Ixabepilone (Epothilone B Analogue BMS-247550) Is Active in Chemotherapy-Naive Patients With Hormone-Refractory Prostate Cancer: A Southwest Oncology Group Trial S0111

COOPERATIVE GROUP TRIALS - SOUTHWEST ONCOLOGY GROUP (SWOG) INNOVATIONS IN ADVANCED PROSTATE CANCER

The major goals of the SWOG-GU committee in the area of advanced prostate cancer are to improve the survival and quality of life of patients with advanced prostate cancer. SWOG trials have examined the role of combined androgen blockade, intermittent androgen deprivation, and the early application of chemotherapy in castration-naïve disease. In addition, they have contributed to advancing the current chemotherapy standard of docetaxel plus prednisone, and ongoing trials seek to improve upon that standard. Finally, surrogate endpoints have been identified and markers of treatment response or resistance with novel technology are under active investigation. This review highlights findings from recent SWOG clinical trials for advanced prostate cancer, emphasizing the clinical impact and future applications of the data.

Emerging therapies in castrate-resistant prostate cancer

PURPOSE OF REVIEW

Prostate cancer continues to represent a major health problem. It represents the most common cancer in US men, with an estimated 186 320 new cases diagnosed in 2008. It is the second leading cause of cancer death in men in the United States. Despite several attempts, the median survival for men with metastatic castrate-resistant prostate cancer is 1-2 years, with improvements in survival seen primarily with docetaxel-based therapies. Treatment options are limited, and there is a clear need for therapies that improve outcome. The purpose of this article is to discuss recent developments in the field of metastatic hormone-refractory prostate cancer, including new cytotoxic agents, antiproliferative agents, immune-based therapies, circulating tumor markers and antiangiogenic agents.

RECENT FINDINGS

During this last year, several promising approaches yielded disappointing results in the phase III setting (GVAX, satraplatin, DN-101); nonetheless, expectations for other agents (abiraterone, zibotentan, Provenge) still remain high.

SUMMARY

These new agents will need to demonstrate survival benefit for approval. Circulating tumor cells have been shown to provide important prognostic information and are anticipated to be incorporated in future clinical decision-making.

The epothilones: how pharmacology relates to clinical utility

OBJECTIVE

To review the pharmacologic properties of a novel class of chemotherapeutic agents, the epothilones, and to summarize findings from recent clinical trials investigating the various epothilones in cancer therapy.

DATA SOURCES

Literature searches were conducted using MEDLINE, PubMed, and the abstract search engines for the American Society of Clinical Oncology and American Association for Cancer Research annual meetings (all searches through November 2008). Primary search terms included epothilone, BMS-247550, ixabepilone, EPO906, patupilone, sagopilone, and ZK-EPO.

STUDY SELECTION AND DATA EXTRACTION

Publications were given priority for inclusion if they discussed structural or pharmacologic properties of the epothilones as a class or if they included preclinical or clinical data for epothilones currently in clinical development.

DATA SYNTHESIS

The epothilones are a novel class of microtubule-stabilizing agents (MSAs). Epothilones are structurally and pharmacologically distinct from taxanes, but the exact ways in which the pharmacophores of the 2 classes differ has not been firmly established. A number of natural, semisynthetic, and fully synthetic epothilones are in various stages of clinical development. These agents differ from each other and from existing MSAs; these differences influence potency, stability, and solubility. Ixabepilone is currently approved to treat multidrug-resistant metastatic breast cancer and has demonstrated efficacy in earlier stages of breast cancer and in several other tumor types. Patupilone and sagopilone are currently under clinical investigation and have each shown promise in a number of treatment settings and tumor types. All 3 agents appear to be associated with manageable toxicities, but no class-wide toxicity profile exists for the epothilones and dose-limiting toxicities differ among the agents.

CONCLUSIONS

The epothilones have demonstrated significant potential for addressing the growing therapeutic challenge of taxane resistance, and the ever-increasing pool of information regarding structure-activity relationships of these MSAs will help to optimize microtubule-targeted chemotherapy.

Phase I study of ixabepilone, mitoxantrone, and prednisone in patients with metastatic castration-resistant prostate cancer previously treated with docetaxel-based therapy: a study of the department of defense prostate cancer clinical trials consortium

PURPOSE

Mitoxantrone plus prednisone and ixabepilone each have modest activity as second-line chemotherapy in docetaxel-refractory castration-resistant prostate cancer (CRPC) patients. Clinical noncrossresistance was previously observed.

PATIENTS AND METHODS

Metastatic CRPC patients progressing during or after taxane-based chemotherapy enrolled in a phase I multicenter study of ixabepilone and mitoxantrone administered every 21 days along with prednisone. Ixabepilone and mitoxantrone doses were alternately escalated in a standard 3 + 3 design. Patients were evaluated for toxicity and disease response. Dose-limiting toxicities (DLTs) were defined as treatment related, occurring during cycle 1, and included grade 4 prolonged or febrile neutropenia, thrombocytopenia (grade 4 or grade 3 with bleeding), or > or = grade 3 nonhematologic toxicity.

