Indium-111 capromab pendetide (ProstaScint) imaging to detect recurrent and metastatic prostate cancer

Radioimmunotheragnosis in Cancer Research

The combination of immunoPET-where an antibody (Ab) is labeled with an isotope for PET imaging-and radioimmunotherapy (RIT), using the same antibody with a therapeutic isotope, offers significant advantages in cancer management. ImmunoPET allows non-invasive imaging of antigen expression, which aids in patient selection for subsequent radioimmunotherapy. It also facilitates the assessment of tumor response to therapy, allowing for treatment adjustments if necessary. In addition, immunoPET provides critical pharmacokinetic data, including antibody biodistribution and clearance rates, which are essential for dosimetry calculations and treatment protocol optimization. There are still challenges to overcome. Identifying appropriate target antigens that are selectively expressed on cancer cells while minimally expressed on normal tissues remains a major hurdle to reduce off-target toxicity. In addition, it is critical to optimize the pharmacokinetics of radiolabeled antibodies to maximize tumor uptake and minimize normal tissue uptake, particularly in vital organs such as the liver and kidney. This approach offers the potential for targeted and personalized cancer therapy with reduced systemic toxicity by exploiting the specificity of monoclonal antibodies and the cytotoxic effects of radiation. However, further research is needed to address remaining challenges and to optimize these technologies for clinical use.

Human ABC and SLC Transporters: The Culprit Responsible for Unspecific PSMA-617 Uptake?

[177Lu]Lu-PSMA-617 has recently been successfully approved by the FDA, the MHRA, Health Canada and the EMA as Pluvicto®. However, salivary gland (SG) and kidney toxicities account for its main dose-limiting side-effects, while its corresponding uptake and retention mechanisms still remain elusive. Recently, the presence of different ATP-binding cassette (ABC) transporters, such as human breast cancer resistance proteins (BCRP), multidrug resistance proteins (MDR1), multidrug-resistance-related proteins (MRP1, MRP4) and solute cassette (SLC) transporters, such as multidrug and toxin extrusion proteins (MATE1, MATE2-K), organic anion transporters (OAT1, OAT2v1, OAT3, OAT4) and peptide transporters (PEPT2), has been verified at different abundances in human SGs and kidneys. Therefore, our aim was to assess whether [177Lu]Lu-PSMA-617 and [225Ac]Ac-PSMA-617 are substrates of these ABC and SLC transporters. For in vitro studies, the novel isotopologue ([α,β-3H]Nal)Lu-PSMA-617 was used in cell lines or vesicles expressing the aforementioned human ABC and SLC transporters for inhibition and uptake studies, respectively. The corresponding probe substrates and reference inhibitors were used as controls. Our results indicate that [177Lu]Lu-PSMA-617 and [225Ac]Ac-PSMA-617 are neither inhibitors nor substrates of the examined transporters. Therefore, our results show that human ABC and SLC transporters play no central role in the uptake and retention of [177Lu]Lu-PSMA-617 and [225Ac]Ac-PSMA-617 in the SGs and kidneys nor in the observed toxicities.

Clinical Applications of PSMA PET Examination in Patients with Prostate Cancer

Simple Summary

The prostate specific membrane antigens, abbreviated as PSMAs, are type II membrane proteins that are highly ex-pressed on the surface of malignant prostate tissue in prostate cancer (PCa), particularly in aggressive, andro-gen-deprived, metastatic, and hormone-refractory PCa. Today, radionuclides that bind to these PSMA peptides are widely available for diagnostic and therapeutic purposes to specifically image and target prostate tumor cells at molec-ular level. In this descriptive review, we aimed to emphasize the usefulness of PSMA positron emission tomography (PET) examination in the management of patients with various stages of PCa. In addition, we outlined the main pitfalls and limitations of this scan to avoid misinterpretation of the results and to improve the decision making process in rela-tion to the patient’s further treatment. We concluded that PSMA PET examination in primary PCa patients has an es-sential role in the high-risk group. It is the new imaging standard in patients with in biochemical recurrence PCa and plays an important role in treatment decision. Furthermore, PSMA PET scan is a gold standard for the evaluation of PSMA targeted therapies in patients having progress of the disease. Future prospective studies, particularly on the im-pact of PSMA PET on therapy stratification, may further strengthen the role of PSMA in the treatment of PCa patients.

Abstract

With the progressive aging of the population in industrially developed countries, as well as advances in diagnostic and biopsy techniques and improvements in patient awareness, the incidence of prostate cancer (PCa) is continuously increasing worldwide. Therefore, PCa is currently considered as the second leading cause of tumor-related death. Early detection of the tumor and its metastasis is essential, as the rate of disease recurrence is high and occurs in 27% to 53% of all patients who underwent curative therapy with radical prostatectomy or local radiotherapy. In this regard, the prostate specific membrane antigens, abbreviated as PSMAs, are type II membrane proteins that are highly expressed on the surface of malignant prostate tissue in PCa, particularly in aggressive, androgen-deprived, metastatic, and hormone-refractory PCa, and they are inversely associated with the androgen level. Up to 95% of adenocarcinomas of the prostate express PSMA receptors on their surface. Today, radionuclides that bind to these PSMA peptides are widely accepted for diagnostic and therapeutic purposes to specifically image and target prostate tumor cells at the molecular level, a process referred to as targeted theranostics. Numerous studies have demonstrated that the integration of these peptides into diagnostic and therapeutic procedures plays a critical role in the primary staging and treatment decisions of especially high-risk PCa, expands therapeutic options for patients with advanced stage of prostate tumor, and prolongs patients’ survival rate. In this review article, we intend to briefly spotlight the latest clinical utilization of the PSMA-targeted radioligand PET imaging modality in patients with different stages of PCa. Furthermore, limitations and pitfalls of this diagnostic technique are presented.

ImmunoPET: Antibody-Based PET Imaging in Solid Tumors

Immuno-positron emission tomography (immunoPET) is a molecular imaging modality combining the high sensitivity of PET with the specific targeting ability of monoclonal antibodies. Various radioimmunotracers have been successfully developed to target a broad spectrum of molecules expressed by malignant cells or tumor microenvironments. Only a few are translated into clinical studies and barely into clinical practices. Some drawbacks include slow radioimmunotracer kinetics, high physiologic uptake in lymphoid organs, and heterogeneous activity in tumoral lesions. Measures are taken to overcome the disadvantages, and new tracers are being developed. In this review, we aim to mention the fundamental components of immunoPET imaging, explore the groundbreaking success achieved using this new technique, and review different radioimmunotracers employed in various solid tumors to elaborate on this relatively new imaging modality.

