Upregulation of Bfl-1/A1 in leukemia cells undergoing differentiation by all-trans retinoic acid treatment attenuates chemotherapeutic agent-induced apoptosis

Synergistic Antiproliferative Effects of All-Trans Retinoic Acid and Paclitaxel on Autosomal Dominant Polycystic Kidney Disease Epithelial Cells

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder characterized by uncontrollable epithelial cell growth, cyst formation, and kidney malfunction. In the present study, we investigated the antiproliferative effects of the treatment with the combination of paclitaxel (PAC) and all-trans retinoic acid (ATRA) on ADPKD epithelial cells. Our results show that the combined treatment with 1 nM PAC and 10 nM ATRA significantly suppressed ADPKD cell proliferation (20%), while the treatment with ATRA or PAC alone had no such effect. Treatment with PAC and ATRA induced cell cycle arrest at the G2/M phase and apoptosis by upregulating p53 and caspase-8 expression and increased the intracellular calcium (Ca²⁺) level possibly by enhancing Ca²⁺ uptake via plasma membrane channels. In addition, this treatment suppressed extracellular signal-regulated kinase signaling possibly through mitogen-activated protein kinase phosphatase-1 activation. Thus, the combination of PAC and ATRA can be explored as a potential treatment regimen for ADPKD.

The Stress-Inducible BCL2A1 Is Required for Ovarian Cancer Metastatic Progression in the Peritoneal Microenvironment

Emerging evidence indicates that hypoxia plays a critical role in governing the transcoelomic metastasis of ovarian cancer. Hence, targeting hypoxia may be a promising approach to prevent the metastasis of ovarian cancer. Here, we report that BCL2A1, a BCL2 family member, acts as a hypoxia-inducible gene for promoting tumor progression in ovarian cancer peritoneal metastases. We demonstrated that BCL2A1 was induced not only by hypoxia but also other physiological stresses through NF-κB signaling and then was gradually reduced by the ubiquitin-proteasome pathway in ascites-derived ovarian cancer cells. The upregulated BCL2A1 was frequently found in advanced metastatic ovarian cancer cells, suggesting its clinical relevance in ovarian cancer metastatic progression. Functionally, BCL2A1 enhanced the foci formation ability of ovarian cancer cells in a stress-conditioned medium, colony formation in an ex vivo omental tumor model, and tumor dissemination in vivo. Under stress conditions, BCL2A1 accumulated and colocalized with mitochondria to suppress intrinsic cell apoptosis by interacting with the BH3-only subfamily BCL2 members HRK/BAD/BID in ovarian cancer cells. These findings indicate that BCL2A1 is an early response factor that maintains the survival of ovarian cancer cells in the harsh tumor microenvironment.

Polymeric micelles of a copolymer composed of all-trans retinoic acid, methoxy-poly(ethylene glycol), and b-poly(N-(2 hydroxypropyl) methacrylamide) as a doxorubicin-delivery platform and for combination chemotherapy in breast cancer

Delivery of combination chemotherapeutic agents to the tumor via nanovesicles has the potential for superior tumor suppression and reduced toxicity. Herein, we prepare a block copolymer (mPH-RA) composed of methoxy-poly(ethylene glycol) (mPEG), b-poly(N-(2 hydroxypropyl) methacrylamide) (pHPMA), and all-trans retinoic acid (ATRA) by conjugating ATRA to the pre-formed copolymer, mPEG-b-pHPMA(mP-b-pH). Doxorubicin-loaded micelles, Dox@mP-b-pH, and Dox@mPH-RA were characterized by determining particle size, zeta potential, % DL, EE, Dox release, hemolysis study, and by DSC. The Dox@mPH-RA micelles (mPH-RA: Dox ratios of 10:0.5-2) displayed nano-size (36-45 nm), EE. 26-74%, and DL. 2.9-5.6%. Dox@mPH-RA micelles displayed the highest penetrability and cytotoxicity than free Dox and Dox@mP-b-pH micelles in breast cancer cell lines. Dox@mPH-RA exhibited the highest induction of apoptosis (94.1 ± 3%) than Dox (52.1 ± 4.5%), and Dox@mP-b-pH (81.7 ± 3%), and arrested cells in the highest population in G2 and S phase. Dox@mPH-RA increased the t_1/2 and C_max of Dox and demonstrated improved therapeutic efficacy and highest Dox distribution to the tumor. The Dox@mPH-RA increased the levels of apoptosis markers, caspase 3, 7, Ki-67, and caused the highest DNA fragmentation. The presence of RA improved the micelles' physicochemical properties, Dox-loading ability, and the therapeutic potential in Dox@mPH-RA via the combination therapeutic strategy.