RESULTS

Thirty-six patients were treated; 59% of patients experienced grade 3/4 neutropenia. DLTs included grade 3 diarrhea (n = 1), prolonged grade 4 neutropenia (n = 4), and grade 5 neutropenic infection (n = 1). Due to prolonged neutropenia, the highest dose levels were repeated with pegfilgrastim on day 2 of each cycle. The maximum tolerated dose in combination with pegfilgrastim was not exceeded. The recommended phase II dose is mitoxantrone 12 mg/m2 and ixabepilone 35 mg/m2 every 21 days, pegfilgrastim 6 mg subcutaneously day 2, and continuous prednisone 5 mg twice per day. Thirty-one percent of patients have experienced > or = 50% prostate-specific antigen (PSA) declines, and two experienced objective responses. Of 21 patients treated with mitoxantrone 12 mg/m2 plus ixabepilone > or = 30 mg/m2, nine (43%) experienced > or = 50% PSA declines (95% CI, 22% to 66%).

CONCLUSION

These results suggest that the combination of ixabepilone and mitoxantrone is feasible and active in CRPC and requires dosing with pegfilgrastim.

The optimal therapeutic use of ixabepilone in patients with locally advanced or metastatic breast cancer

Background. The epothilones are a new class of microtubule-stabilizing drugs that exert potent antitumor activity against taxane-resistant and multidrug resistant cell lines. The most clinically advanced member of this class is the semisynthetic epothilone B derivative ixabepilone.

Purpose. This article reviews the preclinical and clinical data on ixabepilone in patients with locally advanced and metastatic breast cancer (MBC) and provides guidance for pharmacists on its optimal use. Data sources. PubMed and conference proceedings through August 2008.

Results. In preclinical studies, ixabepilone has demonstrated potent antitumor activity and low susceptibility to mechanisms that confer tumor resistance. Clinically meaningful benefits have been achieved with ixabepilone monotherapy in phase 2 trials of patients with MBC who have failed previous chemotherapies (anthracyclines, taxanes, or capecitabine). In a randomized, phase 3 trial, the combination of ixabepilone and capecitabine proved more effective than capecitabine alone after the failure of taxane and anthracycline regimens. At the recommended dose and schedule, the therapeutic ratio of ixabepilone is generally favorable, and its adverse effects (notably neutropenia and peripheral neuropathy) are generally manageable and reversible.

Conclusion. Ixabepilone represents an advance in the treatment of anthracycline - and taxane-pretreated MBC. Future studies will define its efficacy in combination with other drugs used in the treatment of MBC, as well as in other types of cancer. J Oncol Pharm Practice (2009) 15: 95—106.

Synergistic antitumor activity of ixabepilone (BMS-247550) plus bevacizumab in multiple in vivo tumor models

PURPOSE

Angiogenesis is a critical step in the establishment, growth, and metastasis of solid tumors, and combination of antiangiogenic agents with chemotherapy is an attractive therapeutic option. We investigated the potential of ixabepilone, the first in a new class of antineoplastic agents known as epothilones, to synergize with antiangiogenic agents to inhibit tumor growth.

EXPERIMENTAL DESIGN

In vitro and in vivo cytotoxicity of ixabepilone as single agent and in combination with two targeted antiangiogenic agents, bevacizumab or sunitinib, were examined in preclinical tumor models. Direct effects of the agents against endothelial cells was also examined and compared with the effects of paclitaxel as single agent and in combination with bevacizumab.

RESULTS

Ixabepilone showed robust synergistic antitumor activity in combination with bevacizumab and sunitinib in preclinical in vivo models derived from breast, colon, lung, and kidney cancers. The synergistic antitumor effect was greater with ixabepilone compared with paclitaxel. Furthermore, ixabepilone was more effective than paclitaxel at killing endothelial cells expressing P-glycoprotein in vitro and inhibiting endothelial cell proliferation and tumor angiogenesis in vivo.

CONCLUSIONS

Ixabepilone may enhance the antitumor effects of antiangiogenic therapy by direct cytotoxicity and also indirectly via the killing of tumor-associated endothelial cells. Given that ixabepilone has reduced susceptibility to drug efflux pumps compared with taxanes, these data may explain the increased antiangiogenic and antitumor activity of ixabepilone in combination with antiangiogenic agents. Phase II studies to assess the efficacy and safety of ixabepilone plus bevacizumab in locally recurrent or metastatic breast cancer are planned.

Phase I trial and pharmacokinetic study of ixabepilone administered daily for 5 days in children and adolescents with refractory solid tumors

PURPOSE

The objectives of this phase I trial were to determine the maximum-tolerated dose (MTD), toxicity profile, dose-limiting toxicities (DLTs), pharmacokinetics, and preliminary response rate for ixabepilone, a microtubule-stabilizing agent, administered intravenously daily for 5 days in children and adolescents.

PATIENTS AND METHODS

Patients >or= 2 and <or= 18 years with relapsed or refractory solid tumors were enrolled onto sequential cohorts to the following five dose levels: 3.0 (n = 3), 4.5 (n = 4), 6.0 (n = 3), 8.0 (n = 6), and 10 (n = 3) mg/m(2)/d. Eligibility criteria, dose levels, definitions of DLT and MTD, and pharmacokinetic sampling times were designed to be as similar as possible to the adult phase I trial of ixabepilone on the same schedule.

RESULTS

Nineteen children (median age, 10 years; range, 2 to 18 years) were enrolled, and 18 (12 with sarcomas) were assessable for toxicity. DLTs (grade 4 neutropenia for > 5 days and grade 3 fatigue) were observed in two of three patients receiving 10 mg/m(2)/d. The MTD of ixabepilone administered daily for 5 days every 21 days was 8 mg/m(2)/d. Myelosuppression, GI, and hepatic toxicities were common non-DLTs. Peripheral neuropathy was uncommon. Ixabepilone clearance was 475 +/- 247 mL/min/m(2), volume of distribution at steady-state was 12.2 +/- 5.4 L/kg, and half-life was 14 hours.

