BCL-2-Selective BH3 Mimetic ABT-199 Is a Potent Agent For Acute Myeloid Leukemia

• Published in: Blood 2013-11, Vol.122 (21), p.1456-1456
• Main Authors: Pan, Rongqing, Debose, LaKeisha, Benito, Juliana M, Golfman, Leonard S, Zweidler-McKay, Patrick A, Han, Lina, Harutyunyan, Karine G., Mu, Hong, Ruvolo, Vivian R, Park, Eugene, Muschen, Markus, Leverson, Joel, Borthakur, Gautam, Kantarjian, Hagop M, Ruvolo, Peter P., Andreeff, Michael, Konopleva, Marina
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V122.21.1456.1456

Evasion of apoptosis is a key hallmark of cancer. BCL-2 family proteins, the central regulators of apoptosis, are often aberrantly expressed in tumors. Pro-apoptotic BCL-2 members bind and sequester anti-apoptotic BCL-2 proteins via their BH3 domains. Thus, BH3 mimetics represent a promising direction in cancer drug development. ABT-263, designed as a BH3 mimetic to inhibit BCL-2, BCL-XL, and BCL-W, has demonstrated efficacy in preclinical and clinical studies. However, thrombocytopenia is common in patients treated with ABT-263 due to the inhibition of BCL-XL, which is indispensable for platelet survival. ABT-199 (GDC-0199), a second-generation BH3 mimetic, has higher affinities for BCL-2 protein (Ki < 0.01 nM), which enhances the specificity of this agent to kill cancer cells without provoking unwanted thrombocytopenia (Souers, et al, Nature Med, 2013). Since BCL-2 is often overexpressed in hematological malignancies including acute myeloid leukemia (AML), we evaluated the anti-cancer effects of ABT-199 on AML cells. As a measure of BCL-2 specificity, BCL-XL overexpression in sensitive HL-60 cells resulted in complete resistance to ABT-199, while BCL-2 overexpression in these cells conferred moderate resistance to apoptosis induction. Moreover, OCI-AML3 cells with high MCL-1 levels were highly resistant to ABT-199, while knockdown of this protein greatly sensitized cells to this BH3 mimetic. Among 12 genetically diverse AML cell lines tested, seven were sensitive to ABT-199-induced apoptosis with 48-h EC50 ranging from 1.5 nM to 145 nM. In these seven sensitive, BCL-2 dependent cell lines, ABT-199 was uniformly more potent than ABT-737 (another BCL-2 inhibitor with a spectrum similar to ABT-263, p = 0.016). Next, we tested ABT-199 in 15 primary samples from relapsed/refractory AML patients. Twelve patient samples showed high sensitivity to apoptosis induction following 48-h exposure to ABT-199 (EC50 < 10 nM). In a larger set of 23 cryopreserved AML patient samples, including AML cells with diploid cytogenetics and mutations in FLT3, NRAS, and NPM1 genes, 18 (78%) were sensitive to ABT-199 (100 nM). However, samples from patients with complex cytogenetics, t(8;21) and JAK2 mutation (n = 12) were largely insensitive to ABT-199 (17% response rate). Interestingly, in five of six primary AML samples with high blast counts, ABT-199 induced marked apoptosis in CD34+/CD38- AML stem/progenitor cells compared to bulk AML blasts (p = 0.01). Quantitative Western blo