Protein kinase C inhibition by UCN-01 induces apoptosis in human glioma cells in a time-dependent fashion

Targeting Cell Cycle Checkpoint Kinases to Overcome Intrinsic Radioresistance in Brain Tumor Cells

Simple Summary

As cell cycle checkpoint mechanisms maintain genomic integrity, the inhibition of enzymes involved in these control mechanisms may increase the sensitivity of the cells to DNA damaging treatments. In this review, we summarize the knowledge in the field of brain tumor treatment with radiation therapy and cell cycle checkpoint inhibition via targeting ATM, ATR, CHK1, CHK2, and WEE1 kinases.

Abstract

Radiation therapy is an important part of the standard of care treatment of brain tumors. However, the efficacy of radiation therapy is limited by the radioresistance of tumor cells, a phenomenon held responsible for the dismal prognosis of the most aggressive brain tumor types. A promising approach to radiosensitization of tumors is the inhibition of cell cycle checkpoint control responsible for cell cycle progression and the maintenance of genomic integrity. Inhibition of the kinases involved in these control mechanisms can abolish cell cycle checkpoints and DNA damage repair and thus increase the sensitivity of tumor cells to radiation and chemotherapy. Here, we discuss preclinical progress in molecular targeting of ATM, ATR, CHK1, CHK2, and WEE1, checkpoint kinases in the treatment of brain tumors, and review current clinical phase I-II trials.

Combined PDK1 and CHK1 inhibition is required to kill glioblastoma stem-like cells in vitro and in vivo

Glioblastoma (GBM) is the most common and deadly adult brain tumor. Despite aggressive surgery, radiation, and chemotherapy, the life expectancy of patients diagnosed with GBM is ∼14 months. The extremely aggressive nature of GBM results from glioblastoma stem-like cells (GSCs) that sustain GBM growth, survive intensive chemotherapy, and give rise to tumor recurrence. There is accumulating evidence revealing that GSC resilience is because of concomitant activation of multiple survival pathways. In order to decode the signal transduction networks responsible for the malignant properties of GSCs, we analyzed a collection of GSC lines using a dual, but complementary, experimental approach, that is, reverse-phase protein microarrays (RPPMs) and kinase inhibitor library screening. We treated GSCs in vitro with clinically relevant concentrations of temozolomide (TMZ) and performed RPPM to detect changes in phosphorylation patterns that could be associated with resistance. In addition, we screened GSCs in vitro with a library of protein and lipid kinase inhibitors to identify specific targets involved in GSC survival and proliferation. We show that GSCs are relatively insensitive to TMZ treatment in terms of pathway activation and, although displaying heterogeneous individual phospho-proteomic profiles, most GSCs are resistant to specific inhibition of the major signaling pathways involved in cell survival and proliferation. However, simultaneous multipathway inhibition by the staurosporin derivative UCN-01 results in remarkable inhibition of GSC growth in vitro. The activity of UCN-01 on GSCs was confirmed in two in vivo models of GBM growth. Finally, we used RPPM to study the molecular and functional effects of UCN-01 and demonstrated that the sensitivity to UCN-01 correlates with activation of survival signals mediated by PDK1 and the DNA damage response initiated by CHK1. Taken together, our results suggest that a combined inhibition of PDK1 and CHK1 represents a potentially effective therapeutic approach to reduce the growth of human GBM.

PUMA induction by FoxO3a mediates the anticancer activities of the broad-range kinase inhibitor UCN-01

Most targeted anticancer drugs are inhibitors of kinases that are aberrantly activated in cancer cells. However, the mechanisms by which kinase inhibitors suppress tumor growth remain unclear. In this study, we found that UCN-01, a staurosporine analogue and broad-range kinase inhibitor used in clinical trials, inhibits colon cancer cell growth by inducing apoptosis via PUMA, a BH3-only Bcl-2 family member and a p53 target. PUMA expression was markedly elevated in a p53-independent fashion following UCN-01 treatment. The induction of PUMA by UCN-01 was mediated by direct binding of FoxO3a to the PUMA promoter following inhibition of AKT signaling. Deficiency in PUMA abrogated UCN-01-induced apoptosis, caspase activation, and mitochondrial dysfunction, and rendered UCN-01 resistance in a clonogenic assay, whereas elevated PUMA expression or a BH3 mimetic sensitized UCN-01 induced apoptosis. Chemosensitization by UCN-01 seemed to involve simultaneous PUMA induction through both p53-dependent and p53-independent mechanisms. Furthermore, deficiency in PUMA suppressed the antitumor effects of UCN-01 in a xenograft model, concurrent with reduced apoptosis and caspase activation in vivo. These results suggest that PUMA-mediated apoptosis is pivotal for the anticancer activities of UCN-01, and possibly other clinically used kinase inhibitor drugs, and that PUMA manipulation may be useful for improving their anticancer activities.

