Updates on managing advanced breast cancer with palbociclib combination therapy.

BACKGROUND: The objective of this study was to review the pharmacology, efficacy, and safety of palbociclib, a first-in-class cyclin-dependent kinase 4/6 inhibitor, for the management of advanced breast cancer (ABC). METHODS: Pharmacokinetics and drug interactions associated with palbociclib are described. Recent clinical trial data are reviewed, including patient-reported outcomes and subgroup analyses. RESULTS: Palbociclib is indicated in combination with an aromatase inhibitor as initial endocrine therapy (ET) or with fulvestrant for patients with disease progression following ET for hormone receptor positive, human epidermal growth factor receptor 2 negative ABC or metastatic breast cancer. Palbociclib inhibits cyclin-dependent kinases 4/6, resulting in a blockade of phosphorylation of the retinoblastoma protein, which hinders the activation of transcription factors involved in S-phase entry, thereby arresting cell cycle progression at G1 phase. The efficacy and safety of palbociclib in combination with ET was established in three randomized trials (PALOMA-1, -2, and -3); all studies met their primary endpoint of significantly prolonging investigator-assessed progression-free survival versus ET alone. Findings were similar in subgroup analyses of the three PALOMA studies. Palbociclib plus ET also maintained health-related quality of life (QoL) compared with ET alone in PALOMA-2 and -3. A long-term safety profile for palbociclib, up to 3 years, has been established. Neutropenia, the most common any-grade and grade 3 or higher adverse event associated with palbociclib, is consistent with the drug's mechanism of action and can be effectively managed with dose interruption, dose reduction, or delay in starting treatment cycles. CONCLUSIONS: Palbociclib in combination with ET improved progression-free survival and QoL in patients with ABC, including in several patient subgroups.

Reproducibility of perfusion parameters in dynamic contrast-enhanced MRI of lung and liver tumors: effect on estimates of patient sample size in clinical trials and on individual patient responses.

OBJECTIVE: Dynamic contrast-enhanced MRI (DCE-MRI) is a potentially useful noninvasive technique for assessing tissue perfusion, particularly in the context of solid tumors and targeted antiangiogenic and antivascular therapies. Our aim was to determine the reproducibility of perfusion parameters derived at DCE-MRI of tumors of the lung and liver, the most common sites of metastasis. SUBJECTS AND METHODS: Patients with lung and liver tumors underwent two sequential DCE-MRI examinations 2-7 days apart without any intervening therapy. The volume transfer constant between blood plasma and the extravascular extracellular space (K(trans)) and blood-normalized initial area under the signal intensity-time curve (initial AUC(BN)) were computed with a two-compartment pharmacokinetic model. Differences in parameters were assessed with within-patient coefficients of variation. RESULTS: Twenty-three patients had evaluable tumors (12 lung, 11 liver). The within-patient coefficients of variation for K(trans) and initial AUC(BN) for liver lesions were 8.9% and 9.9% and for lung lesions were 17.9% and 18.2%. Sample sizes for reductions in these parameters from 10% to 50% were estimated to range from two to 102 subjects. Estimates of confidence that changes observed in a given patient were due to intervening therapy rather than variability of the technique were calculated to range from 71% to 87% if a 20% reduction in a parameter was observed. CONCLUSION: The rate of reproducibility of DCE-MRI parameters is in the range of 10%-20% and is influenced by lesion location, parameters being significantly more reproducible in the liver than in the lung. These findings provide the foundation for interpretation of results and design of clinical trials in which DCE-MRI studies are used to assess objective responses.

AG-013736, a novel inhibitor of VEGF receptor tyrosine kinases, inhibits breast cancer growth and decreases vascular permeability as detected by dynamic contrast-enhanced magnetic resonance imaging.

Dynamic contrast-enhanced MRI (DCE-MRI) was used to noninvasively evaluate the effects of AG-03736, a novel inhibitor of vascular endothelial growth factor (VEGF) receptor tyrosine kinases, on tumor microvasculature in a breast cancer model. First, a dose response study was undertaken to determine the responsiveness of the BT474 human breast cancer xenograft to AG-013736. Then, DCE-MRI was used to study the effects of a 7-day treatment regimen on tumor growth and microvasculature. Two DCE-MRI protocols were evaluated: (1) a high molecular weight (MW) contrast agent (albumin-(GdDTPA)(30)) with pharmacokinetic analysis of the contrast uptake curve and (2) a low MW contrast agent (GdDTPA) with a clinically utilized empirical parametric analysis of the contrast uptake curve, the signal enhancement ratio (SER). AG-013736 significantly inhibited growth of breast tumors in vivo at all doses studied (10-100 mg/kg) and disrupted tumor microvasculature as assessed by DCE-MRI. Tumor endothelial transfer constant (K(ps)) measured with albumin-(GdDTPA)(30) decreased from 0.034+/-0.005 to 0.003+/-0.001 ml min(-1) 100 ml(-1) tissue (P<.0022) posttreatment. No treatment-related change in tumor fractional plasma volume (fPV) was detected. Similarly, in the group of mice studied with GdDTPA DCE-MRI, AG-013736-induced decreases in tumor SER measures were observed. Additionally, our data suggest that 3D MRI-based volume measurements are more sensitive than caliper measurements for detecting small changes in tumor volume. Histological staining revealed decreases in tumor cellularity and microvessel density with treatment. These data demonstrate that both high and low MW DCE-MRI protocols can detect AG-013736-induced changes in tumor microvasculature. Furthermore, the correlative relationship between microvasculature changes and tumor growth inhibition supports DCE-MRI methods as a biomarker of VEGF receptor target inhibition with potential clinical utility.

