Phase II Clinical Trial of Ixabepilone (BMS-247550), an Epothilone B Analog, in Metastatic and Locally Advanced Breast Cancer

Chemotherapy-induced peripheral neuropathy in children and adolescent cancer patients

Brain cancer and leukemia are the most common cancers diagnosed in the pediatric population and are often treated with lifesaving chemotherapy. However, chemotherapy causes severe adverse effects and chemotherapy-induced peripheral neuropathy (CIPN) is a major dose-limiting and debilitating side effect. CIPN can greatly impair quality of life and increases morbidity of pediatric patients with cancer, with the accompanying symptoms frequently remaining underdiagnosed. Little is known about the incidence of CIPN, its impact on the pediatric population, and the underlying pathophysiological mechanisms, as most existing information stems from studies in animal models or adult cancer patients. Herein, we aim to provide an understanding of CIPN in the pediatric population and focus on the 6 main substance groups that frequently cause CIPN, namely the vinca alkaloids (vincristine), platinum-based antineoplastics (cisplatin, carboplatin and oxaliplatin), taxanes (paclitaxel and docetaxel), epothilones (ixabepilone), proteasome inhibitors (bortezomib) and immunomodulatory drugs (thalidomide). We discuss the clinical manifestations, assessments and diagnostic tools, as well as risk factors, pathophysiological processes and current pharmacological and non-pharmacological approaches for the prevention and treatment of CIPN.

Randomised phase II trial of weekly ixabepilone ± biweekly bevacizumab for platinum-resistant or refractory ovarian/fallopian tube/primary peritoneal cancer

BACKGROUND

This multi-center RP2 study assessed activity/safety of ixabepilone + bevacizumab compared to ixabepilone in platinum-resistant/refractory ovarian/fallopian tube/primary peritoneal cancer. Additional objectives were to examine the role of prior bevacizumab and taxanes, and explore class III-ß-tubulin (TUBB3) as a predictive biomarker.

METHODS

Participants were randomised to receive ixabepilone 20 mg/m2 days 1, 8, 15 with (IXA + BEV) or without (IXA) bevacizumab 10 mg/kg days 1, 15 every 28 days. Patients were stratified by prior BEV. The primary endpoint was PFS. OS, safety, and ORR served as secondary endpoints.

RESULTS

Among 76 evaluable patients who received IXA + BEV (n = 39) compared to IXA (n = 37), the ORR was 33% (n = 13) versus 8% (n = 3)(P = 0.004), durable at 6 months in 37% (n = 14) and 3% (n = 1) (P < 0.001). BEV significantly improved PFS (median:5.5 vs 2.2 months, HR = 0.33, 95%CI 0.19-0.55, P < 0.001) and OS (median:10.0 vs 6.0 months, HR = 0.52, 95%CI 0.31-0.87, P = 0.006). Both regimens were well-tolerated. TUBB3 expression did not predict response. Subgroup analyses revealed minimal effect of prior BEV or taxane resistant/refractory status on response to IXA + BEV.

CONCLUSIONS

IXA + BEV is a well-tolerated, effective combination for platinum/taxane-resistant ovarian cancer that extends PFS and likely OS relative to IXA monotherapy. Prior receipt of BEV should not preclude the use of IXA + BEV. TUBB3 is not a predictive biomarker.

CLINICAL TRIAL REGISTRATION

NCT3093155.

Microtubule Engagement with Taxane Is Altered in Taxane-Resistant Gastric Cancer

PURPOSE

Although taxane-based therapy is standard treatment for advanced gastric cancer, a majority of patients exhibit intrinsic resistance to taxanes. Here, we aim to identify the molecular basis of taxane resistance in gastric cancer.

EXPERIMENTAL DESIGN

We performed a post hoc analysis of the TAX-325 clinical trial and molecular interrogation of gastric cancer cell lines to assess the benefit of docetaxel in diffuse (DIF-GC) versus intestinal (INT-GC) gastric cancer. We assessed drug-induced microtubule stabilization in gastric cancer cells and in biopsies of patients with gastric cancer treated with taxanes. We performed transcriptome analysis in taxane-treated gastric cancer cells and patients to identify molecular drivers of taxane resistance.

RESULTS

Patients with DIF-GC did not derive a clinical benefit from taxane treatment suggesting intrinsic taxane resistance. DIF-GC cell lines displayed intrinsic resistance specific to taxanes because of impaired drug-induced microtubule stabilization, in the absence of tubulin mutations or decreased drug accumulation. Using taxane-treated gastric cancer patient biopsies, we demonstrated that absence of drug-target engagement was correlated with clinical taxane resistance. Taxane-sensitive cell lines displayed faster microtubule dynamics at baseline, implicating proteins that regulate cytoskeletal dynamics in intrinsic taxane resistance. Differential gene expression analysis of untreated and docetaxel-treated gastric cancer lines and patient samples identified kinesins to be associated with taxane sensitivity in vitro and in patient samples.

CONCLUSIONS

Our data reveal that taxane resistance is more prevalent in patients with DIF-GC, support assessment of drug-target engagement as an early read-out of taxane clinical efficacy, and encourage the investigation of kinesins and other microtubule-associated proteins as potentially targetable mediators of taxane resistance in gastric cancer.

Paclitaxel in Breast Cancer

Paclitaxel, a chemotherapeutic drug isolated from the Pacific yew, was approved for the treatment of metastatic breast cancer in 1994 and remains one of the most important agents in the treatment of patients with this disease. It is currently approved for the adjuvant treatment of node-positive breast cancer, administered sequentially after a standard doxorubicin-containing regimen, and for metastatic disease after failure of combination chemotherapy or relapse within 6 months of adjuvant chemotherapy. In this article, data on the pharmacology, clinical efficacy and safety of paclitaxel for the treatment of breast cancer will be reviewed.

