Obatoclax mesylate (GX15-070)

Obatoclax mesylate, also known as GX15-070, is a hydrophobic small molecule that potently inhibits BCL-2 family by binding to the BH3-binding site of BCL-2 and other related BCL-2 family members (including BCL-XL, MCL-1, A1, and BCL-B).  As a pan-BCL-2 inhibitor being investigated for the treatment of refractory malignancies, obatoclax mesylate directly induce apoptosis in cultured acute myeloid leukemia (AML) cells as well as primary patient samples and exhibits antitumor activity in mouse xengografts of solid tumor and myeloma cell lines. Study results have shown that obatoclax mesylate inhibited clonogenic growth of primary AML samples (IC50 < nmol/L) and dissociated Bak and Bim from MCL-1 in cultured AML cells.

Reference

Aaron D. Schimmer, Susan O’Brien, Hagop Kantarjian, Joseph Brandwein, Bruce D. Cheson, Mark D. Minden, Karen Yee, Farhad Ravandi, Francis Giles, Andre Schuh, Vikas Gupta, Michael Andreeff, Charles Koller, Hong Chang, Suzanne Kamel-Reid, Mark Berger, Jean Viallet, and Gautam Borthakur. A phase I study of the Pan BCL-2 family inhibitor obatoclax mesylate in patients with advanced hematologic malignancies. Clin Cancer Res 2008; 14:8295-8301

Phase I study of obatoclax mesylate (GX15-070), a small molecule pan-Bcl-2 family antagonist, in patients with advanced chronic lymphocytic leukemia.[Pubmed:18931344]

Blood. 2009 Jan 8;113(2):299-305.

Obatoclax mesylate is a small molecule pan-Bcl-2 antagonist with in vitro activity against chronic lymphocytic leukemia (CLL) cells. Obatoclax was administered to patients with advanced CLL at doses ranging from 3.5 to 14 mg/m(2) as a 1-hour infusion and from 20 to 40 mg/m(2) as a 3-hour infusion every 3 weeks. Twenty-six patients received a total of 74 cycles. Dose-limiting reactions were neurologic (somnolence, euphoria, ataxia) and associated with the infusion. The maximum tolerated dose (MTD) was 28 mg/m(2) over 3 hours every 3 weeks. One (4%) of 26 patients achieved a partial response. Patients with anemia (3/11) or thrombocytopenia (4/14) experienced improvements in hemoglobin and platelet counts. Circulating lymphocyte counts were reduced in 18 of 26 patients with a median reduction of 24%. Overall, the maximum plasma concentration (C(max)) and area under the curve (AUC) values of obatoclax were dose proportional. Activation of Bax and Bak was demonstrated in peripheral blood mononuclear cells, and induction of apoptosis was related to overall obatoclax exposure, as monitored by the plasma concentration of oligonucleosomal DNA/histone complexes. Obatoclax mesylate has biologic activity and modest single-agent activity in heavily pretreated patients with advanced CLL. Further evaluation in less heavily pretreated patients and in combination with other therapeutic agents is warranted. This trial has been registered with http://clinicaltrials.gov under identifier NCT00600964.

Phase II study of obatoclax mesylate (GX15-070), a small-molecule BCL-2 family antagonist, for patients with myelofibrosis.[Pubmed:20709666]

Clin Lymphoma Myeloma Leuk. 2010 Aug;10(4):285-9.

BACKGROUND: Myelofibrosis (MF) is a disease characterized by the overexpression of the antiapoptotic BCL-2 family of proteins (eg, BCL-XL and MCL-1). PATIENTS AND METHODS: We conducted a multicenter, open-label, noncomparative phase II study of obatoclax mesylate, a small-molecule pan-BCL-2 antagonist, in patients with MF. Obatoclax was administered as a 24-hour infusion (on an outpatient basis) every 2 weeks at a fixed dose of 60 mg. RESULTS: A total of 22 patients were enrolled, with a median age of 63 years (range, 43-89 years). Twelve were men, and all 22 patients were previously treated (median of 2 previous therapies). Ten patients (45%) had a Lille score of 1, and 9 patients (41%) had a Lille score of 2. Thirteen (59%) were red blood cell transfusion dependent. A median of 7 cycles of obatoclax were administered. No patient achieved complete or partial response according to International Working Group criteria. One patient (4%) demonstrated a clinical improvement (in terms of hemoglobin and platelet count) after 7 cycles of therapy. The improvement was sustained for 4 cycles of therapy, after which he underwent allogeneic stem cell transplantation. The most common adverse events included low-grade ataxia and fatigue in 50% of the patients. Dose reduction because of toxicity was required in 1 patient, whereas 2 patients were taken off the study because of grade 3 ataxia and grade 3 heart failure. Grade 3/4 anemia and thrombocytopenia were evident in 6 (27%) and 4 (18%) patients, respectively. CONCLUSION: Obatoclax exhibits no significant clinical activity in patients with MF at the dose and schedule evaluated.

Obatoclax Mesylate (GX15-070 Mesylate), a BH3 mimetic, is a pan-BCL-2 family proteins inhibitor with a Ki of 220 nM for BCL-2. Obatoclax Mesylate induces autophagy-dependent cell death and targets cyclin D1 for proteasomal degradation. Obatoclax Mesylate has anti-cancer and broad-spectrum antiparasitic activity.

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