Activation of p53 by Nutlin-3a, an antagonist of MDM2, induces apoptosis and cellular senescence in adult T-cell leukemia cells

Mutant p53 reactivators protect breast cancer cells from ferroptosis

Ferroptosis is a novel nonapoptotic form of cell death characterized by iron-dependent reactive oxygen species-mediated lipid peroxidation. In several different cell systems, the tumor suppressor p53 can enhance sensitivity to ferroptotic inducers. At least half of all human cancers show loss of function of p53. Furthermore, many of those tumors express mutant forms of p53 that has lost its wild-type function. Several groups have designed small molecules that can reactivate the wild-type function of these missense p53 mutants. We reasoned that p53 reactivators may also enhance sensitivity of certain cancer cells to ferroptosis stimuli. To test this idea we combined a number of different p53 reactivators with small molecule inducers of ferroptosis. In contrast, we observed that several p53 reactivators protected cells from cell death induced by ferroptotic inducers. Surprisingly, this protection still occurred in p53-null cell lines. We observed that these reactivators were neither free radical scavengers nor ion chelators. One of these p53 reactivator molecules, NSC 59984, reduced expression of GPX4, which is unlikely to explain its ability to reduce sensitivity to ferroptosis. We suggest that these p53 reactivators function via an unknown, p53-independent manner to suppress ferroptosis.

The potential for senotherapy as a novel approach to extend life quality in veterinary medicine

Cellular senescence, a condition where cells undergo arrest and can assume an inflammatory phenotype, has been associated with initiation and perpetuation of inflammation driving multiple disease processes in rodent models and humans. Senescent cells secrete inflammatory cytokines, proteins, and matrix metalloproteinases, termed the senescence associated secretory phenotype (SASP), which accelerates the aging processes. In preclinical models, drug interventions termed "senotherapeutics" selectively clear senescent cells and represent a promising strategy to prevent or treat multiple age-related conditions in humans and veterinary species. In this review, we summarize the current available literature describing in vitro evidence for senotheraputic activity, preclinical models of disease, ongoing human clinical trials, and potential clinical applications in veterinary medicine. These promising data to date provide further justification for future studies identifying the most active senotherapeutic combinations, dosages, and routes of administration for use in veterinary medicine.

Nanoencapsulation of MDM2 Inhibitor RG7388 and Class-I HDAC Inhibitor Entinostat Enhances their Therapeutic Potential Through Synergistic Antitumor Effects and Reduction of Systemic Toxicity

Inhibitors of the p53-MDM2 interaction such as RG7388 have been developed to exploit latent tumor suppressive properties in p53 in 50% of tumors in which p53 is wild-type. However, these agents for the most part activate cell cycle arrest rather than death, and high doses in patients elicit on-target dose-limiting neutropenia. Recent work from our group indicates that combination of p53-MDM2 inhibitors with the class-I HDAC inhibitor Entinostat (which itself has dose-limiting toxicity issues) has the potential to significantly augment cell death in p53 wild-type colorectal cancer cells. We investigated whether coencapsulation of RG7388 and Entinostat within polymeric nanoparticles (NPs) could overcome efficacy and toxicity limitations of this drug combination. Combinations of RG7388 and Entinostat across a range of different molar ratios resulted in synergistic increases in cell death when delivered in both free drug and nanoencapsulated formats in all colorectal cell lines tested. Importantly, we also explored the in vivo impact of the drug combination on murine blood leukocytes, showing that the leukopenia induced by the free drugs could be significantly mitigated by nanoencapsulation. Taken together, this study demonstrates that formulating these agents within a single nanoparticle delivery platform may provide clinical utility beyond use as nonencapsulated agents.

Bifenox induces programmed cell death in bovine mammary epithelial cells by impairing calcium homeostasis, triggering ER stress, and altering the signaling cascades of PI3K/AKT and MAPK

Bifenox (methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate), a nitrophenyl ether herbicide, was first introduced in the 1980s to control broadleaf weeds. As a result of its wide and frequent application in diverse agricultural settings and reports on residual traces, potential adverse effects of bifenox have been studied extensively in rat hepatocytes, bovine peripheral lymphocytes, and mice. Despite the reported risks of bifenox exposure in dairy cows, the toxicity of bifenox on bovine lactation system has not been extensively investigated. Therefore, we used bovine mammary epithelial (MAC-T) cells to study the toxic effects of bifenox on mammary glands. We found that bifenox inhibited MAC-T cells proliferation and disturbed the cell cycle, especially in the sub-G1 and G1 phases. Bifenox also disrupted the calcium homeostasis within the cell and impaired mitochondrial membrane potential. We also examined phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) and mitogen-activated protein kinase (MAPK) signaling cascades. The findings indicated hyperactivation of phosphorylated protein kinase B (AKT), p70 ribosomal S6 kinase (p70S6K), S6, extracellular signal-regulated kinases 1 and 2 (ERK1/2), p38, c-Jun N-terminal kinase (JNK), and c-Jun, as well as endoplasmic reticulum (ER) stress caused by bifenox treatment. In conclusion, based on our in vitro study employing MAC-T cells, we report that bifenox can induce damage to the bovine mammary glands, potentially impacting milk production.

7-Geranyloxcycoumarin enhances radio sensitivity in human prostate cancer cells

BACKGROUND

Prostate cancer is the second most prevalent and the fifth deadliest cancer among men worldwide. To improve radiotherapy outcome, we investigated the effects of 7-geranyloxycoumarin, also known as auraptene (AUR), on radiation response of prostate cancer cells.

METHODS AND RESULTS

PC3 cells were pretreated with 20 and 40 µM AUR for 24, 48 and 72 h, followed by X-ray exposure (2, 4 and 6 Gy). After 72 h recovery, cell viability was determined by alamar Blue assay. Flow cytometric analysis was performed to assess apoptosis induction, clonogenic assay was carried out to investigate clonogenic survival, and the expression of P53, BAX, BCL2, CCND1 and GATA6 was analyzed by quantitative polymerase chain reaction (qPCR). Cell viability assay indicated that toxic effects of radiation was enhanced by AUR, which was also confirmed by increased numbers of apoptotic cells and reduced amount of survival fraction. The qPCR results demonstrated significant induction of P53 and BAX, while the expression of BCL2, GATA6, and CCND1 was significantly downregulated.

CONCLUSION

The findings of the present study indicated, for the first time, that AUR improved radio sensitivity in prostate cancer cells, and thus, has the potential to be used in future clinical trials.

The X-linked epigenetic regulator UTX controls NK cell-intrinsic sex differences

Viral infection outcomes are sex biased, with males generally more susceptible than females. Paradoxically, the numbers of antiviral natural killer (NK) cells are increased in males. We demonstrate that while numbers of NK cells are increased in male mice, they display decreased effector function compared to females in mice and humans. These differences were not solely dependent on gonadal hormones, because they persisted in gonadectomized mice. Kdm6a (which encodes the protein UTX), an epigenetic regulator that escapes X inactivation, was lower in male NK cells, while NK cell-intrinsic UTX deficiency in female mice increased NK cell numbers and reduced effector responses. Furthermore, mice with NK cell-intrinsic UTX deficiency showed increased lethality to mouse cytomegalovirus. Integrative multi-omics analysis revealed a critical role for UTX in regulating chromatin accessibility and gene expression critical for NK cell homeostasis and effector function. Collectively, these data implicate UTX as a critical molecular determinant of sex differences in NK cells.