CONCLUSION

The recommended dose of ixabepilone for phase II trials in solid tumors is 8 mg/m(2)/d daily for 5 days every 21 days. This dose is 33% higher than the MTD in adults receiving the same dosing schedule. Pharmacokinetic parameters in children and adolescents were highly variable but similar to adults.

Phase II trial of weekly patupilone in patients with castration-resistant prostate cancer

BACKGROUND

Drug resistance mechanisms can reduce response rate and duration in men with castration-resistant prostate cancer (CRPC) receiving docetaxel-based therapy. Patupilone (epothilone B), a microtubule-targeting agent, may be unaffected by some resistance mechanisms. Therefore, a phase II study assessed the patupilone safety and activity in CRPC patients with and without previous chemotherapy.

METHODS

CRPC patients received patupilone 2.5 mg/m(2) weekly for 3 weeks of a 4-week cycle. Patients were required to have measurable disease or prostate-specific antigen (PSA) progression (levels>20 ng/ml).

RESULTS

All 45 enrolled patients (median age, 69 years) were safety and response assessable. Sixty-four percent had previous chemotherapy (55% had previous taxane therapy). Patients received a median of three patupilone cycles. Patupilone was generally well tolerated. Ten (22%) patients experienced grade 3 diarrhea, six (13%) grade 3 fatigue, and one (2%) grade 3 neuropathy with no neutropenia or thrombocytopenia incidence. Six (13%) patients had >or= 50% decline in PSA (three had previous taxane therapy). No patient with measurable disease had a response. Median overall survival was 13.4 months.

CONCLUSIONS

The safety profile of weekly patupilone in CRPC patients compares favorably with that of other microtubule inhibitors. At the dose and schedule tested, patupilone demonstrated minimal activity in CRPC.

Phase II genomics study of ixabepilone as neoadjuvant treatment for breast cancer

PURPOSE

This phase II study evaluated the efficacy and safety of ixabepilone as neoadjuvant therapy for invasive breast cancer not amenable to breast conservation surgery. Gene expression studies were undertaken using genes that were identified as potentially associated with sensitivity/resistance to ixabepilone in prior preclinical investigations.

PATIENTS AND METHODS

Patients with invasive breast cancer >or= 3 cm were eligible. Ixabepilone 40 mg/m(2) was administered as a 3-hour intravenous infusion on day 1 of a 21-day cycle for four or fewer cycles.

RESULTS

One hundred sixty-one patients were treated. The overall complete pathologic response (pCR) rate was 18% in breast and 29% in estrogen receptor (ER) -negative patients. Gene expression data were available for 134 patients. ER gene expression (ER1) was inversely related to pCR in breast and had a positive predictive value (PPV) of 37% and negative predictive value (NPV) of 92%. A 10-gene penalized logistic regression (PLR) model developed from 200 genes predictive of ixabepilone sensitivity in preclinical experiments included ER and tau and had higher PPV (45%) and comparable NPV (89%) to ER1. Grade 3 to 4 adverse events (AEs) were reported for 32% of patients. Except for neutropenia and leukopenia, all grade 3 to 4 AEs occurred in <or= 3% of patients. Reversible peripheral neuropathy was experienced by 3% of patients. CONCLUSION ER, microtubule-associated protein tau, and a 10-gene PLR model that included ER were identified as predictors of ixabepilone-induced pCR.

RESULTS

indicate an inverse relation between ER expression levels and ixabepilone sensitivity. Neoadjuvant ixabepilone demonstrated promising activity and a manageable safety profile in patients with invasive breast tumors.

Novel microtubule-targeting agents - the epothilones

Epothilones are a new class of antimicrotubule agents currently in clinical trials. Their chemical structures are distinct from taxanes and are more amenable to synthetic modification. Six epothilones have been studied in preclinical and clinical trials: patupilone (epothilone B), ixabepilone (BMS247550), BMS 310705, sagopilone (ZK-EPO), KOS-862 (epothilone D), and KOS-1584. In vitro data have shown increased potency in taxane-sensitive and taxane-resistant cancer cell lines. This enhanced cytotoxic effect has been attributed to epothilone being a poor substrate for p-glycoprotein drug resistance protein and having high affinity to the various beta tubulin isoforms. Phase I clinical data have shown different dose-limiting toxicities for each of the epothilones. These effects are drug specific, dose specific, and schedule of administration specific. While diarrhea and myelosuppression are the dose-limiting toxicities for patupilone and BMS 310705, respectively, neurologic toxicity, as seen with taxanes, is the dose-limiting toxicity of ixabepilone, sagopilone, and KOS-862. In an effort to decrease neurologic toxicity, investigators have modified dosing schedules with limited success. Ixabepilone has the most mature clinical results with published phase II and III data, and regulatory approval for clinical use in the treatment of breast cancer. Ixabepilone has also been combined with other anticancer agents and has regulatory approval in combination with capecitabine for heavily treated breast cancer.

