Characterisation of novel human lung carcinoma cell lines selected for resistance to anti-neoplastic analogues of staurosporine

Midostaurin Reverses ABCB1-Mediated Multidrug Resistance, an in vitro Study

Overexpression of ABC transporters in cancer cells is an underlying mechanism of multidrug resistance (MDR), leading to insensitive response to chemotherapeutic strategies. Thus, MDR is often results in treatment failure in the clinic. In this study, we found midostaurin, a Food and Drug Administration (FDA)-approved anti-leukemia drug, can antagonize ATP-binding cassette subfamily B member 1 (ABCB1)-mediated MDR. Our results indicated that midostaurin has the capacity to antagonize ABCB1-mediated MDR, while no significant reversal effect was found on ATP-binding cassette subfamily G member 2 (ABCG2)-mediated MDR. Our subsequent resistance mechanism studies showed that midostaurin directly inhibited the efflux function of the ABCB1 transporter without alteration of the expression level or the subcellular localization of ABCB1 transporter. In addition, midostaurin inhibited the ATPase activity of ABCB1 transporter in a dose-dependent manner. Moreover, our in silico docking study predicted that midostaurin could interact with the substrate-binding sites of ABCB1 transporter. This novel finding could provide a promising treatment strategy that co-administrating midostaurin with anticancer drugs in the clinic could overcome MDR and improve the efficiency of cancer treatment.

Sustained PKCβII activity confers oncogenic properties in a phospholipase D- and mTOR-dependent manner

Protein kinase C (PKC) is a family of serine/threonine kinases implicated in a variety of physiological processes. We have shown previously that sustained activation of the classical PKCα and PKCβII induces their phospholipase D (PLD)-dependent internalization and translocation to a subset of the recycling endosomes defined by the presence of PKC and PLD (the pericentrion), which results in significant differences in phosphorylation of PKC substrates. Here, we have investigated the biological consequences of sustained PKC activity and the involvement of PLD in this process. We find that sustained activation of PKC results in activation of the mammalian target of rapamycin (mTOR)/S6 kinase pathway in a PLD- and endocytosis-dependent manner, with both pharmacologic inhibitors and siRNA implicating the PLD2 isoform. Notably, dysregulated overexpression of PKCβII in A549 lung cancer cells was necessary for the enhanced proliferation and migration of these cancer cells. Inhibition of PKCβII with enzastaurin reduced A549 cell proliferation by >60% (48 h) and migration by >50%. These biological effects also required both PLD activity and mTOR function, with both the PLD inhibitor FIPI and rapamycin reducing cell growth by >50%. Reciprocally, forced overexpression of wild-type PKCβII, but not an F666D mutant that cannot interact with PLD, was sufficient to enhance cell growth and increase migration of noncancerous HEK cells; indeed, both properties were almost doubled when compared to vector control and PKC-F666D-overexpressing cells. Notably, this condition was also dependent on both PLD and mTOR activity. In summary, these data define a PKC-driven oncogenic signaling pathway that requires both PLD and mTOR, and suggest that inhibitors of PLD or mTOR would be beneficial in cancers where PKC overexpression is a contributing or driving factor.

Monolayers of porcine alveolar epithelial cells in primary culture as an in vitro model for drug absorption studies

Filter-grown monolayers of porcine alveolar epithelial cells (pAEpC) in primary culture have been characterized as an in vitro model for pulmonary absorption screening of xenobiotics, including substrates of efflux systems. Experimental conditions and a protocol for transport experiments were optimized using transepithelial electrical resistances (TEER) and permeability of marker compounds as acceptance criteria. Since new drugs often feature poor water solubility, monolayer integrity in the presence of a solubilizer (dimethyl sulfoxide) was tested. Transport studies were carried out with budesonide and triamcinolone acetonide, i.e., two drugs commonly administered to the lungs. Furthermore, expression of P-glycoprotein (P-gp) was assessed by immunofluorescence microscopy and transport studies employing the substrates rhodamine 123 and digoxin. Hydrocortisone-supplemented (0.5 microg/ml) small airway basal medium as transport buffer and a maximal solubilizer concentration of 1.5% dimethyl sulfoxide were found to provide suitable conditions for drug transport studies across pAEpC, as reflected, e.g., by a minimum TEER of 600 Omega cm(2). Permeation of marker compounds was reproducible throughout several cell preparations and proved the model successful in distinguishing between low- and high-permeable drugs. P-gp expression was confirmed by immunocytochemistry, even though transport studies revealed no polarity in transepithelial marker transport. In conclusion, our results demonstrate that filter-grown monolayers of pAEpC can be used to study drug transport across alveolar epithelial barrier and thus, may represent a suitable in vitro model for pulmonary drug absorption and delivery.