Alvocidib inhibits IRF4 expression via super-enhancer suppression and adult T-cell leukemia/lymphoma cell growth

Adult T-cell leukemia/lymphoma (ATL) is an intractable hematological malignancy with extremely poor prognosis. Recent studies have revealed that super-enhancers (SE) play important roles in controlling tumor-specific gene expression and are potential therapeutic targets for neoplastic diseases including ATL. Cyclin-dependent protein kinase (CDK) 9 is a component of a complex comprising transcription factors (TFs) that bind the SE region. Alvocidib is a CDK9 inhibitor that exerts antitumor activity by inhibiting RNA polymerase (Pol) II phosphorylation and suppressing SE-mediated, tumor-specific gene expression. The present study demonstrated that alvocidib inhibited the proliferation of ATL cell lines and tumor cells from patients with ATL. RNA sequencing (RNA-Seq) and chromatin immunoprecipitation sequencing (ChIP-Seq) disclosed that SE regulated IRF4 in the ATL cell lines. Previous studies showed that IRF4 suppression inhibited ATL cell proliferation. Hence, IRF4 is a putative alvocidib target in ATL therapy. The present study revealed that SE-mediated IRF4 downregulation is a possible mechanism by which alvocidib inhibits ATL proliferation. Alvocidib also suppressed ATL in a mouse xenograft model. Hence, the present work demonstrated that alvocidib has therapeutic efficacy against ATL and partially elucidated its mode of action. It also showed that alvocidib is promising for the clinical treatment of ATL and perhaps other malignancies and neoplasms as well.

Do Bacteria Provide an Alternative to Cancer Treatment and What Role Does Lactic Acid Bacteria Play?

Cancer is one of the leading causes of mortality and morbidity worldwide. According to 2022 statistics from the World Health Organization (WHO), close to 10 million deaths have been reported in 2020 and it is estimated that the number of cancer cases world-wide could increase to 21.6 million by 2030. Breast, lung, thyroid, pancreatic, liver, prostate, bladder, kidney, pelvis, colon, and rectum cancers are the most prevalent. Each year, approximately 400,000 children develop cancer. Treatment between countries vary, but usually includes either surgery, radiotherapy, or chemotherapy. Modern treatments such as hormone-, immuno- and antibody-based therapies are becoming increasingly popular. Several recent reports have been published on toxins, antibiotics, bacteriocins, non-ribosomal peptides, polyketides, phenylpropanoids, phenylflavonoids, purine nucleosides, short chain fatty acids (SCFAs) and enzymes with anticancer properties. Most of these molecules target cancer cells in a selective manner, either directly or indirectly through specific pathways. This review discusses the role of bacteria, including lactic acid bacteria, and their metabolites in the treatment of cancer.

Resistance mechanisms to inhibitors of p53-MDM2 interactions in cancer therapy: can we overcome them?

Since the discovery of the first MDM2 inhibitors, we have gained deeper insights into the cellular roles of MDM2 and p53. In this review, we focus on MDM2 inhibitors that bind to the p53-binding domain of MDM2 and aim to disrupt the binding of MDM2 to p53. We describe the basic mechanism of action of these MDM2 inhibitors, such as nutlin-3a, summarise the determinants of sensitivity to MDM2 inhibition from p53-dependent and p53-independent points of view and discuss the problems with innate and acquired resistance to MDM2 inhibition. Despite progress in MDM2 inhibitor design and ongoing clinical trials, their broad use in cancer treatment is not fulfilling expectations in heterogenous human cancers. We assess the MDM2 inhibitor types in clinical trials and provide an overview of possible sources of resistance to MDM2 inhibition, underlining the need for patient stratification based on these aspects to gain better clinical responses, including the use of combination therapies for personalised medicine.

TP53-Induced Glycolysis and Apoptosis Regulator (TIGAR) Is Upregulated in Lymphocytes Stimulated with Concanavalin A

The glycolytic modulator TP53-Inducible Glycolysis and Apoptosis Regulator (TIGAR) is overexpressed in several types of cancer and has a role in metabolic rewiring during tumor development. However, little is known about the role of this enzyme in proliferative tissues under physiological conditions. In the current work, we analysed the role of TIGAR in primary human lymphocytes stimulated with the mitotic agent Concanavalin A (ConA). We found that TIGAR expression was induced in stimulated lymphocytes through the PI3K/AKT pathway, since Akti-1/2 and LY294002 inhibitors prevented the upregulation of TIGAR in response to ConA. In addition, suppression of TIGAR expression by siRNA decreased the levels of the proliferative marker PCNA and increased cellular ROS levels. In this model, TIGAR was found to support the activity of glucose 6-phosphate dehydrogenase (G6PDH), the first enzyme of the pentose phosphate pathway (PPP), since the inhibition of TIGAR reduced G6PDH activity and increased autophagy. In conclusion, we demonstrate here that TIGAR is upregulated in stimulated human lymphocytes through the PI3K/AKT signaling pathway, which contributes to the redirection of the carbon flux to the PPP.

Nutlin-3a Enhances Natural Killer Cell-Mediated Killing of Neuroblastoma by Restoring p53-Dependent Expression of Ligands for NKG2D and DNAM-1 Receptors

In this study, we explored whether Nutlin-3a, a well-known, nontoxic small-molecule compound antagonizing the inhibitory interaction of MDM2 with the tumor suppressor p53, may restore ligands for natural killer (NK) cell-activating receptors (NK-AR) on neuroblastoma cells to enhance the NK cell-mediated killing. Neuroblastoma cell lines were treated with Nutlin-3a, and the expression of ligands for NKG2D and DNAM-1 NK-ARs and the neuroblastoma susceptibility to NK cells were evaluated. Adoptive transfer of human NK cells in a xenograft neuroblastoma-bearing NSG murine model was assessed. Two data sets of neuroblastoma patients were explored to correlate p53 expression with ligand expression. Luciferase assays and chromatin immunoprecipitation analysis of p53 functional binding on PVR promoter were performed. Primary neuroblastoma cells were also treated with Nutlin-3a, and neuroblastoma spheroids obtained from one high-risk patient were assayed for NK-cell cytotoxicity. We provide evidence showing that the Nutlin-3a-dependent rescue of p53 function in neuroblastoma cells resulted in (i) increased surface expression of ligands for NK-ARs, thus rendering neuroblastoma cell lines significantly more susceptible to NK cell-mediated killing; (ii) shrinkage of human neuroblastoma tumor masses that correlated with overall survival upon adoptive transfer of NK cells in neuroblastoma-bearing mice; (iii) and increased expression of ligands in primary neuroblastoma cells and boosting of NK cell-mediated disaggregation of neuroblastoma spheroids. We also found that p53 was a direct transcription factor regulating the expression of PVR ligand recognized by DNAM-1. Our findings demonstrated an immunomodulatory role of Nutlin-3a, which might be prospectively used for a novel NK cell-based immunotherapy for neuroblastoma.

Cellular senescence and cancer: Focusing on traditional Chinese medicine and natural products

Cancer is the principal cause of death and a dominant public health problem which seriously threatening human life. Among various ways to treat cancer, traditional Chinese medicine (TCM) and natural products have outstanding anti‐cancer effects with their unique advantages of high efficiency and minimal side effects. Cell senescence is a physiological process of cell growth stagnation triggered by stress, which is an important line of defence against tumour development. In recent years, active ingredients of TCM and natural products, as an interesting research hotspot, can induce cell senescence to suppress the occurrence and development of tumours, by inhibiting telomerase activity, triggering DNA damage, inducing SASP, and activating or inactivating oncogenes. In this paper, the recent research progress on the main compounds derived from TCM and natural products that play anti‐cancer roles by inducing cell senescence is systematically reviewed, aiming to provide a reference for the clinical treatment of pro‐senescent cancer.

