somatostatin receptor-targeted radionuclide therapy of tumors: preclinical and clinical findings

Somatostatin Receptor-Targeted Radionuclide Therapy of Tumors: Preclinical and Clinical Findings

Mar ion de Jong, Roelf Valkema, Francois Jamar, Larry K. Kvols, Dik J. Kwekkeboom, Wout A.P. Breeman, Wi l lem H. Bakker, Chuck Smith, Stanislas Pauwels, and Eric P. Krenning

In preclinical studies in rats we evaluated biodistribution and therapeutic effects of different somatostatin analogs, [l~lln- DTPA]octreotide, [s~ and [l??Lu- DOTA,Tyr3]octreotate, currently also being applied in clinical radionuclide therapy studies. [Tyr3]octreotide and [Tyr 3] octreotate, chelated with DTPA or DOTA, both showed high affinity binding to somatostatin receptor subtype 2 (sst 2) in vitro. The radiolabelled compounds all showed high tumor uptake in sst2-positive tumors in vivo in rats, the highest uptake being reached with [l??Lu-DOTA,Tyr3]octreotate. In preclinical therapy studies in vivo in rats, excellent, dose dependent, tumor size responses were found, responses appeared to be dependent on tumor size at therapy start. These preclinical data showed the great promise of radionuclide therapy with radiolabelled somatostatin analogues. They emphasised the concept that especially the combination of somatostatin analogs radiolabeled with different radionuclides, like soy and 177Lu, is most promising to reach a wider tumor size region of high curability. Furthermore, different phase I clinical studies, using [ ~ l n - DTPA]octreotide, [s~ or [I??Lu-DOTA, Tyr3]octreotate are described. Fifty patients with somatostatin receptor-positive tumors were treated with multiple doses of [1111n-DTPA~ Forty patients were evaluable after cumulative doses of at least 20 GBq up to 160 GBq. Therapeutic effects were seen in 21 patients: partial remission in 1 patient, minor remissions in 6 patients, and stabilization of previously

progressive tumors in 14 patients. The toxicity was generally mild bone marrow toxicity, but 3 of the 6 patients who received more than 100 GBq developed a myelodysplastic syndrome or leukemia. Radionuclide therapy with [s~ started in 3 different phase I trials. Overall, antimitotic effects have been observed: about 20% partial response and 60% stable disease (N = 92) along with complete symptomatic cure of several malignant insulinoma and gastrinoma patients. Maximum cumulative [s~ dose was about 26 GBq, wi thout reaching the maximum tolerable dose. New is the use of [l??Lu-DOTA,Tyr3]octreotate, which shows the highest tumor uptake of all tested octreotide analogs so far, with excellent tumor-to-kidney ratios. Radionuclide therapy with this analog in a phase 1 trial started recently in our center in 63 patients (238 administrations), Interim analysis of 18 patients with neuroendocrine tumors was performed very recently. According to the WHO, toxicity criteria no dose limiting toxicity was observed. Minor CT-assessed tumor shrinkage (25% - 50% reduction) was noticed in 5% of 18 patients and partial remission (50% - 100% reduction, SWOG criterial in 39%. Eleven percent of patients had tumor progression and in 44% no changes were seen. These data show that radionuclide therapy with radiolabelled somstostatin analogs, like [DOTA,Tyr3]octreotide and [DOTA, Tyr3]octreotate is a most promising new treatment modality for patients who have sst2-positive tumors. Copyright 2002, Elsevier Science (USA). Aft rights reserved.

R ADIOLABELED SOMATOSTATIN analogues, such as octreotide, have found widespread application for visualization

of somatostatin receptor-positive tumors; this topic is described in detail elsewhere in this issue. The newest and most promising somatostatin analogues are Tyr3-0ctreotide and Tyr3-0ctreotate; in the latter, the alcohol Thr(ol) at the C terminus, as used in octreotide, is replaced with the natural amino acid Thr (Fig. 1).

This analogue was found to have a very high affinity for the somatostatin receptor subtype 2 (sst2) and showed the highest uptake in rat pancreatic CA20948 tumor in a rat biodistribution study that used different l~]In-labeled somatostatin analogues ~ (Fig. 2); in patients, radiolabeled octreotate also seemed to have a higher tumor uptake than ~qn-labeled octreotide. 2

When the success of peptide receptor scintigraphy for tumor visualization became clear, the next logical step was to try to label these peptides with therapeutic radionuclides emitting c~- or 13- particles or Auger or conversion electrons and to perform radiotherapy with these radiolabeled peptides.

