Novel targeted therapeutics: inhibitors of MDM2, ALK and PARP

USP22 promotes gefitinib resistance and inhibits ferroptosis in non-small cell lung cancer by deubiquitination of MDM2

BACKGROUND

The emergence of chemoresistance markedly compromised the treatment efficiency of human cancer, including non-small cell lung cancer (NSCLC). In the present study, we aimed to explore the effects of ubiquitin-specific peptidase 22 (USP22) and murine double minute 2 (MDM2) in gefitinib resistance in NSCLC.

METHODS

Immunohistochemistry (IHC) assay, quantitative real-time polymerase chain reaction (qRT-PCR) assay and western blot assay were carried out to determine the expression of USP22 and MDM2. Transwell assay and flow cytometry analysis were performed to evaluate cell migration and apoptosis. Cell Counting Kit-8 (CCK-8) assay was employed to assess gefitinib resistance. The phenomenon of ferroptosis was estimated by related commercial kits. The oxidized C11-BODIPY fluorescence intensity by C11-BODIPY staining. The relation between USP22 and MDM2 was analyzed by ubiquitination assay and co-immunoprecipitation (Co-IP) assay.

RESULTS

USP22 was abnormally upregulated in NSCLC tissues and cells, and USP22 silencing markedly repressed NSCLC cell migration and facilitated apoptosis and ferroptosis. Moreover, our results indicated that ferroptosis could enhance the suppressive effect of gefitinib on NSCLC cells. Besides, USP22 overexpression enhanced gefitinib resistance and ferroptosis protection in NSCLC cells. Mechanically, USP22 stabilized MDM2 and regulated MDM2 expression through deubiquitination of MDM2. MDM2 deficiency partially restored the effects of USP22 on gefitinib resistance and ferroptosis in NSCLC cells. Of note, we validated the promotional effect of USP22 on gefitinib resistance in NSCLC in vivo through establishing the murine xenograft model.

CONCLUSION

USP22/MDM2 promoted gefitinib resistance and inhibited ferroptosis in NSCLC, which might offer a novel strategy for overcoming gefitinib resistance in NSCLC.

Advances in designing ternary complexes: Integrating in-silico and biochemical methods for PROTAC optimisation in target protein degradation

Target protein degradation (TPD) is an emerging approach to mitigate disease-causing proteins. TPD contains several strategies, and one of the strategies that gained immersive importance in recent times is Proteolysis Targeting Chimeras (PROTACs); the PROTACs recruit small molecules to induce the poly-ubiquitination of disease-causing protein by hijacking the ubiquitin-proteasome system (UPS) by bringing the E3 ligase and protein of interest (POI) into appropriate proximity. The steps involved in designing and evaluating the PROTACs remain critical in optimising the PROTACs to degrade the POI. It is observed that using in-silico and biochemical methods to study the ternary complexes (TCs) of the POI-PROTAC-E3 ligase is essential to understanding the structural activity, cooperativity, and stability of formed TCs. A better understanding of the above-mentioned leads to an appropriate rationale for designing the PROTACs targeting the disease-causing proteins. In this review, we tried to summarise the approaches used to design the ternary complexes, i.e., in-silico and in-vitro methods, to understand the behaviour of the PROTAC-induced ternary complexes.

A Review on Anaplastic Lymphoma Kinase (ALK) Rearrangements and Mutations: Implications for Gastric Carcinogenesis and Target Therapy

Gastric adenocarcinoma is a complex disease with diverse genetic modifications, including Anaplastic Lymphoma Kinase (ALK) gene changes. The ALK gene is located on chromosome 2p23 and encodes a receptor tyrosine kinase that plays a crucial role in embryonic development and cellular differentiation. ALK alterations can result from gene fusion, mutation, amplification, or overexpression in gastric adenocarcinoma. Fusion occurs when the ALK gene fuses with another gene, resulting in a chimeric protein with constitutive kinase activity and promoting oncogenesis. ALK mutations are less common but can also result in the activation of ALK signaling pathways. Targeted therapies for ALK variations in gastric adenocarcinoma have been developed, including ALK inhibitors that have shown promising results in pre-clinical studies. Future studies are needed to elucidate the ALK role in gastric cancer and to identify predictive biomarkers to improve patient selection for targeted therapy. Overall, ALK alterations are a relevant biomarker for gastric adenocarcinoma treatment and targeted therapies for ALK may improve patients' overall survival.

Predicting the Likelihood of Molecules to Act as Modulators of Protein-Protein Interactions

Targeting protein-protein interactions (PPIs) by small molecule modulators (iPPIs) is an attractive strategy for drug therapy, and some iPPIs have already been introduced into the clinic. Blocking PPIs is however considered to be a more difficult task than inhibiting enzymes or antagonizing receptor activity. In this paper, we examine whether it is possible to predict the likelihood of molecules to act as iPPIs. Using our in-house iterative stochastic elimination (ISE) algorithm, we constructed two classification models that successfully distinguish between iPPIs from the iPPI-DB database and decoy molecules from either the Enamine HTS collection (ISE 1) or the ZINC database (ISE 2). External test sets of iPPIs taken from the TIMBAL database and decoys from Enamine HTS or ZINC were screened by the models: the area under the curve for the receiver operating characteristic curve was 0.85-0.89, and the Enrichment Factor increased from an initial 1 to as much as 66 for ISE 1 and 57 for ISE 2. Screening of the Enamine HTS and ZINC data sets through both models results in a library of ∼1.3 million molecules that pass either one of the models. This library is enriched with iPPI candidates that are structurally different from known iPPIs, and thus, it is useful for target-specific screenings and should accelerate the discovery of iPPI drug candidates. The entire library is available in Table S6.

Lung adenocarcinoma with an uncommon CCDC85A‐ALK fusion responding to alectinib: A case report

A 55‐year‐old Chinese man with a right lung mass and lymph node metastasis (T4N3M0 IIIB) was diagnosed with lung adenocarcinoma after a CT‐guided biopsy. With the wide application of next‐generation sequencing (NGS) in tumour detection, we found a rare CCDC85A‐ALK fusion. The patient received alectinib, which had marked efficacy. This is the first report of a lung adenocarcinoma patient harbouring a new uncommon anaplastic lymphocyte kinase fusion that showed a remarkable response to alectinib. NGS aids in selecting treatment in non‐small cell lung cancer patients.

