IDN 5390: a new concept in taxane development

Inhibition of SIRT2 potentiates the anti-motility activity of taxanes: implications for antineoplastic combination therapies

Taxanes are potent inhibitors of cell motility, a property implicated in their antiangiogenic and antimetastatic activity and unrelated to their antiproliferative effect. The molecular mechanism of this anti-motility activity is poorly understood. In this study, we found that paclitaxel induced tubulin acetylation in endothelial and tumor cells, at concentrations that affected cell motility but not proliferation (10(-8) to 10(-9) M, for 4 hours). Induction of tubulin acetylation correlated with inhibition of motility but not proliferation based on a comparison of highly and poorly cytotoxic taxanes (paclitaxel and IDN5390) and tumor cell lines sensitive and resistant to paclitaxel (1A9 and 1A9 PTX22). Consistent with the hypothesis that tubulin deacetylase activity might affect cell response to the anti-motility activity of taxanes, we found that overexpression of the tubulin deacetylase SIRT2 increased cell motility and reduced cell response to the anti-motility activity of paclitaxel. Conversely, the SIRT2 inhibitor splitomicin reduced cell motility and potentiated the anti-motility activity of paclitaxel. The inhibitory effect was further potentiated by the addition of the HDAC6 inhibitor trichostatin A. Paclitaxel and splitomicin promoted translocation into the nucleus--and hence activation--of FOXO3a, a negative regulator of cell motility. This study indicates a role for SIRT2 in the regulation of cell motility and suggests that therapies combining sirtuin inhibitors and taxanes could be used to treat cell motility-based pathologic processes such as tumor angiogenesis, invasion, and metastasis.

Pharmacokinetics and Metabolism in Mice of IDN 5390 (13-(N-Boc-3-i-butylisoserinoyl)-C-7,8-seco-10-deacetylbaccatin III), a New Oral C-seco-Taxane Derivative with Antiangiogenic Property Effective on Paclitaxel-Resistant Tumors

IDN 5390 (13-(N-Boc-3-i-butylisoserinoyl)-C-7,8-seco-10-deacetylbaccatin III) is a new taxane, derived from 7,8-C-seco-10-deacetylbaccatin, selected for its ability to inhibit angiogenesis, mainly by acting on endothelial cell motility, and for its selective activity on class III beta-tubulin. In vivo, IDN 5390 shows activity against paclitaxel-sensitive and -resistant tumors when administered on a prolonged, continuous dosage schedule. We studied the pharmacokinetics and bioavailabilty of the drug in mice after single and repeated oral treatment. IDN 5390 was rapidly absorbed after oral administration, with good bioavailability (43%). After intravenous injection, it was extensively distributed in tissue, mainly the liver, kidney, and heart, with low but persistent levels in brain. The kinetics appear dose-dependent with a clearance of 2.6, 1.4, and 0.9 l/kg at, respectively, 60, 90, and 120 mg/kg, and a half-life 24, 36, and 54 min. After prolonged daily oral doses given for 2 weeks, we found that there was a decrease in drug availability; i.e., the area under the concentration-time curve value after p.o. daily administration on day 14 was 2-fold lower than that on day 1. Metabolism plays a major role in elimination of the drug, and at least 12 metabolites were identified in feces and urine. The percentage excreted as metabolites after an oral dose (42%) was higher than that after the i.v. dose (33%), suggesting a first-pass effect. Four metabolites were found in plasma at detectable levels; one of them, with restored taxane scaffold, is a species 3 times more potent than IDN 5390, possibly contributing to the observed anti-tumor activity.

The Vascular Targeting Property of Paclitaxel Is Enhanced by SU6668, a Receptor Tyrosine Kinase Inhibitor, Causing Apoptosis of Endothelial Cells and Inhibition of Angiogenesis

PURPOSE

Different antiangiogenic approaches have been proposed in cancer treatment where therapeutic efficacy has been shown with the addition of cytotoxic agents. Here, we used SU6668, a small-molecule receptor tyrosine kinase inhibitor, to investigate the combinatorial effect with paclitaxel on the cellular populations of the developing vasculature.

