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Yadav P, Ambudkar SV, Rajendra Prasad N. Emerging nanotechnology-based therapeutics to combat multidrug-resistant cancer. J Nanobiotechnology 2022; 20:423. [PMID: 36153528 PMCID: PMC9509578 DOI: 10.1186/s12951-022-01626-z] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Accepted: 09/07/2022] [Indexed: 11/17/2022] Open
Abstract
Cancer often develops multidrug resistance (MDR) when cancer cells become resistant to numerous structurally and functionally different chemotherapeutic agents. MDR is considered one of the principal reasons for the failure of many forms of clinical chemotherapy. Several factors are involved in the development of MDR including increased expression of efflux transporters, the tumor microenvironment, changes in molecular targets and the activity of cancer stem cells. Recently, researchers have designed and developed a number of small molecule inhibitors and derivatives of natural compounds to overcome various mechanisms of clinical MDR. Unfortunately, most of the chemosensitizing approaches have failed in clinical trials due to non-specific interactions and adverse side effects at pharmacologically effective concentrations. Nanomedicine approaches provide an efficient drug delivery platform to overcome the limitations of conventional chemotherapy and improve therapeutic effectiveness. Multifunctional nanomaterials have been found to facilitate drug delivery by improving bioavailability and pharmacokinetics, enhancing the therapeutic efficacy of chemotherapeutic drugs to overcome MDR. In this review article, we discuss the major factors contributing to MDR and the limitations of existing chemotherapy- and nanocarrier-based drug delivery systems to overcome clinical MDR mechanisms. We critically review recent nanotechnology-based approaches to combat tumor heterogeneity, drug efflux mechanisms, DNA repair and apoptotic machineries to overcome clinical MDR. Recent successful therapies of this nature include liposomal nanoformulations, cRGDY-PEG-Cy5.5-Carbon dots and Cds/ZnS core–shell quantum dots that have been employed for the effective treatment of various cancer sub-types including small cell lung, head and neck and breast cancers.
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Garg D, Henrich S, Salo-Ahen OMH, Myllykallio H, Costi MP, Wade RC. Novel approaches for targeting thymidylate synthase to overcome the resistance and toxicity of anticancer drugs. J Med Chem 2010; 53:6539-49. [PMID: 20527892 DOI: 10.1021/jm901869w] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Divita Garg
- Molecular and Cellular Modeling Group, Heidelberg Institute of Theoretical Studies gGmbH, Heidelberg, Germany
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Tekle C, Giovannetti E, Sigmond J, Graff JR, Smid K, Peters GJ. Molecular pathways involved in the synergistic interaction of the PKC beta inhibitor enzastaurin with the antifolate pemetrexed in non-small cell lung cancer cells. Br J Cancer 2008; 99:750-9. [PMID: 18728666 PMCID: PMC2528136 DOI: 10.1038/sj.bjc.6604566] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Conventional regimens have limited impact against non-small cell lung cancer (NSCLC). Current research is focusing on multiple pathways as potential targets, and this study investigated molecular mechanisms underlying the combination of the PKCβ inhibitor enzastaurin with the multitargeted antifolate pemetrexed in the NSCLC cells SW1573 and A549. Pharmacologic interaction was studied using the combination-index method, while cell cycle, apoptosis induction, VEGF secretion and ERK1/2 and Akt phosphorylation were studied by flow cytometry and ELISAs. Reverse transcription–PCR, western blot and activity assays were performed to assess whether enzastaurin influenced thymidylate synthase (TS) and the expression of multiple targets involved in cancer signaling and cell cycle distribution. Enzastaurin-pemetrexed combination was highly synergistic and significantly increased apoptosis. Enzastaurin reduced both phosphoCdc25C, resulting in G2/M checkpoint abrogation and apoptosis induction in pemetrexed-damaged cells, and GSK3β and Akt phosphorylation, which was additionally reduced by drug combination (−58% in A549). Enzastaurin also significantly reduced pemetrexed-induced upregulation of TS expression, possibly through E2F-1 reduction, whereas the combination decreased TS in situ activity (>50% in both cell lines) and VEGF secretion. The effects of enzastaurin on signaling pathways involved in cell cycle control, apoptosis and angiogenesis, as well as on the expression of genes involved in pemetrexed activity provide a strong experimental basis to their evaluation as pharmacodynamic markers in clinical trials of enzastaurin-pemetrexed combination in NSCLC patients.
