Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2011 Jan 12.
Published in final edited form as: Curr Radiopharm. 2010;3(1):29–36. doi: 10.2174/1874471011003010029

[177Lu]-DOTA0-Tyr3-octreotate: A Potential Targeted Radiotherapeutic for the Treatment of Medulloblastoma

Ganesan Vaidyanathan a,*, Donna J Affleck a, Xiao-Guang Zhao a, Stephen T Keir b, Michael R Zalutsky a
PMCID: PMC3019532  NIHMSID: NIHMS187361  PMID: 21243098

Abstract

Medulloblastoma, the most common pediatric brain tumor, is difficult to treat because conventional therapeutic approaches result in significant toxicity to normal central nervous system tissues, compromising quality of life. Given the fact that medulloblastomas express the somatostatin subtype 2 receptor, [177Lu-DOTA0,Tyr3]octreotate ([177Lu]DOTA-TATE) could be a potentially useful targeted radiotherapeutic for the treatment of this malignancy. The current study was undertaken to evaluate this possibility in preclinical models of D341 MED human medulloblastoma by comparing the properties of [177Lu]DOTA-TATE to those of glucose-[125I-Tyr3]-octreotate ([125I]Gluc-TOCA), a radiopeptide previously shown to target this cell line. In vitro assays indicated that both labeled peptides exhibited similar cell-associated and internalized radioactivity after a 30-min incubation at 37°C; however, at the end of the 4 h incubation period, the internalized radioactivity for [177Lu]DOTA-TATE (6.22 " 0.75%) was nearly twice that for [125I]Gluc-TOCA (3.16 " 0.27%), with similar differences seen in total cell-associated radioactivity levels. Consistent with the results from the internalization assays, results from paired-label tissue distribution studies in athymic mice with subcutaneous D341 MED medulloblastoma xenografts showed a similar degree of tumor accumulation for [177Lu]DOTA-TATE and [125I]Gluc-TOCA at early time points but by 24 h, a more than 5-fold advantage was observed for the 177Lu-labeled peptide. Tumor-to-normal tissue ratios generally were more favorable for [177Lu]DOTA-TATE at all time points, due in part to its lower accumulation in normal tissues except kidneys. Taken together, these results suggest that [177Lu]DOTA-TATE warrants further investigation as a targeted radiotherapeutic for medulloblastoma treatment.

Keywords: Medulloblastoma, Lutetium-177, DOTA-TATE, Targeted Radiotherapy

INTRODUCTION

Medulloblastoma is the most common pediatric malignant brain tumor, with its highest incidence found in children between the ages of 3 and 9 years old [1]. Although aggressive treatment protocols have resulted in improvements in overall survival, particularly for patients with nondisseminated disease, the quality of life of long term survivors has frequently been severely compromised. Several studies have documented severe impairment of neurocognitive function, which are most apparent in children less than 4 years in age, and have been attributed to whole brain and craniospinal axis irradiation [2]. Thus, while conventional radiation therapy can be effective in controlling medulloblastoma, the neurologic and cognitive sequelae that results from its nonspecific application within the neuroaxis is a major limitation of this treatment method. One approach for improving the treatment of medulloblastoma with radiation is to refine the anatomical specificity of the radiation field exemplified by the use of a proton beam [3]. Another approach is to refine the molecular specificity of the radiation field through the use of targeted radionuclide therapy.

Particularly for potential applications in pediatric patients, the translational pathway for a targeted radiotherapeutic is simplified if the molecular target, delivery vehicle and radionuclide have been utilized previously in other patient populations. With regard to the first component, one of the most widely investigated areas of targeted therapy clinical research has involved molecules that bind selectively to somatostatin receptors (SSTR) that are abundantly expressed on a variety of neuroendocrine tumors [4, 5]. Fortunately, the expression of SSTR at high densities also has been documented in medulloblastomas [6-10]. Although the number of samples generally was small, high level expression of SSTR (predominantly as subtype-2) was demonstrated on medulloblastoma biopsies and human cell lines by reverse transcription-PCR, Southern blot analysis, receptor autoradiography, immunohistochemistry and competitive membrane binding assays. Finally, 111In-labeled pentetreotide (Octreoscan7) has been evaluated recently for somatostatin receptor imaging of children with medulloblastoma [11, 12].

With regard to the selection of carrier molecule and radionuclide, the vast majority of studies evaluating the imaging and treatment of SSTR-expressing malignancies have utilized peptides as the delivery vehicle in combination with a wide variety of radionuclides. Much of this work was performed with octreotide, an octapeptide that is a metabolically stable analogue of the natural SSTR ligand somatostatin-14, which was derivatized with chelating agents such as DTPA and DOTA to permit labeling with radiometals such as 111In and 90Y [13]. Octreotate, an analogue of octreotide obtained by replacing its C-terminus residue threonol with threoine, is generally believed to have better biological properties than octreotide itself, in part because of its more rapid clearance from normal tissues [14-17]. Finally, analogues in which the phenylalanine at position 3 has been replaced with tyrosine (Tyr3-octreotide; TOC and Tyr3-octreotate; TOCA) have been developed to make them amenable for radioiodination.

Now that 177Lu has become readily available, this radionuclide is increasingly used for targeted therapy because of certain advantages that it has in comparison with 131I and 90Y [18]. This is exemplified by the recent emergence of [177Lu-DOTA0,Tyr3]octreotate as the peptide of choice for the clinical treatment of SSTR-expressing tumors such as gastroenteropancreatic cancers [19-22]. An important reason for this trend is that 177Lu, like 131I, emits low energy $-particles; however, its (-emissions are of considerably lower energy (113 and 208 keV) and abundance (7% and 11%) than those of 131I. Benefits of the more favorable γ-ray spectrum of 177Lu include less stringent radiation protection requirements for patients and personnel, improved quality and quantification of dosimetric images, shorter periods of patient confinement, and lower collateral radiation dose deposition to normal tissues. The last two advantages would be of particular value in pediatric patients such as those with medulloblastoma, where minimizing isolation from family members and avoiding bystander irradiation of normal central nervous system tissues are critical considerations.

