Novel, 2^ND Generation Histone Deacetylase (HDAC) Inhibitor JNJ-26481585 Exhibits Potent Antitumor Activity Against Chronic Lymphocytic Leukemia Cells In-Vitro and Ex-Vivo.

Chronic lymphocytic leukemia (CLL), the most frequent lymphoproliferative disease is characterized by the insidious accumulation of mature-appearing lymphocytes predominantely in bone marrow, blood and lymphatic tissues. Despite a generally indolent course the vast majority of subjects diagnosed with CLL eventually require treatment. Apart from cytostatic drugs recently antibodies have been added to the therapeutic armamentarium. However, only a minority of patients will enjoy long-term disease-free intervals thus making further intervention of therapy highly desirable. Histone deacetylase inhibitors (HDACi) constitute a new class of epigenetic anti-cancer agents that inhibit growth, induce differentiation and, as recently shown, apoptosis in neoplastic cells. Antitumor acitivity of 1st generation compounds such as SAHA/Zolinza™ is encouraging, yet approval has been limited to treatment of cutaneous T-cell lymphoma so far, a hematologic niche indication. Novel compounds are investigated to assess for more potent antitumor activity, hopefully allowing to broaden the therapeutic spectrum of HDACi. Therefore, we investigated the apoptosis-inducing capacity of JNJ-26481585, a novel “second generation” hydroxamic acid-based oral pan-HDACi in a CLL cell line and primary, patient-derived CLL cells. In the MEC1 cell line JNJ-26481585 induced apoptosis very effectively within 72hrs at an EC50 of approx. 0,01 μM. In comparison, SAHA exhibited an EC50 of approx. 3 μM in the same cell line and the EC50 for Fludarabine is approx. 4 μM. In primary, patient derived CLL samples [n= 12 pts] the mean EC50 for JNJ-26481585 was 0,005 μM [range: 0.14 nM to 25 nM; 5 days of incubation] compared to SAHA which had an EC50 of around 7 μM in primary CLL cells. Strong histone H3 acetylation and HSP70 upregulation was observed as assessed by Western blot, potentially related to HSP90 acetylation. The induction of apoptosis was paralleled by a down-regulation of the bcl-2 protein in western blot. Initial combination therapy explorations showed strong synergism with the proteasome inhibitor bortezomib (Velcade™) shifting the EC50 to the sub nM range both in MEC1 cells as well as in primary CLL samples. In summary, the 2nd generation HDACi JNJ-26481585 induces potent histone acetylation as well as HSP70 upregulation and bcl-2 downregulation in MEC1 cells and primary, patient-derived CLL cells, resulting in an apoptosis-inducing capacity at low nano-molar ranges, far superior to the 1st generation HDACi SAHA/Zolinza™.