An update on the developing mitotic inhibitors for the treatment of non-small cell carcinoma.

INTRODUCTION: Mitosis is necessary to sustain life and is followed immediately by cell division into two daughter cells. Microtubules play a key role in the formation of the mitotic spindle apparatus and cytokinesis at the end of mitosis. Various anti-microtubule agents such as taxanes and vinca alkaloids are widely used in the treatment of advanced non-small cell lung cancer (NSCLC) but their use is associated with hematologic toxicity profile, acquired resistance and hypersensitivity reactions. Areas covered: The Nab-paclitaxels are the more recent antimitotic agents approved in NSCLC showing a better tolerability and activity when compared to previous ones. Despite this, the outcome of patients with advanced non-small cell lung cancer is poor. Due to the key role of mitosis, research is focused on the identification of new mitotic drug targets other than microtubule inhibitors, such as cell cycle targets, aurora kinases and Polo-like kinases. Expert opinion: Despite improvements in chemotherapeutic choices and supportive care, the majority of patients experience a deteriorating quality of life and significant toxicities associated to a poor outcome. Thus, the therapeutic management of patients with advanced NSCLC represents an ongoing challenge and novel agents targeting mitosis are under investigation.

Microtubule destabilising agents: far more than just antimitotic anticancer drugs.

Vinca alkaloids have been approved as anticancer drugs for more than 50 years. They have been classified as cytotoxic chemotherapy drugs that act during cellular mitosis, enabling them to target fast growing cancer cells. With the evolution of cancer drug development there has been a shift towards new "targeted" therapies to avoid the side effects and general toxicities of "cytotoxic chemotherapies" such as the vinca alkaloids. Due to their original classification, many have overlooked the fact that vinca alkaloids, taxanes and related drugs do have a specific molecular target: tubulin. They continue to be some of the most effective anticancer drugs, perhaps because their actions upon the microtubule network extend far beyond the ability to halt cells in mitosis, and include the induction of apoptosis at all phases of the cell cycle. In this review, we highlight the numerous cellular consequences of disrupting microtubule dynamics, expanding the textbook knowledge of microtubule destabilising agents and providing novel opportunities for their use in cancer therapy.

Clinical Development of Anti-mitotic Drugs in Cancer.

Mitosis is one of the most fundamental processes of life by which a mammalian cell divides into two daughter cells. Mitosis has been an attractive target for anticancer therapies since fast proliferation was identified as one of the hallmarks of cancer cells. Despite efforts into developing specific inhibitors for mitotic kinases and kinesins, very few drugs have shown the efficiency of microtubule targeting-agents in cancer cells with paclitaxel being the most successful. A deeper translational research accompanying clinical trials of anti-mitotic drugs will help in identifying potent biomarkers predictive for response. Here, we review the current knowledge of mitosis targeting agents that have been tested so far in the clinics.

Syringic acid from Tamarix aucheriana possesses antimitogenic and chemo-sensitizing activities in human colorectal cancer cells.

CONTEXT: For its variety of biological activities, Tamarix aucheriana (Decne.) Baum. (Tamaricaceae) has an extensive history as a traditional Arab medicine. OBJECTIVES: Antimitogenic and chemo-sensitizing activities of syringic acid (SA) were studied against human colorectal cancer. MATERIALS AND METHODS: Chromatographic and spectral data were used for the isolation and identification of SA. MTT, flow cytometry, in vitro invasion and angiogenesis assays, fluoremetry, ELISA and Real Time qPCR were used to test antimitogenic and chemo-sensitizing activities of SA, cell cycle, apoptosis, proteasome and NFκB-DNA-binding activities, cancer cell invasion and angiogenesis, and expression of cell cycle/apoptosis-related genes. RESULTS: SA showed a time- and dose-dependent (IC50 = 0.95-1.2 mg mL⁻¹) antimitogenic effect against cancer cells with little cytotoxicity on normal fibroblasts (≤20%). SA-altered cell cycle (S/G2-M or G1/G2-M phases) in a time-dependent manner, induced apoptosis, inhibited DNA-binding activity of NFκB (p ≤ 0.0001), chymotrypsin-like/PGPH (peptidyl-glutamyl peptide-hydrolyzing) (p ≤ 0.0001) and the trypsin-like (p ≤ 0.002) activities of 26S proteasome and angiogenesis. SA also differentially sensitized cancer cells to standard chemotherapies with a marked increase in their sensitivity to camptothecin (500-fold), 5FU (20,000-fold), doxorubicin (210-fold), taxol (3134-fold), vinblastine (1000-fold), vincristine (130-fold) and amsacrine (107-fold) compared to standard drugs alone. DISCUSSION: SA exerted its chemotherapeutic and chemo-sensitizing effects through an array of mechanisms including cell-cycle arrest, apoptosis induction, inhibition of cell proliferation, cell migration, angiogenesis, NFκB DNA-binding and proteasome activities. CONCLUSION: These results demonstrate the potential of SA as an antimitogenic and chemo-sensitizing agent for human colorectal cancer.