The current study was performed to evaluate the tissue distribution of [177Lu-DOTA0,Tyr3]octreotate ([177Lu]DOTA-TATE) in athymic mice with human medulloblastoma xenografts as an initial indicator of the potential utility of this labeled peptide for treatment of children with this malignancy. Because we have previously demonstrated that glucose-[131I-Tyr3]-octreotate ([131I]Gluc-TOCA) possessed the best medulloblastoma targeting of the four radioiodinated peptides that were evaluated [17], experiments were performed in paired-label format with [131I]Gluc-TOCA and [177Lu]DOTA-TATE to determine which peptide should be moved forward towards clinical evaluation as a targeted radiotherapeutic for children with medulloblastoma.

EXPERIMENTAL PROCEDURES

General

Lutetium-177 was obtained from the University of Missouri as a solution in 0.05 N HCl at a concentration of 1.2-1.5 Ci/ml and with a specific activity of about 25 Ci/mg. Sodium [125I]iodide with a specific activity of 2200 Ci/mmol was purchased from Perkin-Elmer Life and Analytical Sciences (Boston, MA). DOTA-[Tyr3]-octreotate was obtained from Biosynthema (St. Louis, MO) and had a purity of 99.2%. Iodine-125 labeled Gluc-TOCA was synthesized as reported before [17]. High-pressure liquid chromatography (HPLC) was performed using a Beckman Gold HPLC system equipped with a Model 126 programmable solvent module, a Model 166 NM variable wavelength detector, a Model 170 radioisotope detector and a Beckman System Gold remote interface module SS420X; data were acquired using 32 Karat® software. Reversed-phase HPLC was performed using a 4.6 × 250 mm XTerra RP18 (5 : m) column eluted at 1 ml/min with a gradient of solvents consisted of 0.1% TFA in each water (solvent A) and acetonitrile (solvent B). The composition of B was increased linearly from 0% to 60% over a period of 30 min. Radio- thin layer chromatography (TLC) and paper chromatography (PC) were analyzed initially using a System 200 Imaging Scanner (BioScan, Washington, DC), and then the sheets were cut into strips and counted using an automated gamma counter (LKB 1282, Finland or Perkin-Elmer 1480 Wizard3, Turku, Finland).

Cells and culture conditions

D341 MED is a continuous cell line derived from a tumor biopsy of a patient with a cerebellar medulloblastoma [23]. These cells were grown in 10% FCS and zinc Option medium, and were maintained in a humidified atmosphere (37°C, 5% CO2).

Synthesis of [177Lu]-DOTA-TATE

The method for this synthesis was adapted from procedures reported in the literature [20, 24-26]. Briefly, the DOTA-TATE peptide (10-100 : g) dissolved in 100 : 1 of 25 mM sodium ascorbate in 50 mM sodium acetate, pH 5.0 was added to a plastic vial containing an equal volume of 177Lu (3-22 mCi) in 0.05 N HCl. The vial was sealed and heated at 80°C in a preheated heating block for 20 min. The cooled reaction mixture was diluted with phosphate-buffered saline (PBS). Radiochemical purity was determined by instant thin layer chromatography [20], reversed-phase thin layer chromatography [26], paper chromatography [25], and/or by reversed-phase HPLC. Under the conditions of HPLC (see above), the labeled peptide had a retention time of 20-21 min.

Internalization of [125I]Gluc-TOCA and [177Lu]-DOTA-TATE

About 250,000 cpm (205 nCi) of [125I]Gluc-TOCA and 25,000 cpm (330 nCi) of [177Lu]-DOTA-TATE individually (single label) was incubated at 37°C in triplicate for 30 min, or 1, 2, 3, or 4 h with 1 × 106 D341 MED cells in tubes containing 1 ml of Zinc option medium. In parallel, incubations were performed in the presence of 1 : M octreotide to ascertain nonspecific uptake. To determine the intracellular activity, the surface-bound radioactivity was stripped off by incubation with 1 ml of 20 mM sodium acetate in Hank's buffered salt solution, HBSS (pH 5.0) for 10 min at 37°C. At the end of this the incubation, the cells were washed twice with ice-cold Zinc option medium. After removing the supernatant, the cells were washed once with HBSS (pH 5.0), solubilized in 1 N NaOH, and counted for radioactivity in an automated gamma counter.

Paired-label biodistribution of [125I]Gluc-TOCA and [177Lu]-DOTA-TATE in athymic mice bearing D341 Med xenografts

Animal studies were performed under the guidelines established by the Duke University Institutional Animal Care and Use Committee. Athymic BALB/c-nu(SPF) mice weighing 18–27 g, obtained from the breeding colony maintained at the Duke University Comprehensive Cancer Center Isolation Facility, were used in these studies. The D341 MED cell line was maintained in vivo by serial passage in athymic mice, with passage number 89 being used in these studies. Tumors were transplanted into the right flank with an inoculation volume of 50 : 1 and biodistribution studies were initiated when tumors were about 200–500 mm3. Mice received 3 : Ci each of [125I]I-Gluc-TOCA and [177Lu]DOTA-TATE via the tail vein, and groups of 5 animals were killed at 30 min, and 1 h, 4h, and 24 h after injection of labeled peptides. To determine the specificity of uptake in tumor and normal organs including those known to express SSTR, another group of 5 mice simultaneously was co-injected with 100 : g of octreotide and biodistribution performed 30 min later. Mice were killed with an overdose of isofluorane, dissected, and tissues of interest were isolated. Blot-dried tissues were weighed and counted along with dose standards. From these data, the uptake in different organs was calculated as the percent of injected dose per gram of tissue. A paired Student's t test was used to determine the statistical significance of the difference in the uptake of the two isotopes. For determining the statistical significance of the difference in the uptake between the controls and the octreotide-treated animals, an unpaired t test was used.

