Imaging of renal cell cancer with radiolabelled octreotide

Metastatic clear cell renal cell carcinoma demonstrating intense uptake on 68Ga-DOTATATE positron emission tomography: Three case reports and a review of the literature

⁶⁸Ga-DOTATATE positron emission tomography (PET) is a molecular imaging technology which has shown superiority over ¹¹¹In-octreotide scanning for the detection and staging of neuroendocrine tumors. We report three patients with pancreatic masses that were ultimately diagnosed as clear cell renal cell carcinoma (ccRCC) metastases on histopathology. During their initial diagnostic assessment, the three patients underwent both ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) and ⁶⁸Ga-DOTATATE PET. While all three patients' lesions showed variable ¹⁸F-FDG avidity, uptake on ⁶⁸Ga-DOTATATE PET was comparatively intense. The small case series illustrates the need to consider ccRCC in the differential diagnosis of ⁶⁸Ga-DOTATATE avid lesions.

The role of 111indium-octreotide brain scintigraphy in the diagnosis of cranial, dural-based meningiomas

OBJECTIVE

Meningiomas are common brain tumors with somatostatin receptors that bind octreotide. We report the use of (111)indium-octreotide brain scintigraphy (OBS) for the non-invasive differentiation of meningiomas from other cranial dural-based pathology.

METHODS

A retrospective analysis of our experience with OBS for non-invasive identification of meningiomas was performed. Two neuroradiologists, blinded to clinical data, utilized a standardized grading scheme to define the uptake of octreotide at 6 and 24 h post-administration. The correlation between (18) F-fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET), magnetic resonance imaging (MRI) scans, and octreotide uptake was assessed.

RESULTS

The cohort consisted of 50 patients having a mean age of 62.4 years and a median follow-up time of 24 months. Management consisted of biopsy (n = 4); resection (n = 10); observation (n = 16); radiosurgery (n = 21); and external beam radiotherapy (n = 3). OBS was correlated with MRI (n = 50); FDG-PET brain studies (n = 38); histology (n = 14), and angiography (n = 1). In cases where definitive diagnosis could be made, the sensitivity, specificity, positive and negative predictor values for OBS alone were 100; 50; 75; and 100, respectively. OBS provided false positive data in 3 patients (metastasis, chronic inflammation, lymphoma). Use of OBS with MRI to differentiate meningiomas from other lesions was highly significant (P < 0.001). FDG-PET correctly identified malignant pathology with 100% sensitivity and specificity.

CONCLUSION

OBS may increase the diagnostic specificity of conventional MRI when differentiating meningioma from other dural-based pathologies, while the addition of FDG-PET differentiates benign from malignant lesions.

Intracranial collision tumor mimicking an octreotide-SPECT positive and FDG-PET negative meningioma

OBJECTIVE/IMPORTANCE: Cancer metastasis to a pre-existing intracranial tumor is rare, but several cases have been reported. We report an unusual case of a "collision tumor" consisting of a renal cell carcinoma metastasis to an intracranial meningioma.

CLINICAL PRESENTATION

A 67-year old male with renal cell carcinoma had an asymptomatic right posterior frontal dural-based lesion identified on a screening CT scan. MRI characteristics of the tumor were consistent with meningioma. On octreotide-SPECT and F-18 fluorodeoxyglucose (FDG)-PET scans, the lesion showed octreotide uptake but did not accumulate FDG, both of which are consistent with a diagnosis of benign meningioma. One week later, he presented with a 1-day history of progressive left-sided weakness. The intracranial tumor was resected, and subacute subdural blood was found overlying a soft, reddish tumor. Microscopic examination was consistent with renal cell carcinoma with a minor portion consisting of meningioma. The meningothelial component was strongly immunoreactive to vimentin and weakly reactive to epithelial membrane antigens. Neither area reacted with glucose transporter-1 (GLUT-1), correlating with low FDG-PET uptake.

CONCLUSION

Collision tumor involving metastatic renal cell carcinoma to an intracranial meningioma is a rare occurrence. Diagnosis by non-invasive means, with use of a combination of octreotide-SPECT and FDG-PET may not accurately reflect the malignant component of such a collision tumor. In this case, the collision tumor also demonstrated a propensity to undergo spontaneous hemorrhage. A high degree of suspicion of intracranial metastasis should be maintained for patients who have known systemic cancer and are found incidentally to have a dural-based mass lesion.

