Characterization of the interaction of TZT-1027, a potent antitumor agent, with tubulin

Anti-tumor and cardiotoxic effects of microtubule polymerization inhibitors: The mechanisms and management strategies

Microtubule polymerization inhibitors (MPIs) have long been used as anticancer agents because they inhibit mitosis. Microtubules are thought to play an important role in the migration of tumor cells and the formation of tumor blood vessels, and new MPIs are being developed. Many clinical trials of novel MPIs have been conducted in humans, while some clinical studies in dogs have also been reported. More attempts to apply MPIs not only in humans but also in the veterinary field are expected to be made in the future. Meanwhile, MPIs have a risk of cardiotoxicity. In this paper, we review findings on the pharmacological effects and cardiotoxicity of MPIs, as well as the mechanisms of their cardiotoxicity. Cardiotoxicity of MPIs involves not only the direct effects of MPIs on cardiomyocytes but also their effects on vascular function. For example, hypertension induced by impaired vascular function also contributes to the exacerbation of myocardial damage, and blood pressure control may be useful in reducing cardiotoxicity. By combined administration of MPIs and other anticancer agents, MPI efficacy may be enhanced, thereby potentially allowing to keep MPI dosage low. Measurement of myocardial injury markers in blood and echocardiography may be useful for monitoring cardiotoxicity. In particular, two-dimensional speckle tracking may have high sensitivity for the early detection of MPI-induced cardiac dysfunction. The exploration of the potential of new MPIs while understanding their toxicity and how to deal with them will lead to the further development of cancer chemotherapy.

Early investigational tubulin inhibitors as novel cancer therapeutics

INTRODUCTION

Microtubules represent one of the most logical and strategic molecular targets amongst the current targets for chemotherapy, alongside DNA. In the past decade, tubulin inhibitors as cancer therapeutics have been an area of focus due to the improved understanding and biological relevance of microtubules in cellular functions. Fueled by the objective of developing novel chemotherapeutics and with the aim of establishing the benefits of tubulin inhibition, several clinical trials have been conducted with others ongoing.

AREA COVERED

At present, the antitubulin development pipeline contains an armful of agents under clinical investigation. This review focuses on novel tubulin inhibitors as cancer therapeutics. The article covers the agents which have completed the phase II studies along with the agents demonstrating promising results in phase I studies.

EXPERT OPINION

Countless clinical trials evaluating the efficacy, safety and pharmacokinetics of novel tubulin inhibitors highlights the scientific efforts being paid to establish their candidature as cancer therapeutics. Colchicine binding site inhibitors as vascular disrupting agents (VDAs) and new taxanes appear to be the most likely agents for future clinical interest. Numerous agents have demonstrated clinical benefits in terms of efficacy and survival in phase I and II studies. However conclusive benefits can only be ascertained on the basis of phase III studies.

Marine-derived angiogenesis inhibitors for cancer therapy

Angiogenesis inhibitors have been successfully used for cancer therapy in the clinic. Many marine-derived natural products and their analogues have been reported to show antiangiogenic activities. Compared with the drugs in the clinic, these agents display interesting characteristics, including diverse sources, unique chemical structures, special modes of action, and distinct activity and toxicity profiles. This review will first provide an overview of the current marine-derived angiogenesis inhibitors based on their primary targets and/or mechanisms of action. Then, the marine-derived antiangiogenic protein kinase inhibitors will be focused on. And finally, the clinical trials of the marine-derived antiangiogenic agents will be discussed, with special emphasis on their application potentials, problems and possible coping strategies in their future development as anticancer drugs.

Interactions of halichondrin B and eribulin with tubulin

Compounds that modulate microtubule dynamics include highly effective anticancer drugs, leading to continuing efforts to identify new agents and improve the activity of established ones. Here, we demonstrate that [(3)H]-labeled halichondrin B (HB), a complex, sponge-derived natural product, is bound to and dissociated from tubulin rapidly at one binding site per αβ-heterodimer, with an apparent K(d) of 0.31 μM. We found no HB-induced aggregation of tubulin by high-performance liquid chromatography, even following column equilibration with HB. Binding of [(3)H]HB was competitively inhibited by a newly approved clinical agent, the truncated HB analogue eribulin (apparent K(i), 0.80 μM) and noncompetitively by dolastatin 10 and vincristine (apparent K(i)'s, 0.35 and 5.4 μM, respectively). Our earlier studies demonstrated that HB inhibits nucleotide exchange on β-tubulin, and this, together with the results presented here, indicated the HB site is located on β-tubulin. Using molecular dynamics simulations, we determined complementary conformations of HB and β-tubulin that delineated in atomic detail binding interactions of HB with only β-tubulin, with no involvement of the α-subunit in the binding interaction. Moreover, the HB model served as a template for an eribulin binding model that furthered our understanding of the properties of eribulin as a drug. Overall, these results established a mechanistic basis for the antimitotic activity of the halichondrin class of compounds.

Phase I study of TZT-1027, a novel synthetic dolastatin 10 derivative and inhibitor of tubulin polymerization, given weekly to advanced solid tumor patients for 3 weeks

TZT-1027 is a novel synthetic dolastatin 10 derivative that inhibits tubulin polymerization. A phase I study was conducted to determine the maximum tolerated dose (MTD) of TZT-1027, and to assess its pharmacokinetic profile in Japanese patients with advanced solid tumors following administration of the drug weekly for 3 weeks. Eligible patients had advanced solid tumors that failed to respond to standard therapy or for which no standard therapy was available, and met the following criteria: performance status ≤2 and acceptable organ function. The MTD was defined as the highest dose at which more than two-thirds of the patients experienced grade 4 hematological toxicity or grade 3/4 non-hematological toxicity during weekly TZT-1027 administration for 3 weeks. Forty patients were enrolled in the present study. Twelve doses between 0.3 and 2.1 mg/m2 were evaluated. Grade 4 neutropenia was the principal dose-limiting toxicity (DLT). At a dose of 2.1 mg/m2, two patients developed DLT: one patient developed grade 4 neutropenia, grade 3 myalgia, and grade 4 constipation, and the other one developed grade 4 neutropenia and grade 3 constipation. At a dose level of 1.8 mg/m2, toxicity was acceptable and no DLT was observed. The area under the curve and maximum concentration of TZT-1027 tended to increase linearly with the dose. The DLT observed were neutropenia, myalgia, and constipation, and the MTD was 2.1 mg/m2. The recommended dose for a phase II study was determined to be 1.8 mg/m2 for the drug administered weekly for 3 weeks.