RESULTS AND DISCUSSION

More effective and less debilitating therapeutic approaches are needed for the treatment of medulloblastoma, the most common malignant tumor of the central nervous system in children. Targeted radiotherapy is attractive for this purpose because of the potential for focusing cytotoxic effects on malignant tissue. With medulloblastoma, 30-40% of patients recur either at the original tumor site or within the cerebrospinal fluid compartment [27], making it important to devise strategies for delivering therapeutic doses to tumor cells spread along the spinal cord without compromising normal tissues of the central nervous system. The feasibility of treating tumor within the leptomeningeal compartment in children with a targeted radiotherapeutic has been demonstrated by Kramer et al [28]. Iodine-131 labeled anti-GD2 monoclonal antibody was administered intrathecally to 15 children with neuroblastoma and significant prolongation in survival was observed with acceptable toxicity. The application of this tactic to medulloblastoma has been described in a case report [29]; an 8 year old boy with recurrent medulloblastoma was given 4 cycles of [90Y-DOTA0,Tyr3]octreotate at monthly intervals and was in complete remission for 3 years. Although this result is encouraging, modeling studies indicate that the treatment of leptomeningeal tumor would be best accomplished with a shorter range β-emitter such as 131I or 177Lu [30].

With that goal in mind, we previously evaluated 4 radioiodinated SSTR avid peptides in a series of experiments in human medulloblastoma models and [131I]Gluc-TOCA was demonstrated to be the best peptide in terms of maximizing internalized radioactivity in vitro and providing the highest and most selective tumor uptake in vivo [17]. On this basis, [131I]Gluc-TOCA was selected for direct comparison to [177Lu]DOTA-TATE in the paired-label biodistribution experiments reported herein. In that way, it should be possible to factor out the effects of differences in variables such as receptor number, tumor hemodynamics, and catabolism that can vary within groups of experimental animals. Slight modification of methods reported in the literature for the synthesis of [177Lu]DOTA-TATE delivered the labeled peptide with a consistent incorporation yield of 95-99% (n = 5). A typical HPLC profile of the reaction mixture is shown in Figure 1; similar results were obtained using other analytical techniques including instant thin layer chromatography, reversed-phase thin layer chromatography, and paper chromatography. The specific activity of the [177Lu]DOTA-TATE used in the biological assays was in the range of 600 to 900 μCi/: g, similar to the values reported by other investigators [20, 26].

Figure 1.

Figure 1

Open in a new tab

Typical HPLC profile of reaction mixture from the labeling of DOTA-TATE with 177Lu (see text for HPLC conditions).

With peptide targeted radiotherapy, internalization of the labeled molecule into cancer cells after receptor binding is generally required to prolong tumor residence time and provide a good therapeutic index. In addition, the relative degree of trapping of radioactivity in the intracellular compartment measured in vitro for a series of SSTR-avid peptides can be predictive of their relative level of accumulation in tumor xenografts [15, 17]. Earlier we have shown that, among a group of radioiodinated octreotide analogues, [125I]Gluc-TOCA exhibited the highest tumor retention in vitro in D341 MED cells [17]. In the current study, the total cell-associated and intracellular retention of radioactivity from [177Lu]DOTA-TATE after its internalization by D341 MED cells was compared with that from [125I]Gluc-TOCA (Figure 2). The cell-associated and internalized radioactivity for both radiolabeled peptides was quite similar after a 30-min incubation at 37°C; however, the value of these parameters remained constant for the radioiodinated peptide but increased for the 177Lu-labeled peptide. At the end of the 4 h incubation period, the internalized radioactivity for [177Lu]DOTA-TATE (6.22 " 0.75%) was nearly twice that for [125I]Gluc-TOCA (3.16 " 0.27%), with similar differences seen in total cell-associated activity levels.

Figure 2.

Figure 2

Open in a new tab

Internalization of [125I]Gluc-TOCA and [177Lu]DOTA-TATE by D341 MED cells as a function of time. Cells (1 × 106) were incubated with each labeled peptide individually in the presence or absence of 1 :M octreotide for various time periods. After removing cell culture supernatants containing unbound radioactivity, the surface-bound radioactivity was stripped by treatment with an acidic medium. Radioactivity that was internalized and surface-bound was determined. Shown are the specific (total minus nonspecific) cell-associated (internalized + surface-bound; left panel) and internalized (right panel) radioactivity as percent of input dose.