Inhibitors of BCL2A1/Bfl-1 protein: Potential stock in cancer therapy

The Bcl-2 family members rigorously regulate cell endogenous apoptosis, and targeting anti-apoptotic members is a hot topic in design of anti-cancer drugs. At present, FDA and EMA have approved Bcl-2 inhibitor Venetoclax (ABT-199) for treating chronic lymphocytic leukemia (CLL). However, inhibitors of anti-apoptotic protein BCL2A1/Bfl-1 have not been vigorously developed, and no molecule with ideal activity and selectivity has been found yet. Here we review the biological function and protein structure of Bfl-1, discuss the therapeutic potential and list the currently reported inhibitory peptides and small molecules. This will provide a reference for Bfl-1 targeting drug discovery in the future.

Anticancer Properties of Platinum Nanoparticles and Retinoic Acid: Combination Therapy for the Treatment of Human Neuroblastoma Cancer

Neuroblastoma is the most common extracranial solid tumor in childhood. The different treatments available for neuroblastoma are challenged by high rates of resistance, recurrence, and progression, most notably in advanced cases and highly malignant tumors. Therefore, the development of more targeted therapies, which are biocompatible and without undesired side effects, is highly desirable. The mechanisms of actions of platinum nanoparticles (PtNPs) and retinoic acid (RA) in neuroblastoma have remained unclear. In this study, the anticancer effects of PtNPs and RA on neuroblastoma were assessed. We demonstrated that treatment of SH-SY5Y cells with the combination of PtNPs and RA resulted in improved anticancer effects. The anticancer effects of the two compounds were mediated by cytotoxicity, oxidative stress (OS), mitochondrial dysfunction, endoplasmic reticulum stress (ERS), and apoptosis-associated networks. Cytotoxicity was confirmed by leakage of lactate dehydrogenase (LDH) and intracellular protease, and oxidative stress increased the level of reactive oxygen species (ROS), 4-hydroxynonenal (HNE), malondialdehyde (MDA), and nitric oxide (NO), and protein carbonyl content (PCC). The combination of PtNPs and RA caused mitochondrial dysfunction by decreasing the mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) content, number of mitochondria, and expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). Endoplasmic reticulum-mediated stress and apoptosis were confirmed by upregulation of protein kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1 (IRE1), activating transcription factor 6 (ATF6), activating transcription factor 4 (ATF4), p53, Bax, and caspase-3 and down regulation of B-cell lymphoma 2 (BCl-2). PtNPs and RA induced apoptosis, and oxidative DNA damage was evident by the accumulation of 8-hydroxy-2-deoxyguanosine (8-OHdG) and 8-hydroxyguanosine (8-OHG). Finally, PtNPs and RA increased the differentiation and expression of differentiation markers. Differentiated SH-SY5Y cells pre-treated with PtNPs or RA or the combination of both were more sensitive to the cytotoxic effect of cisplatin than undifferentiated cells. To our knowledge, this is the first study to demonstrate the effect of the combination of PtNPs and RA in neuroblastoma cells. PtNPs may be a potential preconditioning or adjuvant compound in chemotherapeutic treatment. The results of this study provide a rationale for clinical evaluation of the combination of PtNPs and RA for the treatment of children suffering from high-risk neuroblastoma.

Regulating the BCL2 Family to Improve Sensitivity to Microtubule Targeting Agents

Chemotherapeutic targeting of microtubules has been the standard of care in treating a variety of malignancies for decades. During mitosis, increased microtubule dynamics are necessary for mitotic spindle formation and successful chromosomal segregation. Microtubule targeting agents (MTAs) disrupt the dynamics necessary for successful spindle assembly and trigger programmed cell death (apoptosis). As the critical regulators of apoptosis, anti-apoptotic BCL2 family members are often amplified during carcinogenesis that can result in MTA resistance. This review outlines how BCL2 family regulation is positioned within the context of MTA treatment and explores the potential of combination therapy of MTAs with emerging BCL2 family inhibitors.

Cancer stem cells: Road to therapeutic resistance and strategies to overcome resistance

Unlike other normal cells, a subpopulation of cells often termed as "stem cells" are long-lived and generate cellular progeny throughout life. Cancer stem cells (CSCs) are rare immortal cells within a tumor that can both self-renew by dividing and giving rise to many cell types that constitute the tumor. CSCs also have been shown to be involved in fundamental processes of cell proliferation and metastatic dissemination. CSCs are generally resistant to chemotherapy and radiotherapy, a subset of remaining CSCs after therapy can survive and promote cancer relapse and resistance to therapies. Understanding the biological characteristics of CSCs, the pathways leading to their sustainability and proliferation, and the CSCs role in drug resistance is crucial for establishing novel tumor diagnostic and therapeutic strategies. In this review, we address the pathways that regulate CSCs, the role of CSCs in the resistance to therapy, and strategies to overcome therapeutic resistance.

