Multitargeted antifolate LY231514 as first-line chemotherapy for patients with advanced non-small-cell lung cancer: A phase II study. National Cancer Institute of Canada Clinical Trials Group.
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PURPOSE: To evaluate the efficacy and safety of the multitargeted antifolate LY231514 (MTA) in patients receiving initial chemotherapy for unresectable, advanced non-small-cell lung cancer (NSCLC). PATIENTS AND METHODS: Patients with measurable, advanced NSCLC who had not received previous chemotherapy for advanced disease were considered for this study. Eligible patients who gave written informed consent initially received MTA 600 mg/m(2) intravenously (IV) for 10 minutes every 3 weeks. After three patients received treatment at this dose, the dose was reduced to 500 mg/m(2) IV at the same infusion time and frequency because of toxicity seen in this study and another Canadian MTA trial in colorectal cancer. Patients received up to four cycles after complete or partial remission or six cycles after stable disease was documented. RESULTS: Thirty-three patients were accrued onto the study. All were assessable for toxicity, and 30 patients were assessable for response. All but one patient had an Eastern Cooperative Oncology Group performance status score of 0 or 1, 18 patients (55%) had adenocarcinoma, and nine patients (27%) had squamous cell carcinoma. Twenty-five patients (76%) had stage IV disease, and the remainder had stage IIIB disease at trial entry. Seven patients experienced a confirmed partial response and no complete responses were seen; thus, the overall response rate was 23.3% (95% confidence interval, 9.9% to 42.3%). The median duration of response was 3.1 months (range, 2. 3 to 13.5 months) after a median follow-up period of 7.9 months. Four (67%) of six patients with stage IIIB disease and three (12.5%) of 24 with stage IV disease responded to treatment. Four patients (13.3%) experienced febrile neutropenia and 13 (39%) experienced grade 3 or 4 neutropenia, whereas only one patient (3%) developed grade 4 thrombocytopenia. Nonhematologic toxicity was generally mild or moderate, but 39% of patients developed a grade 3 skin rash. Most other toxicities comprised grade 1 or 2 stomatitis, diarrhea, lethargy, and anorexia. Ten patients stopped protocol therapy because of toxicity. CONCLUSION: MTA seems to have clinically meaningful activity as a single agent against advanced NSCLC. Toxicity is generally mild and tolerable. Further study of this agent in combination with cisplatin and other active drugs is warranted in this disease. (+info)
Prolonged inhibition of O(6)-methylguanine DNA methyltransferase in human tumor cells by O(6)-benzylguanine in vitro and in vivo.
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We previously demonstrated that sustained depletion of methylguanine DNA methyltransferase (MGMT) activity is required for optimal reversal of chloroethylnitrosourea resistance in tumor cells. The purpose of this study was to design O(6)-benzylguanine (BG) treatments that deplete MGMT activity in tumor cells and xenograft tumors in a prolonged manner. When SF767 cells were treated with a bolus dose of BG (25 microM for 1 h), >95% of MGMT activity was depleted but 33% of the activity recovered within 24 h. In contrast, MGMT activity was completely depleted for 24 h when cells were pretreated with a low dose of BG (2.5 microM) for 24 h, followed by the bolus dose and same low-dose treatment for 24 h. This combination regimen of pre- and post-treatments with a bolus dose sensitized cells N,N'-bis(2-chloroethyl)-N-nitrosourea in vitro by approximately 2-fold more than the bolus dose alone. Similar BG treatment with Alzet micro-osmotic pumps produced sustained inhibition of MGMT activity in vivo. In xenograft SF767 tumors, low-dose pre- and post-treatments (8 mg/kg over 24 h) combined with an i.p. bolus dose (80 mg/kg) of BG inhibited >95% of MGMT activity for 24 h after the bolus. The bolus dose alone did not deplete MGMT for 24 h. These results demonstrate that combination low-dose and bolus BG treatment is superior to the bolus dose alone in depleting MGMT activity in a sustained manner in vitro and in vivo. When combined with N,N'-bis(2-chloroethyl)-N-nitrosourea treatment, this BG regimen also should also produce greater antitumor activity than the single bolus dose evaluated clinically. (+info)
O(6)-benzylguanine enhances the in vitro immunotoxic activity of temozolomide on natural or antigen-dependent immunity.
