Effect of E7010 on liver metastasis and life span of syngeneic C57BL/6 mice bearing orthotopically transplanted murine Colon 38 tumor

Synthesis of 2-anilinopyridyl-triazole conjugates as antimitotic agents

A series of 2-anilinopyridyl–triazole conjugates (6a–t) were prepared and evaluated for their cytotoxic activity against a panel of three human cancer cell lines. Among them compounds 6q, 6r and 6s showed significant cytotoxic activity with IC50 values ranging from 0.1 to 4.1 μM. Structure–activity relationships were elucidated with various substitutions on these conjugates. Flow cytometric analysis revealed that these compounds arrest the cell cycle at the G2/M phase and induce cell death by apoptosis. The tubulin polymerization assay and immunofluorescence analysis showed that these compounds (6q, 6r and 6s) effectively inhibited the microtubule assembly in human prostate cancer cells (DU-145). The docking studies showed that 6s interacts and binds efficiently with the tubulin protein at the colchicine binding site. This was further confirmed by the colchicine competitive binding assay. Moreover, compounds 6q, 6r and 6s possess anti-tubulin activity both in vitro and within cells as demonstrated by the ratio of soluble versus polymerized tubulin. Further the apoptotic effects of compounds were confirmed by Hoechst staining, caspase 3 activation, annexin-V FITC, mitochondrial membrane potential and DNA fragmentation analysis. Interestingly, these compounds did not affect the normal human embryonic kidney cells, HEK-293.

Stabilizing versus destabilizing the microtubules: a double-edge sword for an effective cancer treatment option?

Microtubules are dynamic and structural cellular components involved in several cell functions, including cell shape, motility, and intracellular trafficking. In proliferating cells, they are essential components in the division process through the formation of the mitotic spindle. As a result of these functions, tubulin and microtubules are targets for anticancer agents. Microtubule-targeting agents can be divided into two groups: microtubule-stabilizing, and microtubule-destabilizing agents. The former bind to the tubulin polymer and stabilize microtubules, while the latter bind to the tubulin dimers and destabilize microtubules. Alteration of tubulin-microtubule equilibrium determines the disruption of the mitotic spindle, halting the cell cycle at the metaphase-anaphase transition and, eventually, resulting in cell death. Clinical application of earlier microtubule inhibitors, however, unfortunately showed several limits, such as neurological and bone marrow toxicity and the emergence of drug-resistant tumor cells. Here we review several natural and synthetic microtubule-targeting agents, which showed antitumor activity and increased efficacy in comparison to traditional drugs in various preclinical and clinical studies. Cryptophycins, combretastatins, ombrabulin, soblidotin, D-24851, epothilones and discodermolide were used in clinical trials. Some of them showed antiangiogenic and antivascular activity and others showed the ability to overcome multidrug resistance, supporting their possible use in chemotherapy.

ABT-751, a novel tubulin-binding agent, decreases tumor perfusion and disrupts tumor vasculature

ABT-751 is an orally bioavailable tubulin-binding agent that is currently under clinical development for cancer treatment. In preclinical studies, ABT-751 showed antitumor activity against a broad spectrum of tumor lines including those resistant to conventional chemotherapies. In this study, we investigated the antivascular properties of ABT-751 in a rat subcutaneous tumor model using dynamic contrast-enhanced magnetic resonance imaging. A single dose of ABT-751 (30 mg/kg, intravenously) induced a rapid, transient reduction in tumor perfusion. After 1 h, tumor perfusion decreased by 57% before recovering to near pretreatment levels within 6 h. In contrast, ABT-751 produced little change in muscle perfusion at either time point. To further elucidate mechanisms of drug action at the cellular level, we examined the effects of ABT-751 on endothelial cells using an in-vitro assay. ABT-751, at concentrations corresponding to plasma levels achieved in vivo, caused endothelial cell retraction and significant loss of microtubules within 1 h. The severity of these morphological changes was dose-dependent but reversible within 6 h after the discontinuation of the drug. Taken together, these results show that ABT-751 is a tubulin-binding agent with antivascular properties. Microtubule disruption and morphological changes in vascular endothelial cells may be responsible, at least in part, for the dysfunction of tumor blood vessels after ABT-751 treatment.

Clinical outcome in children with recurrent neuroblastoma treated with ABT-751 and effect of ABT-751 on proliferation of neuroblastoma cell lines and on tubulin polymerization in vitro

BACKGROUND

ABT-751, an orally bioavailable sulfonamide, binds beta-tubulin to inhibit microtubule polymerization. We described response and event-free survival (EFS) in children with neuroblastoma and other solid tumors receiving ABT-751, assessed in vitro cytotoxicity of ABT-751 and evaluated the effect of ABT-751 on tubulin polymerization in peripheral blood mononuclear cells (PBMC) and pediatric tumor cell lines.