Phase II trial of utidelone as monotherapy or in combination with capecitabine in heavily pretreated metastatic breast cancer patients

Background

The treatment of metastatic breast cancer (MBC) remains a great clinical challenge as drug resistance frequently develops. Alternative agents that can overcome drug resistance would offer new therapeutic options. The primary aim of this phase II study was to evaluate the efficacy and safety of utidelone as a monotherapy or in combination with capecitabine in metastatic breast cancer patients previously treated with and resistant to anthracyclines and taxanes.

Methods

In two open-label, noncomparative clinical studies, patients with metastatic breast cancer who previously received anthracycline- and/or taxane-containing regimens were given (1) 25 to 35 mg/m²/day intravenously infused utidelone, once daily for 5 days, in combination with 14 days of 2000 mg/m² capecitabine, divided in two equal daily oral doses or (2) 40 mg/m²/day intravenously infused utidelone, once daily for 5 days. These regimens were administered per each 21-day treatment cycle, and the maximum of treatment cycles allowed per protocol is 6. Objective response rate (ORR), progression-free survival (PFS), and tolerability were evaluated.

Results

In the combination study, 33 patients completed a median of 6 cycles of therapy, which was the highest cycles a trial patient could receive under the criteria of the study protocol. Efficacy was evaluated (n = 32) with an ORR of 42.4 % (FAS, 95 % CI, 26.6, 60.9) and a median PFS of 7.9 (FAS, 95 % CI, 6.1, 9.8) months. The monotherapy study (n = 63) resulted in an ORR of 28.57 % (FAS, 95 % CI, 18.4, 40.6) and a median PFS of 5.4 (FAS, 95 % CI, 2.9, 9.8) months. In both studies, common toxicities associated with utidelone administration included peripheral neuropathy, fatigue, myalgia, and arthralgia, but the toxicities were limited and manageable. Notably, very mild myelosuppression, low liver and renal toxicities, and very limited gastrointestinal toxic effect were observed, in contrast to other agents in the same class.

Conclusions

Utidelone showed promising efficacy, tolerability, and advantageous safety profiles in the treatment of patients with advanced anthracycline/taxane-refractory metastatic breast cancer and may offer new treatment options to overcome drug resistance.

Trial registration

CHiCTR-TRC-13004205, registered on August 15, 2013.

Evaluation of the pharmacokinetics of ixabepilone for the treatment of breast cancer

INTRODUCTION

Chemotherapeutic agents, such as anthracyclines, taxanes and fluoropyrimidines, have significantly improved the outcome of breast cancer patients. However, mechanisms of resistance limit the effectiveness of these drugs. The microtubule-stabilizing agent ixabepilone has been approved for treatment of metastatic breast cancer (MBC) patients resistant or refractory to taxanes, anthracycline and capecitabine.

AREAS COVERED

In this review, we summarized data on pharmacodynamics, pharmacokinetics, preclinical and clinical studies of ixabepilone in breast cancer. This article was compiled through searches on ixabepilone up to March 2015 in the PubMed and the clinicaltrials.gov databases; the FDA and European Medicine Agency (EMA) websites; and the ASCO and AACR proceedings.

EXPERT OPINION

Ixabepilone is a well-tolerated and effective drug in MBC at the approved dose. The most important challenges that ongoing clinical trials are still addressing are: the optimal dosing schedule that might improve the risk/benefit ratio, the clinical efficacy of ixabepilone in early breast cancer, the efficacy in triple-negative breast cancer (TNBC) patients and the identification of biomarkers predictive of response.

Sorafenib Plus Ixabepilone as First-Line Treatment of Metastatic HER2-Negative Breast Cancer: A Sarah Cannon Research Institute Phase I/II Trial

BACKGROUND

The purposes of the present phase I/II trial were (1) to define tolerable doses of ixabepilone and sorafenib when used in combination and (2) to evaluate the efficacy and toxicity of this combination in the treatment of patients with human epidermal growth factor receptor-negative metastatic breast cancer (MBC).

PATIENTS AND METHODS

The eligible patients had human epidermal growth factor receptor-negative MBC and had not received previous chemotherapy in the metastatic setting. All patients received ixabepilone intravenously on day 1 of each 21-day treatment cycle; sorafenib was administered orally twice daily. Patients in phase II received the maximum doses identified in phase I. The patients were reevaluated after the completion of 3 treatment cycles; treatment continued until disease progression or intolerable toxicity. A total of 67 patients were required in phase II to demonstrate increased median progression-free survival from 4.2 to 6.2 months (90% power, α = 0.05).

RESULTS

Ten patients entered the phase I portion; the maximum tolerated doses were ixabepilone 32 mg/m(2) and sorafenib 400 mg orally twice daily. A total of 76 patients were treated at the phase II dose. The median progression-free survival was 4.8 months (95% confidence interval, 3.5-6.3 months). The overall response rate was 37%. The regimen was difficult to tolerate for many patients; 20 patients discontinued because of toxicity, and dose reductions were frequent. The common toxicities included neutropenia, fatigue, rash, and neuropathy.

CONCLUSION

The combination of ixabepilone and sorafenib was poorly tolerated as first-line treatment of patients with MBC. The activity of the combination was similar to the activity previously reported with single-agent ixabepilone or taxanes. Further development of this combination is not recommended.

PARP inhibitors in the management of breast cancer: current data and future prospects

Poly(ADP-ribose) polymerases (PARP) are enzymes involved in DNA-damage repair. Inhibition of PARPs is a promising strategy for targeting cancers with defective DNA-damage repair, including BRCA1 and BRCA2 mutation-associated breast and ovarian cancers. Several PARP inhibitors are currently in trials in the adjuvant, neoadjuvant, and metastatic settings for the treatment of ovarian, BRCA-mutated breast, and other cancers. We herein review the development of PARP inhibitors and the basis for the excitement surrounding these agents, their use as single agents and in combinations, as well as their toxicities, mechanisms of acquired resistance, and companion diagnostics.