Small-molecule MDM2 inhibitor LQFM030-induced apoptosis in p53-null K562 chronic myeloid leukemia cells

Our group designed and synthesized the N-phenyl-piperazine LQFM030 [1-(4-((1-(4-chlorophenyl)-1H-pyrazol-4-yl)methyl) piperazin-1-yl) ethanone], a small molecule derived from molecular simplification of the Nutlin-1, an inhibitor of the human homologue of murine double minute 2 (MDM2) protein that is expressed in several types of cancer. To better investigate the effects of LQFM030 regarding the p53 mutation status, this study investigated the antiproliferative activity of LQFM030 against the p53-null K562 leukemia cells as well as the cell death pathways involved. In addition, the effects of LQFM030 on the levels of the p53/MDM2 complex were also carried out using 3T3 cells as a p53 wild-type model. Our data suggest that LQFM030 triggered apoptosis in K562 cells via different mechanisms including cell cycle arrest, caspase activation, reduction of mitochondrial activity, decrease in MDM2 expression, and transcriptional modulation of MDMX, p73, MYC, and NF-ĸB. Additionally, it promoted effects in p53/MDM2 binding in p53 wild-type 3T3 cells. Therefore, LQFM030 has antiproliferative effects in cancer cells by a p53 mutation status-independent manner with different signaling pathways. These findings open new perspectives to the treatment of leukemic cells considering the resistance development associated with cancer treatment with conventional cytotoxic drugs.

Prognosis, Biology, and Targeting of TP53 Dysregulation in Multiple Myeloma

Multiple myeloma (MM) is the second most common hematological cancer and is characterized by genetic features including translocations, chromosomal copy number aberrations, and mutations in key oncogene and tumor suppressor genes. Dysregulation of the tumor suppressor TP53 is important in the pathogenesis of many cancers, including MM. In newly-diagnosed MM patients, TP53 dysregulation occurs in three subsets: monoallelic deletion as part of deletion of chromosome 17p (del17p) (~8%), monoallelic mutations (~6%), and biallelic inactivation (~4%). Del17p is an established high-risk feature in MM and is included in current disease staging criteria. Biallelic inactivation and mutation have also been reported in MM patients but are not yet included in disease staging criteria for high-risk disease. Emerging clinical and genomics data suggest that the biology of high-risk disease is complex, and so far, traditional drug development efforts to target dysregulated TP53 have not been successful. Here we review the TP53 dysregulation literature in cancer and in MM, including the three segments of TP53 dysregulation observed in MM patients. We propose a reverse translational approach to identify novel targets and disease drivers from TP53 dysregulated patients to address the unmet medical need in this setting.

Essential genes shape cancer genomes through linear limitation of homozygous deletions

The landscape of somatic acquired deletions in cancer cells is shaped by positive and negative selection. Recurrent deletions typically target tumor suppressor, leading to positive selection. Simultaneously, loss of a nearby essential gene can lead to negative selection, and introduce latent vulnerabilities specific to cancer cells. Here we show that, under basic assumptions on positive and negative selection, deletion limitation gives rise to a statistical pattern where the frequency of homozygous deletions decreases approximately linearly between the deletion target gene and the nearest essential genes. Using DNA copy number data from 9,744 human cancer specimens, we demonstrate that linear deletion limitation exists and exposes deletion-limiting genes for seven known deletion targets (CDKN2A, RB1, PTEN, MAP2K4, NF1, SMAD4, and LINC00290). Downstream analysis of pooled CRISPR/Cas9 data provide further evidence of essentiality. Our results provide further insight into how the deletion landscape is shaped and identify potentially targetable vulnerabilities.

The TP53 Apoptotic Network Is a Primary Mediator of Resistance to BCL2 Inhibition in AML Cells

To study mechanisms underlying resistance to the BCL2 inhibitor venetoclax in acute myeloid leukemia (AML), we used a genome-wide CRISPR/Cas9 screen to identify gene knockouts resulting in drug resistance. We validated TP53, BAX, and PMAIP1 as genes whose inactivation results in venetoclax resistance in AML cell lines. Resistance to venetoclax resulted from an inability to execute apoptosis driven by BAX loss, decreased expression of BCL2, and/or reliance on alternative BCL2 family members such as BCL2L1. The resistance was accompanied by changes in mitochondrial homeostasis and cellular metabolism. Evaluation of TP53 knockout cells for sensitivities to a panel of small-molecule inhibitors revealed a gain of sensitivity to TRK inhibitors. We relate these observations to patient drug responses and gene expression in the Beat AML dataset. Our results implicate TP53, the apoptotic network, and mitochondrial functionality as drivers of venetoclax response in AML and suggest strategies to overcome resistance. SIGNIFICANCE: AML is challenging to treat due to its heterogeneity, and single-agent therapies have universally failed, prompting a need for innovative drug combinations. We used a genetic approach to identify genes whose inactivation contributes to drug resistance as a means of forming preferred drug combinations to improve AML treatment.See related commentary by Savona and Rathmell, p. 831.This article is highlighted in the In This Issue feature, p. 813.

USP7 deubiquitinates and stabilizes NOTCH1 in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is a highly aggressive leukemia that is primarily caused by aberrant activation of the NOTCH1 signaling pathway. Recent studies have revealed that posttranslational modifications, such as ubiquitination, regulate NOTCH1 stability, activity, and localization. However, the specific deubiquitinase that affects NOTCH1 protein stability remains unestablished. Here, we report that ubiquitin-specific protease 7 (USP7) can stabilize NOTCH1. USP7 deubiquitinated NOTCH1 in vivo and in vitro, whereas knockdown of USP7 increased the ubiquitination of NOTCH1. USP7 interacted with NOTCH1 protein in T-ALL cells, and the MATH and UBL domains of USP7 were responsible for this interaction. Depletion of USP7 significantly suppressed the proliferation of T-ALL cells in vitro and in vivo, accompanied by downregulation of the NOTCH1 protein level. Similarly, pharmacologic inhibition of USP7 led to apoptosis of T-ALL cells. More importantly, we found that USP7 was significantly upregulated in human T-ALL cell lines and patient samples, and a USP7 inhibitor exhibited cell cytotoxicity toward primary T-ALL cells, indicating the clinical relevance of these findings. Overall, our results demonstrate that USP7 is a novel deubiquitinase that stabilizes NOTCH1. Therefore, USP7 may be a promising therapeutic target in the currently incurable T-ALL.

Inhibiting the protein ubiquitin-specific protease 7 (USP-7) may offer a treatment option for patients with T-cell acute lymphoblastic leukemia (T-ALL), an incurable and aggressive cancer. T-ALL is primarily caused by aberrant activation of the protein NOTCH1, which regulates gene expression relating to cell survival, proliferation, and metastasis. Ying-Li Wu, from China’s Shanghai Jiao Tong University School of Medicine, and a team of researchers report that, in their experiments, USP-7 prevented the breakdown of NOTCH1 by removing the protein tag that would normally signal it for degradation. In addition, USP-7 expression was upregulated in all human T-ALL cells and samples tested. Inhibition of USP-7 suppressed the proliferation of T-ALL cells in vitro and in vivo. These results reveal the role of USP-7 in the pathophysiology of T-ALL and offer USP-7 as a promising potential therapeutic target.

The diverse role of TIGAR in cellular homeostasis and cancer

TP53-induced glycolysis and apoptosis regulator (TIGAR) is a p53 target protein that plays critical roles in glycolysis and redox balance. Accumulating evidence shows that TIGAR is highly expressed in cancer. TIGAR redirects glycolysis and promotes carcinoma growth by providing metabolic intermediates and reductive power derived from pentose phosphate pathway (PPP). The expression of TIGAR in cancer is positively associated with chemotherapy resistance, suggesting that TIGAR could be a novel therapeutic target. In this review, we briefly presented the function of TIGAR in metabolic homeostasis in normal and cancer cells. Finally, we discussed the future directions of TIGAR research in cancer.