A Phase 1 study of UCN-01 in combination with irinotecan in patients with resistant solid tumor malignancies

PURPOSE

UCN-01 (7-hydroxystaurosporine) is a multi-targeted protein kinase inhibitor that exhibits synergistic activity with DNA-damaging agents in preclinical studies. We conducted a Phase I study to determine the maximum-tolerated dose (MTD), dose-limiting toxicity (DLT), pharmacokinetic, and pharmacodynamic effects of UCN-01 and irinotecan in patients with resistant solid tumors.

EXPERIMENTAL DESIGN

Patients received irinotecan (75-125 mg/m(2) IV on days 1, 8, 15, 22) and UCN-01 (50-90 mg/m(2) IV on day 2 and 25-45 mg/m(2) on day 23 and subsequent doses) every 42 days. Blood for pharmacokinetics of UCN-01 and irinotecan, and blood, normal rectal mucosa, and tumor biopsies for pharmacodynamic studies were obtained.

RESULTS

Twenty-five patients enrolled to 5 dose levels. The MTD was irinotecan 125 mg/m(2) on days 1, 8, 15, 22 and UCN-01 70 mg/m(2) on day 2 and 35 mg/m(2) on day 23. DLTs included grade 3 diarrhea/dehydration and dyspnea. UCN-01 had a prolonged half-life and a low clearance rate. There was a significant reduction in SN-38 C(max) and aminopentanocarboxylic acid (APC) and SN-38 glucuronide half-lives. Phosphorylated ribosomal protein S6 was reduced in blood, normal rectal mucosa, and tumor biopsies at 24 h post-UCN-01. Two partial responses were observed in women with ER, PgR, and HER2-negative breast cancers (TBNC). Both tumors were defective for p53. Twelve patients had stable disease (mean duration 18 weeks, range 7-30 weeks).

CONCLUSION

UCN-01 and irinotecan demonstrated acceptable toxicity and target inhibition. Anti-tumor activity was observed and a study of this combination in women with TNBC is underway.

Enzastaurin induces H2AX phosphorylation to regulate apoptosis via MAPK signalling in malignant glioma cells

Enzastaurin is an acyclic bisindolylmaleimide derived from staurosporine that acts as an ATP competitor, and interferes with the activity of protein kinase C (PKC) isoforms. Our previous studies have shown that clinically achievable concentrations of this agent induce apoptosis in many glioma cell lines. Our goal in this study was to expand on the previous results and to determine the signalling mechanisms responsible for enzastaurin-induced inhibition of cell growth and induction of apoptosis. To address these issues, cell cycle progression following enzastaurin treatment was analysed by fluorescence-activated cell sorting (FACS) in parallel with analyses of growth and apoptosis signalling pathways. Enzastaurin treatment activated H2AX and Chk2 phosphorylation, and enhanced phosphorylation of mitogen-activated protein kinase (MAPK) family kinases. Inhibition of MAP kinases by chemical inhibitors reduced H2AX and Chk2 phosphorylation and decreased apoptosis induced by enzastaurin. These data call attention to a novel signalling pathway (MAPK/H2AX) to regulate apoptosis in malignant glioma 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.

Coadministration of Sorafenib with Rottlerin Potently Inhibits Cell Proliferation and Migration in Human Malignant Glioma Cells

