Anti-PSMA 124I-scFvD2B as a new immuno-PET tool for prostate cancer: preclinical proof of principle

Background

Prostate cancer (PCa) is the second leading cause of cancer-related death in the Western population. The use in oncology of positron emission tomography/computed tomography (PET/CT) with emerging radiopharmaceuticals promises accurate staging of primary disease, restaging of recurrent disease and detection of metastatic lesions. Prostate-specific membrane antigen (PSMA) expression, directly related to androgen-independence, metastasis and progression, renders this tumour associate antigen a good target for the development of new radiopharmaceuticals for PET. Aim of this study was to demonstrate in a preclinical in vivo model (PSMA-positive versus PSMA-negative tumours) the targeting specificity and sensitivity of the anti-PSMA single-chain variable fragment (scFv) labelled with ¹²⁴I.

Methods

The ¹²⁴I-labeling conditions of the antibody fragment scFvD2B were optimized and assessed for purity and immunoreactivity. The specificity of ¹²⁴I-scFvD2B was tested in mice bearing PSMA-positive and PSMA-negative tumours to assess both ex-vivo biodistribution and immune-PET.

Results

The uptake fraction of ¹²⁴I-scFvD2B was very high on PSMA positive cells (range 75–91%) and highly specific and immuno-PET at the optimal time point, defined between 15 h and 24 h, provides a specific localization of lesions bearing the target antigen of interest (PSMA positive vs PSMA negative tumors %ID/g: p = 0.0198 and p = 0.0176 respectively) yielding a median target/background ratio around 30–40.

Conclusions

Preclinical in vivo results of our immuno-PET reagent are highly promising. The target to background ratio is improved notably using PET compared to SPECT previously performed.

These data suggest that, upon clinical confirmation of sensitivity and specificity, our anti-PSMA ¹²⁴I-scFvD2B may be superior to other diagnostic modalities for PCa. The possibility to combine in patients our ¹²⁴I-scFvD2B in multi-modal systems, such as PET/CT, PET/MR and PET/SPECT/CT, will provide quantitative 3D tomographic images improving the knowledge of cancer biology and treatment.

Iodine-131 metaiodobenzylguanidine (I-131 MIBG) diagnosis and therapy of pheochromocytoma and paraganglioma: current problems, critical issues and presentation of a sample case

Iodine-131 metaiodobenzylguanidine (I-131 MIBG) has been used for the diagnosis and treatment of malignant pheochromocytomas (PHEO) and paragangliomas (PGL) since 1980's. Despite increasing amount of experience with iodine-131 (I-131) MIBG therapy, many important questions still exist. In this article, we will discuss the current problems learned from clinical experience in diagnosis and therapy of PHEO/PGL with I-131 MIBG, and present a sample case to emphasize the critical aspects for an optimal treatment strategy.

Dosimetry in 131I-mIBG therapy: moving toward personalized medicine

Internal dosimetry was developed as a basis for 131I-mIBG treatment at an early stage and has continued to develop for over the last 20 years. Whole-body dosimetry was introduced to prevent hematological toxicity. It will be the basis for a forthcoming European multicentre trial, in which the activity of a second administration is determined according to the results calculated from the first. Lesion dosimetry has also been performed in a small number of centres. The major goal of dosimetry now is to establish dose-effect correlation studies, which will be the basis for individualized treatment planning. The aim of this paper is to analyse previously published studies and to consider the potential for improvement in order to obtain a stronger predictive power of dosimetry. The intrinsic radiobiological limits of dosimetry are also illustrated. Due to the development and dissemination of methods of internal dosimetry and radiobiology over the last two decades, and to the increasing availability of quantitative 124I PET imaging, dosimetry could provide in the near future a more systematic basis for standardization and individualization of mIBG therapy. This will however require a number of multicentre trials which are performed under good instrumental and scientific methodology.

Radionuclide therapy and integrated protocols for bone metastases

Bone metastases are responsible for most of the morbidity and mortality associated with solid malignant tumors, occurring in about 65-70% of the patients with advanced breast or prostate cancer. The pathophysiology of skeletal metastasis is a complex process that involves several biologic process leading to cellular invasion, adhesions and stimulation of osteoclasts and osteoblasts with the mediation of several factors including cytokines, serine proteases and tumor-derived factors. The clinical management of pain from bone metastasis, which is mostly due to indirect stimulation of sensory nerve endings by cytokines and other biologically-active compounds released locally in response to the presence of tumor cells in the bone marrow, includes several options that can be used either alone or in varying combinations, such as analgesic drugs, chemo- or hormonal therapy, bisphosponates, external beam radiation therapy, and surgery. Bone-seeking radiopharmaceuticals play an important role in the treatment of pain caused by multiple blastic or mixed-type skeletal lesions; they have in general a favorable toxicity profile and a high rate of overall clinical benefit, although they may differ in terms of duration of pain palliation and suitability for repeat treatments. The palliative effect can be attributed to the radiation targeted to the bone marrow space, and the overall average response ranges between about 45-80%, with complete response in 10-30% of the cases. In selected clinical conditions, radionuclide therapy can also constitute an effective systemic treatment beyond bone pain palliation, and a synergistic anti-tumour effect can be expected by the combination with other agents, such as chemotherapy or bisphosphonates. This review summarizes the current experience with bone-seeking radiopharmaceuticals used for bone pain palliation, focusing on indications, patients' selection, efficacy and toxicity. Finally, the available data on combination therapies showing encouraging results as to potential anti-tumor efficacy are also reviewed.