Microtubule active agents: beyond the taxane frontier

Microtubules are essential to cell transport, signaling, and mitosis. An increasing range of anticancer drugs interferes with the normal formation and function of microtubules. Vinca alkaloids act as microtubule destabilizers and the taxanes act as microtubule stabilizers. Taxanes are widely used cytotoxic agents that are active in a range of solid tumor malignancies and are routinely used in a variety of settings. Significant limitations with the taxanes exist, including acquired and intrinsic tumor resistance through the expression of multidrug resistance proteins such as P-glycoprotein, risk of hypersensitivity reactions, dose-limiting hematopoietic toxicity, and cumulative neurotoxicity. Hence, there is a need to develop novel agents that act on the microtubules. Epothilones are macrolide antibiotics that bind near the taxane-binding site on microtubules and have been extensively studied in recent and ongoing clinical trials. A variety of other agents that act on the microtubules at different sites with a variety of structures are at varying stages of development.

Systemic nonhormonal management of advanced prostate cancer and its likely impact on patients' survival and quality of life

Prostate cancer is a hormonal sensitive disease with a response rate ranging from 80 to 90%; however, the majority of patients develop hormone resistance resulting in poor long term survival. Chemotherapy has demonstrated a benefit over steroids in improving the quality of life in the hormone refractory phase. Furthermore, the introduction of docetaxel succeeded in improving the survival of these patients in first-line therapy. Second-line treatment following docetaxel is challenging with no agent classified as standard in this setting. In the last 5 years, several drugs have shown promising results in initial evaluation. However, randomized phase III trials would be needed to answer this question. The majority of patients develop bone metastasis and the use of bisphosphonates has yielded encouraging results. Our understanding of the biology of hormone refractory prostate cancer has improved dramatically over the past few years and has translated into the developments of new therapeutic targets for this disease. Agents affecting several targets, including calcitriol, endotheline-1, bcl-2, and angiogenesis, are being studied currently and have the potential to change the treatment paradigms of this otherwise fatal disease. This review focuses on current and potential treatment options, including cytotoxic agents, bisphosphonates, and targeted agents, for patients with hormone refractory prostate cancer and the impact of these options on survival and quality of life.

Assessing outcomes in prostate cancer clinical trials: a twenty-first century tower of Babel

BACKGROUND

Because of the osseous distribution of prostate cancer metastases, progression is more readily identified than response in prostate cancer clinical trials. As a result, there is an increased focus on progression-free survival (PFS) as a phase 2 endpoint. PFS, however, is vulnerable to inter-study design variability. The authors sought to identify and quantify this variability and the resultant error in PFS across prostate cancer clinical trials.

METHODS

The authors reviewed phase 2 clinical trials of cytotoxic agents in castration-resistant metastatic prostate cancer over 5 years to evaluate the policies determining extent of disease and the definitions of disease progression. A simulation model was created to define the degree of error in estimating PFS in 3 hypothetical cohorts (median PFS of 12, 24, and 36 weeks) when the frequency of outcome assessments varies.

RESULTS

Imaging policies for trial entry were heterogeneous, as were the type, timing, and indications for outcome assessments. In the simulation, error in the reported PFS varied according to the interval between assessments. The difference between the detected and the true PFS could vary as much as 6.4 weeks per cycle, strictly resulting from the variability of assessment schedules tested.

CONCLUSIONS

Outcome assessment policies are highly variable in phase 2 studies of castration-resistant prostate cancer patients, despite published guidelines designed to standardize authentication of disease progression. The estimated error in PFS can exceed 6 weeks per cycle, exclusively because of variations in the assessment schedules. Comparisons of PFS times from different studies must be made with circumspection.

Chemosensitizing effects of sphingosine kinase-1 inhibition in prostate cancer cell and animal models

We have previously reported that, in prostate cancer, inhibition of the oncogenic sphingosine kinase-1/sphingosine 1-phosphate (SphK1/S1P) pathway is a key element in chemotherapy-induced apoptosis. Here, we show that selective pharmacologic inhibition of SphK1 triggers apoptosis in LNCaP and PC-3 prostate cancer cells, an effect that is reversed by SphK1 enforced expression. More importantly, we show for the first time that the up-regulation of the SphK1/S1P pathway plays a crucial role in the resistance of prostate cancer cells to chemotherapy. Importantly, pharmacologic SphK1 inhibition with the B-5354c compound sensitizes LNCaP and PC-3 cells to docetaxel and camptothecin, respectively. In vivo, camptothecin and B-5354c alone display a limited effect on tumor growth in PC-3 cells, whereas in combination there is a synergy of effect on tumor size with a significant increase in the ceramide to S1P sphingolipid ratio. To conclude, our study highlights the notion that drugs specifically designed to inhibit SphK1 could provide a means of enhancing the effects of conventional treatment through the prosurvival antiapoptotic SphK1/S1P pathway.

Ixabepilone: a new chemotherapeutic option for refractory metastatic breast cancer

Taxane therapy is commonly used in the treatment of metastatic breast cancer. However, most patients will eventually become refractory to these agents. Ixabepilone is a newly approved chemotherapeutic agent for the treatment of metastatic breast cancer. Although it targets microtubules similarly to docetaxel and paclitaxel, ixabepilone has activity in patients that are refractory to taxanes. This review summarizes the pharmacology of ixapebilone and clinical trials with the drug both as a single agent and in combination. Data were obtained using searches of PubMed and abstracts of the annual meetings of the American Society of Clinical Oncology and the San Antonio Breast Cancer Symposium from 1995 to 2008. Ixapebilone is a semi-synthetic analog of epothilone B that acts to induce apoptosis of cancer cells via the stabilization of microtubules. Phase I clinical trials have employed various dosing schedules ranging from daily to weekly to 3-weekly. Dose-limiting toxicites included neuropathy and neutropenia. Responses were seen in a variety of tumor types. Phase II studies verified activity in taxane-refractory metastatic breast cancer. The FDA has approved ixabepilone for use as monotherapy and in combination with capecitabine for the treatment of metastatic breast cancer. Ixabepilone is an efficacious option for patients with refractory metastatic breast cancer. The safety profile is similar to that of taxanes, with neuropathy and neutropenia being dose-limiting. Studies are ongoing with the use of both iv and oral formulations and in combination with other chemotherapeutic and biologic agents.

