Apoptotic effects of different drugs on cultured retinoblastoma Y79 cells

Camptothecin induces apoptosis of human retinoblastoma cells via activation of FOXO1

PURPOSE

The purpose of this study was to investigate the pro-apoptotic effect of camptothecin (CPT) on Y79 retinoblastoma cells and the role of Forkhead box, class O (FOXO1) in CPT-induced apoptosis.

METHODS

CPT-induced apoptosis was determined by flow cytometry with annexin V-FITC positive cells and Western blot of PARP expression, respectively. The expressions of FOXO1 were detected by Western blot. The transcriptional activity of FOXO1 was determined by luciferase reporter assay. siRNAs specifically inhibiting FOXO1 were used, and flow cytometry and Western blot were executed to test the role of FOXO1 in CPT-induced apoptosis.

RESULTS

CPT was extremely effective in inducing apoptosis of Y79 retinoblastoma cells. FOXO1 was highly expressed in Y79 cells. CPT not only elevated the FOXO1 dephosphorylation level but also promoted its transcriptional activity, suggesting that the activation of FOXO1 was, at least in part, triggered by CPT. The decreased annexin V positive cells and less PARP cleavage demonstrated that siRNAs-mediated inhibition of FOXO1 significantly abrogated CPT-induced apoptosis, indicating that FOXO1 plays an important role in CPT-induced apoptosis. Moreover, the expression of Bim was also elevated with the treatment of CPT, which is in accordance with the activation of FOXO1.

CONCLUSIONS

Our study provides the evidence that a high level of endogenous FOXO1 expression in retinoblastoma cells contributes, at least in part, to CPT-induced apoptosis, which may help broad application of CPT in retinoblastoma therapy in the future.

Fenretinide: A p53-independent way to kill cancer cells

The synthetic retinoid fenretinide [N-(4 hydroxyphenyl)retinamide] induces apoptosis of cancer cells and acts synergistically with chemotherapeutic drugs, thus providing opportunities for novel approaches to cancer therapy. The upstream signaling events induced by fenretinide include an increase in intracellular levels of ceramide, which is subsequently metabolized to GD3. This ganglioside triggers the activation of 12-Lox (12-lipoxygenase) leading to oxidative stress and apoptosis via the induction of the transcription factor Gadd153 and the Bcl-2-family member protein Bak. Increased evidence suggests that the apoptotic pathway activated by fenretinide is p53-independent and this may represent a novel way to treat tumors resistant to DNA-damaging chemotherapeutic agents. Therefore, fenretinide offers increased clinical benefit as a novel agent for cancer therapy, able to complement the action of existing chemotherapeutic treatment regimes. Furthermore, synergy between fenretinide and chemotherapeutic drugs may facilitate the use of chemotherapeutic drugs at lower concentrations, with possible reduction in treatment-associated morbidity.

Butyric acid sensitizes Vero cells to ricin-induced apoptosis via accelerated activation of multiple signal transduction pathways

We found that the treatment with 1 mM butyric acid for 2 days renders Vero cells highly sensitive to ricin-induced apoptosis reflected by cytolysis concomitant with apoptotic cellular and nuclear morphological changes, DNA fragmentation, and increase in caspase-3 like activity, whereas butyric acid alone had no cytotoxic effect on Vero cells. During the treatment with butyric acid, gradual increase in alkaline phosphatase activity, an indicator for butyric acid-induced differentiation, was observed in Vero cells. Although the potency of ricin-mediated protein synthesis was increased in butyric acid-treated Vero cells as compared to untreated cells, the binding and internalization of ricin to the cells were not much affected. Furthermore, DNA fragmentation caused by other protein synthesis inhibitors such as diphtheria toxin and anisomysin were also highly potentiated in butyric acid-treated Vero cells, whereas the potencies of these toxins to inhibit the protein synthesis were not affected by butyric acid treatment. These results suggest that the apoptosis signaling pathway, which may be triggered by cytotoxic stress response caused by toxins, is sensitized in butyric acid-treated cells, while the pathways leading to the protein synthesis inhibition by these toxins are relatively unchanged. No significant differences in the expression levels of p21, p53, and Bcl-2 proteins were observed between butyric acid-treated and untreated Vero cells. The treatment with ricin resulted in the activation of p38 MAP kinase, and this activation occurred on an accelerated time schedule in butyric acid-treated Vero cells than in untreated cells. The specific inhibitor of p38 MAP kinase SB203580 showed a partial inhibitory effect on ricin-induced apoptosis in control Vero cells, but it was less effective in butyric acid-treated Vero cells. Taken together, our results suggest that butyric acid-treatment may result in sensitization of multiple intracellular signal transduction pathways including apoptotic signaling pathways and p38 MAP kinase pathway.

