Correlative imaging with monoclonal antibodies in colorectal, ovarian, and prostate cancer

Convex-Optimization-Based Compartmental Pharmacokinetic Analysis for Prostate Tumor Characterization Using DCE-MRI

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a powerful imaging modality to study the pharmacokinetics in a suspected cancer/tumor tissue. The pharmacokinetic (PK) analysis of prostate cancer includes the estimation of time activity curves (TACs), and thereby, the corresponding kinetic parameters (KPs), and plays a pivotal role in diagnosis and prognosis of prostate cancer. In this paper, we endeavor to develop a blind source separation algorithm, namely convex-optimization-based KPs estimation (COKE) algorithm for PK analysis based on compartmental modeling of DCE-MRI data, for effective prostate tumor detection and its quantification. The COKE algorithm first identifies the best three representative pixels in the DCE-MRI data, corresponding to the plasma, fast-flow, and slow-flow TACs, respectively. The estimation accuracy of the flux rate constants (FRCs) of the fast-flow and slow-flow TACs directly affects the estimation accuracy of the KPs that provide the cancer and normal tissue distribution maps in the prostate region. The COKE algorithm wisely exploits the matrix structure (Toeplitz, lower triangular, and exponential decay) of the original nonconvex FRCs estimation problem, and reformulates it into two convex optimization problems that can reliably estimate the FRCs. After estimation of the FRCs, the KPs can be effectively estimated by solving a pixel-wise constrained curve-fitting (convex) problem. Simulation results demonstrate the efficacy of the proposed COKE algorithm. The COKE algorithm is also evaluated with DCE-MRI data of four different patients with prostate cancer and the obtained results are consistent with clinical observations.

Preclinical Pharmacology of a Nonsteroidal Ligand for Androgen Receptor-Mediated Imaging of Prostate Cancer

Proper management of prostate cancer patients is highly dependent on the spread of the disease. High expression levels of the androgen receptor (AR) in prostate tumor offer a target for identifying cancer metastasis. We investigated the use of nonsteroidal AR ligands for receptor-mediated imaging as a diagnostic tool for prostate cancer staging. Compound S-26 [S-3-(4-fluorophenoxy)-2-hydroxy-2-methyl-N-(4-cyano-3-iodophenyl)-propionamide]was identified from a series of iodinated ether-linked derivatives of bicalutamide due to its high-AR binding affinity of 3.3 nM (which is similar to testosterone and approximately 25% of the binding affinity of dihydrotestosterone) in an in vitro competitive binding assay using rat prostate cytosol. Furthermore, S-26 exhibited a greater binding affinity (K(i) = 4.4 nM) in a whole-cell binding assay using COS-7 cells transfected with human AR than testosterone (K(i) = 32.9 nM) and dihydrotestosterone (K(i) = 45.4 nM). We also confirmed that sex hormone-binding globulin (SHBG), a plasma protein that binds steroids with high affinity, does not bind with S-26. Cotransfection studies with the estrogen, progesterone, and glucocorticoid receptor indicated that S-26 does not cross-react with other members of the steroid hormone receptor family. The nonsteroidal structure, high-AR binding affinity, specificity, and lack of binding to SHBG indicate that S-26 exhibits favorable properties for further development as an imaging agent for prostate cancer.

Evaluating the return of prostatic adenocarcinoma

Images

Utility of FDG-PET for investigating unexplained plasma CEA elevation in patients with colorectal cancer

OBJECTIVE

To assess the potential role of positron emission tomography (PET) with 2-[18F]fluoro-2-deoxy-D-glucose (FDG) in patients with unexplained rising carcinoembryonic antigen (CEA) levels after the treatment of colorectal cancer.

BACKGROUND

A rising CEA level after the resection of colorectal cancer is an early indicator of tumor recurrence. However, conventional imaging techniques have limited sensitivity for detecting recurrent disease in such patients. Especially after surgical intervention, FDG-PET is rapidly gaining an important role in establishing the extent of disease in the oncology patient.

METHODS

Twenty-two patients with abnormal CEA levels and normal results of conventional methods of tumor detection were studied with FDG-PET. The PET results were compared with pathologic findings (n = 9) and long-term radiologic and clinical follow-up (n = 13).

RESULTS

FDG-PET was abnormal in 17 of 22 patients. Tissue sampling was available in 7 of these 17 patients; all of these had recurrent disease. Definitive curative surgical intervention was performed in four patients. Subsequent dedicated imaging findings and clinical course confirmed the presence of extensive disease in 8 of the remaining 10 patients; the PET results in the other 2 patients were considered falsely positive. FDG-PET was negative in 5 of 22 patients. No disease was found by tissue sampling (n = 2) and clinical follow-up (n = 3). Overall, the positive-predictive value for PET was 89%, (15 of 17) and the negative-predictive value was 100% (5 of 5).

CONCLUSIONS

When conventional examinations are normal, FDG-PET is a valuable imaging tool in patients who have a rising CEA level after colorectal surgery.

Radiolabeled somatostatin analogs in prostate cancer

Vapreotide (RC-160), a somatostatin analog, was labeled with 99mTC by a direct method and also by using CPTA [1,4,8,11-tetraazacyclotetradecane] as a bifunctional chelating agent. The labeled compounds were evaluated in nude mice bearing experimental human prostate cancers. In these studies, 111In-DTPA-D-Phe-Octreotide (111In-DTPA-octreotide) served as a standard and 99mTc-oxytocin as a receptor-non-specific control. 99mTc-octreotide was also used. The 24 htumor uptake of 99mTc-RC-160 was nearly 400% higher, (p < 0.05), than that of 111In-DTPA-octreotide and diminished upon receptor blocking. In all tissues except the kidneys, the uptake of 99mTc-RC-160 was also higher than that of 111In-DTPA-octreotide. The uptake of 99mTc-RC-160 was influenced by the amount of peptide injected and the best tumor/muscle and tumor/blood ratios were obtained when only one micrograms of the peptide (200 Ci/mmol) was administered.

Quantitative analysis of In-111 satumomab pendetide immunoscintigraphy. An aid to visual interpretation of images in patients with suspected carcinomatosis

The diagnosis of the diffuse intrapertioneal spread of ovarian or colorectal carcinoma (carcinomatosis) can be difficult when based on visual interpretation of immunoscintigraphic images alone. Twenty-nine patients with either colorectal or ovarian cancer were retrospectively evaluated by three technologists for carcinomatosis employing a quantitative analysis technique that compares uptake of In-111 satumomab pendetide (Oncoscint CR/ OV, Cytogen Corp., Princeton, NJ) in a region of interest in the femoral vascular bundle to the uptake in two regions of interest in the lower abdomen, resulting in an uptake ratio (UR). All 29 patients underwent laparotomy after immunoscintigraphy. Of the 29 patients evaluated, 7 had histologically proven carcinomatosis obtained from the laparotomy. Using quantitative analysis, patients who did not have carcinomatosis had a mean uptake ratio of 1.12, and patients with carcinomatosis had a mean uptake ratio of 2.12. The differences between the means of these two groups of patients was statistically significant for all three technologists (P < .05). The results of this study indicate that there is a significant difference in uptake ratios between patients with carcinomatosis and those without it, and that quantitative analysis can be a useful adjunct to visual interpretation.