Although the internalization of DOTA-TATE labeled with other radionuclides in other cell lines has been investigated [31, 32], to our knowledge, there is only one study in which the internalization of [177Lu]DOTA-TATE has been evaluated [14]. Capello et al. [14] have reported that about 0.03% of [177Lu]DOTA-TATE dose was internalized after 1 h of incubation with 1 × 105 CA20948 rat pancreatic tumor cells. In the current study, the fraction of [177Lu]DOTA-TATE dose that was internalized by 1 × 106 D341 MED cells was little more than 6% of the input dose at 4 h. Although this is more than about 20-fold higher than that reported for CA20948 cells by Capello et al., these values were considerably lower than the up to 20-25% levels reported for other analogues in different cell lines [32, 33]. However, the magnitude of intracellularly trapped radioactivity for [125I]Gluc-TOCA in the paired-label assay also was considerably lower than these levels (Figure 2). Although up to about 8-14% intracellular trapping has been seen with radiolabeled [*I]Gluc-TOCA in D341 MED cells [17, 34, 35], considerably lower levels have also been observed in previous studies [36]. One factor to which these differing results had been attributed is the use of differing passage numbers of the cell line. Another possibility is that the lower internalized levels observed in this study were due to the presence of unlabeled peptide in the incubation medium. The [125I]Gluc-TOCA used in the internalization assay was purified by HPLC and thus, should have a specific activity approximating that of the radioiodine, which was ~2200 Ci/mmol. On the other hand, in the synthesis of [177Lu]DOTA-TATE, the starting peptide DOTA-TATE was not separated from the final preparation. The total peptide concentration in each case in the in vitro assay was about 0.1 nM. Several investigators have shown that the presence of unlabeled peptide can decrease the cellular uptake and internalization of labeled octreotide analogues both in vitro and in vivo [14, 37-39]; however, the opposite behavior has been reported for the internalization of [125I]I-TOC in the presence of unlabeled octreotide concentrations of less than 1 nM [39]. Finally, a recent study utilizing both quantitative fluorescent activated cell sorting and Scatchard analysis has indicated that D341 MED cells have an average of about 4 H 105 SSTR per cell [40], and thus the internalization assay was performed in receptor excess. For these reasons, it is unlikely that the presence of unlabeled peptide contributed to the relatively low uptake and internalization of the labeled peptides in these experiments.

The tissue distribution of 177Lu and 125I activity after intravenous injection of [177Lu]DOTA-TATE and [125I]Gluc-TOCA was determined in athymic mice with subcutaneous D341 MED human medulloblastoma xenografts. By performing the experiment in paired-label format, the relative uptake of the two labeled molecules could be compared in the same animals. The percentage injected dose per gram (% ID/g) recovered from tumor and normal tissues of 177Lu and 125I is summarized in Table 1. Tumor accumulation of the two radiolabeled peptides were not significantly different from each other at 30 min, 1 h and 4 h; however, at 24 h, the 177Lu/125I activity ratio was 6.5 ″ 0.5, indicating a significant advantage in tumor retention for [177Lu]DOTA-TATE. The tumor uptake value observed for the uptake of [177Lu]DOTA-TATE in D341 MED human medulloblastoma xenografts is within the same range reported for this targeted therapeutic in mice with other types of human tumor xenografts. At 24 h, the only common time point available for comparison, our current results of 9.1 ″ 5.2% ID/g is intermediate between than those reported for mice with small cell lung cancer (3.7 ± 1.0% ID/g) [41, 42] and those with carcinoid (16.0 ± 1.4 %ID/g) [16] xenografts. One can only speculate that the variation in tumor levels observed among the different xenografts likely reflects the influence of factors such as tumor hemodynamics, receptor number and subtype spectrum, as well as tumor size.

Table 1.

Paired-label biodistribution of [125I]Gluc-TOCA and [177Lu]DOTA-TATE in athymic mice bearing D341 MED xenografts

Tissue Percent injected dose per gram tissuea
0.5 h 1 h 4 h 24 h
Gluc-TOCA DOTA-TATE Gluc-TOCA DOTA-TATE Gluc-TOCA DOTA-TATE Gluc-TOCA DOTA-TATE
Liver 2.13 ± 0.55 0.87 ± 0.20 1.73 ± 0.20 0.69 ± 0.10b 0.64 ± 0.25 0.42 ± 0.11 0.07 ± 0.04 0.21 ± 0.06
Spleen 1.20 ± 0.33 1.02 ± 0.42b 1.33 ± 1.26 1.37 ± 1.52b 0.60 ± 0.16 0.51 ± 0.13 0.05 ± 0.01 0.21 ± 0.05
Lungs 5.66 ± 1.79 7.41 ± 2.20b 2.84 ± 1.99 3.17 ± 2.92b 2.90 ± 1.77 4.12 ± 2.72 0.13 ± 0.07 2.19 ± 1.18
Heart 0.63 ± 0.09 0.42 ± 0.08 0.50 ± 0.16 0.30 ± 0.14 0.34 ± 0.09 0.14 ± 0.04 0.03 ± 0.01 0.08 ± 0.02
Kidneys 4.19 ± 1.19 5.02 ± 1.59b 3.34 ± 0.61 5.10 ± 0.93 1.76 ± 0.43 3.55 ± 1.00 0.23 ± 0.11 1.34 ± 0.26
Stomach 6.70 ± 2.12 6.76 ± 2.06b 11.77 ± 2.77 11.42 ± 2.68b 7.30 ± 2.76 5.00 ± 1.63 0.30 ± 0.22 1.36 ± 0.07
Sm. Intestine 13.13 ± 3.15 3.32 ± 0.98 14.47 ± 3.44 4.76 ± 0.58 3.74 ± 0.74 2.36 ± 0.17 0.08 ± 0.03 0.51 ± 0.07
Lg. Intestine 2.00 ± 0.38 2.38 ± 0.44b 12.56 ± 6.40 4.12 ± 0.52 23.06 ± 4.83 7.03 ± 1.79 0.29 ± 0.05 1.25 ± 0.11
Muscle 0.33 ± 0.07 0.35 ± 0.12b 0.24 ± 0.05 0.16 ± 0.06 0.20 ± 0.06 0.09 ± 0.06 0.01 ± 0.01 0.04 ± 0.02
Blood 1.28 ± 0.29 0.60 ± 0.14 0.77 ± 0.28 0.22 ± 0.12 0.52 ± 0.21 0.12 ± 0.08 0.02 ± 0.01 0.03 ± 0.01b
Bone 0.86 ± 0.24 0.91 ± 0.40b 0.66 ± 0.20 0.51 ± 0.36 0.37 ± 0.06 0.49 ± 0.09 0.02 ± 0.02 0.46 ± 0.18
Brain 0.11 ± 0.08 0.13 ± 0.18b 0.06 ± 0.01 0.03 ± 0.01 0.07 ± 0.02 0.03 ± 0.01 0.00 ± 0.00 0.02 ± 0.01
Pancreas 28.18 ± 4.54 32.77 ± 4.56b 20.82 ± 10.99 25.35 ± 13.60 6.07 ± 2.22 10.67 ± 2.62 0.21 ± 0.10 3.56 ± 1.16
Tumor 17.99 ± 7.17 18.88 ± 6.15b 25.31 ± 15.33 24.26 ± 13.08b 14.80 ± 4.61 14.89 ± 4.55b 1.45 ± 0.94 9.12 ± 5.20
Open in a new tab
a

