Yun Hee Kang

Publications (2)23.97 Total impact

• Article: Mechanism of synergy of N-(4-hydroxyphenyl)retinamide and ABT-737 in acute lymphoblastic leukemia cell lines: Mcl-1 inactivation.

  Min H Kang, Zesheng Wan, Yun Hee Kang, Richard Sposto, C Patrick Reynolds
  [show abstract] [hide abstract]
  ABSTRACT: ABT-737 is a pan-Bcl-2 inhibitor that has a wide range of single-agent activity against acute lymphoblastic leukemia (ALL) cell lines and xenografts. A relationship between expression of myeloid cell leukemia 1 (Mcl-1), an antiapoptotic member of the Bcl-2 family of proteins, and resistance to ABT-737 has been reported for various cancers. The synthetic cytotoxic retinoid N-(4-hydroxyphenyl)retinamide (4-HPR) is known to generate reactive oxygen species (ROS), and ROS have been shown to activate c-Jun kinase (JNK), which in turn phosphorylates and inhibits Mcl-1. Thus, we investigated whether 4-HPR-mediated inactivation of Mcl-1 could act synergistically with ABT-737 to promote leukemia cell death. Cytotoxicity was determined using the fluorescence-based DIMSCAN assay. Synergy was defined as a combination index (CIN) less than 1. The expression of Bcl-2 family messenger RNAs was measured by real-time reverse transcription-polymerase chain reaction, and caspase activity was measured enzymatically. Changes in Bcl-2 family proteins and release of mitochondrial cytochrome c were detected by immunoblotting. ROS, apoptosis, mitochondrial membrane depolarization, and phospho-JNK were measured by flow cytometry. Gene silencing was by small interfering RNA (siRNA). All statistical tests were two-sided. ABT-737 decreased Mcl-1 protein expression in ABT-737-sensitive ALL cell lines but not in ABT-737-resistant lines. Using the antioxidant ascorbic acid and siRNA-mediated knockdown of JNK, we showed that 4-HPR decreased Mcl-1 via ROS generation (that phosphorylates JNK) in ABT-737-resistant cell lines. Combining ABT-737 with 4-HPR enhanced the mitochondrial apoptotic cascade (percentage of cells with depolarized mitochondrial membrane at 6 hours, ABT-737 vs ABT-737 plus 4-HPR: 24.5% vs 45.5%, difference = 20.1%, 95% CI = 18.9% to 13.9%; P < .001) and caused caspase-dependent, synergistic multilog cytotoxicity in all seven ALL cell lines examined (mean CIN = 0.57, 95% CI = 0.37 to 0.87), with minimal cytotoxicity for normal lymphocytes. An increase of Mcl-1 protein in response to ABT-737 is one mechanism of ABT-737 resistance that can be overcome by 4-HPR, resulting in synergistic cytotoxicity of ABT-737 combined with 4-HPR in ALL cell lines.
  CancerSpectrum Knowledge Environment 04/2008; 100(8):580-95. · 14.07 Impact Factor
• Article: Activity of vincristine, L-ASP, and dexamethasone against acute lymphoblastic leukemia is enhanced by the BH3-mimetic ABT-737 in vitro and in vivo.

  Min H Kang, Yun Hee Kang, Barbara Szymanska, Urszula Wilczynska-Kalak, Michael A Sheard, Theresa M Harned, Richard B Lock, C Patrick Reynolds
  [show abstract] [hide abstract]
  ABSTRACT: Defects in apoptosis signaling contribute to poor outcome in pediatric acute lymphoblastic leukemia (ALL), and overexpression of antiapoptotic Bcl-2 (Bcl-2 and Bcl-X(L)) family proteins has been observed in ALL. ABT-737 is a small-molecule BH3-mimetic that inhibits the antiapoptotic Bcl-2 family proteins. We evaluated the cytotoxicity of ABT-737 in combination with vincristine, dexamethasone, and L-asparaginase (VXL) in 7 ALL cell lines. Multilog synergistic cytotoxicity was observed in all 7 cell lines with ABT-737 plus L-asparaginase or vincristine, and in 5 of 7 cell lines with ABT-737 plus dexamethasone or VXL. In leukemia cells, but not in normal lymphocytes, ABT-737 plus L-asparaginase induced greater mitochondrial depolarization (JC-1 staining); mitochondrial cytochrome c release; activation of Bax, Bid, and caspases (immunoblotting); and eventually apoptosis (annexin V staining) than did either drug alone. In mouse xenografts derived from patients with ALL at diagnosis (ALL-7) or at relapse (ALL-19), event-free survival (EFS) was significantly enhanced with ABT-737 plus VXL relative to VXL or ABT-737 alone (P </= .02). Thus, ABT-737 synergistically enhanced VXL cytotoxicity in ALL cell lines via a mitochondrial death pathway and enhanced EFS in VXL-treated mice bearing ALL xenografts. Combining VXL with a BH3-mimetic warrants clinical investigation in ALL at relapse and potentially in chemotherapy-resistant ALL subgroups.
  Blood 09/2007; 110(6):2057-66. · 9.90 Impact Factor