Induction of resistance to Aplidin in a human ovarian cancer cell line related to MDR expression.

Aplidin-resistant IGROV-1/APL cells were derived from the human ovarian cancer IGROV-1 cell line by exposing the cells to increasing concentration of Aplidin for eight months, starting from a concentration of 10 nM to a final concentration of 4 microM. IGROV-1/APL cell line possesses five fold relative resistance to Aplidin. IGROV-1/APL resistant cell line shows the typical MDR phenotype: (1) increased expression of membrane-associated P-glycoprotein, (2) cross-resistance to drugs like etoposide, doxorubicin, vinblastine, vincristine, taxol, colchicin and the novel anticancer drug Yondelis (ET-743). The Pgp inhibitor cyclosporin-A restored the sensitivity of IGROV-1/APL cells to Aplidin by increasing the drug intracellular concentration. The resistance to Aplidin was not due to the other proteins, such as LPR-1 and MRP-1, being expressed at the same level in resistant and parental cell line. The finding that cells over-expressing Pgp are resistant to Aplidin was confirmed in CEM/VLB 100 cells, that was found to be 5-fold resistant to Aplidin compared to the CEM parental cell line.

Antiangiogenesis treatment combined with chemotherapy produces chondrosarcoma necrosis.

A combination therapy protocol using a marine chemotherapeutic and an antiangiogenic molecule was tested in a mouse tumor xenograft model for the ability to curtail the growth of a human chondrosarcoma (CHSA). Ecteinascidin-743 (ET-743), a marine-derived chemotherapeutic, was effective at slowing the growth of a primary CHSA. Plasminogen-related protein B, which antagonizes various endothelial cell activities, also elicited a significant inhibition of neoplastic growth, albeit with reduced effectiveness. The combination of the two agents resulted in only a modest further repression of tumor growth over that associated with ET-743 treatment alone, as measured by tumor volume (82% versus 76% inhibition, respectively). However, analysis of the extent of tumor necrosis and vascularization of the tumor revealed that the coadministration of the two compounds was clearly more effective, eliciting a 2.5-fold increase in tumor necrosis relative to single-agent treatment. The combination therapy also was most effective at antagonizing tumor-associated microvessel formation, as assessed by CD31 immunostaining, suggesting that combination therapy may hold promise for treating CHSA. Tumor necrosis produced by combination therapy of ET-743 and recombinant plasminogen-related protein B was also significantly greater than that produced by conventional doxorubicin treatment, further corroborating the efficacy of combination therapy.

In vitro toxicity of three new antitumoral drugs (trabectedin, aplidin, and kahalalide F) on hematopoietic progenitors and stem cells.

OBJECTIVE: In addition to neutropenias and/or thrombocytopenias as a short-term effect, antineoplastics also can produce long-term effects as a consequence of damage to the hematopoietic stem cells. The aim of the present study was to evaluate the toxicity of three marine-derived antineoplastics on murine hematopoietic stem cells. These antitumoral compounds currently are being evaluated in patients in phase II (aplidin and kahalalide F) and phase II/III (trabectedin) clinical trials. MATERIALS AND METHODS: Long-term competitive repopulating assays were performed in mice to analyze toxic effects on the hematopoietic stem cells responsible for the multipotential long-term repopulation of hematopoiesis. Furthermore, granulocytic and T- and B-lymphoid lineages were studied, as well as myeloid (CFU-GM) and megakaryocytic (CFU-Meg) progenitors. RESULTS: When cells were treated in vitro for 24 hours with CFU-GM IC(50) dose of trabectedin (9.59+/-4.96 nM), no significant effects were observed in the stem cells. The dose of trabectedin that produced 90% of inhibition in CFU-GM (IC(90): 23.71+/-1.27 nM) only inhibited 45% survival of stem cells. Doses of aplidin that produced reductions of 50% (56.9+/-13.32 nM) or 90% (195.88+/-21.39 nM) in myeloid progenitors did not show any effect on hematopoietic stem cells. Kahalalide F did not show any toxic effect in either short-term or long-term repopulating cells up to 10 microM. CONCLUSIONS: Our data show that the hematopoietic stem cells effects of antitumoral drugs can be properly characterized by the murine competitive repopulating assays. Our results suggest that long-term myelosuppression as a consequence of trabectedin, aplidin, or kahalalide F treatment would not be expected.

Preclinical toxicity studies of kahalalide F, a new anticancer agent: single and multiple dosing regimens in the rat.