Mean ± S.D. (n = 5).

b

The difference in the uptake of the two tracers not significant (p > 0.05).

The retention of radioactivity in normal tissues that do not express SSTR such as the liver, muscle and blood was significantly lower (p < 0.05) for the 177Lu-labeled peptide from 30 min to 4 h with the opposite behavior seen at the 24 h time point. A notable exception is the kidneys, where 177Lu/125I activity ratios increased from 1.2 ″ 0.1 at 30 min to 6.3 ″ 1.4 at 24 h. In pancreas and lungs, organs known to express somatostatin receptors, the uptake of the 177Lu-labeled peptide was significantly higher than that of the 125I-labeled peptide, particularly at later time points. Although the stomach also expresses SSTR, comparisons are less clear due to the potential for free iodide to also accumulate in this organ. Lower uptake of 125I in SSTR-positive tissues such as tumor and pancreas and higher uptake in other tissues may partly be due to more rapid metabolism of the radioiodinated peptide. Petrik et al. [43] have compared the metabolism of [125I]I-Gluc-TOCA and [177Lu]DOTA-TATE in rats. While predominantly intact form of [177Lu]DOTA-TATE was present in urine, the radioiodinated analogue underwent extensive metabolism. As is typical with radiometallated radiopharmaceuticals, kidney uptake throughout and bone uptake at later time points for [177Lu]DOTA-TATE were higher.

To determine the specificity of radio-peptide uptake, the tissue distribution of [177Lu]DOTA-TATE and [125I]Gluc-TOCA accumulation also was determined 30 min after co-administration with a blocking dose of 100 :g of octreotide. As shown in Figure 3, the SSTR-specific nature of peptide accumulation in D341 MED xenografts was confirmed by the reduction of [177Lu]DOTA-TATE and [125I]Gluc-TOCA uptake to 8 ″ 3% and 12 ″ 5% of control levels, respectively, in the presence of a blocking dose of cold octreotide. Similar effects were seen in stomach and pancreas and to a lesser extent, the lungs; however, in all tissues, the degree of blocking that was achieved was greater for the 177Lu-labeled peptide.

Figure 3.

Figure 3

Open in a new tab

Effect of the co-injection of unlabeled octreotide on the uptake of [125I]Gluc-TOCA and [177Lu]DOTA-TATE in tumor and SSTR-expressing tissues in athymic mice bearing D341 MED medulloblastoma xenografts at 30 min after injection.

An important metric for determining the potential utility of a labeled compound as a targeted radiotherapeutic is the selectivity of tumor localization, which is generally expressed as the tumor-to-normal tissue ratio. Figure 4 summarizes the tumor-to-normal tissue ratios observed for both labeled peptides. More favorable contrast in uptake between tumor and normal tissues was generally observed, except in the kidneys, with [177Lu]DOTA-TATE. For example, at 1 h after injection tumor-to-normal tissue ratios for blood, liver, kidney, spleen, brain and muscle for [177Lu]DOTA-TATE were 142:1, 35:1, 5:1, 47:1, 1063:1 and 176:1, respectively, compared with values of 39:1, 14:1, 8:1, 37:1, 477:1 and 112:1, respectively, for [125I]Gluc-TOCA.

Figure 4.

Figure 4

Open in a new tab

Tumor-to-normal tissue ratios obtained in athymic mice bearing D341 MED medulloblastoma xenografts after i.v. injection of [125I]Gluc-TOCA (left panel) and [177Lu]DOTA-TATE (right panel). Notice that the values for brain are multiplied by 0.1 to facilitate their display.

In conclusion, [177Lu]DOTA-TATE exhibited excellent accumulation in the D341 MED human medulloblastoma xenograft and high tumor-to normal tissue ratios. Because 177Lu-labeled peptide exhibited more favorable localization characteristics than co-administered [125I]Gluc-TOCA, [177Lu]DOTA-TATE has been selected for more extensive evaluation as a targeted radiotherapeutic for the treatment of medulloblastoma. Toxicity and therapeutic efficacy trials are underway to determine the feasibility of treating human medulloblastoma neoplastic meningitis in athymic rats with intrathecally administered [177Lu]DOTA-TATE.

ACKNOWLEDGEMENTS

This work was supported in part by a grant from the Pediatric Brain Tumor Foundation of the United States. The excellent technical assistance of Phil Welsh is greatly appreciated.

