cytochrome-c-t and apogossypolone

We examined the effect of apogossypolone (ApoG2), a new derivative from gossypol on cell cycle regulation in U937 human leukemic monocyte lymphoma cells in vitro. ApoG2 decreased the viability of U937 cells by inducing G1 arrest followed by apoptosis in a dose-dependent manner. The G0/G1 phase of the cell cycle is regulated by cyclin-dependent kinases (Cdk), cyclins and cyclin-dependent kinase inhibitors (Cdki). We show by western blot analysis, that the ApoG2-induced G1 arrest was mediated through the increased expression of Cdki proteins (p21cip1/waf1) with a simultaneous decrease in cdk2, cdk4, cyclin D1 and cyclin E expression. The induction of apoptosis after treatment with ApoG2 for 12, 24 and 48 h was demonstrated by flow cytometry analysis. ApoG2 also induced cytochrome c release and activation of caspase-3. To our knowledge, this is the first time that ApoG2 has been reported to potently inhibit the proliferation of human monocytic lymphoma U937 cells through G1 arrest. These findings suggest that ApoG2 may be a potential chemotherapeutic agent for the treatment of cancer.

Topics: Antineoplastic Agents; Apoptosis; Caspase 3; Cell Cycle; Cell Proliferation; Cell Survival; Cyclin D1; Cyclin E; Cyclin-Dependent Kinase 2; Cyclin-Dependent Kinase 4; Cyclin-Dependent Kinase Inhibitor p21; Cytochromes c; Dose-Response Relationship, Drug; Gossypol; Humans; Lymphoma; Mitochondria; Proto-Oncogene Proteins c-myc; Time Factors; U937 Cells

Lymphoma is one of the most common types of hematological malignancies and proteins from the Bcl-2 family are highly expressed in human lymphomas. Apogossypolone (ApoG2), the most potent gossypol derivative, has been classified as a novel small-molecule inhibitor of antiapoptotic Bcl-2 family proteins. Here, we assessed the in-vitro cytotoxicity of ApoG2 on human U937 lymphoma cells, and explored the underlying intracellular molecular mechanisms of ApoG2. Using the WST-8 assay, we found that ApoG2 inhibited growth of U937 cells in a dose-dependent and time-dependent manner, and the IC50 values were 30.08, 14.81, and 9.26 mumol/l for 24, 48, and 72 h treatments, respectively. ApoG2 also induced apoptosis in U937 cells, as noted through changes in morphological characteristics, including cellular internucleosomal DNA fragmentation and the appearance of a sub-G1 apoptotic peak. Treatment with ApoG2 downregulated Bcl-xL and Mcl-1 protein expression and blocked the binding of Bcl-2 with Bax protein. Furthermore, ApoG2 led to an abundant release of cytochrome c from mitochondria and a five-fold increase in the activity of caspase-3 and caspase-9. Taken together, our results suggest that ApoG2 could effectively suppress the growth of human lymphoma cell line U937 through the inhibition of the antiapoptotic Bcl-2 family proteins and the induction of mitochondria-dependent apoptotic cell death.

Topics: Antineoplastic Agents; Apoptosis; bcl-2-Associated X Protein; bcl-X Protein; Caspase 3; Caspase 9; Cytochromes c; DNA Fragmentation; Gossypol; Humans; Mitochondria; Myeloid Cell Leukemia Sequence 1 Protein; Proto-Oncogene Proteins c-bcl-2; U937 Cells