Concentration-dependent differential effects of an epothilone analog on cell cycle and p53 signaling

The tumor-suppressor protein p53 is considered to be one of the most important transport hubs of cell signal transduction, playing critical roles in the control of cell cycle arrest, apoptosis and many other processes as a nuclear transcription factor. p53 also acts in the cytoplasm to trigger apoptosis. Paclitaxel and other microtubule inhibitors can inhibit the growth of different types of cancer cells and induce apoptosis which is believed to be p53-independent. In the present study, we demonstrated that UTD1, a genetically engineered epothilone analog and a new microtubule inhibitor, activated p53 as a transcription factor at low concentrations demonstrated by its enhanced transcriptional activity and accumulation of p21, which led to cell cycle arrest. However, at high concentrations of UTD1, p53 was accumulated in the cytoplasm which contributed to induction of apoptosis. These observations indicate that the epothilone analog has differential effects on intracellular signaling and implies that p53 plays different roles in cells exposed to different concentrations of the anticancer agent.

Neurotoxicity as a prognostic factor in patients with metastatic breast cancer treated with ixabepilone as a first-line therapy

OBJECTIVE

This study is a longitudinal follow-up of metastatic breast cancer patients treated with ixabepilone as first-line chemotherapy, with the aim to evaluate the association between a mechanism-based neurotoxicity and the efficacy of ixabepilone.

PATIENTS AND METHODS

At the 2 main investigational sites of a phase II clinical trial, 50 patients previously treated with anthracycline received ixabepilone. A chart review was performed to evaluate overall survival (OS) and time to progression (TTP) and to describe the subsequent treatments.

RESULTS

The severe neurotoxicity induced by ixabepilone (38%) is correlated with a higher overall response rate to ixabepilone (79 vs. 48%; p = 0.042), a longer TTP (11.4 vs. 6.8 months; p = 0.023) and a longer OS (36.6 vs. 19.9 months; p = 0.05). After ixabepilone discontinuation, patients received a median of 4 subsequent chemotherapy lines (range 1-12). Among the 31 patients who received taxanes, neither the neurotoxicity incidence under treatment with taxanes nor the response was affected by a previous occurrence under ixabepilone treatment.

CONCLUSION

These findings suggest that neurotoxicity development under ixabepilone treatment is a predictor of treatment outcomes as well as a favorable prognostic factor. It highlights the risk-to-benefit ratio issue of ixabepilone. We noticed the possibility to treat patients with taxanes after ixabepilone without systematic recurrent neurotoxicity.

Efficacy and safety of ixabepilone in taxane-resistant patients with metastatic breast cancer previously treated with anthracyclines: results of a phase II study in Japan

PURPOSE

Anthracycline and taxane resistance is a key issue in the treatment of metastatic breast cancer (MBC), particularly in Asian patients who often present with advanced disease. The objective of this study was to investigate the efficacy and safety of ixabepilone monotherapy in Japanese patients with taxane-resistant MBC previously treated with anthracycline.

PATIENTS AND METHODS

Japanese patients with taxane-resistant MBC previously treated with anthracycline were treated with 40 mg/m(2) ixabepilone every 3 weeks. Primary endpoint was overall response rate. Secondary endpoints included duration of response, time to progression (TTP), and safety.

RESULTS

Fifty-two patients were treated with ixabepilone. Overall response rate was 11.5 % (95 % confidence interval 4.4-23.4), stable disease rate was 38.5 %, duration of response was 3.6 months (range 2.4-5.3 months), and TTP was 2.8 months (range 0.7-8.1 months). The most frequent grade 3/4 toxicities were neutropenia (82.7 %), leukopenia (75 %), myalgia (19.2 %), and peripheral neuropathy (19.2 %).

CONCLUSION

Ixabepilone monotherapy was effective and toxicities were manageable in this phase II study of Japanese patients with taxane-resistant metastatic breast cancer previously treated with anthracyclines.

Locoregional interaction of ixabepilone (ixempra) after breast cancer radiation

BACKGROUND

Radiation recall is an acute inflammatory reaction within a previously irradiated field triggered by chemotherapy administration. We observed a series of patients with unexpectedly severe reactions that included radiation recall and delayed healing when patients received the microtubule stabilizer ixabepilone (Ixempra; Bristol-Myers Squibb, Princeton, NJ) after radiation. We therefore decided to evaluate our experience in patients receiving ixabepilone following radiotherapy.

METHODS

We performed a retrospective chart review of all patients treated with curative intent in the Department of Radiation Oncology at the MD Anderson Cancer Center from 2008-2011 who received any ixabepilone after completion of external-beam radiation therapy. These patients received adjuvant ixabepilone on one of two protocols, either for locally advanced breast cancer or for metastatic breast cancer. In total, 19 patients were identified and their charts were subsequently reviewed for evidence of ixabepilone-related toxicity.

RESULTS

Of the 19 patients identified who received ixabepilone following radiation therapy, three (15.8%) had unexpectedly serious reactions in the months following radiation therapy. Complications included delayed wound closure and drain placement into the seroma, intense erythema, and delayed wound closure and grade 4 chest wall necrosis requiring latissimus flap and skin grafting. The average number of days between the end of radiation therapy and documentation of reaction was 99.

CONCLUSIONS

Ixabepilone chemotherapy may induce radiation recall and delayed wound healing when used shortly after the completion of external-beam radiotherapy. Significant clinical interactions have not been previously reported and merit further evaluation.