A phase 1 trial of E7974 administered on day 1 of a 21-day cycle in patients with advanced solid tumors.

BACKGROUND: E7974, a synthetic analog of hemiasterlin, interacts with the tubulin molecule and overcomes resistance to other antitubulin drugs (taxanes and vinca alkaloids). METHODS: In a phase 1 study, E7974 was given intravenously over a 2- to 5-minute infusion on day 1 of every 21-day cycle. Adult patients with advanced refractory solid tumors who had adequate organ function and Eastern Cooperative Oncology Group performance status 0 to 2 were eligible for this study. A modified Fibonacci schema was used. The maximal tolerated dose (MTD) was the dose where <2 of 6 patients developed a dose-limiting toxicity (DLT). RESULTS: Twenty-eight patients (19 men and 9 women; median age, 64 years) treated at different cohort dose levels (0.18 mg/m(2) , 0.27 mg/m(2) , 0.36 mg/m(2) , 0.45 mg/m(2) , and 0.56 mg/m(2) ) received a total of 66 courses of E7974. The MTD was established at 0.45 mg/m(2) , where 1 of 6 patients experienced DLT (grade 4 febrile neutropenia). Of the 17 refractory colon cancer patients with a median of 3 prior treatments, stable disease was seen in 7 patients (41%). There were no tumor responses. Median progression-free survival was 1.2 months, and median overall survival was 6.7 months. In pharmacokinetic analysis, E7974 was characterized by a fast and moderately large distribution (37.95-147.93 L), slow clearance (2.23-7.15 L/h), and moderate to slow elimination (time to half-life, 10.4-30.5 hours). CONCLUSIONS: This study shows that E7974 once every 21-day cycle shows antitumor activity in patients with refractory solid tumors. The recommended phase 2 dose is 0.45 mg/m(2).

Phase I/II multicenter study to assess the safety, tolerability, pharmacokinetics and pharmacodynamics of AZD4877 in patients with refractory acute myeloid leukemia.

Eg5 (kinesin spindle protein) is a microtubule motor protein, essential for centrosome separation during mitosis. This Phase I/II, open-label, multicenter, two-part study investigated AZD4877, a potent Eg5 inhibitor, in patients with acute myeloid leukemia. Primary objectives were to determine the maximum tolerated dose (MTD) (part A), assess efficacy (part B) and determine the pharmacokinetic profile (parts A and B). Secondary objectives included assessment of safety and tolerability. AZD4877 was administered at a range of doses (2, 4, 7, 10, 13, 16 and 18 mg/day) as a 1-hour intravenous infusion on three consecutive days of a continuous 2-week schedule. The MTD in part A was defined as 16 mg/day based on dose-limiting stomatitis at 16 and 18 mg/day, hyperbilirubinemia at 16 mg/day and palmar-plantar erythrodysesthesia syndrome at 18 mg/day. Systemic exposure to AZD4877 generally increased with increasing dose whereas half-life was not dose dependent. No evaluable patients experienced a complete remission (CR) or CR with incomplete blood count recovery (CRi), demonstrating no evidence of AZD4877 efficacy in this population. Evidence of monoasters in all but the 4 mg/day dose group provided proof of mechanism for AZD4877. This study was terminated due to lack of efficacy. (ClinicalTrials.gov identifier NCT00486265).