TRIM17 and TRIM28 antagonistically regulate the ubiquitination and anti-apoptotic activity of BCL2A1

BCL2A1 is an anti-apoptotic member of the BCL-2 family that contributes to chemoresistance in a subset of tumors. BCL2A1 has a short half-life due to its constitutive processing by the ubiquitin-proteasome system. This constitutes a major tumor-suppressor mechanism regulating BCL2A1 function. However, the enzymes involved in the regulation of BCL2A1 protein stability are currently unknown. Here, we provide the first insight into the regulation of BCL2A1 ubiquitination. We present evidence that TRIM28 is an E3 ubiquitin-ligase for BCL2A1. Indeed, endogenous TRIM28 and BCL2A1 bind to each other at the mitochondria and TRIM28 knock-down decreases BCL2A1 ubiquitination. We also show that TRIM17 stabilizes BCL2A1 by blocking TRIM28 from binding and ubiquitinating BCL2A1, and that GSK3 is involved in the phosphorylation-mediated inhibition of BCL2A1 degradation. BCL2A1 and its close relative MCL1 are thus regulated by common factors but with opposite outcome. Finally, overexpression of TRIM28 or knock-out of TRIM17 reduced BCLA1 protein levels and restored sensitivity of melanoma cells to BRAF-targeted therapy. Therefore, our data describe a molecular rheostat in which two proteins of the TRIM family antagonistically regulate BCL2A1 stability and modulate cell death.

Low Autophagy (ATG) Gene Expression Is Associated with an Immature AML Blast Cell Phenotype and Can Be Restored during AML Differentiation Therapy

Autophagy is an intracellular degradation system that ensures a dynamic recycling of a variety of building blocks required for self-renewal, homeostasis, and cell survival under stress. We used primary acute myeloid leukemia (AML) samples and human AML cell lines to investigate the regulatory mechanisms of autophagy and its role in AML differentiation. We found a significantly lower expression of key autophagy- (ATG-) related genes in primary AML as compared to healthy granulocytes, an increased autophagic activity during all-trans retinoic acid- (ATRA-) induced neutrophil differentiation, and an impaired AML differentiation upon inhibition of ATG3, ATG4D, and ATG5. Supporting the notion of noncanonical autophagy, we found that ATRA-induced autophagy was Beclin1-independent compared to starvation- or arsenic trioxide- (ATO-) induced autophagy. Furthermore, we identified PU.1 as positive transcriptional regulator of ATG3, ATG4D, and ATG5. Low PU.1 expression in AML may account for low ATG gene expression in this disease. Low expression of the autophagy initiator ULK1 in AML can partially be attributed to high expression of the ULK1-targeting microRNA-106a. Our data clearly suggest that granulocytic AML differentiation relies on noncanonical autophagy pathways and that restoring autophagic activity might be beneficial in differentiation therapies.

Perturbing mitosis for anti-cancer therapy: is cell death the only answer?

Interfering with mitosis for cancer treatment is an old concept that has proven highly successful in the clinics. Microtubule poisons are used to treat patients with different types of blood or solid cancer since more than 20 years, but how these drugs achieve clinical response is still unclear. Arresting cells in mitosis can promote their demise, at least in a petri dish. Yet, at the molecular level, this type of cell death is poorly defined and cancer cells often find ways to escape. The signaling pathways activated can lead to mitotic slippage, cell death, or senescence. Therefore, any attempt to unravel the mechanistic action of microtubule poisons will have to investigate aspects of cell cycle control, cell death initiation in mitosis and after slippage, at single-cell resolution. Here, we discuss possible mechanisms and signaling pathways controlling cell death in mitosis or after escape from mitotic arrest, as well as secondary consequences of mitotic errors, particularly sterile inflammation, and finally address the question how clinical efficacy of anti-mitotic drugs may come about and could be improved.

Sorafenib Inhibition of Mcl-1 Accelerates ATRA-Induced Apoptosis in Differentiation-Responsive AML Cells

PURPOSE

All trans-retinoic acid (ATRA) is successful in treating acute promyelocytic leukemia (APL) by inducing terminal differentiation-mediated cell death, but it has limited activity in non-APL acute myeloid leukemia (AML). We aim to improve ATRA therapy of AML by enhancing apoptosis through repression of the antiapoptotic proteins Bcl-2 and Mcl-1.