Fructose 2,6-Bisphosphate in Cancer Cell Metabolism

For a long time, pioneers in the field of cancer cell metabolism, such as Otto Warburg, have focused on the idea that tumor cells maintain high glycolytic rates even with adequate oxygen supply, in what is known as aerobic glycolysis or the Warburg effect. Recent studies have reported a more complex situation, where the tumor ecosystem plays a more critical role in cancer progression. Cancer cells display extraordinary plasticity in adapting to changes in their tumor microenvironment, developing strategies to survive and proliferate. The proliferation of cancer cells needs a high rate of energy and metabolic substrates for biosynthesis of biomolecules. These requirements are met by the metabolic reprogramming of cancer cells and others present in the tumor microenvironment, which is essential for tumor survival and spread. Metabolic reprogramming involves a complex interplay between oncogenes, tumor suppressors, growth factors and local factors in the tumor microenvironment. These factors can induce overexpression and increased activity of glycolytic isoenzymes and proteins in stromal and cancer cells which are different from those expressed in normal cells. The fructose-6-phosphate/fructose-1,6-bisphosphate cycle, catalyzed by 6-phosphofructo-1-kinase/fructose 1,6-bisphosphatase (PFK1/FBPase1) isoenzymes, plays a key role in controlling glycolytic rates. PFK1/FBpase1 activities are allosterically regulated by fructose-2,6-bisphosphate, the product of the enzymatic activity of the dual kinase/phosphatase family of enzymes: 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase (PFKFB1-4) and TP53-induced glycolysis and apoptosis regulator (TIGAR), which show increased expression in a significant number of tumor types. In this review, the function of these isoenzymes in the regulation of metabolism, as well as the regulatory factors modulating their expression and activity in the tumor ecosystem are discussed. Targeting these isoenzymes, either directly or by inhibiting their activating factors, could be a promising approach for treating cancers.

Caffeine Sensitizes U87-MG Human Glioblastoma Cells to Temozolomide through Mitotic Catastrophe by Impeding G2 Arrest

Temozolomide (TMZ) is the first-line chemotherapeutic agent in the treatment of glioblastoma multiforme (GBM). Despite its cytotoxic effect, TMZ also induces cell cycle arrest that may lead to the development of chemoresistance and eventual tumor recurrence. Caffeine, a widely consumed neurostimulant, shows anticancer activities and is reported to work synergistically with cisplatin and camptothecin. The present study aimed to investigate the effects and the mechanisms of action of caffeine used in combination with TMZ in U87-MG GBM cells. As anticipated, TMZ caused DNA damage mediated by the ATM/p53/p21 signaling pathway and induced significant G2 delay. Concurrent treatment with caffeine repressed proliferation and lowered clonogenic capacity on MTT and colony formation assays, respectively. Mechanistic study showed that coadministration of caffeine and TMZ suppressed the phosphorylation of ATM and p53 and downregulated p21 expression, thus releasing DNA-damaged cells from G2 arrest into premature mitosis. Cell cycle analysis demonstrated that the proportion of cells arrested in G2 phase decreased when caffeine was administered together with TMZ; at the same time, the amount of cells with micronucleation and multipolar spindle poles increased, indicative of enhanced mitotic cell death. Pretreatment of cells with caffeine further enhanced mitotic catastrophe development in combined treatment and sensitized cells to apoptosis when followed by TMZ alone. In conclusion, our study demonstrated that caffeine enhanced the efficacy of TMZ through mitotic cell death by impeding ATM/p53/p21-mediated G2 arrest.

Expression of miR-34a in T-Cells Infected by Human T-Lymphotropic Virus 1

Human T-lymphotropic virus 1 (HTLV-1) immortalizes T-cells and is the causative agent of adult T-cell leukemia/lymphoma (ATLL). HTLV-1 replication and transformation are governed by multiple interactions between viral regulatory proteins and host cell factors that remain to be fully elucidated. The present study investigated the impact of HTLV-1 infection on the expression of miR-34a, a microRNA whose expression is downregulated in many types of cancer. Results of RT-PCR assays showed that five out of six HTLV-1-positive cell lines expressed higher levels of miR-34a compared to normal PBMC or purified CD4+ T-cells. ATLL cell line ED, which did not express miR-34a, showed methylation of the miR-34a promoter. Newly infected PBMC and samples from 10 ATLL patients also showed a prominent increase in miR-34a expression compared to PBMC controls. The primary miR-34a transcript expressed in infected cell line C91PL contained binding motifs for NF-κB and p53. Pharmacological inhibition of NF-κB with Bay 11-7082 indicated that this pathway contributes to sustain miR-34a levels in infected cells. Treatment of infected cell lines with the p53 activator nutlin-3a resulted in a further increase in miR-34a levels, thus confirming it as a transcriptional target of p53. Nutlin-3a-treated cells showed downregulation of known miR-34a targets including the deacetylase SIRT1, which was accompanied by increased acetylation of p53, a substrate of SIRT1. Transfection of C91PL cells with a miR-34a mimic also led to downregulation of mRNA targets including SIRT1 as well as the pro-apoptotic factor BAX. Unlike nutlin-3a, the miR-34a mimic did not cause cell cycle arrest or reduce cell viability. On the other hand, sequestration of miR-34a with a sponge construct resulted in an increase in death of C91PL cells. These findings provide evidence for a functional role for miR-34a in fine-tuning the expression of target genes that influence the turnover of HTLV-1-infected cells.

p53 and metabolism: from mechanism to therapeutics

The tumor cell changes itself and its microenvironment to adapt to different situations, including action of drugs and other agents targeting tumor control. Therefore, metabolism plays an important role in the activation of survival mechanisms to keep the cell proliferative potential. The Warburg effect directs the cellular metabolism towards an aerobic glycolytic pathway, despite the fact that it generates less adenosine triphosphate than oxidative phosphorylation; because it creates the building blocks necessary for cell proliferation. The transcription factor p53 is the master tumor suppressor; it binds to more than 4,000 sites in the genome and regulates the expression of more than 500 genes. Among these genes are important regulators of metabolism, affecting glucose, lipids and amino acids metabolism, oxidative phosphorylation, reactive oxygen species (ROS) generation and growth factors signaling. Wild-type and mutant p53 may have opposing effects in the expression of these metabolic genes. Therefore, depending on the p53 status of the cell, drugs that target metabolism may have different outcomes and metabolism may modulate drug resistance. Conversely, induction of p53 expression may regulate differently the tumor cell metabolism, inducing senescence, autophagy and apoptosis, which are dependent on the regulation of the PI3K/AKT/mTOR pathway and/or ROS induction. The interplay between p53 and metabolism is essential in the decision of cell fate and for cancer therapeutics.

Protein-protein interaction networks and different clustering analysis in Burkitt's lymphoma

OBJECTIVE

Burkitt's lymphoma (BL) is a highly aggressive malignant lymphoma, its molecular biological mechanism has not been fully investigated. The construction of protein-protein interaction (PPI) networks and the identification of complexes through a cluster analysis are important research directions in the post-genome era. However, different cluster analysis algorithms have their own characteristics, and a single analysis has some limitations. In this study, we obtained the target and pathway information of BL using different clustering analyses.

MATERIAL AND METHODS

First, we obtained 50 BL genes by screening the Online Mendelian Inheritance in Man (OMIM) database; their related genes were further extracted from the literature. The PPI network was constructed with the Search Tool for Retrieval of Interacting Genes/Proteins (STRING). Afterward, the interaction data were input in Cytoscape3.4.0 software and related plug-ins were used to implement topology analysis and clustering analysis. Functional analysis based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database were used to characterize the biological importance of the clusters.

