Eribulin -- a review of preclinical and clinical studies

Eribulin mesylate is a non-taxane, structurally simplified, completely synthetic, halichondrin B derivative with an end poisoning, microtubule inhibitory action. Preclinical studies have demonstrated activity in various cancer cell lines and synergistic action with gemcitabine, epirubicin, trastuzumab, cisplatin, docetaxel and vinorelbine. Eribulin has recently been approved by United States Food and Drug Administration as a third line therapy for metastatic breast cancer patients, who have previously been treated with an anthracycline and a taxane. It has also advanced to phase II trials in non-small cell lung cancer, pancreatic, prostate, bladder, head and neck cancers, sarcomas and ovarian and other gynecological tumors. Combination trials with carboplatin, gemcitabine, pemetrexed, cisplatin, and erlotinib are currently ongoing. Eribulin potentially has a low incidence of peripheral neuropathy. The predominant side effects are neutropenia and fatigue, which are manageable. This article reviews the available information on eribulin with respect to its clinical pharmacology, mechanism of action, pharmacokinetics, pharmacodynamics, metabolism, preclinical studies and clinical trials.

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.

Circulating tumor cell number and prognosis in progressive castration-resistant prostate cancer

PURPOSE

The development of tumor-specific markers to select targeted therapies and to assess clinical outcome remains a significant area of unmet need. We evaluated the association of baseline circulating tumor cell (CTC) number with clinical characteristics and survival in patients with castrate metastatic disease considered for different hormonal and cytotoxic therapies.

EXPERIMENTAL DESIGN

CTC were isolated by immunomagnetic capture from 7.5-mL samples of blood from 120 patients with progressive clinical castrate metastatic disease. We estimated the probability of survival over time by the Kaplan-Meier method. The concordance probability estimate was used to gauge the discriminatory strength of the informative prognostic factors.

RESULTS

Sixty-nine (57%) patients had five or more CTC whereas 30 (25%) had two cells or less. Higher CTC numbers were observed in patients with bone metastases relative to those with soft tissue disease and in patients who had received prior cytotoxic chemotherapy relative to those who had not. CTC counts were modestly correlated to measurements of tumor burden such as prostate-specific antigen and bone scan index, reflecting the percentage of boney skeleton involved with tumor. Baseline CTC number was strongly associated with survival, without a threshold effect, which increased further when baseline prostate-specific antigen and albumin were included.

CONCLUSIONS

Baseline CTC was predictive of survival, with no threshold effect. The shedding of cells into the circulation represents an intrinsic property of the tumor, distinct from extent of disease, and provides unique information relative to prognosis.