Monoclonal antibody based radiopharmaceuticals for imaging and therapy

The concept of personalized medicine has been steadily growing for the past decades. Monoclonal antibodies (mAbs) are undoubtedly playing an important role in the transition away from conventional medical practice to a more tailored approach to deliver the best therapy with the highest safety margin to a specific patient. In certain instances, mAbs and antibody drug conjugates (ADCs) may represent the preferred therapeutic option for several types of cancers due to their high specificity and affinity to the antigen. Monoclonal antibodies can be labeled with specific radionuclides well-suited for PET (Positron Emission Tomography) or gamma camera scintigraphy. The use of radiolabeled mAbs allows the interrogation of specific biomarkers and assessment of tumor heterogeneity in vivo by a single diagnostic imaging scan that includes the whole-body in the field-of-view. Moreover, the same mAb can then be radiolabeled with an analogous radionuclide for the delivery of beta-minus radiation or alpha-particles as part of a radioimmunotherapy (RIT) approach. However, the path to develop, validate, and implement mAb-based radiopharmaceuticals from bench-to-bedside is complex due to the extensive pre-clinical experiments and toxicological studies required, and the necessity of labor-intensive clinical trials that often require multi-time-point imaging and blood draws for internal radiation dosimetry and pharmacokinetics. As more mAb-based radiopharmaceuticals have been developed and evaluated, the opportunities and limitations offered by mAbs have become better defined. Our aim with this manuscript is therefore to provide an overview of the recent advances in the development of mAb-based radiopharmaceuticals and their clinical applications in Oncology.

Prostate-Specific Membrane Antigen-Targeted Radiopharmaceuticals in Diagnosis and Therapy of Prostate Cancer: Current Status and Future Perspectives

Prostate cancer is the most common cancer to affect men in the United States and the second most common cancer in men worldwide. Prostate-specific membrane antigen (PSMA)-based positron emission tomography (PET) imaging has become increasingly popular as a novel molecular imaging technique capable of improving the clinical management of patients with prostate cancer. To date, several ⁶⁸Ga and ¹⁸F-labeled PSMA-targeted molecules have shown promising results in imaging patients with recurrent prostate cancer using PET/computed tomography (PET/CT). Studies of involving PSMA-targeted radiopharmaceuticals also suggest a higher sensitivity and specificity, along with an improved detection rate over conventional imaging (CT scan and methylene diphosphonate bone scintigraphy) and ¹¹C/¹⁸F-choline PET/CT. In addition, PSMA-617 and PSMA I&T ligands can be labeled with α- and β-emitters (e.g., ²²⁵Ac, ⁹⁰Y, and ¹⁷⁷Lu) and serve as a theranostic tool for patients with metastatic prostate cancer. While the clinical impact of such concept remains to be verified, the preliminary results of PSMA molecular radiotherapy are very encouraging. Herein, we highlighted the current status of development and future perspectives of PSMA-targeted radiopharmaceuticals and their clinical applications.

ImmunoPET: Concept, Design, and Applications

Immuno-positron emission tomography (immunoPET) is a paradigm-shifting molecular imaging modality combining the superior targeting specificity of monoclonal antibody (mAb) and the inherent sensitivity of PET technique. A variety of radionuclides and mAbs have been exploited to develop immunoPET probes, which has been driven by the development and optimization of radiochemistry and conjugation strategies. In addition, tumor-targeting vectors with a short circulation time (e.g., Nanobody) or with an enhanced binding affinity (e.g., bispecific antibody) are being used to design novel immunoPET probes. Accordingly, several immunoPET probes, such as 89Zr-Df-pertuzumab and 89Zr-atezolizumab, have been successfully translated for clinical use. By noninvasively and dynamically revealing the expression of heterogeneous tumor antigens, immunoPET imaging is gradually changing the theranostic landscape of several types of malignancies. ImmunoPET is the method of choice for imaging specific tumor markers, immune cells, immune checkpoints, and inflammatory processes. Furthermore, the integration of immunoPET imaging in antibody drug development is of substantial significance because it provides pivotal information regarding antibody targeting abilities and distribution profiles. Herein, we present the latest immunoPET imaging strategies and their preclinical and clinical applications. We also emphasize current conjugation strategies that can be leveraged to develop next-generation immunoPET probes. Lastly, we discuss practical considerations to tune the development and translation of immunoPET imaging strategies.

Review of Gallium-68 PSMA PET/CT Imaging in the Management of Prostate Cancer

Over 90% of prostate cancers over-express prostate specific membrane antigen (PSMA) and these tumor cells may be accurately targeted for diagnosis by 68Ga-PSMA-positron emission tomography/computed tomography (68Ga-PSMA-PET/CT) imaging. This novel molecular imaging modality appears clinically to have superseded CT, and appears superior to MR imaging, for the detection of metastatic disease. 68Ga-PSMA PET/CT has the ability to reliably stage prostate cancer at presentation and can help inform an optimal treatment approach. Novel diagnostic applications of 68Ga-PSMA PET/CT include guiding biopsy to improve sampling accuracy, and guiding surgery and radiotherapy. In addition to facilitating the management of metastatic castrate resistant prostate cancer (mCRPC), 68Ga-PSMA can select patients who may benefit from targeted systemic radionuclide therapy. 68Ga-PSMA is the diagnostic positron-emitting theranostic pair with the beta emitter Lutetium-177 PSMA (177Lu-PSMA) and alpha-emitter Actinium-225 PSMA (225Ac-PSMA) which can both be used to treat PSMA-avid metastases of prostate cancer in the molecular tumor-targeted approach of theranostic nuclear oncology.

Hybrid Imaging in Oncology

In oncology various imaging modalities play a crucial role in diagnosis, staging, restaging, treatment monitoring and follow up of various cancers. Stand-alone morphological imaging like computerized tomography (CT) and magnetic resonance imaging (MRI) provide a high magnitude of anatomical details about the tumor but are relatively dumb about tumor physiology. Stand-alone functional imaging like positron emission tomography (PET) and single photon emission tomography (SPECT) are rich in functional information but provide little insight into tumor morphology. Introduction of first hybrid modality PET/CT is the one of the most successful stories of current century which has revolutionized patient care in oncology due to its high diagnostic accuracy. Spurred on by this success, more hybrid imaging modalities like SPECT/CT and PET/MR were introduced. It is the time to explore the potential applications of the existing hybrid modalities, developing and implementing standardized imaging protocols and train users in nuclear medicine and radiology. In this review we discuss three existing hybrid modalities with emphasis on their technical aspects and clinical applications in oncology.

Targeting of radiolabeled J591 antibody to PSMA-expressing tumors: optimization of imaging and therapy based on non-linear compartmental modeling

Background

We applied a non-linear immunokinetic model to quantitatively compare absolute antibody uptake and turnover in subcutaneous LNCaP human prostate cancer (PCa) xenografts of two radiolabeled forms of the humanized anti-prostate-specific membrane antigen (PSMA) monoclonal antibody J591 (¹²⁴I-J591 and ⁸⁹Zr-J591). Using the model, we examined the impact of dose on the tumor and plasma positron emission tomography (PET)-derived time-activity curves. We also sought to predict the optimal targeting index (ratio of integrated-tumor-to-integrated-plasma activity concentrations) for radioimmunotherapy.

Methods

The equilibrium rates of antibody internalization and turnover in the tumors were derived from PET images up to 96 h post-injection using compartmental modeling with a non-linear transfer rate. In addition, we serially imaged groups of LNCaP tumor-bearing mice injected with ⁸⁹Zr-J591 antibody doses ranging from antigen subsaturating to saturating to examine the suitability of using a non-linear approach and derived the time-integrated concentration (in μM∙hours) of administered tracer in tumor as a function of the administered dose of antibody.