Mitogen-activated protein kinase (MAPK) and protein kinase C (PKC) are activated in the majority of gliomas and contribute to tumor cell growth and survival. Sorafenib (Bay43-9006; Nexavar) is a dual-action Raf and vascular endothelial growth factor receptor inhibitor that blocks receptor phosphorylation and MAPK-mediated signaling and inhibits growth in a number of tumor types. Because our initial studies of this agent in a series of glioma cell lines showed only partial growth inhibition at clinically achievable concentrations, we questioned whether inhibition of PKC signaling using the PKC-delta inhibitor rottlerin might potentiate therapeutic efficacy. Proliferation assays, apoptosis induction studies, and Western immunoblot analysis were conducted in cells treated with sorafenib and rottlerin as single agents or in combination. Sorafenib and rottlerin reduced proliferation in all cell lines when used as single agents, and the combination produced marked potentiation of growth inhibition. Flow-cytometric measurements of cells stained with Annexin V-propidium iodide and immunocytochemical assessment of cytochrome c and apoptosis-inducing factor release demonstrated that addition of rottlerin resulted in significantly higher levels of apoptosis than sorafenib alone. In addition, the combination of sorafenib and rottlerin reduced or completely inhibited the phosphorylation of extracellular signal-regulated kinase and Akt and down-regulated cell cycle regulatory proteins such as cyclin-D1, cyclin-D3, cyclin-dependent kinase (cdk)4, and cdk6 in a dose- and time-dependent manner. Our results clearly indicate that inhibition of PKC-delta signaling enhances the antiproliferative effect of sorafenib in malignant human glioma cell lines and support the examination of combinations of signaling inhibitors in these tumors.

PKC eta as a therapeutic target in glioblastoma multiforme

Gliomas are the most common major subgroup of primary CNS tumours. Approximately 17,000 new cases are reported each year and, of these, 11,500 patients die. Glioblastoma multiforme (GBM) is highly proliferative and typically invades distal portions of the brain, thereby making complete surgical resection of these tumours nearly impossible. Moreover, GBMs are often resistant to current chemotherapy and radiation regimens. Therefore, there is a need for better therapeutic interventions. One class of proteins that is involved in the formation of malignant brain tumours is protein kinase C (PKC) and these kinases have not been thoroughly explored for their chemotherapeutic value in GBMs. The PKC isozyme, PKCeta (PKC-eta) increases cell proliferation and resistance to radiation of GBM cell lines. These properties make PKCeta an attractive target for chemotherapeutic intervention in the management of GBMs.

Molecular neuro-oncology and the development of targeted therapeutic strategies for brain tumors. Part 5: apoptosis and cell cycle

Brain tumors are a diverse group of malignancies that remain refractory to conventional treatment approaches. Molecular neuro-oncology has now begun to clarify the transformed phenotype of brain tumors and identify oncogenic pathways that might be amenable to targeted therapy. Abnormalities of the apoptotic and cell cycle signaling pathways are key molecular features of many brain tumors and are currently under evaluation for potential therapeutic intervention. The apoptosis pathway has numerous targets for molecular therapeutic development, including p53, Bax, Bcl-2, cFLIP, effector caspases, growth factor receptors, phosphatidylinositol-3-kinase, Akt and apoptosis inhibitors. Current molecular treatment approaches include antisense techniques, gene therapy and small-molecule modulators and inhibitors. Potential targets of the cell cycle pathway include the cyclins, cyclin-dependent kinases, p53, retinoblastoma, E2F and the cyclin-dependent kinase inhibitors. Developmental molecular therapeutics for this pathway include adenoviral and gene therapy, small-peptide cyclin-dependent kinase modulators, proteasomal inhibitors and small-molecule cyclin-dependent kinase inhibitors. Several of these recently identified agents have begun evaluation in clinical trials. Further development of targeted therapies designed to modulate apoptosis and the cell cycle, and evaluation of these new agents in clinical trials, will be needed to improve survival and quality of life for patients with brain tumors.

Phase I trial of UCN-01 in combination with topotecan in patients with advanced solid cancers: a Princess Margaret Hospital Phase II Consortium study

BACKGROUND

7-Hydroxystaurosporine (UCN-01) inhibits serine-threonine kinases including the Ca2+ and phospholipid-dependent protein kinase C (PKC), CDKs 2, 4, 6, Chk-1 and PDK1. UCN-01 mediates distinct effects in vitro/in vivo: cell cycle arrest in G1, abrogation of G2 arrest by inhibiting chk1, induction of apoptosis and potentiation of cytotoxicity of S-phase-active chemotherapeutics including the topoisomerase 1 inhibitor topotecan (T). This phase I study was designed to determine the maximal tolerated dose (MTD), recommended phase 2 dose (RPTD), toxicity profile, pharmacokinetics and antitumor activity of T and UCN-01 in patients with refractory solid tumors.

DESIGN

Both agents were administered every 21 days intravenously through central venous access in escalating doses to eligible patients. On day 1, following antiemetic prophylaxis with dexamethasone and a serotonin type 3(A) receptor (5HT3) inhibitor, UCN-01 was infused over 3 h, followed by T infused over 30 min. On days 2-5, patients received T only. UCN-01 doses were reduced by 50% in cycles 2 and beyond because of its prolonged half-life.