Studies with an Auger electron emitter (~tlln), a high-energy 13- particle emitter (9Oy), and a low-energy 13-particle emitter (]77Lu) complexed to octreotide analogues have been reported. Promising results with regard to tumor growth inhibition were shown in preclinical studies and in patient studies with [~]In- diethylenetriamine pentaacetic acid (DTPA)]octreotide, 3-6 [9oy_ tetraazacyl-cododecanetetraacenic acid (DOTA)~ - tide, 4"7-1~ and [177Lu-DOTA~

OCTREOTIDE

E x p e r i m e n t a l D a t a

Somatostatin receptors are integral membrane glycoproteins; 5 different human somatostatin receptor subtypes have been cloned. 15-]7 Somatostatin binds to all subtypes with high affinity, whereas the affinity of the different somatostatin analogues for these subtypes differs considerably. For example, octreotide binds with high affinity to sst 2 and with lower affinities to sst s and sst 3. It shows no binding ]6 to sst I and sst 4.

For successful scintigraphy and radionuclide therapy via somatostatin receptor targeting, a long retention of the radionuclide in the tumor cell is very important. To meet this criterion, internalization of the radiolabeled peptide is essential. We have studied internalization of radiolabelled [DTPA]octreotide in somatostatin receptor-positive rat pancreatic tumor cell lines and detected internalization of the radiopharmaceutical in vitro, ~8 in accordance with the findings of Andersson et a1,19 and found that this process

From the Department of Nuclear Medicine, Erasmus University Medical Center Rotterdam, Rotterdam, The Netherlands; Universitaire Cutholique Louvain, Brussels, Belgium; Lee Moffitt Cancer Center, University of South Florida, Tampa, FL; and Novartis Pharmaceutical Corporation, East Hunover, NJ.

Address reprint requests to M. de Jong, PhD, Department of Nuclear Medicine, Erasmus University Center Rotterdam, 3015 GD Rotterdam, The Netherlands.

Copyright 2002, Elsevier Science (USA). All rights reserved. 0001-2998/02/3202-0007535.00 doi: l O. 105 3/snuc.2002.31027

Seminars in Nuclear Medicine, Vol XXXII, No 2 (April), 2002: pp 133-140 133

134 oE JONG ET AL

octreotide D-Phe-cyclo(Cvs-Phe-D-Trp-Lys-Thr-Cys)-Thr(ol)

[Tyr3]octreotide O-Phe-cyclo(Cvs-Tyr-D-Trp-Lvs-Thr-Cvs)-Thr(ol)

ITvr~loctreotate D-Phe-cyclo(Cys-Tyr-D-Trp-Lys-Thr-Cys)-Thr

Fig. 1. Structures of octreotide, [Tyr~]octreoUde, and [~rS]octreotate.

was receptor specific and temperature dependent. Earlier, we reported internalization of [laSI-Tyr3]octreotide in in vitro studies. z~ Receptor-mediated internalization of [111in_DTPA]octreotide results in degradation to the final radiolabeled metabolite IHIn- DTPA-D-Phe in the lysosomes, al This metabolite is not capable of passing the lysosomal or other cell membranes and will therefore stay in the lysosomes, causing the long retention time of 11~In in sst2-positive (tumor) cells. Internalization is especially important for radionuclide therapy of tumors when radionuclides emitting therapeutic particles with very short path lengths are used, such as those emitting Auger electrons (eg, 11]In). These electrons are effective only in a short distance of only a few nanometers to micrometers from their target, the nuclear DNA. Recently, Hornick et al 2z described in vitro cellular internalization, nuclear translocation, and DNA binding of radiolabeled somatostatin analogues, which significantIy increased after prolonged exposure. Therefore, ~HIn-labeled peptides are suitable for both scintigraphy and radi0nuclide therapy.