Results

The comparison of ¹²⁴I-J591 and ⁸⁹Zr-J591 yielded similar model-derived values of the total antigen concentration and internalization rate. The association equilibrium constant (k_a) was twofold higher for ¹²⁴I, but there was a ~tenfold greater tumoral efflux rate of ¹²⁴I from tumor compared to that of ⁸⁹Zr. Plots of surface-bound and internalized radiotracers indicate similar behavior up to 24 h p.i. for both ¹²⁴I-J591 and ⁸⁹Zr-J591, with the effect of differential clearance rates becoming apparent after about 35 h p.i. Estimates of J591/PSMA complex turnover were 3.9–90.5 × 10¹² (for doses from 60 to 240 μg) molecules per hour per gram of tumor (20 % of receptors internalized per hour).

Conclusions

Using quantitative compartmental model methods, surface binding and internalization rates were shown to be similar for both ¹²⁴I-J591 and ⁸⁹Zr-J591 forms, as expected. The large difference in clearance rates of the radioactivity from the tumor is likely due to differential trapping of residualizing zirconium versus non-residualizing iodine. Our non-linear model was found to be superior to a conventional linear model. This finding and the calculated activity persistence time in tumor have important implications for radioimmunotherapy and other antibody-based therapies in patients.

Use of radiopharmaceuticals in diagnostic nuclear medicine in the United States: 1960-2010

To reconstruct reliable nuclear medicine-related occupational radiation doses or doses received as patients from radiopharmaceuticals over the last five decades, the authors assessed which radiopharmaceuticals were used in different time periods, their relative frequency of use, and typical values of the administered activity. This paper presents data on the changing patterns of clinical use of radiopharmaceuticals and documents the range of activity administered to adult patients undergoing diagnostic nuclear medicine procedures in the U.S. between 1960 and 2010. Data are presented for 15 diagnostic imaging procedures that include thyroid scan and thyroid uptake; brain scan; brain blood flow; lung perfusion and ventilation; bone, liver, hepatobiliary, bone marrow, pancreas, and kidney scans; cardiac imaging procedures; tumor localization studies; localization of gastrointestinal bleeding; and non-imaging studies of blood volume and iron metabolism. Data on the relative use of radiopharmaceuticals were collected using key informant interviews and comprehensive literature reviews of typical administered activities of these diagnostic nuclear medicine studies. Responses of key informants on relative use of radiopharmaceuticals are in agreement with published literature. Results of this study will be used for retrospective reconstruction of occupational and personal medical radiation doses from diagnostic radiopharmaceuticals to members of the U.S. radiologic technologists' cohort and in reconstructing radiation doses from occupational or patient radiation exposures to other U.S. workers or patient populations.

A paradigm shift from anatomic to functional and molecular imaging in the detection of recurrent prostate cancer

Approximately a third of men with localized prostate cancer who are treated with external beam radiation therapy (EBRT) or radical prostatectomy (RP) develop biochemical failure (BF). Presumably, BF will progress to distant metastasis and prostate cancer-specific mortality in some patients over subsequent years. Accurate detection of recurrent disease is important because it allows for appropriate treatment selection (e.g., local vs systemic therapy) and early delivery of therapy (e.g., salvage EBRT), which affect patient outcome. In this article, we discuss the paradigm shift in imaging technology in the detection of recurrent prostate cancer. First, we discuss the commonly used morphological and anatomical imaging modalities and their role in the post-RP and post-EBRT settings of BF. Second, we discuss the accuracy of functional and molecular imaging techniques, many of which are under investigation. Further studies are needed to establish the role of imaging techniques for detection of cancer recurrence and clinical decision-making.

Oncologic applications of diffusion-weighted MRI in the body

Diffusion-weighted MRI (DWI) allows the detection of malignancies in the abdomen and pelvis. Lesion detection and characterization using DWI largely depends on the increased cellularity of solid or cystic lesions compared with the surrounding tissue. This increased cellularity leads results in restricted diffusion as indicated by reduction in the apparent diffusion coefficient (ADC). Low pretreatment ADC values of several malignancies have been shown to be predictive of better outcome. DWI can assess response to systemic or regional treatment of cancer at a cellular level and will therefore detect successful treatment earlier than anatomical measures. In this review, we provide a brief technical overview of DWI, discuss quantitative image analysis approaches, and review studies which have used DWI for the purpose of detection and characterization of malignancies as well as the early prediction of treatment response.

ACR Appropriateness Criteria® posttreatment follow-up of prostate cancer

Although prostate cancer can be effectively treated, recurrent or residual disease after therapy is not uncommon and is usually detected by a rise in prostate-specific antigen. Patients with biochemical prostate-specific antigen relapse should undergo a prompt search for the presence of local recurrence or distant metastatic disease, each requiring different forms of therapy. Various imaging modalities and image-guided procedures may be used in the evaluation of these patients. Literature on the indications and usefulness of these radiologic studies and procedures in specific clinical settings is reviewed. The ACR Appropriateness Criteria(®) are evidence-based guidelines for specific clinical conditions that are reviewed every 2 years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer-reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances in which evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.

Tissue distribution studies of protein therapeutics using molecular probes: molecular imaging

Molecular imaging techniques for protein therapeutics rely on reporter labels, especially radionuclides or sometimes near-infrared fluorescent moieties, which must be introduced with minimal perturbation of the protein's function in vivo and are detected non-invasively during whole-body imaging. PET is the most sensitive whole-body imaging technique available, making it possible to perform biodistribution studies in humans with as little as 1 mg of injected antibody carrying 1 mCi (37 MBq) of zirconium-89 radiolabel. Different labeling chemistries facilitate a variety of optical and radionuclide methods that offer complementary information from microscopy and autoradiography and offer some trade-offs in whole-body imaging between cost and logistic difficulty and image quality and sensitivity (how much protein needs to be injected). Interpretation of tissue uptake requires consideration of label that has been catabolized and possibly residualized. Image contrast depends as much on background signal as it does on tissue uptake, and so the choice of injected dose and scan timing guides the selection of a suitable label and helps to optimize image quality. Although only recently developed, zirconium-89 PET techniques allow for the most quantitative tomographic imaging at millimeter resolution in small animals and they translate very well into clinical use as exemplified by studies of radiolabeled antibodies, including trastuzumab in breast cancer patients, in The Netherlands.

123I-MIP-1072, a small-molecule inhibitor of prostate-specific membrane antigen, is effective at monitoring tumor response to taxane therapy

Because traditional endpoints in oncology trials are not always applicable for metastatic prostate cancer, better ways of following response to treatment are needed. Prostate-specific membrane antigen (PSMA) is a transmembrane protein expressed in normal human prostate epithelium and is upregulated in prostate cancer. (S)-2-(3-((S)-1-carboxy-5-((4-(123)I-iodobenzyl)amino)pentyl)ureido)pentanedioic acid, (123)I-MIP-1072, targets PSMA and was evaluated for monitoring the growth of PSMA-positive LNCaP cells in vitro and as xenografts after paclitaxel therapy.