Synergistic induction of apoptosis of neuroblastoma by fenretinide or CD437 in combination with chemotherapeutic drugs

Retinoic acid therapy improves the survival of children with neuroblastoma and 13-cis retinoic acid now forms an important component of treatment for residual disease of stage IV neuroblastoma after chemotherapy. However, although 13-cis retinoic acid induces differentiation, other retinoids are effective at inducing apoptosis of neuroblastoma in vitro, including the novel compounds fenretinide and CD437 and these may be alternative retinoids for neuroblastoma therapy. The aim of our study was to evaluate the ability of fenretinide, CD437 (6-¿3-(1-adamantyl)-4-hydroxyphenyl¿ -2-naphthalene carboxylic acid) and different retinoic acid isomers to induce apoptosis of neuroblastoma in conjunction with the chemotherapeutic drugs, cisplatin, etoposide and carboplatin. Neuroblastoma cell lines were treated with retinoids prior to treatment with chemotherapeutic agents and flow cytometry used to measure apoptosis and free radical generation. Pre-treatment of neuroblastoma cell lines with fenretinide or CD437 prior to treatment with cisplatin, etoposide or carboplatin synergistically increased apoptosis, an effect not seen with 13-cis, all-trans or 9-cis retinoic acid. Contrary to retinoic acid isomers or chemotherapeutic drugs, apoptosis of neuroblastoma cells induced by fenretinide or CD437 was accompanied by the generation of intracellular free radicals. Quenching of fenretinide- or CD437-induced free radicals with antioxidants abolished the synergistic response seen with the subsequent addition of chemotherapeutic agents. Therefore, the generation of free radicals by fenretinide or CD437 may be the key property of these retinoids leading to synergistic responses with chemotherapeutic drugs. Clearly, these synthetic retinoids provide new opportunities for novel neuroblastoma therapy.

Distinct properties of fenretinide and CD437 lead to synergistic responses with chemotherapeutic reagents

The RARbeta/gamma-selective retinoids fenretinide and CD437 induce caspase-dependent apoptosis but generate free radicals independently of caspases. Apoptosis, but not free radical generation, induced by these retinoids is inhibited by RARbeta/gamma-specific antagonists. Both fenretinide and CD437 induce apoptosis synergistically with cisplatin, carboplatin, or etoposide. However, antioxidants inhibit this synergy to the level obtained with chemotherapeutic drugs alone, and this implies that free radical generation is important in the synergistic response. Since apoptosis induced by fenretinide or CD437 is mediated by apoptotic pathways involving RARs and/or mitochondria and differs from mechanisms of chemotherapy-induced apoptosis this may explain the strong synergistic response seen between these synthetic retinoids and chemotherapeutic drugs. These results suggest that fenretinide or CD437 may be useful adjuncts to neuroblastoma therapy.

Protective effect of suramin against cell death in rat cerebellar granular neurons and mouse neuroblastoma cells

In this report, we examined the effect of suramin on the cell death induced by glutamate in cerebellar granule neurons or by staurosporine in NB-2a neuroblastoma cells. Excitotoxicity induced by glutamate was associated with an extensive chromatin condensation, nuclear fragmentation and disintegration of nuclear DNA into the high molecular weight (HMW)-DNA fragments of about 50-100 kb without formation of an oligonucleosomal DNA ladder or caspase activation. Staurosporine-induced cytotoxicity was accompanied by the activation of caspase 3-like protease(s) and disintegration of nuclear DNA into the HMW- and oligonucleosomal DNA fragments. Suramin (100 microM) effectively protected both cultured cerebellar neurons and NB-2a cells against cell death, which appeared as the inhibition of caspase 3-like activity in NB-2a cells, abrogation of both HMW- and internucleosomal DNA fragmentation and maintaining the nuclear morphology indistinguishable of the control cells. Eventually, suramin lead to the marked increase in the cell viability of both cerebellar neurons and NB-2a neuroblastoma cells challenged with glutamate and staurosporine, respectively. We suggest that the novel, neuroprotective activity of suramin may have a therapeutic value in several neuropathological paradigms.