Drug development from marine natural products

Drug discovery from marine natural products has enjoyed a renaissance in the past few years. Ziconotide (Prialt; Elan Pharmaceuticals), a peptide originally discovered in a tropical cone snail, was the first marine-derived compound to be approved in the United States in December 2004 for the treatment of pain. Then, in October 2007, trabectedin (Yondelis; PharmaMar) became the first marine anticancer drug to be approved in the European Union. Here, we review the history of drug discovery from marine natural products, and by describing selected examples, we examine the factors that contribute to new discoveries and the difficulties associated with translating marine-derived compounds into clinical trials. Providing an outlook into the future, we also examine the advances that may further expand the promise of drugs from the sea.

Structural insight into the inhibition of tubulin by vinca domain peptide ligands

The tubulin vinca domain is the target of widely different microtubule inhibitors that interfere with the binding of vinblastine. Although all these ligands inhibit the hydrolysis of GTP, they affect nucleotide exchange to variable extents. The structures of two vinca domain antimitotic peptides--phomopsin A and soblidotin (a dolastatin 10 analogue)--bound to tubulin in a complex with a stathmin-like domain show that their sites partly overlap with that of vinblastine and extend the definition of the vinca domain. The structural data, together with the biochemical results from the ligands we studied, highlight two main contributors in nucleotide exchange: the flexibility of the tubulin subunits' arrangement at their interfaces and the residues in the carboxy-terminal part of the beta-tubulin H6-H7 loop. The structures also highlight common features of the mechanisms by which vinca domain ligands favour curved tubulin assemblies and destabilize microtubules.

Phase I study of TZT-1027, a novel synthetic dolastatin 10 derivative, for the treatment of patients with non-small cell lung cancer

PURPOSE

The purpose of this phase I study was to evaluate the maximum-tolerated dose (MTD), dose-limiting toxicity (DLT), the recommended dose for phase II study, pharmacokinetics, and antitumor activity of TZT-1,027 (soblidotin) in patients with non-small cell lung cancer (NSCLC) when administered every 3-4 weeks.

METHODS

Eligible patients had the following characteristics: stage III/b or IV NSCLC that was refractory to conventional therapy or for which no standard therapy was available; Eastern Cooperative Oncology Group (ECOG) performance status (PS) <or=2; adequate organ function; and age >or=20 and <75 years. The patients were administered TZT-1,027 in escalating doses from 0.5 to 5.6 mg/m(2). Pharmacokinetic samples were collected during each treatment course.

RESULTS

Forty-nine patients were enrolled. Three patients had DLTs, including neutropenia, neutropenia complicated by fever, myalgia, and neuropathic pain. The common toxicities included constipation, anorexia, alopecia, nausea, leukopenia, and neutropenia. One complete response and three partial responses were observed. The pharmacokinetic parameters (AUC and C (max)) of TZT-1,027 tended to increase linearly with dose.

CONCLUSIONS

DLTs included neutropenia, neutropenia complicated by fever, myalgia, and neuropathic pain. The MTD was 4.8 mg/m(2). The recommended phase II study dose of TZT-1027 is 4.8 mg/m(2) administered every 3-4 weeks.

Comparison of the antivascular and cytotoxic activities of TZT-1027 (Soblidotin) with those of other anticancer agents

TZT-1027 (Soblidotin), a microtubule-depolymerizing agent exerts both a direct cytotoxic activity against cancer cells and an indirect antivascular activity against tumor vascular endothelial cells. We compared both activities of TZT-1027 with those of various anticancer agents having different mechanisms of action, including vinca alkaloids, a vascular targeting agent, a taxane and nonmicrotubule-binding agents. In the MTT assay, TZT-1027 most potently inhibited the growth of both murine colon C26 cancer cells and human umbilical vein endothelial cells, implying its potent antivascular activity against tumor vasculature in addition to its cytotoxic activity against cancer cells. Treatment with 0.1 microg/ml TZT-1027 significantly enhanced vascular permeability in human umbilical vein endothelial cell monolayers and a single intravenous administration of 2 mg/kg TZT-1027 significantly reduced the perfusion of Colon26 tumors implanted into mice, with efficacies superior to vinca alkaloids and comparable to a known vascular targeting agent. These results strongly suggest that TZT-1027 exerts marked antivascular activity. Next, to clarify the mechanism of the antivascular activity, we have taken a novel approach, and analyzed the relationships among human umbilical vein endothelial cells cytotoxicity, vascular permeability and tumor perfusion, on the basis of efficacies of each agent. Analyses revealed strong and significant correlations, and indicated that the vascular endothelial cell damage leads to endothelial barrier dysfunction and, thereby, tumor vascular shutdown. In summary, TZT-1027 was verified to have not only an excellent cytotoxic activity, but also an attractive antivascular activity through the induction of damage to vascular endothelial cells. We believe that these dual activities may make TZT-1027 useful for treating solid tumors.

Treatment parameters modulating regression of human melanoma xenografts by an antibody–drug conjugate (CR011-vcMMAE) targeting GPNMB

PURPOSE

To investigate the pharmacological properties of the CR011-vcMMAE fully human antibody-drug conjugate (ADC), such as dose titrations, quantitation of the time (days) to complete regression, pharmacokinetics, and schedule dependency. Our prior study characterized a fully human antibody to GPNMB covalently linked to monomethylauristatin E, CR011-vcMMAE, and further demonstrated cell surface staining of melanoma lines susceptible to the immunoconjugate's cytotoxicity (Clin Cancer Res 2005; 12(4): 1373-1382).

METHODS

The human SK-MEL-2 and SK-MEL-5 melanoma xenografts were used in athymic mice to assess anti-tumor efficacy. After s.c. implantation, tumors became established (60-100 mg), and treatment commenced by i.v. injection of the immunoconjugate or vinblastine or paclitaxel. Short-term anti-tumor effects (inhibition of tumor growth) and long-term effects (complete regression) were observed.