In our preclinical radionuclide therapy studies, we used the rat pancreatic CA20948 tumor as a model for receptor-targeted scintigraphy and radionuclide therapy with radiolabeled somatostatin analogues. This tumor is transplantable in Lewis rats, not only subcutaneously in the flank, but also metastasized to the liver. The latter is achieved by inoculation of tumor cells into the portal vein of the liver. The CA20948 tumor is somatostatin receptor- positive and is therefore an excellent model for studying receptor- targeted scintigraphy and radionuclide therapy in rats with radiolabeled somatostatin analogues. 23

We performed radionuclide therapy by using [H~In- DTPA]octreotide in the CA20948 liver metastases model. 6 Radio- nuclide therapy with administrations of 370 MBq (coupled to 0.5 lag of octreotide) of [HlIn-DTPA]octreotide on day 1, day 8, or both after intraportal CA20948 tumor cell inoculation induced a significant decrease in the number of hepatic metastases at day 21 (Fig. 3). Coinjection with 1 mg of unlabeled octreotide resulted in

inhibition of the tumor response to radionuclide therapy, pointing to a receptor-dependent therapeutic effect. Also, dose-dependent effects of radionuclide therapy by injection of 370, 37, or 3.7 MBq of [111In-DTPA]octreotide 1 day after tumor inoculation were investigated. 4 The 370-MBq dosage had significantly more of an effect on tumor score, determined at 20 days after tumor inoculation, and inhibited the increase of liver weight caused by tumor growth more than the 37- or 3.7-MBq doses. Radionuclide therapy on day 6 or 12 after tumor implant also induced a significant decrease in tumor score versus the control group. We thus showed that tumor growth can be inhibited with radionuclide therapy by using [111In-DTPA]octreotide, even 12 days after inoculation of the somatostatin receptor-positive tumor cells into the portal vein.

The aim of a different study was to evaluate whether radionu- elide therapy with [~]lIn-DTPA]octreotide was able to reduce tumor growth even under tumor growth-stimulating conditions induced by partial hepatectomy (PHx). In this study rats underwent 70% PHx or sham operation. The development of metastases (on a scale of 0 [no metastases] to 5+ [severe tumor load]) was determined 21 days after injection of somatostatin receptor- positive (CA20948) or -negative (CC531) tumor cells into the portal vein. Groups of 8 or 9 animals that underwent PHx or sham operation were treated with octreotide 50 lag/kg subcutaneously twice daily or with 370 MBq of [l~In-DTPA]octreotide intrave- nously (iv) at day 1 and 8. Non-tumor-beating rats were used to determine the influence of [1]lln-DTPA]octreotide on liver regeneration after PHx. An increase in tumor growth was induced after PHx in all experiments (P < .01). Octreotide treatment did not influence tumor growth after PHx or sham operation. [n l In- DTPA]octreotide, however, effectively reduced tumor growth in the liver of somatostatin receptor-positive tumors even under conditions of increased tumor growth, as generated by PHx (P < .01; Table 1). [111in_DTPA]octreotide was also effective on somatostatin receptor-negative tumors after PHx (P = .01), but not after sham operation (Table 2). An explanation for the effect of radionuclide therapy on somatostatin receptor-negative tumors could be that the neovasculature of regenerating livers expresses a high density of somatostatin receptors, as has been demonstrated in peritumoral veins in primary tumors and their metastases. The effect of radionuclide therapy on these somatostatin receptor- negative tumors could then be ascribed to accumulation of the radionuclide close to the tumor cells and the inhibitory effect on angioneogenesis (manuscript in preparation).

tumor kidney tumor/kidney

200t I I ~176 oo '~176 I I I 0' 0 0 ~

o o uJ w o o LY W o c~ w w

Fig. 2. Uptake in CA20948 tumor and kidney and tumor to kidney ratio of 4 different 111In-labeled DTPA-chelated somatostatin analogues--[1111n - DTPA]octreotide (OC), [1111n-DTPA, "ryr3]octreotide (TyrOC), [~111n-DTPA]octreotate (TATE), and [11qn-DTPA, Tyr3]octreotate (TyrTATE)~24 hours postinjection in male Lewis rats. Data are expressed as percentage of uptake or the tumor to kidney ratio of OC.

SOMATOSTATIN RECEPTOR-TARGETED RADIONUCLIDE THERAPY 135

Fig. 3. Livers from the control (A) and experimental (B) groups. (A) liver with metastases (control). (B) liver with no visible metastases after peptlde receptor radlonucllde therapy on days 1 and 8 after Intraportal CA20948 tumor cell inoculation with 370 MBq [1111n-DTPA]octreotide.

We concluded that radionuclide therapy with [1 ~lin - DTPA~ was effective in somatostatin receptor-positive tumors, and during liver regeneration this treatment also reduced the growth of somatostatin receptor-negative tumors. This effect seemed not to be induced by impairment of liver regeneration or liver function. Radionuclide therapy could therefore also be a promising treatment modality for patients with symptomatic liver metastases from neuroendocrine tumors after resection of liver metastases.