Value of immunohistochemistry for somatostatin receptor subtype sst2A in cancer tissues: lessons from the comparison of anti-sst2A antibodies with somatostatin receptor autoradiography

The somatostatin receptor sst2A is highly expressed at the cellular surface of neuroendocrine and other human tumor cells, allowing somatostatin receptor-targeted scintigraphic tumor imaging and tumor therapy. In vitro information on tumoral somatostatin receptor expression is provided mainly by receptor autoradiography, based on binding of radiolabeled somatostatin analogs to tumoral somatostatin receptors. Recent availability of anti-sst2A antibodies opens the possibility of sst2A assessment in human tumors with immunohistochemistry. The aim of the present study was to evaluate the usefulness of several commercial anti-sst2A antibodies for this purpose in comparison with the extensively characterized antibody R2-88 and with receptor autoradiography. sst2A immunohistochemistry was performed in 64 formalin-fixed tumors known to frequently express sst2A (pancreatic, gastrointestinal, pulmonary neuroendocrine tumors, breast carcinomas, meningiomas, pituitary adenomas, neuroblastomas, medulloblastomas, pheochromocytomas, and paragangliomas); receptor autoradiography could be performed simultaneously in 37 of these cases. The commercial antibody SS-800 clearly identified sst2A and correlated excellently with R2-88: compared with R2-88, SS-800 immunohistochemistry generally yielded the same tissular and subcellular staining distribution. Results of R2-88 and SS-800 immunohistochemistry correlated excellently with those obtained with receptor autoradiography; compared with receptor autoradiography, immunohistochemistry with both R2-88 and SS-800 resulted in a slightly lower tumoral sst2A incidence, but a higher resolution, with frequent identification of heterogeneous sst2A distribution at high magnification. Finally, not only membranous, but also cytoplasmic, sst2A immunostaining was simultaneously observed with both antibodies in some tumors. In conclusion, the commercially available SS-800 antibody promises to be useful for the routine immunohistochemical assessment of sst2A in formalin-fixed human tumors.

Radiolabeled peptides in oncology: role in diagnosis and treatment

There has been an exponential growth in the development of radiolabeled peptides for diagnostic and therapeutic applications in the last decade. The automated means of synthesizing these compounds in large quantities and the simplified methods of purifying, characterizing, and optimizing them have kindled attention to peptides as carrier molecules. These new techniques have accelerated the commercial development of radiolabelled peptides, which has provided additional radiopharmaceuticals for the nuclear medicine community. Peptides have many key properties including fast clearance, rapid tissue penetration, and low antigenicity, and can be produced easily and inexpensively. However, there may be problems with in vivo catabolism, unwanted physiologic effects, and chelate attachment. Radiolabeled peptides have made their greatest impact in the management of relatively rare neuroendocrine malignancies. Indeed, Indium-111 ((111)In)-pentetreotide ((111)In-DTPA-octreotide, Octreoscan), which binds to somatostatin receptors (SSTRs), has become the diagnostic 'gold standard' in these diseases. However, (111)In-pentetreotide has been less successful in the diagnosis of other more prevalent diseases in which SSTRs are upregulated. Technetium-99m (99mTc)-depreotide (NeoTect), a 99mTc-labeled SSTR-analog, could have wider impact since it has high sensitivity and specificity for lung cancer lesion detection. However, this impact may be minimized by the increased availability of positron emission tomography imaging with Fluorine-18 (18F)-flourodeoxyglucose, which has similar sensitivity and specificity for lesion identification in this disease, and is currently more widely used. The receptors for bombesin, alpha-melanocyte-stimulating hormone, neurotensin, and the integrin alpha(v)beta3, are under active investigation as targets for radiolabelled peptides, but are still in the pre-clinical stage. Compounds directed at the cholecystokinin-B/gastrin receptor have shown promising results in clinical trials in humans. Radiolabelled peptide therapy is usually indicated for patients with widespread disease that is not amenable to focused radiation therapy or is refractory to chemotherapy. Phase I/II studies using various radiolabelled peptides (including (111)In-pentetreotide, Yttrium-90 [90Y]-DOTA-Phe1-Tyr3-octreotide, 90Y-DOTA-lanreotide, and Lutetium-177 [177Lu]-DOTA-octreotate) for the treatment of patients with neuroendocrine malignancy are in progress. Over 400 patients have been treated, and the response rate has ranged from 60% to 75%, although few patients have had a complete response. Patients have been given individual doses ranging from 2 to 11 GBq with a slow infusion every 4-8 weeks (up to 12 times). The kidney is the dose-limiting organ and most patients experience a transient decline in blood cell counts. A concomitant infusion of an amino acid mixture can reduce kidney toxicity and increase the effective tumor dose. Other peptides currently under investigation, some of which have shown promising results, include Rhenium-188 (188Re)-P2045 and 90Y-alpha(v)beta3 antagonist.