PARP Inhibitors: An Innovative Approach to the Treatment of Inflammation and Metabolic Disorders in Sepsis

Sepsis is not only a threat to the health of individual patients but also presents a serious epidemiological problem. Despite intensive research, modern sepsis therapy remains based primarily on antimicrobial treatment and supporting the functions of failing organs. Finding a cure for sepsis represents a great and as yet unfulfilled need in modern medicine. Research results indicate that the activity of poly (adenosine diphosphate (ADP)-ribose) polymerase (PARP) may play an important role in the inflammatory response and the cellular metabolic disorders found in sepsis. Mechanisms by which PARP-1 may contribute to inflammation and metabolic disorders include effects on the regulation of gene expression, impaired metabolism, cell death, and the release of alarmins. These findings suggest that inhibition of this enzyme may be a promising solution for the treatment of sepsis. In studies using experimental sepsis models, inhibition of PARP-1 has been shown to ameliorate the inflammatory response and increase survival. This action was described, among others, for olaparib, a PARP-1 inhibitor approved for use in oncology. While the results of current research are promising, the use of PARP inhibitors in non-oncological diseases raises some concerns, mainly related to the enzyme's role in deoxyribonucleic acid (DNA) repair. However, the results of studies on experimental models indicate the effectiveness of even short-term PARP-1 inhibition and do not confirm concerns regarding its impact on the integrity of nuclear DNA. Current research presents PARP inhibition as a potential solution for the treatment of sepsis and indicates the need for further research.

Ubiquitin-proteasome system and the role of its inhibitors in cancer therapy

Despite all the other cells that have the potential to prevent cancer development and metastasis through tumour suppressor proteins, cancer cells can upregulate the ubiquitin–proteasome system (UPS) by which they can degrade tumour suppressor proteins and avoid apoptosis. This system plays an extensive role in cell regulation organized in two steps. Each step has an important role in controlling cancer. This demonstrates the importance of understanding UPS inhibitors and improving these inhibitors to foster a new hope in cancer therapy. UPS inhibitors, as less invasive chemotherapy drugs, are increasingly used to alleviate symptoms of various cancers in malignant states. Despite their success in reducing the development of cancer with the lowest side effects, thus far, an appropriate inhibitor that can effectively inactivate this system with the least drug resistance has not yet been fully investigated. A fundamental understanding of the system is necessary to fully elucidate its role in causing/controlling cancer. In this review, we first comprehensively investigate this system, and then each step containing ubiquitination and protein degradation as well as their inhibitors are discussed. Ultimately, its advantages and disadvantages and some perspectives for improving the efficiency of these inhibitors are discussed.

C/EBPβ promotes poly(ADP-ribose) polymerase inhibitor resistance by enhancing homologous recombination repair in high-grade serous ovarian cancer

PARP inhibitors (PARPi) are efficacious in treating high-grade serous ovarian cancer (HG-SOC) with homologous recombination (HR) deficiency. However, they exhibit suboptimal efficiency in HR-proficient cancers. Here, we found that the expression of CCAAT/enhancer-binding protein β (C/EBPβ), a transcription factor, was inversely correlated with PARPi sensitivity in vitro and in vivo, both in HR-proficient condition. High C/EBPβ expression enhanced PARPi tolerance; PARPi treatment in turn induced C/EBPβ expression. C/EBPβ directly targeted and upregulated multiple HR genes (BRCA1, BRIP1, BRIT1, and RAD51), thereby inducing restoration of HR capacity and mediating acquired PARPi resistance. C/EBPβ is a key regulator of the HR pathway and an indicator of PARPi responsiveness. Targeting C/EBPβ could induce HR deficiency and rescue PARPi sensitivity accordingly. Our findings indicate that HR-proficient patients may benefit from PARPi via targeting C/EBPβ, and C/EBPβ expression levels enable predicting and tracking PARPi responsiveness during treatment.

IU1 suppresses proliferation of cervical cancer cells through MDM2 degradation

Previous studies have demonstrated that the antitumor potential of IU1 (a pharmacological compound), which was mediated by selective inhibition of proteasome-associated deubiquitinase ubiquitin-specific protease 14 (USP14). However, the underlying molecular mechanisms remain elusive. It has been well established that mdm2 (Murine double minute 2) gene was amplified and/or overexpressed in a variety of human neoplasms, including cervical cancer. Furthermore, MDM2 is critical to cervical cancer development and progression. Relatively studies have reported that USP15 and USP7 stabilized MDM2 protein levels by removing its ubiquitin chain. In the current study, we studied the cell proliferation status after IU1 treatment and the USP14-MDM2 protein interaction in cervical cancer cells. This study experimentally revealed that IU1 treatment reduced MDM2 protein expression in HeLa cervical cancer cells, along with the activation of autophagy-lysosomal protein degradation and promotion of ubiquitin-proteasome system (UPS) function, thereby blocked G0/G1 to S phase transition, decreased cell growth and triggered cell apoptosis. Thus, these results indicate that IU1 treatment simultaneously targets two major intracellular protein degradation systems, ubiquitin-proteasome and autophagy-lysosome systems, which leads to MDM2 degradation and contributes to the antitumor effect of IU1.

Delivery of Long Non-coding RNA NEAT1 by Peripheral Blood Monouclear Cells-Derived Exosomes Promotes the Occurrence of Rheumatoid Arthritis via the MicroRNA-23a/MDM2/SIRT6 Axis

Emerging evidence has pointed out the importance of long non-coding RNAs (lncRNAs) in multiple diseases, the knowledge of rheumatoid arthritis (RA)-associated lncRNAs remains limited. In this present study, we aimed to elucidate the mechanism of lncRNA nuclear paraspeckle assembly transcript 1 (NEAT1) from peripheral blood monouclear cell (PBMC)-derived exosomes (exos) on RA development by modulating the microRNA-23a (miR-23a)/murine double minute-2 (MDM2)/Sirtuin 6 (SIRT6) axis. RA was modeled in vivo by collagen induction in mice and in vitro by exposing fibroblast-like synoviocytes (FLSs) to lipopolysaccharide. Exos were isolated from human or mouse PBMCs, which were then were co-cultured with FLSs. Based on gain- and loss-of-function experiments, the cell proliferation and secretion of inflammatory factors were measured. LncRNA NEAT1 was found to be highly expressed in RA, and PBMCs-derived exos contributed to RA development by delivering lncRNA NEAT1. In lipopolysaccharide-induced FLSs, miR-23a inhibited the expression of MDM2, and overexpression of MDM2 partially rescued the inhibitory effect of miR-23a on FLS proliferation and inflammatory response. Mechanistically, MDM2 ubiquitination degraded SIRT6 in RA. LncRNA NEAT1 shuttled by PBMC-derived exos promoted FLS proliferation and inflammation through regulating the MDM2/SIRT6 axis. Furthermore, in vivo experiments suggested that downregulated lncRNA NEAT1 shuttled by PBMC-derived exos or upregulated miR-23a impeded RA deterioration in mice. This study highlights that lncRNA NEAT1 shuttled by PBMC-derived exos contributes to RA development with the involvement of the miR-23a/MDM2/SIRT6 axis.