RESULTS

We constructed a PPI network consisting of 459 nodes (proteins) and 1399 sides (interactions), 12 genes and 8 signaling pathways were found to be closely related to BL.

CONCLUSION

In this study, the use of combined algorithms to analyse gene interactions provides a new perspective for network-based analysis. The results of this study reveal new insights into the molecular mechanisms underlying BL, which may be novel therapeutic targets for disease management and may provide a bioinformatic basis for the further understanding of BL.

The IGF-1R/AKT pathway has opposing effects on Nutlin-3a-induced apoptosis

Nutlin-3a is a small molecule MDM2 antagonist and potent activator of wild-type p53. Nutlin-3a disrupts MDM2 binding to p53, thus increasing p53 levels and allowing p53 to inhibit proliferation or induce cell death. Factors that control sensitivity to Nutlin-3a-induced apoptosis are incompletely understood. In this study we isolated cisplatin-resistant clones from MHM cells, an MDM2-amplified and p53 wild-type osteosarcoma cell line. Cisplatin resistance in these clones resulted in part from heightened activation of the IGF-1R/AKT pathway. Interestingly, these cisplatin resistant clones showed hyper-sensitivity to Nutlin-3a induced apoptosis. Increased Nutlin-3a sensitivity was associated with reduced authophagy flux and a greater increase in p53 levels in response to Nutlin-3a treatment. IGF-1R and AKT inhibitors further increased apoptosis by Nutlin-3a in parental MHM cells and the cisplatin-resistant clones, confirming IGF-1R/AKT signaling promotes apoptosis resistance. However, IGF-1R and AKT inhibitors also reduced p53 accumulation in Nutlin-3a treated cells and increased autophagy flux, which we showed can promote apoptosis resistance. We conclude the IGF-1R/AKT pathway has opposing effects on Nutlin-3a-induced apoptosis. First, it can inhibit apoptosis, consistent with its well-established role as a survival-signaling pathway. Second, it can enhance Nutlin-3a induced apoptosis through a combination of maintaining p53 levels and inhibiting pro-survival autophagy.

cMyc-p53 feedback mechanism regulates the dynamics of T lymphocytes in the immune response

Activation and proliferation of T cells are tightly regulated during the immune response. We show here that kinetics of proliferation of PHA activated T cells follows the expression of cMyc. Expression of p53 is also elevated and remains high several days after activation. To investigate the role of p53 in activated T cells, its expression was further elevated with nultin-3 treatment, a small molecule that dissociates the E3 ubiquitin protein ligase MDM2 from p53. Concomitantly, cMyc expression and proliferation decreased. At the other end of the cMyc-p53 axis, inhibition of cMyc with 10058-F4 led to down regulation of p53, likely through the lower level of cMyc induced p14ARF, which is also known to dissociate the p53-MDM2 complex. Both compounds induced cell cycle arrest and apoptosis. We conclude that the feedback regulation between cMyc and p53 is important for the T cell homeostasis. We also show that the two compounds modulating p53 and cMyc levels inhibited proliferation without abolishing the cytotoxic function, thus demonstrating the dichotomy between proliferation and cytotoxicity in activated T cells.

The cellular senescence of leukemia-initiating cells from acute lymphoblastic leukemia is postponed by β-Arrestin1 binding with P300-Sp1 to regulate hTERT transcription

Although we previously reported that the self-renewal of leukemia-initiating cells of B-lineage acute lymphoblastic leukemia (B-ALL LICs) was regulated by β-Arrestin1, a multiple-function protein, the cellular senescence is critical for LICs fate and leukemia progress, and worthy for further investigation. Here we found that depletion of β-Arrestin1 extended the population doubling time and the percentage of senile cells, the signatures of cellular senescence, of B-ALL LICs. Moreover, lack of β-Arrestin1 enhanced the expression of proteins (CBX, HIRA) and genes (P53, P16) related to senescence in leukemic Reh cells and B-ALL-LICs-derived leukemic mice. Further results showed that loss of β-Arrestin1 induced senescence of Reh cells through mediating hTERT-telomerase-telomere axis, which was reversed by BIBR1532, the telomerase activity inhibitor. Importantly, depletion of β-Arrestin1 decreased the binding of Sp1 to hTERT promoter at the region of −28 to −36 bp. The anti-sense oligonucleotide of this key region downregulated the transcription of hTERT and aggravated the senescence of Reh cells. Further data demonstrated that the depleted β-Arrestin1 reduced the interaction of P300 with Sp1, thus to reduce Sp1 binding to hTERT promoter, downregulate hTERT transcription, decrease telomerase activity, shorten telomere length, and promote Reh cell senescence. Interestingly, the percentage of senile cells in B-ALL LICs was decreased, which was negatively correlated to good prognosis and β-Arrestin1 mRNA expression in childhood B-ALL patients. Our study shed a light on the senescence of B-ALL LICs and is regulated by β-Arrestin1, providing the potential therapeutic target of leukemia by promoting cellular senescence with a key region of hTERT promoter.

The IGF-1R/AKT pathway determines cell fate in response to p53

p53 that is activated in response to DNA-damaging stress can induce apoptosis or either transient or permanent cell cycle arrests. Apoptosis and permanent cell cycle arrest (senescence) are bona-fide tumor suppressor mechanisms through which p53 inhibits cancer cell survival. In contrast, transient cell cycle arrests induced by p53 can increase survival by allowing cells time to repair their DNA before proceeding with cell division. Mechanisms that control the choice of response to p53 (apoptosis vs arrest) are not fully understood. There is abundant crosstalk between p53 and the IGF-1R/AKT/mTORC1 signaling pathway. Recent studies indicate this crosstalk can determine the choice of response to p53. These findings have clear implications for the potential use of IGF-1R pathway inhibitors against p53 wild-type or p53-null or mutant cancers.

New mouse model of acute adult T-cell leukemia generated by transplantation of AKT, BCLxL, and HBZ-transduced T cells

Adult T‐cell leukemia/lymphoma (ATL) develops in human T‐cell leukemia virus type 1 (HTLV‐1) carriers. Although the HTLV‐1‐encoded HBZ gene is critically involved, HBZ alone is insufficient and additional, cooperative “hits” are required for the development of ATL. Candidate cooperative hits are being defined, but methods to rapidly explore their roles in ATL development in collaboration with HBZ are lacking. Here, we present a new mouse model of acute type ATL that can be generated rapidly by transplanting in vitro‐induced T cells that have been retrovirally transduced with HBZ and two cooperative genes, BCLxL and AKT, into mice. Co‐transduction of HBZ and BCLxL/AKT allowed these T cells to grow in vitro in the absence of cytokines (Flt3‐ligand and interleukin‐7), which did not occur with any two‐gene combination. Although transplanted T cells were a mixture of cells transduced with different combinations of the genes, tumors that developed in mice were composed of HBZ/BCLxL/AKT triply transduced T cells, showing the synergistic effect of the three genes. The genetic/epigenetic landscape of ATL has only recently been elucidated, and the roles of additional “hits” in ATL pathogenesis remain to be explored. Our model provides a versatile tool to examine the roles of these hits, in collaboration with HBZ, in the development of acute ATL.