PROCEDURE

Patients with neuroblastoma (n = 50) or other solid tumors (n = 26) enrolled on the ABT-751 pediatric phase I and pilot trials were reviewed. The sulforhodamine B (SRB) and ACEA Real-Time Cell Electronic Sensing (RT-CES) assays were used to determine the in vitro cytotoxicity. Pharmacodynamic effects on tubulin polymerization/depolymerization were assessed by Western blot and confocal microscopy using antibodies specific for post-translational modifications of polymerized tubulin.

RESULTS

Forty-five patients with neuroblastoma were evaluated for anti-tumor response. No complete or partial responses were documented. The median EFS was 9.3 weeks for children with neuroblastoma and 3.3 weeks for children other solid tumors (P < 0.0001). The ABT-751 IC(50) was 0.6-2.6 mcM in neuroblastoma and 0.7-4.6 mcM in other solid tumor cell lines. Following drug exposure, polymerized tubulin decreased in a concentration- and time-dependent manner in cell lines.

CONCLUSIONS

In children treated with ABT-751, the EFS is longer in children with neuroblastoma as compared to other diagnoses. In vitro, ABT-751 was cytotoxic at concentrations tolerable in children. Effects of ABT-751 on polymerization and microtubule structure were time- and dose-dependent but not dependent on tumor type.

STX140 is efficacious in vitro and in vivo in taxane-resistant breast carcinoma cells

PURPOSE

The aim of these studies was to characterize the action of STX140 in a P-glycoprotein-overexpressing tumor cell line both in vitro and in vivo. In addition, its efficacy was determined against xenografts derived from patients who failed docetaxel therapy.

EXPERIMENTAL DESIGN

The effects of STX140, Taxol, and 2-methoxyestradiol (2-MeOE2) on cell proliferation, cell cycle, and apoptosis were assessed in vitro in drug-resistant cells (MCF-7(DOX)) and the parental cell line (MCF-7(WT)). Mice bearing an MCF-7(DOX) tumor on one flank and an MCF-7(WT) tumor on the other flank were used to assess the in vivo efficacy. Furthermore, the responses to STX140 of three xenografts, derived from drug-resistant patients, were assessed.

RESULTS

In this study, STX140 caused cell cycle arrest, cyclin B1 induction, and subsequent apoptosis of both MCF-7(DOX) and MCF-7(WT) cells. Taxol and 2-MeOE2 were only active in the MCF-7(WT) parental cell line. Although both STX140 and Taxol inhibited the growth of xenografts derived from MCF-7(WT) cells, only STX140 inhibited the growth of tumors derived from MCF-7(DOX) cells. 2-MeOE2 was ineffective at the dose tested against both tumor types. Two out of the three newly derived docetaxel-resistant xenografts, including a metastatic triple-negative tumor, responded to STX140 but not to docetaxel treatment.

CONCLUSIONS

STX140 shows excellent efficacy in both MCF-7(WT) and MCF-7(DOX) breast cancer xenograft models, in contrast to Taxol and 2-MeOE2. The clinical potential of STX140 was further highlighted by the efficacy seen in xenografts recently derived from patients who had failed on taxane therapy.

Emerging therapeutic options for Philadelphia-positive acute lymphocytic leukemia

Acute lymphocytic leukemia (ALL) is a heterogeneous group of disorders that are associated with a cure rate of > 80% in children. The prognosis in adults is considerably inferior, with age, disease bulk, leukemia karyotype and immune phenotype being prognostically relevant. Adult ALL treatment programs include induction, intensified consolidation and maintenance phases with CNS prophylaxis. The addition of imatinib in patients with BCR-ABL-positive ALL has improved the prognosis of this subgroup, but their survival is still poor. Initial data on the second-generation BCR-ABL inhibitors, dasatinib and nilotinib, indicate a potentially greater efficacy than imatinib, but the improvement is likely to be modest. The overall efforts in terms of developmental therapeutics in ALL are very modest and not in keeping with the urgent need for improvement. Most agents being investigated have mechanisms of action similar to those of existing agents for ALL therapy and thus represent modest opportunities to improve results. Of such agents, data on BCR-ABL inhibitors, sphingosomal vincristine, pemetrexed, talotrexin, annamycin and ABT-751 are reviewed.

Evaluation of ABT-751 against childhood cancer models in vivo

OBJECTIVE

ABT-751 is a novel antimitotic agent that binds tubulin at the colchicine binding site. ABT-751 is undergoing Phase I trials in children, but has not been evaluated against a range of pediatric tumor models in vivo.