Heterogeneity in the angiogenic response of a BT474 human breast cancer to a novel vascular endothelial growth factor-receptor tyrosine kinase inhibitor: assessment by voxel analysis of dynamic contrast-enhanced MRI.

PURPOSE: To investigate the heterogeneity in the angiogenic response of a human breast cancer xenograft to a novel vascular endothelial growth factor (VEGF)-receptor tyrosine kinase inhibitor, AG-013736, using dynamic contrast-enhanced MR imaging (DCE-MRI). MATERIALS AND METHODS: Changes in pharmacokinetic parameters in a seven-day interval were compared between AG-treated and control groups, using Gd-DTPA and albumin-(Gd-DTPA)30. A voxel-by-voxel analysis was performed to produce parametric spatial pharmacokinetic parametric maps and histograms. Histogram segmentation was used to quantify the heterogeneity in tumor response to therapy, and compared with conventional descriptive measures of distribution in terms of their capacity to separate control from AG-treated tumors. RESULTS: The albumin-(Gd-DTPA)30 endothelial transfer constant, Kps, showed changes with AG-013736 treatment and tumor growth. The changes were highly heterogeneous for individual segments of the histogram with different Kps values, and the overall patterns in which the frequency distribution changed differed significantly between the two groups. A change in the number of voxels with Kps ranging from 0.03 to 0.14 mL/min/(100 mL tissue) was the most sensitive variable for separating control from AG-treated tumors (P = 0.0008). Parametric maps of the kinetic parameters also showed spatial heterogeneity in tumor response to treatment. The Kps maps depicted rapid development of central necrosis as a result of AG-013736 treatment. Maps of v(p) demonstrated a marked increase at peripheral regions of necrotic areas. Similar trends were noted in the Gd-DTPA rate constant Ktrans distribution. CONCLUSION: This study demonstrates the value of histogram analysis of maps of pharmacokinetic parameters for assessing heterogeneity in tumor response to antiangiogenic therapy. Changes in the number of voxels within certain segments of the Kps histogram were the most sensitive variable for separating control from AG-treated tumors.

Dynamic contrast-enhanced magnetic resonance imaging as a pharmacodynamic measure of response after acute dosing of AG-013736, an oral angiogenesis inhibitor, in patients with advanced solid tumors: results from a phase I study.

PURPOSE: Identifying suitable markers of biologic activity is important when assessing novel compounds such as angiogenesis inhibitors to optimize the dose and schedule of therapy. Here we present the pharmacodynamic response to acute dosing of AG-013736 measured by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). PATIENTS AND METHODS: Thirty-six patients with advanced solid tumors were treated with various doses of AG-013736. In addition to standard measures of objective disease response and pharmacokinetic analysis, DCE-MRI scans were acquired at baseline and repeated at cycle 1--day 2 after the scheduled morning dose of the AG-013736 in 26 patients. Indicators of a vascular response, such as the volume transfer constant (K(trans)) and initial area under the curve (IAUC), were calculated to assess the effect of treatment on tumor vascular function. RESULTS: Evaluable vascular response data were obtained in 17 (65%) of 26 patients. A linear correlation was found in which the percentage change from baseline to day 2 in K(trans) and IAUC was inversely proportional to AG-013736 exposure. Using a conservative a priori assumption that a > or = 50% decrease in K(trans) was indicative of an objective vascular response, a 50% decrease in K(trans) was achieved and corresponded to a plasma AUC(0-24) of > 200 ng . h/mL. CONCLUSION: A sufficient decrease in tumor vascular parameters was observed at a dose chosen for additional phase II testing by conventional toxicity criteria. In addition, the day 2 vascular response measured using DCE-MRI seems to be a useful indicator of drug pharmacology, and additional research is needed to determine if it is a suitable marker for predicting clinical activity.

Development and use of biomarkers in oncology drug development.

Successful development and use of biomarkers will improve the productivity of oncology drug development. Recognition of the importance of biomarkers for speeding drug development is reflected in the precise definitions and concepts proposed by an NIH Working Group to standardize terminology and promote a more coherent and systematic approach to the development and use of biomarkers. Potential clinical biomarkers of drug efficacy are often identified through pre-clinical studies or basic research. Identification of potential biomarkers for use in oncology is moving rapidly forward through continuing advances in clinical imaging technologies, especially molecular and functional imaging. Other rapid advances are a product of the growing availability of new scientific reagents for established technologies and of high-throughput genomic and proteomic technologies that can generate hundreds of potential biomarkers for further evaluation. In certain cases, conventional clinical diagnostic techniques or assays can be adapted for use in pre-clinical models to evaluate their ability to serve as biomarkers for predicting clinical responses to new drug candidates. Evaluation (pre-clinical and clinical) of a potential biomarker is often the longest stage of biomarker development, and standards for evaluation or validation depend on the intended use and stage of clinical development. Biomarkers verified for use in preclinical studies can be used to help select appropriate animal models and lead compounds. Biomarkers verified for use in clinical trials can confirm a drug's pharmacological or biological mechanism of action, guide protocol design, aid patient and dose selection, and help to minimize safety risks. Oncology drug development can be optimized by using a tiered set of clinical biomarkers that predict compound efficacy and safety with increasing confidence at each rise in tier thereby aiding corporate decision-making about advancing compounds. In oncology, a special class of extensively evaluated biomarkers of efficacy (surrogate endpoints) that generally correlate with desired clinical outcomes can be used as a basis for corporate decisions as well as for gaining accelerated provisional regulatory approval of a drug.