RESULTS

CR011-vcMMAE induced regression of established human SK-MEL-2 and SK-MEL-5 xenografts at doses from 1.25 to 80 mg/kg treatment when administered intravenously every 4 days (4 treatments); strikingly, regressions were not associated with re-growth during the observation period (200 days). The disappearance rate of implants was dose dependent (minimum time, 18.5 days). Detectable serum CR011-vcMMAE >or=1 microg/mL (approximately 0.01 microM) was observed for >30 days post-dose; CR011-vcMMAE showed an elimination half-life of 10.3 days. A low volume of distribution suggested that CR011-vcMMAE was confined to blood and interstitial fluid. CR011-vcMMAE could be delivered by either a single bolus dose or by intermittent dosing (i.e., every 1, 2, 4, 8, or 16 days) with no discernible differences in the proportion of tumor-free survivors, indicating a lack of schedule dependency. The antibody-drug conjugate produced complete regressions, but the equivalent doses of free monomethylauristatin E or unconjugated antibody did not show anti-tumor effects. In addition, decreases in plasma tumor-derived human interleukin-8 coincided with tumor nodule disappearance.

CONCLUSIONS

Short-term anti-tumor effects and long-term effects (complete regression) were observed with CR011-vcMMAE, but not with the reference agents. These results suggest that CR011-vcMMAE may provide therapeutic benefit in malignant melanoma.

The novel microtubule-interfering agent TZT-1027 enhances the anticancer effect of radiation in vitro and in vivo

TZT-1027 is a novel anticancer agent that inhibits microtubule polymerisation and manifests potent antitumour activity in preclinical models. We have examined the effect of TZT-1027 on cell cycle progression as well as the anticancer activity of this drug both in vitro and in vivo. With the use of tsFT210 cells, which express a temperature-sensitive mutant of Cdc2, we found that TZT-1027 arrests cell cycle progression in mitosis, the phase of the cell cycle most sensitive to radiation. A clonogenic assay indeed revealed that TZT-1027 increased the sensitivity of H460 cells to gamma-radiation, with a dose enhancement factor of 1.2. Furthermore, TZT-1027 increased the radiosensitivity of H460 and A549 cells in nude mice, as revealed by a marked delay in tumour growth and an enhancement factor of 3.0 and 2.2, respectively. TZT-1027 also potentiated the induction of apoptosis in H460 cells by radiation both in vitro and in vivo. Histological evaluation of H460 tumours revealed that TZT-1027 induced morphological damage to the vascular endothelium followed by extensive central tumour necrosis. Our results thus suggest that TZT-1027 enhances the antitumour effect of ionising radiation, and that this action is attributable in part to potentiation of apoptosis induction and to an antivascular effect. Combined treatment with TZT-1027 and radiation therefore warrants investigation in clinical trials as a potential anticancer strategy.

Tumor-specific antivascular effect of TZT-1027 (Soblidotin) elucidated by magnetic resonance imaging and confocal laser scanning microscopy

TZT-1027 (soblidotin), an antimicrotubule agent, has previously been evaluated in terms of its antivascular effects. In this study, Evans blue perfusion, magnetic resonance imaging (MRI), and confocal laser scanning microscopy (CLSM) were utilized to further elucidate the antivascular effect of TZT-1027 in female nude mice and rats bearing human breast tumor MX-1, as well as in female Sprague-Dawley rats that developed breast tumors induced by dimethylbenz(a)anthracene (DMBA). Therapeutic doses of TZT-1027 caused nearly complete regression of implanted MX-1 tumors in nude mice and rats as well as DMBA-induced tumors in rats. The perfusion in MX-1 tumor implanted in nude mice was drastically reduced within 30 min after TZT-1027 administration and was completely inhibited after 6 h or more, although not reduced in normal tissue of kidney. The study using MRI demonstrated that rich blood flow within tumors was remarkably reduced 1-3 h after TZT-1027 administration both in nude rats bearing MX-1 tumors and in rats with DMBA-induced tumors. Furthermore, the study with CLSM in nude mice bearing MX-1 tumors revealed a disruption of tumor microvessels at 1 h and a destruction of tumor microvessel network at 3 h after TZT-1027 administration. In contrast, these types of vascular disorders were not observed in heart and kidney. These results suggest that TZT-1027 specifically damages tumor vasculatures, leading to extensive tumor necrosis within tolerable dose range, and confirms earlier observations that TZT-1027 exerts a considerable antivascular effect in addition to an excellent cytotoxic effect.

Vascular disrupting agents

A clear definition for vascular targeting agents (VTAs) and vascular disrupting agents (VDAs) has separated the two as distinct methods of cancer treatment. VDAs differ from VTAs (antiangiogenesis drugs) in their mechanism of action. VTAs attempt to keep new blood vessels from forming and do not act on blood vessels that already feed existing tumors. In contrast, VDAs cause the vascular structure inside a solid tumor to collapse, depriving the tumor of blood and oxygen it needs to survive. Therefore, VDAs are an attractive way to approach the cancer problem by combating developed tumors. The following review discusses six small molecule VDAs, namely DMXAA, ZD6126, TZT1027, CA4P, AVE8062, and Oxi4503, their synthesis, biological mechanism of action, and current clinical status.

Antivascular effects of TZT-1027 (Soblidotin) on murine Colon26 adenocarcinoma

We investigated the ability of TZT-1027 (Soblidotin), a novel antimicrotubule agent, to induce antivascular effects, because most vascular targeting agents that selectively disrupt tumor vasculature also inhibit tubulin polymerization. Treatment with 10(-7) g/mL TZT-1027 rapidly disrupted the microtubule cytoskeleton in human umbilical vascular endothelial cells (HUVEC), and significantly enhanced vascular permeability in HUVEC monolayers. In addition, single intravenous administration of 2 mg/kg TZT-1027 to mice bearing Colon26 tumors significantly reduced tumor perfusion and caused extravascular leakage of erythrocytes 1 h after administration. Subsequently, thrombus formation with deposition of fibrin and tumor necrosis was observed 3 and 24 h after administration, respectively. These results strongly suggest that TZT-1027 possesses antivascular effects. TZT-1027 induced apoptosis not only in HUVEC but also in C26 cancer cells (cell line of Colon26 solid tumor) in vitro, suggesting it exerts direct cytotoxicity against tumor cells in addition to its antivascular effects. A single intravenous administration of 1, 2 and 4 mg/kg TZT-1027 significantly prolonged the survival of mice with advanced-stage Colon26 tumors in a dose-dependent manner. Furthermore, TZT-1027 itself less markedly enhanced the permeability of normal vessels, but was additive with vascular endothelial growth factor, indicating the possibility that TZT-1027 selectively exerts its activity on tumor vessels. In summary, these results suggest that TZT-1027 exerts both an indirect antivascular effect and a direct cytotoxic effect, resulting in strong antitumor activity against advanced-stage tumors, and that TZT-1027 may be useful clinically for treating solid tumors.