EXPERIMENTAL DESIGN

APL and AML cell lines, as well as primary AML samples, were used to explore the mechanisms regulating differentiation and apoptosis during ATRA treatment. Stable transfection and gene silencing with siRNA were used to identify the key factors that inhibit apoptosis during induction of differentiation and drugs that accelerate apoptosis.

RESULTS

In differentiation-responsive AML cells, ATRA treatment induces long-lasting repression of Bcl-2 while first upmodulating and then reducing the Mcl-1 level. The Mcl-1 level appears to serve as a gatekeeper between differentiation and apoptosis. During differentiation induction, activation of MEK/ERK and PI3K/Akt pathways by ATRA leads to activation of p90RSK and inactivation of glycogen synthase kinase 3β (GSK3β), which increase Mcl-1 levels by increasing its translation and stability. Sorafenib blocks ATRA-induced Mcl-1 increase by reversing p90RSK activation and GSK3β inactivation, maintains the repressed Bcl-2 level, and enhances ATRA induced apoptosis in non-APL AML cell lines and in primary AML cells.

CONCLUSIONS

Inhibition of Mcl-1 is required for apoptosis induction in ATRA differentiation-responsive AML cells. ATRA and sorafenib can be developed as a novel drug combination therapy for AML patients because this drug combination augments apoptosis by inhibiting Bcl-2 and Mcl-1.

Combination chemotherapy of doxorubicin, all-trans retinoic acid and low molecular weight heparin based on self-assembled multi-functional polymeric nanoparticles

Based on the complementary effects of doxorubicin (DOX), all-trans retinoic acid (ATRA) and low molecular weight heparin (LMWH), the combination therapy of DOX, ATRA and LMWH was expected to exert the enhanced anti-tumor effects and reduce the side effects. In this study, amphiphilic LMWH-ATRA conjugate was synthesized for encapsulating the DOX. In this way, DOX, ATRA and LMWH were assembled into a single nano-system by both chemical and physical modes to obtain a novel anti-tumor targeting drug delivery system that can realize the simultaneous delivery of multiple drugs with different properties to the tumor. LMWH-ATRA nanoparticles exhibited good loading capacities for DOX with excellent physico-chemical properties, good biocompatibility, and good differentiation-inducing activity and antiangiogenic activity. The drug-loading capacity was up to 18.7% with an entrapment efficiency of 78.8%. It was also found that DOX-loaded LMWH-ATRA nanoparticles (DHR nanoparticles) could be efficiently taken up by tumor cells via endocytic pathway, and mainly distributed in cytoplasm at first, then transferred into cell nucleus. Cell viability assays suggested that DHR nanoparticles maintained the cytotoxicity effect of DOX on MCF-7 cells. Moreover, the in vivo imaging analysis indicated that DiR-loaded LMWH-ATRA nanoparticles could target the tumor more effectively as compared to free DiR. Furthermore, DHR nanoparticles possessed much higher anticancer activity and reduced side effects compared to free drugs solution. These results suggested that DHR nanoparticles could be considered as a promising targeted delivery system for combination cancer chemotherapy with lower adverse effects.

Linear-dendritic copolymer composed of polyethylene glycol and all-trans-retinoic acid as drug delivery platform for paclitaxel against breast cancer

A new linear-dendritic copolymer composed of poly(ethylene glycol) (PEG) and all-trans-retinoic acid (ATRA) was synthesized as the anticancer drug delivery platform (PEG-G3-RA8). It can self-assemble into core-shell micelles with a low critical micelle concentration (CMC) at 3.48 mg/L. Paclitaxel (PTX) was encapsulated into PEG-G3-RA8 to form PEG-G3-RA8/PTX micelles for breast cancer treatment. The optimized formulation had high drug loading efficacy (20% w/w of drug copolymer ratio), nanosized diameter (27.6 nm), and narrow distribution (PDI = 0.103). Compared with Taxol, PEG-G3-RA8/PTX remained highly stable in the serum-containing cell medium and exhibited 4-fold higher cellular uptake. Besides, near-infrared fluorescence (NIR) optical imaging results indicated that fluorescent probe loaded micelle had a preferential accumulation in breast tumors. Pharmacokinetics and biodistribution studies (10 mg/kg) showed the area under the plasma concentration-time curve (AUC0-∞) and mean residence time (MRT0-∞) for PEG-G3-RA8/PTX and Taxol were 12.006 ± 0.605 mg/L h, 2.264 ± 0.041 h and 15.966 ± 1.614 mg/L h, 1.726 ± 0.097 h, respectively. The tumor accumulation of PEG-G3-RA8/PTX group was 1.89-fold higher than that of Taxol group 24 h postinjection. With the advantages like efficient cellular uptake and preferential tumor accumulation, PEG-G3-RA8/PTX showed superior therapeutic efficacy on MCF-7 tumor bearing mice compared to Taxol.

