Second-generation taxanes effectively suppress subcutaneous rat lymphoma: role of disposition, transport, metabolism, in vitro potency and expression of angiogenesis genes.

The study investigated possible mechanisms by which second-generation taxanes, established as significantly more effective than paclitaxel in vitro, suppress a rat lymphoma model in vivo. The studied mechanisms included taxane pharmacokinetics, expression of genes dominating their metabolism (Cyp3a1/2) and transport (Abcb1) and genes controlling tumour angiogenesis (growth factors and receptors). SB-T-1214, SB-T-12854 and IDN5109 suppressed rat lymphoma more effectively than paclitaxel, SB-T-12851, SB-T-12852, SB-T-12853 or IDN5390 as well as P388D1 leukaemia cells in vitro. The greater anti-lymphoma effects of SB-T-1214 in rats corresponded to a higher bioavailability than with SB-T-12854, and lower systemic toxicity of SB-T-1214 for rats reflected its lower cytotoxicity for P388D1 cells in vitro. Suppression of Abcb1 and CYP3a1 expression by SB-T-1214 and IDN5109 could partly explain their anti-lymphoma effects, but not that of SB-T-12854. Growth factors genes Egf, Fgf, Pdgf, and Vegf associated with tumour angiogenesis had significantly lower expression following treatment with anti-lymphoma effective IDN5109 and their receptors were unaffected, whereas inefficient IDN5390 increased expression of the most important Vegf. The effective SB-T-12854 inhibited Egf, Egfr, Fgfr and Pdgfr expression, while the ineffective SB-T-12851, SB-T-12852 and SB-T-12853 inhibited only Egf or Egfr expression. Vegfr expression was inhibited significantly by SB-T-12851 and SB-T-12854, but effect of SB-T-12851 was compromised by induced Vegf expression. The very effective SB-T-1214 decreased the expression of Vegf, Egf and all receptors most prominently indicating the possible supporting role of these genes in anti-lymphoma effects. In conclusion, SB-T-1214, SB-T-12854 and IDN5109 are good candidates for further study.

In vivo modulation of angiogenic gene expression by acyclic nucleoside phosphonates PMEDAP and PMEG.

Acyclic nucleoside phosphonates PMEDAP and PMEG modulate expression of selected proangiogenic genes in SD-lymphoma bearing rats. Antiangiogenic efficacy of PMEDAP is relatively weak and is manifested mainly by down-regulation of vascular endothelial growth factor (VEGF) and its receptor VEGFR detectable 24 hours after treatment. Compound PMEG (an active metabolite of the prodrug GS-9219) down-regulates selected proangiogenic genes EGF, FGF, PDGF, VEGF, EGFR, FGFR, PDGFR and VEGFR much more efficiently. Its antiangiogenic potency persists and is more intensive 48 hours after treatment. Findings show that in vivo antitumour efficacy of both antimitotic acyclic nucleoside phosphonates PMEDAP and PMEG consequently affect the angiogenesis in T-cell lymphoma.

Effects of paclitaxel, docetaxel and their combinations on subcutaneous lymphomas in inbred Sprague-Dawley/Cub rats.

We investigated, whether the effects on paclitaxel, docetaxel or their combinations on T-cell lymphomas in Sprague-Dawley/Cub rats were mainly caused by their different efficiency or combination of different mechanism of action, or limited by metabolic inactivation by P450 enzymes or drug efflux caused by P-glycoprotein (P-gp). Docetaxel most effectively prolonged the survival of rats and the time of lymphoma appearance, inhibited their intravital size and weight after sacrifice. Paclitaxel was poorly effective and combined administration had intermediate effects. Blood levels of both drugs were similar. Repeated administration of paclitaxel, but not docetaxel, decreased its area under concentration, but the effect disappeared 6h after dosing and was not sufficient to explain lower effects of paclitaxel. The faster metabolism of docetaxel than paclitaxel in vitro did not limit its higher efficiency and repeated administration of paclitaxel did not induce its metabolism to decrease its blood levels sufficiently. Likewise, undetectable expression of P-gp protein in tumours could not explain lower effects of paclitaxel, which is a better substrate of P-gp. Docetaxel was three-fold more effective than paclitaxel against P388D1 lymphoma cell line, used as a model of the T-cell lymphoma and combined action was dominated by the effects of docetaxel. Thus, docetaxel was effective against T-cell lymphomas and may be a potential anticancer drug in similar indications.

Inhibition of thymidine phosphorylase (PD-ECGF) from SD-lymphoma by phosphonomethoxyalkyl thymines.