Ixabepilone-associated peripheral neuropathy: data from across the phase II and III clinical trials

PURPOSE

Dose-limiting neuropathy is a major adverse event associated with most of the microtubule-stabilizing agent-based chemotherapy regimens. Ixabepilone, a semisynthetic analogue of the natural epothilone B, has activity against a wide range of tumor types. Peripheral neuropathy (PN), associated with ixabepilone treatment, is usually mild to moderate, predominantly sensory and cumulative. Preclinical studies demonstrate that ixabepilone and taxanes produce a similar neurotoxicity profile.

METHODS

We searched databases of phase II/III clinical trials involving patients receiving ixabepilone as a monotherapy or in combination with capecitabine for incidences of neuropathy. Potential risk factors for grade 3/4 PN were identified by a Cox regression analysis on a dataset of 1,540 patients with different tumor types across multiple studies.

RESULTS

Rates for incidence of ixabepilone-induced severe PN (Common Terminology Criteria for Adverse Events grade 3/4) ranged from 1% in early untreated breast cancer up to 24% in heavily pretreated metastatic breast cancer; grade 4 PN was rare (≤ 1%). Common symptoms included numbness, paresthesias, and sometimes dysesthesias. Cox regression analysis identified only preexisting neuropathy as a risk factor for increased ixabepilone-associated PN. The management of PN has been primarily through dose adjustments (dose delays and/or dose reduction). Patients had resolution of their neuropathy within a median time of 5 to 6 weeks.

CONCLUSIONS

PN is a dose-limiting toxicity associated with ixabepilone treatment, is reversible in most patients, and can be managed with dose reduction and delays.

Managing ixabepilone adverse events with dose reduction

Ixabepilone is a synthetic analogue of epothilone B approved for the treatment of patients with metastatic or locally advanced breast cancer in combination with capecitabine for cancer resistant to an anthracycline and a taxane, and as monotherapy for cancer resistant or refractory to anthracyclines, taxanes, and capecitabine. The principal dose-limiting adverse events (AEs) of ixabepilone's standard dose (40 mg/m(2) administered by 3-hour infusion once every 3 weeks) are peripheral neuropathy, neutropenia, and fatigue. An effective strategy to manage ixabepilone-related AEs is dose reduction by 20% (from 40 to 32 to 25 mg/m(2)); this does not appear to affect treatment efficacy and enables continuation of treatment after recovery (grade 1 or resolved). When appropriate, treatment can be restarted with a 20% dose reduction (to 32 mg/m(2)). For heavily pretreated patients, especially those with a low performance status, 32 mg/m(2) is an appropriate initial dose; the dose of capecitabine should also be lowered by 20%. Weekly ixabepilone (15-20 mg/m(2) on days 1, 8, and 15 every 28 days) may have an improved tolerability profile, but prospective studies with a large number of patients are required to determine whether it has therapeutic benefit comparable with the current approved regimen. More information is required on dosage and scheduling of ixabepilone in combination with other agents, including novel targeted therapies.

Phase II trial of ixabepilone and carboplatin with or without bevacizumab in patients with previously untreated advanced non-small-cell lung cancer

BACKGROUND

Epothilones, a new class of cytotoxic agents, have demonstrated activity in non-small-cell lung cancer (NSCLC). This phase II study examined ixabepilone/carboplatin (cohort A) and ixabepilone/carboplatin/bevacizumab (cohort B) as first-line therapy for patients with advanced NSCLC.

METHOD

Patients were enrolled to either cohort A or B at physician discretion and when eligibility met. Eligible patients had newly diagnosed stage III/IV NSCLC, ECOG PS 0-1, adequate organ function, no active CNS metastases, and, in cohort B, bevacizumab treatment criteria. Both cohorts received ixabepilone 30 mg/m2 and carboplatin AUC=6 IV day 1 every 3-weeks for a maximum of 6 cycles. Patients assigned to cohort B also received bevacizumab 15 mg/kg IV day 1 of each cycle, and could continue single-agent bevacizumab for 6 additional cycles.

RESULTS

Eighty-two patients (median age, 63 years; majority stage IV and former smokers) were enrolled from 11/08 to 10/09 (A-42, B-40) and received medians of 4 and 6 cycles, respectively. The ORRs were 29% and 50%. After median follow up of 17.5 months (A) and 15.7 months (B), median progression free survivals were A-5.3 months (95% CI 2.8-8.6) and B-6.7 months (95% CI 5.1-8.4), with median overall survivals of 9.3 months (95% CI 6.4-16.6) 13.2 months (95% CI 8.9-upper limit not reached), respectively. Grade 3/4 toxicity included: anemia (A-10%, B-27%), neutropenia (A-31%, B-48%), thrombocytopenia (A-19%, B-20%), fatigue (A-10%, B-23%), infection (A-5%, B-20%), and hypersensitivity reaction (A-2%, B-5%). There was one treatment-related death, due to hemoptysis in a cohort B patient with squamous histology.

CONCLUSIONS

Ixabepilone can be safely combined with carboplatin in newly diagnosed patients with advanced NSCLC. The benefits of treatment appear consistent with those achieved with other modern platinum-doublet regimens. The addition of bevacizumab increases toxicities, however, these are largely expected and reversible. The high ORR and OS observed in the bevacizumab-cohort are encouraging, but would require validation in a larger randomized trial of cohort A versus B.