METHODS

LNCaP and 22Rv1 cells were treated with paclitaxel (0-100 nM) for 48 h, after which binding of (123)I-MIP-1072 was examined. Cell number was determined by MTS assay, and PSMA expression was analyzed by Western blotting. LNCaP xenograft-bearing mice were treated with paclitaxel (6.25 mg/kg) for 3.5 cycles of 5 d on and 2 d off. Tissue distribution of (123)I-MIP-1072 was determined on days 2 and 23 from the start of paclitaxel treatment.

RESULTS

Paclitaxel (10-100 nM) inhibited LNCaP and 22Rv1 cell growth after 48 h, and binding of (123)I-MIP-1072 was proportional to cell number. Western blot analysis verified there was no paclitaxel-dependent change in PSMA expression. Treatment of LNCaP xenografts with paclitaxel resulted in a decrease in tumor volume (-21%), compared with an increase in the untreated xenografts (+205%) by day 23. Tumor uptake of (123)I-MIP-1072 was proportional to changes in tumor mass: decreased by paclitaxel treatment and increased in untreated mice.

CONCLUSION

Treatment of LNCaP cells or xenograft tumors with paclitaxel resulted in growth inhibition, which was detected with (123)I-MIP-1072. The high specificity of (123)I-MIP-1072 for prostate cancer may allow monitoring of tumor progression in patients before, during, and after chemotherapy.

Salvage radiotherapy for patients with PSA relapse following radical prostatectomy: issues and challenges

A progressively rising level of serum prostate specific antigen (PSA) after radical prostatectomy (RP) invariably indicates the recurrence of prostate cancer. The optimal management of patients with post-RP PSA relapse has remained uncertain due to a wide variability in the natural course of post-RP PSA relapse and the inability to separate a recurrent disease confined to the prostate bed from that with occult distant metastasis. Management uncertainty is further compounded by the lack of phase III clinical studies demonstrating which therapeutic approach, if any, would prolong life with no significant morbidity. Radiotherapy has been the main therapeutic modality with a curative potential for patients with post-RP PSA relapse. This review article depicts issues and challenges in the management of patients with post-RP PSA relapse, presents the literature data for the efficacy of salvage radiotherapy, either alone or in combination of androgen ablation therapy, and discusses future directions that can optimize treatment strategies.

Antibody mass escalation study in patients with castration-resistant prostate cancer using 111In-J591: lesion detectability and dosimetric projections for 90Y radioimmunotherapy

J591, a monoclonal antibody that targets the external domain of the prostate-specific membrane antigen, has potential as an agent for radioimmunotherapy. A pilot trial was performed in patients with prostate cancer using repetitive administrations of escalating masses of J591. An analysis was performed to assess lesion detectability by (111)In-J591 gamma-camera imaging compared with standard imaging methods and the effect of increasing antibody mass on lesion detectability, biodistribution, and dosimetry.

METHODS

Fourteen patients with metastatic prostate cancer received escalating amounts (10, 25, 50, and 100 mg) of J591 in a series of administrations each separated by 3 wk. All antibody administrations included a fixed amount of the radiolabeled antibody (111)In-1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid-J591 ((111)In-DOTA-J591) (2 mg of J591 labeled with 185 MBq [5 mCi] of (111)In via the chelating agent DOTA). Three whole-body gamma-camera scans with at least 1 SPECT scan together with multiple whole-body counting-rate measurements and serum activity-concentration measurements were obtained in all patients. Images were analyzed for distribution and lesion targeting. Estimates of clearance rates and liver and lesion uptake were made for each treatment cycle. These estimates were used to generate dosimetric projections for radioimmunotherapy with (90)Y-labeled J591.

RESULTS

A total of 80 lesions in 14 patients were detected. Both skeletal and soft-tissue diseases were targeted by the antibody as seen on (111)In-J591 scans. The antibody localized to 93.7% of skeletal lesions detected by conventional imaging. Clearance of radioactivity from the whole body, serum, and liver was dependent on antibody mass. Normalized average values of the ratio of residence times between lesion and liver for 10, 25, 50, and 100 mg of antibody were 1.0, 1.9, 3.2, and 4.0. Dosimetric projections for radioimmunotherapy with (90)Y-labeled J591 suggested similar absorbed doses to lesions for treatment at the maximally tolerated activity (MTA), irrespective of antibody mass. However, absorbed doses to liver at the MTA would be antibody mass-dependent with estimates of 20, 10, 7, and 5 Gy for 10, 25, 50, and 100 mg of J591.

CONCLUSION

The proportion of the amount of antibody increased in lesions and decreased in the liver with increasing mass of administered antibody up to a dose of 50 mg. Proportional hepatic uptake continued to decrease with increasing antibody mass up to 100 mg. The optimal antibody mass for radioimmunotherapy would therefore appear to be greater than or equal to 50 mg.

Targeting of biotinylated oligonucleotides to prostate tumors with antibody-based delivery vehicles

Specific delivery of therapeutic agents to tumor sites remains a problem and requires a nontoxic carrier able to bind a specific tumor cell marker. Although antibodies have been utilized as protein carriers for different types of drugs, they have not been employed for delivery of antisense oligonucleotides (ODNs). In this study, we modified monoclonal antibodies to target biotinylated ODNs to prostatic tumors which express prostate specific antigen (PSA) and prostate specific membrane antigen (PSMA). Modified antibodies retained immunoreactivity and demonstrated an ability to form complexes with ODNs. Biodistribution of (35)S-oligonucleotide-antibody complexes was also examined in nude mice bearing human derived LNCaP prostatic tumors. Delivering ODNs with modified prostate specific antibodies produced greater tissue uptake and higher blood levels with both PSA and PSMA directed antibodies. While tumor uptake was not significantly improved after 24 h, the overall results of this study provide some additional insights into the complexity of the antibody-mediated delivery of ODNs in vivo. The strategies employed here for the selective delivery of ODNs warrant further investigation.

Enhancing the utility of prostascint SPECT scans for patient management

This project investigated reducing the artifact content of In-ill ProstaScint SPECT scans for use in treatment planning and management. Forty-one patients who had undergone CT or MRI scans and simultaneous Tc-99m RBC/In-111 ProstaScint SPECT scans were included. SPECT volume sets, reconstructed using Ordered Set-Expectation Maximum (OS-EM) were compared against those reconstructed with standard Filtered Back projection (FBP). Bladder activity in Tc-99m scans was suppressed within an ellipsoidal volume. Tc-99m voxel values were subtracted from the corresponding In-111 after scaling based on peak activity within the descending aorta. The SPECT volume data sets were merged with the CT or MRI scans before and after processing. Volume merging, based both on visual assessment and statistical evaluation, was not affected. Thus iterative reconstruction together with bladder suppression and blood pool subtraction may improve the interpretation and utility of ProstaScint SPECT scans for patient management.