Antagonism between granulocytic maturation and deacetylase inhibitor-induced apoptosis in acute promyelocytic leukaemia cells

Background:

Transcriptional repression is a key mechanism driving leukaemogenesis. In acute promyelocytic leukaemia (APL), the fusion protein promyelocytic leukaemia-retinoic acid receptor-α fusion (PML-RARα) recruits transcriptional repressors to myeloid differentiation genes. All-trans-retinoic acid (ATRA) induces the proteasomal degradation of PML-RARα and granulocytic differentiation. Histone deacetylases (HDACs) fall into four classes (I–IV) and contribute to the transcription block caused by PML-RARα.

Methods:

Immunoblot, flow cytometry, and May-Grünwald–Giemsa staining were used to analyze differentiation and induction of apoptosis.

Results:

A PML-RARα- and ATRA-dependent differentiation programme induces granulocytic maturation associated with an accumulation of the myeloid transcription factor CCAAT/enhancer binding protein (C/EBP)ɛ and of the surface protein CD11b. While this process protects APL cells from inhibitors of class I HDAC activity, inhibition of all Zinc-dependent HDACs (classes I, II, and IV) with the pan-HDACi (histone deacetylase inhibitor(s)) LBH589 induces apoptosis of immature and differentiated APL cells. LBH589 can eliminate C/EBPɛ and the mitochondrial apoptosis regulator B-cell lymphoma (BCL)-xL in immature and differentiated NB4 cells. Thus, BCL-xL and C/EBPɛ are newly identified molecular markers for the efficacy of HDACi against APL cells.

Conclusions:

Our results could explain the therapeutic limitations occurring with ATRA and class I HDACi combinations. Pro-apoptotic effects caused by pan-HDAC inhibition are not blunted by ATRA-induced differentiation and may provide a clinically interesting alternative.

BCL-xL/MCL-1 inhibition and RARγ antagonism work cooperatively in human HL60 leukemia cells

The acute promyelocytic leukemia (APL) subtype of acute myeloid leukemia (AML) is characterized by chromosomal translocations that result in fusion proteins, including the promyelocytic leukemia-retinoic acid receptor, alpha fusion protein (PML-RARα). All-trans retinoic acid (atRA) treatment is the standard drug treatment for APL yielding cure rates > 80% by activating transcription and proteasomal degradation of retinoic acid receptor, alpha (RARα). Whereas combination therapy with As2O3 has increased survival further, patients that experience relapse and are refractory to atRA and/or As2O3 is a clinically significant problem. BCL-2 family proteins regulate apoptosis and over-expression of anti-apoptotic B-cell leukemia/lymphoma 2 (BCL-2) family proteins has been associated with chemotherapeutic resistance in APL including impairment of the ability of atRA to induce growth arrest and differentiation. Here we investigated the novel BH3 domain mimetic, JY-1-106, which antagonizes the anti-apoptotic BCL-2 family members B-cell lymphoma-extra large (BCL-xL) and myeloid cell leukemia-1 (MCL-1) alone and in combination with retinoids including atRA, AM580 (RARα agonist), and SR11253 (RARγ antagonist). JY-1-106 reduced cell viability in HL-60 cells alone and in combination with retinoids. The combination of JY-1-106 and SR11253 had the greatest impact on cell viability by stimulating apoptosis. These studies indicate that dual BCL-xL/MCL-1 inhibitors and retinoids could work cooperatively in leukemia treatment.

Cell adhesion molecules and their relation to (cancer) cell stemness

Despite decades of search for anticancer drugs targeting solid tumors, this group of diseases remains largely incurable, especially if in advanced, metastatic stage. In this review, we draw comparison between reprogramming and carcinogenesis, as well as between stem cells (SCs) and cancer stem cells (CSCs), focusing on changing garniture of adhesion molecules. Furthermore, we elaborate on the role of adhesion molecules in the regulation of (cancer) SCs division (symmetric or asymmetric), and in evolving interactions between CSCs and extracellular matrix. Among other aspects, we analyze the role and changes of expression of key adhesion molecules as cancer progresses and metastases develop. Here, the role of cadherins, integrins, as well as selected transcription factors like Twist and Snail is highlighted, not only in the regulation of epithelial-to-mesenchymal transition but also in the avoidance of anoikis. Finally, we briefly discuss recent developments and new strategies targeting CSCs, which focus on adhesion molecules or targeting tumor vasculature.