Induction of apoptosis by HBI-8000 in adult T-cell leukemia/lymphoma is associated with activation of Bim and NLRP3

Adult T‐cell leukemia/lymphoma (ATL) is an aggressive T‐cell malignancy caused by human T‐cell lymphotropic virus 1. Treatment options for acute ATL patients include chemotherapy, stem cell transplantation, and recently the anti‐chemokine (C‐C motif) receptor 4 antibody, although most patients still have a poor prognosis and there is a clear need for additional options. HBI‐8000 is a novel oral histone deacetylase inhibitor with proven efficacy for treatment of T‐cell lymphomas that recently received approval in China. In the present study, we evaluated the effects of HBI‐8000 on ATL‐derived cell lines and primary cells obtained from Japanese ATL patients. In most cases HBI‐8000 induced apoptosis in both primary ATL cells and cell lines. In addition, findings obtained with DNA microarray suggested Bim activation and, interestingly, the contribution of the NLR family, pyrin domain containing 3 (NLRP3) inflammasome pathway in HBI‐8000‐induced ATL cell death. Further investigations using siRNAs confirmed that Bim contributes to HBI‐8000‐induced apoptosis. Our results provide a rationale for a clinical investigation of the efficacy of HBI‐8000 in patients with ATL. Although the role of NLRP3 inflammasome activation in ATL cell death remains to be verified, HBI‐8000 may be part of a novel therapeutic strategy for cancer based on the NLRP3 pathway.

CPUY201112, a novel synthetic small-molecule compound and inhibitor of heat shock protein Hsp90, induces p53-mediated apoptosis in MCF-7 cells

Heat-shock protein 90 (Hsp90) is highly expressed in many tumor cells and is associated with the maintenance of malignant phenotypes. Targeting Hsp90 has had therapeutic success in both solid and hematological malignancies, which has inspired more studies to identify new Hsp90 inhibitors with improved clinical efficacy. Using a fragment-based approach and subsequent structural optimization guided by medicinal chemistry principles, we identified the novel compound CPUY201112 as a potent Hsp90 inhibitor. It binds to the ATP-binding pocket of Hsp90 with a kinetic dissociation (K_d) constant of 27 ± 2.3 nM. It also exhibits potent in vitro antiproliferative effects in a range of solid tumor cells. In MCF-7 cells with high Hsp90 expression, CPUY201112 induces the degradation of Hsp90 client proteins including HER-2, Akt, and c-RAF. We prove that treating MCF-7 cells with CPUY201112 results in cell cycle arrest and apoptosis through the wild-type (wt) p53 pathway. CPUY201112 also synergizes with Nutlin-3a to induce cancer cell apoptosis. CPUY201112 significantly inhibited the growth of MCF-7 xenografts in nude mice without apparent body weight loss. These results demonstrate that CPUY201112 is a novel Hsp90 inhibitor with potential use in treating wild-type p53 related cancers.

Heat shock protein 90 inhibitor NVP-AUY922 exerts potent activity against adult T-cell leukemia-lymphoma cells

Adult T-cell leukemia–lymphoma (ATL), an aggressive neoplasm etiologically associated with HTLV-1, is a chemoresistant malignancy. Heat shock protein 90 (HSP90) is involved in folding and functions as a chaperone for multiple client proteins, many of which are important in tumorigenesis. In this study, we examined NVP-AUY922 (AUY922), a second generation isoxazole-based non-geldanamycin HSP90 inhibitor, and confirmed its effects on survival of ATL-related cell lines. Analysis using FACS revealed that AUY922 induced cell-cycle arrest and apoptosis; it also inhibited the growth of primary ATL cells, but not of normal PBMCs. AUY922 caused strong upregulation of HSP70, a surrogate marker of HSP90 inhibition, and a dose-dependent decrease in HSP90 client proteins associated with cell survival, proliferation, and cell cycle in the G₁ phase, including phospho-Akt, Akt, IKKα, IKKβ, IKKγ, Cdk4, Cdk6, and survivin. Interestingly, AUY922 induced downregulation of the proviral integration site for Moloney murine leukemia virus (PIM) in ATL cells. The PIM family (PIM-1, -2, -3) is made up of oncogenes that encode a serine/threonine protein kinase family. As PIM kinases have multiple functions involved in cell proliferation, survival, differentiation, apoptosis, and tumorigenesis, their downregulation could play an important role in AUY922-induced death of ATL cells. In fact, SGI-1776, a pan-PIM kinase inhibitor, successfully inhibited the growth of primary ATL cells as well as ATL-related cell lines. Our findings suggest that AUY922 is an effective therapeutic agent for ATL, and PIM kinases may be a novel therapeutic target.

Combination of 9-aminoacridine with Campath-1H provides effective therapy for a murine model of adult T-cell leukemia

BACKGROUND

Adult T-cell leukemia/lymphoma (ATL) is an aggressive malignancy of CD4+CD25+ lymphocytes caused by human T-cell lymphotropic virus type 1. While much progress has been made in understanding the mechanisms of cellular dysregulation, the prognosis for aggressive ATL still remains poor. Therefore, new therapeutic approaches need to be developed.

RESULTS

Previously, we demonstrated that the viral protein Tax inactivates p53 in HTLV-1-infected T-cells. Here we show that 9-aminoacridine (9AA) through p53 reactivation and NF-κB inhibition has selective toxicity for infected leukemic cells independent of their p53 status. We further demonstrate that 9AA activates caspase-3/7 resulting in PARP cleavage. Next we investigated the efficacy of 9AA in the MET-1 ATL model. Alone, 9AA did not cause significant drops in surrogate tumor markers, soluble IL-2Rα or β2-micorglobulin (β2μ) levels with only a slight increase in survival of MET-1-bearing mice. However, in combination with Campath-1H, 9AA treatment resulted in low soluble IL-2Rα and β2μ levels at 2 and 4 weeks. Consistent with reduced tumor cell burden, combination treatment significantly increased survival of MET-1-bearing mice compared to mice treated with either drug alone. Splenic cells isolated from 9AA or combination treated mice showed increased p53 protein levels and transcriptional activity. Consistent with increased tumor suppressor activity, we found increased PARP-1 cleavage in 9AA and combination treated cells.

CONCLUSION

Our results indicate that targeting reactivation of p53 and inhibition of NF-κB with acridine-derivatives in combination with other chemotherapeutics could result in increased efficacy and selective killing of tumor cells.

TIGAR, TIGAR, burning bright

Cancers cells shift their metabolism towards glycolysis in order to help them support the biosynthetic demands necessary to sustain cell proliferation and growth, adapt to stress and avoid excessive reactive oxygen species (ROS) accumulation. While the p53 tumor suppressor protein is known to inhibit cell growth by inducing apoptosis, senescence and cell cycle arrest, recent studies have found that p53 is also able to influence cell metabolism. TIGAR is a p53 target that functions as a fructose-2,6-bisphosphatase, thereby lowering glycolytic flux and promoting antioxidant functions. By protecting cells from oxidative stress, TIGAR may mediate some of the tumor suppressor activity of p53 but could also contribute to tumorigenesis. Here we discuss the activities of TIGAR described so far, and the potential consequences of TIGAR expression on normal and tumor cells.

TIGAR is correlated with maximal standardized uptake value on FDG-PET and survival in non-small cell lung cancer

OBJECTIVE

Evaluation of (18)F-FDG uptake value via PET is central to current methods of diagnosis and staging of non-small cell lung cancer (NSCLC) due to its ability to evaluate expression levels of key regulators associated with glucose metabolism in tumor cells. Tp53-induced glycolysis and apoptosis regulator (TIGAR) is an important P53-induced protein that can inhibit glycolysis; however, there have been few clinical studies on its mechanism. Here we have investigated the relationship between TIGAR expression and (18)F-FDG PET in tumors, along with its relationship with the clinical characteristics of NSCLC.