A series of thymine phosphonomethoxyalkyl derivatives were evaluated for their ability to inhibit thymidine phosphorylase (dThdPase) purified from rat spontaneous T-cell lymphoma. A kinetic study of thymidine phosphorolysis catalyzed by dThdPase was performed with thymidine and/or inorganic phosphate as substrates. Data show that the substantial inhibitory effect of these acyclic nucleotide analogues is decreasing in the order of (R)-FPMPT>(S)-FPMPT>or=(R)-HPMPT>(S)-PMPT>(S)-HPMPT>PMET>or=(R)-PMPT. The inhibitory potency (K(i)/(dThd)K(m)) of the most efficient inhibitors from this series against T-cell lymphoma enzyme is 0.0026 for (R)-FPMPT and 0.0048 for (S)-FPMPT. The studied compounds do not inhibit Escherichia coli and human enzyme and possess lower inhibitory potency against rat liver thymidine phosphorylase.

PMEDAP and its N6-substituted derivatives: genotoxic effect and apoptosis in in vitro conditions.

Genotoxic properties expressed as acquired chromosomal aberrations and induction of apoptosis after treatment with acyclic nucleoside phosphonates PMEG, PMEDAP and its N6-substituted derivatives Me2NEt-PMEDAP, allyl-PMEDAP, Me2-PMEDAP and cypr-PMEDAP, were studied in in vitro conditions. The genotoxic and antiproliferative effect of compounds was investigated on CCRF-CEM, HeLa S3, MRC-5 and Reh cell lines. PMEG and cypr-PMEDAP exhibit high genotoxic and cytostatic effect. PMEDAP and its N6-substituted derivatives Me2NEt-PMEDAP, allyl-PMEDAP and Me2-PMEDAP are considerably less genotoxic. Time- and dose-dependent suppression of proliferation by these nucleotide analogues is accompanied by induction of apoptosis, which is dependent on cell line type. However, an increased proliferation was observed after treatment of the cell culture with very low dose of PMEDAP. The sensitivity of cell lines to PMEDAP decreased in the order: CCRF-CEM > Reh > HeLa > MRC-5. The potential embryotoxic or teratogenic effect of PMEDAP and cypr-PMEDAP was examined in inbred rats involving the mutant allele Lx that determines the polydactyly-luxate syndrome. While the prevalent effect of cypr-PMEDAP during fetus development is embryolethality, PMEDAP did not induce any embryo-lethal or teratogenic effect.

Slower molecular response to treatment predicts poor outcome in patients with TEL/AML1 positive acute lymphoblastic leukemia: prospective real-time quantitative reverse transcriptase-polymerase chain reaction study.

BACKGROUND: The translocation t(12;21)(p13;q22), which produces the TEL/AML1 fusion gene, is the most frequent chromosomal abnormality in patients with childhood acute lymphoblastic leukemia (ALL) and generally is associated with a favorable prognosis. Furthermore, real-time quantitative-polymerase chain reaction (RQ-PCR)-based detection of TEL/AML1 represents an accurate technique for the reproducible assessment of minimal residual disease (MRD). METHODS: The authors employed RQ-reverse transcriptase-PCR (RQ-RT-PCR) technology to analyze MRD levels in 57 newly diagnosed patients with TEL/AML1 positive ALL in a prospective study. RESULTS: On Day + 33, a particularly important time point in terms of outcome prediction based on MRD monitoring, 75% of patients reached negativity, 13% of patients were positive at very low levels (< 10(-4); i.e., 1 or more leukemic cell per 10(4) normal cells), and another 13% of patients were positive at the level of 10(-2) to 10(-4) cells. No patient showed MRD levels > or = 10(-2) cells at this time. The data demonstrate that patients with TEL/AML1 positive ALL had a better response to induction chemotherapy on Day + 33 compared with a group of unselected patients with ALL (P = 0.0001). However, four patients with TEL/AML1 positive ALL developed relapse disease. Remarkably, these children were positive for MRD on Day + 33 at a level between 10(-2) cells and 10(-4) (n = 3 patients) and at < 10(-4) (n = 1 patient). Kaplan-Meier analysis of disease free survival showed the statistical significance of this distribution (MRD positive vs. MRD negative; log-rank P = 0.0016). CONCLUSIONS: The authors conclude that, although the TEL/AML1 positive leukemias generally are associated with a favorable outcome, MRD positivity assessed by RQ-RT-PCR analysis at the end of induction therapy represents a significantly negative prognostic feature.

Tenofovir diphosphate is a poor substrate and a weak inhibitor of rat DNA polymerases alpha, delta, and epsilon*.

Tenofovir diphosphate (PMPApp) is a weak inhibitor of DNA polymerases (pol) alpha, delta, and epsilon*, with values for the Ki for PMPApp ((PMPApp)Ki) relative to the Km for dATP ((dATP)Km) of 10.2, 10.2, and 15.2, respectively. Its incorporation into DNA was about 1,000-fold less efficient than that of dATP, with (PMPApp)Km values 350-, 2,155-, and 187-fold higher than (dATP)Km values for pol alpha, delta, and epsilon*, respectively.