Antimitotic chemotherapeutics promote adhesive responses in detached and circulating tumor cells.

In the clinical treatment of breast cancer, antimitotic cytotoxic agents are one of the most commonly employed chemotherapies, owing largely to their antiproliferative effects on the growth and survival of adherent cells in studies that model primary tumor growth. Importantly, the manner in which these chemotherapeutics impact the metastatic process remains unclear. Furthermore, since dissemination of tumor cells through the systemic circulation and lymphatics necessitates periods of detached survival, it is equally important to consider how circulating tumor cells respond to such compounds. To address this question, we exposed both nontumorigenic and tumor-derived epithelial cell lines to two antitumor compounds, jasplakinolide and paclitaxel (Taxol), in a series of attached and detached states. We report here that jasplakinolide promoted the extension of microtubule-based projections and microtentacle protrusions in adherent and suspended cells, respectively. These protrusions were specifically enriched by upregulation of a stable post-translationally modified form of alpha-tubulin, and this occurred prior to, and independently of any reductions in cellular viability. Microtubule stabilization with Taxol significantly enhanced these effects. Additionally, Taxol promoted the attachment and spreading of suspended tumor cell populations on extracellular matrix. While the antiproliferative effects of these compounds are well recognized and clinically valuable, our findings that microfilament and microtubule binding chemotherapeutics rapidly increase the mechanisms that promote endothelial adhesion of circulating tumor cells warrant caution to avoid inadvertently enhancing metastatic potential, while targeting cell division.

Tumour-selective antivascular effects of the novel anti-mitotic compound A-318315: An in vivo rat regional haemodynamic study.

1. It has been shown that tubulin-binding agents can destabilize cellular microtubules and suppress tumour growth; but it has also become apparent that some compounds can exert anti-vascular effects within the neovasculature of a solid tumour. To date, the difficulty with these targets has been the ability to selectivity induce vascular damage to the tumour while leaving normal vasculature unaffected. The data presented here characterizes the in vivo, tumour selective, anti-vascular effects of the novel tubulin-binding agent A-318315. 2. To that purpose, we have used an anaesthetized in vivo rat model designed to quantify acute changes in regional vascular resistance (VR) in both tumour and non-tumour vascular beds, simultaneously. Tissue-isolated tumours (approximately 1.25 gm) with blood flow supplied by a single epigastric artery were grown in the hindlimb of adult male rats. Blood flow to the tumour, mesenteric, renal and normal (non-tumour epigastric) arteries was measured pre-dose and post-dose under anaesthesia. 3. A-318315 was tested at 3, 10 and 30 mg/kg, i.v. These doses produced modest, transient increases in mean arterial pressure with little to no effect on heart rate. At peak effect, tumour VR increased to 175 +/- 47, 337 +/- 77 and 751 +/- 151% above the baseline, for the 3, 10 and 30 mg/kg doses, respectively, whereas VR was only modestly and transiently increased in normal epigastric (88 +/- 19%), mesenteric (33 +/- 3.3%) and renal arteries (17 +/- 8.6%). 4. These data demonstrate that A-318315 produces marked reductions in tumour blood flow in the rat at doses that exert minor effects on normal vascular function.

Cevipabulin (TTI-237): preclinical and clinical results for a novel antimicrotubule agent.

Antimitotic agents are among the most effective drugs for the treatment of solid tumors and metastatic cancer. These drugs promote cell death by interfering with the crucial structural and regulatory function of microtubules in cells. Most of the agents of clinical relevance are natural products or semisynthetic derivatives thereof, and they fall into two major classes: microtubule stabilizers such as the taxanes, which enhance tubulin polymerization, and microtubule destabilizers such as the Vinca alkaloids, which lead to the depolymerization of existing microtubules. While these drugs are effective in inhibiting the progression of certain types of tumors, their utility is limited in part by incomplete tumor responses and/or significant side effects. In addition, inherent resistance is encountered in many tumor types, or acquired resistance may occur as a result of multiple cycles of therapy. Cevipabulin (TTI-237) is a novel, small synthetic molecule with an unusual biological mode of action. It appears to bind at the vinca site, but exhibits some properties similar to those of taxane-site ligands, such as enhancing tubulin polymerization. The compound works against a variety of tumors, including those resistant to paclitaxel and vincristine. Furthermore, cevipabulin is stable and water-soluble, and can be administered i.v. or p.o. in saline. It can be synthesized in bulk quantities efficiently. Based on these properties, cevipabulin was selected for clinical development.