Novel therapies in genitourinary cancer: an update

In recent years, new treatment for renal cell carcinoma (RCC) has been a spotlight in the field of cancer therapeutics. With several emerging agents branded as 'targeted therapy' now available, both medical oncologists and urologists are progressively more hopeful for better outcomes. The new remedies may provide patients with improved survival and at the same time less toxicity when compared to traditional cytotoxic agents. This article will center on current and emerging treatment strategies for advanced RCC and other GU malignancies with updates from 2008 annual ASCO meeting.

Ixabepilone: a new antimitotic for the treatment of metastatic breast cancer

OBJECTIVE

To evaluate the safety and efficacy of ixabepilone as a new antimitotic chemotherapeutic agent for the treatment of breast cancer.

DATA SOURCES

Data were identified by searches of MEDLINE, PubMed, and American Society of Clinical Oncology abstracts from 1966 to March 2008, using the primary search terms ixabepilone, epothilones, BMS-247550, and breast cancer.

STUDY SELECTION AND DATA EXTRACTION

Phase 1, Phase 2, and Phase 3 clinical trials examining the safety and efficacy of ixabepilone and its place in cancer treatment were reviewed. Preference was given to large Phase 2 and 3 clinical trials in the breast cancer population. Manufacturer product information was used to supplement data lacking in published trials.

DATA SYNTHESIS

Ixabepilone belongs to a novel class of drugs, the epothilones, which are nontaxane microtubule-stabilizing agents. Ixabepilone, in combination with capecitabine, has been approved by the Food and Drug Administration for treatment in patients with metastatic or locally advanced breast cancer that progresses after anthracycline and taxane therapy, or in patients with taxane-resistant cancer with contraindication to further anthracycline therapy. Ixabepilone has also been approved as monotherapy in patients with metastatic and locally advanced breast cancer refractory to taxanes, anthracyclines, and capecitabine. The most common adverse reactions reported by 20% or more of the patients receiving ixabepilone were peripheral sensory neuropathy, fatigue/asthenia, myalgia/arthralgia, alopecia, nausea, vomiting, stomatitis/mucositis, diarrhea, and musculoskeletal pain. The most common hematologic abnormalities seen in more than 40% of the patients include neutropenia, leukopenia, anemia, and thrombocytopenia. Premedication with histamine H(1) and H(2) antagonists is recommended to prevent hypersensitivity reactions.

CONCLUSIONS

Based on the clinical trials reviewed here and the current information available, ixabepilone is a welcome addition to the options available for the treatment of patients with metastatic breast cancer refractory to standard therapy.

Novel cytotoxic agents: epothilones

PURPOSE

The epothilones are effective antitumor medications for patients with breast cancer, including patients who have been previously treated with or are resistant to anthracyclines or the taxanes.

SUMMARY

With the best currently available therapies, the median survival time for patients with metastatic breast cancer is only 2-3 years, and many patients develop resistance to taxanes or other chemotherapy drugs. The epothilones are a novel class of antitumor medications, similar to the taxanes in some respects, but that also possess several advantages. Like taxanes, epothilones are believed to produce antitumor effects by binding to and stabilizing intracellular microtubules, which are essential in DNA replication and cell division. Several in vitro and animal studies have shown that the epothilones are more potent microtubule stabilizers than the taxanes, they are effective against cancer cell lines with high levels of drug resistance, and they induce the regression of taxane-resistant human tumors. Preclinical studies also have demonstrated synergistic increases in tumor cell killing when the epothilones are combined with other antitumor medications. Epothilone B (patupilone) has been evaluated in a series of phase I and II clinical trials, which demonstrated disease stabilization or objective responses in patients with a variety of cancers, including ovarian, prostate, breast, colon, stomach, and kidney cancers. This agent is currently being evaluated in phase III clinical trials. A second epothilone, ixabepilone, was recently approved by the FDA for the treatment of metastatic breast cancer. Ixabepilone was evaluated as monotherapy for the treatment of breast cancer in phase II clinical trials of previously untreated patients and in taxane-experienced and taxane-resistant disease. A phase III clinical trial demonstrated that the combination of ixabepilone and capecitabine was superior to capecitabine alone in heavily pretreated, taxane-resistant patients.

CONCLUSION

Ongoing clinical trials will continue to define the role of the epothilones in cancer therapy.

Epothilones and new analogues of the microtubule modulators in taxane-resistant disease

BACKGROUND

Microtubule-stabilising agents typified by the epothilone class of drug have demonstrated promising activity in Phase II and III clinical trials.

OBJECTIVE

Data supporting the efficacy of these agents are reviewed and their potential use in taxane-refractory disease assessed.

METHODS

Preclinical evidence assessing the role of the spindle assembly checkpoint in determining the cellular response to microtubule stabilization are presented together with clinical data documenting the efficacy of non-taxane microtubule modulators.

