Novel selective inhibitors for human topoisomerase I, BM2419-1 and -2 derived from saintopin.
(1/2758)
Compounds BM2419-1 and -2 were isolated from a culture broth of a fungus Paecilomyces sp. BM2419. It was shown that these novel compounds were artifacts derived from saintopin, a dual inhibitor of topoisomerase I and II by independent processes. In the human topoisomerase I inhibition assay using the recombinant Saccharomyces cerevisiae, BM2419-1 and -2 inhibited selectively the yeast growth dependent on human topoisomerase I induction with IC50 values of 0.3 ng/ml and 6.0 ng/ml, respectively. (+info)
Replication-mediated DNA damage by camptothecin induces phosphorylation of RPA by DNA-dependent protein kinase and dissociates RPA:DNA-PK complexes.
(2/2758)
Replication protein A (RPA) is a DNA single-strand binding protein essential for DNA replication, recombination and repair. In human cells treated with the topoisomerase inhibitors camptothecin or etoposide (VP-16), we find that RPA2, the middle-sized subunit of RPA, becomes rapidly phosphorylated. This response appears to be due to DNA-dependent protein kinase (DNA-PK) and to be independent of p53 or the ataxia telangiectasia mutated (ATM) protein. RPA2 phosphorylation in response to camptothecin required ongoing DNA replication. Camptothecin itself partially inhibited DNA synthesis, and this inhibition followed the same kinetics as DNA-PK activation and RPA2 phosphorylation. DNA-PK activation and RPA2 phosphorylation were prevented by the cell-cycle checkpoint abrogator 7-hydroxystaurosporine (UCN-01), which markedly potentiates camptothecin cytotoxicity. The DNA-PK catalytic subunit (DNA-PKcs) was found to bind RPA which was replaced by the Ku autoantigen upon camptothecin treatment. DNA-PKcs interacted directly with RPA1 in vitro. We propose that the encounter of a replication fork with a topoisomerase-DNA cleavage complex could lead to a juxtaposition of replication fork-associated RPA and DNA double-strand end-associated DNA-PK, leading to RPA2 phosphorylation which may signal the presence of DNA damage to an S-phase checkpoint mechanism. KEYWORDS: camptothecin/DNA damage/DNA-dependent protein kinase/RPA2 phosphorylation (+info)
The topoisomerase-related function gene TRF4 affects cellular sensitivity to the antitumor agent camptothecin.
(3/2758)
Camptothecin is an antitumor agent that kills cells by converting DNA topoisomerase I into a DNA-damaging poison. Although camptothecin derivatives are now being used to treat tumors in a variety of clinical protocols, the cellular factors that influence sensitivity to the drug are only beginning to be understood. We report here that two genes required for sister chromatid cohesion, TRF4 and MCD1/SCC1, are also required to repair camptothecin-mediated damage to DNA. The hypersensitivity to camptothecin in the trf4 mutant does not result from elevated expression of DNA topoisomerase I. We show that Trf4 is a nuclear protein whose expression is cell cycle-regulated at a post-transcriptional level. Suppression of camptothecin hypersensitivity in the trf4 mutant by gene overexpression resulted in the isolation of three genes: another member of the TRF4 gene family, TRF5, and two genes that may influence higher order chromosome structure, ZDS1 and ZDS2. We have isolated and sequenced two human TRF4 family members, hTRF4-1 and hTRF4-2. The hTRF4-1 gene maps to chromosome 5p15, a region of frequent copy number alteration in several tumor types. The evolutionary conservation of TRF4 suggests that it may also influence mammalian cell sensitivity to camptothecin. (+info)
Fractionated administration of irinotecan and cisplatin for treatment of lung cancer: a phase I study.