Phase I study of TZT-1027, a novel synthetic dolastatin 10 derivative and inhibitor of tubulin polymerization, which was administered to patients with advanced solid tumors on days 1 and 8 in 3-week courses

PURPOSE

To determine the maximum tolerated dose (MTD), dose-limiting toxicity (DLT), and pharmacokinetics of TZT-1027 (soblidotin), a dolastatin 10 analogue, in Japanese patients with advanced solid tumors when administered on days 1 and 8 in 3-week courses.

METHODS

Eligible patients had advanced solid tumors that failed to respond to standard therapy or for which no standard therapy was available, and also met the following criteria: prior chemotherapy < or = 2 regimens, Eastern Cooperative Oncology Group (ECOG) performance status < or = 1, and acceptable organ function. The MTD was defined as the highest dose at which no more than one of six patients experienced a DLT during course 1. Pharmacokinetic samples were collected in courses 1 and 2.

RESULTS

Eighteen patients were enrolled in the present study. Three doses (1.5, 1.65, and 1.8 mg/m(2)) were evaluated. Neutropenia was the principal DLT at doses of 1.65 and 1.8 mg/m(2). In addition, one patient also experienced grade 3 pneumonia with neutropenia, and another patient experienced grade 3 constipation, neuropathy, grade 4 neutropenia, and hyponatremia as DLTs at 1.65 mg/m(2). Phlebitis, the most frequent nonhematological toxicity, was improved by administration of additional saline after TZT-1027 administration. The MTD was 1.5 mg/m(2), at which DLT was not observed in a total of nine patients. The pharmacokinetic profile did not differ from that for the European population. One patient with metastatic esophageal cancer achieved partial response, and each of two patients with non-small cell lung cancer had a minor response.

CONCLUSIONS

When TZT-1027 was administered on days 1 and 8 in 3-week courses to Japanese patients, the MTD was 1.5 mg/m(2) and was lower than the value of 2.4 mg/m(2) in European patients. However, antitumor activity was observed at low doses. TZT-1027 was tolerated well at the MTD, without grade 3 nonhematological toxicities or neutropenia up to grade 2. TZT-1027 is a promising new tubulin polymerization inhibitor that requires further investigation in phase II studies.

A phase 2 study of TZT-1027, administered weekly to patients with advanced non-small cell lung cancer following treatment with platinum-based chemotherapy

INTRODUCTION

: TZT-1027, a derivative of dolastatin-10, has a wide spectrum of in vitro activity against cancer cell lines. We conducted a phase 2 trial of TZT-1027 in patients with previously treated non-small cell lung cancer (NSCLC).

PATIENTS AND METHODS

Patients with stage IV or recurrent NSCLC who had received one prior platinum-based chemotherapy regimen were eligible. Patients received 2.4mg/m(2) of TZT-1027 on days 1 and 8 of a 21-day cycle. The primary endpoint was response rate as measured by RECIST.

RESULTS

Thirty-two patients were enrolled (16 women, 16 men). The most common grade 3/4 adverse effects were leukopenia and neutropenia. Four patients died within 30 days of receiving TZT-1027, three from progressive disease and one with pneumonia and neutropenia. No objective response was observed (0% observed rate, 95% confidence interval 0-11%). The median time to progression was 1.5 months. The median overall survival was 8.5 months.

CONCLUSIONS

This phase 2 trial showed that TZT-1027 administered on days 1 and 8 of a 21-day cycle had no anticancer activity. Further development of TZT-1027 in patients with previously treated NSCLC is not warranted.

A phase I study of intravenous TZT-1027 administered on day 1 and day 8 of a three-weekly cycle in combination with carboplatin given on day 1 alone in patients with advanced solid tumours

BACKGROUND

TZT-1027 is a tubulin-binding drug and synthetic derivative of dolastatin-10 with cytotoxic and antivascular activity in vitro and in vivo. Studies have demonstrated anti-tumour activity in several tumour types.

METHODS

Patients were treated with escalating doses of TZT-1027 and carboplatin at doses from 1.6 to 2.0 mg/m2 and AUC 4 and 5 respectively. For pharmacokinetic analysis, plasma sampling was done during the first course using a high-performance liquid chromatographic assay.

RESULTS

14 patients received a total of 55 cycles at three dose levels. Dose limiting toxicities (DLTs) were first observed with 1.6 mg/m2 TZT-1027 and carboplatin AUC 5; 1 patient had grade 4 neutropenia and a delay in day 8 treatment occurred in two patients (gr 2 fatigue, gr 3 diarrhoea). At TZT-1027 2 mg/m2 and carboplatin AUC 5, one patient experienced grade 3 paralytic ileus. The most frequent toxicities were neutropenia, anaemia, fatigue, constipation, infection and vomiting. Peripheral neuropathy was reported in 36% of patients. One patient (pancreatic adenocarcinoma) achieved a partial response lasting 181 days. Pharmacokinetic analysis did not demonstrate any interaction between TZT-1027 and carboplatin.

CONCLUSIONS

The recommended phase II dose is TZT-1027 1.6 mg/m2 and carboplatin AUC 5. No evidence of a PK interaction between these agents was observed.

Reference profiling of the genomic response induced by an antimicrotubule agent, TZT-1027 (Soblidotin), in vitro

TZT-1027 is an antimicrotubule agent targeting beta-tubulin that is undergoing clinical development. The genomic response of cancer cells to TZT-1027 was profiled to evaluate its biochemical activity. A lung cancer cell line, PC-14, was exposed to antimicrotubule agents including dolastatins, Vinca alkaloids and taxanes at an equivalent toxicity level. Alterations in the TZT-1027-induced gene expression of approximately 600 genes were then examined using microarray technology and the resulting gene profiles were compared with those for cells exposed to the other antimicrotubule agents. A principle component analysis using the whole gene set demonstrated that TZT-1027 produced similar gene profiles to those produced by dolastatin 10, but that these gene profiles differed from those produced by other agents. The agents were classified according to their induced genomic response in a molecular structure-dependent manner. Genes whose expression profiles differed according to drug class included intermediate filaments, extracellular matrix protein and Rho regulatory genes that may be involved in cytoskeletal and angiogenesis processes that are regulated by microtubule dynamics. TZT-1027 produces a unique genomic response profile distinct from that of Vinca alkaloids and taxanes, suggesting that this agent has a different mechanism of action. The selected genes may act as pharmacodynamic biomarkers allowing the unique mode of action of TZT-1027 to be discriminated from those of other antimicrotubule agents.

