Phase I and pharmacokinetic study of tomudex combined with 5-fluorouracil plus levofolinic acid in advanced head and neck cancer and colorectal cancer. (49/1894)

In vitro studies have shown a schedule-dependent synergism between Tomudex and 5-fluorouracil (5-FU). Incubation of different types of head and neck and colorectal cancer cells with levofolinic acid (LFA) plus 5-FU for 4 or 24 h, after 24-h incubation with Tomudex, produces a clear synergism. The purpose of this study was to evaluate the tolerability and activity of a combination of Tomudex, LFA, and 5-FU in advanced head and neck and colorectal cancer. Furthermore, the potential for 5-FU pharmacomodulation by Tomudex was also evaluated through an intrapatient assessment of dihydropyrimidine dehydrogenase (DPD) activity and 5-FU AUC with and without pretreatment with Tomudex. Eligible patients were treated with Tomudex at the starting dose of 1.5 mg/m2 on day 1, LFA at a fixed dose of 250 mg/m2 on day 2, immediately followed by bolus 5-FU at the starting dose of 600 mg/m2. Tomudex and 5-FU doses were alternately escalated. Courses were repeated every 2 weeks. In the second course, LFA and 5-FU were administered on day 1 and Tomudex on day 2; further treatment was given according to the sequence used in the first course. Plasma 5-FU concentrations were analyzed on courses 1 and 2 using a high-performance liquid chromatography assay with UV detection. DPD activity was measured in peripheral blood mononuclear cells on courses 1 and 2 using incubation of cytosol with [14C]FU and quantitation of metabolite formation. Fifty-eight patients were enrolled in the study. Dose escalation was stopped at step 8, because of the occurrence of dose-limiting toxicity in two of three patients. The dose level immediately before (3 mg/m2 Tomudex, 1050 mg/m2 5-FU) was selected for further evaluation. Tomudex and 5-FU mean dose intensities actually delivered at the seventh step were 1.32 and 462 mg/m2/week, respectively. Six of 40 patients with metastatic colorectal cancer obtained an objective response (15%; 95% confidence interval, 6-30%). In particular, three complete responses and three partial responses were observed. Six of 17 patients with locally advanced or metastatic head and neck cancer obtained an objective response (1 complete response + 5 partial responses; 35%; 95% confidence interval, 14-62%). Median duration of response in colorectal cancer patients was 12 months. 5-FU AUC was not significantly different between the two courses (median intrapatient difference, 9.3%; P = 0.28). DPD activity in course 1 was significantly higher than course 2 (P = 0.041) in the 16 patients in which values were evaluable. The combination of Tomudex, LFA, and 5-FU is well tolerated and active in colorectal and head and neck cancer. The Tomudex mean dose intensity actually delivered is higher than usually achieved in monotherapy. The absence of a clear pharmacokinetic interaction suggests that the synergism of Tomudex and 5-FU might occur at the cellular level.  (+info)

Balb/c mice as a preclinical model for raltitrexed-induced gastrointestinal toxicity. (50/1894)

