Phase II Clinical Trial of Ixabepilone in Metastatic Cervical Carcinoma

Abstract

Lessons learned: Accrual to cervical cancer studies remains a puzzling challenge given the lack of options and the dismal prognosis of this disease. The majority of patients referred for a trial such as this have very advanced disease that is difficult to manage.The observation of 4 partial responses among the 41 patients indicates that ixabepilone has some activity but not sufficient for further development without greater understanding of mechanisms of sensitivity and resistance.

Background: Ixabepilone is a microtubule-stabilizing agent approved for metastatic breast cancer. Preclinical data have shown that ixabepilone is active in taxane-sensitive and -resistant cells. Metastatic cervical carcinoma (mCC) has a poor prognosis and no established second-line therapies. This study assessed the efficacy and safety of ixabepilone in previously treated mCC.

Methods: Patients with histologically confirmed mCC and at least one prior cisplatin-containing regimen were treated with ixabepilone [6 mg/m(2) per day for 5 days] every 21 days. The primary endpoint was progression-free survival (PFS) according to the Response Evaluation Criteria in Solid Tumors (RECIST). Secondary endpoints were response rate, rate of tumor growth, overall survival (OS), and safety. Levels of glu-terminated and acetylated tubulin, markers of microtubule stabilization, and surrogates for target engagement were assessed by Western blot.

Results: In total, 41 patients were enrolled; 34 had tumors with primarily squamous histology. The median number of prior therapies was 2 (range 1-6). Four patients (9.7%) had a partial response. Median PFS in months was 2.3 for all, 3.84 for taxane-naïve, and 2.03 for taxane-pretreated patients (p = .13). Consistent with this, we found statistically similar (p = 1) rates of growth in taxane-naive patients (0.0035 per day) and taxane pretreated patients (0.0053 per day). Median OS was 5.84 months. G1/2 toxicities included vomiting (43%), sensory neuropathy (21%), and fatigue (60%). Bowel fistulas were observed in 7% of patients. Glu and acetylated tubulin were assessed in tumor samples from 11 patients during the first cycle of treatment. Although there was clear evidence of "target engagement" and microtubule stabilization in all tumors, a correlation between the extent of tubulin stabilization and response to therapy could not be demonstrated.

Conclusion: Ixabepilone was well tolerated but showed very modest activity in second- or later-line mCC and cannot be recommended as a therapy. Target engagement was demonstrated but was not correlated with responses, suggesting that other factors mediate drug sensitivity. New strategies are needed for refractory mCC.

Trial registration: ClinicalTrials.gov NCT01967576.

©AlphaMed Press; the data published online to support this summary is the property of the authors.

Figures

Figure 1.

The top two panels show the fold change between the pre- and post-ixabepilone tumor biopsies in the levels of two α-tubulin modifications that occur when polymerization is induced by engagement of ixabepilone with its target. The bottom panel depicts a waterfall plot for these patients. There was no correlation between the fold change in the α-tubulin modifications and tumor response, suggesting that in addition to target engagement, other factors influence the tumor response to therapy. Abbreviation: RECIST, Response Evaluation Criteria in Solid Tumors.