Modulation of function of multidrug resistance associated-proteins by Kaempferia parviflora extracts and their components

In this study, the effects of extracts and flavone derivatives from the rhizome of Kaempferia parviflora on multidrug resistance associated-proteins (MRP)-mediated transport in A549 cells were examined. The cells employed express MRP1 and MRP2, but not P-glycoprotein. The cellular accumulation of calcein, an MRP substrate, was significantly increased by various MRP inhibitors without being affected by verapamil, a typical P-glycoprotein inhibitor. Ethanol and aqueous extracts from K. parviflora rhizome increased the accumulation of calcein and doxorubicin in A549 cells in a concentration-dependent manner. The inhibitory potency of the ethanol extract for MRP function was greater than that of the aqueous extract. Among six flavone derivatives isolated from K. parviflora rhizome, 5,7-dimethoxyflavone exhibited a maximal stimulatory effect on the accumulation of doxorubicin in A549 cells. The accumulation of doxorubicin was increased by four flavone derivatives without 5-hydroxy group, but not by the other two flavone derivatives with 5-hydroxy group. In addition, 5,7-dimethoxyflavone and 3,5,7,3',4'-pentamethoxyflavone decreased resistance to doxorubicin in A549 cells. These findings indicate that extracts and flavone derivatives from the rhizome of K. parviflora suppress MRP function, and therefore may be useful as modulators of multidrug resistance in cancer cells.

Phase I and pharmacokinetic study of UCN-01 in combination with irinotecan in patients with solid tumors

PURPOSE

7-Hydroxystaurosporine (UCN-01) is a protein kinase inhibitor that inhibits several serine-threonine kinases including PKC and PDK1. Due to the preclinical synergistic effects seen with topoisomerase I inhibitors and non-overlapping toxicity, UCN-01 and irinotecan were combined in a dose-finding study designed to determine the maximum tolerated dose (MTD), toxicity profile, and pharmacokinetics (PK) of UCN-01 and irinotecan.

METHODS

Patients with incurable solid malignancies received UCN-01 intravenously (IV) as a 3-h infusion on day 1 and irinotecan IV over 90 min on days 1 and 8 of a 21-day cycle. Doses of UCN-01 for subsequent cycles were half the starting dose. Dose level 1 (DL1) consisted of UCN-01 and irinotecan doses of 50 and 60 mg/m(2), respectively. Blood samples were collected in cycle 1 for UCN-01, irinotecan, and irinotecan metabolites.

RESULTS

A total of 16 patients were enrolled on the trial at UCN-01/Irinotecan doses of 50/60 mg/m(2) (DL1; n = 1), 70/60 mg/m(2) (DL2; n = 6), 90/60 mg/m(2) (DL3; n = 4), and 70/90 mg/m(2) (DL4; n = 5). Two dose-limiting toxicities were observed each in DL3 and DL4 (2 grade 3 hypophosphatemia, 1 grade 4 hyperglycemia and grade 3 hypophosphatemia, 1 grade 4 febrile neutropenia). Fatigue, diarrhea, nausea, and anorexia were the most prevalent toxicities. No objective responses were documented, and four patients had stable disease for at least ten cycles. The long half-life (292.0 +/- 135.7 h), low clearance (0.045 +/- 0.038 l/h), and volume of distribution (14.3 +/- 5.9 l) observed for UCN-01 are consistent with prior UCN-01 data. There was a significant decrease in C(max) of APC, AUC of APC and SN-38, and AUC ratio of SN-38:irinotecan when comparing days 1 and 8 PK.

