Early work on the function of Bcl-2, an interview with David Vaux

The history of oral decitabine/cedazuridine and its potential role in acute myeloid leukemia

Decitabine, a member of the 5-azanucleosides, has a dose-dependent mechanism of action in vitro: termination of DNA replication at high doses, and inhibition of DNA methyltransferase at low doses. The alteration of DNA methylation patterns by low-dose decitabine is hypothesized to upregulate genes, which promote myeloblast differentiation. In a phase III clinical trial, low-dose decitabine achieved a superior overall response rate (ORR) when compared with 'treatment choice' [consisting of low-dose cytarabine (80%) and supportive care (20%)] as a frontline treatment for elderly patients with acute myeloid leukemia (AML). Despite an improved ORR, the median overall survival (OS) for elderly patients with AML was poor, <1 year. In turn, venetoclax was added to low-dose decitabine, the combination of which significantly improved the ORR and median OS in elderly patients with AML. Currently, hypomethylating agents are being combined with other novel therapies as investigational strategies for elderly and unfit patients with AML. They are also being evaluated as components of maintenance therapy in patients achieving remission. An oral formulation of decitabine has been developed which relies on the concomitant use of oral cedazuridine to protect against first pass metabolism. This oral formulation, which has been approved in myelodysplastic syndrome, is intended to increase convenience of use and therefore compliance in patients. This review characterizes the evolution of decitabine, its oral formulation, and its future in the treatment of AML.

Modulation of Ca2+ signaling by antiapoptotic Bcl-2 versus Bcl-xL: From molecular mechanisms to relevance for cancer cell survival

Members of the Bcl-2-protein family are key controllers of apoptotic cell death. The family is divided into antiapoptotic (including Bcl-2 itself, Bcl-xL, Mcl-1, etc.) and proapoptotic members (Bax, Bak, Bim, Bim, Puma, Noxa, Bad, etc.). These proteins are well known for their canonical role in the mitochondria, where they control mitochondrial outer membrane permeabilization and subsequent apoptosis. However, several proteins are recognized as modulators of intracellular Ca²⁺ signals that originate from the endoplasmic reticulum (ER), the major intracellular Ca²⁺-storage organelle. More than 25 years ago, Bcl-2, the founding member of the family, was reported to control apoptosis through Ca²⁺ signaling. Further work elucidated that Bcl-2 directly targets and inhibits inositol 1,4,5-trisphosphate receptors (IP₃Rs), thereby suppressing proapoptotic Ca²⁺ signaling. In addition to Bcl-2, Bcl-xL was also shown to impact cell survival by sensitizing IP₃R function, thereby promoting prosurvival oscillatory Ca²⁺ release. However, new work challenges this model and demonstrates that Bcl-2 and Bcl-xL can both function as inhibitors of IP₃Rs. This suggests that, depending on the cell context, Bcl-xL could support very distinct Ca²⁺ patterns. This not only raises several questions but also opens new possibilities for the treatment of Bcl-xL-dependent cancers. In this review, we will discuss the similarities and divergences between Bcl-2 and Bcl-xL regarding Ca²⁺ homeostasis and IP₃R modulation from both a molecular and a functional point of view, with particular emphasis on cancer cell death resistance mechanisms.

Regulation of Developmental Cell Death in the Animal Kingdom: A Critical Analysis of Epigenetic versus Genetic Factors

The present paper proposes a new level of regulation of programmed cell death (PCD) in developing systems based on epigenetics. We argue against the traditional view of PCD as an altruistic “cell suicide” activated by specific gene-encoded signals with the function of favoring the development of their neighboring progenitors to properly form embryonic organs. In contrast, we propose that signals and local tissue interactions responsible for growth and differentiation of the embryonic tissues generate domains where cells retain an epigenetic profile sensitive to DNA damage that results in its subsequent elimination in a fashion reminiscent of what happens with scaffolding at the end of the construction of a building. Canonical death genes, including Bcl-2 family members, caspases, and lysosomal proteases, would reflect the downstream molecular machinery that executes the dying process rather than being master cell death regulatory signals.

c-Myc induction of programmed cell death may contribute to carcinogenesis: a perspective inspired by several concepts of chemical carcinogenesis

The c-Myc protein, encoded by c-myc gene, in its wild-type form can induce tumors with a high frequency and can induce massive programmed cell death (PCD) in most transgenic mouse models, with greater efficiency than other oncogenes. Evidence also indicates that c-Myc can cause proliferative inhibition, i.e. mitoinhibition. The c-Myc-induced PCD and mitoinhibition, which may be attributable to its inhibition of cyclin D1 and induction of p53, may impose a pressure of compensatory proliferation, i.e. regeneration, onto the initiated cells (cancer progenitor cells) that occur sporadically and are resistant to the mitoinhibition. The initiated cells can thus proliferate robustly and progress to a malignancy. This hypothetical thinking, i.e. the concurrent PCD and mitoinhibition induced by c-Myc can promote carcinogenesis, predicts that an optimal balance is achieved between cell death and ensuing regeneration during oncogenic transformation by c-Myc, which can better promote carcinogenesis. In this perspective, we summarize accumulating evidence and challenge the current model that oncoprotein induces carcinogenesis by promoting cellular proliferation and/or inhibiting PCD. Inspired by c-myc oncogene, we surmise that many tumor-suppressive or growth-inhibitory genes may also be able to promote carcinogenesis in a similar way, i.e. by inducing PCD and/or mitoinhibition of normal cells to create a need for compensatory proliferation that drives a robust replication of initiating cells.