MATERIALS AND METHODS

ABT-751 was evaluated against 27 subcutaneously implanted xenograft models of childhood cancer including neuroblastoma [4], osteosarcoma [4], Ewing sarcoma [2] rhabdomyosarcoma [8], medulloblastoma [1] and eight kidney cancer lines (six Wilms tumors, two rhabdoid). ABT-751 was administered at 100 mg/kg P.O. on a schedule of 5 days on, 5 days off, 5 days on, repeating the cycle at 21 days. Tumor diameters were measured at 7 day intervals for a period of 12 weeks. Three measures of antitumor activity were used: (1) clinical response criteria [e.g., partial response (PR), complete response (CR), etc.]; (2) treated to control (T/C) tumor volume at day 21; and (3) a time to event measure based on the median event free survival (EFS) of treated and control lines.

RESULTS

ABT-751 induced regression in 4 of 25 models (16%) including models of neuroblastoma that are refractory to vincristine and paclitaxel. Other regressions occurred in rhabdomyosarcoma and Wilms tumor models. ABT-751 significantly increased event free survival (EFS > 2.0) in eight models (33%) in addition to those with objective responses.

CONCLUSIONS

ABT-751 demonstrated intermediate activity against this tumor panel. Neuroblastoma models appear somewhat more sensitive to this agent, with objective regressions also in rhabdomyosarcoma and Wilms tumor. ABT-751 was also active in several tumor lines intrinsically refractory to vincristine or paclitaxel.

An orthotopic colon cancer model for studying the B7-H3 antitumor effect in vivo

We established an orthotopic animal model of colon cancer in mice and applied this model to study the antitumor effects of B7-H3, the newest member of the B7 family of costimulatory molecules. Colon-26 murine colon adenocarcinoma cells were inoculated into the cecal subserosum of mice to induce colon tumor growth. The tumor growth rate and the survival time of the mice were observed. A stable B7-H3 transfected Colon-26 cell line was established and the immunogenic effect was investigated. All mice implanted with wild-type tumor cells had tumor growth in the colon and died. The mean survival rate was 23 days. Mice implanted with C26-B7-H3 had a significantly prolonged survival time of 38 days. Our data suggest that B7-H3 exerts an antitumor effect on adenocarcinoma of the colon and may be considered as an adjuvant immunotherapy in the treatment of colon cancers. Our orthotopic animal model of colon cancer in mice could be applied to in vivo experimental studies of colon cancer.

Novel benzopyridothiadiazepines as potential active antitumor agents

The synthesis of novel thiadiazepine derivatives, that could be considered as constraint analogues of E-7010, are reported. These molecules were evaluated for their antiproliferative activity toward the murine L1210 leukemia cell line. Flow cytometric studies performed on L1210 cells with the most cytotoxic compounds showed an accumulation of the cells in the G2/M phases of the cell cycle with a significant percentage of tetraploid cells (8N DNA content). Submicromolar cytotoxicities were observed with compounds 2b, 4b, 4e, 4g, and 4i. Two of them, compounds 2b and 4b, were found to be potent inhibitors of tubulin polymerization with IC50 of respectively 3.8 and 2.4 microM compared to 2.4 microM for desoxypodophyllotoxin. A 4-methoxyphenylethyl substitution on the pyridinyl nitrogen of the benzopyridothiadiazepine was found to be essential for the antiproliferative activity. The in vitro activities of compounds 2b and 4b make benzopyridothiadiazepine dioxides a promising new class of tubulin binders which warrant further in vivo evaluation.

E7070: a novel synthetic sulfonamide targeting the cell cycle progression for the treatment of cancer

Cell cycle regulation and cell growth are interesting targets in the search for new antitumor agents as these processes are highly disturbed in malignant cells. E7070 is a novel synthetic sulfon-amide that targets the G1 phase of the cell cycle and is currently in clinical development for the treatment of solid tumors. The potential antitumor activity of the compound was discovered through optimization of the structure-activity relationships of a series of sulfonamide structures. E7070 causes a blockade in the G1/S transition through inhibition of the activation of both cyclin-dependent kinase 2 and cyclin E. Preclinical studies with E7070 showed activity in multiple tumor types, most prominently in colon and lung cancer. A phase I clinical program was conducted with E7070 evaluating different treatment regimens. Dose-limiting toxicities were hematological, including neutropenia and thrombocytopenia. Preliminary results of phase II studies demonstrated limited antitumor activity following treatment with E7070 as single agent in heavily pretreated patients with non-small cell lung and colon cancer. Studies evaluating the activity of E7070 in combination with other chemotherapeutic agents are being conducted.