Inhibition of checkpoint kinase 2 (CHK2) enhances sensitivity of pancreatic adenocarcinoma cells to gemcitabine

Guarding against digestive-system cancers: Unveiling the role of Chk2 as a potential therapeutic target

Digestive-system cancers represent major threats to human health; however, the mechanisms underlying tumorigenesis and radiochemotherapy resistance have remained elusive. Therefore, an urgent need exists for identifying key drivers of digestive system tumorigenesis and novel targeted therapeutics. The checkpoint kinase 2 (Chk2) regulates cell-cycle progression, and Chk2 dysregulation or Chk2 mutations can lead to the development of various cancers, which makes Chk2 an important research topic. This review summarizes the roles of Chk2 in DNA-damage responses, cell-cycle regulation, autophagy, and homeostasis maintenance. We describe relationships between tumorigenesis and cell-cycle dysregulation induced by Chk2 mutations. In addition, we summarize evidence indicating that Chk2 can serve as a novel therapeutic target, based on its contributions to radiochemotherapy-resistance reversion and progress made in developing antitumor agents against Chk2. The prevailing evidence supports the conclusion that further research on Chk2 will provide a deeper understanding of digestive-system tumorigenesis and should suggest novel therapeutic targets.

Applications of Modified Mesenchymal Stem Cells as Targeted Systems against Tumor Cells

Combined gene and cell therapy are promising strategies for cancer treatment. Given the complexity of cancer, several approaches are actively studied to fight this disease. Using mesenchymal stem cells (MSCs) has demonstrated dual antitumor and protumor effects as they exert massive immune/regulatory effects on the tissue microenvironment. MSCs have been widely investigated to exploit their antitumor target delivery system. They can be genetically modified to overexpress genes and selectively or more efficiently eliminate tumor cells. Current approaches tend to produce more effective and safer therapies using MSCs or derivatives; however, the effect achieved by engineered MSCs in solid tumors is still limited and depends on several factors such as the cell source, transgene, and tumor target. This review describes the progress of gene and cell therapy focused on MSCs as a cornerstone against solid tumors, addressing the different MSC-engineering methods that have been approached over decades of research. Furthermore, we summarize the main objectives of engineered MSCs against the most common cancers and discuss the challenges, limitations, risks, and advantages of targeted treatments combined with conventional ones.

The Landscape and Therapeutic Targeting of BRCA1, BRCA2 and Other DNA Damage Response Genes in Pancreatic Cancer

Genes participating in the cellular response to damaged DNA have an important function to protect genetic information from alterations due to extrinsic and intrinsic cellular insults. In cancer cells, alterations in these genes are a source of genetic instability, which is advantageous for cancer progression by providing background for adaptation to adverse environments and attack by the immune system. Mutations in BRCA1 and BRCA2 genes have been known for decades to predispose to familial breast and ovarian cancers, and, more recently, prostate and pancreatic cancers have been added to the constellation of cancers that show increased prevalence in these families. Cancers associated with these genetic syndromes are currently treated with PARP inhibitors based on the exquisite sensitivity of cells lacking BRCA1 or BRCA2 function to inhibition of the PARP enzyme. In contrast, the sensitivity of pancreatic cancers with somatic BRCA1 and BRCA2 mutations and with mutations in other homologous recombination (HR) repair genes to PARP inhibitors is less established and the subject of ongoing investigations. This paper reviews the prevalence of pancreatic cancers with HR gene defects and treatment of pancreatic cancer patients with defects in HR with PARP inhibitors and other drugs in development that target these molecular defects.