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Affiliation(s)
- C Tekle
- Department of Medical Oncology, VU University Medical Center, Amsterdam, The Netherlands
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Le François BG, Maroun JA, Birnboim HC. Expression of thymidylate synthase in human cells is an early G(1) event regulated by CDK4 and p16INK4A but not E2F. Br J Cancer 2007; 97:1242-50. [PMID: 17923872 PMCID: PMC2360461 DOI: 10.1038/sj.bjc.6604020] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Thymidylate synthase (TS) is the enzyme that catalyses the last step in de novo thymidylate synthesis. It is of interest clinically because it is an effective target for drugs such as 5-fluorouracil, often used in combination therapy. Despite a number of earlier reports indicating that TS is a cell cycle-dependent enzyme, this remains equivocal. Here, we show that in HCT116 cells synchronised by serum starvation, there is a clear dissociation between the expression of cyclin E (a well-characterised cell-cycle protein) and TS. Although both cyclin E and TS mRNA and protein increased during G1, TS upregulation was delayed. Moreover, TS levels did not decrease following S-phase completion while cyclin E decreased sharply. Similarly, clear differences were seen between cyclin E and TS as asynchronously growing HCT116 cells were growth-inhibited by low-serum treatment. In contrast to previous reports using rodent cells, adenovirus-mediated over-expression of E2F1 and cyclin E in three human cell lines had no effect on TS. Cell-cycle progression was blocked by treatment of cells with pharmacological inhibitors of CDK2 and CDK4 and by ectopic expression of p16INK4A. Whereas CDK2 inhibition had no effect on TS levels, inhibition of CDK4 was associated with decreased TS protein levels. These results provide the first evidence that drugs targeting CDK4 may be useful with anti-TS drugs as combination therapy for cancer.
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Affiliation(s)
- B G Le François
- Department of Biochemistry Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada
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Sigmond J, Peters GJ. Pyrimidine and purine analogues, effects on cell cycle regulation and the role of cell cycle inhibitors to enhance their cytotoxicity. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2006; 24:1997-2022. [PMID: 16438061 DOI: 10.1080/15257770500269556] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
In anti-cancer treatment, deoxynucleoside analogues are widely used in combination chemotherapy. Improvement can be achieved by rational design of novel combinations with cell cycle inhibitors. These compounds inhibit protein kinases, preventing the cell cycle from continuing when affected by deoxynucleoside analogs. The efficacy is dependent on the site of cell cycle inhibition, whether multiple cyclin-dependent kinases are inhibited and whether the inhibitors should be given before or after the deoxynucleoside analogs. The action of cell cycle inhibition in vivo may be limited by unfavorable pharmacokinetics. Preclinical and clinical studies will be discussed, aiming to design improved future strategies.
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Affiliation(s)
- Jennifer Sigmond
- Department of Medical Oncology, VU University Medical Center, Amsterdam, The Netherlands
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Bhonde MR, Hanski ML, Magrini R, Moorthy D, Müller A, Sausville EA, Kohno K, Wiegand P, Daniel PT, Zeitz M, Hanski C. The broad-range cyclin-dependent kinase inhibitor UCN-01 induces apoptosis in colon carcinoma cells through transcriptional suppression of the Bcl-x(L) protein. Oncogene 2005; 24:148-56. [PMID: 15467762 DOI: 10.1038/sj.onc.1207842] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
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.