Targeted and novel therapy in advanced gastric cancer

The systemic treatment options for advanced gastric cancer (GC) have evolved rapidly in recent years. We have reviewed the recent data of clinical trial incorporating targeted agents, including inhibitors of angiogenesis, human epidermal growth factor receptor 2 (HER2), mesenchymal-epithelial transition, epidermal growth factor receptor, mammalian target of rapamycin, claudin-18.2, programmed death-1 and DNA. Addition of trastuzumab to platinum-based chemotherapy has become standard of care as front-line therapy in advanced GC overexpressing HER2. In the second-line setting, ramucirumab with paclitaxel significantly improves overall survival compared to paclitaxel alone. For patients with refractory disease, apatinib, nivolumab, ramucirumab and TAS-102 have demonstrated single-agent activity with improved overall survival compared to placebo alone. Pembrolizumab has demonstrated more than 50% response rate in microsatellite instability-high tumors, 15% response rate in tumors expressing programmed death ligand 1, and non-inferior outcome in first-line treatment compared to chemotherapy. This review summarizes the current state and progress of research on targeted therapy for advanced GC.

Poly-ADP-ribose polymerases (PARPs) as a therapeutic target in the treatment of selected cancers

Introduction: The implementation of poly-ADP-ribose polymerase (PARP) inhibitors for therapy has created potential treatments for a wide spectrum of malignancies involving DNA damage repair gene abnormalities. PARPs are a group of enzymes that are responsible for detecting and repairing DNA damage and therefore play a key role in maintaining cell function and integrity. PARP inhibitors are drugs that target DNA repair deficiencies. Inhibiting PARP activity in cancer cells causes cell death. Areas covered: This review summarizes the role of PARP inhibitors in the treatment of cancer. We performed a systematic literature search in February 2019 in the electronic databases PubMed and EMBASE. Our search terms were the following: PARP, PARP inhibitors, PARPi, Poly ADP ribose polymerase, cancer treatment. We discuss PARP inhibitors currently being investigated in cancer clinical trials, their safety profiles, clinical resistance, combined therapeutic approaches and future challenges. Expert Opinion: The future could bring novel PARP inhibitors with greater DNA trapping potential, better safety profiles and improved combined therapies involving hormonal, chemo-, radio- or immunotherapies. Progress may afford wider indications for PARP inhibitors in the treatment of cancer and the utilization for cancer prevention in high-risk mutation carriers. Research efforts should focus on identifying novel drugs that target DNA repair deficiencies.

Recent therapeutic trends and promising targets in triple negative breast cancer

Breast cancer accounts for 25% of all types of cancer in women, and triple negative breast cancer (TNBC) comprises around 15~20% of breast cancers. Conventional chemotherapy and radiation are the primary systemic therapeutic strategies; no other FDA-approved targeted therapies are yet available as for TNBC. TNBC is generally characterized by a poor prognosis and high rates of proliferation and metastases. Due to these aggressive features and lack of targeted therapies, numerous attempts have been made to discover viable molecular targets for TNBC. Massive cohort studies, clinical trials, and in-depth analyses have revealed diverse molecular alterations in TNBC; however, controversy exists as to whether many of these changes are beneficial or detrimental in caner progression. Here we review the complicated tumorigenic processes and discuss critical findings and therapeutic trends in TNBC with a focus on promising therapeutic approaches, the clinical trials currently underway, and potent experimental compounds under preclinical and evaluation.

PRMT5 as a druggable target for glioblastoma therapy

Background

In spite of standard multimodal therapy consisting of surgical resection followed by radiation and concurrent chemotherapy, prognosis for glioblastoma (GBM) patients remains poor. The identification of both differentiated and undifferentiated "stem cell like" populations in the tumor highlights the significance of finding novel targets that affect the heterogeneous tumor cell population. Protein arginine methyltransferase 5 (PRMT5) is one such candidate gene whose nuclear expression correlates with poor survival and has been reported to be required for survival of differentiated GBM cells and self-renewal of undifferentiated GBM cells. In the current study we screened the specificity and efficacy of 4 novel PRMT5 inhibitors in the treatment of GBM.

Methods

Efficacies of these inhibitors were screened using an in vitro GBM neurosphere model and an in vivo intracranial zebrafish model of glioma. Standard molecular biology methods were employed to investigate changes in cell cycle, growth, and senescence.

Results

In vitro and in vivo studies revealed that among the 4 PRMT5 inhibitors, treatment of GBM cells with compound 5 (CMP5) mirrored the effects of PRMT5 knockdown wherein it led to apoptosis of differentiated GBM cells and drove undifferentiated primary patient derived GBM cells into a nonreplicative senescent state.

Conclusion

In vivo antitumor efficacy combined with the specificity of CMP5 underscores the importance of developing it for translation.

An evaluation in vitro of the efficacy of nutlin-3 and topotecan in combination with 177Lu-DOTATATE for the treatment of neuroblastoma

Targeted radiotherapy of metastatic neuroblastoma using the somatostatin receptor (SSTR)-targeted octreotide analogue DOTATATE radiolabelled with lutetium-177 (¹⁷⁷Lu-DOTATATE) is a promising strategy. This study evaluates whether its effectiveness may be enhanced by combination with radiosensitising drugs. The growth rate of multicellular tumour spheroids, derived from the neuroblastoma cell lines SK-N-BE(2c), CHLA-15 and CHLA-20, was evaluated following treatment with ¹⁷⁷Lu-DOTATATE, nutlin-3 and topotecan alone or in combination. Immunoblotting, immunostaining and flow cytometric analyses were used to determine activation of p53 signalling and cell death. Exposure to ¹⁷⁷Lu-DOTATATE resulted in a significant growth delay in CHLA-15 and CHLA-20 spheroids, but not in SK-N-BE(2c) spheroids. Nutlin-3 enhanced the spheroid growth delay induced by topotecan in CHLA-15 and CHLA-20 spheroids, but not in SK-N-BE(2c) spheroids. Importantly, the combination of nutlin-3 with topotecan enhanced the spheroid growth delay induced by X-irradiation or by exposure to ¹⁷⁷Lu-DOTATATE. The efficacy of the combination treatments was p53-dependent. These results indicate that targeted radiotherapy of high risk neuroblastoma with ¹⁷⁷Lu-DOTATATE may be improved by combination with the radiosensitising drugs nutlin-3 and topotecan.