REFERENCES

  • 1.Packer RJ, Vezina G. Management of and prognosis with medulloblastoma: therapy at a crossroads. Arch. Neurol. 2008;65:1419–24. doi: 10.1001/archneur.65.11.1419. [DOI] [PubMed] [Google Scholar]
  • 2.Ris MD, Packer R, Goldwein J, Jones-Wallace D, Boyett JM. Intellectual outcome after reduced-dose radiation therapy plus adjuvant chemotherapy for medulloblastoma: a Children's Cancer Group study. J. Clin. Oncol. 2001;19:3470–6. doi: 10.1200/JCO.2001.19.15.3470. [DOI] [PubMed] [Google Scholar]
  • 3.Fossati P, Ricardi U, Orecchia R. Pediatric medulloblastoma: toxicity of current treatment and potential role of proton therapy. Cancer Treat. Rev. 2009;35:79–96. doi: 10.1016/j.ctrv.2008.09.002. [DOI] [PubMed] [Google Scholar]
  • 4.Forrer F, Valkema R, Kwekkeboom DJ, de Jong M, Krenning EP. Neuroendocrine tumors. Peptide receptor radionuclide therapy. Best Pract. Res. Clin. Endocrinol. Metab. 2007;21:111–29. doi: 10.1016/j.beem.2007.01.007. [DOI] [PubMed] [Google Scholar]
  • 5.Van Essen M, Krenning EP, De Jong M, Valkema R, Kwekkeboom DJ. Peptide receptor radionuclide therapy with radiolabelled somatostatin analogues in patients with somatostatin receptor positive tumours. Acta Oncol. 2007;46:723–34. doi: 10.1080/02841860701441848. [DOI] [PubMed] [Google Scholar]
  • 6.Cervera P, Videau C, Viollet C, Petrucci C, Lacombe J, Winsky-Sommerer R, Csaba Z, Helboe L, Daumas-Duport C, Reubi JC, Epelbaum J. Comparison of somatostatin receptor expression in human gliomas and medulloblastomas. J. Neuroendocrinol. 2002;14:458–71. doi: 10.1046/j.1365-2826.2002.00801.x. [DOI] [PubMed] [Google Scholar]
  • 7.Fruhwald MC, O'Dorisio MS, Pietsch T, Reubi JC. High expression of somatostatin receptor subtype 2 (sst2) in medulloblastoma: implications for diagnosis and therapy. Pediatr. Res. 1999;45:697–708. doi: 10.1203/00006450-199905010-00016. [DOI] [PubMed] [Google Scholar]
  • 8.Fruhwald MC, Rickert CH, O'Dorisio MS, Madsen M, Warmuth-Metz M, Khanna G, Paulus W, Kuhl J, Jurgens H, Schneider P, Muller HL. Somatostatin receptor subtype 2 is expressed by supratentorial primitive neuroectodermal tumors of childhood and can be targeted for somatostatin receptor imaging. Clin. Cancer Res. 2004;10:2997–3006. doi: 10.1158/1078-0432.ccr-03-0083. [DOI] [PubMed] [Google Scholar]
  • 9.Guyotat J, Champier J, Pierre GS, Jouvet A, Bret P, Brisson C, Belin MF, Signorelli F, Montange MF. Differential expression of somatostatin receptors in medulloblastoma. J. Neurooncol. 2001;51:93–103. doi: 10.1023/a:1010624702443. [DOI] [PubMed] [Google Scholar]
  • 10.Muller HL, Fruhwald MC, Scheubeck M, Rendl J, Warmuth-Metz M, Sorensen N, Kuhl J, Reubi JC. A possible role for somatostatin receptor scintigraphy in the diagnosis and follow-up of children with medulloblastoma. J. Neurooncol. 1998;38:27–40. doi: 10.1023/a:1005961302340. [DOI] [PubMed] [Google Scholar]
  • 11.Khanna G, O'Dorisio MS, Menda Y, Glasier C, Deyoung B, Smith BJ, Graham M, Juweid M. Somatostatin receptor scintigraphy in surveillance of pediatric brain malignancies. Pediatr. Blood Cancer. 2008;50:561–6. doi: 10.1002/pbc.21194. [DOI] [PubMed] [Google Scholar]
  • 12.Yuksel M, Lutterbey G, Biersack HJ, Elke U, Hasan C, Gao Z, Bode U, Ezziddin S. 111In-pentetreotide scintigraphy in medulloblastoma: a comparison with magnetic resonance imaging. Acta Oncol. 2007;46:111–7. doi: 10.1080/02841860600833152. [DOI] [PubMed] [Google Scholar]
  • 13.Albert R, Smith-Jones P, Stolz B, Simeon C, Knecht H, Bruns C, Pless J. Direct synthesis of [DOTA-dPhe1]-octreotide and [DOTA-dPhe1,Tyr3]-octreotide (SMT487): two conjugates for systemic delivery of radiotherapeutical nuclides to somatostatin receptor positive tumors in man. Bioorg. Med. Chem. Lett. 1998;8:1207–10. doi: 10.1016/s0960-894x(98)00187-5. [DOI] [PubMed] [Google Scholar]
  • 14.Capello A, Krenning EP, Breeman WA, Bernard BF, Konijnenberg MW, de Jong M. Tyr3-octreotide and Tyr3-octreotate radiolabeled with 177Lu or 90Y: peptide receptor radionuclide therapy results in vitro. Cancer Biother. Radiopharm. 2003;18:761–8. doi: 10.1089/108497803770418300. [DOI] [PubMed] [Google Scholar]
  • 15.de Jong M, Breeman WA, Bakker WH, Kooij PP, Bernard BF, Hofland LJ, Visser TJ, Srinivasan A, Schmidt MA, Erion JL, Bugaj JE, Macke HR, Krenning EP. Comparison of (111)In-labeled somatostatin analogues for tumor scintigraphy and radionuclide therapy. Cancer Res. 1998;58:437–41. [PubMed] [Google Scholar]