Advances in the management of metastatic breast cancer: options beyond first-line chemotherapy

This article provides an overview of recent advances in chemotherapy that may be used for the treatment of patients with locally advanced or metastatic breast cancer (MBC). Key phase ii and iii trial data for eribulin mesylate, ixabepilone, and nab-paclitaxel, published since 2006, are discussed on the basis of recency, depth, and quality.Eribulin mesylate is the first monotherapy to significantly increase overall survival in patients with pretreated MBC, but nab-paclitaxel offers a novel and safer mode of delivery in comparison with standard taxanes. By contrast, the use of ixabepilone will be limited for now, until the associated neurotoxicity can be better managed. Alongside a brief overview of the other major chemotherapies currently in use, we have aimed to provide a Canadian context for how these novel agents may be integrated into clinical practice.

Treating metastatic breast cancer with systemic chemotherapies: current trends and future perspectives

Treatment selection for metastatic breast cancer (MBC) is guided by multiple factors, most importantly hormone receptor (HR) or HER2 expression, treatment history, and prognostic factors such as short disease-free interval, presence of visceral metastases, performance status, and degree of symptoms. Chemotherapy is indicated as initial therapy for patients with HR-negative disease and following failure of hormonal therapies in HR-positive disease. Patients treated with an anthracycline or a taxane in early-stage settings may no longer be candidates for those drugs in MBC, thus underscoring the need for alternative options. Sequential single-agent therapy or combination therapy are viable strategies. Trials have shown that ixabepilone plus capecitabine significantly improves progression-free survival compared with capecitabine alone in anthracycline- or taxane-pretreated or -resistant patients, and single-agent eribulin improves survival compared with the physician's choice of treatment in patients treated previously with at least two regimens for MBC. Regardless of the regimen, proactive management to detect treatment-related adverse events in a timely manner remains important for ensuring effective delivery of treatment. Many promising investigational agents are in development, including T-DM1 (trastuzumab emtansine) and pertuzumab for HER2-positive disease, as well as PARP-1 (poly[adenosine diphosphate ribose] polymerase-1) inhibitors and cetuximab for triple-negative disease. In addition, new options for the treatment of MBC following failure of an anthracycline and a taxane promise to improve patient outcomes. Nurses should remain vigilant for adverse events and remember that the goal of treatment remains control of the disease and palliation.

Arsenic trioxide induces depolymerization of microtubules in an acute promyelocytic leukemia cell line

Background

Arsenic trioxide (As₂O₃) is a well-known and effective treatment that can result in clinical remission for patients diagnosed with acute promyelocytic leukemia (APL). The biologic efficacy of As₂O₃ in APL and solid tumor cells has been explained through its actions on anti-proliferation, anti-angiogenesis, and apoptotic signaling pathways. We theorize that As₂O₃ activates a pathway that disrupts microtubule dynamics forming abnormal, nonfunctioning mitotic spindles, thus preventing cellular division. In this study, we investigated how As₂O₃ induces apoptosis by causing microtubule dysfunction.

Methods

Cultured NB4 cells were treated with As₂O₃, paclitaxel, and vincristine. Flow cytometric analysis was then performed. An MTT assay was used to determine drug-mediated cytotoxicity. For tubulin polymerization assay, each polymerized or soluble tubulin was measured. Microtubule assembly-disassembly was measured using a tubulin polymerization kit. Cellular microtubules were also observed with fluorescence microscopy.

Results

As₂O₃ treatment disrupted tubulin assembly resulting in dysfunctional microtubules that cause death in APL cells. As₂O₃ markedly enhanced the amount of depolymerized microtubules. The number of microtubule posttranslational modifications on an individual tubulin decreased with As₂O₃ concentration. Immunocytochemistry revealed changes in the cellular microtubule network and formation of polymerized microtubules in As₂O₃-treated cells.

Conclusion

The microtubules alterations found with As₂O₃ treatment suggest that As₂O₃ increases the depolymerized forms of tubulin in cells and that this is potentially due to arsenite's negative effects on spindle dynamics.

Advancements in the Treatment of Metastatic Breast Cancer (MBC): The Role of Ixabepilone

Successful management of breast cancer in the metastatic setting is often confounded by resistance to chemotherapeutics, in particular anthracyclines and taxanes. The limited number of effective treatment options for patients with more aggressive biological subtypes, such as triple-negative metastatic breast cancer, is especially concerning. As such, a therapy clinically proven to be effective in this subtype would be of great value. Ixabepilone, a novel synthetic lactam analog of epothilone B, demonstrated better clinical outcomes in metastatic disease, particularly in triple-negative breast cancer. Most recently, studies have shown the activity of ixabepilone in the neoadjuvant setting, suggesting a role for this drug in primary disease. Notably, treating in the neoadjuvant setting might allow clinicians to explore the predictive value of biomarkers and response to treatment, as pharmacogenomic approaches to therapy continue to evolve. In this article, we review the efficacy and safety data of ixabepilone as a monotherapy and as a component of combination therapy for metastatic and primary breast cancer.

Phase I trial of ixabepilone administered as three oral doses each separated by 6 hours every 3 weeks in patients with advanced solid tumors

BACKGROUND

Ixabepilone, which stabilizes microtubules, has low susceptibility to drug resistance mediated by P-glycoprotein or βIII-tubulin.

MATERIALS AND METHODS

This study was designed to determine the maximum tolerated dose (MTD) of oral ixabepilone when administered every 6 h for three doses, every 3 weeks, to patients with refractory advanced cancers. Eighteen patients were treated with escalating doses of ixabepilone: three at cohort 1 (30 mg/dose; 90 mg on Day 1), nine at cohort 2 (40 mg/dose; 120 mg on Day 1), and six at cohort 3 (50 mg/dose; 150 mg on Day 1). Serial plasma samples were collected during cycle 1 for pharmacokinetic (PK) measurements.