Neuropeptide Y receptors in renal cell carcinomas and nephroblastomas

Numerous peptide receptors are overexpressed in human cancer, permitting in vivo tumor targeting. Among such receptors, those for the neurotransmitter neuropeptide Y (NPY) are overexpressed in various tumors. Since NPY can play a role in the kidney, NPY receptor expression and/or endogenous production of peptides of the NPY family (NPY, PYY, PP) were evaluated in 40 renal cell carcinomas (RCCs) and 18 nephroblastomas. NPY receptor protein expression was investigated by in vitro autoradiography using (125)I-labeled PYY in competition with NPY receptor subtype-selective analogs. NPY, PYY and PP production was assessed immunohistochemically. Fifty-six percent of RCCs expressed the Y1 receptor subtype in moderate density, and 80% of nephroblastomas expressed Y1 and Y2 subtypes in moderate to high density. Y1 was also highly expressed in intratumoral blood vessels. In selected cases, NPY was observed in nerve fibers in close association with intratumoral blood vessels and in the vicinity of tumor cells, while no PYY or PP was detected immunohistochemically in these sites. NPY receptors on renal tumor cells and tumor blood vessels may therefore be the molecular targets of endogenous NPY released by intratumoral nerve fibers. With regard to clinical applications, NPY receptors may act as in vivo targets for receptor-directed therapy of RCCs and nephroblastomas for which alternative therapeutic approaches are still required.

Receptor-Mediated Tumor Targeting with Radiopeptides. Part 1. General Concepts and Methods: Applications to Somatostatin Receptor-Expressing Tumors

Radiolabeled peptides have become important tools in nuclear oncology, both as diagnostics and more recently also as therapeutics. They represent a distinct sector of the molecular targeting approach, which in many areas of therapy will implement the old "magic bullet" concept by specifically directing the therapeutic agent to the site of action. In this three-part review, we present a comprehensive overview of the literature on receptor-mediated tumor targeting with the different radiopeptides currently studied. Part I summarizes the general concepts and methods of targeting, the selection of radioisotopes, chelators, and the criteria of peptide ligand development. Then, the >400 studies on the application to somatostatin/somatostatin-release inhibiting factor receptor-mediated tumor localization and treatment will be reviewed, demonstrating that peptide radiopharmaceuticals have gained an important position in clinical medicine.

Peptide receptors as molecular targets for cancer diagnosis and therapy

During the past decade, proof of the principle that peptide receptors can be used successfully for in vivo targeting of human cancers has been provided. The molecular basis for targeting rests on the in vitro observation that peptide receptors can be expressed in large quantities in certain tumors. The clinical impact is at the diagnostic level: in vivo receptor scintigraphy uses radiolabeled peptides for the localization of tumors and their metastases. It is also at the therapeutic level: peptide receptor radiotherapy of tumors emerges as a serious treatment option. Peptides linked to cytotoxic agents are also considered for therapeutic applications. The use of nonradiolabeled, noncytotoxic peptide analogs for long-term antiproliferative treatment of tumors appears promising for only a few tumor types, whereas the symptomatic treatment of neuroendocrine tumors by somatostatin analogs is clearly successful. The present review summarizes and critically evaluates the in vitro data on peptide and peptide receptor expression in human cancers. These data are considered to be the molecular basis for peptide receptor targeting of tumors. The paradigmatic peptide somatostatin and its receptors are extensively reviewed in the light of in vivo targeting of neuroendocrine tumors. The role of the more recently described targeting peptides vasoactive intestinal peptide, gastrin-releasing peptide, and cholecystokinin/gastrin is discussed. Other emerging and promising peptides and their respective receptors, including neurotensin, substance P, and neuropeptide Y, are introduced. This information relates to established and potential clinical applications in oncology.