The radiotherapeutic effect of different doses of [ ~ I n - DTPA]octreotide was also studied in rats bearing solid pancreatic CA20948 tumors of different sizes in the flank. 4 For [lllln-DTPA] octreotide, a dose response was found, leading in rats bearing small tumors (<1 cm 2) to a 50% cure after the highest dose (3 injections of 370 MBq, given with an interval of 1 week), whereas in rats bearing large tumors (>10 cm2), only a partial response could be achieved. In larger tumors, more clonogenic, presumably hypoxic, cells are present, thereby limiting radiocurability. These findings show that, even on established tumors in rats, after radionuclide therapy, reduction of tumor volume can be obtained because of the radiotherapeutic effect of ~ ~In-labeled octreotide. The findings also hold promise for the application of radionuclide therapy with ~qn-labeled octreotide in an adjuvant, micrometa- static setting, eg, after surgery to eradicate occult metastases.

Clinical Data

Fifty patients with somatostatin receptor-positive tumors were treated with multiple doses of [~tqn-DTPA]octreotide. Forty patients were evaluable after cumulative doses of at least 20 GBq

up to 160 GBq. Therapeutic effects were seen in 21 patients: partial remission in 1 patient, minor remissions in 6 patients, and stabilization of previously progressive tumors in 14 patients. The toxicity was generally mild bone marrow toxicity, but 3 of the 6 patients who received more than 100 GBq developed a myelodysplastic syndrome or leukemia. Therefore, we consider 100 GBq as the maximal tolerable dose. No significant changes in renal parameters were observed, despite high cumulative doses in many patients. 35 Clinical studies with [~ l ln-DTPA]octreotide are described in more detail elsewhere in this issue.

[ T Y R 3 ] O C T R E O T I D E A N D [ T Y R 3 ] O C T R E O T A T E

Experimental Data

DOTA is an universal chelator capable of forming stable com- plexes with metals such as ~ I n , 67Ga, 68Ga, 86y, and 6+Cu for imaging, as well as with 90y (a high-energy 13-particle emitter) and with radiolanthanides such as, eg, 177Lu (a low-energy 13-particle and ~/emitter), for receptor-mediated radionuclide therapy. Reubi et a124 recently evaluated the in vitro binding characteristics of labeled (indium, yttrium, gallium) and unlabeled [DOTA, Tyr3]octreotide, [DOTA]octreotide, [DOTA]lanreotide, [DOT- A]vapreotide (RC-160), [DTPA, Tyr3]octreotate, and [DOTA, Tyr3]octreo-tate by using cell lines transfected with the human somatostatin receptor subtypes sst t, sstz, sst3, sst4, or sst 5. They found that small structural modifications, chelator substitution, or metal replacement considerably affected the receptor binding affinity. For example, a marked improvement of sst z affinity was found for [Ga- DOTA, Tyr3]octreotide (50% inhibitory concentration [IC5o], 2.5

Table 1. The Effect of Radionuclide Therapy with [1111n-DTPA]octreotide on Somatostatin Receptor-Positive Liver Metastases After Sham Operation or 70% Partial Hepatectomy

Treatment Liver Weight Tumor Load Score No. (~) 0 1 + 2+ 3+ 4+ 5+ Mean Rats

Sham operation Control 17.3 _+ 3.1 PRRT* 10.1 _+ 0.4

70% Partial hepatectomy Control t 23.0 _+ 2.7 PRRT* 9.3 _+ 1.1

- - 1 - - - - 2 5 4.3 8 1 7 . . . . 0.9 8

. . . . 8 5.0 8 7 1 - - - - - - 1.1 8

Abbreviat ion: PRRT, peptide receptor radionuclide therapy.

*P < .01 vs controls.

P < .01 vs sham operation.

136 DE J O N G ET AL

Table 2. The Effect of Radionuclide Therapy With [1111n-DTPA]octreotide on Somatostatin Receptor-Negative Liver Metastases After Sham Operation or 70% Partial Hepatectomy

T r e a t m e n t L i ve r W e i g h t T u m o r Load Score No.

(g) 0 1+ 2 + 3 + 4 + 5 + M e a n Rats

S h a m o p e r a t i o n

C o n t r o l 14.1 -- 5.3 1 2 5 1 - - - - 1.7 9 PRRT 18.5 _+ 8.0 1 1 5 2 - - - - 1.9 9

7 0 % Part ia l h e p a t e c t o m y

C o n t r o l * 43.4 _+ 8.0 . . . . 2 7 4.8 9

P R R T t 30.8 _+ 5.6 - - - - - - 5 2 - - 3.3 7

*P < .01 vs sham operation. t P = .01 vs controls.

nmol/L) compared with the Y-labeled compound and [In- DTPA]octreotide. An excellent binding affinity for sst 2 in the same range was also found for [In-DTPA, Tyr3]octreotate (ICso, 1.3 nmol/L) and for [Y-DOTA, Tyr3]octreotate (IC5o, 1.6 nmol/L).