A Novel Use of Olaparib for the Treatment of Metastatic Castration-Recurrent Prostate Cancer

Although mortality from prostate cancer has declined over the past 20 years as a result of early detection and treatment, the 5-year survival rate for men with prostate cancer who develop metastatic disease is only 29%. Current treatment options for metastatic castration-recurrent prostate cancer (mCRPC) are associated with toxicity and a limited durable response; therefore, additional lines of efficacious and minimally toxic therapy are needed. Olaparib, a poly(adenosine 5'-diphosphate) ribose polymerase (PARP) inhibitor, received a U.S. Food and Drug Administration breakthrough therapy designation in January 2016 for the treatment of patients with BRCA1/2 or ATM gene-mutated mCRPC based on results of a compelling phase II trial of olaparib in patients with advanced castration-resistant prostate cancer (TOPARP-A). This study found that men with mCRPC and genetic mutations in DNA damage repair genes had an overall response rate of nearly 90% with olaparib treatment. In this review, we describe current therapies for mCRPC, the rationale for anti-PARP therapies, the pharmacology of olaparib for prostate cancer, clinical trials of olaparib for mCRPC, our clinical experience with olaparib for prostate cancer at a comprehensive cancer center, and future directions of olaparib for the treatment of mCRPC. Olaparib may constitute a promising treatment to prolong survival in patients with mCRPC, with an acceptable adverse effect profile. As the role of PARP inhibition in prostate cancer and other malignancies becomes further elucidated, olaparib may be shown to be beneficial for other patient populations.

Ubiquitination: Friend and foe in cancer

Dynamic modulation and posttranslational modification of proteins are tightly controlled biological processes that occur in response to physiological cues. One such dynamic modulation is ubiquitination, which marks proteins for degradation via the proteasome, altering their localization, affecting their activity, and promoting or interfering with protein interactions. Hence, ubiquitination is crucial for a plethora of physiological processes, including cell survival, differentiation and innate and adaptive immunity. Similar to kinases, components of the ubiquitination system are often deregulated, leading to a variety of diseases, such as cancer and neurodegenerative disorders. In a context-dependent manner, ubiquitination can regulate both tumor-suppressing and tumor-promoting pathways in cancer. This review outlines how components of the ubiquitination systems (e.g. E3 ligases and deubiquitinases) act as oncogenes or tumor suppressors according to the nature of their substrates. Furthermore, I interrogate how the current knowledge of the differential roles of ubiquitination in cancer lead to technical advances to inhibit or reactivate the components of the ubiquitination system accordingly.

The novel anticancer agent JNJ-26854165 is active in chronic myeloid leukemic cells with unmutated BCR/ABL and T315I mutant BCR/ABL through promoting proteosomal degradation of BCR/ABL proteins

Chronic myeloid leukemia (CML) is a clonal malignant disease caused by the expression of BCR/ABL. MDM2 (human homolog of the murine double minute-2) inhibitors such as Nutlin-3 have been shown to induce apoptosis in a p53-dependent manner in CML cells and sensitize cells to Imatinib. Here, we demonstrate that JNJ-26854165, an inhibitor of MDM2, inhibits proliferation and triggers cell death in a p53-independent manner in various BCR/ABL-expressing cells, which include primary leukemic cells from patients with CML blast crisis and cells expressing the Imatinib-resistant T315I BCR/ABL mutant. The response to JNJ-26854165 is associated with the downregulation of BCR/ABL dependently of proteosome activation. Moreover, in all tested CML cells, with the exception of T315I mutation cells, combining JNJ-26854165 and tyrosine kinase inhibitor (TKI) Imatinib or PD180970 leads to a synergistic effect. In conclusion, our results suggest that JNJ-26854165, used either alone or in combination with TKIs, represents a promising novel targeted approach to overcome TKI resistance and improve patient outcome in CML.

Gene mutations and actionable genetic lesions in mantle cell lymphoma

Mutations and epigenetic alterations are key events in transforming normal cells to cancer cells. Mantle cell lymphoma (MCL), a non-Hodgkin's lymphoma of the B-cell, is an aggressive malignancy with poor prognosis especially for those patients who are resistant to the frontline drugs. There is a great need to describe the molecular basis and mechanism of drug resistance in MCL to develop new strategies for treatment. We reviewed frequent somatic mutations and mutations involving the B-cell pathways in MCL and discussed clinical trials that attempted to disrupt these gene pathways and/or epigenetic events. Recurrent gene mutations were discussed in the light of prognostic and therapeutic opportunity and also the challenges of targeting these lesions. Mutations in the ATM, CCND1, TP53, MLL2, TRAF2 and NOTCH1 were most frequently encountered in mantle cell lymphoma. Translational models should be built that would assess mutations longitudinally to identify important compensatory, pro-survival and anti-apoptic pathways and actionable genetic targets.

Pre-clinical efficacy and synergistic potential of the MDM2-p53 antagonists, Nutlin-3 and RG7388, as single agents and in combined treatment with cisplatin in ovarian cancer

Ovarian cancer is the fifth leading cause of cancer-related female deaths. Due to serious side effects, relapse and resistance to standard chemotherapy, better and more targeted approaches are required. Mutation of the TP53 gene accounts for 50% of all human cancers. In the remaining malignancies, non-genotoxic activation of wild-type p53 by small molecule inhibition of the MDM2-p53 binding interaction is a promising therapeutic strategy. Proof of concept was established with the cis-imidazoline Nutlin-3, leading to the development of RG7388 and other compounds currently in early phase clinical trials. This preclinical study evaluated the effect of Nutlin-3 and RG7388 as single agents and in combination with cisplatin in a panel of ovarian cancer cell lines. Median-drug-effect analysis showed Nutlin-3 or RG7388 combination with cisplatin was additive to, or synergistic in a p53-dependent manner, resulting in increased p53 activation, cell cycle arrest and apoptosis, associated with increased p21^WAF1 protein and/or caspase-3/7 activity compared to cisplatin alone. Although MDM2 inhibition activated the expression of p53-dependent DNA repair genes, the growth inhibitory and pro-apoptotic effects of p53 dominated the response. These data indicate that combination treatment with MDM2 inhibitors and cisplatin has synergistic potential for the treatment of ovarian cancer, dependent on cell genotype.

