term cell proliferation assay, PIX was not as potent as DOX (IC50 values ranging from 22 nM to 2737 nM for PIX and 2.8 nM to 67 nM for DOX). The two drugs were significantly more potent in the long-term clonogenic assay with IC50 values in low nanomolar range (5.1 nM to 82.8 nM) and the difference between PIX and DOX was much smaller. Cells treated with PIX displayed less increases in DNA double-strand breaks compared to those of DOX as quantified by the number of γH2AX positive foci formed in the cells. Furthermore, PIX treatment significantly increased the formation of micronuclei in a drug concentration and time dependent manner. Conclusions: The findings from the current study indicate that PIX induces DNA damages that impair the chromosomal segregation but do not significantly trigger double-strand breakage checkpoint response. Overall, our results suggest that PIX may exert its antitumor activity via mechanisms that are different from those of DOX. Citation Format: Serina Ng, Ruben Muñoz, Daniel Von Hoff, Haiyong Han. Mechanism of action of pixantrone in non-Hodgkin's lymphoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2113. doi:10.1158/1538-7445.AM2017-2113