R-Roscovitine simultaneously targets both the p53 and NF-κB pathways and causes potentiation of apoptosis: implications in cancer therapy

NFkappaB signaling in carcinogenesis and as a potential molecular target for cancer therapy

It has become increasingly clear that deregulation of the NFkappaB signaling cascade is a common underlying feature of many human ailments including cancers. The past two decades of intensive research on NFkappaB has identified the basic mechanisms that govern the functioning of this pathway but uncovering the details of why this pathway works differently in different cellular contexts or how it interacts with other signaling pathways remains a challenge. A thorough understanding of these processes is needed to design better and more efficient therapeutic approaches to treat complex diseases like cancer. In this review, we summarize the literature documenting the involvement of NFkappaB in cancer, and then focus on the approaches that are being undertaken to develop NFkappaB inhibitors towards treatment of human cancers.

Transcription inhibition of heat shock proteins: a strategy for combination of 17-allylamino-17-demethoxygeldanamycin and actinomycin d

The heat shock protein (HSP) 90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) is currently in clinical trials because of its unique mechanism of action and antitumor activity. However, 17-AAG triggers the transcription and elevation of antiapoptotic HSP90, HSP70, and HSP27, which lead to chemoresistance in tumor cells. We hypothesized that inhibiting HSP90, HSP70, and HSP27 transcription may enhance 17-AAG-induced cell death in multiple myeloma cell lines. Actinomycin D (Act D), a clinically used agent and transcription inhibitor, was combined with 17-AAG. The concentrations for 17-AAG and Act D were selected based on the target actions and plasma levels during therapy. Inducible and constitutive HSP27, HSP70, and HSP90 mRNA and protein levels were measured by real-time reverse transcription-PCR and immunoblot assays. Compared with no treatment, Act D alone decreased HSP mRNA levels in MM.1S and RPMI-8226 cell lines. Combining Act D with 17-AAG did not attenuate 17-AAG-mediated increases in transcript levels of inducible HSP70; however, constitutive HSP mRNA levels were decreased. In contrast to its effect on mRNA levels, Act D was able to abrogate 17-AAG-mediated increases in all HSP protein levels. The cytotoxicity of combined Act D and 17-AAG was assessed. Treatment with Act D alone caused <40% cell death, whereas the combination of 17-AAG and Act D resulted in an increase of cell death in both multiple myeloma cell lines. In conclusion, these results indicate that 17-AAG-mediated induction of HSP70 and HSP27 expression can be attenuated by Act D and therefore can potentially improve the clinical treatment of multiple myeloma.

Inhibition of cyclin-dependent kinases by olomoucine and roscovitine reduces lipopolysaccharide-induced inflammatory responses via down-regulation of nuclear factor kappaB

OBJECTIVES

Initiation and maintenance of pro-inflammatory reactions elicited by bacterial lipopolysaccharide and/or cytokines in the macrophage lineage have been reported to play a crucial role in acute and chronic pathogenic effects. Whether pro-inflammatory responses triggered by lipopolysaccharide in growth arrested cells differ from those in proliferating cells remains unanswered.

MATERIALS AND METHODS

Olomoucine and roscovitine are cyclin-dependent kinase (CDK) inhibitors that prevent progression through the cell cycle. After treatment with CDK inhibitors, expression of pro-inflammatory genes was analysed by reverse transcriptase-polymerase chain reaction. Protein levels of inducible nitric oxide synthase (iNOS) and nuclear factor kappaB (NF-kappaB) were determined by Western blotting. Promoter activity of iNOS was measured by the luciferase activity assay.

RESULTS

In this study we have demonstrated that both olomoucine and roscovitine inhibit cell proliferation and diminish nitric oxide production and cytokine gene expression, in lipopolysaccharide-stimulated murine RAW264.7 macrophages. In addition, olomoucine reduces iNOS promoter activity and alleviates NF-kappaB transcription activation. After co-transfection with E2F1 interference RNA, suppression of lipopolysaccharide-mediated iNOS promoter activity and NF-kappaB activation was observed. Furthermore, we demonstrated that olomoucine-induced growth arrested cells reduce expression of the p65 subunit of NF-kappaB.

CONCLUSIONS

The findings of this study suggest that inhibition of cell-cycle progression is capable of reducing pro-inflammatory responses via down-regulation of NF-kappaB.

Double-edged swords as cancer therapeutics: simultaneously targeting p53 and NF-kappaB pathways

The p53 and nuclear factor-kappaB (NF-kappaB) pathways play crucial roles in human cancer, in which inactivation of p53 and hyperactivation of NF-kappaB is a common occurrence. Activation of p53 and inhibition of NF-kappaB promotes apoptosis. Although drugs are being designed to selectively activate p53 or inhibit NF-kappaB, there is no concerted effort yet to deliberately make drugs that can simultaneously do both. Recent results suggest that a surprising selection of small molecules have this desirable dual activity. In this Review we describe the principles behind such dual activities, describe the current candidate molecules and suggest mechanisms and approaches to their further development.

Enhancement of radiosensitivity by roscovitine pretreatment in human non-small cell lung cancer A549 cells

Roscovitine has been reported to have anti-proliferative properties and is in process of undergoing clinical trials. In addition to its intrinsic anticancer properties, it has recently been suggested that roscovitine may also enhance the activity of traditional chemo- and radio- therapies in certain cancer cell lines. The purpose of this study was to define the activity of roscovitine in increasing radiosensitivity of human non-small cell lung cancer (NSCLC) cell line A549 cells in vitro. A549 cells were exposed to ionizing radiation (IR) of gamma-ray with or without roscovitine pretreatment. Clonogenic assay was performed and cell cycle and apoptosis were analyzed by flow cytometry. Expression of PARP, Ku70 and Ku80 proteins was detected by Western blot. The active form of caspase-3 positive cells were measured by flow cytometry. Our results showed that roscovitine caused dose-dependent apoptosis in A549 cells. Pretreatment with minimally toxic concentration of roscovitine significantly radiosensitized A549 cells by inhibiting colony formation. We then examined potential mechanisms that may contribute to the enhanced radiation response induced by roscovitine. Our results showed that the combination treatment significantly induced apoptosis in A549 cells compared to roscovitine or IR treatment alone. Meanwhile, in the co-treatment group, the percentage of cells with the active form of caspase-3 was markedly increased, while roscovitine or IR alone had little effect. Roscovitine decreased S phase cells when used alone or in sequential combination with IR. Furthermore, this combination treatment blocked DNA repair process after IR, indicated by down regulation of Ku70 and Ku80 proteins, while the singly used treatment did not. Taken together, these results suggest that roscovitine has the potential to act as a radio-sensitizer in A549 cells by promoting caspase-3 activity and increasing apoptosis, affecting cell cycle distribution and impairing DNA repair process.

Transcriptional inhibitors, p53 and apoptoss

Transcriptional inhibitors (TI) repress global transcription and induce apoptosis. It has been suggested that induction of p53 is one of the hallmarks of global transcriptional repression. Two recent papers suggested that treatment of human cancer cells with TIs, leads to p53-dependent, transcription-independent or p53-dependent, transcription-dependent apoptosis. The latter mechanism is linked to the fact that TIs can be selective in their inhibitory effects thereby permitting transcription of some genes. However, the majority of other published data suggest that these drugs induce p53-independent apoptosis. In this article I discuss the mechanisms of TI-dependent cell death and the potential role of p53 in this process.