Radiolabeled peptides in the diagnosis and therapy of oncological diseases

There has been an exponential growth in the development of radiolabeled peptides for diagnostic and therapeutic applications in oncology. Peptides have fast clearance, rapid tissue penetration, low antigenicity and can be produced easily and inexpensively. However, peptides have problems with in vivo catabolism, unwanted physiological effects, and chelate attachment. The approved 111In-DTPA-OctreoScan, a somatostatin receptor binder, is well established for diagnosis of neuroendocrine tumors. NeoTect, an approved, 99mTc-labeled, somatostatin-receptor-binding analogue has good specificity for lung cancer detection. The receptors for Vasoactive Intestinal Peptide, Cholecystokinin-B/gastrin, Bombesin, Epidermal Growth Factor, and Alpha Melanocyte Stimulating Hormone and the Integrin, alpha(v)beta(3), are under active investigation as targets. Octreotide and its analogues labeled with 111In, 90Y, 64Cu or 177Lu are under study for the treatment of patients with promising results.

Radiolabeled peptides in diagnosis and therapy

During the past few years, there has been exponential growth in the development of radiolabeled peptides for diagnosis and therapy. This is because the peptides can be synthesized easily and inexpensively, they have fast clearance and rapid tissue penetration, and they are less likely to be immunogenic. More importantly, most peptides have a high affinity for characteristic receptor molecules that are overexpressed on malignant mammalian cells. Peptides can be labeled with a variety of radionuclides intended for specific applications, diagnostic or therapeutic, by using both conventional and novel chelating moieties, many of which can be incorporated during the solid state synthesis of a chosen peptide. High specific-activity peptides can be prepared and used to minimize unwanted physiologic effects, and known sequences of amino acids can be modified to slow their in vivo catabolic rate. These characteristics have paved the way for the preparation of a large number of radiolabeled peptides for a variety of clinical and experimental applications. This article briefly discusses the peptide chemistry; it also summarizes the preparation of radiolabeled peptides and outlines their applications in imaging vascular thrombosis, detecting infection and inflammation, and localizing tumors. Their therapeutic applications in oncology are also presented and the future directions outlined. Peptides that have been approved for human use, such as AcuTect (Diatide, Londonderry, NH) or OctreoScan (Mallinckrodt, St. Louis, MO), or those that have made it to clinical trials, are emphasized. Also discussed are selected promising agents that are still in preclinical investigation.

Segmental expression of somatostatin receptor subtypes sst(1) and sst(2) in tubules and glomeruli of human kidney

Somatostatin is known to modulate mesangial and tubular cell function and growth, but the somatostatin receptor (sst) subtypes responsible for these effects have not been defined. There are at least five different sst receptor subtypes (sst(1)-sst(5)). We used RT-PCR to demonstrate that normal human kidney consistently expresses mRNA for sst(1) and sst(2) (9 of 9 donors). Some donors expressed sst(4) or sst(5) mRNA, but none expressed sst(3) mRNA. Expression of sst(1) and sst(2) was further assessed by staining serial sections of normal human kidney with sst(1) and sst(2) antisera, Arachis hypogaea (AH) lectin (to define distal tubule/collecting duct cells), Phaseolus vulgaris lectin (proximal tubules), and Tamm-Horsfall protein (THP) antiserum (thick ascending limb of the loop of Henle). Specificity of antisera was demonstrated by transfection and absorption studies. Sst(2), but not sst(1), was expressed in glomeruli. Intense sst(1) and sst(2) staining localized exclusively to AH+ and THP+ tubules. Thus sst(1) and sst(2) subtype-selective analogs may be useful to beneficially modulate renal cell function in pathological conditions.

Indium-111 octreotide scintigraphy in patients with bone tumours of the extremities

Radiolabelled somatostatin analogues are of potential value in the imaging of somatostatin receptor-positive tumours. Recently, somatostatin receptors have been demonstrated in the osteoblast precursor cells. In this preliminary study, we evaluated the uptake characteristics of indium-111 octreotide in two benign and two malignant bone tumours. Tracer accumulation was observed in all four cases, and overall lesion to background ratio (mean+/-SD) was 2. 74+/-0.84 and 2.98+/-1.49 at 4 h and 24 h, respectively. There was no clear relationship between 111In-octreotide accumulation and the benign or malignant nature of the tumour. In one patient, tracer uptake was inhibited by unlabelled octreotide administration. These results suggest that 111In-octreotide can be taken up by benign and malignant bone tumours. The inhibition of tumour uptake by treatment with cold octreotide supports the concept that specific uptake mechanisms are responsible for 111In-octreotide deposition by bone tumours.