Biomedical subjects

G T Faircloth

Publications and source records attributed to G T Faircloth.

8 recordsLinked to original sources

PubMed2001

Unique pattern of ET-743 activity in different cellular systems with defined deficiencies in DNA-repair pathways.

The cytotoxic activity of ecteinascidin 743 (ET-743), a natural product derived from the marine tunicate Ecteinascidia turbinata that exhibits potent anti-tumor activity in pre-clinical systems and promising activity in phase I and II clinical trials, was investigated in a number of cell systems with well-defined deficiencies in DNA-repair mechanisms. ET-743 binds to N2 of guanine in the minor groove, but its activity does not appear to be related to DNA-topoisomerase I poisoning as the drug is equally active in wild-type yeast and in yeast with a deletion in the DNA-topoisomerase I gene. Defects in the mismatch repair pathway, usually associated with increased resistance to methylating agents and cisplatin, did not affect the cytotoxic activity of ET-743. However, ET-743 did show decreased activity (from 2- to 8-fold) in nucleotide excision repair (NER)-deficient cell lines compared to NER-proficient cell lines, from either hamsters or humans. Restoration of NER function sensitized cells to ET-743 treatment. The DNA double-strand-break repair pathway was also investigated using human glioblastoma cell lines MO59K and MO59J, respectively, proficient and deficient in DNA-dependent protein kinase (DNA-PK). ET-743 was more effective in cells lacking DNA-PK; moreover, pre-treatment of HCT-116 colon carcinoma cells with wortmannin, a potent inhibitor of DNA-PK, sensitized cells to ET-743. An increase in ET-743 sensitivity was also observed in ataxia telangiectasia-mutated cells. Our data strongly suggest that ET-743 has a unique mechanism of interaction with DNA.

Androstadienes↗

PubMed2001

Ecteinascidin-743 (ET-743), a natural marine compound, with a unique mechanism of action.

The mode of action of Ecteinascidin-743 (ET-743), a marine tetrahydroisoquinoline alkaloid isolated from Ecteinascidia turbinata, which has shown very potent antitumour activity in preclinical systems and encouraging results in Phase I clinical trials was investigated at a cellular level. Both SW620 and LoVo human intestinal carcinoma cell lines exposed for 1 h to ET-743 progress through S phase more slowly than control cells and then accumulate in the G2M phase. The sensitivity to ET-743 of G1 synchronised cells was much higher than that of cells synchronised in S phase and even higher than that of cells synchronised in G2M. ET-743 concentrations up to four times higher than the IC(50) value caused no detectable DNA breaks or DNA-protein cross-links as assessed by alkaline elution techniques. ET-743 induced a significant increase in p53 levels in cell lines expressing wild-type (wt) (p53). However, the p53 status does not appear to be related to the ET-743 cytotoxic activity as demonstrated by comparing the drug sensitivity in p53 (-/-) or (+/+) mouse embryo fibroblasts and in A2780 ovarian cancer cells or the A2780/CX3 sub-line transfected with a dominant-negative mutant TP53. The cytotoxic potency of ET-743 was comparatively evaluated in CHO cell lines proficient or deficient in nucleotide excision repair (NER), and it was found that ET-743 was approximately 7-8 times less active in ERCC3/XPB and ERCC1-deficient cells than control cells. The findings that G1 phase cells are hypersensitive and that NER-deficient cells are resistant to ET-743 indicate that the mode of action of ET-743 is unique and different from that of other DNA-interacting drugs.

Antineoplastic Agents, Alkylating↗

PubMed1999

Cytotoxicity and neurocytotoxicity of new marine anticancer agents evaluated using in vitro assays.