METHODS

We analyzed SUVmax in 79 patients with NSCLC through immunohistochemical staining of TIGAR and five other biological markers associated with tumor cell glycolysis, in order to evaluate the correlation between their expression and SUVmax. We also plotted Kaplan-Meier survival curves to assess TIGAR expression with the prognosis and survival of patients with NSCLC.

RESULTS

The key findings were as follows: SUVmax was negatively correlated with the expression of TIGAR (r = -0.31, p<0.01); TIGAR expression was correlated with tumor size (p = 0.01), histological type (p<0.01), differentiation degree (p<0.01) and lymph node metastasis(p<0.01) in patients with NSCLC; and the survival time of patients whose TIGAR was negatively expressed was significantly shorter than for those whose TIGAR was positively expressed (P = 0.023).

CONCLUSIONS

The expression of TIGAR in primary tumors is significantly correlated with SUVmax, and low expression of TIGAR may predict a worse clinical outcome in patients with NSCLC.

Oral administration of an HSP90 inhibitor, 17-DMAG, intervenes tumor-cell infiltration into multiple organs and improves survival period for ATL model mice

In the peripheral blood leukocytes (PBLs) from the carriers of the human T-lymphotropic virus type-1 (HTLV-1) or the patients with adult T-cell leukemia (ATL), nuclear factor kappaB (NF-κB)-mediated antiapoptotic signals are constitutively activated primarily by the HTLV-1-encoded oncoprotein Tax. Tax interacts with the I κB kinase regulatory subunit NEMO (NF-κB essential modulator) to activate NF-κB, and this interaction is maintained in part by a molecular chaperone, heat-shock protein 90 (HSP90), and its co-chaperone cell division cycle 37 (CDC37). The antibiotic geldanamycin (GA) inhibits HSP90's ATP binding for its proper interaction with client proteins. Administration of a novel water-soluble and less toxic GA derivative, 17-dimethylaminoethylamino-17-demethoxygeldanamycin hydrochloride (17-DMAG), to Tax-expressing ATL-transformed cell lines, C8166 and MT4, induced significant degradation of Tax. 17-DMAG also facilitated growth arrest and cellular apoptosis to C8166 and MT4 and other ATL cell lines, although this treatment has no apparent effects on normal PBLs. 17-DMAG also downregulated Tax-mediated intracellular signals including the activation of NF-κB, activator protein 1 or HTLV-1 long terminal repeat in Tax-transfected HEK293 cells. Oral administration of 17-DMAG to ATL model mice xenografted with lymphomatous transgenic Lck-Tax (Lck proximal promoter-driven Tax transgene) cells or HTLV-1-producing tumor cells dramatically attenuated aggressive infiltration into multiple organs, inhibited de novo viral production and improved survival period. These observations identified 17-DMAG as a promising candidate for the prevention of ATL progression.

A model of sensitivity and resistance to histone deacetylase inhibitors in diffuse large B cell lymphoma: Role of cyclin-dependent kinase inhibitors

Diffuse large B cell lymphoma (DLBCL) is an aggressive form of non-Hodgkin lymphoma. While the initial treatment strategy is highly effective, relapse occurs in 40% of cases. Histone deacetylase inhibitors (HDACi) are a promising class of anti-cancer drugs but their single agent efficacy against relapsed DLBCL has been variable, ranging from few complete/partial responses to some stable disease. However, most patients showed no response to HDACi monotherapy for unknown reasons. Here we show that sensitivity and resistance to the hydroxamate HDACi, PXD101, can be modeled in DLBCL cell lines. Sensitivity is characterized by G₂/M arrest and apoptosis and resistance by reversible G₁ growth arrest. These responses to PXD101 are independent of several negative prognostic indicators such as DLBCL subtype, BCL2 and MYC co-expression, and p53 mutation, suggesting that HDACi might be used effectively against highly aggressive DLBCL tumors if they are combined with other therapeutics that overcome HDACi resistance. Our investigation of mechanisms underlying HDACi resistance showed that cyclin-dependent kinase inhibitors (CKIs), p21 and p27, are upregulated by PXD101 in a sustained fashion in resistant cell lines concomitant with decreased activity of the cyclin E/cdk2 complex and decreased Rb phosphorylation. PXD101 treatment results in increased association of CKI with the cyclin E/cdk2 complex in resistant cell lines but not in a sensitive line, indicating that the CKIs play a key role in G₁ arrest. The results suggest several treatment strategies that might increase the efficacy of HDACi against aggressive DLBCL.

Nutlin-3, a small-molecule MDM2 inhibitor, sensitizes Caki cells to TRAIL-induced apoptosis through p53-mediated PUMA upregulation and ROS-mediated DR5 upregulation

Nutlin-3 is a novel small-molecule antagonist of the human homolog of mouse double minute (MDM2) that binds MDM2 in the p53-binding pocket and activates the p53 signaling pathway. In this study, we show that nutlin-3 sensitizes Caki human renal cancer cells, but not normal human skin fibroblast (HSF) cells or human mesangial cells, to TRAIL-mediated apoptosis. Combined treatment with nutlin-3 and TRAIL markedly induces apoptosis in HCT116 cells (p53 wild type), but not in HCT116 p53-/- cells, suggesting that p53 is critical for the sensitizing effect of nutlin-3 on TRAIL-induced apoptosis. Pretreatment with N-acetylcysteine (NAC) significantly inhibited nutlin-3-induced DR5 upregulation and cell death induced by the combined treatment with nutlin-3 and TRAIL, suggesting that reactive oxygen species (ROS) mediate nutlin-3-induced DR5 upregulation, which contributes toward TRAIL-mediated apoptosis. However, the upregulation of the p53-mediated protein p53 upregulated modulator of apoptosis (PUMA) by nutlin-3 is likely to be ROS independent because antioxidants failed to block PUMA upregulation. Interestingly, a combined treatment with NAC and PUMA small interfering RNAs significantly blocks nutlin-3-induced and TRAIL-induced apoptosis. Therefore, the present study shows that nutlin-3 enhances TRAIL-induced apoptosis in human renal cancer cells by ROS-mediated or p53-mediated DR5 upregulation and p53-induced PUMA upregulation. These results may offer a novel therapeutic approach to TRAIL-based cancer therapy.

Targeting p53 by small molecules in hematological malignancies

p53 is a powerful tumor suppressor and is an attractive cancer therapeutic target. A breakthrough in cancer research came from the discovery of the drugs which are capable of reactivating p53 function. Most anti-cancer agents, from traditional chemo- and radiation therapies to more recently developed non-peptide small molecules exert their effects by enhancing the anti-proliferative activities of p53. Small molecules such as nutlin, RITA, and PRIMA-1 that can activate p53 have shown their anti-tumor effects in different types of hematological malignancies. Importantly, nutlin and PRIMA-1 have successfully reached the stage of phase I/II clinical trials in at least one type of hematological cancer. Thus, the pharmacological activation of p53 by these small molecules has a major clinical impact on prognostic use and targeted drug design. In the current review, we present the recent achievements in p53 research using small molecules in hematological malignancies. Anticancer activity of different classes of compounds targeting the p53 signaling pathway and their mechanism of action are discussed. In addition, we discuss how p53 tumor suppressor protein holds promise as a drug target for recent and future novel therapies in these diseases.