  • 16.Sward C, Bernhardt P, Johanson V, Schmitt A, Ahlman H, Stridsberg M, Forssell-Aronsson E, Nilsson O, Kolby L. Comparison of [177Lu-DOTA0,Tyr3]-octreotate and [177Lu-DOTA0,Tyr3]-octreotide for receptor-mediated radiation therapy of the xenografted human midgut carcinoid tumor GOT1. Cancer Biother. Radiopharm. 2008;23:114–20. doi: 10.1089/cbr.2007.0421. [DOI] [PubMed] [Google Scholar]
  • 17.Vaidyanathan G, Friedman HS, Affleck DJ, Schottelius M, Wester HJ, Zalutsky MR. Specific and high-level targeting of radiolabeled octreotide analogues to human medulloblastoma xenografts. Clin. Cancer Res. 2003;9:1868–76. [PubMed] [Google Scholar]
  • 18.Dvorakova Z, Henkelmann R, Lin X, Turler A, Gerstenberg H. Production of 177Lu at the new research reactor FRM-II: Irradiation yield of 176Lu(n,()177Lu. Appl. Radiat. Isot. 2008;66:147–51. doi: 10.1016/j.apradiso.2007.08.013. [DOI] [PubMed] [Google Scholar]
  • 19.Kwekkeboom DJ, Bakker WH, Kam BL, Teunissen JJ, Kooij PP, de Herder WW, Feelders RA, van Eijck CH, de Jong M, Srinivasan A, Erion JL, Krenning EP. Treatment of patients with gastro-entero-pancreatic (GEP) tumours with the novel radiolabelled somatostatin analogue [177Lu-DOTA(0),Tyr3]octreotate. Eur. J. Nucl. Med. Mol. Imaging. 2003;30:417–22. doi: 10.1007/s00259-002-1050-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 20.Kwekkeboom DJ, Bakker WH, Kooij PP, Konijnenberg MW, Srinivasan A, Erion JL, Schmidt MA, Bugaj JL, de Jong M, Krenning EP. [177Lu-DOTA0Tyr3]octreotate: comparison with [111In-DTPA0]octreotide in patients. Eur. J. Nucl. Med. 2001;28:1319–25. doi: 10.1007/s002590100574. [DOI] [PubMed] [Google Scholar]
  • 21.Kwekkeboom DJ, de Herder WW, Kam BL, van Eijck CH, van Essen M, Kooij PP, Feelders RA, van Aken MO, Krenning EP. Treatment with the radiolabeled somatostatin analog [177 Lu-DOTA0,Tyr3]octreotate: toxicity, efficacy, and survival. J. Clin. Oncol. 2008;26:2124–30. doi: 10.1200/JCO.2007.15.2553. [DOI] [PubMed] [Google Scholar]
  • 22.Kwekkeboom DJ, Teunissen JJ, Bakker WH, Kooij PP, de Herder WW, Feelders RA, van Eijck CH, Esser JP, Kam BL, Krenning EP. Radiolabeled somatostatin analog [177Lu-DOTA0,Tyr3]octreotate in patients with endocrine gastroenteropancreatic tumors. J. Clin. Oncol. 2005;23:2754–62. doi: 10.1200/JCO.2005.08.066. [DOI] [PubMed] [Google Scholar]
  • 23.Friedman HS, Burger PC, Bigner SH, Trojanowski JQ, Brodeur GM, He XM, Wikstrand CJ, Kurtzberg J, Berens ME, Halperin EC, Bigner DD. Phenotypic and genotypic analysis of a human medulloblastoma cell line and transplantable xenograft (D341 Med) demonstrating amplification of c-myc. Am. J. Pathol. 1988;130:472–84. [PMC free article] [PubMed] [Google Scholar]
  • 24.Breeman WA, De Jong M, Visser TJ, Erion JL, Krenning EP. Optimising conditions for radiolabelling of DOTA-peptides with 90Y, 111In and 177Lu at high specific activities. Eur. J. Nucl. Med. Mol. Imaging. 2003;30:917–20. doi: 10.1007/s00259-003-1142-0. [DOI] [PubMed] [Google Scholar]
  • 25.Das T, Chakraborty S, Banerjee S, Venkatesh M. On the preparation of a therapeutic dose of 177Lu-labeled DOTA-TATE using indigenously produced 177Lu in medium flux reactor. Appl. Radiat. Isot. 2007;65:301–8. doi: 10.1016/j.apradiso.2006.09.011. [DOI] [PubMed] [Google Scholar]
  • 26.Lewis JS, Wang M, Laforest R, Wang F, Erion JL, Bugaj JE, Srinivasan A, Anderson CJ. Toxicity and dosimetry of 177Lu-DOTA-Y3-octreotate in a rat model. Int. J. Cancer. 2001;94:873–7. doi: 10.1002/ijc.1540. [DOI] [PubMed] [Google Scholar]
  • 27.Bouffet E. Embryonal tumours of the central nervous system. Eur. J. Cancer. 2002;38:1112–20. doi: 10.1016/s0959-8049(02)00071-0. [DOI] [PubMed] [Google Scholar]
  • 28.Kramer K, Humm JL, Souweidane MM, Zanzonico PB, Dunkel IJ, Gerald WL, Khakoo Y, Yeh SD, Yeung HW, Finn RD, Wolden SL, Larson SM, Cheung NK. Phase I study of targeted radioimmunotherapy for leptomeningeal cancers using intra-Ommaya 131I-3F8. J. Clin. Oncol. 2007;25:5465–70. doi: 10.1200/JCO.2007.11.1807. [DOI] [PubMed] [Google Scholar]
  • 29.Beutler D, Avoledo P, Reubi JC, Macke HR, Muller-Brand J, Merlo A, Kuhne T. Three-year recurrence-free survival in a patient with recurrent medulloblastoma after resection, high-dose chemotherapy, and intrathecal Yttrium-90-labeled DOTA0-D-Phe1-Tyr3-octreotide radiopeptide brachytherapy. Cancer. 2005;103:869–73. doi: 10.1002/cncr.20822. [DOI] [PubMed] [Google Scholar]