Phase II study of intravenous TZT-1027 in patients with advanced or metastatic soft-tissue sarcomas with prior exposure to anthracycline-based chemotherapy

BACKGROUND

TZT-1027, a novel chemotherapeutic agent, is derived from dolastatin 10, and blocks cells during G2/M-phase by interfering with microtubule assembly and stability. TZT-1027 has exhibited potential cytotoxic activity in several human cancer cell lines (in vitro) and also demonstrated antitumor activity in human xenografts (in vivo). In addition, Phase I clinical investigations suggested activity in STS (soft-tissue sarcoma).

METHODS

Eligible patients were those who had histologic evidence of locally advanced or metastatic STS and who had received 1 prior treatment regimen with an anthracycline-based chemotherapy for metastatic disease. Subjects received intravenous infusions of TZT-1027 over 1 hour on Day 1 and Day 8 of each 21-day treatment course. Efficacy was evaluated per Response Evaluation Criteria in Solid Tumors (RECIST) criteria.

RESULTS

Twenty-nine patients were enrolled and 28 patients received at least 1 course of study drug and were eligible for efficacy and safety evaluation. The median age of the patients was 48 years (range, 23-73 years) and the median baseline Eastern Cooperative Oncology Group (ECOG) performance status was 1 (range, 0-2). A total of 67 courses (range, 1-9 courses; median, 2 courses) of TZT-1027 were administered. No patient in the study demonstrated an objective response to treatment. Of 6 patients (21.4%) who experienced disease stabilization, 1 continued to have stable disease for 9.3 months. The median time to tumor progression was 44 days (95% confidence interval [95% CI], 43.0-54.0) and the median survival was 178 days (95% CI, 134.0-317.0). The most commonly reported toxicities were neutropenia, fatigue, and constipation.

CONCLUSIONS

TZT-1027 was found to be safe and well tolerated, and the hematologic toxicities observed were consistent with preclinical toxicology and Phase I study findings. No confirmed responses were seen in the current study.

Phase I and Pharmacokinetic Study of the Dolastatin 10 Analogue TZT-1027, Given on Days 1 and 8 of a 3-Week Cycle in Patients with Advanced Solid Tumors

PURPOSE

TZT-1027 [N(2)-(N,N-dimethyl-l-valyl)-N-[(1S,2R)-2-methoxy-4-[(2S)-2-[(1R,2R)-1-methoxy-2-methyl-3-oxo-3-[(2-phenylethyl)]amino]propyl]-1-pyrrolidinyl]-1-[(S)-1-methylpropyl]-4-oxobutyl]-N-methyl-l-valinamide] is a cytotoxic dolastatin 10 derivative inhibiting microtubule assembly through the binding to tubulins. The objectives of this phase I study was to assess the dose-limiting toxicities (DLT), to determine the maximum tolerated dose, and to study the pharmacokinetics of TZT-1027 when given i.v. over 60 minutes on days 1 and 8 every 3 weeks to patients with advanced solid tumors.

EXPERIMENTAL DESIGN

Patients were treated with escalating doses of TZT-1027 at doses ranging from 1.35 to 2.7 mg/m(2). For pharmacokinetic analysis, plasma sampling was done during the first and second course and assayed using a validated high-performance liquid chromatographic assay with mass spectrometric detection.

RESULTS

Seventeen patients received a total of >70 courses. The stopping dose was reached at 2.7 mg/m(2), with neutropenia and infusion arm pain as DLT. Neutropenia was not complicated by fever. Over all dose levels, eight patients experienced pain in the infusion arm 1 to 2 days after administration of the drug, which seemed ameliorated by adding additional flushing after drug administration. Other side effects included nausea, vomiting, diarrhea, and fatigue. One partial response lasting >54 weeks was observed in an extensively pretreated patient with metastatic liposarcoma. The pharmacokinetics of TZT-1027 suggested linearity over the dose ranges. No correlation between body surface area and absolute CL of TZT-1027 was established, vindicating that a flat dosing regimen might be used in the future. A correlation was observed between the percentage decrease in neutrophil count and the AUC of TZT-1027.

CONCLUSIONS

In this study, the DLT of TZT-1027 was neutropenia and infusion arm pain. The recommended dose for phase II studies of TZT-1027 is 2.4 mg/m(2) given i.v. over 60 minutes, on days 1 and 8 every 21 days. Phase II studies have recently started.

Natural products to drugs: natural product derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or in registration (current 31 December 2004) have been reviewed. Natural product derived drugs launched in the United States of America, Europe and Japan since 1998 and new natural product templates discovered since 1990 are discussed.

Total Assignment of the 1H- and 13C-NMR Spectra for TZT-1027 and Related Compounds

The total assignment of the (1)H- and (13)C-NMR spectra for TZT-1027 was carried out using various NMR methods (1D, 2D NMR). It was found that TZT-1027 exists in two different conformations resulting from the cis-trans isomerization of the amide bond at N-11 and C-12 in DMSO-d(6). The (1)H- and (13)C-NMR spectra of compound 1 and 2 comprised of the partial structure of TZT-1027 were also assigned to be TZT-1027. These assignments showed that compound 1 is in good agreement with TZT-1027 with regard to formation of the conformers.