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Affiliation(s)
- Mandar R Bhonde
- Department of Gastroenterology, Charité-Universitaetsmedizin Berlin, Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany
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Kortmansky J, Shah MA, Kaubisch A, Weyerbacher A, Yi S, Tong W, Sowers R, Gonen M, O'reilly E, Kemeny N, Ilson DI, Saltz LB, Maki RG, Kelsen DP, Schwartz GK. Phase I trial of the cyclin-dependent kinase inhibitor and protein kinase C inhibitor 7-hydroxystaurosporine in combination with Fluorouracil in patients with advanced solid tumors. J Clin Oncol 2005; 23:1875-84. [PMID: 15699481 DOI: 10.1200/jco.2005.03.116] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
PURPOSE Preclinical studies indicate that the cyclin-dependent kinase and protein kinase C inhibitor 7-hydroxystaurosporine (UCN-01) potentiates the cytotoxic effects of fluorouracil (FU). We designed a phase I clinical trial of FU in combination with UCN-01. PATIENTS AND METHODS FU was administered as a weekly 24-hour infusion. Doses were escalated in successive cohorts according to a modified Fibonacci design. UCN-01 was administered once every 4 weeks, immediately after disconnection from FU, at a dose of 135 mg/m(2) over 72 hours in cycle 1 and 67.5 mg/m(2) over 36 hours in subsequent cycles. FU and UCN-01 pharmacokinetics were obtained on all patients, and thymidylate synthetase (TS) activity was measured in peripheral-blood mononuclear cells by reverse-transcriptase polymerase chain reaction. RESULTS We escalated the weekly FU dose to 2,600 mg/m(2) in combination with once a month infusions of UCN-01. Dose-limiting toxicity included arrhythmia and syncope. Other toxicities included hyperglycemia, headache, and nausea and vomiting. The mean maximal plasma concentration of UCN-01 was 33.5 micromol/L. There was significant interpatient variability, which correlated with plasma concentrations of alpha-1 acid glycoprotein. FU was rapidly cleared and the dose had no effect on the area under the curve of UCN-01. Changes in TS expression were detectable in peripheral-blood mononuclear cells after administration of UCN-01 but did not correlate with toxicity or activity. We observed no objective response, although seven patients had stable disease, six of whom had received prior fluoropyrimidines. CONCLUSION The combination of weekly infusions of FU and monthly UCN-01 can be administered safely and warrants further study in phase II trials. The recommended phase II dose of FU in combination with monthly UCN-01 is 2,600 mg/m(2).
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Affiliation(s)
- Jeremy Kortmansky
- Memorial Sloan-Kettering Cancer Center, 1275 York Ave, New York, NY 10021, USA.
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Katsuki M, Chuang VTG, Nishi K, Kawahara K, Nakayama H, Yamaotsu N, Hirono S, Otagiri M. Use of Photoaffinity Labeling and Site-directed Mutagenesis for Identification of the Key Residue Responsible for Extraordinarily High Affinity Binding of UCN-01 in Human α1-Acid Glycoprotein. J Biol Chem 2005; 280:1384-91. [PMID: 15509559 DOI: 10.1074/jbc.m411076200] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
7-Hydroxystaurosporine (UCN-01) is a protein kinase inhibitor anticancer drug currently undergoing a phase II clinical trial. The low distribution volumes and systemic clearance of UCN-01 in human patients have been found to be caused in part by its extraordinarily high affinity binding to human alpha1-acid glycoprotein (hAGP). In the present study, we photolabeled hAGP with [3H]UCN-01 without further chemical modification. The photolabeling specificity of [3H]UCN-01 was confirmed by findings in which other hAGP binding ligands inhibited formation of covalent bonds between hAGP and [3H]UCN-01. The amino acid sequence of the photolabeled peptide was concluded to be SDVVYTDXK, corresponding to residues Ser-153 to Lys-161 of hAGP. No PTH derivatives were detected at the 8th cycle, which corresponded to the 160th Trp residue. This strongly implies that Trp-160 was photolabeled by [3H]UCN-01. Three recombinant hAGP mutants (W25A, W122A, and W160A) and wild-type recombinant hAGP were photolabeled by [3H]UCN-01. Only mutant W160A showed a marked decrease in the extent of photoincorporation. These results strongly suggest that Trp-160 plays a prominent role in the high affinity binding of [3H]UCN-01 to hAGP. A docking model of UCN-01 and hAGP around Trp-160 provided further details of the binding site topology.