The radiotherapeutic effect of different doses of [9~ Tyr3]octreotide was compared in rats bearing pancreatic CA20948 tumors of different sizes in the f lankY After 370 MBq [9~ Tyr3]octreotide, 50% complete response was reached for rats bearing small tumors (<1 cm2), whereas only tumor growth delay was found in rats bearing very large tumors (>12 cm2). Rats beating medium-sized tumors (approximately 8 cm2), however, showed 100% cure after 370 MBq [9~ Tyr3]octreotide. So in this study, a difference was found in the radiotherapeutic effects in CA20948 tumors of different sizes. In larger tumors, more clonogenic, presumably hypoxic, cells are present, thereby limiting radiocurability. The small tumors, however, will not absorb all energy emitted by 9Oy, thereby decreasing tumor curability. The results found here show again the efficacy of radiolabeled octreotide analogues to control tumor growth. Tumor growth inhibition in the same model was also found after treatment of CA20948 tumor- bearing rats with [9~ With 370 MBq/kg of [9~ Tyr3]octreotide the same group even produced complete tumor reduction in 5 of 7 rats, in accordance with our findings, a~ These preclinical studies show the great promise of 9~ octreotide analogues for the clinical studies that started recently (see below). 8'27-30

The radionuclides ra in , 88y, and 177Lu were linked to [DOTA, Tyr3]octreotate, and biodistribution and tumor uptake were compared in CA20948 tumor-bearing rats. 31 The three radionuclides enabled high specific activity labeling, with labeling yield more than 99%. In vivo, for all 3 radiolabeled analogues, a rapid clearance from the blood and very high, specific uptake in sst2-positive organs and tumor were found, making these analogues most promising for radionuclide therapy.

In radionuclide therapy studies with radiolabeled octreotate, 14'31 100% cure was found in the groups of rats beating small (--<1 cm 2) CA20948 tumors after 2 repeated doses of 277.5 MBq or after a single dose of 555 MBq [a77Lu-DOTA, Tyr3]octreotate (estimated tumor radiation dose, 60 Gy). After therapy with the same doses of [177Lu-DOTA, Tyr3]octreotide, which has a lower tumor uptake than the octreotate analogue, the data showed 50% and 60% cure in rats bearing small tumors. In rats beating larger (->1 cm 2, range, 1.4-10 cm 2) tumors, 40% and 50% cures were found in the groups that received 1 or 2 277.5-MBq injections of [177Lu-DOTA, Tyr3]octreotate, respectively.

When dealing with tumors receiving high radiation doses, ie, more than 100 Gy, the size dependence of tumor curability may be less clear. In another preclinical radionuclide therapy study that we performed in a different rat pancreatic tumor model (AR42J), in which a more favorable tumor dose was reached after 555 MBq [a77Lu-DOTA, Tyr3]octreotate (140 Gy), all rats but 1 were cured irrespective of the size of their tumor (manuscript in preparation). So, in this different model with tumor radiation doses higher than 100 Gy, [aVVLu-DOTA, Tyr3]octreotate showed excellent therapeutic results in rats bearing both small and large tumors. We therefore conclude that [a77Lu-DOTA, Tyr3]octreotate is a very promising somatostatin analogue for radionuclide therapy in patients with sst2-expressing tumors.

In our studies, striking differences were found in the radiotherapeutic effects of [a77Lu-DOTA, Tyr3]octreotate and [9~ Tyr3]octreotide in tumors of different sizes (Fig. 4). On the basis of a mathematical model examining tumor curability in relation to tumor size for 22 different [3-emitting radionuclides, the optimal tumor diameter for cure calculated by O'Donoghue et al32 for 9Oy was 34 mm, in accordance with the 100% cure that we found in rats bearing 8-cm 2 tumors after [9~ Tyr3]octreotide radionuclide therapy. Tumors smaller than the optimal size are less vulnerable to radiation because a substantial part of the disinte- grating energy escapes and is deposited outside the tumor volume, as was the case in the tumors --<1 cm 2, in which only approximately 55% of the radiation energy of the 9Oy electrons is absorbed. Therefore, a better effect of 9Oy in the 8-cm 2 tumors than in the small tumors in our study could be expected and was indeed found. For 177Lu, the optimal diameter calculated was 2 mm, 32 in accordance with the fact that we found a higher cure rate in rats beating tumors smaller than 1 cm 2 (100% cure) than in those with tumors larger than 1 cm 2 (50% cure) after radionuclide therapy with [177Lu-DOTA, Tyr3]octreotate.