Anaplastic thyroid cancer: prevalence, diagnosis and treatment

Anaplastic thyroid cancer (ATC) is a rare aggressive tumor arising from the follicular cells of the thyroid gland (as does well differentiated thyroid cancer, WDTC), but ATC cells do not retain any of the biological features of the original follicular cells, such as uptake of iodine and synthesis of thyroglobulin. Prognosis is almost invariably fatal. In this article the Authors review the pathology, epidemiology, clinical presentation, diagnosis and treatment options of ATC. ATC incidence typically peaks at the 6-7th decade of life (mean age at diagnosis 55-65 years), women representing 55-77% of all patients. ATC represents 2-5% of all thyroid tumors, with a decreasing trend with respect to the incidence of WDTC. The histologic patterns of ATC include giant-cell, spindle-cell and squamoid-cell tumors; these subtypes frequently coexist and are not predictive of patients' outcome. Immuno-cyto-chemistry for thyroglobulin is usually negative or weakly positive and some cases are also negative for keratin, particularly in the spindle-cell areas. ATC may arise de novo, but in most cases it develops from a pre-existing WDTC, especially the follicular subtype. Most ATC patients complain of local compressive symptoms, such as dysphagia, dysphonia, stridor and dyspnea in addition to neck pain and tenderness; in over 70% of the patients the tumor infiltrates surrounding tissues, such as fat, trachea, muscle, esophagus, and larynx. The clinical course of a rapidly enlarging mass that is firm and fixed to surrounding structures in an elderly patient is quite suggestive for ATC. Diagnosis can be confirmed by fine needle aspiration cytology or, in doubtful cases, by histology on core biopsy. Computed tomography (CT) scan and magnetic resonance imaging (MRI) are useful for defining the local extent of disease and for identifying distant metastases, as is also positron-emission tomography (PET) with [(18)F]FDG. Tracheoscopy and esophagoscopy should be performed every two months, or whenever patients refer the appearance or worsening of local symptoms. Bone scintigraphy may be included in the follow-up of patients with a longer survival and relatively good health. Because of its aggressive behavior, the latest American Joint Committee on Cancer Staging Manual classifies all ATCs as T4 and Stage IV tumors, regardless of their actual overall tumor burden. Treatment of ATC has not been standardized because it is not clear whether or not therapy is effective in prolonging survival; most patients die within six momths from diagnosis, primarily because of asphyxiation caused by local tumor invasion. When employed alone, surgery, radiotherapy, or chemotherapy are seldom adequate to achieve overall control of the disease, but a combination of these treatments may improve local control. Surgical treatment of local disease offers the best opportunity for prolonged survival if the tumor is intrathyroidal. When the tumor is extrathyroidal, the surgical approach to ATC is controversial. Some favourable results have recently been reported with newly developed chemotherapy agents and hyper-fractioned radiation therapy. Tracheostomy should be performed in patients with impending airway obstruction when death is not imminent from other sites of disease, and if patients are not candidates for local resection or chemoradiation. Interventional bronchoscopy, including Nd-YAG laser and airways stenting are alternatives to surgery in inoperable ATC-induced tracheal obstruction. Gene therapy is under investigation. Although very rare, ATC is a highly aggressive tumor that belongs to the group of killer tumors with median survival time not longer than 6-8 months. Surgery, chemotherapy and radiotherapy are the conventional therapeutic strategies performed in the attempt to improve survival. Unfortunately, very often they do not succeed any clinical benefit but only palliative

RESULTS

New therapeutic strategies based on molecular approaches are desirable.

[The impact of echo-guided percutaneous biopsy in the diagnosis of focal hepatic lesions]

In order to assess the clinical efficacy of percutaneous echo-guided biopsy (PBE), the authors evaluated its contribution to the diagnostic work-up and therapy selection in 165 cases of confirmed focal hepatic lesions. The cases were studied prospectively using a survey form. PBE yielded a significant contribution to the diagnosis in 79.4% of the cases. It was of substantial or conclusive value to therapeutic selection in 65% of the cases. Moreover, PBE allowed a high number of diagnoses which were unsuspected considering the previous standard clinical and instrumental work-ups. The clinical usefulness of PBE in focal hepatic lesion diagnoses is stressed. Its use saves time in the diagnostic management with considerable cost saving.

[Abnormalities of the female genital tract. Comparison of radiographic and echographic pictures]

An anatomical study of uterine malformations has become quite frequent in obstetrics and gynaecology because of the increasing use of corrective surgery. More than 100 cases were reviewed and the authors discuss some examples in order to present all kinds of uterine malformations which can be detected by ultrasound together with hysterosalpingography. A comparison of the diagnostic data obtained with the two methods shows US to be able to solve several cases. Hysterosalpingography is mandatory in female infertility when there is a need for examining Fallopian tube patency in addition to the morphological characteristics of the uterine cavity. The results obtained with the two methods in the study of uterine malformations allow the formulation of a diagnostic protocol concerning the study of infertile women. First of all, US must be performed, in order to exclude some causes of ovarian infertility and major uterine malformations. Hysterosalpingography should be performed when US does not prove to be totally reliable.

[Total parenteral nutrition and evaluation of nutritional status for the identification of patients at high risk]

The importance of using standardised parameters in pre-operative patient assessment is emphasised. This will identify nutritional deficiencies that are often unrecognised but play a decisive part in the patients' post-operative course. Above all such an assessment enables the clinician to administer the appropriate restorative treatment especially in the elderly patient.

[The elderly and the risk of biliary surgery]

In a review of the results obtained in 5 years surgical treatment of elderly patients, the primary importance of performing elective operations on senile patients and building up such patients after careful assessment of nutritional parameters are emphasised. This reduces the risk of postoperative complications in patients who are mostly debilitated by concomitant conditions as well as presenting a reduced capacity for defence and organic recovery.