Mutations in key driver genes of pancreatic cancer: molecularly targeted therapies and other clinical implications

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers, with a minimal difference between its incidence rate and mortality rate. Advances in oncology over the past several decades have dramatically improved the overall survival of patients with multiple cancers due to the implementation of new techniques in early diagnosis, therapeutic drugs, and personalized therapy. However, pancreatic cancers remain recalcitrant, with a 5-year relative survival rate of <9%. The lack of measures for early diagnosis, strong resistance to chemotherapy, ineffective adjuvant chemotherapy and the unavailability of molecularly targeted therapy are responsible for the high mortality rate of this notorious disease. Genetically, PDAC progresses as a complex result of the activation of oncogenes and inactivation of tumor suppressors. Although next-generation sequencing has identified numerous new genetic alterations, their clinical implications remain unknown. Classically, oncogenic mutations in genes such as KRAS and loss-of-function mutations in tumor suppressors, such as TP53, CDNK2A, DPC4/SMAD4, and BRCA2, are frequently observed in PDAC. Currently, research on these key driver genes is still the main focus. Therefore, studies assessing the functions of these genes and their potential clinical implications are of paramount importance. In this review, we summarize the biological function of key driver genes and pharmaceutical targets in PDAC. In addition, we conclude the results of molecularly targeted therapies in clinical trials and discuss how to utilize these genetic alterations in further clinical practice.

Doxycycline potentiates the anti-proliferation effects of gemcitabine in pancreatic cancer cells

Gemcitabine is often recommended as a first-line treatment for patients with metastatic pancreatic cancer. However, gemcitabine resistance is a major challenge in the treatment of pancreatic ductal adenocarcinoma. Our group serendipitously identified the role of doxycycline as a potentiator of gemcitabine efficacy in pancreatic cancer cells. Doxycycline and gemcitabine co-treatment was significantly more cytotoxic to pancreatic cancer cells compared to gemcitabine alone. Interestingly, doxycycline only exerted synergistic effects when coupled with gemcitabine as opposed to other conventional chemotherapeutics including nucleoside analogs. The anti-clonogenic effects of gemcitabine on pancreatic cancer cells were also enhanced by doxycycline. According to cell cycle analyses, doxycycline prolonged gemcitabine-mediated S phase cell cycle arrest. Further, gene expression profiling analyses indicated that a small set of genes involved in cell cycle regulation were uniquely modulated by gemcitabine and doxycycline co-treatment compared to gemcitabine alone. Western blot analyses indicated that several cell cycle-related proteins, including cyclin D1, p21, and DNA damage inducible transcript 4 (DDIT4), were further modulated by doxycycline and gemcitabine co-treatment. Taken together, our findings indicate that doxycycline enhances the effects of gemcitabine on cell cycle progression, thus rendering pancreatic cancer cells more sensitive to gemcitabine. However, additional studies are required to assess the mechanisms of doxycycline and gemcitabine synergism, which might lead to novel treatment options for pancreatic cancer.

Dual Inhibition of AKT and MEK Pathways Potentiates the Anti-Cancer Effect of Gefitinib in Triple-Negative Breast Cancer Cells

There is an unmet medical need for the development of new targeted therapeutic strategies for triple-negative breast cancer (TNBC). With drug combination screenings, we found that the triple combination of the protein kinase inhibitors (PKIs) of the epidermal growth factor receptor (EGFR), v-akt murine thymoma viral oncogene homolog (AKT), and MAPK/ERK kinase (MEK) is effective in inducing apoptosis in TNBC cells. A set of PKIs were first screened in combination with gefitinib in the TNBC cell line, MDA-MB-231. The AKT inhibitor, AT7867, was identified and further analyzed in two mesenchymal stem-like (MSL) subtype TNBC cells, MDA-MB-231 and HS578T. A combination of gefitinib and AT7867 reduced the proliferation and long-term survival of MSL TNBC cells. However, gefitinib and AT7867 induced the activation of the rat sarcoma (RAS)/ v-raf-1 murine leukemia viral oncogene homolog (RAF)/MEK/ extracellular signal-regulated kinase (ERK) pathway. To inhibit this pathway, MEK/ERK inhibitors were further screened in MDA-MB-231 cells in the presence of gefitinib and AT7867. As a result, we identified that the MEK inhibitor, PD-0325901, further enhanced the anti-proliferative and anti-clonogenic effects of gefitinib and AT7867 by inducing apoptosis. Our results suggest that the dual inhibition of the AKT and MEK pathways is a novel potential therapeutic strategy for targeting EGFR in TNBC cells.