Targeting NAD+ in Metabolic Disease: New Insights Into an Old Molecule

Nicotinamide adenine dinucleotide (NAD+) is an established cofactor for enzymes serving cellular metabolic reactions. More recent research identified NAD+ as a signaling molecule and substrate for sirtuins and poly-adenosine 5'-diphosphate polymerases; enzymes that regulate protein deacetylation and DNA repair, and translate changes in energy status into metabolic adaptations. Deranged NAD+ homeostasis and concurrent alterations in mitochondrial function are intrinsic in metabolic disorders, such as type 2 diabetes, nonalcoholic fatty liver, and age-related diseases. Contemporary NAD+ precursors show promise as nutraceuticals to restore target tissue NAD+ and have demonstrated the ability to improve mitochondrial function and sirtuin-dependent signaling. This review discusses the accumulating evidence for targeting NAD+ metabolism in metabolic disease, maps the different strategies for NAD+ boosting, and addresses the challenges and open questions in the field. The health potential of targeting NAD+ homeostasis will inform clinical study design to identify nutraceutical approaches for combating metabolic disease and the unwanted effects of aging.

Aminoguanidine pretreatment prevents methotrexate-induced small intestinal injury in the rat by attenuating nitrosative stress and restoring the activities of vital mitochondrial enzymes

BACKGROUND

One of the major toxic side effects of methotrexate (MTX) is enterocolitis, for which there is no efficient standard treatment. Nitric oxide overproduction has been reported to play an important role in MTX-induced mucositis. This study was designed to investigate whether pretreatment with aminoguanidine (AG) - a selective iNOS inhibitor - prevents MTX-induced mucositis in rats.

METHODS

Rats were pretreated with AG (30 and 50 mg/kg body weight) i.p. daily 1 h before MTX (7 mg/kg body weight) administration for 3 consecutive days. After the final dose of MTX, the rats were killed, and the small intestines were used for analysis.

RESULTS

The small intestines of MTX-treated rats showed moderate to severe injury. Pretreatment with AG had a dose-dependent protective effect on MTX-induced mucositis. AG pretreatment reduced iNOS protein levels, mucosal nitric oxide levels, and protein tyrosine nitration. AG pretreatment also restored the activities of electron transport chain (ETC) complexes, vital tricarboxylic acid (TCA cycle) enzymes, and mitochondrial antioxidant enzymes.

CONCLUSIONS

These findings suggest that AG is beneficial in ameliorating MTX-induced enteritis in rats.

ALK gene copy number in lung cancer: Unspecific polyploidy versus specific amplification visible as double minutes

BACKGROUND

Gains of a gene due to DNA polyploidy versus amplification of the specific locus are distinct molecular alterations in tumors.

OBJECTIVE

We quantified copy number gains of ALK gene due to unspecific polyploidy versus amplifications of the specific locus in a series of non-small cell lung cancers.

METHODS

The locus specific ALK copy (LSI) number status was evaluated in 205 cases by FISH. Ratio LSI ALK copy number corrected for control probes CEP2, CEP3 and CEP17 (CEPs) was scored. Amplification of the specific ALK locus was defined when ratio set to ≥ 2 while polyploidy was interpreted when the increase in gene copy resulted < 2 in ratio (LSI/control CEPs).

RESULTS

Twenty one cases (10.2%) showed ≥ 8 ALK signals, 68 cases (33.2%) 3-7 signals and 116 cases (56.6%) a mean of 2 signals. Only 2/21 cases of the cohort harboring ≥ 8 signals showed a ratio ≥ 2 after CEPs correction interpretable as amplified, showing numerous doubled fluorescent spots. All the remaining cases showed a mirrored number of fluorescent spots per each CEPs, interpretable as polyploidy.

CONCLUSION

We detected a high prevalence of ALK gene copy number usually due to polyploidy rather than ALK locus amplification, the latter visible prevalently as double minutes.

Proteasome inhibitors in cancer therapy: Treatment regimen and peripheral neuropathy as a side effect

Proteasomal system plays an important role in protein turnover, which is essential for homeostasis of cells. Besides degradation of oxidized proteins, it is involved in the regulation of many different signaling pathways. These pathways include mainly cell differentiation, proliferation, apoptosis, transcriptional activation and angiogenesis. Thus, proteasomal system is a crucial target for treatment of several diseases including neurodegenerative diseases, cystic fibrosis, atherosclerosis, autoimmune diseases, diabetes and cancer. Over the last fifteen years, proteasome inhibitors have been tested to highlight their mechanisms of action and used in the clinic to treat different types of cancer. Proteasome inhibitors are mainly used in combinational therapy along with classical chemo-radiotherapy. Several studies have proved their significant effects but serious side effects such as peripheral neuropathy, limits their use in required effective doses. Recent studies focus on peripheral neuropathy as the primary side effect of proteasome inhibitors. Therefore, it is important to delineate the underlying mechanisms of peripheral neuropathy and develop new inhibitors according to obtained data. This review will detail the role of proteasome inhibition in cancer therapy and development of peripheral neuropathy as a side effect. Additionally, new approaches to prevent treatment-limiting side effects will be discussed in order to help researchers in developing effective strategies to overcome side effects of proteasome inhibitors.

The role of p53 in myelodysplastic syndromes and acute myeloid leukemia: molecular aspects and clinical implications

TP53 gene mutations occurring in patients with myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) are associated with high-risk karyotypes including 17p abnormalities, monosomal and complex cytogenetics. TP53 mutations in these disorders portend rapid disease progression and resistance to conventional therapeutics. Notably, the size of the TP53 mutant clone as measured by mutation allele burden is directly linked to overall survival (OS) confirming the importance of p53 as a negative prognostic variable. In nucleolar stress-induced ribosomopathies, such as del(5q) MDS, disassociation of MDM2 and p53 results in p53 accumulation in erythroid precursors manifested as erythroid hypoplasia. P53 antagonism by lenalidomide or other therapeutics such as antisense oligonucleotides, repopulates erythroid precursors and enhances effective erythropoiesis. These findings demonstrate that p53 is an intriguing therapeutic target that is currently under investigation in MDS and AML. This study reviews molecular advances in understanding the role of p53 in MDS and AML, and explores potential therapeutic strategies in this era of personalized medicine.