CONCLUSIONS

APC and SN-38 exposure decreased when administered in combination with UCN-01. The MTD of the combination based on protocol criteria was defined as 70 mg/m(2) of UCN-01 on day 1 and 60 mg/m(2) of irinotecan on days 1 and 8 in a 21-day cycle.

Cell culture models of the respiratory tract relevant to pulmonary drug delivery

The respiratory tract holds promise as an alternative site of drug delivery due to fast absorption and rapid onset of drug action, with avoidance of hepatic and intestinal first-pass metabolism as an additional benefit compared to oral drug delivery. At present, the pharmaceutical industry increasingly relies on appropriate in vitro models for the faster evaluation of drug absorption and metabolism as an alternative to animal testing. This article reviews the various existing cell culture systems that may be applied as in vitro models of the human air-blood barrier, for instance, in order to enable the screening of large numbers of new drug candidates at low cost with high reliability and within a short time span. Apart from such screening, cell culture-based in vitro systems may also contribute to improve our understanding of the mechanisms of drug transport across such epithelial tissues, and the mechanisms of action how advanced drug carriers, such as nanoparticles or liposomes, can help to overcome these barriers. After all, the increasing use and acceptance of such in vitro models may lead to a significant acceleration of the drug development process by facilitating the progress into clinical studies and product registration.

Cell cycle modulators for the treatment of lung malignancies

It has become clear in the past decade that most human malignancies, including lung neoplasms, have aberrations in cell cycle control. The tumor suppressor gene retinoblastoma is an important player in the G1/S transition and its function is abnormal in most human neoplasms. Retinoblastoma function is lost as a result of phosphorylation by the cyclin-dependent kinases (CDKs). Thus, modulation of CDKs may have an important use for the therapy and prevention of human neoplasms. Direct CDK modulators are small molecules that target specifically the adenosine triphosphate binding site of CDKs. In contrast, indirect CDK modulators affect CDK function by modulation of upstream pathways required for CDK activation. The first example of a direct small-molecule CDK modulator tested in the clinic, flavopiridol, is a pan-CDK inhibitor that not only promotes cell cycle arrest but also halts transcriptional elongation, promotes apoptosis, induces differentiation, and has antiangiogenic properties. The second example of direct small-molecule CDK modulators tested in clinical trials is UCN-01 (7-hydroxystaurosporine). UCN-01 has interesting preclinical features: it inhibits Ca2+-dependent protein kinase C, promotes apoptosis, arrests cell cycle progression at G1/S, and abrogates checkpoints upon DNA damage. In summary, novel small-molecule CDK modulators are being tested in the clinic with interesting results. Although these small molecules are directed toward a very prevalent cause of carcinogenesis, their role in the clinical armamentarium is still uncertain.

Constitutive expression of p-glycoprotein in normal lung alveolar epithelium and functionality in primary alveolar epithelial cultures

The multidrug resistant (MDR) transporter P-glycoprotein (P-gp) is constitutively expressed in normal tissues, where its spatial distribution defines it as an important element reducing the systemic exposure and tissue access of potentially harmful xenobiotics. We sought to determine whether P-gp is functionally expressed within alveolar epithelium of lung, in particular within the predominant cell type of this barrier, the alveolar epithelial (AE) type I cell. By immunohistochemistry, MDR-1/mdr-1 P-gp was localized to luminal membranes of AE type I epithelium within normal human and rat lung tissue. Using a primary rat cell culture model affording study of AE type II to AE type I differentiation, we observed increased expression (reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and immunoflow cytometry techniques) of mdr-1a and mdr-1b P-gp in the cultures as they adopted an AE type I phenotype; freshly isolated AE type II cells were negative for mdr-1/P-gp. The functionality of P-gp within the AE cultures was demonstrated by a flow cytometric accumulation-retention assay using rhodamine-123 as substrate, and also by the polarized transport of vinblastine across confluent AE type I monolayers (basal-to-apical permeability was 3-fold that of apical-to-basal permeability), which was found to be comparable with the P-gp transport barrier presented by Caco-2 cell monolayers. The implications of localizing P-gp within alveolar epithelium is of significance to studies of fundamental respiratory cell biology as well as to further clarifying the nature of the barrier to xenobiotic transfer from alveolar airspace to pulmonary interstitium and capillary blood.