RESULTS

Thirty-three patients were entered in three cohorts: Dose Level (DL) 1 (UCN-01 70 mg/m2, T 0.75 mg/m2), three patients; DL 2 (UCN-01 70 mg/m2, T 1.0 mg/m2), 24 patients; DL 3 (UCN-01 90 mg/m2, T 1.0 mg/m2), six patients. All but three patients were PS 0 or 1, median age was 54 years (range, 29-72), 91% were female. Primary tumor types: ovary/peritoneal (23 patients), colon (three patients), salivary gland (two patients), others (five patients). All patients were eligible for adverse event (AE) analysis and 22 patients were eligible for survival and tumor response analysis. Two of six patients had dose limiting toxicity (DLT) at DL 3 (grade 3 N/V; grade 4 neutropenia with infection). One DLT was seen in one patient at DL 2, consisting of grade 4 leukopenia. This cohort was expanded and no further DLTs were observed. Most common drug-related AEs were mild (grade 1-2). Non-hematological grade 3-4 AEs consisted of transient hyperglycemia (4), infection (3), coagulation, fatigue, hypotension, nausea (2), hypomagnesemia, vomiting, headache (1). Hematologic toxicities occurred in 100% of patients. Grade 3-4 hematologic abnormalities included neutropenia (16, including three with infection), leukopenia (11), lymphopenia (7), thrombocytopenia (5). Best response for 22 evaluable patients was PD (8), SD for at least six cycles (12), PR (1: carcinoma of ovary, dose level 2) and one not assessable. Pharmacokinetic analysis confirmed the prolonged half-life of UCN-01 of approximately 15 days.

CONCLUSIONS

DLT was observed at DL 3 and RPTD was determined to be DL 2. To date, this combination has been relatively well tolerated with some preliminary evidence of efficacy. A phase II study of this combination in patients with ovarian cancer is underway.

The broad-range cyclin-dependent kinase inhibitor UCN-01 induces apoptosis in colon carcinoma cells through transcriptional suppression of the Bcl-x(L) protein

The broad-range cyclin-dependent kinase inhibitor 7-hydroxystaurosporine (UCN-01) is known to induce both a G1 cell cycle arrest and apoptosis. The mechanism of UCN-01-induced apoptosis is largely unknown. We analysed the mechanism of cytotoxicity of UCN-01 in four established colon carcinoma cell lines. The cell lines SW48 and LS513 responded to UCN-01 treatment by undergoing apoptosis in a concentration-dependent manner while the cell lines HT-29 and WiDr were completely resistant. Apoptosis in LS513 and SW48 cell lines was concomitant with the suppression of Bcl-x(L) on mRNA and protein level. In contrast, in the apoptosis-resistant cell lines, Bcl-x(L) expression was not affected by UCN-01. Stable overexpression of the Bcl-x(L) protein abrogated UCN-01-triggered apoptosis, but only partially restored growth, indicating that both cell cycle arrest and apoptosis exert the anticancer effect in a coordinated manner. The inhibition of Akt phosphorylation did not correlate with the apoptotic phenotype. UCN-01 inhibited the activating STAT3 phosphorylations on Ser727 and, notably, on Tyr705, but STAT3 did not contribute to Bcl-x(L) expression in colon carcinoma cells. Moreover, we show for the first time that UCN-01 induces apoptosis by suppression of Bcl-x(L) expression. The inhibition of this pathway is a new aspect of cytotoxic and modulatory potential of UCN-01.

Staurosporine-induced apoptosis is independent of p16 and p21 and achieved via arrest at G2/M and at G1 in U251MG human glioma cell line

OBJECTIVE

The mechanisms involved in the cell cycle and cell death remain unresolved despite much investigation. Staurosporine induces cell death and G1 or G2/M arrest in a dose-dependent manner, but the mechanisms remain unknown.

METHODS

In the present study an adenovirus vector expressing p16 or p21 genes in human glioma cell lines was used to examine cell cycle regulation and cell death induced by staurosporine.

RESULTS

A low concentration (</=10 n M) of staurosporine induced G1 arrest of U251MG cells, whereas a high concentration (>/=30 n M) induced G2/M arrest and finally induced apoptosis via a caspase-3-activated pathway from both the G2/M and G1 phases. However, pRb was dephosphorylated and cdc2 was inhibited at both the low and the high concentrations of staurosporine, indicating that the mechanisms of cell cycle regulation are not simply p53-Rb- or cdc2-dependent pathways.