Clinical Utility of Radiolabeled Monoclonal Antibodies in Prostate Cancer

Prostate cancer represents an ideal target for radioimmunotherapy based on the pattern of spread, including bone marrow and lymph nodes, sites that typically receive high levels of circulating antibody, and the small volume of disease, ideally suited for antibody delivery and antigen access. This review explores possible antibody targets in prostate cancer and focuses on the potential role for radioimmunotherapy by highlighting several clinical trials involving radiolabeled anti-prostate-specific membrane antigen monoclonal antibody J591. Prostate-specific membrane antigen, a highly prostate-restricted transmembrane glycoprotein with increased expression in high-grade, metastatic, and hormone-refractory disease, represents an ideal target for monoclonal antibody therapy in prostate cancer. Radiolabeled anti-prostate-specific membrane antigen monoclonal antibody J591 trials using the radiometals yttrium-90 and lutetium-177 have demonstrated manageable myelotoxicity, no significant nonhematologic toxicity, excellent targeting of soft-tissue and bone metastases, and preliminary efficacy including prostate-specific antigen and measurable disease responses. Additional studies are under way to better define the activity of radiolabeled antibody therapy as well as the role for fractionated therapy and combination approaches with taxane-based chemotherapy.

The progress and promise of molecular imaging probes in oncologic drug development

As addressed by the recent Food and Drug Administration Critical Path Initiative, tools are urgently needed to increase the speed, efficiency, and cost-effectiveness of drug development for cancer and other diseases. Molecular imaging probes developed based on recent scientific advances have great potential as oncologic drug development tools. Basic science studies using molecular imaging probes can help to identify and characterize disease-specific targets for oncologic drug therapy. Imaging end points, based on these disease-specific biomarkers, hold great promise to better define, stratify, and enrich study groups and to provide direct biological measures of response. Imaging-based biomarkers also have promise for speeding drug evaluation by supplementing or replacing preclinical and clinical pharmacokinetic and pharmacodynamic evaluations, including target interaction and modulation. Such analyses may be particularly valuable in early comparative studies among candidates designed to interact with the same molecular target. Finally, as response biomarkers, imaging end points that characterize tumor vitality, growth, or apoptosis can also serve as early surrogates of therapy success. This article outlines the scientific basis of oncology imaging probes and presents examples of probes that could facilitate progress. The current regulatory opportunities for new and existing probe development and testing are also reviewed, with a focus on recent Food and Drug Administration guidance to facilitate early clinical development of promising probes.

Two constructed antibody-derived delivery vehicles for targeting oligodeoxynucleotides to prostate tumors expressing prostate specific antigen

We evaluated the ability of antibody-derived delivery vehicles (DVs) to direct synthetic biotinylated oligodeoxynucleotides (ODNs) to prostate tumors in vitro. A monoclonal mouse antibody raised against prostate-specific antigen (PSA) was modified by two approaches to produce either: (1) a bispecific delivery vehicle recognizing both PSA and biotin (DV(Hc)), or (2) an avidin-conjugated anti-PSA delivery vehicle (DV(PSA)). Immunoreactivity of the DVs and their ability to form complexes were tested in vitro. Although both DVs retained immunoreactivity and were able to form complexes with biotinylated ODNs, the avidin modification method was more efficient. This method may be useful for selective delivery of antisense ODNs to prostate tumors.

Histologic confirmation of lesions identified by Prostascint scan following definitive treatment

The purpose of the study was to determine the accuracy of the monoclonal antibody (Mab) [Prostascint, Cytogen, Inc.] scan for the detection of nodal metastases using histologic examination of surgical lymphadenectomy specimens as the standard of reference. We reviewed the records of 31 patients who had undergone biopsy after monoclonal antibody scan. Histologic evaluation was obtained for a total of 31 patients and 43 pathology samples. When analyzed by surgical site, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy of the Mab scan were 94%, 42%, 53%, 92% and 65%, respectively. When analyzed by individual patient, the same data for the Mab scan were 100%, 33%, 62%, 100% and 68%, respectively. Current noninvasive studies are not sufficiently accurate to reliably determine the presence of metastatic nodal disease from prostate cancer. This series illustrates the importance of rigorous clinical evaluation of future methods that are designed to detect microscopic metastatic disease of any neoplasm.

Phase I trial of yttrium-90-labeled anti-prostate-specific membrane antigen monoclonal antibody J591 for androgen-independent prostate cancer

PURPOSE

To determine the maximum-tolerated dose (MTD), toxicity, human antihuman antibody (HAHA) response, pharmacokinetics, organ dosimetry, targeting, and preliminary efficacy of yttrium-90-labeled anti-prostate-specific membrane antigen monoclonal antibody J591 ((90)Y-J591) in patients with androgen-independent prostate cancer (PC).

PATIENTS AND METHODS

Patients with androgen-independent PC and evidence of disease progression received indium-111-J591 for pharmacokinetic and biodistribution determinations followed 1 week later by (90)Y-J591 at five dose levels: 5, 10, 15, 17.5, and 20 mCi/m(2). Patients were eligible for up to three re-treatments if platelet and neutrophil recovery was satisfactory.

RESULTS

Twenty-nine patients with androgen-independent PC received (90)Y-J591, four of whom were re-treated. Dose limiting toxicity (DLT) was seen at 20 mCi/m(2), with two patients experiencing thrombocytopenia with non-life-threatening bleeding episodes requiring platelet transfusions. The 17.5-mCi/m(2) dose level was determined to be the MTD. No re-treated patients experienced DLT. Nonhematologic toxicity was not dose limiting. Targeting of known sites of bone and soft tissue metastases was seen in the majority of patients. No HAHA response was seen. Antitumor activity was seen, with two patients experiencing 85% and 70% declines in prostate-specific antigen (PSA) levels lasting 8 and 8.6 months, respectively, before returning to baseline. Both patients had objective measurable disease responses. An additional six patients (21%) experienced PSA stabilization.

CONCLUSION

The recommended dose for (90)Y-J591 is 17.5 mCi/m(2). Acceptable toxicity, excellent targeting of known sites of PC metastases, and biologic activity in patients with androgen-independent PC warrant further investigation of (90)Y-J591 in the treatment of patients with PC.

DC therapy for prostate cancer

The wide range of currently available treatments for metastatic prostate cancer have demonstrated a modest palliative effect, but none to date has shown an increase in overall survival. The immune system has evolved to protect against infection, however, the modulation of this system represents the possibility of allowing it to identify and destroy cancer cells. The immune system is capable of inciting a powerful immune response against tissues, in the form of transplant rejection, and the potential exists to harness these powers to fight against tumors. Modest clinical responses have been seen in patients with metastatic prostate cancer treated with DC therapies; however, no increase in overall survival has been demonstrated. The current state of DC immunotherapy for prostate cancer is reviewed.