Roles of TP53 in determining therapeutic sensitivity, growth, cellular senescence, invasion and metastasis

TP53 is a critical tumor suppressor gene that regulates cell cycle progression, apoptosis, cellular senescence and many other properties critical for control of normal cellular growth and death. Due to the pleiotropic effects that TP53 has on gene expression and cellular physiology, mutations at this tumor suppressor gene result in diverse physiological effects. T53 mutations are frequently detected in numerous cancers. The expression of TP53 can be induced by various agents used to treat cancer patients such as chemotherapeutic drugs and ionizing radiation. Radiation will induce Ataxia telangiectasia mutated (ATM) and other kinases that results in the phosphorylation and activation of TP53. TP53 is also negatively regulated by other mechanisms, such as ubiquitination by ligases such as MDM2. While TP53 has been documented to control the expression of many "classical" genes (e.g., p21^Cip-1, PUMA, Bax) by transcriptional mechanisms for quite some time, more recently TP53 has been shown to regulate microRNA (miR) gene expression. Different miRs can promote oncogenesis (oncomiR) whereas others act to inhibit tumor progression (tumor suppressor miRs). Targeted therapies to stabilize TP53 have been developed by various approaches, MDM2/MDM4 inhibitors have been developed to stabilize TP53 in TP53-wild type (WT) tumors. In addition, small molecules have been isolated that will reactivate certain mutant TP53s. Both of these types of inhibitors are in clinical trials. Understanding the actions of TP53 may yield novel approaches to suppress cancer, aging and other health problems.

Enhancing radiosensitivity of TE1, TE8, and TE 11 esophageal squamous carcinoma cell lines by Hdm2-siRNA targeted gene therapy in vitro

Introduction: Human double minute2 (hdm2) level increases in most human malignancies. Therefore, inhibition of tumor growth and also induction of radiosensitivity may be provided by hdm2 inhibitors. The effects of hdm2-siRNA on hdm2 protein expression, cell apoptosis rate, and radiosensitivity of human esophageal squamous cell carcinoma (ESCC) were studied.

Methods: The hdm2 gene was silenced in TE1, TE8, and TE11 ESCC cell lines using 200nM siRNA by liposomal transfection method followed by irradiation with 0.5, 1, 2, 4, and 6 Gy γ-rays in vitro. The gene expression levels were evaluated by real time PCR and Western Blotting methods. MTT, TUNEL, and also colony forming assays were used to compare the radiosensitivity of the cell lines before and after the treatments.

Results: Hdm2-siRNA reduced the hdm2 protein as compared to the vehicle control and scrambled groups, and also increased the radiation-induced apoptosis especially in TE11 cells. The related dose reduction factors (DRFs) for the silenced TE1, TE8, and TE11 cells calculated to be 1.20, 1.30, and 2.75, respectively.

Conclusion: Increasing radiosensitivity of tumor cells may be provided by silencing the oncogenes.

An Integrative Pharmacogenomic Approach Identifies Two-drug Combination Therapies for Personalized Cancer Medicine

An individual tumor harbors multiple molecular alterations that promote cell proliferation and prevent apoptosis and differentiation. Drugs that target specific molecular alterations have been introduced into personalized cancer medicine, but their effects can be modulated by the activities of other genes or molecules. Previous studies aiming to identify multiple molecular alterations for combination therapies are limited by available data. Given the recent large scale of available pharmacogenomic data, it is possible to systematically identify multiple biomarkers that contribute jointly to drug sensitivity, and to identify combination therapies for personalized cancer medicine. In this study, we used pharmacogenomic profiling data provided from two independent cohorts in a systematic in silico investigation of perturbed genes cooperatively associated with drug sensitivity. Our study predicted many pairs of molecular biomarkers that may benefit from the use of combination therapies. One of our predicted biomarker pairs, a mutation in the BRAF gene and upregulated expression of the PIM1 gene, was experimentally validated to benefit from a therapy combining BRAF inhibitor and PIM1 inhibitor in lung cancer. This study demonstrates how pharmacogenomic data can be used to systematically identify potentially cooperative genes and provide novel insights to combination therapies in personalized cancer medicine.

Neoadjuvant treatment for resectable pancreatic adenocarcinoma

Pancreatic adenocarcinoma is the fourth leading cause of cancer mortality in the United States in both men and women, with a 5-year survival rate of less than 5%. Surgical resection remains the only curative treatment, but most patients develop systemic recurrence within 2 years of surgery. Adjuvant treatment with chemotherapy or chemoradiotherapy has been shown to improve overall survival, but the delivery of treatment remains problematic with up to 50% of patients not receiving postoperative treatment. Neoadjuvant therapy can provide benefits of eradication of micrometastasis and improved delivery of intended treatment. We have reviewed the findings from completed neoadjuvant clinical trials, and discussed the ongoing studies. Combinational cytotoxic chemotherapy such as fluorouracil, leucovorin, irinotecan, and oxaliplatin and gemcitabine plus nanoparticle albumin-bound (nab)-paclitaxel, active in the metastatic setting, are being studied in the neoadjuvant setting. In addition, novel targeted agents such as inhibitor of immune checkpoint are incorporated with cytotoxic chemotherapy in early-phase clinical trial. Furthermore we have explored the utility of biomarkers which can personalize treatment and select patients for target-driven therapy to improve treatment outcome. The treatment of resectable pancreatic adenocarcinoma requires multidisciplinary approach and novel strategies including innovative trials to make progress.

MDM2 promotes rheumatoid arthritis via activation of MAPK and NF-κB

Murine double minute-2 (MDM2) has pleiotropic roles in immune activation and regulation. However, the role of MDM2 in rheumatoid arthritis (RA) remains unknown. We undertook this study to investigate the role of MDM2 in rheumatoid arthritis (RA). Fibroblast-like synoviocytes (FLS) were isolated from 25 patients with active RA and 25 patients with osteoarthritis (OA). FLS were stimulated in the presence or absence of IL-1β in vitro. Mice with collagen-induced arthritis (CIA) were treated with Nutlin-3a (100mg/kg) or vehicle twice daily for 2weeks. MDM2 expression was determined by Western blot. MDM2 was down-regulated by specific gene silencing. The concentrations of pro-inflammatory cytokines and matrix metalloproteinases (MMPs) were analyzed using enzyme-linked immunosorbent assay (ELISA). The pathways of mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) were investigated by Western blot. Arthritis scoring and histological analysis were conducted. MDM2 expression was significantly higher in RA-FLS than in OA-FLS. MDM2 protein expression was positively correlated with disease activity of RA. MDM2 promoted the production of TNF-α, IL-6, MMP1 and MMP13 through MAPK and NF-κB pathways in RA-FLS. Nutlin-3a treatment decreased the arthritis severity and joint damage in CIA. Nutlin-3a also inhibited the activation of MAPK and NF-κB in arthritic joints. In conclusion, MDM2 inhibition exhibits anti-inflammatory activity and MDM2 might be a new therapeutic target for RA.