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Affiliation(s)
- Masaaki Katsuki
- Department of Biopharmaceutics, Graduate School of Medical and Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-honmachi, Kumamoto, 862-0973, Japan
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Mack PC, Jones AA, Gustafsson MH, Gandara DR, Gumerlock PH, Goldberg Z. Enhancement of Radiation Cytotoxicity by UCN-01 in Non-small Cell Lung Carcinoma Cells. Radiat Res 2004; 162:623-34. [PMID: 15548112 DOI: 10.1667/rr3253] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Thoracic ionizing radiation is a standard component of combined-modality therapy for locally advanced non-small cell lung cancer. To improve low 5-year survival rates (5- 15%), new strategies for enhancing the effectiveness of ionizing radiation are needed. The kinase inhibitor UCN-01 has multiple cell cycle effects, including abrogation of DNA damage-induced S- and G(2)-phase arrest, which may limit DNA repair prior to mitosis. To test the hypothesis that therapy-induced cell cycle effects would have an impact on the efficacy of a combination of UCN-01 plus ionizing radiation, the cell cycle responses of the non-small cell lung cancer cell lines Calu1 (TP53-null) and A549 (wild-type TP53) to 2 Gy ionizing radiation were correlated with clonogenic survival after irradiation plus UCN-01. Irradiated cells were exposed to UCN-01 simultaneously and at 3-h increments after irradiation. In Calu1 cells but not A549 cells, sequence-dependent potentiation of radiation by UCN-01 was observed, with maximal interaction occurring when UCN-01 was administered 6 h after irradiation. This coincided with the postirradiation time with the greatest depletion of cells from G(1). Abrogation of G(2) arrest was observed regardless of TP53 status. The role of TP53 was investigated using siRNA to achieve gene silencing. These studies demonstrated that radiation plus UCN-01 was more effective in cells with diminished TP53 activity, associated with a reduced G(1) checkpoint arrest. These studies indicate that simultaneous elimination of multiple DNA damage-induced checkpoints in G(1), S and G(2) may enhance the effects of radiation and that drug scheduling may have an impact on clinical efficacy.
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Affiliation(s)
- Philip C Mack
- Cancer and Molecular Research Laboratory, Division of Hematology/Oncology, Department of Internal Medicine, Sacramento, California 95817, USA.
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Koh J, Kubota T, Koyama T, Migita T, Hashimoto M, Hosoda Y, Kitajima M. Combined antitumor activity of 7-hydroxystaurosporine (UCN-01) and tamoxifen against human breast carcinoma in vitro and in vivo. Breast Cancer 2004; 10:260-7. [PMID: 12955040 DOI: 10.1007/bf02966727] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
BACKGROUND 7-Hydroxystaurosporine (UCN-01) was originally isolated as a protein kinase C inhibitor and has shown antitumor activity against several human cancer cell lines. UCN-01 inhibits cell cycle progression from the G1 to the S phase and is associated with inhibition of cyclin-dependent kinase (CDK) activity and induction of intrinsic CDK inhibitor p21, leading to dephosphorylation of retinoblastoma (Rb) protein. Tamoxifen (TAM) traps cancer cells in the G1 phase, suggesting that the mechanism of action of TAM is similar to that of UCN-01. The present study was conducted to assess the antitumor activity of UCN-01 combined with TAM against human breast carcinoma cells in vitro and in vivo. MATERIALS AND METHODS MCF-7 cells were treated with UCN-01, TAM, or UCN-01 combined with TAM at various concentrations in vitro. The antitumor effect was evaluated as the inhibition rate (I.R.%) by MTT assay. Two human breast carcinoma xenografts in nude mice, MCF-7 and Br-10, were treated with UCN-01, TAM or both agents together. The expression of p21 and the phosphorylation status of Rb protein in MCF-7 cells were detected by Western blotting. RESULTS UCN-01 or TAM alone inhibited the proliferation of MCF-7 cells in a concentration-dependent manner. Combined treatment with UCN-01 followed by TAM inhibited the growth of MCF-7 cells synergistically and no significant differences in cytotoxicity were observed between the different sequences of UCN-01/TAM and TAM/UCN-01. Combination treatment with UCN-01 and TAM against MCF-7 and Br-10 in vivo exhibited superior antitumor effects compared with either agent treatment alone. Although 0.1 microg UCN-01 per ml (I.R.: 48.1%) or 2 microM TAM (I.R.: 31%) induced p21 expression, phosphorylation of Rb protein was not inhibited. However, combination treatment with UCN-01 and TAM at the same concentrations resulted in an I.R. of 67% and dephosphorylation of Rb protein. CONCLUSION The present study suggests that combining UCN-01 and TAM could result in augmented cytotoxicity because of their similar mechanism of action. This combination may have potential clinical applications for breast cancer treatment, by reducing the toxicity of UCN-01.
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Affiliation(s)
- Junichi Koh
- Department of Surgery, Saitama Social Insurance Hospital, 4-9-3, Kitaurawa, Saitama-shi, Saitama 330-0074, Japan.