CHEK2 mutation in a patient with pancreatic adenocarcinoma-a rare case report

Pancreatic cancer (PaCa) is very aggressive malignancy with poor prognosis. Individuals with a family history of PaCa have a higher risk of developing cancer which points to a hereditary component. Here, we report a unique case of CHEK2 mutant PaCa in a patient with no medical but significant family history. A 59-year old female presented with 3-month history of worsening epigastric pain and jaundice. CT abdomen/pelvis with contrast showed pancreatic head mass which was confirmed by endoscopic ultrasound guided biopsy. She was diagnosed with pancreatic adenocarcinoma harboring CHEK2 mutation. She had extensive surgery followed by adjuvant chemotherapy. Follow up imaging in 3 months obtained after surgery and adjuvant chemotherapy showed extensive liver metastasis and patient decided to pursue hospice. Germline testing in all PaCa patients has become essential as mutations in CHEK2 and other DNA repair genes constitute a unique subset of PaCas. Not only does it help in assessment of cancer risk in the individual and family members but also guide anticancer therapy selection. PaCa patients harboring CHEK2 mutations do not usually respond to chemotherapeutic agents such as gemcitabine. However, new treatment strategies such as PARP inhibitors targeting defective DNA repair mechanism are currently being investigated and showed some promise in treating CHEK2 mutant PaCa patients.

ATM Dysfunction in Pancreatic Adenocarcinoma and Associated Therapeutic Implications

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most lethal solid malignancies with very few therapeutic options to treat advanced or metastatic disease. The utilization of genomic sequencing has identified therapeutically relevant alterations in approximately 25% of PDAC patients, most notably in the DNA damage response and repair (DDR) genes, rendering cancer cells more sensitive to DNA-damaging agents and to DNA damage response inhibitors, such as PARP inhibitors. ATM is one of the most commonly mutated DDR genes, with somatic mutations identified in 2% to 18% of PDACs and germline mutations identified in 1% to 34% of PDACs. ATM plays a complex role as a cell-cycle checkpoint kinase, regulator of a wide array of downstream proteins, and responder to DNA damage for genome stability. The disruption of ATM signaling leads to downstream reliance on ATR and CHK1, among other DNA-repair mechanisms, which may enable exploiting the inhibition of downstream proteins as therapeutic targets in ATM-mutated PDACs. In this review, we detail the function of ATM, review the current data on ATM deficiency in PDAC, examine the therapeutic implications of ATM alterations, and explore the current clinical trials surrounding the ATM pathway.

PGRMC1 phosphorylation affects cell shape, motility, glycolysis, mitochondrial form and function, and tumor growth

BACKGROUND

Progesterone Receptor Membrane Component 1 (PGRMC1) is expressed in many cancer cells, where it is associated with detrimental patient outcomes. It contains phosphorylated tyrosines which evolutionarily preceded deuterostome gastrulation and tissue differentiation mechanisms.

RESULTS

We demonstrate that manipulating PGRMC1 phosphorylation status in MIA PaCa-2 (MP) cells imposes broad pleiotropic effects. Relative to parental cells over-expressing hemagglutinin-tagged wild-type (WT) PGRMC1-HA, cells expressing a PGRMC1-HA-S57A/S181A double mutant (DM) exhibited reduced levels of proteins involved in energy metabolism and mitochondrial function, and altered glucose metabolism suggesting modulation of the Warburg effect. This was associated with increased PI3K/AKT activity, altered cell shape, actin cytoskeleton, motility, and mitochondrial properties. An S57A/Y180F/S181A triple mutant (TM) indicated the involvement of Y180 in PI3K/AKT activation. Mutation of Y180F strongly attenuated subcutaneous xenograft tumor growth in NOD-SCID gamma mice. Elsewhere we demonstrate altered metabolism, mutation incidence, and epigenetic status in these cells.

CONCLUSIONS

Altogether, these results indicate that mutational manipulation of PGRMC1 phosphorylation status exerts broad pleiotropic effects relevant to cancer and other cell biology.