Direct photoaffinity labeling by dolastatin 10 of the amino-terminal peptide of beta-tubulin containing cysteine 12

Tubulin with bound [5-3H]dolastatin 10 was exposed to ultraviolet light, and 8-10% of the bound drug cross-linked to the protein, most of it specifically. The primary cross-link was to the peptide spanning amino acid residues 2-31 of beta-tubulin, but the specific amino acid could not be identified. Indirect studies indicated that cross-link formation occurred between cysteine 12 and the thiazole moiety of dolastatin 10. An equipotent analog of dolastatin 10, lacking the thiazole ring, did not form an ultraviolet light-induced cross-link to beta-tubulin. Preillumination of tubulin with ultraviolet light, known to induce cross-link formation between cysteine 12 and exchangeable site nucleotide, inhibited the binding of [5-3H]dolastatin 10 and cross-link formation more potently than it inhibited the binding of colchicine or vinblastine to tubulin. Conversely, binding of dolastatin 10 to tubulin inhibited formation of the cross-link between cysteine 12 and the exchangeable site nucleotide. Dithiothreitol inhibited formation of the beta-tubulin/dolastatin 10 cross-link but not the beta-tubulin/exchangeable site nucleotide cross-link. Modeling studies revealed a highly favored binding site for dolastatin 10 at the + end of beta-tubulin in proximity to the exchangeable site GDP. Computational docking of an energy-minimized dolastatin 10 conformation at this site placed the thiazole ring of dolastatin 10 8-9 A from the sulfur atom of cysteine 12. Dolastatin 15 and cryptophycin 1 could also be docked into positions that overlapped more extensively with the docked dolastatin 10 than with each other. This result was consistent with the observed binding properties of these peptides.

Phase I and pharmacokinetic study of TZT-1027, a novel synthetic dolastatin 10 derivative, administered as a 1-hour intravenous infusion every 3 weeks in patients with advanced refractory cancer

BACKGROUND

TZT-1027 is a synthetic dolastatin 10 analog with antineoplastic properties in various cell lines and tumor xenografts. The purpose of this phase I study was to evaluate the safety and toxicity, maximum tolerated dose, pharmacokinetics and pharmacodynamics, clinical and metabolic antitumor activity of TZT-1027 when given as a 1-h intravenous infusion every 3 weeks in patients with refractory solid tumors.

PATIENTS AND METHODS

Patients had a histologically verified refractory tumor with measurable disease, were > or = 18 years old, had an Eastern Cooperative Oncology Group performance status <2 and adequate bone marrow, liver, renal and cardiac function. Dose-limiting toxicity was defined as platelets <25 x 10(9)/l, neutrophils <0.5 x 10(9)/l for >5 days, febrile neutropenia > or = 38.5 degrees C with grade 4 (National Cancer Institute-common toxicity criteria) neutropenia, or grade 3/4 non-hematological toxicity excluding nausea and vomiting. The last dose was the dose where > or = 2 out of six patients experienced dose-limiting toxicity in cycle one. The maximum tolerated dose was one dose level below with less than two of six patients with dose-limiting events.

RESULTS

Twenty-one non-selected, fully evaluable patients were enrolled. The majority were male (19) and the median age was 55 years (range 39-67). Dose levels of TZT-1027 ranged from 1.35 to 3.0 mg/m(2). The median number of cycles was two (range 1-4). Dose-limiting toxicities were observed in three patients at the 3.0 mg/m(2) dose level, including neutropenia, fatigue and a short lasting, reversible peripheral neurotoxic syndrome. The most common toxicities per patient were fatigue, anorexia, alopecia, nausea, constipation, leukopenia and neutropenia. Based on RECIST criteria, the best response was stable disease in seven patients. The pharmacokinetic evaluation revealed a T(1/2) of approximately 7 h and linear kinetics.

CONCLUSIONS

The recommended dose of TZT-1027 for the 3-weekly administration is 2.7 mg/m(2). Neutropenia, fatigue and a reversible peripheral neurotoxic syndrome are dose-limiting with this schedule. TZT-1027 may be associated with neurological side-effects in patients previously exposed to neurotoxic compounds such as oxaliplatin.

Antitumor activity of TZT-1027 (Soblidotin) against vascular endothelial growth factor-secreting human lung cancer in vivo

TZT-1027 (Soblidotin), an antimicrotubule agent, has been demonstrated to show potent antitumor effects, though the relationships among antitumor effect, cytotoxicity and anti-vascular effect of TZT-1027 have not been studied. We established in vivo human lung vascular-rich tumor models using a vascular endothelial growth factor-secreting tumor (SBC-3/VEGF). SBC-3/VEGF tumors exhibited a high degree of angiogenesis in comparison with the mock transfectant (SBC-3/Neo) tumors in a dorsal skinfold chamber model and grew much faster and larger than SBC-3/Neo tumors in the tumor growth study. The antitumor activity of antimicrotubule agents, including TZT-1027, was evaluated in both early- and advanced-stage SBC-3/Neo and SBC-3/VEGF tumor models to elucidate the relationship between the antitumor activity and anti-vascular effect of these agents. TZT-1027 exhibited potent antitumor activity against both early- and advanced-stage SBC-3/Neo and SBC-3/VEGF tumors, whereas combretastatin A4 phosphate did not. Vincristine and docetaxel exhibited potent antitumor activity against early-stage SBC-3/Neo and SBC-3/VEGF tumors, and advanced-stage SBC-3/Neo tumors, but did not exhibit activity against advanced-stage SBC-3/VEGF tumors. The difference in antitumor activity between these agents could be ascribed to differences in direct cytotoxicity and anti-vascular effect. Furthermore, a prominent accumulation of erythrocytes in the tumor vasculature, followed by leakage and scattering of these erythrocytes from the tumor vasculature, was observed after TZT-1027 administration to mice bearing advanced-stage SBC-3/VEGF tumors. These findings strongly suggest that TZT-1027 has a potent anti-vascular effect, in addition to direct cytotoxicity.

