"LBH589 is a novel deacetylase inhibitor with promising anti-myeloma activity."
Dr. Enrique M. Ocio

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Enrique M. Ocio, David Vilanova, Laura San-Segundo, Patricia Maiso, Mercedes Garayoa, Peter Atadja, Atanasio Pandiella, J.F. San Miguel Hematology, Hospital Universitario de Salamanca, Spain; Centro de Investigacin del Cncer, Universidad de Salamanca, Spain; Novartis Pharmaceuticals, East Hanover, NJ, USA

Introduction Panobinostat (LBH589) is a novel histone deacetylase (HDAC) inhibitor being evaluated in clinical trials in hematological and solid malignancies. In multiple myeloma (MM), investigators have demonstrated its in vitro antimyeloma effect in cell lines and patients cells. Cancer treatment is typically based on the concept of combining agents with different mechanisms of action to overcome drug resistance. This was the rationale of the present study in which the in vitro and in vivo benefit of combinations of pabinostat with conventional antimyeloma agents has been explored. Material and Methods The potential in vitro synergism of pabinostat with 6 antimyeloma agents (melphalan, doxorubicin, dexamethasone, thalidomide, lenalidomide, bortezomib) was analyzed in MM1S cell line. The two most favorable combinations were tested in 120 NOD/SCID mice implanted with a human subcutaneous plasmocytoma. Mice were randomized into 12 treatment groups. Drugs were given ip, 5 days/week x 7 weeks. Doses were: pabinostat: 10 mg/Kg x 3 weeks and 5 mg/Kg afterwards; dexamethasone (D): 1 mg/Kg; bortezomib (B): 0.1 mg/Kg; and lenalidomide (L): 15 mg/Kg. Tumor volumes clinical features and weight were monitored three times a week. Mice were sacrificed when their tumors reached 2 cm. Immunohistochemistry was performed in selected tumors. Results Three agents potentiated the effect of pabinostat in vitro: bortezomib, dexamethasone and, to a lesser extent, lenalidomide. Moreover, the triple combination of pabinostat+L+D and pabinostat+B+D resulted in high synergistic activity. These studies provided the rationale for testing these combinations in vivo: Single agent pabinostat at a dose of 10 mg/Kg completely abrogated the growth of plasmocytomas without significant toxicity. In fact, after three weeks of treatment, the median volume of tumors in the pabinostat group was 16375 mm3 as compared to 18911182 mm3 in the control group (p=0.001). Immunohistochemistry of pabinostat treated tumors revealed a decrease in BrdU uptake, an increase in histone acetylation and phosphorylation of H2AX suggesting DNA damage. This antiproliferative action was associated with survival advantage: median survival 701.8 vs 302.1 days (p<0.001) for the pabinostat and vehicle treated groups respectively. Subsequently the dose of pabinostat was decreased by 50% in order to gain further insights into the potential advantage of the combinations. Interestingly, the addition of D and suboptimal doses of either B or L significantly improved the antimyeloma effect of pabinostat. In this sense, median survival increased up to 862.6 days in pabinostat+D+B (p<0.001) and 881.2 days for pabinostat+D+L (p<0.001). The efficacy of these triple combinations was significantly higher than any of the respective double combinations (pabinostat+D; pabinostat+B; pabinostat+L; B+D; L+D). Some of these combinations (including or not pabinostat) initially induced a slight toxicity (5%-15% body weight loss) which spontaneously recovered after the third week of treatment. Conclusion Combinations of pabinostat + dexamethasone with either bortezomib or lenalidomide are safe and display promising antimyeloma efficacy. This study provides the rationale for the clinical development of triple combinations of these drugs to improve the outcome of MM patients.

Abstract #1514 appears in Blood, Volume 110, issue 11, November 16, 2007

Keywords: Targeted Therapy|Histone deacetylase Inhibitor|Plasma Cells

Disclosure: Employment: Peter Atadja is employee of Novartis Pharmaceuticals. Paid Expert Testimony Information: J.F. San Miguel is a member of the advisory board of Novartis Pharmaceuticals.

Saturday, December 8, 2007 5:30 PM

Session Info: Poster Session: Myeloma: Pathophysiology and Pre-Clinical Studies, excluding Therapy-Novel Targets and Pathways (5:30 p.m.-7:30 p.m.)