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Temozolomide (TMZ) is a new cytotoxic triazene compound of clinical interest that is able to generate methyl adducts at the O(6)-guanine of DNA, which can be repaired by O(6)-alkylguanine-DNA alkyltransferase (OGAT). It was previously found that triazene compounds are highly immunosuppressive in mice. In the present study, we investigate whether TMZ could affect immune functions of human competent cells and whether methylation of O(6)-guanine could be involved in the immunosuppressive activity of the drug. Mononuclear cells (MNCs) obtained from peripheral blood of healthy donors were tested for OGAT activity and treated with TMZ alone or combined with the OGAT inhibitor O(6)-benzylguanine. Control or drug-treated MNCs were then assayed for natural killer activity and for the ability to proliferate and to generate cytotoxic effector cells in response to interleukin-2 or allogeneic MT-2 tumor cells. The results show that TMZ inhibited both proliferation and induction of lytic activity in response to interleukin-2 or allogeneic MT-2 cells. Moreover, an inverse correlation was found between the OGAT activity of MNCs and their sensitivity to TMZ. The involvement of O(6)-guanine methylation in the immunosuppressive effects of TMZ was further confirmed by the finding that O(6)-benzylguanine increased the activity of the drug. On the other hand, the natural killer activity of MNCs was only moderately affected by TMZ, and no relationship was observed between OGAT levels and sensitivity to the drug. These data suggest that in patients with tumors who are undergoing TMZ treatment, the drug may impair immune responses involving cell proliferation, depending on OGAT levels of MNCs, and that O(6)-benzylguanine may potentiate this activity. (+info)
9-(2-phosphonylmethoxyethyl) derivatives of purine nucleotide analogs: A comparison of their metabolism and interaction with cellular DNA synthesis.
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Incubation of CEM cells for 24 h with the guanine, 2,6-diaminopurine, and adenine nucleotide analogs of the 9-(2-phosphonylmethoxyethyl) series, 9-(2-phosphonylmethoxyethyl)guanine (PMEG), 9-(2-phosphonylmethoxyethyl)-2,6-diaminopurine (PMEDAP), and 9-(2-phosphonylmethoxyethyl)adenine (PMEA), was found to inhibit DNA synthesis 50% at concentrations of 1, 6, and 25 microM, respectively. Possible reasons for the marked differences were investigated, including cellular transport of the analogs, different efficiencies of intracellular phosphorylation, differential effects on 2'-deoxynucleotide (dNTP) pools, and differences in the affinities of the cellular DNA polymerases for the diphosphate derivatives of the drugs. No significant differences in cellular uptake were found among the analogs; however, they did differ in the efficiency of phosphorylation, i.e., CEM cells were found to accumulate higher levels of PMEG-diphosphate (PMEGpp) than PMEDAP-diphosphate (PMEDAPpp) or PMEA-diphosphate (PMEApp). Treatment of cells with any of the nucleotide analogs resulted in increased dNTP pools, with PMEG producing the greatest increase. All three analogs had the greatest effect on the dATP pool size, whereas the dGTP pool size was not significantly affected. Comparison of the ratios of nucleotide analog diphosphates to their corresponding dNTPs under conditions where DNA synthesis is inhibited 50% suggested that cellular DNA polymerases were approximately twice as sensitive to PMEGpp than to PMEDAPpp and 5-fold more sensitive to PMEGpp than to PMEApp. Consistent with this hypothesis, examination of the efficiencies with which the replicative DNA polymerases alpha, delta, and epsilon incorporated the analogs showed that DNA polymerase delta, the most sensitive of the DNA polymerases, incorporated PMEGpp twice as efficiently as PMEDAPpp and 7-fold more efficiently than PMEApp. (+info)
The relationship of thermodynamic stability at a G x U recognition site to tRNA aminoacylation specificity.
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The G x U pair at the third position in the acceptor helix of Escherichia coli tRNA(Ala) is critical for aminoacylation. The features that allow G x U recognition are likely to include direct interaction of alanyl-tRNA synthetase with distinctive atomic groups and indirect recognition of the structural and stability information encoded in the sequence of G x U and its immediate context. The present work investigates the thermodynamic stability and acceptor activity for a comprehensive set of variant RNAs with substitutions of the G x U pair of E. coli tRNA(Ala). The four RNAs with Watson-Crick substitutions had a lower acceptor activity and a higher stability relative to the G x U RNA. On the other hand, the RNAs with mispair substitutions had a lower stability, but either a higher or a lower acceptor activity. Thus, the entire set of variant RNAs does not exhibit a correlation between thermodynamic stability of the free, unbound tRNA and its acceptor activity. The substantial acceptor activity of tRNAs with particular mispair substitutions may be explained by their ability to assume the conformational preferences of alanyl-tRNA synthetase. Moreover, the G x U pair may provide a point of deformability for the substrate tRNA to adapt to the enzyme's active site. (+info)
Phase II study of first-line LY231514 (multi-targeted antifolate) in patients with locally advanced or metastatic colorectal cancer: an NCIC Clinical Trials Group study.