Reviewing once more the c-myc and Ras collaboration: converging at the cyclin D1-CDK4 complex and challenging basic concepts of cancer biology

The c-myc is a proto-oncogene that manifests aberrant expression at high frequencies in most types of human cancer. C-myc gene amplifications are often observed in various cancers as well. Ample studies have also proved that c-myc has a potent oncogenicity, which can be further enhanced by collaborations with other oncogenes such as Bcl-2 and activated Ras. Studies on the collaborations of c-myc with Ras or other genes in oncogenicity have established several basic concepts and have disclosed their underlying mechanisms of tumor biology, including "immortalization" and "transformation". In many cases, these collaborations may converge at the cyclin D1-CDK4 complex. In the meantime, however, many results from studies on the c-myc, Ras and cyclin D1-CDK4 also challenge these basic concepts of tumor biology and suggest to us that the immortalized status of cells should be emphasized. Stricter criteria and definitions for a malignantly transformed status and a benign status of cells in culture also need to be established to facilitate our study of the mechanisms for tumor formation and to better link up in vitro data with animal results and eventually with human cancer pathology.

Apoptosis and cancer: the genesis of a research field

In multicellular organisms, the total number of cells is a balance between the cell-generating effects of mitosis and cell death that is induced through apoptosis. A disruption of this delicate balance can lead to the development of cancer. This Timeline article focuses on how the field of apoptosis biology has developed in the context of its contribution to our understanding of cell death, or lack of it, in the development of malignant disease. It traces the course of research from key discoveries in fundamental biology to potential therapeutic applications.

Inhibitory effect of extract of fungi of Huaier on hepatocellular carcinoma cells

This study investigated the inhibitory effect of the extract of fungi of Huaier (EFH) on the growth of hepatocellular carcinoma (HCC) cells. Hep-G2 cells, a human HCC cell line, were cultured in DMEM containing 10% fetal bovine serum and treated with EFH of different concentrations (1, 2, 4, 8 mg/mL) for 24, 48 and 72 h respectively. The apoptosis rate of the cells was flow cytometrically measured. Thirty-six tumor-bearing New Zealand rabbits were randomly divided into 3 groups: group A (control group), in which the rabbits were infused with 0.2 mL/kg normal saline via the hepatic artery; group B (transhepatic artery chemoembolization [TACE] group), in which the rabbits were given lipiodol at 0.2 mL/kg plus MMC at 0.5 mg/kg via the hepatic artery; group C (TACE+EFH group), in which EFH (500 mg/kg) were orally administered after TACE. Two weeks after TACE, the rabbits were sacrificed and the implanted tumors were sampled. The tumor volume and the necrosis rate were determined. The tumor tissues were immunohistochemically detected for the expressions of factor VIII, VEGF, P53, Bax and Bcl-2. The microvessel density (MVD) was calculated by counting the factor VIII-positive endothelial cells. Our results showed that after treatment with EFH, the apoptosis rate of Hep-G2 cells was enhanced in a concentration- and time-dependent manner. Two weeks after the treatment, the average tumor volume, the necrosis rate and the growth rate of the implanted tumor in group C were significantly different from those in groups A and B (P<0.05). MVD and VEGF expressions were significantly decreased in the group C when compared with those in groups B (P<0.05 for all). The Bax expression was weakest in group A and strongest in group C. The expressions of P53 and Bcl-2 were minimal in group C and maximal in group A. There were significant differences in the expressions of P53, Bax and Bcl-2 among the 3 groups (P<0.05 for all) and there was significant difference between group B and group C (P<0.05). It was concluded that EFH could suppress not only the growth of HCC cells but also tumor angiogenesis and it can induce the apoptosis of HCC cells. EFH serves as an alternative for the treatment of HCC.

Raised differentiation and apoptosis of Walker-256 hepatocarcinoma cells treated with all trans-retinoitc acid

AIM: To observe differentiation and apoptosis of Walker-256 hepatocarcinoma cells induced by all trans-retinoitc acid (ATRA), and to explore its possible mechanism.

METHODS: Walker-256 hepatocarcinoma cell lines were treated with ATRA at various concentrations (100, 10, 5 and 1 μmol/L, respectively). Forty-eight hours later, morphological changes were measured using inverted microscopy; The proliferation effect of Walker-256 cell lines treated with ATRA was determined using MTT assay; cellular distribution of DNA content and the apoptotic incidence of cells treated with ATRA was measured using flow cytometry (FCM); the changes of Fas and bcl-2 mRNA expression were determined using RT-PCR, and Caspase 3 and Caspase 8 protein expressions were determined using Western blot.

RESULTS: With the increasing concentration of ATRA, Walker-256 cells showed morphological changes in cell differentiation and apoptosis. ATRA inhibited cell proliferation of Walker-256, with the maximum inhibitory effects at concentrations of 5 and 10 μmol/L. Proliferation rates at 24, 48 and 72 h at concentrations of 5 and 10 μmol/L were 21.86%, 57.39%, 68.17%, and 27.23%, 80.09%, 92.15%, respectively, showing a concentration- and time-dependent relationship. There was significance in apoptosis incidence among 5, 10 μmol/L groups and the control group(t = 9.61, t = 11.38, all P <0.05); For Walker-256 cells treated with ATRA, the Fas expression mRNA was significantly up-regulated and the bcl-2 mRNA was significantly down-regulated at the concentration of 10 μmol/L ATRA, compared with the control group (t = 12.33, t = 10.78, P < 0.05). After treatment with 10 μmol/L ATRA for 48 h, the Caspase 3 and Caspase 8 zymogen were significantly activated, compared with the control group (t = 9.76, t = 10.21, P < 0.05).

CONCLUSION: ATRA induces Walker-256 hepatocarcinoma cell differentiation and apoptosis.