Potent interaction of flavopiridol with MRP1

The multidrug resistance protein 1 (MRP1) is an ATP-dependent transport protein for organic anions, as well as neutral or positively charged anticancer agents. In this study we show that flavopiridol, a synthetic flavonoid currently studied in phase 1 trials for its anti-proliferative characteristics, interacts with MRP1 in a potent way. Flavopiridol, as well as other (iso)flavonoids stimulate the ATPase activity of MRP1 in a dose-dependent way at low micromolar concentrations. A new specific monoclonal antibody against MRP1 (MIB6) inhibits the (iso)flavonoid-induced ATPase activity of plasma membrane vesicles prepared from the MRP1 overexpressing cell line GLC4/ADR. The accumulation of daunorubicin in GLC4/ADR cells is increased by flavopiridol and by other non-glycosylated (iso)flavonoids that interact with MRP1 ATPase activity. However, flavopiridol is the only tested compound that affects the daunorubicin accumulation when present at concentrations below 1 μM. Glycosylated (iso)flavonoids do not affect MRP1-mediated transport or ATPase activity. Finally, MRP1 overexpressing and transfected cells are resistant to flavopiridol, but not to other (iso)flavonoids tested. These findings may be of relevance for the development of anticancer therapies with flavopiridol. © 1999 Cancer Research Campaig

Enhancement of the activity of phenoxodiol by cisplatin in prostate cancer cells

Phenoxodiol is a novel isoflav-3-ene, currently undergoing clinical trials, that has a broad in vitro activity against a number of human cancer cell lines. Phenoxodiol alone inhibited DU145 and PC3 in a dose- and time-dependent manner with IC50 values of 8±1 and 38±9 μM, respectively. The combination of phenoxodiol and cisplatin was synergistic in DU145, and additive in PC3, as assessed by the Chou–Talalay method. Carboplatin was also synergistic in combination with phenoxodiol in DU145 cells. The activity of the phenoxodiol and cisplatin combination was confirmed in vivo using a DU145 xenograft model in nude mice. Pharmacokinetic data from these mice suggest that the mechanism of synergy may occur through a pharmacodynamic mechanism. An intracellular cisplatin accumulation assay showed a 35% (P<0.05) increase in the uptake of cisplatin when it was combined in a ratio of 1 μM: 5 μM phenoxodiol, resulting in a 300% (P<0.05) increase in DNA adducts. Taken together, our results suggest that phenoxodiol has interesting properties that make combination therapy with cisplatin or carboplatin appealing

The cyclin-dependent kinase inhibitor 5, 6-dichloro-1-beta-D-ribofuranosylbenzimidazole induces nongenotoxic, DNA replication-independent apoptosis of normal and leukemic cells, regardless of their p53 status

<p>Abstract</p> <p>Background</p> <p>Current chemotherapy of human cancers focuses on the DNA damage pathway to induce a p53-mediated cellular response leading to either G1 arrest or apoptosis. However, genotoxic treatments may induce mutations and translocations that result in secondary malignancies or recurrent disease. In addition, about 50% of human cancers are associated with mutations in the <it>p53 </it>gene. Nongenotoxic activation of apoptosis by targeting specific molecular pathways thus provides an attractive therapeutic approach.</p> <p>Methods</p> <p>Normal and leukemic cells were evaluated for their sensitivity to 5, 6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) through cell viability and caspase activation tests. The apoptotic pathway induced by DRB was analysed by immunfluorescence and immunoblot analysis. H2AX phosphorylation and cell cycle analysis were performed to study the dependance of apoptosis on DNA damage and DNA replication, respectively. To investigate the role of p53 in DRB-induced apoptosis, specific p53 inhibitors were used. Statistical analysis on cell survival was performed with the test of independence.</p> <p>Results</p> <p>Here we report that DRB, an inhibitor of the transcriptional cyclin-dependent kinases (CDKs) 7 and 9, triggers DNA replication-independent apoptosis in normal and leukemic human cells regardless of their p53 status and without inducing DNA damage. Our data indicate that (i) in p53-competent cells, apoptosis induced by DRB relies on a cytosolic accumulation of p53 and subsequent Bax activation, (ii) in the absence of p53, it may rely on p73, and (iii) it is independent of ATM and NBS1 proteins. Notably, even apoptosis-resistant leukemic cells such as Raji were sensitive to DRB.</p> <p>Conclusion</p> <p>Our results indicate that DRB represents a potentially useful cancer chemotherapeutic strategy that employs both the p53-dependent and -independent apoptotic pathways without inducing genotoxic stress, thereby decreasing the risk of secondary malignancies.</p

Clinical anticancer drug development: targeting the cyclin-dependent kinases

Cell division involves a cyclical biochemical process composed of several step-wise reactions that have to occur once per cell cycle. Dysregulation of cell division is a hallmark of all cancers. Genetic and epigenetic mechanisms frequently result in deranged expression and/or activity of cell-cycle proteins including the cyclins, cyclin-dependent kinases (Cdks), Cdk inhibitors and checkpoint control proteins. The critical nature of these proteins in cell cycling raises hope that targeting them may result in selective cytotoxicity and valuable anticancer activity

RADVAN: a randomised phase 2 trial of WBRT plus vandetanib for melanoma brain metastases - results and lessons learnt

BACKGROUND: Brain metastases occur in up to 75% of patients with advanced melanoma. Most are treated with whole-brain radiotherapy (WBRT), with limited effectiveness. Vandetanib, an inhibitor of vascular endothelial growth factor receptor, epidermal growth factor receptor and rearranged during transfection tyrosine kinases, is a potent radiosensitiser in xenograft models. We compared WBRT with WBRT plus vandetanib in the treatment of patients with melanoma brain metastases. METHODS: In this double-blind, multi-centre, phase 2 trial patients with melanoma brain metastases were randomised to receive WBRT (30 Gy in 10 fractions) plus 3 weeks of concurrent vandetanib 100 mg once daily or placebo. The primary endpoint was progression-free survival in brain (PFS brain). The main study was preceded by a safety run-in phase to confirm tolerability of the combination. A post-hoc analysis and literature review considered barriers to recruiting patients with melanoma brain metastases to clinical trials. RESULTS: Twenty-four patients were recruited, six to the safety phase and 18 to the randomised phase. The study closed early due to poor recruitment. Median PFS brain was 3.3 months (90% confidence interval (CI): 1.6-5.6) in the vandetanib group and 2.5 months (90% CI: 0.2-4.8) in the placebo group (P=0.34). Median overall survival (OS) was 4.6 months (90% CI: 1.6-6.3) and 2.5 months (90% CI: 0.2-7.2), respectively (P=0.54). The most frequent adverse events were fatigue, alopecia, confusion and nausea. The most common barrier to study recruitment was availability of alternative treatments. CONCLUSIONS: The combination of WBRT plus vandetanib was well tolerated. Compared with WBRT alone, there was no significant improvement in PFS brain or OS, although we are unable to provide a definitive result due to poor accrual. A review of barriers to trial accrual identified several factors that affect study recruitment in this difficult disease area