The HDAC inhibitor LBH589 enhances the anti-myeloma effect of the RTK inhibitor picropodophyllin

Previous experiments using arrays demonstrated synergistic effects of histon deacetylase (HDAC) inhibitors to picropodophyllin (PPP), an IGF-1R Tyrosine Kinase (IGF-1RTK) inhibitor. We here report the in vitro and in vivo treatment of Multiple Myeloma (MM) using PPP in combination wtih LBH589, a HDAC inhibitor. In the RPMI8226 human MM cell line, simultaneous treatment with both compounds for 48h caused a 5-fold increase of apoptotic and late apoptotic/necrotic cells compared to controls, while treatment with either compound alone only induced a 3-fold increase. The effect of both compounds on the expression of cycline B1, -E and -D2 was additive, as demonstrated by western blot.
After 24h cleavage of apoptotic proteins caspase -9, -8 and -3 could be found in RPMI8226 cells treated with both drugs individually but in the combination we observed an additive effect on the cleavage of the active forms of caspase 8 compared to single drug treatments. Similar in vitro experiments using cells of the 5T33MM murine model confirm these data. Next, we studied the effect of the combination on the VEGF secretion by 5T33MM cells. At lower combinatorial concentrations we observed a significant additive reduction of VEGF secretion (56%) when compared to the single treatments (45% and 13% for LBH589 and PPP respectively). Finally we examined the in vivo
effect of the combinatorial treatment using sub-optimal concentrations of LBH589 (2,5mg/kg/day i.p. injection) and PPP (1,5mg/day orally) and assessed the overall survival rate using Kaplan-Meier analysis. Combined treatment resulted in a significant (pBased on these results we have an important indication that LBH589 is able to potentiate