Phase II, Multicenter, Single-arm Trial of Eribulin as First-line Therapy for Patients With Aggressive Taxane-pretreated HER2-Negative Metastatic Breast Cancer: The MERIBEL Study.

BACKGROUND: Eribulin has efficacy in patients with progression after ≥ 1 chemotherapeutic regimen for metastatic breast cancer (MBC). A short disease-free interval (DFI) and previous use of taxanes in the neoadjuvant or adjuvant setting have been associated with worse outcomes for patients receiving first-line chemotherapy for HER2-negative MBC. The aim of the present trial was to evaluate the efficacy and safety of eribulin as first-line therapy for patients with HER2-negative MBC with these poor prognostic factors. PATIENTS AND METHODS: Eribulin monotherapy was administered until disease progression or unacceptable toxicity. The principal selection criteria were HER2 negativity without previous chemotherapy for MBC, the previous use of taxanes for early-stage breast cancer, and a DFI of < 36 months (subsequently amended to 48 months). The primary endpoint was the investigator-assessed time to progression. The secondary endpoints included overall survival, progression-free survival, objective response rate, clinical benefit rate, duration of response, and toxicity profile. A total of 53 patients were enrolled and received ≥ 1 dose of eribulin. RESULTS: The median patient age was 47 years (range, 23-82.8 years). The median DFI was 15.7 months (range, 0.1-46.4 months). The median investigator-assessed time to progression was 4.1 months (range, 0.2-27.8 months; 95% confidence interval, 3.2-6.2 months). The objective response and clinical benefit rate was 20.8% and 26.4%, respectively. All-grade and grade 3/4 adverse events developed in 96.2% and 69.8% of patients, respectively. The most common treatment-related adverse events were neutropenia, leukopenia, alopecia, nausea, and anemia. CONCLUSION: Eribulin is effective and safe as first-line therapy for aggressive taxane-pretreated HER2-negative MBC.

Phase I dose-escalation study of chiauranib, a novel angiogenic, mitotic, and chronic inflammation inhibitor, in patients with advanced solid tumors.

BACKGROUND: Chiauranib is a novel orally active multi-target inhibitor that simultaneously inhibits the angiogenesis-related kinases (VEGFR2, VEGFR1, VEGFR3, PDGFRα, and c-Kit), mitosis-related kinase Aurora B, and chronic inflammation-related kinase CSF-1R. This phase I dose-escalation study was to determine the maximum tolerated dose (MTD), safety, pharmacokinetics, and preliminary antitumor activity of chiauranib in patients with refractory advanced solid tumor and lymphoma. METHODS: Eighteen patients were treated with continuous dosing of chiauranib from 10 to 65 mg once daily in a dose-escalation 3 + 3 design and evaluated in 28-day cycles. Pharmacokinetic profile of plasma chiauranib was analyzed in both single and multiple dose studies. RESULTS: Dose-limiting toxicity (DLT) as of grade 3 hypertension occurred in two patients at 65 mg/day, and one dose level below as MTD was 50 mg/day. The most common treatment-related adverse events included fatigue (61.1%), proteinuria (44.4%), hematuria (38.9%), hypothyroidism (38.9%), hypertriglyceridemia (33.3%), and hypertension (33.3%). A linear and dose-dependent pharmacokinetic profile of chiauranib was characterized with rapid absorption and slow elimination feature in both single and multiple dose studies. The accumulative exposure of chiauranib reached the steady state within 8 days and was approximately increased by twofold as those in the single dose study. No complete or partial response was observed, and 12 patients (66.7%) achieved stable disease (SD). CONCLUSIONS: Chiauranib demonstrated an acceptable safety and favorable pharmacokinetic profile with potential antitumor activity. Several phase Ib/II clinical studies are currently under further investigation. TRIAL REGISTRATION: NCT, NCT02122809 . Registered 25 April 2014.

Tumour lysis syndrome following eribulin for metastatic uterine leiomyosarcoma.