Raltitrexed (RTX) is an antifolate thymidylate synthase (TS) inhibitor used for the treatment of advanced colorectal cancer. RTX induces proliferating tissue toxicities that are largely confined to the intestine, with diarrhea being a severe side effect in a small but significant minority of patients. Similarly, weight loss and diarrhea were observed in BALB/c mice, and a maximum tolerated dose (MTD) was determined as approximately 5-10 mg/kg/day x 5 days. At an equivalent dose of 10 mg/kg/day x 5 days (dl-5), DBA2 mice lost considerably less weight, leading to a higher MTD (>500 mg/kg/day x 5 days), and there was no evidence of diarrhea. Histopathological consequences of damage, such as changes in small intestinal crypt architecture and villus atrophy induced by the 10-mg/kg/day dose, were greater and of longer duration in BALB/c mice. A higher dose of RTX (100 mg/kg/day x 5) induced weight loss and histopathological damage similar to that seen in BALB/c mice (10 mg/kg/ day x 5) but was of later onset, nadir, and recovery. Small changes to the colon were only observed in BALB/c mice. Pretreatment levels of plasma thymidine, deoxyuridine (approximately 1 microM), and folate (approximately40 ng/ml) were similar in both mouse strains. A single injection of radiolabeled RTX (5 mg/kg/ day) did not lead to any marked difference 24 h later in the total drug concentration and distribution of polyglutamates (comprising 70-80% of drug extracted) in the liver, kidney, and intestinal epithelium (large and small intestine) between the two mouse strains. Further studies used a RIA to measure RTX polyglutamate formation in tissues at various times and drug doses. This led to the conclusion that, although there was a higher accumulation of RTX in BALB/c small intestinal epithelium (days 4-6), it may be an effect secondary to another undetermined cause of increased drug sensitivity. This model represents a vehicle by which the etiology and treatment of severe clinical toxicity induced by RTX may be evaluated.  (+info)

Overexpression of Bax enhances antitumor activity of chemotherapeutic agents in human head and neck squamous cell carcinoma. (51/1894)

Overexpression of the Bax protein in human head and neck squamous cell carcinoma A253 cells was reported to result in an increased sensitivity to various chemotherapeutic agents in vitro (Guo et al., Oncol. Res., 11: 91-99, 1999). In the present study, the relationship between Bax expression and response to chemotherapy was further investigated in vitro and in vivo model systems. For in vitro study, A253, A253/Vec (pcDNA3 vector transfectant), and A253/Bax (pcDNA3/Bax transfectant, expressing 50-fold higher Bax protein than A253 and A253/Vec) cells were exposed to various concentrations of raltitrexed (a specific thymidylate synthase inhibitor) and SN-38 (a topoisomerase I inhibitor) for 2 h, and cell growth inhibition was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide clonogenic assay. Compared to A253/Vec, A253/Bax cells exhibited 9.5- and 13.5-fold increases in sensitivity to raltitrexed and SN-38, respectively. For in vivo study, A253/Vec and A253/Bax tumor xenografts were established by s.c. injection of tumor cells into nude mice. The antitumor activity and toxicity of raltitrexed (i.v. push daily for 5 days) and irinotecan (a prodrug of SN-38; i.v. push daily for 3 days) were evaluated. The maximum tolerated doses of raltitrexed and irinotecan were 30 and 100 mg/kg/day, respectively. At the maximum tolerated doses, minimal antitumor activity was observed with raltitrexed, although irinotecan was more active than raltitrexed against A253 or A253/Vec tumors. In contrast, both raltitrexed and irinotecan were significantly more active against A253/Bax xenografts than against A253/Vec xenografts; the yield for complete tumor regression (cure) was 40% and 100% with raltitrexed and irinotecan, respectively, with no significant toxicity. Furthermore, the observed increase of antitumor activity in A253/Bax tumors was associated with an enhanced induction of apoptosis in vivo. The in vivo results demonstrated a proof of the principal concept that selecting up-regulation of the proapoptosis gene Bax can provide the basis for a greater therapeutic efficacy to a variety of chemotherapeutic agents with different structures and mechanisms of action.  (+info)

Evidence that activation of central 5-HT(2B) receptors causes renal sympathoexcitation in anaesthetized rats. (52/1894)