ROS and the DNA damage response in cancer

Reactive oxygen species (ROS) are a group of short-lived, highly reactive, oxygen-containing molecules that can induce DNA damage and affect the DNA damage response (DDR). There is unequivocal pre-clinical and clinical evidence that ROS influence the genotoxic stress caused by chemotherapeutics agents and ionizing radiation. Recent studies have provided mechanistic insight into how ROS can also influence the cellular response to DNA damage caused by genotoxic therapy, especially in the context of Double Strand Breaks (DSBs). This has led to the clinical evaluation of agents modulating ROS in combination with genotoxic therapy for cancer, with mixed success so far. These studies point to context dependent outcomes with ROS modulator combinations with Chemotherapy and radiotherapy, indicating a need for additional pre-clinical research in the field. In this review, we discuss the current knowledge on the effect of ROS in the DNA damage response, and its clinical relevance.

Skp2 Expression Is Inhibited by Arsenic Trioxide through the Upregulation of miRNA-330-5p in Pancreatic Cancer Cells

Arsenic trioxide (ATO) has been found to exert its anti-cancer activity in various human malignancies. In our previous report, we have shown that ATO inhibited cell growth and invasion via downregulation of Skp2 in pancreatic cancer (PC) cells. It has been extensively demonstrated that microRNAs (miRNAs) play a pivotal role in tumorigenesis. ATO might induce PC cell apoptosis and regulate Skp2 downregulation through the regulation of miRNAs. One study has demonstrated that miR-330-5p exerts a tumor-suppressive function in PC cell lines. Here, we investigated the role of miRNA-330-5p in ATO-mediated anti-tumor activity and explored whether ATO could regulate miR-330-5p in PC cells. We found that ATO treatment upregulated the expression of miR-330-5p. Moreover, miR-330-5p inhibitor rescued the ATO-mediated tumor-suppressive function. The combination of miR-330-5p mimic with ATO reduced cell growth, motility, and invasion, and enhanced apoptosis to a greater degree in PC cells. This study suggests that the combination of miR-330-5p mimic with ATO may be a potential therapeutic strategy for the treatment of PC.

Arsenic trioxide inhibits Skp2 expression to increase chemosensitivity to gemcitabine in pancreatic cancer cells

The S-phase kinase associated protein 2 (Skp2), a member of the F-box protein family, regulates cell cycle progression and is highly expressed in pancreatic cancer (PC). Recently, we reported that arsenic trioxide (ATO) inhibited cell growth and invasion via downregulation of Skp2 in PC cells. Emerging evidence has revealed that Skp2 plays a crucial role in drug resistance in several kinds of cancers. Here, we determined whether ATO enhanced the sensitivity of PC cell lines to gemcitabine (GEM). We found that the combined treatment of ATO and GEM demonstrated strong antitumor effects in Patu8988 and Panc-1 PC cells. In addition, ATO potentiated the effects of GEM via downregulation of the Skp2 pathway in PC cells. Together, these findings suggested that Skp2 may be a promising therapeutic target to overcome resistance to GEM in PC.

Deacetylation of CHK2 by SIRT1 protects cells from oxidative stress-dependent DNA damage response

Growing evidence indicates that metabolic signaling pathways are interconnected to DNA damage response (DDR). However, factors that link metabolism to DDR remain incompletely understood. SIRT1, an NAD+-dependent deacetylase that regulates metabolism and aging, has been shown to protect cells from DDR. Here, we demonstrate that SIRT1 protects cells from oxidative stress-dependent DDR by binding and deacetylating checkpoint kinase 2 (CHK2). We first showed that essential proteins in DDR were hyperacetylated in Sirt1-deficient cells and that among them, the level of acetylated CHK2 was highly increased. We found that Sirt1 formed molecular complexes with CHK2, BRCA1/BRCA2-associated helicase 1 (BACH1), tumor suppressor p53-binding protein 1 (53BP1), and H2AX, all of which are key factors in response to DNA damage. We then demonstrated that CHK2 was normally inhibited by SIRT1 via deacetylation but dissociated with SIRT1 under oxidative stress conditions. This led to acetylation and activation of CHK2, which increased cell death under oxidative stress conditions. Our data also indicated that SIRT1 deacetylated the K235 and K249 residues of CHK2, whose acetylation increased cell death in response to oxidative stress. Thus, SIRT1, a metabolic sensor, protects cells from oxidative stress-dependent DDR by the deacetylation of CHK2. Our findings suggest a crucial function of SIRT1 in inhibiting CHK2 as a potential therapeutic target for cancer treatment.