RESULTS

Of the 18 treated patients, eight were male and ten were female. The median age was 59 years, and most had an excellent performance status (KPS 90-100; 61%). There were two dose limiting toxicities (DLT): Grade 4 febrile neutropenia at the 120 mg dose and Grade 4 neutropenic sepsis at the 150 mg dose. Because of the severity and duration of neutropenic sepsis at level 3, level 2 (120 mg) was defined as the MTD and this cohort was expanded to nine patients. High inter-individual variability in plasma drug concentrations was observed during the study, with particularly high levels in two patients with DLT.

CONCLUSIONS

On the basis of this safety profile, the MTD of oral ixabepilone was defined as 120 mg given as three 40 mg doses each separated by 6 h on Day 1 of a 3-week cycle. However, the PK variability observed makes further development of this oral formulation unlikely.

Beyond taxanes: the next generation of microtubule-targeting agents

Taxanes are a standard first-line option for metastatic breast cancer (MBC), but their utility may be limited by primary or acquired resistance. New microtubule-targeting agents have been developed to overcome taxane resistance and provide additional options for improving patient outcomes. This article reviews these alternative microtubule-targeting agents and their potential clinical benefits for MBC patients. Relevant clinical data were compiled through searches within PubMed and congress abstract databases. Ixabepilone, a novel microtubule-stabilizing drug approved by the US Food and Drug Administration (FDA), has proven efficacy across multiple lines of therapy, including patients with taxane-resistant/refractory disease. In phase III trials, ixabepilone plus capecitabine significantly improved progression-free survival compared with capecitabine alone in anthracycline/taxane-pretreated patients. Eribulin has recently been approved by the FDA and by the European Medicines Agency for the treatment of patients with MBC who have received at least two prior chemotherapy regimens for late-stage disease. In a phase III trial, eribulin extended overall survival compared with the physician’s treatment choice in heavily pretreated MBC patients. In addition, several investigational microtubule-targeting agents may have therapeutic potential in MBC. The development of new microtubule-targeting agents helps to address the need for additional effective regimens for patients progressing after standard treatment with anthracycline- and taxane-containing regimens.

Eribulin mesylate as a microtubule inhibitor for treatment of patients with metastatic breast cancer

Metastatic breast cancer (MBC) remains an incurable disease, with the goals of care aimed at maximizing the patient's duration and quality of life. Treatment options for MBC have become more efficacious and numerous. In addition to endocrine and chemotherapy agents, a number of targeted agents, including trastuzumab and bevacizumab, have further enhanced the landscape of therapeutic options. Eribulin mesylate (E7389) is a nontaxane microtubule dynamics inhibitor, and a structurally simplified synthetic analog of the natural marine product, halichondrin B, with a novel mechanism of action that has shown antitumor activity in pretreated MBC. Eribulin has shown a manageable tolerability profile in Phase I-II clinical trials and an improvement in overall survival compared with treatment of physician's choice, without relevant toxicities in a recently published Phase III trial. This review will focus on eribulin as a new active agent for MBC and its role in the management of breast disease.

The epothilones: new therapeutic agents for castration-resistant prostate cancer

The management of castration-resistant prostate cancer (CRPC) presents a clinical challenge because of limitations in efficacy and durability with currently available therapeutics. The epothilones represent a novel class of anticancer therapy that stabilizes microtubules, causing cell death and tumor regression in preclinical models. The structure of the tubulin-binding site for epothilones is distinct from that of the taxanes. Moreover, preclinical studies suggest nonoverlapping mechanisms of resistance between epothilones and taxanes. In early-phase studies in patients with CRPC, treatment with ixabepilone, a semisynthetic analog of epothilone B, induced objective responses and prostate-specific antigen declines in men previously progressing on docetaxel-based regimens. Clinical activity has been observed in nonrandomized trials for patients with CRPC using ixabepilone in the first- and second-line settings as a single agent and in combination with estramustine. Patupilone and sagopilone were also shown to have promising efficacy in phase II clinical trials of patients with CRPC. All three epothilones appear to be well tolerated, with modest rates of neutropenia and peripheral neuropathy. The lack of crossresistance between epothilones and taxanes may allow sequencing of these agents. Evaluating epothilones in phase III comparative trials would provide much-needed insight into their potential place in the management of patients with CRPC.

Global experience with ixabepilone in breast cancer

Ixabepilone approval in a number of countries across the world as monotherapy and in combination with capecitabine has led to widespread uptake in the later-line breast cancer setting. However, individualized data for ixabepilone in different ethnic groups are limited. Overall, data from small numbers of ethnic subgroups including Hispanic, Japanese and Chinese patients have revealed no clinically significant variation in the disposition, efficacy or tolerability of ixabepilone from that established in pivotal trials. Global use of ixabepilone, while usually along the lines of standard practice, may vary because of local regulatory decisions, clinical practice guidelines and cost considerations. Further information on the global patterns of use of ixabepilone will assist in optimizing the use of this novel therapy.

Peripheral neuropathy with microtubule-targeting agents: occurrence and management approach

Microtubule-targeting agents (MTAs), which include vinca alkaloids, taxanes, and the recently introduced epothilone, ixabepilone, are widely used chemotherapeutic agents for treatment of patients with cancer. MTAs interfere with the normal structure and function of microtubules, leading to cell-cycle arrest and tumor cell death. Microtubule function is critical to normal neuronal function, thus MTA therapy is commonly associated with some form of neuropathy. There is poor agreement between tools for clinical assessment of MTA-associated peripheral neuropathy, and standardization of grading scales is needed to reduce variability. For a majority of patients, MTA-associated neuropathy is mild to moderate in intensity and reversible, but it can be severe and resolve incompletely. The incidence and severity of MTA-associated neuropathy is drug, dose, and schedule dependent. The first-generation vinca alkaloids (eg, vincristine) are associated with severe mixed sensory and motor neuropathy, whereas the newer vinca alkaloids (eg, vinorelbine, vinflunine) induce a milder sensory neuropathy. Taxane-associated sensory neuropathy occurs more often with standard (polyoxyethylated castor oil-based) and albumin-bound paclitaxel than with docetaxel. The incidence and presentation of peripheral neuropathy with ixabepilone, alone or in combination with capecitabine, are similar to that with taxanes. Management of neuropathy may involve reducing or delaying the MTA dose, or in severe persistent or disabling cases discontinuing treatment. Reversal of neuropathy after dosage intervention appears to be more rapid with ixabepilone than with other MTAs.