The effects of injections i.c.v. of alpha-methyl-5-(2-thienylmethoxy)-1H-indole-3-ethanamine (BW723C86; 0.02 - 2 micromol kg(-1)), a 5-HT(2B) receptor agonist, on renal sympathetic and phrenic nerve activity, mean arterial blood pressure and heart rate were investigated in alpha-chloralose anaesthetized rats pretreated with a peripherally acting 5-HT(2) receptor antagonist. BW723C86 i.c.v. caused a dose-related increase in renal nerve activity reaching a maximum of 67+/-6%, which at the highest dose was associated with a small and maintained fall in mean arterial blood pressure of 7+/-3 mmHg. These changes were not associated with any significant changes in heart rate or phrenic nerve activity. BW723C86-evoked increases in renal nerve activity and hypotension were attenuated by pretreatment (i.c.v.) with SB204741 (300 nmol kg(-1); a 5-HT(2B) receptor antagonist) but not by the same dose (i.c.v.) of ketanserin (a 5-HT(2A) receptor antagonist) or RS102221 (a 5-HT(2C) receptor antagonist). None of these antagonists alone had any effect on the variables being measured. It is concluded that central 5-HT(2B) receptors may play a selective role in the control of sympathetic supply to the kidney, which could be important in the central mechanisms involved in blood volume regulation. British Journal of Pharmacology (2000) 129, 177 - 183  (+info)

Novel inhibitors of the condensing enzymes of the type II fatty acid synthase of pea (Pisum sativum). (53/1894)

The type II fatty acid synthases (FASs) of higher plants (and Escherichia coli) contain three condensing enzymes called beta-ketoacyl-ACP synthases (KAS), where ACP is acyl-carrier-protein. We have used novel derivatives of the antibiotic thiolactomycin to inhibit these enzymes. Overall de novo fatty acid biosynthesis was measured using [1-(14)C]acetate substrate and chloroplast preparations from pea leaves, and [1-(14)C]laurate was used to distinguish between the effects of the inhibitors on KAS I from those on KAS II. In addition, the activities of these enzymes, together with the short-chain condensing enzyme, KAS III, were measured directly. Six analogues were tested and two, both with extended hydrocarbon side chains, were found to be more effective inhibitors than thiolactomycin. Incubations with chloroplasts and direct assay of the individual condensing enzymes showed that all three compounds inhibited the pea FAS condensing enzymes in the order KAS II > KAS I > KAS III. These results demonstrate the general activity of thiolactomycin and its derivatives against these FAS condensation reactions, and suggest that such compounds will be useful for further detailed studies of inhibition and for use as pharmaceuticals against Type II FASs of pathogens.  (+info)

Retroviral transfer of the hENT2 nucleoside transporter cDNA confers broad-spectrum antifolate resistance in murine bone marrow cells. (54/1894)

Antifolate drugs such as methotrexate are commonly used in cancer chemotherapy. It may be possible to increase the antitumor activity of antifolates by the coadministration of drugs that inhibit nucleoside transport, thereby blocking the capacity of tumor cells to salvage nucleotide precursors. An important limitation of this approach is severe myelosuppression caused by many of these drug combinations. For this reason, we have developed a gene therapy strategy to protect bone marrow cells against combined treatment with antifolates and nitrobenzylmercaptopurine riboside (NBMPR), a potent inhibitor of the es nucleoside transporter. A retroviral vector (MeiIRG) was constructed that expressed the NBMPR-insensitive ei transporter, hypothesizing that transduced bone marrow cells would survive drug treatment because of the preservation of nucleoside salvage pathways. In vitro clonogenic assays confirmed that the MeiIRG vector did protect myeloid progenitors against the toxic effects of 3 different antifolates when each was combined with NBMPR. On testing this system in vivo, decreased myelosuppression was observed in mice transplanted with MeiIRG-transduced bone marrow cells and subsequently treated with trimetrexate and NBMPR-P. In these mice, significant increases were noted in absolute neutrophil count nadirs, reticulocyte indices, and the numbers of myeloid progenitors in the bone marrow. Furthermore, a survival advantage was associated with transfer of the MeiIRG vector, indicating that significant dose intensification was possible with this approach. In summary, the MeiIRG vector can decrease the toxicity associated with the combined use of antifolates and NBMPR-P and thereby may provide a strategy for simultaneously sensitizing tumor cells while protecting hematopoietic cells.  (+info)

The crystal structures of human alpha-thrombin complexed with active site-directed diamino benzo[b]thiophene derivatives: a binding mode for a structurally novel class of inhibitors. (55/1894)