Pharmacotherapeutic Management of Pancreatic Ductal Adenocarcinoma: Current and Emerging Concepts

Pancreatic ductal adenocarcinoma is a devastating malignancy, which is the result of late diagnosis, aggressive disease, and a lack of effective treatment options. Thus, pancreatic ductal adenocarcinoma is projected to become the second leading cause of cancer-related death by 2030. This review summarizes recent developments of oncological therapy in the palliative setting of metastatic pancreatic ductal adenocarcinoma. It further compiles novel targets and therapeutic approaches as well as promising treatment combinations, which are presently in preclinical evaluation, covering several aspects of the hallmarks of cancer. Finally, challenges to the implementation of an individualized therapy approach in the context of precision medicine are discussed.

Silencing of NRF2 Reduces the Expression of ALDH1A1 and ALDH3A1 and Sensitizes to 5-FU in Pancreatic Cancer Cells

Pancreatic cancer remains an intractable cancer with a poor five-year survival rate, which requires new therapeutic modalities based on the biology of pancreatic oncogenesis. Nuclear factor E2 related factor-2 (NRF2), a key cytoprotective nuclear transcription factor, regulates antioxidant production, reduction, detoxification and drug efflux proteins. It also plays an essential role in cell homeostasis, cell proliferation and resistance to chemotherapy. We aimed to evaluate the possibility that modulation of NRF2 expression could be effective in the treatment of pancreatic cancer cells. We investigated whether the depletion of NRF2 by using small interfering RNAs (siRNAs) is effective in the expression of biomarkers of pancreatic cancer stemness such as aldehyde dehydrogenase 1 family, member A1 (ALDH1A1) and aldehyde dehydrogenase 3 family, member A1 (ALDH3A1). NRF2 knockdown markedly reduced the expression of NRF2 and glutamate-cysteine ligase catalytic subunit (GCLC) in cell lines established from pancreatic cancers. NRF2 silencing also decreased the ALDH1A1 and ALDH3A1 expression. Furthermore, this NRF2 depletion enhanced the antiproliferative effects of the chemotherapeutic agent, 5-fluorouracil (5-FU) in pancreatic cancer cells.

ATM, ATR, CHK1, CHK2 and WEE1 inhibitors in cancer and cancer stem cells

DNA inevitably undergoes a high number of damages throughout the cell cycle. To preserve the integrity of the genome, cells have developed a complex enzymatic machinery aimed at sensing and repairing DNA lesions, pausing the cell cycle to provide more time to repair, or induce apoptosis if damages are too severe. This so-called DNA-damage response (DDR) is yet considered as a major source of resistance to DNA-damaging treatments in oncology. Recently, it has been hypothesized that cancer stem cells (CSC), a sub-population of cancer cells particularly resistant and with tumour-initiating ability, allow tumour re-growth and cancer relapse. Therefore, DDR appears as a relevant target to sensitize cancer cells and cancer stem cells to classical radio- and chemotherapies as well as to overcome resistances. Moreover, the concept of synthetic lethality could be particularly efficiently exploited in DDR. Five kinases play pivotal roles in the DDR: ATM, ATR, CHK1, CHK2 and WEE1. Herein, we review the drugs targeting these proteins and the inhibitors used in the specific case of CSC. We also suggest molecules that may be of interest for preclinical and clinical researchers studying checkpoint inhibition to sensitize cancer and cancer stem cells to DNA-damaging treatments.