Anti-proliferative effects of new staurosporine derivatives isolated from a marine ascidian and its predatory flatworm

Nine indolocarbazole alkaloids of the staurosporine type, including three new derivatives, were evaluated for their potential as inhibitors of cell proliferation and macromolecule synthesis. Four derivatives were tested as inhibitors of cell proliferation with twelve human leukemia cell lines and demonstrated powerful antiproliferative activities, with 3-hydroxystaurosporine being the most potent. IC(50) values were determined using the cell line MONO-MAC-6 and with an IC(50) of 13 ng/ml, 3-hydroxystaurosporine turned out to be one of the most active staurosporine-type inhibitors described so far. All derivatives, except 3-hydroxy-3'-demethoxy-3'-hydroxystaurosporine and 4'-N-methylstaurosporine very strongly reduced RNA and DNA synthesis with 3-hydroxystaurosporine again being the strongest inhibitor. Analysis of structure-activity relationships demonstrated that hydroxylation of staurosporine at position 3 of the indolocarbazole moiety caused an increase in anti-proliferative activity, while hydroxylation at carbon 11 resulted in a decrease in activity. Our results suggest that not only the presence or absence of hydrophilic substitutions, but also the position of the alteration within the molecule, is important in the antiproliferative properties of the various staurosporine analogues.

Modulation of protein kinase C in antitumor treatment

PKC isoenzymes were found to be involved in proliferation, antitumor drug resistance and apoptosis. Therefore, it has been tried to exploit PKC as a target for antitumor treatment. PKC alpha activity was found to be elevated, for example, in breast cancers and malignant gliomas, whereas it seems to be underexpressed in many colon cancers. So it can be expected that inhibition of PKC activity will not show similar antitumor activity in all tumors. In some tumors it seems to be essential to inhibit PKC to reduce growth. However, for inhibition of tumor proliferation it may be an advantage to induce apoptosis. In this case an activation of PKC delta should be achieved. The situation is complicated by the facts that bryostatin leads to the activation of PKC and later to a downmodulation and that the PKC inhibitors available to date are not specific for one PKC isoenzyme. For these reasons, PKC modulation led to many contradicting results. Despite these problems, PKC modulators such as miltefosine, bryostatin, safingol, CGP41251 and UCN-01 are used in the clinic or are in clinical evaluation. The question is whether PKC is the major or the only target of these compounds, because they also interfere with other targets. PKC may also be involved in apoptosis. Oncogenes and growth factors can induce cell proliferation and cell survival, however, they can also induce apoptosis, depending on the cell type or conditions in which the cells or grown. PKC participates in these signalling pathways and cross-talks. Induction of apoptosis is also dependent on many additional factors, such as p53, bcl-2, mdm2, etc. Therefore, there are also many contradicting results on PKC modulation of apoptosis. Similar controversial data have been reported about MDR1-mediated multidrug resistance. At present it seems that PKC inhibition alone without direct interaction with PGP will not lead to successful reversal of PGP-mediated drug efflux. One possibility to improve chemotherapy would be to combine established antitumor drugs with modulators of PKC. However, here also very contrasting results were obtained. Many indicate that inhibition, others, that activation of PKC enhances the antiproliferative activity of anticancer drugs. The problem is that the exact functions of the different PKC isoenzymes are not clear at present. So further investigations into the role of PKC isoenzymes in the complex and interacting signalling pathways are essential. It is a major challenge in the future to reveal whether modulation of PKC can be used for the improvement of cancer therapy.