RESULTS/CONCLUSIONS

Evidence suggests that microtubule-stabilising agents prolong activation of the spindle assembly checkpoint which may promote cancer cell death in mitosis or following mitotic exit. A weakened spindle assembly checkpoint is associated with altered sensitivity to agents targeting the microtubule and therefore pathways of drug resistance may be shared by these cytotoxic therapies. Preliminary clinical trial data do suggest modest activity of epothilones in truly taxane-resistant patient cohorts, indicating the potential niche for these agents in a molecularly undefined patient group, potentially implicating the role of P-glycoprotein in the acquisition of taxane-resistant disease. Trial data of these antimitotic agents will be presented together with their potential role in taxane-resistant disease and the implications for future clinical trial design.

Therapies in development for castrate-resistant prostate cancer

The paucity of active medical therapies for advanced prostate cancer underlies a critical need for clinical research in this area. Multiple new treatments are being evaluated, including therapies that target adrenal androgens, such as abiraterone; new chemotherapies, such as the oral platinum analog, satraplatin, and an epothilone analog, ixabepilone; combinations of chemotherapy with other agents, such as the VEGF inhibitor, bevacizumab, and calcitriol; as well as multiple immunotherapeutics, including sipuleucel-T, GVAX and ipilimumab. This review will highlight the promise of these new approaches and the challenges to their development.

Ixabepilone for the treatment of solid tumors: a review of clinical data

BACKGROUND

Microtubule stabilizing agents such as taxanes are an integral part of therapy for multiple solid tumors. However, due to limitations of these agents, newer more effective cytotoxic agents are necessary. Ixabepilone, an epothilone B analog, is a novel microtubule stabilizing agent.

OBJECTIVE

This review provides an updated summary of emerging clinical experience with Ixabepilone.

METHODS

Phase I, II and III clinical trials presented in abstract form or journal articles found within a PubMed search through November 2007 are described in this review.

RESULTS/CONCLUSION

Ixabepilone offers promising clinical activity in a variety of solid tumors. Ixabepilone is FDA-approved for the treatment of breast cancer refractory to anthracyclines and taxanes. The optimal dose and schedule are still being defined, and the predominant side effects are bone marrow suppression and neuropathy.

Preclinical efficacy spectrum and pharmacokinetics of ixabepilone

PURPOSE

Ixabepilone, a semisynthetic analog of natural epothilone B, was developed for use in cancer treatment. This study extends previous findings regarding the efficacy of ixabepilone and its low susceptibility to tumor resistance mechanisms and describes the pharmacokinetics of this new antineoplastic agent.

METHODS

The cytotoxicity of ixabepilone was assessed in vitro in breast, lung, and colon tumor cell lines and in vivo in human xenografts in mice. Antitumor activities of ixabepilone and taxanes were compared in multidrug-resistant models in vivo. Differential drug uptake of ixabepilone and paclitaxel was assessed in a P-glycoprotein (P-gp)-resistant colon cancer model in vitro. The pharmacokinetic profile of ixabepilone was established in mice and humans.

RESULTS

Ixabepilone demonstrated potent cytotoxicity in a broad range of human cancer cell lines in vitro and in a wide range of xenografts in vivo. Ixabepilone was *3-fold more potent than docetaxel in the paclitaxel-resistant Pat-21 xenograft model (resistant due to overexpression of betaIII-tubulin and a lack of betaII-tubulin). Ixabepilone activity against P-gp-overexpressing breast and colon cancer was confirmed in in vivo models. Cellular uptake of ixabepilone, but not paclitaxel, was established in a P-gp-overexpressing model. The pharmacokinetics of ixabepilone was characterized by rapid tissue distribution and extensive tissue binding.

CONCLUSIONS

Cytotoxicity studies against a range of tumor types in vitro and in vivo demonstrate that ixabepilone has potent and broad-spectrum antineoplastic activity. This is accompanied by favorable pharmacokinetics. Ixabepilone has reduced susceptibility to resistance due to P-gp overexpression, tubulin mutations, and alterations in beta-tubulin isotype expression.

Ixabepilone; Nilotinib

The increasing complexity of cancer chemotherapy now requires that pharmacists be familiar with these highly toxic agents. This column will review various issues related to preparation, dispensing, and administration of cancer chemotherapy, and review various agents, both commercially available and investigational, used to treat malignant diseases.

Current perspectives in the treatment of advanced prostate cancer

Prostate cancer (PC) continues to be an important world health problem for men. Patients with locally confined PC are treated with either radiotherapy or surgery. However, treatment of more advanced stages of the disease is problematic. Initially, androgen deprivation offers a period of clinical stability, which is however invariably followed by progression to non-responsiveness to hormonal manipulation. Current management of patients with androgen-independent prostate cancer (AIPC) displays modest response rates and achieves only short-term benefit. Recently, knowledge in the complex pathophysiology of advanced PC has led to the identification of mechanisms and target molecules permitting the introduction of new therapies. Consequently, many investigational treatments are ongoing for AIPC in Phase-II and Phase-III trials aiming at the combination of chemotherapeutic regimens along with immunotherapy targeting PC-associated antigens. Other attractive options are gene therapy, as well as the targeting of survival signaling, differentiation, and apoptosis of the malignant PC cells. Further treatment modalities are directed against the tumor microenvironment, bone metastasis, or both. Collectively, the aforementioned efforts introduce a new era in the management of advanced PC. Novel pharmaceutical compounds and innovative approaches, integrated into the concept of individualized therapy will hopefully, during the next decade, improve the outcome and survival for hundreds of thousands of men worldwide.