Cancer TARGETases: DSB repair as a pharmacological target

Cancer is a disease attributed to the accumulation of DNA damages due to incapacitation of DNA repair pathways resulting in genomic instability and a mutator phenotype. Among the DNA lesions, double stranded breaks (DSBs) are the most toxic forms of DNA damage which may arise as a result of extrinsic DNA damaging agents or intrinsic replication stress in fast proliferating cancer cells. Accurate repair of DSBs is therefore paramount to the cell survival, and several classes of proteins such as kinases, nucleases, helicases or core recombinational proteins have pre-defined jobs in precise execution of DSB repair pathways. On one hand, the proper functioning of these proteins ensures maintenance of genomic stability in normal cells, and on the other hand results in resistance to various drugs employed in cancer therapy and therefore presents a suitable opportunity for therapeutic targeting. Higher relapse and resistance in cancer patients due to non-specific, cytotoxic therapies is an alarming situation and it is becoming more evident to employ personalized treatment based on the genetic landscape of the cancer cells. For the success of personalized treatment, it is of immense importance to identify more suitable targetable proteins in DSB repair pathways and also to explore new synthetic lethal interactions with these pathways. Here we review the various alternative approaches to target the various protein classes termed as cancer TARGETases in DSB repair pathway to obtain more beneficial and selective therapy.

DNA repair targeted therapy: The past or future of cancer treatment?

The repair of DNA damage is a complex process that relies on particular pathways to remedy specific types of damage to DNA. The range of insults to DNA includes small, modest changes in structure including mismatched bases and simple methylation events to oxidized bases, intra- and interstrand DNA crosslinks, DNA double strand breaks and protein-DNA adducts. Pathways required for the repair of these lesions include mismatch repair, base excision repair, nucleotide excision repair, and the homology directed repair/Fanconi anemia pathway. Each of these pathways contributes to genetic stability, and mutations in genes encoding proteins involved in these pathways have been demonstrated to promote genetic instability and cancer. In fact, it has been suggested that all cancers display defects in DNA repair. It has also been demonstrated that the ability of cancer cells to repair therapeutically induced DNA damage impacts therapeutic efficacy. This has led to targeting DNA repair pathways and proteins to develop anti-cancer agents that will increase sensitivity to traditional chemotherapeutics. While initial studies languished and were plagued by a lack of specificity and a defined mechanism of action, more recent approaches to exploit synthetic lethal interaction and develop high affinity chemical inhibitors have proven considerably more effective. In this review we will highlight recent advances and discuss previous failures in targeting DNA repair to pave the way for future DNA repair targeted agents and their use in cancer therapy.

Combination of dasatinib and gemcitabine reduces the ALDH1A1 expression and the proliferation of gemcitabine-resistant pancreatic cancer MIA PaCa-2 cells

Gemcitabine-based chemotherapy is the standard for treatment of pancreatic cancer; however, intrinsic and acquired resistance to gemcitabine commonly occurs. Aldehyde dehydrogenase 1A1 (ALDH1A1), one of the characteristic features of tumor-initiating and/or cancer stem cell (CSC) properties, is important in both intrinsic and acquired resistance to gemcitabine. In this study, we investigated the effectiveness of dasatinib, an SRC inhibitor, and gemcitabine combination to inhibit the survivals of parental (MIA PaCa-2/P) and gemcitabine-resistant (MIA PaCa-2/GR) cell lines. In MIA PaCa-2/GR cells, the levels of phospho-SRC and ALDH1A1 were increased compared to MIA PaCa-2/P cells. Inhibition of SRC by dasatinib or siRNA synergistically enhanced gemcitabine-induced anti-proliferative effects and induced apoptotic cell death in these cells. Furthermore, combination of SRC inhibition (either by dasatinib or siRNA) and gemcitabine significantly decreased the levels of ALDH1A1 expression. These results suggest that dasatinib and gemcitabine combination may be a potential therapeutic strategy to overcome gemcitabine resistance by decreasing the levels of ALDH1A1 expression.