Vitamin A enhances antitumor effect of a green tea polyphenol on melanoma by upregulating the polyphenol sensing molecule 67-kDa laminin receptor

Background

Green tea consumption has been shown to have cancer preventive qualities. Among the constituents of green tea, (-)-Epigallocatechin-3-O-gallate (EGCG) is the most effective at inhibiting carcinogenesis. However, the concentrations of EGCG that are required to elicit the anticancer effects in a variety of cancer cell types are much higher than the peak plasma concentration that occurs after drinking an equivalent of 2–3 cups of green tea. To obtain the anticancer effects of EGCG when consumed at a reasonable concentration in daily life, we investigated the combination effect of EGCG and food ingredient that may enhance the anticancer activity of EGCG on subcutaneous tumor growth in C57BL/6N mice challenged with B16 melanoma cells.

Methodology/Principal Findings

All-trans-retinoic acid (ATRA) enhanced the expression of the 67-kDa laminin receptor (67LR) and increased EGCG-induced cell growth inhibition in B16 melanoma cells. The cell growth inhibition seen with the combined EGCG and ATRA treatment was abolished by treatment with an anti-67LR antibody. In addition, the combined EGCG and ATRA treatment significantly suppressed the melanoma tumor growth in mice. Expression of 67LR in the tumor increased upon oral administration of ATRA or a combined treatment of EGCG and ATRA treatment. Furthermore, RNAi-mediated silencing of the retinoic acid receptor (RAR) α attenuated the ATRA-induced enhancement of 67LR expression in the melanoma cells. An RAR agonist enhanced the expression levels of 67LR and increased EGCG-induced cell growth inhibition.

Conclusions/Significance

Our findings provide a molecular basis for the combination effect seen with dietary components, and indicate that ATRA may be a beneficial food component for cancer prevention when combined with EGCG.

Defective ubiquitin-mediated degradation of antiapoptotic Bfl-1 predisposes to lymphoma

The antiapoptotic Bcl-2 family member Bfl-1 is up-regulated in many human tumors in which nuclear factor-kappaB (NF-kappaB) is implicated and contributes significantly to tumor cell survival and chemoresistance. We previously found that NF-kappaB induces transcription of bfl-1 and that the Bfl-1 protein is also regulated by ubiquitin-mediated proteasomal degradation. However, the role that dysregulation of Bfl-1 turnover plays in cancer is not known. Here we show that ubiquitination-resistant mutants of Bfl-1 display increased stability and greatly accelerated tumor formation in a mouse model of leukemia/lymphoma. We also show that tyrosine kinase Lck is up-regulated and activated in these tumors and leads to activation of the IkappaB kinase, Akt, and extracellular signal-regulated protein kinase signaling pathways, which are key mediators in cancer. Coexpression of Bfl-1 and constitutively active Lck promoted tumor formation, whereas Lck knockdown in tumor-derived cells suppressed leukemia/lymphomagenesis. These data demonstrate that ubiquitination is a critical tumor suppression mechanism regulating Bfl-1 function and suggest that mutations in bfl-1 or in the signaling pathways that control its ubiquitination may predispose one to cancer. Furthermore, because bfl-1 is up-regulated in many human hematopoietic tumors, this finding suggests that strategies to promote Bfl-1 ubiquitination may improve therapy.

Retinoic acid protects human breast cancer cells against etoposide-induced apoptosis by NF-kappaB-dependent but cIAP2-independent mechanisms

Background

Retinoids, through their cognate nuclear receptors, exert potent effects on cell growth, differentiation and apoptosis, and have significant promise for cancer therapy and chemoprevention. These ligands can determine the ultimate fate of target cells by stimulating or repressing gene expression directly, or indirectly through crosstalking with other signal transducers.