Protein kinase C isoforms involved in regulation of cell shape and locomotion of human fibrosarcoma HT1080 cells

The role of protein kinase C (PKC) isoforms in the regulation of cell shape [switch between fibroblast-like and crescent shape (CS)] and of locomotion of human fibrosarcoma HT1080 cells has been investigated. The PKC activator phorbol myristate acetate (PMA) induced the transition of elongated fibroblast-like cells into CS cells and stimulated locomotion. Both responses to PMA were inhibited by the PKC inhibitor Ro 31-8220. Analysis of the time course showed that stimulation of shape changes (formation of CS cells) and locomotor activity (increase in the proportion and speed of locomoting cells) was maximal in the early phase of the response (up to 2.5 hr) and significantly decreased later (15 to 21 hr). CS formation and stimulated locomotion correlated closely with a marked redistribution from the cytosol to the membrane of PKC isoforms alpha, beta1 and gamma in the early phase (0.5 to 2 hr) following activation with PMA. The subsequent reduction of the proportion of CS cells and of cell locomotion correlated with down-regulation of these isoforms in the second phase (16 to 21 hr). In contrast, the total amount and distribution of PKC beta2 remained almost unchanged with 10(-8) M PMA up to 21 hr. Furthermore, changes in shape and locomotion did not correlate with the responses of PKC delta to PMA. Inhibition of PMA-stimulated locomotion by the more specific inhibitor Gö 6976 is consistent with a role of PKC alpha and beta1 in this response. Ro 31-8220 alone induced a moderate down-regulation of PKC isoforms alpha and delta, but it also inhibited the more pronounced down-regulation of these isoforms by PMA. Our results indicate that activation of PKC isoforms alpha, gamma and beta1, but not beta2 or delta, stimulates locomotion and formation of CS cells in human fibrosarcoma HT1080 cells.

Staurosporine analogues - pharmacological toys or useful antitumour agents?

This review summarises the evidence for the potential antineoplastic activity of the staurosporine analogues 7-hydroxystaurospine (UCN-01) and N-benzoylstaurosporine (CGP 41251) and defines the role of the enzyme family protein kinase C (PKC) in the mechanisms by which these agents interfere with malignant cell growth. PKC function is altered in some neoplasias, and this dysfunction has been related to uncontrolled proliferation. PKC also influences resistance of cancer cells against cytotoxic drugs. Staurosporine analogues compete with ATP, even though the exact action by which they inhibit PKC is more complicated. Staurosporine analogues do not exhibit specificity for particular PKC isoenzymes, but they inhibit 'conventional' PKC isoenzymes more potently than 'novel' and 'atypical' ones. They also interfere directly with the cell cycle machinery. Both CGP 41251 and UCN-01 are currently progressing through clinical evaluation. There is a remarkable difference in pharmacokinetic handling of CGP 41251 and UCN-01 between rodents and humans. CGP 41251 and UCN-01 might offer advantages in cancer therapy when applied in combination with conventional cytotoxic agents.

Molecular determinants of UCN-01-induced growth inhibition in human lung cancer cells

UCN-01 (7-hydroxystaurosporine) inhibits the growth of various malignant cell lines in vitro and in vivo. In this study, a human small cell lung carcinoma subline resistant to UCN-01, SBC-3/UCN, was established and characterized. SBC-3/UCN cells showed 8-fold greater resistance to the UCN-01-induced growth-inhibitory effect than the parent cells, SBC-3. No UCN-01-induced G1 accumulation in SBC-3 cells was observed in SBC-3/UCN cells and decreased expression of phosphorylated RB protein was found in SBC-3 cells. Neither basal expression nor induction of p21(Cip1) by UCN-01 treatment was detected in the SBC-3/UCN cell line. An inhibitory effect of UCN-01 on CDK2 activity, which is mediated by p21(Cip1)/CDK2 complex formation upon UCN-01 treatment, was observed in SBC-3 but not in SBC-3/UCN cells. SBC-3/UCN showed higher CDK6 activity than SBC-3 cells. UCN-01 did not inhibit the CDK4 and CDK6 activities in both cells. We screened the cell cycle regulatory molecules associated with G(1)/S progression and found a remarked decrease in interferon regulatory factor 1 (IRF-1), which is known to cooperate with p53 in p21(Cip1) induction. Our results suggest that p21(Cip1) regulation via the IRF-1-associated pathway may represent a major determinant of UCN-01-induced growth inhibition in human lung cancer cells.