Phosphodiesterase 5 inhibitors enhance chemotherapy killing in gastrointestinal/genitourinary cancer cells

The present studies determined whether clinically relevant phosphodiesterase 5 (PDE5) inhibitors interacted with clinically relevant chemotherapies to kill gastrointestinal/genitourinary cancer cells. In bladder cancer cells, regardless of H-RAS mutational status, at clinically achievable doses, PDE5 inhibitors interacted in a greater than additive fashion with doxorubicin/mitomycin C/gemcitabine/cisplatin/paclitaxel to cause cell death. In pancreatic tumor cells expressing mutant active K-RAS, PDE5 inhibitors interacted in a greater than additive fashion with doxorubicin/gemcitabine/paclitaxel to cause cell death. The most potent PDE5 inhibitor was sildenafil. Knock down of PDE5 expression recapitulated the combination effects of PDE5 inhibitor drugs with chemotherapy drugs. Expression of cellular FLICE-like inhibitory protein-short did not significantly inhibit chemotherapy lethality but did significantly reduce enhanced killing in combination with sildenafil. Overexpression of B-cell lymphoma-extra large suppressed individual and combination drug toxicities. Knock down of CD95 or Fas-associated death domain protein suppressed drug combination toxicity. Combination toxicity was also abolished by necrostatin or receptor interacting protein 1 knock down. Treatment with PDE5 inhibitors and chemotherapy drugs promoted autophagy, which was maximal at ∼24 hour posttreatment, and 3-methyl adenine or knock down of Beclin1 suppressed drug combination lethality by ∼50%. PDE5 inhibitors enhanced and prolonged the induction of DNA damage as judged by Comet assays and γhistone 2AX (γH2AX) and checkpoint kinase 2 (CHK2) phosphorylation. Knock down of ataxia telangiectasia mutated suppressed γH2AX and CHK2 phosphorylation and enhanced drug combination lethality. Collectively our data demonstrate that the combination of PDE5 inhibitors with standard of care chemotherapy agents for gastrointestinal/genitourinary cancers represents a novel modality.

Inhibition of NRF2 by PIK-75 augments sensitivity of pancreatic cancer cells to gemcitabine

We describe the potential benefit of PIK-75 in combination of gemcitabine to treat pancreatic cancer in a preclinical mouse model. The effect of PIK-75 on the level and activity of NRF2 was characterized using various assays including reporter gene, quantitative PCR, DNA-binding and western blot analyses. Additionally, the combinatorial effect of PIK-75 and gemcitabine was evaluated in human pancreatic cancer cell lines and a xenograft model. PIK-75 reduced NRF2 protein levels and activity to regulate its target gene expression through proteasome-mediated degradation of NRF2 in human pancreatic cancer cell lines. PIK-75 also reduced the gemcitabine-induced NRF2 levels and the expression of its downstream target MRP5. Co-treatment of PIK-75 augmented the antitumor effect of gemcitabine both in vitro and in vivo. Our present study provides a strong mechanistic rationale to evaluate NRF2 targeting agents in combination with gemcitabine to treat pancreatic cancers.

Recombinant adenovirus-p53 (Gendicine) sensitizes a pancreatic carcinoma cell line to radiation

OBJECTIVE

In this study, we examine the effects of recombinant adenovirus-p53 (rAd-p53) on the pancreatic carcinoma cell line SW1990. Specifically, we determine if expression of rAd-p53 sensitizes these cells to radiation.

METHODS

Following transfection of SW1990 cells with rAd-p53, we measured expression of P53, P21 and Bax by immunocytochemistry. Both transfected and control cell lines were irradiated with a range of doses, and the survival fractions (SF) were calculated. Dose survival curves were constructed and modeled for comparison.

RESULTS

Transfection of SW1990 cells with rAd-p53 resulted in increased expression of P53, P21 and Bax in a time-dependent manner. At 96 h after transfection, 89.92% of cells expressed P53, 56.8% expressed P21, and 76.50% expressed Bax. The SF following radiation was lower in the rAd-p53 transfected cells compared to the control cells, suggesting that rAd-p53 sensitizes SW1990 cells to radiation (D0 for the experimental and control groups was 2.199 and 2.462, respectively).

CONCLUSIONS

Use of the adenoviral vector is an effective means of transfecting SW1990 cells with wild-type P53, and this sensitizes the cell line to irradiation. This work suggests that combining rAd-p53 with radiation therapy in pancreatic cancer may be therapeutically beneficial.