Results

Using different breast cancer cell models, we show here that depending on the cellular context retinoids can signal either towards cell death or cell survival. Indeed, retinoids can induce the expression of pro-apoptotic (i.e. TRAIL, TNF-Related Apoptosis-Inducing Ligand, Apo2L/TNFSF10) and anti-apoptotic (i.e. cIAP2, inhibitor of apoptosis protein-2) genes. Promoter mapping, gel retardation and chromatin immunoprecipitation assays revealed that retinoids induce the expression of this gene mainly through crosstalk with NF-kappaB. Supporting this crosstalk, the activation of NF-kappaB by retinoids in T47D cells antagonizes the apoptosis triggered by the chemotherapeutic drugs etoposide, camptothecin or doxorubicin. Notably apoptosis induced by death ligands (i.e. TRAIL or antiFAS) is not antagonized by retinoids. That knockdown of cIAP2 expression by small interfering RNA does not alter the inhibition of etoposide-induced apoptosis by retinoids in T47D cells reveals that stimulation of cIAP2 expression is not the cause of their anti-apoptotic action. However, ectopic overexpression of a NF-kappaB repressor increases apoptosis by retinoids moderately and abrogates almost completely the retinoid-dependent inhibition of etoposide-induced apoptosis. Our data exclude cIAP2 and suggest that retinoids target other regulator(s) of the NF-kappaB signaling pathway to induce resistance to etoposide on certain breast cancer cells.

Conclusions

This study shows an important role for the NF-kappaB pathway in retinoic acid signaling and retinoic acid-mediated resistance to cancer therapy-mediated apoptosis in breast cancer cells, independently of cIAP2. Our data support the use of NF-kappaB pathway activation as a marker for screening that will help to develop novel retinoids, or retinoid-based combination therapies with improved efficacy.

All-trans retinoic acid induces Thrombospondin-1 expression in acute promyelocytic leukemia cells though down-regulation of its transcription repressor, c-MYC oncoprotein

Thrombospondin-1 (TSP-1) was found to mediate the therapeutic effects of all-trans retinoic acid (ATRA) for leukemia. The aim of the present study was to evaluate the role of c-MYC, a key transcription factor that contributes to the genesis of many human tumors, in TSP-1 induction by ATRA in acute promyelocytic leukemia (APL). ATRA treatment markedly increased TSP-1 level and inhibited c-MYC expression in NB4 APL leukemic cells compared with controls. Promoter assays indicated that c-MYC responsive element is functional relevant to the induction of TSP-1 promoter activity by ATRA. c-MYC recruitment to TSP-1 promoter was dramatically decreased in NB4 cells following ATRA treatment. shRNA-mediated inhibition of c-MYC resulted in a marked up-regulation of endogenous TSP-1 expression. Moreover, transient over-expression of c-MYC totally abolished TSP-1 induction by ATRA in NB4 cells. Collectively, our results indicate that ATRA induces TSP-1 expression in APL cells though down-regulation of its transcription repressor, c-MYC oncoprotein.

TP53, BCL-2 and BAX analysis in 199 ovarian cancer patients treated with taxane-platinum regimens

OBJECTIVE

In cell line studies, BCL-2 and BAX proteins interfere with cancer response to taxanes. This issue has not received much attention with regard to taxane-platinum (TP)-treated ovarian cancer patients.

METHODS

We evaluated prognostic/predictive significance of BCL-2 and BAX with regard to TP53 status. Immunohistochemical analysis was performed on 199 ovarian carcinomas FIGO stage IIB-IV treated with TP; the results were analyzed by the Cox and logistic regression models.

RESULTS

Clinicopathological parameters (residual tumor size, FIGO stage and/or tumor grade, but not patient's age) were the only or the strongest predictors of patient's outcome. Platinum highly sensitive response showed a positive association with TP53 accumulation (p=0.045). As in our previously published analysis on platinum-cyclophosphamide-treated group, complete remission showed a borderline negative (paradoxic) association with high BAX expression in the whole group (p=0.058) and with BCL-2 expression in the TP53(-) group (p=0.058).

CONCLUSION

Our results suggest that TP53, BCL-2 and BAX proteins carry some predictive potential in taxane-platinum-treated ovarian cancer patients, auxiliary to clinicopathological factors. We have confirmed on another patient group that clinical importance of BCL-2 may depend on TP53 status.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Combination of all-trans retinoic acid and paclitaxel-induced differentiation and apoptosis in human glioblastoma U87MG xenografts in nude mice

BACKGROUND

Glioblastoma, which is the most malignant brain tumor, remains incurable and almost always causes death. As a new treatment strategy, the combination of all-trans retinoic acid (ATRA) and paclitaxel was explored for controlling the growth of glioblastoma U87MG xenografts.

METHODS

Human glioblastoma U87MG xenografts were developed in athymic nude mice for treatments with ATRA, paclitaxel, and ATRA plus paclitaxel. The efficacy of treatments in controlling tumor growth was assessed by histologic examination, Western blot analysis, and immunofluorescent labelings.