The crystal structures of four active site-directed thrombin inhibitors, 1-4, in a complex with human alpha-thrombin have been determined and refined at up to 2.0 A resolution using X-ray crystallography. These compounds belong to a structurally novel family of inhibitors based on a 2,3-disubstituted benzo[b]thiophene structure. Compared to traditional active-site directed inhibitors, the X-ray crystal structures of these complexes reveal a novel binding mode. Unexpectedly, the lipophilic benzo[b]thiophene nucleus of the inhibitor appears to bind in the S1 specificity pocket. At the same time, the basic amine of the C-3 side chain of the inhibitor interacts with the mostly hydrophobic proximal, S2, and distal, S3, binding sites. The second, basic amine side chain at C-2 was found to point away from the active site, occupying a location between the S1 and S1' sites. Together, the aromatic rings of the C-2 and C-3 side chains sandwich the indole ring of Trp60D contained in the thrombin S2 insertion loop defined by the sequence "Tyr-Pro-Pro-Trp." [The thrombin residue numbering used in this study is equivalent to that reported for chymotrypsinogen (Hartley BS, Shotton DM, 1971, The enzymes, vol. 3. New York: Academic Press. pp 323-373).] In contrast to the binding mode of more classical thrombin inhibitors (D-Phe-Pro-Arg-H, NAPAP, Argatroban), this novel class of benzo[b]thiophene derivatives does not engage in hydrogen bond formation with Gly216 of the thrombin active site. A detailed analysis of the three-dimensional structures not only provides a clearer understanding of the interaction of these agents with thrombin, but forms a foundation for rational structure-based drug design. The use of the data from this study has led to the design of derivatives that are up to 2,900-fold more potent than the screening hit 1.  (+info)

The effects of central aromatic amino acid DOPA decarboxylase inhibition on the motor actions of L-DOPA and dopamine agonists in MPTP-treated primates. (56/1894)

1. Endogenous L-DOPA may act as a neuromodulator contributing to the production of motor activity. We now investigate the effects of the centrally acting aromatic amino acid dopa decarboxylase (AADC) inhibitor NSD-1015 (3-hydroxybenzyl hydrazine) on the motor actions of L-DOPA and dopamine agonist drugs in MPTP treated common marmosets. 2. Pretreatment with NSD-1015 (10 - 50 mg kg(-1); i.p.) worsened baseline motor deficits in MPTP-treated common marmosets. Similarly, it abolished L-DOPA (5 - 18 mg kg(-1) s.c.) induced locomotor activity and reversal of disability. NSD-1015 pretreatment inhibited dopamine formation and elevated L-DOPA levels in plasma. 3. The increase in locomotor activity and improvement in disability produced by the administration of the D-1 agonist A-86929 (0.03 - 0. 04 mg kg(-1) s.c.) or the D-2 agonist quinpirole (0.05 - 0.3 mg kg(-1) i.p.) was abolished by NSD-1015 (25 mg kg(-1) i.p.) pretreatment. While the effects of a low dose combination of A-86929 (0.04 mg kg(-1) s.c.) and quinpirole (0.05 mg kg(-1) i.p.) were inhibited by NSD-1015 (25 mg kg(-1) i.p.), there was little effect on the action of a high dose combination of these drugs (0.08 mg kg(-1) A-86929 and 0.1 mg kg(-1) quinpirole). 4. Following central AADC inhibition with NSD-1015 (25 mg kg(-1) i.p.), locomotor behaviour induced by administration of high dose combinations of A-86929 (0.08 mg kg(-1) s.c.) and quinpirole (0.1 mg kg(-1) i.p.) was unaffected by L-DOPA (5 mg kg(-1) s.c.) pretreatment. 5. These results do not support a role for endogenous L-DOPA in spontaneous or drug induced locomotor activity. Rather, they strengthen the argument for the importance of endogenous dopaminergic tone in the motor actions of dopamine agonists.  (+info)