A middle-aged woman with a history of leiomyosarcoma of the uterus treated with surgery and adjuvant chemotherapy suffered a bulky metastatic recurrence 1 year later. She elected treatment with palliative eribulin, presenting with acute renal failure and electrolyte abnormalities consistent with tumour lysis syndrome on cycle 1 day 8. Despite aggressive supportive care and treatment including intravenous hydration, bicarbonate and rasburicase, she continued to decline, ultimately foregoing haemodialysis in favour of palliative care and passed away in the hospital.

Anti-mitotic agents: Are they emerging molecules for cancer treatment?

Mutations in cancer cells frequently result in cell cycle alterations that lead to unrestricted growth compared to normal cells. Considering this phenomenon, many drugs have been developed to inhibit different cell-cycle phases. Mitotic phase targeting disturbs mitosis in tumor cells, triggers the spindle assembly checkpoint and frequently results in cell death. The first anti-mitotics to enter clinical trials aimed to target tubulin. Although these drugs improved the treatment of certain cancers, and many anti-microtubule compounds are already approved for clinical use, severe adverse events such as neuropathies were observed. Since then, efforts have been focused on the development of drugs that also target kinases, motor proteins and multi-protein complexes involved in mitosis. In this review, we summarize the major proteins involved in the mitotic phase that can also be targeted for cancer treatment. Finally, we address the activity of anti-mitotic drugs tested in clinical trials in recent years.

Sponging off nature for new drug leads.

Marine sponges have consistently been the richest source of new marine natural products with unprecedented chemical scaffolds and potent biological activities that have been reported in the chemical literature since the early 1970s. During the last 40years, chemists in the Andersen laboratory at UBC, in collaboration with biologists, have discovered many novel bioactive sponge natural products. Four experimental drug candidates for treatment of inflammation and cancer, that were inspired by members of this sponge natural product collection, have progressed to phase I/II/III clinical trials. This review recounts the scientific stories behind the discovery and development of these four drug candidates; IPL576,092, HTI-286 (Taltobulin), EPI-506 (Ralaniten acetate), and AQX-1125.

Estudo comparativo da inibição da proliferação de fibroblastos in vitro na conjuntiva utilizando mitomicina C e ciclofosfamida / Comparative study of inhibition of fibroblasts proliferation in vitro in the conjunctiva using mitomycin and ciclophosphamide

RESUMO Objetivo: Avaliar a inibição da proliferação de fibroblastos in vitro das conjuntivas obtidas através de exérese de pterígios de pacientes utilizando mitomicina C (MMC) e ciclofosfamida (CF). Métodos: Os pterígios foram retirados de 7 pacientes e submetidos a cultivo celular. Após o cultivo, 3 fragmentos de dimensões iguais deste material foram colhidos de áreas adjacentes do pterígio removido de cada paciente. Eles foram randomicamente selecionados de tal forma que: um fragmento de cada paciente foi exposto: ao meio de cultura (grupo controle), a MMC e a CF por igual período de tempo nas concentrações de 0,4 mg/ml e 10 mg/ml respectivamente. Após este período realizou-se a contagem celular de fibroblastos destes 3 grupos. Cada grupo continha 7 fragmentos. Resultados: Com a utilização da MMC tivemos uma taxa de 95% da inibição da proliferação dos fibroblastos, enquanto com a CF 100%. Conclusões: Ambas as drogas apresentaram elevada taxa da inibição da proliferação de fibroblastos, porém a CF apresentou inibição maior que a MMC.

Abstract Objective: To evaluate the inhibition of fibroblast proliferation in vitro of conjunctiva obtained by excision of pterygium from patients using mitomycin (MMC) and cyclophosphamide (CF). Methods: Pterygiums were removed from 7 patients and subjected to cell culture. After cell cultivation, 3 fragments of equal dimensions of these tissues were collected from adjacent areas of each patient removed pterygium. They were randomly selected in such a way that one fragment of each patient was exposed to: the culture medium (group control), to MMC and to CF for an equal period of time at concentrations of 0,4 mg/dl and 10 mg/dl respectively. After this period, the fibroblast cell count of these groups were performed. Each group had seven fragments. Results: With the use of MMC we had a 95% rate of inhibition of fibroblast proliferation, while with CF 100%. Conclusion: Both drugs showed a high rate of inhibition of fibroblast proliferation, but CF showed greater inhibition than MMC.