Diagnosis of local recurrence after radical prostatectomy

In the long-term there is biochemical evidence of recurrent prostate carcinoma in approximately 40% of patients after radical prostatectomy (RP). Detecting the site of recurrence (local vs distant) is critical for defining the optimum treatment. Pathological and clinical variables, e.g. Gleason score, involvement of seminal vesicles or lymph nodes, margin status at surgery, and especially the timing and pattern of prostate-specific antigen (PSA) recurrence, may help to predict the site of relapse. Transrectal ultrasonography (TRUS) of the prostatic fossa in association with TRUS-guided needle biopsy is considered more sensitive than a digital rectal examination for detecting local recurrence, especially if PSA levels are low. Although it cannot detect minimal tumour mass at very low PSA levels (< 1 ng/mL) TRUS biopsy is presently the most sensitive method for detecting local recurrence. Nevertheless, the conclusive role of biopsy of the vesico-urethral anastomosis remains unclear. However, 111In-capromab pendetide scintigraphy and [11C]-choline tomography (which are better than conventional imaging for detecting metastatic tumour), have low detection rates for local disease and are considered complementary to TRUS in this setting. Patients with a high PSA after RP may be managed with external beam salvage radiotherapy. An initial PSA of < 1 ng/mL, Gleason score < 8 and radiation dose of 66-70 Gy seem to be key factors in determining success. Although a positive TRUS anastomotic biopsy may predict a better outcome after radiation therapy, the need to take a biopsy in the event of PSA failure remains under investigation. The value of salvage radiation to the prostatic bed for PSA-only progression after RP remains in question.

Variables in predicting survival based on treating "PSA-only" relapse

Prostate cancer recurrence (after prior local treatment) that is detectable only by a rise in serum prostate specific antigen (PSA) level is a very common problem facing clinicians. Given that the majority of contemporary era men with PSA-only or biochemical recurrence are relatively young and otherwise healthy, treatment requires approaches that both improve clinical outcomes and preserve quality of life. Treatment is in one of two broad categories, additional local therapies, termed "salvage" local therapy and systemic therapies. For radical prostatectomy patients, salvage external beam radiotherapy to the prostate bed is commonly employed, being reserved for early biochemical recurrence in men with low risk at distant metastases. For primary radiation patients, salvage radical prostatectomy or cryotherapy can similarly be used for those men felt not to harbor distant metastases. Systemic therapy generally involves hormonal therapy. Traditional hormonal therapy (orchiectomy, luteinizing hormone-releasing hormone agonists, or maximum androgen blockade) is the current mainstay of systemic treatment for biochemical recurrence, although nontraditional approaches, such as antiandrogen monotherapy, are increasingly being used. Variables in predicting survival based on treating PSA relapse is problematic. The condition of biochemical failure has only been recognized in the last decade and few "PSA-era" patients with biochemical recurrence have actually died of disease. Hence, the validation of prediction variables in this setting is just emerging. Early work would suggest that timing of recurrence, Gleason grade, and PSA velocity or doubling time during relapse are important prognostic factors. New data on PSA doubling time will be presented.

Markers and meaning of primary treatment failure

BCR is the most clinically used endpoint for identification of treatment failure. Approximately 15% to 53% of patients undergoing primary curative therapy will develop BCR. BCR often precedes clinically detectable recurrence by years. It does not necessarily translate directly into PCa morbidity and mortality, nor does it always reflect the desired endpoint. Furthermore, it has not been validated as a surrogate endpoint, in that interventions that have been shown to alter the PSA level have not been shown to also alter survival. The utility of PSA level as a surrogate endpoint is brought into question by the knowledge that the overall survival rate of patients at 10 years is similar in patients with and without BCR, and that in a significant proportion of men, the only evidence of disease during their lifetime will be a detectable PSA level. The likelihood of developing BCR post-therapy can be predicted by using multiple clinical and pathologic variables. With the development of nomograms that incorporate several markers, the accuracy of prediction has improved. Until recently, the natural history of BCR post-RRP has not been well understood. Pound et al showed the heterogenous and prolonged natural history of BCR. In this large series of men with BCR following RRP, only 34% of men developed metastatic disease. The median time from development of BCR to identification of metastases was 8 years, and the median time from the development of metastatic disease to death was just under 5 years. These data highlight the extremely variable and potentially indolent nature of BCR. The risk of metastatic disease following BCR has been relatively well defined and relates to PSADT and time to PSA recurrence. It generally is accepted that a PSADT of less than 6 to 10 months and a time to PSA recurrence of less than 1 to 2 years relates to a higher risk of developing metastatic disease. Local recurrence, however, remains poorly understood with respect to its true incidence, clinical significance, and natural history. The significance of BCR post-RT remains unclear due to the lack of data on its natural history. Attempts have been made to identify patients at high risk for metastatic progression by looking at time to PSA recurrence and PSADT. A PSADT of less than 6 to 12 months and a time to PSA recurrence of less than 12 months reflects a higher risk of developing metastatic disease. Accurate risk stratification by means of an algorithm similar to that produced by Pound et al has not been performed on a large cohort, thus making risk assessment for an individual patient difficult. The major dilemma for clinicians in the management of BCR is the identification of the site of disease recurrence, which ultimately guides therapy decisions. Clinicopathologic features allow for risk stratification for recurrence, and multiple investigations have attempted to localize the site of recurrence. Time to biochemical progression, Gleason score, and PSADT are predictive of the probability and time to development of metastatic disease, and allow for stratification of patients into different risk groups (see Table 2). TRUS, CT, PET, and DRE all have limited utility in the identification of local recurrence. ProstaScint and MRI have demonstrated encouraging initial results: however, they require further investigation. Bone scintigraphy is of little value for the initial investigation of BCR. In patients with a PSA level of less than 10 ng/mL, the risk of having a positive bone scan is less than 1% and, until the PSA level rises above 40 ng/mL, the risk of having a positive bone scan is less than 5%. Therefore, bone scintigraphy should be reserved for patients with a PSA level greater than 10 to 20 ng/mL or patients with a rapidly rising PSA level. Using new MRI sequences, there is some evidence that MRI is better for the detection of bony metastatic disease; however, this technique requires further investigation. BCR causes anxiety for the patient and the treating doctor, because the best way to manage patients with PSA-only progression is unknown. Currently, there are no validated treatment recommendations for the management of BCR. The information in this review provides the framework for assignment of patients into clinical trials based on different risk categories. Patients at high risk for metastatic progression could be identified early and thus entered into appropriate clinical trials for systemic therapies. Similarly, patients with a low risk of progression could be placed into observation protocols, potentially sparing them from exhaustive and inappropriate investigations.

Indium-111-capromab pendetide radioimmunoscintigraphy and prognosis for durable biochemical response to salvage radiation therapy in men after failed prostatectomy

PURPOSE

We evaluated the prognostic significance of indium-111 (111In)-capromab pendetide imaging for patients with prostate cancer who underwent salvage radiotherapy (RT) for recurrent disease after prostatectomy.

PATIENTS AND METHODS

Records were reviewed for all men who underwent 111In-capromab pendetide imaging at a single institution from February 1997 through December 1999. We identified 30 eligible men who were radiographically negative for metastatic disease, who had increasing serum prostate-specific antigen (PSA) after primary radical prostatectomy, and who received salvage RT. Clinical interpretations of indium monoclonal antibody (In-mab) scan results were compared with postsalvage RT PSA response.