RESULTS

Astrocytic differentiation in U87MG xenografts was associated with increased GFAP expression and decreased telomerase expression. The combination of ATRA and paclitaxel was found to cause more apoptosis than paclitaxel alone. Apoptosis occurred with down-regulation of MEK-2 and overexpression of p-ERK, p-JNK, and p-p38 MAPK. Down-regulation of both Akt and p-Akt also favored the apoptotic process. Combination therapy activated the receptor-mediated pathway of apoptosis with induction of TNF-alpha, activation of caspase-8, and cleavage of Bid to tBid. Combination therapy also induced the mitochondria-mediated pathway of apoptosis with an increase in the Bax:Bcl-2 ratio and mitochondrial release of cytochrome c and Smac/Diablo into the cytosol. In addition, combination therapy promoted phosphorylation of Bcl-2 for its inactivation and down-regulated NF-kappaB and BIRC proteins, indicating suppression of several cell survival factors. Western blot analysis demonstrated that activation of cysteine proteases such as calpain, caspase-12, caspase-9, and caspase-3 contributed to apoptosis. Immunofluorescent labelings confirmed overexpression of cysteine proteases in apoptosis.

CONCLUSIONS

Treatment of U87MG xenografts with a combination of ATRA and paclitaxel induced differentiation and also multiple molecular mechanisms for apoptosis.

TP53 status and taxane-platinum versus platinum-based therapy in ovarian cancer patients: a non-randomized retrospective study

Background

Taxane-platinum therapy (TP) has replaced platinum-based therapy (PC or PAC, DNA damaging chemotherapy) in the postoperative treatment of ovarian cancer patients; however, it is not always effective. TP53 protein plays a differential role in response to DNA-damaging agents and taxanes. We sought to define profiles of patients who benefit the most from TP and also of those who can be treated with PC.

Methods

We compared the effectiveness of PC/PAC (n = 253) and TP (n = 199) with respect to tumor TP53 accumulation in ovarian cancer patients with FIGO stage IIB-IV disease; this was a non-randomized retrospective study. Immunohistochemical analysis was performed on 452 archival tumors; univariate and multivariate analysis by the Cox's and logistic regression models was performed in all patients and in subgroups with [TP53(+)] and without TP53 accumulation [TP53(-)].

Results

The advantage of taxane-platinum therapy over platinum-based therapy was seen in the TP53(+), and not in the TP53(-) group. In the TP53(+) group taxane-platinum therapy enhanced the probability of complete remission (p = .018), platinum sensitivity (p = .014), platinum highly sensitive response (p = .038) and longer survival (OS, p = .008). Poor tumor differentiation diminished the advantage from taxane-platinum therapy in the TP53(+) group. In the TP53(-) group PC/PAC was at least equally efficient as taxane-platinum therapy and it enhanced the chance of platinum highly sensitive response (p = .010). However, in the TP53(-) group taxane-platinum therapy possibly diminished the risk of death in patients over 53 yrs (p = .077). Among factors that positively interacted with taxane-platinum therapy in some analyses were endometrioid and clear cell type, FIGO III stage, bulky residual tumor, more advanced age of patient and moderate tumor differentiation.

Conclusion

Our results suggest that taxane-platinum therapy is particularly justified in patients with TP53(+) tumors or older than 53 years. In the group of patients ≤53 yrs and with TP53(-) tumors platinum-based therapy is possibly equally efficient. We provide hints for planning randomized trials to verify these observations.

The design of selective and non-selective combination therapy for acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is an unique subtype of acute myeloid leukemia typically carrying a specific reciprocal chromosome translocation, t(15;17), leading to the expression of a leukemia-generating fusion protein, PML-RARalpha. APL patients are responsive to APL-selective reagents such as all-trans retinoic acid (ATRA) or arsenic trioxide and non-selective cytotoxic chemotherapy. Nearly all de novo APL patients undergo clinical remission when treated with ATRA plus chemotherapy or with the combinational selective therapy, ATRA plus As2O3. Combining ATRA with As2O3 as an induction followed by chemotherapy consolidation results in more profound clinical remissions compared to treatment with any agent alone or any of the other possible combinations. The mechanism of action of each of these agents differs. ATRA induces APL cell differentiation and PML-RARalpha proteolysis. As2O3 induces APL cell partial differentiation, PML-RARalpha proteolysis, and apoptosis. Chemotherapy, mainly using anthracyclines, induces APL cell death. The combined effects of selective APL therapy (ATRA and As2O3) and/or non-selective chemotherapy in APL cells in vitro and their mechanisms in relation to clinical protocol design are discussed.