Presentation Abstract

Abstract Number: 5431
Presentation Title: Histone deacetylase inhibitor (HDAC) panobinostat (LBH589) enhances the antiproliferative effect of a topoisomerase II (topo II) inhibitor in doxorubicin-resistant HL-60 cells, despite high MDR expression
Presentation Time: Wednesday, Apr 21, 2010, 8:00 AM -11:00 AM
Location: Exhibit Hall A-C, Poster Section 23
Poster Section: 23
Poster Board Number: 4
Author Block: Anna K. Brady1, Anjali S. Advani2, Dale Grabowski2, Ram Ganapathi2, Mahrukh K. Ganapathi2. 1Cleveland Clinic Lerner College of Medicine, Cleveland, OH; 2Cleveland Clinic, Cleveland, OH
Abstract Body: Acute myeloid leukemia (AML) is difficult to treat, particularly in the relapsed or refractory setting due to drug resistance. Topo II inhibitors are effectively used to treat AML, and histone deacetylase (HDAC) inhibitors have been used pre-clinically and clinically with some success. We previously reported that vorinostat (SAHA) was effective in combination with topo II inhibitors in AML cells (Proc. AACR, 2009, Abstract 4567). In the present study we evaluate LBH589, a novel class I/II HDAC inhibitor. Since resistance to HDAC inhibitors has not been well described, we hypothesized that LBH589 would be effective in combination with a topo II inhibitor in a doxorubicin-resistant AML cell line that expresses MDR and resistant by MDR-independent mechanism.A sensitive HL60 parent line (S) and the doxorubicin-resistant sub-line (R) were used. Early studies revealed that vorinostat (SAHA) had comparable anti-proliferative effects in S & R cells but the R cells were relatively more resistant to LBH589. This resistance was likely MDR-mediated. We then tested whether sub-lethal doses of SAHA or LBH589, used in combination with sub-lethal doses of etoposide (VP-16), would be effective. S and R cells were treated with VP-16 for 1 h, washed, and re-incubated with SAHA or LBH, or drug-free media, for a total of 144 hours. Cell viability and apoptosis were measured at 72 h and 144 h following treatment. At 72 h and at 144 h, the combination of VP-16 and LBH was significantly more effective (p<0.01) in reducing proliferation in HL60/S and HL60/R cells, compared to either agent alone. At both 72 h and 144 h the combination of VP-16 and LBH also led to significantly (p<0.05) greater apoptosis in both S & R cells. Western blotting for phospho-histone H2AX, a marker of DNA damage, showed increased DNA damage in the R cells treated with VP-16 and LBH589 compared to either drug alone. Overall, the effects of LBH589 in combination with VP-16 were significantly (p<0.05) more effective than SAHA in the S & R cells. In summary, our results demonstrate that MDR may mediate resistance to LBH589. Further, in spite of MDR expression, LBH589 is a useful adjunct to VP-16 treatment and enhances the anti-proliferative effect of the topo II inhibitor via increased apoptosis, even in the doxorubicin-resistant cells. Thus, post-treatment with LBH589 in combination with a topo II inhibitor may be useful treatment strategy in relapsed / refractory AML.