Therefore, in patients with tumors of different sizes, including small metastases, the administration of combinations of different radionuclides, eg, 90y, which is optimal for bigger tumors, and 177Lu, which is optimal for smaller tumors, coupled to octreotide or octreotate, is important. This is to obtain the widest range of high tumor curability. This is especially important in tumors with intermediate tumor uptake, leading to tumor radiation doses below 100 Gy.

A different class of peptides interesting for scintigraphy and radionuclide therapy is the RGD(Arg-Gly-Asp) peptides, because they can antagonize tumor angioneogenesis, eg, by binding to av[33 receptors on newly formed blood vessels. We introduced the


Fig. 4. Cure rate (expressed as percentage of cured rata) found In groups of rats bearing CA20948 tumors of dlfferent Indlcated sizes after 370 MBq [~~176 l~rS]octreot lde or 555 MBq [ lWLu- DOTA, "ryr3]octreotate. PR, psrtlal response; CR, complete response.

o~

[~Y-DOTA,Tyr3]octreotide

/,.

I

[177Lu.DOTA,Tyr3]octreotate

100'~ --

I 75.

=~ 50

q. '1,

/. -/

PR r - " l CR

RGD analogue c(Arg-Gly-Asp-D-Tyr-Lys) chelated with DTPA. In vitro and in vivo, the analogue seemed to bind with high affinity to O~v133 receptors on blood vessels and tumor cells in different rat and human cancers. 33 To combine tumor uptake via sst 2 and avl33 receptors, we synthesized an [RGD-DTPA-Tyr3]octreotate hybrid peptide. Labeling studies showed high specific activity labeling with 11qn, and in vitro binding studies showed that the radiolabeled compound had retained high affinity in the nanomolar range for both sst 2 and ~tvl33 receptors. Binding could be blocked with an excess of the different competing analogues. In animal studies, the high uptake found in the (sstE and art33 receptor-positive) rat pancreatic (CA20948) tumor was mainly via sstE targeting, presumably because of the higher affinity of Tyra-octreotate for sst 2 than that of RGD for the etvl33 receptor. The therapeutic effects of [DTPA-Tyr3]octreotate, [RGD-DTPA-Tyr3]octreotate, and [DT- PA]RGD, labeled with the Auger electron emitter I~Jln, were evaluated in vitro in a single-cell colony-forming assay (100 cells per well in 6-well plates, 1 hour of incubation with ~ qn-labeled peptide, and 10 days of colony growth) with CA20948 cells. These cells showed relative radioresistance in external beam radiation studies (survival after 1 and 2 Gy was 70% and 50% of control). In our in vitro system, all analogues were able to control tumor growth (to 0% survival), but the effects were dependent on radiation dose, incubation time, and specific activity used. This hybrid peptide radiopharmaceutical not only is therefore suitable for tumor scintigraphy, but also has potential for radionuclide therapy. 34

Clinical Data

Currently, different phase I and II studies are being performed with [9~ Tyr3]octreotide. Otte et al 7's described a study with 29 patients who received 4 or more single doses of [9Oy_ DOTA, Tyr3]octreotide with ascending activity at intervals of approximately 6 weeks (cumulative dose 6,120 +_ 1,347 MBq/m E) with the aim of performing an intrapatient dose escalation study. In total, 127 single treatments were given. In 8 of these 127 single treatments, total doses of >-3,700 MBq were administered. In an effort to prevent renal toxicity, 2 patients received Hartmann-Hepa 8% amino acid (including lysine and arginine) solution during all therapy cycles, whereas 13 patients did so during some but not all therapy cycles; in 14 patients no solution was administered during the therapy cycles. Of 29 patients, 24 patients showed no severe renal or hematologic toxicity (toxicity grade -<2 according to the National Cancer Institute grading criteria; NCIGC). These 24

patients received a cumulative dose of -<7,400 MBq/m 2. Five patients developed renal toxicity, hematologic toxicity, or both. All 5 patients received a cumulative dose of >7,400 MBq/m 2 and had received no Hartmann-Hepa 8% solution during the therapy cycles. Four of the 5 patients developed renal toxicity; 2 of these patients showed stable renal insufficiency, and 2 required hemo- dialysis. Two of the 5 patients exhibited anemia (both grade 3) and thrombocytopenia (grade 2 and 4). Twenty of the 29 patients have shown a disease stabilization, 2 a partial remission, 4 a reduction of tumor mass <50%, and 3 a progression of tumor growth.