RESULTS

Using an American Society of Therapeutic Radiation and Oncology definition of PSA failure, in men with a positive scan in at least one location (n = 14), the cumulative 2-year PSA control after salvage RT was 0.38 +/- 0.13 (+/- SE) compared with 0.31 +/- 0.13 for men with a normal antibody scan in and outside the prostate fossa (n = 15; proportional hazard ratio [PHR] = 1.32; 95% confidence interval [CI], 0.52 to 3.36). For men with a positive antibody scan limited to the prostate fossa (n = 9), PSA control at 2 years was 0.13 +/- 0.12 (PHR 1.77; 95% CI, 0.65 to 4.85). The 2-year probability of PSA control after salvage RT for men with positive scan results outside the prostate bed irrespective of In-mab findings in the prostate fossa (n = 5) was 0.60 +/- 0.22 (PHR 0.81; 95% CI, 0.17 to 3.78).

CONCLUSION

In contrast to previous reports, for patients with postprostatectomy biochemical relapse who received salvage RT, presalvage RT In-mab scan findings outside the prostate fossa were not predictive of biochemical control after RT.

National Comprehensive Cancer Network guidelines for the management of prostate cancer

Guidelines for the management of prostate cancer issued by the National Comprehensive Cancer Network provide a basis for rational treatment decisions. These guidelines represent consensus recommendations by a panel of experts that are evidence based and are designated according to the degree of consensus within the expert panel. The initial stratification point is the patient's life expectancy (>5 or <5 years). If life expectancy is >5 years, the recommended intervention is based on clinical stage, prostate-specific antigen (PSA) level, and Gleason score, as well as the presence of symptoms. These assessments establish the patient's risk of recurrence after therapy. Specific initial therapies are then recommended according to whether the risk category is low, intermediate, high, or very high. The guidelines also describe the appropriate use of observation ("watchful waiting") versus active intervention in certain patients. After definitive therapy, patients should be monitored with PSA determinations, digital rectal examination, and bone scans, as outlined in the guidelines. Patients who exhibit increasing PSA levels after prostatectomy are candidates for salvage therapy with androgen ablation, radiotherapy, or observation. If PSA levels begin to increase after radiotherapy, surgery may then be an additional option. Systemic salvage therapy generally consists of androgen ablation; the benefit of total androgen blockade versus initial monotherapy remains controversial. Relapse after initial androgen ablation is treated with an antiandrogen, if none had been administered previously. Patients refractory to further hormonal manipulations are observed or receive palliative therapy, including chemotherapy. The treatment of prostate cancer is complex. Optimal treatment is risk-adapted to the specific characteristics of the cancer and the expected longevity and personal preferences of the patient.

PSA progression following radical prostatectomy and radiation therapy: new standards in the new Millennium

Prostate-specific antigen (PSA) progression following radical treatments of clinically localized prostate cancer is a common problem facing both the patient and the urologist. Not all patients with relapsing disease have an equal risk of death due to prostate cancer. After surgery, biochemical failure can be defined as persisting detectable levels of PSA after radical prostatectomy or a PSA rise after a period of normalization. On the other hand, definitions of PSA progression after radiation therapy vary and no clear consensus can be found. This review of the recent international literature updates the knowledge about the diagnostic procedures used in relapsing patients. Predictors of progression are precised leading to a better patient selection, based on currently available tables and nomograms. Indeed, identification of high risk patients may allow a more appropriate treatment decision. After radical treatment, the analysis of time to recurrence, PSA doubling time, PSA kinetics combined to modern imaging techniques such as 111In capromab penditide scan may allow a better identification of the recurrence site. Thus, an optimal treatment strategy may be envisaged such as local irradiation, salvage surgery, hormone therapy or combinations for which indications and results are provided. Alternative options such as cryotherapy still need further investigation. At last, the use of artificial neural networks will certainly enhance the selection of patients submitted to radical treatments as well as the selection of relapsing patients to allow a more appropriate adjuvant therapy.

Dual-modality imaging of cancer with SPECT/CT

Dual-modality imaging is an in vivo diagnostic technique that obtains structural and functional information directly from patient studies in a way that cannot be achieved with separate imaging systems alone. Dual-modality imaging systems are configured by combining computed tomography (CT) with radionuclide imaging (using positron emission tomography (PET) or single-photon emission computed tomography (SPECT)) on a single gantry which allows both functional and structural imaging to be performed during a single imaging session without having the patient leave the imaging system. A SPECT/CT system developed at UCSF is being used in a study to determine if dual-modality imaging offers advantages for assessment of patients with prostate cancer using (111)In-ProstaScint, a radiolabeled antibody for the prostate-specific membrane antigen. (111)In-ProstaScint images are reconstructed using an iterative maximum-likelihood expectation-maximization (ML-EM) algorithm with correction for photon attenuation using a patient-specific map of attenuation coefficients derived from CT. The ML-EM algorithm accounts for the dual-photon nature of the 111In-labeled radionuclide, and incorporates correction for the geometric response of the radionuclide collimator. The radionuclide image then can be coregistered and overlaid in color on a grayscale CT image for improved localization of the functional information from SPECT. Radionuclide images obtained with SPECT/CT and reconstructed using ML-EM with correction for photon attenuation and collimator response improve image quality in comparison to conventional radionuclide images obtained with filtered backprojection reconstruction. These results illustrate the potential advantages of dual-modality imaging for improving the quality and the localization of radionuclide uptake for staging disease, planning treatment, and monitoring therapeutic response in patients with cancer.

Anti-tumor effects of toxins targeted to the prostate specific membrane antigen

BACKGROUND

There is presently no effective therapy for relapsing, metastatic, androgen-independent prostate cancer. Immunotherapy with monoclonal antibody-vehicled toxins (Immunotoxins, ITs) may be a promising novel treatment option for the management of prostate cancer in these cases.

METHODS

Three anti-prostate specific membrane antigen (anti-PSMA) monoclonals (J591, PEQ226.5, and PM2P079.1) were cross-linked to ricin A-chain (RTA; native or recombinant), and their cytotoxic effects were investigated in monolayer and three-dimensional (3-D) cell cultures of prostate carcinoma cells (LNCaP).

RESULTS

The various Immunotoxins showed effects in the nanomolar range (IC(50s) of 1.6-99 ng/ml) against PSMA+ cells (IC(50) being the concentration inhibiting 50% cell proliferation or protein synthesis). PSMA(-) cell lines were 62- to 277-fold less sensitive to anti-PSMA ITs, evidencing an appreciable therapeutic window. Treatment with J591-smpt-nRTA (0.35-31.7ng/ml) resulted in complete eradication of 3-D tumor micromasses or in 1.46- to 0.35-log reduction of target cells number, depending on the dose.

CONCLUSION

Anti-PSMA ITs appear to be promising for use in the eradication of small prostate tumor cell aggregates present in tissues and in the bone marrow.

[Clinical and biological surveillance after radiotherapy for localized prostate cancer]

Serum PSA is an excellent marker of disease status after external beam radiotherapy or brachytherapy for patients with prostate carcinoma. A low PSA nadir < or = 1 even < or = 0.5 ng/mL has been shown to be as a surrogate end point for disease control. Three successive increases of this marker after achieving the nadir defines recurrence as recommended by the American Society for Therapeutic Radiology and Oncology. The biochemical relapse or PSA failure after treatment precedes clinical disease relapse by several months. PSA profile or kinetics may have implications for patterns of failure and prognosis. Prostate post-radiotherapy biopsies should not be part of routine follow-up as its interpretation is frequently problematic. Other exams should not be performed unless clinical symptoms are present. Post-radiotherapy relapse treatment has generally no curative intent.