Overcoming tumor multidrug resistance using drugs able to evade P-glycoprotein or to exploit its expression

Multidrug resistance (MDR) is a major obstacle to the effective treatment of cancer. Cellular overproduction of P-glycoprotein (P-gp), which acts as an efflux pump for various anticancer drugs (e.g. anthracyclines, Vinca alkaloids, taxanes, epipodophyllotoxins, and some of the newer antitumor drugs) is one of the more relevant mechanisms underlying MDR. P-gp belongs to the superfamily of ATP-binding cassette transporters and is encoded by the ABCB1 gene. Its overexpression in cancer cells has become a therapeutic target for circumventing MDR. As an alternative to the classical pharmacological strategy of the coadministration of pump inhibitors and cytotoxic substrates of P-gp and to other approaches applied in experimental tumor models (e.g. P-gp-targeting antibodies, ABCB1 gene silencing strategies, and transcriptional modulators) and in the clinical setting (e.g. incapsulation of P-gp substrate anticancer drugs into liposomes or nanoparticles), a more intriguing strategy for circumventing MDR is represented by the development of new anticancer drugs which are not substrates of P-gp (e.g. epothilones, second- and third-generation taxanes and other microtubule modulators, topoisomerase inhibitors). Some of these drugs have already been tested in clinical trials and, in most of cases, show relevant activity in patients previously treated with anticancer agents which are substrates of P-gp. Of these drugs, ixabepilone, an epothilone, was approved in the United States for the treatment of breast cancer patients pretreated with an anthracycline and a taxane. Another innovative approach is the use of molecules whose activity takes advantage of the overexpression of P-gp. The possibility of overcoming MDR using the latter two approaches is reviewed herein. 

Ixabepilone as monotherapy or in combination with capecitabine for the treatment of advanced breast cancer

Breast Cancer is the most prevalent cancer in the world with 4.4 million survivors up to 5 years following the diagnosis.1 In the US alone approximately forty thousand women die annually of metastatic breast cancer (MBC). Despite many effective systemic treatment options approximately 50% of women with MBC succumb to the disease within 24 months of the diagnosis.2 Ixabepilone is a novel, first in class member of the epothilone class of antineoplastic agents. Ixabepilone is indicated as monotherapy for the treatment of metastatic or locally advanced breast cancer in patients whose tumors are resistant or refractory to anthracyclines, taxanes, and Capecitabine. Ixabepilone is also indicated in combination with Capecitabine for the treatment of patients with metastatic or locally advanced breast cancer resistant to treatment with an anthracycline and a taxane, or whose cancer is taxane resistant and for whom further anthracycline therapy is contraindicated. Ixabepilone was extensively studied as a single agent in patients with MBC and was found to be effective and well tolerated with a predictable and manageable safety profile. Not surprisingly prior exposure to anthracyclines and taxanes affects significantly the potential for response to therapy with single agent Ixabepilone in metastatic setting. MBC patients with taxane resistant MBC have objective response rate (RR) of 12%, patients with prior low exposure to taxanes and/or resistance RR = 22%, Ixabepilone treatment after adjuvant anthracycline therapy exposure renders RR = 42% and in Taxane naïve patients RR = 57%. In two large phase III studies of Ixabepilone + Capecitabine versus Capecitabine alone, progression free survival (PFS) and overall response rates (RR) were higher in the combination treatment arms, but no survival advantage was seen overall. Treatment with Ixabepilone + Capecitabine in a phase II study resulted in an overall response rate (ORR) of 23% in ER/PR/HER2 negative, triple-negative breast cancer patients (TNBC) while ORR of 31% was seen in a preplanned pooled analysis of TNBC in the phase III trials of Ixabepilone + Capecitabine. Significantly prolonged median PFS was seen for TNBC treated with the combination of Ixabepilone + Capecitabine compared to Capecitabine alone 4.2 vs. 1.7 months respectively. Ixabepilone as single agent appears to show excellent antitumor activity in patients with TNBC MBC. Addition of Ixabepilone to Capecitabine results in approximately doubling in median PFS for TNBC versus Capecitabine alone. Single agent Ixabepilone is generally well tolerated, and its toxicity profile does not overlap with that of Capecitabine and therefore depending on prior exposure to chemotherapy both single agent Ixabepilone or in combination with Capecitabine can be used safely and effectively for treatment of advanced breast cancer.

Synergistic activity of ixabepilone plus other anticancer agents: preclinical and clinical evidence

Ixabepilone demonstrates marked synergistic activity in combination with capecitabine, which served as the rationale for the evaluation of this combination in the clinic. Ixabepilone plus capecitabine is currently approved for patients with locally advanced or metastatic breast cancer (MBC) progressing after treatment with an anthracycline and a taxane; approval was based on the results of two phase III trials comparing the combination with capecitabine monotherapy. An array of preclinical studies in multiple solid tumor types show that ixabepilone demonstrates therapeutic synergy with targeted therapies including trastuzumab, bevacizumab, brivanib, and cetuximab; with immune-modulating agents such as anti-CTLA-4 antibody; and with other chemotherapy drugs such as irinotecan and epirubicin. Notably, experiments in several xenograft models show that ixabepilone provides greater antitumor synergism when combined with bevacizumab than either paclitaxel or nab-paclitaxel combined with bevacizumab. These preclinical findings provide a foundation for ongoing phase II clinical trials using ixabepilone in combination with trastuzumab or lapatinib in HER2-positive breast cancer; with bevacizumab in breast cancer, endometrial cancer, renal cancer, and non-small cell lung cancer (NSCLC); with cetuximab in breast cancer, NSCLC, and pancreatic cancer; and with brivanib, dasatinib, sorafinib, sunitinib, or vorinostat in MBC. Preliminary results from several of these trials suggest that ixabepilone-based combinations have promising anticancer activity.