DNA damage response in peripheral nervous system: coping with cancer therapy-induced DNA lesions.

In the absence of blood brain barrier (BBB) the DNA of peripheral nervous system (PNS) neurons is exposed to a broader spectrum of endogenous and exogenous threats compared to that of the central nervous system (CNS). Hence, while CNS and PNS neurons cope with many similar challenges inherent to their high oxygen consumption and vigorous metabolism, PNS neurons are also exposed to circulating toxins and inflammatory mediators due to relative permeability of PNS blood nerve barrier (BNB). Consequently, genomes of PNS neurons incur greater damage and the question awaiting investigation is whether specialized repair mechanisms for maintenance of DNA integrity have evolved to meet the additional needs of PNS neurons. Here, I review data showing how PNS neurons manage collateral DNA damage incurred in the course of different anti-cancer treatments designed to block DNA replication in proliferating tumor cells. Importantly, while PNS neurotoxicity and concomitant chemotherapy-induced peripheral neuropathy (CIPN) are among major dose limiting barriers in achieving therapy goals, CIPN is partially reversible during post-treatment nerve recovery. Clearly, cell recovery necessitates mobilization of the DNA damage response and underscores the need for systematic investigation of the scope of DNA repair capacities in the PNS to help predict post-treatment risks to recovering neurons.

First-time-in-human study of GSK923295, a novel antimitotic inhibitor of centromere-associated protein E (CENP-E), in patients with refractory cancer.

PURPOSE: GSK923295 is an inhibitor of CENP-E, a key cellular protein important in the alignment of chromosomes during mitosis. This was a Phase I, open-label, first-time-in-human, dose-escalation study, to determine the maximum-tolerated dose (MTD), safety, and pharmacokinetics of GSK923295. PATIENTS AND METHODS: Adult patients with previously treated solid tumors were enrolled in successive cohorts at GSK923295 doses ranging from 10 to 250 mg/m(2). GSK923295 was administered by a 1-h intravenous infusion, once weekly for three consecutive weeks, with treatment cycles repeated every 4 weeks. RESULTS: A total of 39 patients were enrolled. The MTD for GSK923295 was determined to be 190 mg/m(2). Observed dose-limiting toxicities (all grade 3) were as follows: fatigue (n = 2, 5%), increased AST (n = 1, 2.5%), hypokalemia (n = 1, 2.5%), and hypoxia (n = 1, 2.5%). Across all doses, fatigue was the most commonly reported drug-related adverse event (n = 13; 33%). Gastrointestinal toxicities of diarrhea (n = 12, 31%), nausea (n = 8, 21%), and vomiting (n = 7, 18%) were generally mild. Frequency of neutropenia was low (13%). There were two reports of neuropathy and no reports of mucositis or alopecia. GSK923295 exhibited dose-proportional pharmacokinetics from 10 to 250 mg/m(2) and did not accumulate upon weekly administration. The mean terminal elimination half-life of GSK923295 was 9-11 h. One patient with urothelial carcinoma experienced a durable partial response at the 250 mg/m(2) dose level. CONCLUSIONS: The novel CENP-E inhibitor, GSK923295, had dose-proportional pharmacokinetics and a low number of grade 3 or 4 adverse events. The observed incidence of myelosuppression and neuropathy was low. Further investigations may provide a more complete understanding of the potential for GSK923295 as an antiproliferative agent.

Evaluation of the oral antimitotic agent (ABT-751) in dogs with lymphoma.