Drug resistance in lung cancer

The major problem in lung cancer chemotherapy is the emergence of inherent and acquired drug resistance of the cancer cells. Establishment of drug-resistant sublines and comparative investigations of such cell lines with their parental cells to determine their molecular, biologic, and biochemical properties are important research strategies. Genetic changes in tumor cells may induce changes in their biochemical properties and chemosensitivity. Many mechanisms that render tumor cells resistant have been identified, and they have provided new molecular targets for surrogate markers to predict chemosensitivity. The new categories of anticancer drugs, such as topoisomerase I inhibitors and taxanes, and non-cytotoxic new drugs, have been introduced clinically. It is important to define the molecular determinants of resistance to these drugs. The development of an appropriate model for overcoming drug resistance is one of the important issues that should be solved before carrying out further clinical trials.

Analogs of staurosporine: potential anticancer drugs?

1. Protein kinase C (PKC) is a family of serine/threonine-directed protein kinases that are pivotal regulators of cellular growth, transformation and death. PKC has therefore been considered to be a suitable target for novel antineoplastic drugs. 2. Twenty years ago, staurosporine was isolated from bacteria and identified as a potent inhibitor of PKC activity. Its analogs UCN-01 and CGP 41251 effectively arrest the growth of several human-derived tumor cell lines in vitro. They also possess antineoplastic activity in vivo in human tumors grown as xenografts in nude mice. CGP 41251 reverses the multidrug-resistance phenotype of cancer cells. Both agents are currently under clinical evaluation as potential antitumor drugs. 3. Staurosporine analogs inhibit "conventional" PKC isoenzymes more potently than "novel" and "atypical" ones. They are also potent modulators of the cyclin-dependent kinase system, which determines the progression of cells through the cell cycle. The nature of this interaction is complex. UCN-01 blocks cells in G1 phase by promoting accumulation of dephosphorylated retinoblastoma protein as a consequence of inhibition of the activity of certain cyclin-dependent kinases, downregulation of their partner cyclins and an increase in the expression of cyclin-dependent kinase inhibitor proteins. 4. Preliminary results of early clinical trials suggest that UCN-01 and CGP41251 are without remarkable toxicity but display high binding to human plasma protein.

New perspectives on PKCtheta, a member of the novel subfamily of protein kinase C

Members of the protein kinase C (PKC) family of serine/threonine protein kinases have been implicated in numerous cellular responses in a large variety of cell types. Expression patterns of individual members and differences in their cofactor requirements and potential substrate specificity suggest that each isoenzyme may be involved in specific regulatory processes. The PKCtheta isoenzyme exhibits a relatively restricted expression pattern with high protein levels found predominantly in hematopoietic cells and skeletal muscle. PKCtheta was found to be expressed in T, but not B lymphocytes, and to colocalize with the T-cell antigen receptor (TCR) at the site of contact between the antigen-responding T cell and the antigen-presenting cell (APC). Colocalization of PKCtheta with the TCR was selective for this isoenzyme and occurred only upon antigen-mediated responses leading to T-cell activation and proliferation. PKCtheta was found to be involved in the regulation of transcriptional activation of early-activation genes, predominantly AP-1, and its cellular distribution and activation were found to be regulated by the 14-3-3 protein. Other findings indicated that PKCtheta can associate with the HIV negative factor (Nef) protein, suggesting that altered regulation of PKCtheta by Nef may contribute to the T-cell impairments that are characteristic of infection by HIV. PKCtheta is expressed at relatively high levels in skeletal muscle, where it is suggested to play a role in signal transduction in both the developing and mature neuromuscular junction. In addition, PKCtheta appears to be involved in the insulin-mediated response of intact skeletal muscle, as well as in experimentally induced insulin resistance of skeletal muscle. Further studies suggest that PKCtheta is expressed in endothelial cells and is involved in multiple processes essential for angiogenesis and wound healing, including the regulation of cell cycle progression, formation and maintenance of actin cytoskeleton, and formation of capillary tubes. Here, we review recent progress in the study of PKCtheta and discuss its potential role in various cellular responses.