PURPOSE: New classes of anticancer drugs, isolated from marine organisms, have been shown to possess cytotoxic activity against multiple tumor types. Aplidine, didemnin B, and isohomohalichondrin B (IHB), among the more promising antitumor candidates, have been evaluated in the present study on a comparative basis in terms of their antiproliferative activity and neurotoxic effects in vitro. METHODS: Using a panel of different human, prostatic cancer cell lines (DU 145, PC-3 and LNCaP-FGC) the effects of Aplidine, didemnin B, and IHB on tumor cell proliferation were tested in a colorimetric (XTT) assay and compared with the effects of vincristine, vinorelbine, and Taxol. Under analogous in vitro conditions these drugs were also monitored for neurocytotoxic effects using a PC 12 cell line based model. RESULTS: Didemnin B and - especially - Aplidine were more effective in the inhibition of prostate cancer cell proliferation than vincristine, vinorelbine or Taxol at concentration levels between 5 and 50 pmol/ml. At these same concentrations, however, Didemnin B and Aplidine were also most potent in the in vitro neurotoxicity assays. IHB was found to exert even more potent antiproliferative activity (at concentration levels between 0.05 and 0.1 pmol/ml). However, neurotoxic effects were also found to be present at these levels. After drug withdrawal, the neurotoxic damage, inflicted by aplidine or IHB appeared to be more long lasting than after vincristine or vinorelbine exposure. CONCLUSIONS: These results point to high antiproliferative activity of aplidine and IHB in prostate cancer. At the same time, the data urge some caution in the clinical use of these agents because of potential neurotoxic side-effects. The use of a newly formulated Aplidine may involve a more favorable therapeutic profile.

Animals↗

PubMed1999

High antitumour activity of ET743 against human tumour xenografts from melanoma, non-small-cell lung and ovarian cancer.

BACKGROUND: Ecteinascidin-743 (ET743) is a novel antitumour agent originating from the Caribbean tunicate Ecteinascidia turbinata. It has potent cytotoxic and antitumour activity and a potential new mechanism of action. The aim of the present study was to further explore the antitumour activity of ET743 in human tumour xenografts from melanoma, non-small-cell lung and ovarian cancer. DESIGN: As the antitumour profile of ET743 was largely unknown a chemo-sensitive and a marginal chemo-resistant human tumour xenograft were selected for each tumour type. ET743 was administered intravenously using two administration schedules (days 0, 4, 8 and 0-2, 13-15). RESULTS: ET743 was very active at the maximum tolerated dose (MTD) in the chemo-sensitive xenograft melanoma MEXF 989, non-small-cell lung cancer LXFL 529, and ovarian cancers HOC22 and (marginally resistant to cisplatin) HOC18. Activity was also seen at 1/2 MTD. Apart from HOC18, ET743 caused complete remissions in the responding xenografts. The compound was inactive in the chemo-resistant xenograft melanoma MEXF 514 and non-small-cell lung cancer LXFA 629. In terms of antitumour activity the days 0, 4, 8 schedule had advantages over the days 0-2, 13-15 schedule. CONCLUSIONS: ET743 is a very effective agent in chemo-sensitive and marginal chemo-resistant xenografts, but inactive in chemo-resistant tumour xenografts. The activity of ET743 in the marginally cisplatin-resistant ovarian cancer HOC18 might indicate absence or incomplete cross-resistance against cisplatin. It is recommended to include melanoma, non-small-cell lung cancer, and ovarian cancer in phase II clinical trials and to use an intermittent schedule.

Adult↗

PubMed1998

In vitro activity of aplidine, a new marine-derived anti-cancer compound, on freshly explanted clonogenic human tumour cells and haematopoietic precursor cells.

Aplidine is a new marine anti-cancer depsipeptide isolated from the Mediterranean tunicate Aplidium albicans. We have evaluated its antiproliferative action against a variety of freshly explanted human tumour specimens. Concentration ranges of 0.01-1.0 microM and 0.0001-1.0 microM were used in short- and long-term exposure schedules respectively. After exposure for 1 h in 49 evaluable specimens, aplidine showed a clear concentration-dependent anti-tumour effect. At 0.05 microM, 85% of the specimens were markedly inhibited. Continuous exposure for 21-28 days in 54 tumour specimens also led to a concentration-dependent activity relationship. Fifty per cent and 100% tumour inhibitions were achieved with 0.001 microM and 0.05 microM respectively. A head to head evaluation assessing short vs continuous exposure was carried out, resulting in evidence of an activity-time of exposure relationship. Breast, melanoma and non-small-cell lung cancer appear to be sensitive to low concentrations of aplidine. In addition the evaluation of the effects of aplidine on haematopoietic cells showed a concentration-dependent toxicity. However, under continuous exposure, active concentrations induced mild bone marrow toxicity, indicating that a therapeutic window at marginally myelotoxic concentrations might exist.