EXPERIMENTAL DESIGN

The effect of this combination was evaluated in vitro in a 72-hour proliferation assay on human umbilical vein endothelial cells (HUVEC) and human microvascular endothelial cells derived from lungs, endothelial cells, aortic smooth muscle cells, and human ovarian carcinoma cells sensitive (1A9) and resistant (1A9-PTX22) to paclitaxel. Combination data were assessed by isobologram analysis. Cell survival was determined by terminal deoxyribonucleotide transferase-mediated nick-end labeling and Annexin V staining. The activity of the combination in vivo was evaluated in fibroblast growth factor-2-induced angiogenesis in Matrigel plugs s.c. implanted in mice. The 1A9-PTX22, paclitaxel-resistant xenograft model was used to evaluate tumor response.

RESULTS

Combination index values and isobologram analysis showed synergy in inhibition of proliferation of HUVEC, human microvascular endothelial cells derived from lungs, and aortic smooth muscle cells. The combination induced greater apoptosis in HUVEC than the single agents. The addition of paclitaxel to the treatment with SU6668 significantly decreased the hemoglobin content and the number of CD31-positive vessels in Matrigel plugs in vivo. The combination of the drugs was more active than either single agent against 1A9-PTX22 xenografts; the tumor growth delay was accompanied by a significant reduction of vascular density.

CONCLUSIONS

These findings show that the activity of angiogenesis inhibitors on vascular cells could be potentiated when administered in combination with chemotherapeutic agents that themselves have vascular targeting properties.

Pharmacokinetic measurements of IDN 5390 using electrospray ionization tandem mass spectrometry: structure characterization and quantification in dog plasma

In this report, electrospray ionization tandem mass spectrometry (ESI-MS/MS) for a pharmacokinetic study of IDN 5390, a novel C-seco taxane derivative, which is under preclinical evaluation, has been investigated. Our results showed that IDN 5390 and other taxanes including paclitaxel and IDN 5109 could ionize well in not only positive-, but also in negative-ion mode. Under collision-induced dissociation (CID) conditions, these compounds could fragment into similar M- (molecular), T- (taxane ring) and S- (side chain) series ions. In positive-ion ESI, the formation of both T- and S-series ions involved the breaking of the C-13 ester bond. In negative-ion ESI, however, while the formation mechanism of S-series ions remained the same, the breaking of the C-1' carboxylic ester bond resulted in T-series ions. At optimum collision energy (CE) values, M-, T- and S-series ions of IDN 5390 in both positive- and negative-ion ESI-MS/MS spectra had good intensity. This phenomenon makes both positive- and negative-ion ESI-MS/MS good methods for IDN 5390 metabolite structural characterization, i.e. to reveal the location of modification groups in IDN 5390 metabolites versus IDN 5390 either on the side chain or the taxane ring. A liquid chromatography (LC)/ESI-MS/MS method using the multiple-reaction monitoring (MRM) technique was thereafter developed to quantify IDN 5390 in dog plasma using paclitaxel as internal standard. The method was validated using a concentration range between 5 and 1000 ng/mL and had a limit of detection of 1 ng/mL. The inter-day %CV (%coefficient of variation) of the calibration standards ranged between 4.36 and 9.64%, the intra-day %CV of the calibration standards between 0.61 and 13.44%, and the mean % accuracy of the quality control samples at the low, middle and high end of the concentration curves were 12.5, 6.8 and 9.6%, respectively.

Modelling approaches for angiogenesis

The development of a functional vasculature within a tumour is a requisite for its growth and progression. This fact has led to the design of therapies directed toward the tumour vasculature, aiming either to prevent the formation of new vessels (anti-angiogenic) or to damage existing vessels (vascular targeting). The development of agents with different mechanisms of action requires powerful preclinical models for the analysis and optimization of these therapies. This review concerns 'classical' assays of angiogenesis in vitro and in vivo, recent approaches to target identification (analysis of gene and protein expression), and the study of morphological and functional changes in the vasculature in vivo (imaging techniques). It mainly describes assays designed for anti-angiogenic compounds, indicating, where possible, their application to the study of vascular-targeting agents.