Waldherr et al 3~ reported on their further experience of a phase II study evaluating the tumor responses of neuroendocrine tumors. Forty-one patients (mean age, 53 years) with neuroendocrine gastroenteropancreatic and bronchial tumors were included. Eighty-two percent of the patients had therapy-resistant and progressive disease. The treatment consisted of 4 iv injections of 6,000 MBq/m E [9~ Tyr3]octreotide, administered at intervals of 6 weeks, and all patients had renal protection with iv amino acid infusion. The overall response rate was 24%. For endocrine pancreatic tumors it was 36%. Complete remissions were found in 2% (1 of 41), partial remissions in 22% (9 of 41), minor responses in 12% (5 of 41 ), stable disease in 49% (20 of 41 ), and progressive disease in 15% (6 of 41). The median follow-up was 15 months (range, l month to 36 months). The median duration of response has not been reached at 26 months. Adverse effects included grade 3 (NCIGC) pancytopenia in 5% and vomiting shortly after injection in 23%. No grade 3 or 4 renal toxicity was observed.

Paganelli et al Es treated 30 patients, who received 3 equal iv injections of [9~ Tyr3]octreotide. Cohorts of 6 patients were treated starting with l . l GBq per cycle in escalating dosage (0.4-GBq increments) in subsequent groups. No patient showed acute or delayed major adverse reactions up to the dose of 2.6 GBq per cycle (7.8 GBq total). One patient, after a 3.3-GBq total dose, developed delayed kidney grade 2 toxicity. Complete and partial tumor mass reductions were measured in 23% of patients, along with 64% showing stable disease and 13% progressive disease.

W e 27 a re performing a phase I, Novartis (Basel, Switzerland)- sponsored study with [9~ Tyr3]octreotide, to define the maximal tolerated single and 4-cycle dose of [9~ Tyr3]octreotide. Forty-two patients (23 women and 19 men) are included up to now. Twenty-one patients had carcinoid tumors; 10, islet cell carcinoma; and l l , other neuroendocrine tumors. At baseline 34 patients were progressive, and 8 had stable tumors. Before treatment, all patients underwent quantitative positron emission tomography with [S6y-DOTA, Tyr3]octreotide, thus la-

138 DE JONG ET AL

Baseline Cycle 4 Wk6

10 x 10 mm Baseline 5 x 5 m m C y c l e 3 W k 4

luu

140

�9 . . . 1 1 ,w= a f t - - -

4O

-260 -t30

I I

OChromogranin A (%) ~-~ &Y-90-SMT487 [

.O O- [ ] [ ]

�9 A & �9 130 260 390 520

Days since start [g~ r~joct reotid e

650 780

Fig. 5. Baseline and follow-up 6 weeks after cycle 4 (octreotide scintigraphy, anterior abdominal views, top row) and 4 weeks after cycle 3 (computed tomography [CT], middle row) of a patient with liver metastases of a gastrinoma who received 4 • 104 mCi of [9~ Before the start of therapy she had severe diarrhea and increasing levels of gastrin and chromogranin A (bottom graph). After 3 cycles she had a partial response (>50% decrease of tumor volume on CT) accompa- nied by a lower uptake of [1111n-DTPA]octreotide on scintigraphy, normalization of serum gastrin levels (under continued use of omeprazole 40 mg three times a day), and decreasing levels of chromogranin. The diarrhea disappeared after the second cycle. This response has continued for more than 2 years.

