A protein kinase Cbeta inhibitor attenuates multidrug resistance of neuroblastoma cells

Evo312: An Evodiamine Analog and Novel PKCβI Inhibitor with Potent Antitumor Activity in Gemcitabine-Resistant Pancreatic Cancer

As an obstinate cancer pancreatic cancer (PC) poses a major challenge due to limited treatment options which include resection surgery, radiation therapy, and gemcitabine-based chemotherapy. In cancer cells, protein kinase C βI (PKCβI) participates in diverse cellular processes, including cell proliferation, invasion, and apoptotic pathways. In the present study, we created a scaffold to develop PKCβI inhibitors using evodiamine-based synthetic molecules. Among the candidate inhibitors, Evo312 exhibited the highest antiproliferative efficacy against PC cells, PANC-1, and acquired gemcitabine-resistant PC cells, PANC-GR. Additionally, Evo312 robustly inhibited PKCβI activity. Mechanistically, Evo312 effectively suppressed the upregulation of PKCβI protein expression, leading to the induction of cell cycle arrest and apoptosis in PANC-GR cells. Furthermore, Evo312 exerted an antitumor activity in a PANC-GR cell-implanted xenograft mouse model. These findings position Evo312 as a promising lead compound for overcoming gemcitabine resistance in PC through novel mechanisms.

Didymin: an orally active citrus flavonoid for targeting neuroblastoma

Neuroblastoma, a rapidly growing yet treatment responsive cancer, is the third most common cancer of children and the most common solid tumor in infants. Unfortunately, neuroblastoma that has lost p53 function often has a highly treatment-resistant phenotype leading to tragic outcomes. In the context of neuroblastoma, the functions of p53 and MYCN (which is amplified in ~25% of neuroblastomas) are integrally linked because they are mutually transcriptionally regulated, and because they together regulate the catalytic activity of RNA polymerases. Didymin is a citrus-derived natural compound that kills p53 wild-type as well as drug-resistant p53-mutant neuroblastoma cells in culture. In addition, orally administered didymin causes regression of neuroblastoma xenografts in mouse models, without toxicity to non-malignant cells, neural tissues, or neural stem cells. RKIP is a Raf-inhibitory protein that regulates MYCN activation, is transcriptionally upregulated by didymin, and appears to play a key role in the anti-neuroblastoma actions of didymin. In this review, we discuss how didymin overcomes drug-resistance in p53-mutant neuroblastoma through RKIP-mediated inhibition of MYCN and its effects on GRK2, PKCs, Let-7 micro-RNA, and clathrin-dependent endocytosis by Raf-dependent and -independent mechanisms. In addition, we will discuss studies supporting potential clinical impact and translation of didymin as a low cost, safe, and effective oral agent that could change the current treatment paradigm for refractory neuroblastoma.

Guaiazulene biochemical activity and cytotoxic and genotoxic effects on rat neuron and N2a neuroblastom cells

AIM

Neuroblastoma (NB)cells are often used in cancer researches such as glioblastoma cells since they have the potential of high mitotic activity, nuclear pleomorphism, and tumor necrosis. Guaiazulene (GYZ 1,4-dimethyl-7-isopropylazulene)is present in several essential oils of medicinal and aromatic plants. Many studies have reported the cytotoxic effect of GYZ; however, there are no studies that compare such effects between cancer cell lines and normal human cells after treatment with GYZ.

MATERIALS AND METHODS

In this study, we aimed to describe in vitro antiproliferative and/or cytotoxic properties (by 3-[4,5 dimetylthiazol -2-yl]-2,5 diphenlytetrazolium bromide [MTT] test), oxidative effects (by total antioxidant capacity [TAC] and total oxidative stress [TOS] analysis)and genotoxic damage potentials (by single cell gel electrophoresis)of GYZ.

RESULT

The results indicated that GYZ have anti-proliferative activity suppressing the proliferation of neuron and N2a-NB cells at high doses. In addition, GYZ treatments at higher doses led to decreases of TAC levels and increases of TOS levels in neuron and N2a-NB cells. On the other hand, the mean values of the total scores of cells showing DNA damage were not found different from the control values.

CONCLUSION

From this study, it is observed that GYZ has in vitro cytotoxic activity against neuron and N2a-NB cells.