Dolastatin 15 binds in the vinca domain of tubulin as demonstrated by Hummel-Dreyer chromatography

The antimitotic depsipeptide dolastatin 15 was radiolabeled with tritium in its amino-terminal dolavaline residue. Dolastatin 15, although potently cytotoxic, is a relatively weak inhibitor of tubulin assembly and does not inhibit the binding of any other ligand to tubulin. The only methodology found to demonstrate an interaction between the depsipeptide and tubulin was Hummel-Dreyer equilibrium chromatography on Sephadex G-50 superfine. The average apparent Kd value obtained in these studies was about 30 microM, with no difference observed when column size or tubulin concentration was varied. This relatively high dissociation constant is consistent with the apparent weak interaction of dolastatin 15 with tubulin demonstrated indirectly in the assembly assay. We attempted to gain insight into the binding site for dolastatin 15 on tubulin by studying inhibitory effects of other drugs when the gel filtration column was equilibrated with both [3H]dolastatin 15 and a second, nonradiolabeled drug. No inhibition was detected with either the colchicine site agent combretastatin A-4 or with an analog of the antimitotic marine peptide diazonamide A (both the analog and diazonamide A are potent inhibitors of tubulin assembly). Weak inhibition was observed with cemadotin, a structural analog of dolastatin 15, and with the depsipeptide cryptophycin 1. Moderate inhibition occurred with vinblastine and vincristine, and strong inhibition with maytansine, halichondrin B, and the peptides dolastatin 10 and phomopsin A. These observations suggest that the binding site(s) for peptide and depsipeptide antimitotic drugs may consist of a series of overlapping domains rather than a well-defined locus on the surface of beta-tubulin.

Diazonamide A and a synthetic structural analog: disruptive effects on mitosis and cellular microtubules and analysis of their interactions with tubulin

The marine ascidian Diazona angulata was the source organism for the complex cytotoxic peptide diazonamide A. The molecular structure of this peptide was recently revised after synthesis of a biologically active analog of diazonamide A in which a single nitrogen atom was replaced by an oxygen atom. Diazonamide A causes cells to arrest in mitosis, and, after exposure to the drug, treated cells lose both interphase and spindle microtubules. Both diazonamide A and the oxygen analog are potent inhibitors of microtubule assembly, equivalent in activity to dolastatin 10 and therefore far more potent than dolastatin 15. This inhibition of microtubule assembly is accompanied by potent inhibition of tubulin-dependent GTP hydrolysis, also comparable with the effects observed with dolastatin 10. However, the remaining biochemical properties of diazonamide A and its analog differ markedly from those of dolastatin 10 and closely resemble the properties of dolastatin 15. Neither diazonamide A nor the analog inhibited the binding of [3H]vinblastine, [3H]dolastatin 10, or [8-14C]GTP to tubulin. Nor were they able to stabilize the colchicine binding activity of tubulin. These observations indicate either that diazonamide A and the analog have a unique binding site on tubulin differing from the vinca alkaloid and dolastatin 10 binding sites, or that diazonamide A and the analog bind weakly to unpolymerized tubulin but strongly to microtubule ends. If the latter is correct, diazonamide A and its oxygen analog should have uniquely potent inhibitory effects on the dynamic properties of microtubules.

The molecular pharmacology of symplostatin 1: a new antimitotic dolastatin 10 analog

Symplostatin 1, an analog of dolastatin 10, was recently isolated from cyanobacteria of the genus Symploca. Symplostatin 1 is a potent inhibitor of cell proliferation with IC(50) values in the low nanomolar range and it exhibits efficacy against a variety of cancer cell types. Symplostatin 1 caused the formation of abnormal mitotic spindles and accumulation of cells in metaphase at concentrations that had only minor effects on interphase microtubules. At higher concentrations, symplostatin 1 caused the loss of interphase microtubules. Cell cycle analysis revealed that symplostatin 1 caused G(2)/M arrest, consistent with its effects on mitotic spindles. Symplostatin 1 initiated the phosphorylation of Bcl-2, formation of micronuclei and activation of caspase 3, indicating induction of apoptosis. The cellular effects of symplostatin 1 are consistent with other antimitotic tubulin-targeting drugs. Tubulin polymerization experiments indicated that symplostatin 1 potently inhibits the assembly of purified tubulin, suggesting that tubulin may be its intracellular target. Some microtubule-targeting agents are reported to have antiangiogenic activity and therefore the effects of symplostatin 1 on endothelial cell proliferation and invasion were evaluated. Symplostatin 1 was found to be a potent inhibitor of both endothelial cell proliferation and invasion. Because of its potent and broad activity in vitro, symplostatin 1 was evaluated in vivo. Symplostatin 1 was active against murine colon 38 and murine mammary 16/C; however, it was poorly tolerated and the mice were slow to recover from the toxicity. The data indicate that symplostatin 1 has a mechanism of action similar to dolastatin 10.

Interactions of antimitotic peptides and depsipeptides with tubulin

Tubulin is the target for an ever increasing number of structurally unusual peptides and depsipeptides isolated from a wide range of organisms. Since tubulin is the subunit protein of microtubules, the compounds are usually potently toxic to mammalian cells. Without exception, these (depsi)peptides disrupt cellular microtubules and prevent spindle formation. This causes cells to accumulate at the G2/M phase of the cell cycle through inhibition of mitosis. In biochemical assays, the compounds inhibit microtubule assembly from tubulin and suppress microtubule dynamics at low concentrations. Most of the (depsi)peptides inhibit the binding of Catharanthus alkaloids to tubulin in a noncompetitive manner, GTP hydrolysis by tubulin, and nucleotide turnover at the exchangeable GTP site on beta-tubulin. In general, the (depsi)peptides induce the formation of tubulin oligomers of aberrant morphology. In all cases tubulin rings appear to be formed, but these rings differ in diameter, depending on the (depsi)peptide present during their formation.

Gene expression profiling of exposure to TZT-1027, a novel microtubule-interfering agent, in non-small cell lung cancer PC-14 cells and astrocytes

Clinical use of TZT-1027, a microtubule-interfering agent that inhibits the polymerization of tubulin, is expected because of its potent effects on solid tumors. TZT-1027 is thought to act directly on cellular microtubules, and arrest cell mitosis, however, the molecular mechanisms of the microtubule damage by TZT-1027 have not been fully identified. To investigate the possible novel mechanisms of action of TZT-1027, we used the cDNA macroarray technique to examine its effect on the expression of hundreds of tightly transcriptionally controlled genes. We used two cell lines, one was human non-small cell lung carcinoma PC-14 cells as a model for cancer cells, and the other was human astrocytes as a model for normal neuronal cells, because the dose-limiting-factor of microtubule-interfering agents is mainly peripheral neurotoxicity. mRNAs prepared from the PC-14 and astrocyte cell lines treated with TZT-1027 were compared with 588 genes spotted onto the filter, and which gene groups TZT-1027 modulated between the two cell lines was investigated. TZT-1027 exposure modulated expression of a variety of genes including the genes encoding cell-cycle and growth regulators, receptors, angiogenesis and invasion regulators, rho family small GTPases and their regulators and growth factors and cytokines. However, the way of gene regulation by TZT-1027 exposure was different between PC-14 cells and astrocytes. Genes up-regulated in both PC-14 cells and astrocytes were those for RAR-epsilon, TNFR 1 and 2 and so on. Specifically altered genes in PC-14 cells, such as the genes coding for cytokeratin 8, XPG, fau and the genes regulated only in PC-14 cells may be involved in the antitumor activity of TZT-1027. On the other hand, growth factor receptor precursors was upregulated specifically in astrocytes by TZT-1027 and this gene regulation only in astrocytes may be candidates related with neurotoxicity.