beled with an radioisotope of Y different from 9Oy, to predict the renal exposure expected with [9~ Tyr3]octreotide. The cumulative radiation dose to the kidneys was limited to 27 Gy. Because iv amino acids were shown by [S6y-DOTA, Tyr3]octreotide to reduce renal exposure, all patients received amino acids concomitant with [9~ Tyr3]octreotide. In 31 patients, the intention was to give 4 cycles of escalating doses of 25, 50, 75, and 100 mCi/m 2 (0.9, 1.8, 2.8, and 3.7 GBq), repeated every 6 to 9 weeks. Patients received lower doses per cycle if the cohort dose would induce renal radiation exposure beyond this limit. In 11 patients, escalating single doses of 100, 125, and 150 mCi/m 2 (3.7, 4.6, and 5.5 GBq) were given. The median follow-up is 15 months. With cycle doses ranging from 36 to 291 mCi (1.3-10.8 GBq) and cumulative doses from 47 to 733 mCi (1.7-27 GBq), the maximal tolerable dose has not been reached so far. Three patients had dose-limiting toxicity: 1 had liver toxicity grade 3, 1 had thrombocytopenia grade 4, and 1 had myelodysplasfic

syndrome (2 years after the start of [9~ Tyr3]octreotide therapy and previous chemotherapy). Renal toxicity was mild; 2 patients had grade 1 proteinuria and 1 had grade 2 serum creatinine. In 10 patients, after 2 years a 37% increase in serum creatinine and a 16% to 18% decrease in creatinine clearance occurred. Five patients showed thrombocytopenia grade 3 and 1 showed grade 4 (5 of 6 patients had prior chemotherapy); 9 patients showed grade 2 and 6 showed grade 3 leukopenia, usually reversible, and 9 patients had grade 2 and 4 patients had grade 3 anemia. No endocrine dysfunction of pituitary axes (thyroid, adrenal, gonadal) or diabetes mellitus induction was seen; in men a >80% decrease in serum inhibin B with a concurrent increase in serum follicle-stimulating hormone (FSH) suggested a negative effect on spermatogenesis. In 32 patients who were given the planned dose, 3 had partial (50%-100% reduction; Southwest Oncology Group [SWOG] criteria) and 3 had minor remissions (25%-50% reduction), whereas 17 were stable and 9 progressive.


In 2 of 2 insulinoma and 1 of 1 gastrinoma patients, hormone values and symptomatology completely normalized (Fig. 5). Six- teen (50%) patients had symptomatic improvement. We concluded that renal toxicity is mild in [9oy-DOTA, Tyr3]octreotide therapy, with individualized (renal) dosimetry and coinfusion of protective amino acids, when the renal radiation dose is limited to <27 Gy. Prior chemotherapy predisposes to hematologic toxicity. The antitumor effects and symptomatic improvement in this phase I trial are most encouraging. A phase II Novartis-sponsored trial of [9~ Tyr3]octreotide treatment in patients with neuroendocrine tumors started recently.

New is the use of [177Lu-DOTA, Tyr3]octreotate for radionu-

clide therapy. ~4 It shows the highest tumor uptake of all tested octreotide analogues so far, not only in rats, but also in patients with neuroendocrine tumors, with excellent tumor to kidney ratios. 2 Radiotherapy with this analogue started only very recently in our center in 63 patients (238 administrations). Interim analysis of 18 patients with neuroendocrine tumors who had received at least 600 to 800 mCi (22-30 GBq) and were observed for at least 3 months was performed very recently. Most patients had progressive disease before enrollment. All had amino acid coinfusion to reduce kidney dose. Mild nausea, vomiting, and mild abdominal discomfort were present in 29%, 14%, and 11%, respectively. According to the World Health Organization toxicity criteria, no dose-limiting toxicity was observed. Serum creatinine did not

change significantly in any patient. Similar changes in serum inhibin B and FSH, as described previously, have been observed, suggesting a negative effect on spermatogenesis. Minor computed tomography-assessed tumor shrinkage (25%-50% reduction) was noticed in 6% of 18 patients, and partial remission (50%-100% reduction; SWOG criteria) was seen in 39%. Eleven percent of patients had tumor progression, and in 44%, no changes were seen.

These early results of antitumor effects with [9~ Tyr3]octreotide and [177Lu-DOTA, Tyr3]octreotate are most encouraging and more pronounced than the results of studies reported with nonradiolabeled somatostatin analogues. 35

S U M M A R Y A N D CONCLUSION

This review shows that radionuclide therapy with radiolabeled somatostatin analogues, such as [DOTA, Tyr3]octreotide and [DOTA, Tyra]octreo - rate, is a most promising new treatment modality for patients who have sst2-positive tumors.

A variety of other peptide-based radioligands, such as bomb- esin, gastrin/cholecystokinin, and neurotensin analogues, whose receptors are expressed in a variety of common cancers, and the new RGD peptides, which can be targeted to many common tumors because of their binding to receptors expressed on newly formed blood vessels, are currently under development.

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somatostatin receptor-targeted radionuclide therapy of tumors: preclinical and clinical findings

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