FZD1 activates protein kinase C delta-mediated drug-resistance in multidrug-resistant MES-SA/Dx5 cancer cells

Multidrug-resistant (MDR) cancer is a major clinical problem in chemotherapy of cancer patients. We have noted inappropriate PKCδ hypomethylation and overexpression of genes in the PKCδ/AP-1 pathway in the human uterus sarcoma drug-resistant cell line, MES-SA/Dx5 cells, which also overexpress p-glycoprotein (ABCB1). Recent studies have indicated that FZD1 is overexpressed in both multidrug-resistant cancer cell lines and in clinical tumor samples. These data have led us to hypothesize that the FZD1-mediated PKCδ signal-transduction pathway may play an important role in drug resistance in MES-SA/Dx5 cells. In this work, the PKCδ inhibitor Rottlerin was found to reduce ABCB1 expression and to inhibit the MDR drug pumping ability in the MES-SA/Dx5 cells when compared with the doxorubicin-sensitive parental cell line, MES-SA. PKCδ was up-regulated with concurrent up-regulation of the mRNA levels of the AP-1-related factors, c-JUN and c-FOS. Activation of AP-1 also correlated with up-regulation of the AP-1 downstream genes HGF and EGR1. Furthermore, AP-1 activities were reduced and the AP-1 downstream genes were down-regulated in Rottlerin-treated or PKCδ shRNA-transfected cells. MES-SA/Dx5 cells were resensitized to doxorubicin-induced toxicity by co-treatment with doxorubicin and Rottlerin or PKCδ shRNA. In addition, cell viability and drug pump-out ability were significantly reduced in the FZD1 inhibitor curcumin-treated and FZD1 shRNA-knockdown MES-SA/Dx5 cells, indicating involvement of PKCδ in FZD1-modulated ABCB1 expression pathway. Taken together, our data demonstrate that FZD1 regulates PKCδ, and the PKCδ/AP-1 signalling transduction pathway plays an important role in drug resistance in MES-SA/Dx5 cells.

Cytotoxicity and genotoxicity of zingiberene on different neuron cell lines in vitro

The main objective of this study is to investigate the cytotoxic, genotoxic and antioxidant properties of zingiberene (ZBN) in an in vitro rat brain cell culture study. The cytotoxic effect was determined against the rat neuron and N2a neuroblastoma (N2a-NB) cell lines using the 3,(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, while the antioxidant activity was assessed using the total antioxidant capacity (TAC) and total oxidative stress (TOS) assays. The effects on DNA damage were also evaluated in this study by the single cell gel electrophoresis assay. The results indicated that ZBN has an anti-proliferative activity suppressing the proliferation of N2a-NB cells at concentrations over 50 mg L(-1) and neuron cells at concentrations over 150 mg L(-1). In addition, ZBN treatments at higher doses (≤50 mg L(-1)) led to increases of TOS levels in N2a-NB cell cultures. However 25 mg L(-1) of ZBN treatment caused increases of TAC levels in cultured neuron and N2a-NB cell cultures while ZBN at doses of 10-400 mg L(-1) did not increase the number of total damage score in both cell lines. This study clearly indicates that ZBN has a significant potential to be used as a natural anticancer agent in cultured N2a-NBs.

Protein kinase C iota as a therapeutic target in alveolar rhabdomyosarcoma

Alveolar rhabdomyosarcoma is an aggressive pediatric cancer exhibiting skeletal muscle differentiation. New therapeutic targets are required to improve the dismal prognosis for invasive or metastatic alveolar rhabdomyosarcoma. Protein kinase C iota (PKCι) has been shown to play an important role in tumorigenesis of many cancers but little is known about its role in rhabdomyosarcoma. Our gene expression studies in human tumor samples revealed overexpression of PRKCI. We confirmed overexpression of PKCι at the mRNA and protein level using our conditional mouse model that authentically recapitulates the progression of rhabdomyosarcoma in humans. Inhibition of Prkci by RNA interference resulted in a dramatic decrease in anchorage-independent colony formation. Interestingly, treatment of primary cell cultures using aurothiomalate (ATM), which is a gold-containing classical anti-rheumatic agent and a PKCι-specific inhibitor, resulted in decreased interaction between PKCι and Par6, decreased Rac1 activity and reduced cell viability at clinically relevant concentrations. Moreover, co-treatment with ATM and vincristine, a microtubule inhibitor currently used in rhabdomyosarcoma treatment regimens, resulted in a combination index (C. I.) of 0.470–0.793 through cooperative accumulation of non-proliferative multinuclear cells in the G2/M phase, indicating that these two drugs synergize. For in vivo tumor growth inhibition studies, ATM demonstrated a trend towards enhanced vincristine sensitivity. Overall, these results suggest that PKCι is functionally important in alveolar rhabdomyosarcoma anchorage-independent growth and tumor cell proliferation and that combination therapy with ATM and microtubule inhibitors holds promise for the treatment of alveolar rhabdomyosarcoma.

A novel PKC-ι inhibitor abrogates cell proliferation and induces apoptosis in neuroblastoma