(4/2758)
A combination chemotherapy of irinotecan (CPT-11) and cisplatin (CDDP) has been reported to be active for lung cancer. In the previous trial, however, diarrhoea and leucopenia became the major obstacle for sufficient dose escalation of CPT-11 to improve the treatment outcome. We conducted a phase I study to investigate whether the fractionated administration of CDDP and CPT-11 at escalated dose was feasible and could improve the treatment outcome. Twenty-four previously untreated patients with unresectable non-small-cell lung cancer (NSCLC) or extensive disease of small-cell lung cancer (SCLC) were eligible. Both CDDP and CPT-11 were given on days 1 and 8, and repeated every 4 weeks. The dose of CDDP was fixed at 60 mg m(-2) and given by 1-h infusion before CPT-11 administration. The starting dose of CPT-11 was 40 mg m(-2), and the dose was escalated by an increase of 10 mg m(-2). The maximally tolerated dose of CPT-11 was determined as 60 mg m(-2) because grade 4 haematological or grade 3 or 4 non-haematological toxicities developed in six patients out of 11 patients evaluated. Diarrhoea became a dose-limiting toxicity. The objective response rates were 76% for NSCLC and 100% for SCLC. The recommended dose of CPT-11 and CDDP in a phase II study will be 50 mg m(-2) and 60 mg m(-2) respectively. (+info)
Enhanced antitumor activity of 6-hydroxymethylacylfulvene in combination with irinotecan and 5-fluorouracil in the HT29 human colon tumor xenograft model.
(5/2758)
6-Hydroxymethylacylfulvene (MGI-114) is a semisynthetic analogue of the toxin illudin S, a product of the Omphalotus mushroom. MGI-114 induces cytotoxicity in a variety of solid tumors in vivo, including the refractory HT29 human colon cancer xenograft. In this study, the potential application of MGI-114 in the treatment of colon cancer was further explored by evaluating the activity of MGI-114 in combination with irinotecan (CPT-11) and 5-fluorouracil (5FU). Groups of 9 nude mice bearing HT29 xenografts were treated with either single agent MGI-114, CPT-11, or 5FU, or MGI-114 in combination with CPT-11 or 5FU. MGI-114 was administered at doses of 3.5 and 7 mg/kg i.p. daily on days 1 through 5, and CPT-11 and 5FU were administered at doses of 50 and 100 mg/kg i.p. on days 1, 12, and 19. In the single agent studies, MGI-114, CPT-11, and 5FU all resulted in decreased final tumor weights compared with vehicle-treated controls (P<0.05), but only MGI-114 at 7 mg/kg produced partial responses. When MGI-114 at 3.5 mg/kg was combined with CPT-11, significant decrements in final tumor weights occurred compared with monotherapy with the same doses of MGI-114 and CPT-11 (P< or =0.001). Also, administration of the low-dose combination (MGI-114 at 35 mg/kg and CPT-11 at 50 mg/kg) resulted in final tumor weights similar to those achieved after administration of high-dose MGI-114 as a single agent. Moreover, the combination of MGI-114 and CPT-11 produced partial responses in nearly all of the animals, with some animals achieving complete responses. The outcome with the combination of MGI-114 and 5FU was less striking, with fewer partial responses and no complete responses. These results suggest enhanced activity when MGI-114 is combined with CPT-11, and clinical trials to further evaluate this combination regimen are planned. (+info)
Combined irinotecan and oxaliplatin plus granulocyte colony-stimulating factor in patients with advanced fluoropyrimidine/leucovorin-pretreated colorectal cancer.