CONCLUSIONS

Forced G1 arrest by transfection with p16 or p21 genes did not alter the rate of staurosporine-induced cell death. This implies that an unknown pathway of apoptosis occurs from the G1 phase.

7-Hydroxystaurosporine-induced apoptosis in 9L glioma cells provides an effective antigen source for dendritic cells and yields a potent vaccine strategy in an intracranial glioma model

OBJECTIVE

On the basis of recent studies indicating that tumoral apoptotic bodies may provide a potent source of antigen for delivery to antigen-presenting cells, as well as observations that signal transduction modulation may constitute a promising approach for inducing glioma cell apoptosis, we explored the efficacy of vaccination with glioma apoptotic body-pulsed dendritic cells (DCs) for inhibiting tumor growth in the syngeneic 9L glioma/Fischer rat model.

METHODS

For induction of apoptosis, 7-hydroxystaurosporine (UCN-01) (200-300 ng/ml), a selective protein kinase C inhibitor, was co-incubated with 9L cells in vitro for 72 or 96 hours. After this pretreatment period, glioma cells and DCs were mixed, and the interaction between DCs and apoptotic 9L tumor cells was assessed using two-color flow cytometry. In a series of experiments, the efficacy of vaccination strategies using DCs co-cultured with apoptotic 9L cells was then examined in animals harboring intracranial tumors.

RESULTS

Pretreatment of 9L cells with UCN-01 resulted in approximately 50% of cells' being observed to undergo apoptosis as compared with less than 3% of controls. After subsequent co-culture, two-color flow cytometry demonstrated a time-dependent physical association of DCs with the apoptotic glioma cells. Survival in animals harboring intracranial tumors was significantly longer for the animals treated with a glioma apoptotic body-pulsed DC vaccine than in the animals that received apoptotic glioma cells and DCs alone or vehicle (i.e., the controls), especially those that underwent a sequential vaccination strategy (P < 0.0001). Long-term survival (>90 d) was demonstrated in 6 (75%) of 8 animals that underwent this vaccination approach versus 0 (0%) of 16 controls. In contrast, no survival benefit was observed in animals that received DCs that were co-cultured with vehicle-treated (non-apoptotic) 9L cells. Three of four long-term survivors that were rechallenged intracranially with tumor cells also survived over the long term.

CONCLUSION

These studies suggest that induction of apoptosis in glioma cells by use of UCN-01 may promote the uptake of tumor antigens by DCs. This finding is important because apoptotic body-stimulated DCs may hold promise in promoting a host response against an established intracranial glioma, particularly if the parameters for apoptotic induction, duration of co-culture, and vaccination can be optimized.

Anticancer drug resistance in primary human brain tumors

The difficult clinical situation still associated with most types of primary human brain tumors has fostered significant interest in defining novel therapeutic modalities for this heterogeneous group of neoplasms. Beginning in the 1980s chemotherapy has been incorporated into the treatment protocol of a number of intractable brain tumors. However, it has predominantly failed to improve patient outcome. The unsatisfactory results with chemotherapeutic intervention have chiefly been attributed to tumor cell resistance. In recent years, there has been a literal explosion in our understanding about the mechanisms by which cancer cells become chemoresistant. During the course of their evolution (intrinsic resistance) or in response to chemotherapy (acquired resistance) these cells may follow a number of pathways of genetic alterations to possess a common (multidrug) or drug-specific (individual drug) resistant phenotype. Genomic aberrations, deregulation of membrane transporting proteins and cellular enzymes, and an altered susceptibility to commit to apoptosis are among the steps on the way that contribute to the genesis of chemotherapeutic treatment failure. Although, through the years we have come to yield information and inferences as to the roles that different molecular events may have in the resistance phenotype of cancer cells, the actual involvement of single genetic alterations in conferring drug resistance in primary brain tumors remains debatable. This uncertainty and, besides, the lack of proper drug resistance diagnostics, in a vicious circle, hinder the development of effective resistance-modulation strategies. Clinical non-responsiveness to chemotherapy remains a formidable obstacle to the successful treatment of brain tumors and one of the most serious problems to be solved in the therapy of these lesions. Future advances in the chemotherapeutic management of these neoplasms will come with an improved understanding of the significance and interrelationship of the multiple biological systems operative in promoting resistance to this treatment modality. The focus of this review is to summarize current knowledge concerning major drug resistance-related markers, to describe their functional interaction en route to chemoresistance, and to discuss their implication in rendering human brain tumor cells resistant to chemotherapy.