Personalized Approaches to Gastrointestinal Cancers: Importance of Integrating Genomic Information to Guide Therapy

Cancers are characterized by complex tumor heterogeneity driven by subclones with differential genotypes and phenotypes, which then drives cancer behavior. As genomic strategies become feasible on smaller samples such as biopsies, coupled with decreasing costs of these approaches, clinicians will increasingly use genomic information to drive therapeutic decision making. Early applications of such personalized approaches are discussed. Genetic testing of high-risk family members may identify patients with germline mutations who can have prophylactic surgeries as a cancer prevention strategy. This article discusses examples of successful targeted therapy. Clinical trials need to incorporate genetic testing to stratify patients into different groups.

Novel chemotherapeutics and other therapies for treating high-grade glioma

INTRODUCTION

Despite extensive research, high-grade glioma (HGG) remains a dire diagnosis with no change in the standard of care in almost a decade. However, recent advancements uncovering molecular biomarkers of brain tumors and tumor-specific antigens targeted by immunotherapies provide opportunities for novel personalized treatment regimens to improve survival.

AREAS COVERED

In this review, the authors provide a comprehensive overview of recent therapeutic advancements in HGG. Furthermore, they describe new molecular biomarkers and molecular classifications, in addition to updated research on bevacizumab, targeted molecular therapies, immunotherapy and alternative delivery methods that overcome the blood-brain barrier to reach the target tumor tissue. Challenges regarding each therapy are also outlined. The authors also provide some insight into a novel non-chemotherapeutic treatment for malignant glioma, NovoTTFA, as well as a summary of current treatment options for recurrence.

EXPERT OPINION

Current research for treating malignant gliomas are paving the path to personalized therapy, including immunotherapy, that involve integrated genomic and histolopathologic data, as well as a multi-modal treatment regimen. Immunotherapy will potentially be the next addition to the current standard of care, specialized to the antigens presented on the tumors. The results of the current trials of multi-antigen vaccines are eagerly anticipated.

NSC-87877 inhibits DUSP26 function in neuroblastoma resulting in p53-mediated apoptosis

Dual specificity protein phosphatase 26 (DUSP26) is overexpressed in high-risk neuroblastoma (NB) and contributes to chemoresistance by inhibiting p53 function. In vitro, DUSP26 has also been shown to effectively inhibit p38 MAP kinase. We hypothesize that inhibiting DUSP26 will result in decreased NB cell growth in a p53 and/or p38-mediated manner. NSC-87877 (8-hydroxy-7-[(6-sulfo-2-naphthyl)azo]-5-quinolinesulfonic acid), a novel DUSP26 small molecule inhibitor, shows effective growth inhibition and induction of apoptosis in NB cell lines. NB cell lines treated with small hairpin RNA (shRNA) targeting DUSP26 also exhibit a proliferation defect both in vitro and in vivo. Treatment of NB cell lines with NSC-87877 results in increased p53 phosphorylation (Ser37 and Ser46) and activation, increased activation of downstream p38 effector proteins (heat shock protein 27 (HSP27) and MAP kinase-activated protein kinase 2 (MAPKAPK2)) and poly ADP ribose polymerase/caspase-3 cleavage. The cytotoxicity resulting from DUSP26 inhibition is partially reversed by knocking down p53 expression with shRNA and also by inhibiting p38 activity with SB203580 (4-[4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-1H-imidazol-5-yl]pyridine). In an intrarenal mouse model of NB, NSC-87877 treatment results in decreased tumor growth and increased p53 and p38 activity. Together, these results suggest that DUSP26 inhibition with NSC-87877 is an effective strategy to induce NB cell cytotoxicity in vitro and in vivo through activation of the p53 and p38 mitogen-activated protein kinase (MAPK) tumor-suppressor pathways.

Resistance acquisition to MDM2 inhibitors

Various experimental strategies aim to (re)activate p53 signalling in cancer cells. The most advanced clinically are small-molecule inhibitors of the autoregulatory interaction between p53 and MDM2 (murine double minute 2). Different MDM2 inhibitors are currently under investigation in clinical trials. As for other targeted anti-cancer therapy approaches, relatively rapid resistance acquisition may limit the clinical efficacy of MDM2 inhibitors. In particular, MDM2 inhibitors were shown to induce p53 mutations in experimental systems. In the present article, we summarize what is known about MDM2 inhibitors as anti-cancer drugs with a focus on the acquisition of resistance to these compounds.

Host-based Prophylaxis Successfully Targets Liver Stage Malaria Parasites

Eliminating malaria parasites during the asymptomatic but obligate liver stages (LSs) of infection would stop disease and subsequent transmission. Unfortunately, only a single licensed drug that targets all LSs, Primaquine, is available. Targeting host proteins might significantly expand the repertoire of prophylactic drugs against malaria. Here, we demonstrate that both Bcl-2 inhibitors and P53 agonists dramatically reduce LS burden in a mouse malaria model in vitro and in vivo by altering the activity of key hepatocyte factors on which the parasite relies. Bcl-2 inhibitors act primarily by inducing apoptosis in infected hepatocytes, whereas P53 agonists eliminate parasites in an apoptosis-independent fashion. In combination, Bcl-2 inhibitors and P53 agonists act synergistically to delay, and in some cases completely prevent, the onset of blood stage disease. Both families of drugs are highly effective at doses that do not cause substantial hepatocyte cell death in vitro or liver damage in vivo. P53 agonists and Bcl-2 inhibitors were also effective when administered to humanized mice infected with Plasmodium falciparum. Our data demonstrate that host-based prophylaxis could be developed into an effective intervention strategy that eliminates LS parasites before the onset of clinical disease and thus opens a new avenue to prevent malaria.

