Implications of anthracycline-resistant and taxane-resistant metastatic breast cancer and new therapeutic options

Patients with advanced or metastatic breast cancer commonly develop disease resistant to chemotherapy (typically anthracyclines and taxanes), which presents a major obstacle to therapy and leaves few effective treatment options. Drug resistance can occur due to various mechanisms including modification of drug efflux membrane transporters such as P-glycoprotein, as well as alterations in beta-tubulin. The novel epothilone B analog, ixabepilone, which has low susceptibility to various drug-resistance mechanisms, has demonstrated preclinical activity in drug-resistant breast cancer. The clinical activity of ixabepilone was evaluated in metastatic breast cancer patients with highly pretreated and/or resistant/refractory disease. Results were reviewed from three phase II trials in which ixabepilone was administered as monotherapy and one phase III trial that evaluated ixabepilone in combination with capecitabine. As a single agent, ixabepilone demonstrated activity in women who were heavily pretreated and resistant to an anthracycline, a taxane, and/or capecitabine. The combination of ixabepilone and capecitabine was significantly more active than capecitabine alone in patients with prior treatment or resistance to anthracyclines and taxanes. Treatment-related adverse events were generally low grade except for grade 3/4 toxicities, including neutropenia (53-54%) and reversible peripheral sensory neuropathy (14-16%). Ixabepilone has significant activity in patients with heavily pretreated metastatic breast cancer who are disease resistant or refractory to anthracyclines and taxanes. Further clinical evaluation of this agent in patients with drug-resistant breast cancer and in specific patient subsets is warranted.

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 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.

Epothilones: a novel class of microtubule-stabilizing drugs for the treatment of cancer

Microtubule-targeted anticancer drugs are effective in treating various cancers but are limited in use due to development of resistance and unacceptable toxicities. The epothilones are a novel class of microtubule-stabilizing anticancer drugs and may have a role in treating taxane-resistant cancers. Revised and updated data from several clinical studies for ixabepilone were recently published and subsequently resulted in ixabepilone becoming the first epothilone approved as monotherapy or in combination for treatment of locally advanced or metastatic breast cancer. BMS-310705, patupilone, KOS-862, KOS-1584 and ZK-EPO are epothilones that have been developed. Although peripheral sensory neuropathy and neutropenia are the dose-limiting toxicities for ixabepilone, these dose-limiting toxicities are ixabepilone specific. This review will discuss the current preclinical, clinical pharmacokinetic and pharmacodynamic, efficacy and toxicity data of the epothilones.

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.

Potential clinical applications of epothilones: a review of phase II studies

BACKGROUND

Epothilones are cytotoxic macrolides that share a similar mechanism of action with the taxanes but demonstrate antitumor activity in taxane-resistant settings. Six epothilones are in early clinical trials for cancer treatment.

DESIGN

This review summarizes data from phase II clinical studies of the epothilones ixabepilone (BMS-247550), patupilone (EPO906), and KOS-862. Data were identified by searches of PubMed and of the proceedings of the American Society of Clinical Oncology annual meetings and the Federation of European Cancer Societies biennial conference for the period 2000-2006. Studies were included if safety and efficacy data were available for at least 10 patients with a given tumor type in a standard phase II design.

RESULTS

Epothilones have demonstrated activity in lung, ovarian, breast, prostate, and renal carcinomas and in non-Hodgkin's lymphoma in phase II studies. Little or no evidence of clinical activity has been reported in studies of epothilones in other tumor types. Preliminary data indicate that epothilones can be combined safely with other cytotoxic agents such as carboplatin.

CONCLUSIONS

The epothilones may play a role as an alternative to taxanes if activity in resistant settings can be confirmed together with an acceptable toxicity profile. Randomized studies are awaited to investigate the utility of epothilones in single-agent and combination regimens.

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.

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.

Changes in Neurologic Function Tests May Predict Neurotoxicity Caused by Ixabepilone

Purpose

To investigate baseline factors and neurologic function tests (NFTs) that may predict the development of grade 2 or higher peripheral neuropathy (PN) after treatment with ixabepilone, an epothilone microtubule-stabilizing agent with antitumor activity.

Patients and Methods

Advanced breast cancer patients were treated with ixabepilone (6 mg/m2) for 5 consecutive days every 3 weeks in a phase II clinical trial. Physical examinations, questionnaires, nerve conduction studies, and NFTs, including the Jebsen Test of Hand Function (JTH) and the Grooved Pegboard Test (GPT), were performed at baseline and during subsequent cycles.

Results

Forty-seven patients assessable for PN received a median of five cycles of therapy (range, one to 22 cycles). Nine of these patients developed grade 2 PN, and two developed grade 3 PN, with a median time to onset of 144 days (range, 6 to 189 days). Among these 11 patients, PN resolved in eight patients, with a median of 15 days (range, 6 to 346 days) after onset, but PN did not resolve in three patients during follow-ups at 76, 361, and 746 days after onset. GPT and changes of JTH scores at onset of PN were significantly different between patients with and without PN at comparable follow-up times (P = .006 and P = .002, respectively). Changes in GPT and JTH scores over the first two cycles were often associated with the development of PN by exploratory actuarial analysis.

Conclusion

Serious ixabepilone-induced neuropathy was relatively rare on the treatment schedule used. NFTs, such as JTH and GPT, may have utility for predicting PN, but further testing is needed.