Protein Kinase C-iota (PKC-ι), an atypical protein kinase C isoform manifests its potential as an oncogene by targeting various aspects of cancer cells such as growth, invasion and survival. PKC-ι confers resistance to drug-induced apoptosis in cancer cells. The acquisition of drug resistance is a major obstacle to good prognosis in neuroblastoma. The focus of this research was to identify the efficacy of [4-(5-amino-4-carbamoylimidazol-1-yl)-2,3-dihydroxycyclopentyl] methyl dihydrogen phosphate (ICA-1) as a novel PKC-ι inhibitor in neuroblastoma cell proliferation and apoptosis. ICA-1 specifically inhibits the activity of PKC-ι but not that of PKC-zeta (PKC-ζ), the closely related atypical PKC family member. The IC(50) for the kinase activity assay was approximately 0.1μM which is 1000 times less than that of aurothiomalate, a known PKC-ι inhibitor. Cyclin dependent kinase 7 (Cdk7) phosphorylates cyclin dependent kinases (cdks) and promotes cell proliferation. Our data shows that PKC-ι is an in vitro Cdk7 kinase and the phosphorylation of Cdk7 by PKC-ι was potently inhibited by ICA-1. Furthermore, our data shows that neuroblastoma cells proliferate via a PKC-ι/Cdk7/cdk2 cell signaling pathway and ICA-1 mediates its antiproliferative effects by inhibiting this pathway. ICA-1 (0.1μM) inhibited the in vitro proliferation of BE(2)-C neuroblastoma cells by 58% (P=0.01). Additionally, ICA-1 also induced apoptosis in neuroblastoma cells. Interestingly, ICA-1 did not affect the proliferation of normal neuronal cells suggesting its potential as chemotherapeutic with low toxicity. Hence, our results emphasize the potential of ICA-1 as a novel PKC-ι inhibitor and chemotherapeutic agent for neuroblastoma.

Antisense expression of PKCα improved sensitivity of SGC7901/VCR cells to doxorubicin

AIM: To explore whether antisense blocking of protein kinase C alpha (PKCα) would reverse multi-drug resistance (MDR) in the vincristine (VCR)-resistant human gastric cancer cell line SGC7901/VCR.

METHODS: SGC7901/VCR cells expressing antisense PKCα, SGC7901/VCR/aPKC, were established by transfection with a recombinant plasmid reversely inserted with PKCα cDNA. Empty vector (PCI-neo)-transfected cell clones, SGC7901/VCR/neo, served as the control. Western blot method was used to detect PKCα content in SGC7901, SGC7901/VCR, SGC7901/VCR/neo and SGC7901/VCR/aPKC cells, using PKCα-specific antibody. The sensitivity of SGC7901, SGC7901/VCR, SGC7901/VCR/neo and SGC7901/VCR/aPKC cells to doxorubicin (DOX) in vitro was determined by MTT assay. The uptake of DOX in these cells was detected with fluorescence spectrophotometer.

RESULTS: Western blot analysis showed that the PKCα protein level was about 8.7-fold higher in SGC7901/VCR cells than that in SGC7901 cells, whereas the protein expression of PKCα was reduced by 78% in SGC7901/VCR/aPKC cells when compared with the SGC7901/VCR cells. SGC7901/VCR/aPKC cells had a 4.2-fold increase in DOX cytotoxicity, accompanied by a 1.7-fold increase of DOX accumulation in comparison with SGC7901/VCR cells.

CONCLUSION: PKCα positively regulates MDR in SGC7901 cells, and inhibition of PKCα can partially attenuate MDR in human gastric cancer cells.

New approaches to pharmacotherapy of tumors of the nervous system during childhood and adolescence

Tumors of the nervous system are among the most common and most chemoresistant neoplasms of childhood and adolescence. Malignant tumors of the brain collectively account for 21% of all cancers and 24% of all cancer-related deaths in this age group. Neuroblastoma, a peripheral nervous system tumor, is the most common extracranial solid tumor of childhood, and 65% of children with this tumor have only a 10 or 15% chance of living 5 years beyond the time of initial diagnosis. Novel pharmacological approaches to nervous system tumors are urgently needed. This review presents the role of and current challenges to pharmacotherapy of malignant tumors of the nervous system during childhood and adolescence and discusses novel approaches aimed at overcoming these challenges.

Protein kinase C activation and its role in kidney disease (Review Article)

Protein kinase C (PKC) comprises a superfamily of isoenzymes, many of which are activated by cofactors such as diacylglycerol and phosphatidylserine. In order to be capable of activation, PKC must first undergo a series of phosphorylations. In turn, activated PKC phosphorylates a wide variety of intracellular target proteins and has multiple functions in signal transduced cellular regulation. A role for PKC activation had been noted in several renal diseases, but two that have had most investigation are diabetic nephropathy and kidney cancer. In diabetic nephropathy, an elevation in diacylglycerol and/or other cofactor stimulants leads to an increase in activity of certain PKC isoforms, changes that are linked to the development of dysfunctional vasculature. The ability of isoform-specific PKC inhibitors to antagonize diabetes-induced vascular disease is a new avenue for treatment of this disorder. In the development and progressive invasiveness of kidney cancer, increased activity of several specific isoforms of PKC has been noted. It is thought that this may promote the kidney cancer's inherent resistance to apoptosis, in natural regression or after treatments, or it may promote the invasiveness of renal cancers via cellular differentiation pathways. In general, however, a more complete understanding of the functions of individual PKC isoforms in the kidney, and development or recognition of specific inhibitors or promoters of their activation, will be necessary to apply this knowledge for treatment of cellular dysregulation in renal disease.