Anticancer therapy with novel tubulin-interacting drugs

Antimitotic agents that target tubulin, including the taxanes and vinca alkaloids, are important components of current anticancer therapy. Whilst these antimitotic drugs are highly effective in the treatment of a number of cancers, both acquired and intrinsic resistance to these agents is a major clinical problem. Furthermore, the systemic toxicity, and in some cases lack of oral availability, make these agents less than ideal. Recently much effort has been directed on the isolation and synthesis of new antimitotic drugs that target the tubulin/microtubule system and display efficacy against drug-refractory carcinomas. Newly described compounds include structurally diverse natural products, such as dolastatin, epothilones and discodermolide, derivatives and structural analogues of traditional antimitotics, and novel synthetic molecules. Additionally, new developments in drug targeting are improving efficacy and therapeutic indices of traditional agents. A number of promising 'new generation' antimitotics are now undergoing clinical testing. These new agents are reviewed here in terms of their mechanism(s) of action on microtubules, effectiveness against drug-resistant tumour cells and clinical potential.

Association of p53 gene mutations with sensitivity to TZT-1027 in patients with clinical lung and renal carcinoma

BACKGROUND

It has been revealed that chemotherapy using DNA-damaging agents and radiotherapy were influenced by the p53 status of tumors; however, p53 status did not influence chemotherapy using antimicrotubule agents. To elucidate whether a novel antimicrotubule agent, TZT-1027, is influenced by the p53 status of tumors, the authors investigated the sensitivities of specimens obtained from patients with nonsmall cell lung carcinoma (NSCLC) and renal cell carcinoma (RCC) to various anticancer agents, including TZT-1027, and the status of the p53 gene in those specimens.

METHODS

Twenty-nine NSCLC specimens and 22 RCC specimens were analyzed for their sensitivity to various anticancer agents and their p53 status. Sensitivities of the specimens to nine anticancer agents were determined by flow cytometric analysis. To determine p53 status, polymerase chain reaction amplification with primers for exons 5--9 was conducted, and the products were subjected to single-strand conformation polymorphism analysis.

RESULTS

In the NSCLC specimens, anticancer agents, including TZT-1027, showed strong antitumor activity against 50--75% of specimens with the wild type p53 gene. TZT-1027 showed strong antitumor activity against 40% of specimens with the mutant type p53 gene, whereas DNA-damaging agents showed such activity only in 16--28% of specimens. In RCC specimens, TZT-1027 showed potent antitumor activity in 29% of specimens with the wild type gene, and DNA-damaging agents showed such activity in 6--18% of specimens. TZT-1027 showed strong antitumor activity in 40% of specimens with the mutant type p53 gene, whereas DNA-damaging agents showed such activity only in 0--20% of specimens.

CONCLUSIONS

We found evidence to suggest that TZT-1027 was influenced less by the p53 status of specimens than DNA-damaging agents. Therefore, TZT-1027 is expected to show similar antitumor activity against tumors with a loss of p53 function as well as those with normal function of p53 in clinical fields.

An antimicrotubule agent, TZT-1027, does not induce neuropathologic alterations which are detected after administration of vincristine or paclitaxel in animal models

One of the major dose-limiting toxicities induced by antimicrotubule antitumor agents such as vinca alkaloids and taxanes is peripheral neuropathy. The neurotoxicity of TZT-1027 (a dolastatin 10 derivative antimicrotubule agent) was thus assessed using the animal models for antimicrotubule agent-induced neurotoxicity. Rabbits were intravenously given TZT-1027 or vincristine weekly for 5 weeks. In the mouse study, TZT-1027, vincristine or paclitaxel was intravenously given every 2 days and/or weekly. Despite the neuropathologic evidence such as myelinated axonal and fiber degeneration in the peripheral nerves and in the sensory tracts of the spinal cord following the treatment with vincristine or paclitaxel, no drug-induced alteration was observed in the TZT-1027 groups. Although there are reports that some other dolastatin derivatives with antimicrotubule activity showed no neurotoxic potential in humans, the present study represents the first demonstration in experimental animals that a dolastatin derivative has no, or at least a lower, neurotoxic potential compared to other antimicrotubule agents.

TZT-1027, an antimicrotubule agent, attacks tumor vasculature and induces tumor cell death

TZT-1027, a dolastatin 10 derivative, is an antimicrotubule agent with potent antitumor activity both in vitro and in vivo. In this study, we performed biochemical and histopathological examinations, and evaluated TZT-1027-induced tumoral vascular collapse and tumor cell death in an advanced tumor model, murine colon 26 adenocarcinoma. In addition, we studied the effects of TZT-1027 on cultured human umbilical vein endothelial cells (HUVEC). Tolerable doses of TZT-1027 induced tumor-selective hemorrhage within 1 h. This hemorrhage occurred mainly in the peripheral area of the tumor mass. Measurements of tumoral hemoglobin content and dye permeation revealed that the hemorrhage occurred firstly and tumor blood flow stopped secondarily. The vascular damage was followed by continuous induction of apoptosis of the tumor cells, tumor tissue necrosis, and tumor regression. In cultured HUVEC, TZT-1027 induced marked cell contraction with membrane blebbing in 30 min. These cell changes were completely inhibited by K252a, a broad-spectrum inhibitor of protein kinases. These effects of TZT-1027 on both tumor vasculature and HUVEC were greater than those of vincristine. In conclusion, TZT-1027 quickly attacked the well-developed vascular system of advanced tumors by a putative protein kinase-dependent mechanism, and then blocked tumor blood flow. Therefore, TZT-1027 has both a conventional antitumor activity and a unique anti-tumoral vascular activity, making it a potentially powerful tool for clinical cancer therapy.