Ixabepilone for the treatment of breast cancer

Patients with breast cancer that becomes resistant to taxanes and anthracyclines experience considerable morbidity and mortality. The Food and Drug Administration has approved the use of ixabepilone for the treatment of patients with locally advanced or metastatic breast cancer that is refractory or resistant to taxanes and anthracyclines. The purpose of this review is to summarize the evidence from published studies on the pharmacological data and clinical activity of ixabepilone in patients with breast cancer. The conclusion of this review is that ixabepilone demonstrated a high efficacy in combination with capecitabine and as a single agent in breast cancer refractory to taxanes and anthracyclines. The clinical activity of ixabepilone combined with bevacizumab for advanced breast cancer was very promising.

Algorithms for the treatment of patients with metastatic breast cancer and prior exposure to taxanes and anthracyclines

At present, metastatic breast cancer (MBC) remains an incurable disease, with the goals of care aimed at maximizing the patient's duration and quality of life. Treatment options for a patient with MBC have become more efficacious and numerous. In addition to endocrine and chemotherapy agents, a number of targeted agents, including trastuzumab and bevacizumab, are available. The option to use novel agents combined with a multitude of standard chemotherapies has further enhanced the landscape of therapeutic options. As such, specific regimens must be evaluated within the framework of the individual patient, answering such questions as whether to treat with sequential single agents or combination regimens as well as which agents to use and in what sequence. The concept of personalized care is even more apparent in the setting of MBC, where the goal of palliation is intrinsically more nuanced than that of curative intent. This review will broadly assess the evidence for current treatment options with attention to varying clinical scenarios. Ultimately, delivering quality of care necessitates balancing an understanding of evidence-based data with sensitive attention to quality-of-life goals.

Phase II trial of sagopilone, a novel epothilone analog in metastatic melanoma

BACKGROUND

Sagopilone is a novel fully synthetic epothilone with promising preclinical activity and a favourable toxicity profile in phase I testing.

METHODS

A phase II pharmacokinetic and efficacy trial was conducted in patients with metastatic melanoma. Patients had measurable disease, Eastern Cooperative Oncology Group performance status 0-2, adequate haematological, and organ function, with up to 2 previous chemotherapy and any previous immunotherapy regimens. Sagopilone, 16 mg m⁻², was administered intravenously over 3 h every 21 days until progression or unacceptable toxicity.

RESULTS

Thirty-five patients were treated. Sagopilone showed multi-exponential kinetics with a mean terminal half-life of 64 h and a volume of distribution of 4361 l m⁻² indicating extensive tissue/tubulin binding. Only grade 2 or lower toxicity was observed: these included sensory neuropathy (66%), leukopenia (46%), fatigue (34%), and neutropenia (31%). The objective response rate was 11.4% (one confirmed complete response, two confirmed partial responses, and one unconfirmed partial response). Stable disease for at least 12 weeks was seen in an additional eight patients (clinical benefit rate 36.4%).

CONCLUSION

Sagopilone was well tolerated with mild haematological toxicity and sensory neuropathy. Unlike other epothilones, it shows activity against melanoma even in pretreated patients. Further clinical testing is warranted.

Ixabepilone, a new treatment option for metastatic breast cancer

Patients with metastatic breast cancer (MBC) who develop resistance to anthracyclines and taxanes have limited therapeutic options. There is an unmet need for agents that can overcome tumor resistance and are effective in treating drug-resistant disease. The novel epothilone B analog, ixabepilone, binds to β-tubulin and stabilizes microtubules, leading to growth inhibition and apoptosis. Ixabepilone is able to overcome common mechanisms of resistance that limit the efficacy of many chemotherapeutic agents such as anthracyclines, taxanes, and capecitabine. Single-agent ixabepilone has clinical activity and a manageable safety profile against several different solid tumors including MBC, nonsmall cell lung cancer (NSCLC), and prostate cancer. Several phase II and III trials have demonstrated that ixabepilone-as monotherapy and in combination with capecitabine-is active in patients with pretreated or resistant MBC. Ixabepilone is the first epothilone approved for use as monotherapy or in combination with capecitabine in the treatment of metastatic or locally advanced breast cancer that is resistant or refractory to anthracyclines, taxanes, and/or capecitabine. Further clinical studies are evaluating the combination of ixabepilone with targeted agents such as trastuzumab or bevacizumab to further define the role of this novel agent in the treatment of MBC.

Present and future evolution of advanced breast cancer therapy

Although the introduction of novel therapies and drug combinations has improved the prognosis of metastatic breast cancer, the disease remains incurable. Increased knowledge of the biology and the molecular alterations in breast cancer has facilitated the design of targeted therapies. These agents include receptor and nonreceptor tyrosine kinase inhibitors (epidermal growth factor receptor family), intracellular signaling pathways (phosphatidylinositol-3-kinase, AKT, mammalian target of rapamycin) angiogenesis inhibitors and agents that interfere with DNA repair (poly(ADP-ribose) polymerase inhibitors). In the present review, we present the most promising studies of these new targeted therapies and novel combinations of targeted therapies with cytotoxic agents.