PARP inhibitors

Poly (ADP-ribose) polymerases, abbreviated as PARPs, are a group of familiar proteins that play a central role in DNA repair employing the base excision repair (BER) pathway. There about 17 proteins in this family out of which the primary nuclear PARPs are PARP-1, PARP-2, PARP-3, and tankyrases 1 and 2 (PARP-5a and -5b) .The PARP family members are known to engage in a wide range of cellular activities, for example, DNA repair, transcription, cellular signaling, cell cycle regulation and mitosis amongst others. The chief functional units of PARP-1 are an amino terminal DNA binding domain (DBD), a central auto modification domain (AMD), and a carboxyl-terminal catalytic domain (CD). PARP inhibitors are currently undergoing clinical trials as targeted treatment modalities of breast, uterine, colorectal and ovarian cancer. This review summarizes current insights into the mechanism of action of PARP inhibitors, its recent clinical trials, and potential next steps in the evaluation of this promising class of anti-cancer drugs.

Advances in the targeted therapy of liposarcoma

Liposarcoma (LPS) is the most common type of soft-tissue sarcoma. Complete surgical resection is the only curative means for localized disease; however, both radiation and conventional cytotoxic chemotherapy remain controversial for metastatic or unresectable disease. An increasing number of trials with novel targeted therapy of LPS have provided encouraging data during recent years. This review will provide an overview of the advances in our understanding of LPS and summarize the results of recent trials with novel therapies targeting different genetic and molecular aberrations for different subtypes of LPS.

Future perspectives in melanoma research: meeting report from the "Melanoma Bridge", Napoli, December 5th-8th 2013

The fourth "Melanoma Bridge Meeting" took place in Naples, December 5 to 8th, 2013. The four topics discussed at this meeting were: Diagnosis and New Procedures, Molecular Advances and Combination Therapies, News in Immunotherapy, and Tumor Microenvironment and Biomarkers.

T cell immune abnormalities in immune thrombocytopenia

Immune thrombocytopenia is an autoimmune disease with abnormal T cell immunity. Cytotoxic T cells, abnormal T regulatory cells, helper T cell imbalance, megakaryocyte maturation abnormalities and abnormal T cell anergy are involved in the pathogenesis of this condition. The loss of T cell-mediated immune tolerance to platelet auto-antigens plays a crucial role in immune thrombocytopenia. The induction of T cell tolerance is an important mechanism by which the pathogenesis and treatment of immune thrombocytopenia can be studied. Studies regarding the roles of the new inducible costimulator signal transduction pathway, the ubiquitin proteasome pathway, and the nuclear factor kappa B signal transduction pathway in the induction of T cell tolerance can help improve our understanding of immune theory and may provide a new theoretical basis for studying the pathogenesis and treatment of immune thrombocytopenia.

Integrative Pathway Analysis Using Graph-Based Learning with Applications to TCGA Colon and Ovarian Data

Recent method development has included multi-dimensional genomic data algorithms because such methods have more accurately predicted clinical phenotypes related to disease. This study is the first to conduct an integrative genomic pathway-based analysis with a graph-based learning algorithm. The methodology of this analysis, graph-based semi-supervised learning, detects pathways that improve prediction of a dichotomous variable, which in this study is cancer stage. This analysis integrates genome-level gene expression, methylation, and single nucleotide polymorphism (SNP) data in serous cystadenocarcinoma (OV) and colon adenocarcinoma (COAD). The top 10 ranked predictive pathways in COAD and OV were biologically relevant to their respective cancer stages and significantly enhanced prediction accuracy and area under the ROC curve (AUC) when compared to single data-type analyses. This method is an effective way to simultaneously predict binary clinical phenotypes and discover their biological mechanisms.

Inhibition of human esophageal squamous cell carcinomas by targeted silencing of tumor enhancer genes: an overview

Esophageal cancer has been reported as the ninth most common malignancy and ranks as the sixth most frequent cause of death worldwide. Esophageal cancer treatment involves surgery, chemotherapy, radiation therapy, or combination therapy. Novel strategies are needed to boost the oncologic outcome. Recent advances in the molecular biology of esophageal cancer have documented the role of genetic alterations in tumorigenesis. Oncogenes serve a pivotal function in tumorigenesis. Targeted therapies are directed at the unique molecular signature of cancer cells for enhanced efficacy with low toxicity. RNA interference (RNAi) technology is a powerful tool for silencing endogenous or exogenous genes in mammalian cells. Related results have shown that targeting oncogenes with siRNAs, specifically the mRNA, effectively reduces tumor cell proliferation and induces apoptotic cell death. This article will briefly review studies on silencing tumor enhancer genes related to the induction of esophageal cancer.

Discussion of PARP inhibitors in cancer therapy

Poly (ADP-ribose) polymerases (PARP) are a family of enzymes that play a very important role in preserving the integrity of the genome. Recently, PARP inhibitors have been shown to enhance the therapeutic ratio in cancer patients due to their specific targeting of homologous recombination repair-defective tumors, through a synthetic lethal interaction. Researchers are also presently investigating novel strategies for the treatment of sporadic cancers by combining PARP inhibitors with other DNA-damaging agents. This review will focus on recently patented PARP inhibitors and literature that supports the reported claims presented in these patents. The patents reviewed were categorized into two groups: PARP inhibitors as a single-agent or in combination with other agents for the treatment of various types of cancer. These compounds are currently in clinical trials and, if successful, can greatly impact therapeutic index in cancer therapy.

PARP inhibitor attenuated colony formation can be restored by MAP kinase inhibitors in different irradiated cancer cell lines

Abstract Purpose: Sensitizing cancer cells to irradiation is a major challenge in clinical oncology. We aimed to define the signal transduction pathways involved in poly(ADP-ribose) polymerase (PARP) inhibitor-induced radiosensitization in various mammalian cancer lines.

MATERIALS AND METHODS

Clonogenic survival assays and Western blot examinations were performed following telecobalt irradiation of cancer cells in the presence or absence of various combinations of PARP- and selective mitogen-activated protein kinase (MAPK) inhibitors.

RESULTS

HO3089 resulted in significant cytotoxicity when combined with irradiation. In human U251 glioblastoma and A549 lung cancer cell lines, Erk1/2 and JNK/SAPK were found to mediate this effect of HO3089 since inhibitors of these kinases ameliorated it. In murine 4T1 breast cancer cell line, p38 MAPK rather than Erk1/2 or JNK/SAPK was identified as the main mediator of HO3089's radiosensitizing effect. Besides the aforementioned changes in kinase signaling, we detected increased p53, unchanged Bax and decreased Bcl-2 expression in the A549 cell line.

CONCLUSIONS

HO3089 sensitizes cancer cells to photon irradiation via proapoptotic processes where p53 plays a crucial role. Activation of MAPK pathways is regarded the consequence of irradiation-induced DNA damage, thus their inhibition can counteract the radiosenzitizing effect of the PARP inhibitor.