Molecular hallmarks of adult T cell leukemia

The molecular hallmarks of adult T cell leukemia (ATL) comprise outstanding deregulations of signaling pathways that control the cell cycle, resistance to apoptosis, and proliferation of leukemic cells, all of which have been identified by early excellent studies. Nevertheless, we are now confronted the therapeutic difficulties of ATL that is a most aggressive T cell leukemia/lymphoma. Using next-generation strategies, emerging molecular characteristics such as specific surface markers and an additional catalog of signals affecting the fate of leukemic cells have been added to the molecular hallmarks that constitute an organizing principle for rationalizing the complexities of ATL. Although human T cell leukemia virus type 1 is undoubtedly involved in ATL leukemogenesis, most leukemic cells do not express the viral protein Tax. Instead, cellular gene expression changes dominate homeostasis disorders of infected cells and characteristics of ATL. In this review, we summarize the state of the art of ATL molecular pathology, which supports the biological properties of leukemic cells. In addition, we discuss the recent discovery of two molecular hallmarks of potential generality; an abnormal microRNA pattern and epigenetic reprogramming, which strongly involve the imbalance of the molecular network of lymphocytes. Global analyses of ATL have revealed the functional impact of crosstalk between multifunctional pathways. Clinical and biological studies on signaling inhibitory agents have also revealed novel oncogenic drivers that can be targeted in future. ATL cells, by deregulation of such pathways and their interconnections, may become masters of their own destinies. Recognizing and understanding of the widespread molecular applicability of these concepts will increasingly affect the development of novel strategies for treating ATL.

Novel therapeutic approaches for acute lymphoblastic leukemia

Therapy for ALL in adults remains a tremendous challenge for clinicians. The use of pediatric-intensive regimens in young and middle-aged adults shows promise in improving outcomes. The addition of monoclonal antibody therapy to chemotherapy appears to hold great promise in lessening relapse rates. The anti-CD20 antibody, rituximab, which has been of such benefit in patients with non-Hodgkin lymphoma, now seems poised to bring significant benefit to adults with ALL. Other monoclonal antibody approaches are in earlier stages of development, but will likely be of significant benefit. The BiTE antibody, blinatumomab, represents an exciting new approach in this arena. As new molecular abnormalities are identified in ALL, these will certainly become new targets for drug development. The increasing use of MRD testing by molecular or flow cytometric techniques will also be invaluable in further refining prognostication in ALL in helping with the selection of patients most likely to benefit from BMT. Several new small molecules and chemotherapeutic agents will, it is hoped, also find a niche in the therapy for ALL. Early examples including NOTCH1 inhibitors; hypomethylating agents such as decitabine, folic acid, antagonists, flavopiridol, bortezomib, and mTOR inhibitors will all hopefully find a role in the therapy for this challenging disorder. Although many challenges remain, there is hope that the therapy for adults with ALL can make significant progress in the next few years, in comparison with the relative plateau that has been experienced over the last several decades.

Aberrant overexpression of membrane-associated mucin contributes to tumor progression in adult T-cell leukemia/lymphoma cells

Aberrant overexpression of membrane-associated mucin (MUC1) is implicated in the pathogenesis of cancer, particularly of adenocarcinomas. Adult T-cell leukemia/lymphoma (ATL), an aggressive neoplasm etiologically associated with human T-lymphotropic virus type-1 (HTLV-1), exhibits invasive tropism into various organs, resulting in disease progression and resistance to treatment. In the present study, we showed that MUC1 is overexpressed exclusively in cells of ATL among hematological malignancies. Furthermore, increased expression of MUC1 correlated with a poor prognosis, suggesting MUC1 to be a prognostic marker in ATL. Various functional analyses with knockdown experiments using a specific siRNA for MUC1 revealed that MUC1 is involved in cell growth, cell aggregation, and resistance to apoptosis. Although it has been shown that the anti-adhesive properties of MUC1 facilitate migration and metastasis of tumor cells, our findings indicated that MUC1 contributes to cell-cell adhesion. Mucins thus seem to play a role in the pathogenesis and/or progression of ATL.

Targeting p53 as a therapeutic strategy in sensitizing TRAIL-induced apoptosis in cancer cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has been intensively studied as a cancer therapeutic agent due to its unique ability to induce apoptosis in malignant cells but not in normal cells. However, as more human cancer cells are reported to be resistant to TRAIL treatment, it is important to develop new therapeutic strategies to overcome this resistance. p53 is an important tumor suppressor that is widely involved in cellular responses to various stresses. In this mini-review, we aim to provide an overview of the intricate relationship between p53 and the TRAIL-mediated apoptosis pathway, and to summarize the current approaches of targeting p53 as a therapeutic strategy to sensitize TRAIL-induced apoptosis in human cancer cells. Although in some cases TRAIL kills cancer cells in a p53-independent manner, it is believed that in cancers with wild-type and functional p53, targeting p53 may be an important strategy for overcoming TRAIL-resistance in cancer therapy.

TP53 induced glycolysis and apoptosis regulator (TIGAR) knockdown results in radiosensitization of glioma cells

BACKGROUND AND PURPOSE

The TP53 induced glycolysis and apoptosis regulator (TIGAR) functions to lower fructose-2,6-bisphosphate (Fru-2,6-P(2)) levels in cells, consequently decreasing glycolysis and leading to the scavenging of reactive oxygen species (ROS), which correlate with a higher resistance to cell death. The decrease in intracellular ROS levels in response to TIGAR may also play a role in the ability of p53 to protect from the accumulation of genomic lesions. Given these good prospects of TIGAR for metabolic regulation and p53-response modulation, we analyzed the effects of TIGAR knockdown in U87MG and T98G glioblastoma-derived cell lines.

METHODS/RESULTS

After TIGAR-knockdown in glioblastoma cell lines, different metabolic parameters were assayed, showing an increase in Fru-2,6-P(2), lactate and ROS levels, with a concomitant decrease in reduced glutathione (GSH) levels. In addition, cell growth was inhibited without evidence of apoptotic or autophagic cell death. In contrast, a clear senescent phenotype was observed. We also found that TIGAR protein levels were increased shortly after irradiation. In addition, avoiding radiotherapy-triggered TIGAR induction by gene silencing resulted in the loss of capacity of glioblastoma cells to form colonies in culture and the delay of DNA repair mechanisms, based in γ-H2AX foci, leading cells to undergo morphological changes compatible with a senescent phenotype. Thus, the results obtained raised the possibility to consider TIGAR as a therapeutic target to increase radiotherapy effects.

CONCLUSION

TIGAR abrogation provides a novel adjunctive therapeutic strategy against glial tumors by increasing radiation-induced cell impairment, thus allowing the use of lower radiotherapeutic doses.

Pharmacotherapeutic advances in the treatment of acute lymphoblastic leukaemia in adults

Acute lymphoblastic leukaemia (ALL) in adults is a challenging malignancy in that many patients will show evidence of initial chemotherapy responsiveness but will subsequently relapse. The disease is heterogeneous and outcomes vary dramatically depending on the prognostic factors present in an individual patient. An important determinant of outcome is the age of the patient. The stunning success of therapy in paediatric ALL has led to the use of intensive paediatric regimens in adolescents and young adults with what appear to be improved outcomes. For patients who relapse or have high-risk features, blood and marrow transplantation (BMT) continues to play an important role in the therapeutic armamentarium. The use of reduced-intensity conditioning regimens for allogeneic BMT suggests that outcomes may be improved by this approach. Monoclonal antibodies are showing benefit as single agents in the relapsed setting or in combination with chemotherapy in newly diagnosed patients. In recent years, several new chemotherapeutic agents have shown promise as single agents and are being incorporated into multi-agent chemotherapy. The development of tyrosine kinase inhibitors for Philadelphia chromosome-positive leukaemias has significantly improved outcomes. The molecular revolution has led to the identification of new aberrant molecular pathways in the pathogenesis of ALL, and drugs targeting these aberrancies are in various stages of development preclinically and clinically. These developments bring the hope that therapeutic outcomes in adult ALL can begin to approach those seen in the paediatric setting.