Comparison of anti-prostate-specific membrane antigen antibodies and other immunomarkers in metastatic prostate carcinoma

OBJECTIVES

To compare the immunohistochemical properties of the 7E11 anti-prostate-specific membrane antigen (anti-PSMA) monoclonal antibody (mAb) with the recently developed anti-PSMA mAb, PM2J004.5, and with other common immunomarkers in metastatic prostate cancer. PSMA is a type II integral membrane glycoprotein highly expressed in prostate cancer cells. The mAb 7E11 is currently used in the radioisotopic evaluation of prostate cancer, and its immunohistochemical properties have been examined in primary prostate cancer specimens.

METHODS

We examined 23 formalin-fixed, paraffin-embedded, metastatic prostate carcinoma specimens from various anatomic sites, including bone, lymph node, liver, lung, and soft tissue. Using the biotin-streptavidin method, we performed immunohistochemical reactions with the anti-PSMA mAbs 7E11 and PM2J004.5 and with antibodies to prostate-specific antigen and prostatic acid phosphatase. The immunoreactions were scored by pathologists unaware of the clinical and pathologic data according to a staining intensity scale and the percentage of cells stained.

RESULTS

All four mAbs consistently stained the metastatic prostate cancer specimens. In 2 (8.7%) of 23 cases, however, the prostate-specific antigen immunoreaction was negative but the anti-PSMA mAbs had positive staining. Although 7E11 and PM2J004.5 had a similar staining intensity and percentage of cells stained for most specimens, in 3 (13%) of 23 specimens, 7E11 had less intense staining. None of the specimens were negative for all four antibodies.

CONCLUSIONS

Anti-PSMA mAbs consistently immunoreacted with metastatic prostate cancer specimens and were positive in instances when prostate-specific antigen staining was negative. The anti-PSMA mAbs demonstrated similar staining patterns; however, in select cases, the PM2J004.5 mAb did show more intense staining. The anti-PSMA mAbs 7E11 and PM2J004.5 are useful in the pathologic evaluation of paraffin-embedded metastatic prostate cancer specimens.

The clinical role of prostate-specific membrane antigen (PSMA)

Prostate cancer remains the most common cancer type in men in the United States. Efforts are increasing to evaluate and to discover diagnostic and therapeutic markers for prostate cancer patients. One of these, prostate-specific membrane antigen (PSMA), is a transmembrane protein highly expressed in all types of prostatic tissue, especially cancer. The radio-immunoconjugate form of the anti-PSMA monoclonal antibody (mAb) 7E11, known as the ProstaScint scan, is currently being used to diagnose prostate cancer metastasis and recurrence. Early promising results from various Phase I and II trials have utilized PSMA as a therapeutic target. Recently, PSMA expression in endothelial cells of tumor-associated neovasculature has been described. PSMA's possible role in malignant angiogenesis newly expands the realm of its possible beneficial uses, especially as new anti-PSMA mAbs continue to be developed and refined.

Metastatic renal cell carcinoma neovasculature expresses prostate-specific membrane antigen

OBJECTIVES

To determine whether the tumor-associated neovasculature of metastatic prostate and metastatic conventional (clear cell) renal carcinoma express prostate-specific membrane antigen (PSMA). PSMA is a type II integral membrane glycoprotein highly expressed in prostate cancer cells and also recently discovered to be expressed in the neovasculature of non-prostatic primary malignancies.

METHODS

We examined metastatic prostate carcinoma (22 patients) and metastatic conventional (clear cell) renal carcinoma (20 patients) in various anatomic sites, including bone, lymph nodes, liver, lung, and soft tissue. Using the biotin-streptavidin method, we performed immunohistochemical reactions with the anti-PSMA monoclonal antibodies (mAbs) 7E11 and PM2J004.5 and with the anti-endothelial cell mAb CD34.

RESULTS

Metastatic conventional (clear cell) renal carcinoma consistently expressed PSMA. The PM2J004.5 mAb was positive in 20 of 20 specimens, and the 7E11 mAb was positive in 15 of 20. The anti-PSMA immunoreactions with the neovasculature were confirmed by similar staining by the anti-CD34 mAb (20 of 20). Although the metastatic prostatic cancer cells expressed PSMA in all the specimens, only 2 of 22 had neovasculature PSMA expression.

CONCLUSIONS

As in primary prostatic adenocarcinomas, the neovasculature of metastatic prostate cancer, regardless of site, rarely express PSMA. The neovascular endothelial cells of metastatic clear cell renal carcinoma, however, express PSMA. This expression may make PSMA an effective target for mAb-based antineovasculature therapy in metastatic renal carcinoma.

Multicenter ProstaScint imaging findings in 2154 patients with prostate cancer. The ProstaScint Imaging Centers

OBJECTIVES

To report the results of a retrospective study of 2290 ProstaScint scans of 2154 patients with prostate carcinoma done at 15 institutions.

METHODS

The results were analyzed by logistic regression after stratification of the patients into four groups: group 1, newly diagnosed; group 2, after radical prostatectomy with a rising prostate-specific antigen (PSA) level; group 3, after radiation therapy with a rising PSA level; and group 4, after hormonal therapy.

RESULTS

The PSA level and ProstaScint scans positive in the prostate bed (P <0.001) and for pelvic metastases (P <0.001), but not for extrapelvic metastases, correlated significantly in group 1 patients. In group 2, the association for detecting fossa recurrence was weaker (P = 0.033) and was insignificant for pelvic and extrapelvic metastases. Patients in group 3 also exhibited a weak PSA-ProstaScint association for detecting fossa recurrence (P = 0.038), and was insignificant for pelvic and extrapelvic metastases. No significant PSA-ProstaScint correlation was found in patients in group 4 for fossa recurrence, pelvic or extrapelvic metastases. The distribution of positive ProstaScint results among the prostate/prostate bed, pelvic nodes, and extrapelvic nodes was nearly equal for all groups, except that a significantly greater percentage of extrapelvic metastases was found in the hormonal group (group 4). The ProstaScint results were independent of the Gleason score for 260 patients before and 285 patients after therapy.

CONCLUSIONS

The results of this study underscore the complementary diagnostic value of ProstaScint to PSA level and Gleason score as an independent indicator of prostate cancer recurrence and metastases and in identifying extrapelvic metastases in both newly diagnosed and recurrent prostate cancer.

Approach to pulmonary metastases

The prognosis and response to therapy of metastases to the lungs are variable and highly dependent on the origin of the primary tumor and on the extent and pattern of spread. Due to the complex pathogenesis underlying the development of pulmonary metastases, specific tumor types often display characteristic clinical and radiographic patterns. Understanding these concepts is of paramount importance when planning a diagnostic work-up for patients with possible pulmonary metastases. This review presents state of the art strategies in imaging, medical therapy, and surgery. It should provide the busy pulmonologist with the information needed to devise safe and efficient diagnostic and treatment strategies for patients with pulmonary metastases of extrathoracic origin.