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Koh J, Kubota T, Migita T, Abe S, Hashimoto M, Hosoda Y, Kitajima M. UCN-01 (7-hydroxystaurosporine) inhibits the growth of human breast cancer xenografts through disruption of signal transduction. Breast Cancer 2002; 9:50-4. [PMID: 12196722 DOI: 10.1007/bf02967547] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND 7-Hydroxystaurosporine (UCN-01), originally isolated as a phospholipid-dependent protein kinase C inhibitor, has been shown to have antitumor activity against several human cancer cell lines. UCN-01 inhibits cell cycle progression from the G1 to S phase by inhibition of cyclin-dependent kinase (CDK) activity and induction of intrinsic CDK inhibitor protein, leading to dephosphorylation of retinoblastoma (Rb) protein. MATERIALS AND METHODS The antitumor activity of UCN-01 has been investigated against three human breast carcinoma strains serially transplanted into nude mice, including estrogen-dependent MCF-7, Br-10, and estrogen-independent MX-1. When the inoculated tumors started growing exponentially, UCN-01 (7.5 mg/kg) was administered intraperitoneally on five consecutive days a week for 2 weeks. The antitumor effect was evaluated as the lowest T/C ratio (%) during the experiments, where T was the relative mean tumor weight of the treated group and C was that of the control group. At the end of UCN-01 administration expression of p21, a protein of the CDK inhibitor family, and phosphorylated and dephosphorylated Rb protein was detected by Western blotting using treated and control tumors. RESULTS UCN-01 had activity against MCF-7 and Br-10, with the lowest T/C ratios of 25.0% and 27.0%, respectively, while MX-1 was resistant to UCN-01 with a T/C ratio of 65.9%. The antitumor spectrum of UCN-01 was different from that of other conventional agents such as doxorubicin and cyclophosphamide which were ineffective against Br-10 but were active against MX-1. Although p21 was induced in three tested strains by UCN-01, little dephosphorylated Rb protein was expressed in MX-1 compared with Br-10 and MCF-7 (in vitro). CONCLUSION UCN-01 appeared to be a promising agent for the treatment of breast cancer, with a different mode of action and antitumor spectrum from other currently available antitumor drugs.
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Affiliation(s)
- Junichi Koh
- Department of Surgery, Saitama Social Insurance Hospital, 4-9-3, Kitaurawa, Saitama-shi, Japan.
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Abe S, Kubota T, Otani Y, Furukawa T, Watanabe M, Kumai K, Akiyama T, Akinaga S, Kitajima M. UCN-01 (7-hydoxystaurosporine) inhibits in vivo growth of human cancer cells through selective perturbation of G1 phase checkpoint machinery. Jpn J Cancer Res 2001; 92:537-45. [PMID: 11376563 PMCID: PMC5926745 DOI: 10.1111/j.1349-7006.2001.tb01127.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Mechanisms underlying tumor sensitivity to the antitumor agent UCN‐01 (7‐hydroxystaurosporine) were examined in the nude mouse model using three human tumor xenografts, two pancreatic cancers (PAN‐3‐JCK and CRL 1420) and a breast cancer (MX‐1). UCN‐01 antitumor activity was evaluated in terms of relative tumor weights in treated and untreated mice bearing the tumor xenografts. The activity of cyclin‐dependent kinase 2 (CDK2), levels of p21 and p27 proteins, pRb status and cell cycle were evaluated. Induction of p21 and apoptosis were also assessed immuno‐histochemically in CRL 1420. UCN‐01 was administered intraperitoneally at a dose of either 5 or 10 mg/kg daily for 5 days followed by a further 5 injections after an interval of 2 days. UCN‐01 significantly suppressed the growth of both pancreatic cancers, but was ineffective against MX‐1. p21 protein expression was markedly induced in the UCN‐01‐sensitive pancreatic carcinoma xenografts at both doses, but p21 induction was only evident in the UCN‐01‐resistant MX‐1 at 10 mg/kg. MX‐1 exhibited CDK2 activity that was 6‐fold higher than that of pancreatic cancer strains, which may explain the resistance of MX‐1 to UCN‐01 despite the induction of p21 at the dose of 10 mg/kg. The UCN‐01‐sensitive tumors exhibited G1 arrest and increased levels of apoptosis, changes not observed in resistant MX‐1. In conclusion, it appears that a determining factor of in vivo UCN‐01 sensitivity involves the balance of CDK2 kinase activity and p21 protein induction, resulting in augmented pRb phosphorylation, G1 cell cycle arrest and apoptosis.
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Affiliation(s)
- S Abe
- Department of Surgery, School of Medicine, Keio University, Shinjuku-ku, Tokyo 160-8582, Japan
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