BACKGROUND: ABT-751 is a novel orally available antimitotic agent that targets microtubule polymerization. This mechanism may suggest potential activity in canine lymphoma. OBJECTIVE: Determine a maximum tolerated dose for ABT-751, and assess long-term tolerability and activity in canine lymphoma. ANIMALS: Thirty dogs with newly diagnosed (n = 19) or relapsed (n = 11) non-Hodgkin's lymphoma. METHODS: Dogs (n = 11) were enrolled in a rapid dose escalation study to define the maximum tolerated dose. Upon definition of a maximally tolerated dose, a cohort expansion of 19 dogs allowed verification of long-term tolerability and assessment of activity. Study endpoints in the cohort expansion included chronic tolerability, response rate, response duration, and time to progression. Additional endpoints included serum pharmacokinetics, lymph node drug concentrations, and changes in circulating endothelial cells. RESULTS: The maximum tolerated dose of ABT-751 was 350 mg/m(2) PO q24h. Dose-limiting toxicities included vomiting and diarrhea, which resolved with a schedule adjustment to 350 mg/m(2) PO q48h. ABT-751 was consistently detected in lymphoma tissue samples from dogs treated at or above the maximum tolerated dose. In the cohort expansion, objective responses were seen in 3/15 (20%) dogs with a response duration ranging from 21 to 111 days. Decreases in circulating endothelial cells were seen in 10 dogs at day 7 (2 responding dogs and 8 nonresponding dogs). CONCLUSION: ABT-751 was well tolerated at 350 mg/m(2) PO q24h for 7 days and then q48h thereafter. Activity of ABT-751 suggested a rationale for additional studies of ABT-751 as part of a combination chemotherapy protocol for lymphoma or other canine cancers.

Pseudolaric acid B induces mitotic catastrophe followed by apoptotic cell death in murine fibrosarcoma L929 cells.

Pseudolaric acid B (PAB) is the primary biologically active compound isolated from the root bark of P. kaempferi Gordon. Previous studies have demonstrated that PAB arrests cells in G2/M phase in several cancer cell lines without significantly perturbing the G2/M transition-associated proteins. CylinB1, a marker for mitotic phase arrest, was up-regulated in cells treated with PAB. Therefore, we investigated whether PAB affects cell cycle progression at the mitotic phase. The mitotic index increased during a 24h treatment with PAB, suggesting that PAB arrested cell cycle progression at mitosis. In addition, after a prolonged mitotic arrest, the cells underwent mitotic catastrophe. After an extended treatment with PAB (longer than 24h), the protein levels of cylinB1 and cdc2 significantly decreased in both nuclear and cytosolic extracts. According to these results, we concluded that mitotic slippage could be due to the inactivation of the cylinB1-cdc2 complex resulting from prolonged treatment with PAB. The cells undergoing mitotic catastrophe died via apoptosis.

I-387, a novel antimitotic indole, displays a potent in vitro and in vivo antitumor activity with less neurotoxicity.

(3-(1H-indol-2-yl)phenyl)(3,4,5-trimethoxyphenyl)methanone (I-387) is a novel synthetic compound that inhibits tubulin action and exhibits potent antitumor activity in various preclinical models. I-387 inhibited the in vitro growth of several human cancer cell lines with IC50 values in the range of 15 to 39 nmol/L. Nanomolar concentrations of the compound induced apoptosis and caused phosphorylation of the antiapoptotic protein Bcl-2. I-387 induced a strong and concentration-dependent G2-M arrest in PC-3 cells by constitutive activation of Cdc2/cyclin B1 complex and destabilized polymerization of purified tubulin in vitro by binding to the colchicine-binding site. In vivo, I-387 treatment effectively inhibited tumor growth in mice bearing PC-3 tumor xenografts. In vitro studies of nerve growth factor-dependent neurite outgrowth in PC12 pheochromocytoma cells and in vivo studies of mouse behavior showed that I-387 was less neurotoxic than vinblastine and vincristine, tubulin destabilizers with known neurotoxicity. Interestingly, multidrug-resistant cell lines that overexpressed P-glycoprotein (P-gp), multidrug resistance-associated proteins, and breast cancer resistance protein were rendered resistant to docetaxel, vinblastine, SN-38, and doxorubicin, but not to I-387. I-387 dosed at 10 mg/kg was equally effective with 76% tumor growth inhibition in xenograft models using MES-SA uterine sarcoma cells and MES-SA/DX5 cells overexpressing P-gp. In contrast, docetaxel and vinblastine were not effective in MES-SA/DX5 xenograft models. The potent in vitro and in vivo antitumor activity of I-387 suggests that it may represent a new antimitotic agent for management of various malignancies, particularly for patients with drug-resistant cancer.