Therapeutic options for hormone-refractory prostate cancer in 2007

Prostate cancer is the most commonly diagnosed cancer in American men and a major health problem. While localized disease has an excellent chance for cure, metastatic disease leads to androgen-independent progression and death within a few years. Although docetaxel represents an important therapeutic milestone and is the current standard of care for metastatic hormone-refractory prostate cancer (HRPC), most patients eventually progress because of clonal selection of therapy-resistant cells or the development of cells with a drug-resistant phenotype. By understanding the molecular basis of resistance to androgen withdrawal and chemotherapy, the rational design of targeted therapeutics is possible. Over the last few years, many gene targets that regulate apoptosis, proliferation, and cell signalling have been identified, and numerous novel compounds have entered clinical trials either as single agents or in combination with cytotoxic chemotherapy. Neoadjuvant trials in particular must be further encouraged since they allow detection of biological activity in the prostatectomy specimen. This article reviews new treatment options available for men with advanced prostate cancer. Even though HRPC remains incurable, it is not untreatable. Recent findings are very promising, but challenges remain in demonstrating effective anti-tumor activity and showing a clinically relevant survival benefit in Phase III trials.

[Promising new treatment options for metastatic androgen-independent prostate cancer]

OBJECTIVE

Review the recent advances in the treatment of androgen independent prostate cancer (AIPC).

METHODS

Review recent abstracts and literature utilizing Medline/PubMed using key words: androgen independent/hormone refractory prostate cancer, novel treatment options, Phase II, III trials and meeting abstracts/presentations.

CONCLUSION

Two pivotal trials SWOG (Southwest Oncology Group) study 9916 and Taxotere 327 have shown that survival can be improved in this population by administration of chemotherapy with docetaxel every three weeks intravenously. An overall survival of 19 months could be achieved with docetaxel/prednisone compared to 16 months with mitoxantrone/prednisone. Despite this, there is a need to improve on this survival benefit because the relapse free survival among responders is often short (6 months) and patients often would have progression of their cancer leading to death. Satraplatin, a novel platinum analogue had been found to provide an additional 1.5 week progression free survival benefit in this population in the second line setting. There is however, a need to develop less toxic drugs that would improve survival significantly.

Epothilones in the treatment of cancer

Epothilones are cytotoxic macrolides with a similar mechanism of action to paclitaxel but with the potential advantage of activity in taxane-resistant settings in preclinical models. The epothilones ixabepilone, patupilone, BMS-310705, KOS-862 and ZK-EPO are in early clinical trials for cancer treatment. Phase I studies have shown that dose-limiting toxicities of epothilones are generally neurotoxicity and neutropoenia although initial studies with patupilone indicated that diarrhoea was dose limiting. Neuropathy induced by ixabepilone may be schedule dependent. Over 20 Phase II studies of epothilones in cancer treatment have been reported, and significant activity in taxane-sensitive tumour types (such as breast, lung and prostate cancers) has been noted. Response rates in taxane-refractory metastatic breast cancer are relatively modest, but ixabepilone and patupilone have shown promising efficacy in hormone-refractory metastatic prostate cancer and in taxane-refractory ovarian cancer.

Novel cytotoxic drugs: old challenges, new solutions

The discovery of cytotoxic agents was revolutionary for anticancer therapy in the last century, improving survival rates and the quality of life of patients with different types of tumours. However, the development of agents that combine efficacy, safety and convenience remains a great challenge, due to the narrow therapeutic index of some drugs, the fact that they may damage not only cancer cells, but also normal and healthy tissue and the occurrence of resistance, limiting anticancer efficacy. Novel cytotoxic agents have brought certain advantages over the conventional ones, such as shorter administration time, mechanisms to overcome drug resistance and lower incidence of adverse events. In this review we highlight the development of promising novel cytotoxic drugs that will hopefully offer not only gains in efficacy, but also in safety, tolerability and convenience in the treatment of patients with cancer.

Efficacy and Safety of Ixabepilone (BMS-247550) in a Phase II Study of Patients With Advanced Breast Cancer Resistant to an Anthracycline, a Taxane, and Capecitabine

Purpose

To evaluate the efficacy and safety of ixabepilone in patients with metastatic breast cancer (MBC) resistant to anthracycline, taxane, and capecitabine, in this multicenter, phase II study.

Patients and Methods

Patients with measurable disease who had tumor progression while receiving prior anthracycline, taxane, and capecitabine were enrolled. Ixabepilone 40 mg/m2monotherapy was administered as a 3-hour intravenous infusion on day 1 of a 21-day cycle. The primary end point was objective response rate (ORR), assessed by an independent radiology facility (IRF).

Results

A total of 126 patients were treated and 113 were assessable for response. Patients were heavily pretreated: 88% had received at least two lines of prior chemotherapy in the metastatic setting. IRF-assessed ORR was 11.5% (95% CI, 6.3% to 18.9%) for response-assessable patients. Investigator-assessed ORR for all treated patients was 18.3% (95% CI, 11.9% to 26.1%). Fifty percent of patients achieved stable disease (SD); 14.3% achieved SD ≥ 6 months. Median duration of response and progression-free survival were 5.7 and 3.1 months, respectively. Median overall survival was 8.6 months. Patients received a median of 4.0 treatment cycles (range, one to 16 cycles), and 25% of patients received ≥ eight cycles. Grade 3/4 treatment-related events included peripheral sensory neuropathy (14%), fatigue/asthenia (13%), myalgia (8%), and stomatitis/mucositis (6%). Resolution of grade 3/4 peripheral sensory neuropathy occurred after a median period of 5.4 weeks.