PURPOSE: Kahalalide F (KF) is a new anticancer agent currently in clinical trials for solid tumors, including prostate cancer. During the preclinical development of this drug, the studies reported here were conducted to determine the acute and multiple dose toxicities of KF when administered intravenously (i.v.) to rats. This dosing route is the intended route of clinical administration. METHODS: KF was administered i.v. to male and female CD rats using single- and multiple-dose (daily for 5 days) schedules. Animals were observed for clinical signs, and body weight, hematology, and clinical chemistry parameters determined. Animals were necropsied, gross observations and organ weights recorded, and numerous tissues were collected and examined microscopically. RESULTS: KF produced lethality at 375 and 450 microg/kg in males and females, respectively, and the maximum tolerated dose (MTD) was estimated to be 300 microg/kg (1800 microg/m(2)). The nervous system appeared to be a potential site of action for the production of lethality. Single-dose administration of KF at 150 and 300 microg/kg produced organ toxicity in which the kidney was the primary target. Injury to distal convoluted tubules was the most toxicologically significant lesion, and was observed on day 4. However, by day 29, resolution of renal toxicity had occurred in the 150-microg/kg group, but only partial resolution was seen at 300 microg/kg. Renal injury correlated with increased serum creatinine, BUN, and kidney weights at 300 microg/kg, indicating impairment of renal function. Subacute, necrotizing inflammation of bone marrow and peritrabecular osteocyte hyperplasia of bone were seen at 300 microg/kg on day 4, with recovery thereafter. Injury to blood vessels and surrounding tissue at the injection site were produced by KF, likely due to local cytotoxicity. In general, reversibility of toxicity was seen at 150 microg/kg but not at 300 microg/kg. When KF was administered once daily for five consecutive days at a dose of 80 microg/kg per day (400 microg/kg total dose), slightly decreased body weight gain was the primary drug-related effect. Therefore, the no-adverse-effect dose was at or near 80 microg/kg per day (480 microg/m(2) per day). CONCLUSIONS: These findings demonstrate that fractionation of a lethal or MTD dose of KF by daily administration for 5 days reduces drug-induced toxicity, and appears to be a viable option for the clinical evaluation of KF for the treatment of cancer.

Combination of trabectedin and irinotecan is highly effective in a human rhabdomyosarcoma xenograft.

Our objective was to evaluate in vitro and in vivo the effect of the combination of trabectedin (Yondelis, ET-743) and irinotecan (CPT-11) or its major metabolite SN-38 in a human rhabdomyosarcoma cell line. The schedule trabectedin (1 h) followed by irinotecan or SN-38 (24 h) and the opposite sequence (irinotecan or SN-38 24 h followed by trabectedin 1 h) were analyzed in a rhabdomyosarcoma cell line. In vivo studies were conducted with trabectedin and irinotecan at the doses of 0.2 and 20 mg/kg, respectively, simultaneously administered with a q4d x 3 schedule. In vitro studies indicated an overall additive effect [combination index (CI) relatively close to 1.0], with the former schedule slightly superior to the latter (at the IC50 effect levels: CI=0.89 versus 1.07). Neither transcription nor expression of DNA topoisomerase I was affected by trabectedin treatment. In vivo the therapeutic results of the combination were certainly more impressive: trabectedin and irinotecan combination caused a strong and long-lasting effect on tumor growth (tumor volume inhibition=89%, log10 cell kill=1.6), whereas each drug given as a single agent was only marginally active. The discrepancy between the in vitro and in vivo results suggests possible mechanisms involving host cells, other than tumor cells. The striking effects of the combination observed in vivo could be related to a combination of a direct cytotoxic and an anti-inflammatory indirect effect. The very marked and long-lasting effect of the trabectedin and irinotecan combination in vivo suggests a basis for a clinical evaluation in pediatric patients with rhabdomyosarcoma.

A nondisposable microplate for use with organic solvents.

A nondisposable, or "hard", multiwell microplate is described for use with small volumes of biological solutions containing organic solvents. The design of this teflon-coated, aluminum device resembles the 96-well layout of the disposable variety of tissue culture microplates. The reusable, hard microplate has been specifically developed to hold and evaporate volatile organic solvents from aliquots of crude sample extractions or partitions intended for testing in various in vitro biological screening assays. This device is a valuable adjunct for converting numerous small volumes of nonpolar or nonaqueous dissolved compounds into reconstituted solutions containing acceptable assay solvents.

Unique features of the mode of action of ET-743.

This paper describes the current knowledge of the primary mode of action of a natural product, ecteinascidin 743 (ET-743), derived from the marine tunicate Ecteinascidia turbinata. ET-743 was initially selected for preclinical development because of its potent antitumor activity observed against several human solid tumor types. In vitro, the drug is cytotoxic in the nanomolar range, and in the case of some very sensitive cell lines, in the picomolar range. The large potency differences observed among several solid tumor types indicate that this compound possesses some tumor selectivity, but the molecular basis of these differential effects remains to be elucidated. The present studies were undertaken to evaluate the mechanism of action of ET-743 in this context. The available information on ET-743 binding to DNA and its effects on transcriptional regulation point to a unique behavior of this drug, as it independently affects specific gene transcription in a promoter-dependent way. In addition, ET-743 shows a peculiar pattern of selectivity in cells with different defects in their DNA-repair pathways. These results highlight a unique property of ET-743, possibly explaining why it possesses antitumor activity against tumors that are refractory to standard anticancer drugs, all of which certainly act by mechanisms that are different from that of ET-743.