  • 30.Millar WT, Barrett A. Dosimetric model for antibody targeted radionuclide therapy of tumor cells in cerebrospinal fluid. Cancer Res. 1990;50:1043s–48s. [PubMed] [Google Scholar]
  • 31.Melicharova L, Laznicek M, Laznickova A, Petrik M. The Affinity of receptor specific peptides 111In-DOTA-NOC and 111In-DOTA-TATE to somatostatin receptors in vivo and in vitro. Biomed. Pap. Med. Fac. Univ. Palacky. Olomouc. Czech. Repub. 2007;151(Suppl 1):55–6. [Google Scholar]
  • 32.Storch D, Behe M, Walter MA, Chen J, Powell P, Mikolajczak R, Macke HR. Evaluation of [99mTc/EDDA/HYNIC0]octreotide derivatives compared with [111In-DOTA0,Tyr3, Thr8]octreotide and [111In-DTPA0]octreotide: does tumor or pancreas uptake correlate with the rate of internalization? J. Nucl. Med. 2005;46:1561–9. [PubMed] [Google Scholar]
  • 33.Wild D, Schmitt JS, Ginj M, Macke HR, Bernard BF, Krenning E, De Jong M, Wenger S, Reubi JC. DOTA-NOC, a high-affinity ligand of somatostatin receptor subtypes 2, 3 and 5 for labelling with various radiometals. Eur. J. Nucl. Med. Mol. Imaging. 2003;30:1338–47. doi: 10.1007/s00259-003-1255-5. [DOI] [PubMed] [Google Scholar]
  • 34.Vaidyanathan G, Affleck DJ, Schottelius M, Wester H, Friedman HS, Zalutsky MR. Synthesis and evaluation of glycosylated octreotate analogues labeled with radioiodine and 211At via a tin precursor. Bioconjugate Chem. 2006;17:195–203. doi: 10.1021/bc0502560. [DOI] [PubMed] [Google Scholar]
  • 35.Vaidyanathan G, Boskovitz A, Shankar S, Zalutsky MR. Radioiodine and 211At-labeled guanidinomethyl halobenzoyl octreotate conjugates: potential peptide radiotherapeutics for somatostatin receptor-positive cancers. Peptides. 2004;25:2087–97. doi: 10.1016/j.peptides.2004.08.018. [DOI] [PubMed] [Google Scholar]
  • 36.Vaidyanathan G, Affleck DJ, Norman J, O'Dorisio S, Zalutsky MR. A radioiodinated MIBG-octreotate conjugate exhibiting enhanced uptake and retention in SSTR2-expressing tumor cells. Bioconjugate Chem. 2007;18:2122–30. doi: 10.1021/bc700240r. [DOI] [PubMed] [Google Scholar]
  • 37.Breeman WA, Kwekkeboom DJ, Kooij PP, Bakker WH, Hofland LJ, Visser TJ, Ensing GJ, Lamberts SW, Krenning EP. Effect of dose and specific activity on tissue distribution of indium-111-pentetreotide in rats. J. Nucl. Med. 1995;36:623–7. [PubMed] [Google Scholar]
  • 38.de Jong M, Breeman WA, Bernard BF, van Gameren A, de Bruin E, Bakker WH, van der Pluijm ME, Visser TJ, Macke HR, Krenning EP. Tumour uptake of the radiolabelled somatostatin analogue [DOTA0, TYR3]octreotide is dependent on the peptide amount. Eur. J. Nucl. Med. 1999;26:693–8. doi: 10.1007/s002590050439. [DOI] [PubMed] [Google Scholar]
  • 39.Hofland LJ, van Koetsveld PM, Waaijers M, Zuyderwijk J, Breeman WA, Lamberts SW. Internalization of the radioiodinated somatostatin analog [125I-Tyr3]octreotide by mouse and human pituitary tumor cells: increase by unlabeled octreotide. Endocrinology. 1995;136:3698–706. doi: 10.1210/endo.136.9.7649075. [DOI] [PubMed] [Google Scholar]
  • 40.Kuan C-T, Wikstrand CJ, McLendon RE, Zalutsky MR, Kumar U, Bigner DD. Detection of the amino-terminal extracellular domain of the somatostatin receptor 2 by specific Mabs and quantification of receptor density in medulloblastoma. Hybridoma. 2009 doi: 10.1089/hyb.2009.0049. in press. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 41.Schmitt A, Bernhardt P, Nilsson O, Ahlman H, Kolby L, Forssell-Aronsson E. Differences in biodistribution between 99mTc-depreotide, 111In-DTPA-octreotide, and 177Lu-DOTA-Tyr3-octreotate in a small cell lung cancer animal model. Cancer Biother. Radiopharm. 2005;20:231–6. doi: 10.1089/cbr.2005.20.231. [DOI] [PubMed] [Google Scholar]
  • 42.Schmitt A, Bernhardt P, Nilsson O, Ahlman H, Kolby L, Schmitt J, Forssel-Aronsson E. Biodistribution and dosimetry of 177Lu-labeled [DOTA0,Tyr3]octreotate in male nude mice with human small cell lung cancer. Cancer Biother. Radiopharm. 2003;18:593–9. doi: 10.1089/108497803322287682. [DOI] [PubMed] [Google Scholar]
  • 43.Petrik M, Laznickova A, Laznicek M, Zalutsky MR. Radiolabelling of glucose-Tyr3-octreotate with 125I and analysis of its metabolism in rats: comparison with radiolabelled DOTA-Tyr3-octreotate. Anticancer Res. 2007;27:3941–6. [PubMed] [Google Scholar]

RESOURCES