Conclusion

Ixabepilone demonstrated clear activity and a manageable safety profile in patients with MBC resistant to anthracycline, taxane, and capecitabine. Responses were durable and notable in patients who had not previously responded to multiple prior therapies.

Phase II Clinical Trial of the Epothilone B Analog, Ixabepilone, in Patients With Non–Small-Cell Lung Cancer Whose Tumors Have Failed First-Line Platinum-Based Chemotherapy

Purpose

Ixabepilone is the first in a new class of antineoplastic agents, the epothilones and their analogs. This international, randomized, phase II trial assessed two administration schedules of ixabepilone as second-line therapy in patients with non–small-cell lung cancer (NSCLC).

Patients and Methods

Patients had experienced disease progression after one prior cisplatin- or carboplatin-based chemotherapy regimen. Ixabepilone was administered as a single 32 mg/m23-hour infusion (77 patients; arm A) or a 6 mg/m21-hour infusion daily for 5 consecutive days (69 patients; arm B) in a 3-week cycle.

Results

The intent-to-treat objective response rate was 14.3% in arm A and 11.6% in arm B. Median duration of response was 8.7 months (95% CI, 5.3 to 9.5 months) in arm A and 9.6 months (95% CI, 6.1 to 19.7 months) in arm B. Median time to progression was 2.1 months (95% CI, 1.4 to 2.8 months) for arm A and 1.5 months (95% CI, 1.4 to 2.8 months) for arm B. Median survival was 8.3 months (95% CI, 5.8 to 11.5 months) for arm A, and 7.3 months (95% CI, 5.7 to 11.7 months) for arm B; the 1-year survival rate (both cohorts) was 38%. Responses occurred in patients with taxane-pretreated and platinum-refractory tumors. Both regimens had an acceptable toxicity profile. Myelosuppression was manageable, manifesting primarily as neutropenia and leukopenia. Neuropathy was primarily sensory, generally mild to moderate in severity, and mostly reversible (both regimens).

Conclusion

Single-agent ixabepilone had clinically relevant activity and an acceptable safety profile in patients with advanced NSCLC whose tumors had failed one prior platinum-based chemotherapy regimen.

Castration resistant, taxane naïve metastatic prostate cancer: current clinical approaches and future directions

PURPOSE

With the wide use of prostate specific antigen to detect response and disease progression resistance to androgen deprivation is being detected at an increasingly earlier stage. We focused on the current management and novel investigational strategies for the chemonaïve patient population with castration resistant metastatic disease.

MATERIALS AND METHODS

We reviewed standard and investigational hormonal, chemotherapeutic, biological and immune based strategies for patients with castration resistant metastatic prostate cancer who have not yet received taxane based chemotherapy.

RESULTS

Our understanding of the natural history of this group of patients is evolving. A variety of standard and experimental treatment options are available for this group of patients. Manipulating the androgen receptor signaling axis, targeting antiapoptotic pathways, using antiangiogenic strategies, harnessing the immune system and optimizing docetaxel based regimens and novel cytotoxic agents are under investigation.

CONCLUSIONS

Multiple agents currently under development offer a promise of palliation and prolongation of survival above and beyond that of docetaxel. In the absence of guidance from randomized trials with regard to chemotherapy timing, and considering the modest effects of docetaxel on survival, decisions regarding choice of therapy (standard chemotherapy or experimental therapies) must be based on careful consideration of the functional status of each individual, presence of symptoms, comorbidities and overall therapeutic objectives.

Phase II study of KOS-862 in patients with metastatic androgen independent prostate cancer previously treated with docetaxel

Based on the pre-clinical spectrum of activity in taxane-resistant cell lines, we evaluated KOS-862 (epothilone D; 12,13-desoxyepothilone B) as second-line chemotherapy in androgen-independent prostate cancer.Thirty-eight men with metastatic androgen-independent prostate cancer and evidence of progression following docetaxel-based chemotherapy were treated with KOS-862, 100 mg/m(2) (maximum of 240 mg) i.v. weekly for 3 weeks, repeated every 4 weeks. The primary objective for this study was to determine the antitumor activity, measured by PSA decline by more then 50% confirmed 4 weeks later. Two patients (5.3%, 90% CI 1-16%) met criteria for confirmed PSA decline. While both of these patients had previously been treated with docetaxel, neither had confirmed docetaxel-refractory disease. None of the 24 patients with measurable disease had a confirmed partial response. Seventy-three percent of patients had an adverse event leading to dose delay, reduction, or treatment discontinuation. Neurological toxicity and fatigue predominated. Seventeen patients (44.7%) had treatment related grade 3 neurological adverse events including peripheral sensory neuropathy (n = 4, 10.5%), ataxia (n = 3, 7.9%), peripheral motor neuropathy (n = 1, 2.6%), involuntary muscle contractions (n = 1, 2.6%) and neuropathic pain (n = 1, 2.6%). One subject (2.6%) had a grade 4 treatment peripheral motor neuropathy. Further study of this dose and schedule of KOS-862 in this patient population cannot be recommended due to both lack of activity and excessive toxicity.