(6/2758)
PURPOSE: To evaluate the efficacy and tolerance of combined irinotecan and oxaliplatin in patients with advanced colorectal cancer pretreated with leucovorin-modulated fluoropyrimidines. PATIENTS AND METHODS: Thirty-six patients with metastatic colorectal cancer, who progressed while receiving or within 6 months after discontinuing palliative chemotherapy with fluoropyrimidines/leucovorin, were enrolled onto this study. Treatment consisted of oxaliplatin 85 mg/m2 on days 1 + 15 and irinotecan 80 mg/m2 on days 1 + 8 + 15 every 4 weeks. Depending on the absolute neutrophil counts (ANC) on the day of scheduled chemotherapeutic drug administration, a 5-day course of granulocyte colony-stimulating factor (G-CSF) 5 microg/kg/d was given. RESULTS: The overall response rate was 42% for all 36 assessable patients (95% confidence interval, 26% to 59%), including two complete remissions (6%). Thirteen additional patients (36%) had stable disease, and only eight (22%) progressed. The median time to treatment failure was 7.5 months (range, 1 to 13.5+ months). After a median follow-up time of 14 months, 19 patients (53%) are still alive. Hematologic toxicity was commonly observed, although according to the ANC-adapted use of G-CSF (in 31 patients during 81 of 174 courses), it was generally mild: grade 3 and 4 granulocytopenia occurred in only five and two cases, respectively. The most frequent nonhematologic adverse reactions were nausea/emesis and diarrhea, which were rated severe in 17% and 19%, respectively. CONCLUSION: Our data suggest that the combination of irinotecan and oxaliplatin with or without G-CSF has substantial antitumor activity in patients with progressive fluoropyrimidine/leucovorin-pretreated colorectal cancer. Overall toxicity was modest, with gastrointestinal symptoms constituting the dose-limiting side effects. Further evaluation of this regimen seems warranted. (+info)
Phase I study of a weekly schedule of irinotecan, high-dose leucovorin, and infusional fluorouracil as first-line chemotherapy in patients with advanced colorectal cancer.
(7/2758)
PURPOSE: To determine the maximum-tolerated dose (MTD) of a weekly schedule of irinotecan (CPT-11), leucovorin (LV), and a 24-hour infusion of fluorouracil (5-FU24h) as first-line chemotherapy in advanced colorectal cancer and to assess preliminary data on the antitumor activity. PATIENTS AND METHODS: Twenty-six patients with measurable metastatic colorectal cancer were entered onto this phase I study. In the first six dose levels, fixed doses of CPT-11 (80 mg/m2) and LV (500 mg/m2) in combination with escalated doses of 5-FU24h ranging from 1.8 to 2.6 g/m2 were administered on a weekly-times-four (dose levels 1 to 4) or weekly-times-six (dose levels 5 to 6) schedule. The dose of CPT-11 was then increased to 100 mg/m2 (dose level 7). RESULTS: Seventy-nine cycles of 5-FU24h/LV with CPT-11 were administered in an outpatient setting. No dose-limiting toxicities were observed during the first cycle at dose levels 1 to 6, but diarrhea of grade 4 (National Cancer Institute common toxicity criteria) was observed in three patients after multiple treatment cycles. Other nonhematologic and hematologic side effects, specifically alopecia and neutropenia, did not exceed grade 2. With the escalation of CPT-11 to 100 mg/m2 (dose level 7), diarrhea of grade 3 or higher was observed in four of six patients during the first cycle; thus, the MTD was achieved. Sixteen of 25 response-assessable patients (64%; 95% confidence interval, 45% to 83%) achieved an objective response. CONCLUSION: The recommended doses for further studies are CPT-11 80 mg/m2, LV 500 mg/m2, and 5-FU24h 2.6 g/m2 given on a weekly-times-six schedule followed by a 1-week rest period. The addition of CPT-11 to 5-FU24h/LV seems to improve the therapeutic efficacy in terms of tumor response with manageable toxicity. (+info)
Cyclosporine inhibited calcium-mediated apoptosis of HL-60 cells.
(8/2758)
AIM: To study the effects of cyclosporine (Cyc) on apoptosis of HL-60 cells. METHODS: Apoptotic cells induced by harringtonine (Har), camptothecin (Cam), or calcimycin (Cal), thapsigargin (Tha) were identified with DNA electrophoresis, morphology, and flow cytometry. Relative [Ca2+]i alteration of apoptotic HL-60 cells were determined with flow cytometry. RESULTS: Cal 1 mg.L-1 or Tha 0.5 mg.L-1 induced apoptosis of HL-60 cells. This effect was inhibited by nontoxic concentration of Cyc 1 mg.L-1. Cyc did not inhibit Har- or Cam-induced apoptosis of HL-60 cells. Both Cal and Tha increased intracellular calcium, whereas Har or Cam did not. CONCLUSION: Cyc inhibited apoptosis only induced by calcium increasement in HL-60 cells. The mechanism of apoptosis induced by Cal or Tha was different from that by Har or Cam. (+info)