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BACKGROUND: Metastatic colon cancer is difficult to treat with treatment being palliative and with little effect on survival. This trial has evaluated the effects of LY231514 (Multitargeted antifolate (MTA)) given to previously untreated patients with recurrent or metastatic colorectal carcinoma. PATIENTS AND METHODS: All patients were required to have a histological diagnosis of colorectal adenocarcinoma with measurable disease and no prior chemotherapy for metastatic disease. Patients had to have had performance status of 0-2, pretreatment absolute granulocyte count of > or = 1.5 x 10(9)/l and a platelet count of > or = 150 x 10(9)l. Patients received MTA at a dose of 600 mg/m2 by 10 minute infusion on day 1 repeated every 21 days. After the first 9 patients, this dose was reduced down to 500 mg/m2 every 21 days because of toxicity. Doses of MTA were modified depending on nadir counts. RESULTS: Thirty-two eligible patients were enrolled and twenty-nine were evaluable for response. Three patients did not have repeat radiological testing to determine response because they went off study after only one cycle of treatment due to toxicity. In the 29 evaluable patients, there was 1 complete response, 4 partial responses and 14 patients with stable disease. Response rate was 17.2% (95% confidence intervals: 5.8%-35.8%). All responses occurred in the patients receiving a starting dose of MTA 500 mg/m2. Median time to progression for all eligible patients was 3.3 months. The most common toxicities experienced were mild to moderate fever, lethargy, anorexia, nausea, vomiting, stomatitis, abdominal pain, diarrhea, and skin rash. There was one death due to sepsis. CONCLUSION: Single-agent MTA at 500 mg/m2 given every three weeks has modest activity in metastatic colorectal carcinoma. (+info)
Inhibition of O(6)-methylguanine-DNA methyltransferase increases azoxymethane-induced colonic tumors in rats.
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Azoxymethane (AOM) causes O(6)-methylguanine adduct formation which leads to G-->A transitions. Their repair is carried out by O(6)-methylguanine-DNA methyltransferase (MGMT). To evaluate the importance of this repair event in AOM-induced carcinogenesis, we examined the effect of O(6)-benzylguanine (BG), a potent inhibitor of MGMT, on colonic tumor development. Rats were treated weekly for 2 weeks at 0 and 24 h with BG (60 mg/kg body wt i.p.) or vehicle (40% polyethylene glycol, PEG-400), followed 2 h after the first dose of BG with AOM (15 mg/kg body wt) or vehicle (saline) i.p. Rats were killed 35 weeks later and tumors harvested and DNA extracted. In the AOM-treated groups, BG caused a significant increase in tumor incidence with tumors in 65.9%, versus 30.8% in the AOM/PEG-treated group (P < 0.05). In the BG/AOM group there was also a significant increase in tumor multiplicity, with 2.3 tumors/tumor-bearing rat, versus 1.6 tumors/tumor- bearing rat in the AOM/PEG group (P < 0.05). Since O(6)-methylguanine adducts can cause activating mutations in the K-ras and beta-catenin genes, we examined the effects of BG on these mutations. In the BG group there were seven mutations in codon 12 or 13 of exon 1 of the K-ras gene in 51 tumors examined, compared with no K-ras mutations in 17 tumors analyzed in the AOM/PEG group (P = 0.12). In the BG/AOM group there were 10 mutations in exon 3 of the beta-catenin gene among 48 tumors evaluated, compared with six mutations in 16 tumors analyzed in the PEG/AOM group (P = 0.16). In summary, MGMT inhibition increases AOM-induced colonic tumor incidence and multiplicity in rats. (+info)
X-ray crystallographic analysis of the structural basis for the interaction of pokeweed antiviral protein with guanine residues of ribosomal RNA.
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Pokeweed antiviral protein (PAP) is a ribosome-inactivating protein (RIP), which enzymatically removes a single adenine base from a conserved, surface exposed loop sequence of ribosomal rRNA. We now present unprecedented experimental evidence that PAP can release not only adenine but guanine as well from Escherichia coli rRNA, albeit at a rate 20 times slower than for adenine. We also report X-ray structure analysis and supporting modeling studies for the interactions of PAP with guanine. Our modeling studies indicated that PAP can accommodate a guanine base in the active site pocket without large conformational changes. This prediction was experimentally confirmed, since a guanine base was visible in the active site pocket of the crystal structure of the PAP-guanine complex. (+info)