Animals↗

PubMed1996

Immunosuppressive cyclolignans.

The immunosuppressive activity of several lactonic, nonlactonic, and heterocycle-fused cyclolignans has been demonstrated for the first time by use of a T-cell-mediated immune response. Of the compounds tested, 4'-demethyldeoxypodophyllotoxin (8), beta-apopicropodophyllin (6), and the isoxazoline-fused cyclolignan 15 are the most potent with respect to their suppression of activated splenocytes.

Animals↗

PubMed1986

Differential subcellular distribution of bioactive human chorionic gonadotropin in pseudopregnant rat ovary.

The subcellular metabolism of internalized hCG was examined by monitoring the distribution of bioactive and immunoreactive hCG in subcellular fractions of pseudopregnant rat ovaries. Homogenates of ovaries from rats injected with 1.0 microgram (12.8 IU; bioassay) hCG were fractionated on self-generating Percoll gradients into three hCG-containing compartments: soluble proteins (cytosolic fraction), a combined plasma membrane/prelysosomal vesicle fraction, and lysosomes. The hCG level in each fraction was measured by RIA and in vitro bioassay. When necessary, receptor-bound hCG was dissociated at low pH before assay. Levels of cytosolic hCG were highest 1-3 h after injection, attaining peak immunoreactive concentrations of 18 ng/ovarian pair. Cytosolic hormone was not primarily derived from nonspecific trapping of serum or interstitial fluid, because after 1.0 microgram [125I]iodobovine gamma-globulin was injected into rats, cytosolic globulin levels (nanograms per ovarian pair) were approximately 7-10 times lower than those of hCG. Cytosolic hCG retained significant bioactivity for at least 10 h after hCG stimulation. Peak immunoreactive hCG levels associated with the plasma membrane/prelysosomal fraction were 82 ng/ovarian pair between 3 and 6 h after hCG injection, and hormone associated with that fraction retained the highest bioactivity of the three fractions examined. Peak lysosomal hCG levels reached 55 ng/ovarian pair 10 and 14 h after hCG stimulation, but lysosomal hCG was not bioactive. These results suggest that the lysosomal compartment is a major pathway for hCG inactivation. A nonlysosomal pathway for hCG inactivation may exist, because the cytosolic compartment contained partially inactivated hormone that did not appear to be of lysosomal origin. Cytosolic hCG may reflect hormone delivered to the cell cytoplasm or to the extracellular fluid that is either modified within prelysosomal vesicles or is degraded subsequently by nonlysosomal proteases.

Animals↗

PubMed1984

Metabolism of luteinizing hormone by the pseudopregnant rat ovary.

Ovarian metabolism of highly purified human LH (hLH) was studied in pseudopregnant rats. The animals were injected with 1.0 microgram (11.1 IU) hLH, iv, and groups of animals were killed between 15 and 300 min. The hLH present in ovarian cytosol and sera and eluted from ovarian membrane was determined by RIA. Ovarian membrane-bound LH increased rapidly for 1 h, after which it plateaued and then decreased 4 h after the injection. Cytosolic LH peaked at 1 h, but concentrations declined thereafter. When ovarian cytosol obtained from rats injected with 10 micrograms hLH was chromatographed on a Sephadex G-100 column, the major immunoreactive fraction cochromatographed with the LH used for injection. Cytosol harvested 15 min after LH stimulation contained a small peak which coeluted with LH alpha. No LH beta was detected. No evidence for extensive dissociation of the LH subunits was found. When hLH present in serum and ovarian cytosol or bound to ovarian membrane was chromatographed on Concanavalin A-Sepharose, different patterns of binding and elution with that lectin were observed and were consistent with differential modification of the oligosaccharide side chains of LH present in serum and associated with the ovary. The biological to immunological ratio of cytosolic LH decreased from 1.7 15 min after LH injection to 0.8 at 5 h. Compared to our previous studies with hCG, LH was metabolized more rapidly. Whether that difference in the rates of ovarian metabolism of the two gonadotropins contributes to the marked disparity in their quantitative biochemical effects induced by those hormones should be examined.

Animals↗