Dose-response effect of Gelofusine on renal uptake and retention of radiolabelled octreotate in rats with CA20948 tumours

Purpose

Peptide receptor radionuclide therapy using β-emitting radiolabelled somatostatin analogues like DOTA,Tyr³-octreotate shows beneficial results in patients suffering from somatostatin receptor overexpressing tumours. However, after high-dose therapy partial renal reabsorption of radiopeptides may lead to nephrotoxicity. Co-infusion of lysine/arginine lowers renal retention of these radiopeptides without affecting tumour uptake. Recently co-administration of Gelofusine has been described to have a comparable kidney-protecting effect in rats. In the present study optimal dosing of Gelofusine co-administration was studied in tumour-bearing rats.

Methods

Doses of 40, 80, 120 or 160 mg/kg Gelofusine were co-injected with 15 µg DOTA,Tyr³-octreotate, labelled with 3 MBq ¹¹¹In for biodistribution (24 h post-injection, n = 4 per group) and with 60 MBq ¹¹¹In for microSPECT imaging experiments at 3, 24 and 48 h post-injection. An additional group of rats received 80 mg/kg Gelofusine plus 400 mg/kg lysine co-injection. Biodistribution studies were performed both in older (475 g) and younger (300 g) rats, the latter bearing CA20948 tumours.

Results

Co-injection of 40 mg/kg Gelofusine resulted in 40–50% reduction of renal uptake and retention of ¹¹¹In-DOTA,Tyr³-octreotate, whereas higher doses further increased the reduction to 50–60% in both groups of rats. Combining Gelofusine and lysine caused 70% reduction of renal uptake. The uptake of radiolabelled octreotate both in somatostatin receptor-expressing normal tissues and tumours was not affected by Gelofusine co-injection.

Conclusion

In rats co-injection of 80 mg/kg Gelofusine resulted in maximum reduction of renal retention of ¹¹¹In-DOTA,Tyr³-octreotate, which was further improved when combined with lysine. Tumour uptake of radiolabelled octreotate was not affected, resulting in an increased tumour to kidney ratio.

Nephrotoxicity in mice after repeated imaging using 111In-labeled peptides

We determined the renal radiation dose of a series of (111)In-labeled peptides using animal SPECT. Because the animals' health deteriorated, renal toxicity was assessed.

METHODS

Wild-type and megalin-deficient mice were imaged repeatedly at 3- to 6-wk intervals to quantify renal retention after injection of 40-50 MBq of (111)In-diethylenetriaminepentaacetic acid-labeled peptides (octreotide, exendin, octreotate, neurotensin, and minigastrin analogs), and the absorbed kidney radiation doses were estimated. Body weight, renal function parameters, and renal histology were determined at 16-20 wk after the first scan and compared with those in naive animals.

RESULTS

Because of high renal retention, (111)In-diethylenetriaminepentaacetic acid-exendin-4 scans resulted in a 70-Gy kidney radiation dose in wild-type mice. Megalin-deficient kidneys received 20-40 Gy. The other peptides resulted in much lower renal doses. Kidney function monitoring indicated renal damage in imaged animals.

CONCLUSION

Micro-SPECT enables longitudinal studies in 1 animal. However, long-term nephrotoxic effects may be induced after high renal radiation doses, even with (111)In-labeled radiotracers.

Up-regulation of somatostatin receptor density on rat CA20948 tumors escaped from low dose [177Lu-DOTA0,Tyr3]octreotate therapy

AIM

Peptide receptor radionuclide therapy using the somatostatin analogue [(177)Lu-DOTA(0),Tyr(3)]octreotate is a convincing treatment modality for metastasized neuroendocrine tumors. Therapeutic doses are administered in 4 cycles with 6-10 week intervals. A high somatostatin receptor density on tumor cells is a prerequisite at every administration to enable effective therapy. In this study, the density of the somatostatin receptor subtype 2 (sst2) was investigated in the rat CA20948 pancreatic tumor model after low dose [(177)Lu-DOTA(0), Tyr(3)]octreotate administration resulting in approximately 20 Gy tumor radiation absorbed dose, whereas 60 Gy is needed to induce complete tumor regression in these and the majority of tumors.

METHODS

Sixteen days after inoculation of the CA20948 tumor, male Lewis rats were injected with 185 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate to initiate a decline in tumor size. Approximately 40 days after injection, tumors re-grew progressively after initial response. Quantification of sst2 expression was performed using in vitro autoradiography on frozen sections of three groups: control (not-treated) tumors, tumors in regression and tumors in re-growth. Histology and proliferation were determined using HE- and anti-Ki-67-staining.

RESULTS

The sst2 expression on CA20948 tumor cells decreased significantly after therapy to 5% of control level. However, tumors escaping from therapy showed an up-regulated sst2 level of 2-5 times higher sst2 density compared to control tumors.

CONCLUSION

After a suboptimal therapeutic dose of [(177)Lu-DOTA(0),Tyr(3)]octreotate, escape of tumors is likely to occur. Since these cells show an up-regulated sst2 receptor density, a next therapeutic administration of radiolabelled sst2 analogue can be expected to be highly effective.

From outside to inside? Dose-dependent renal tubular damage after high-dose peptide receptor radionuclide therapy in rats measured with in vivo (99m)Tc-DMSA-SPECT and molecular imaging

In peptide receptor radionuclide therapy (PRRT), the dose-limiting organ is, most often, the kidney. However, the precise mechanism as well as the exact localization of kidney damage during PRRT have not been fully elucidated. We studied renal damage in rats after therapy with different amounts of [(177)Lu-DOTA(0), Tyr(3)]octreotate and investigated (99m)Tc-DMSA (dimercaptosuccinic acid) as a tool to quantify renal damage after PRRT.

EXPERIMENTAL DESIGN

Twenty-nine (29) rats were divided into 3 groups and injected with either 0, 278, or 555 MBq [(177)Lu-DOTA(0), Tyr(3) ]octreotate, leading to approximately 0, 46, and 92 Gy to the renal cortex. More than 100 days after therapy, kidney damage was investigated using (99m)Tc-DMSA single-photon emission computed tomography (SPECT) autoradiography, histology, and blood analyses.

RESULTS

In vivo SPECT with (99m)Tc-DMSA resulted in high-resolution (<1.6-mm) images. The (99m)Tc-DMSA uptake in the rat kidneys was inversely related with the earlier injected activity of [(177)Lu-DOTA(0), Tyr(3)]octreotate and correlated inversely with serum creatinine values. Renal ex vivo autoradiograms showed a dose-dependent distribution pattern of (99m)Tc-DMSA. (99m)Tc-DMSA SPECT could distinguish between the rats that were injected with 278 or 555 MBq [(177)Lu-DOTA(0), Tyr(3) ]octreotate, whereas histologic damage grading of the kidneys was nearly identical for these 2 groups. Histologic analyses indicated that lower amounts of injected radioactivity caused damage mainly in the proximal tubules, whereas as well the distal tubules were damaged after high-dose radioactivity.

CONCLUSIONS

Renal damage in rats after PRRT appeared to start in a dose-dependent manner in the proximal tubules and continued to the more distal tubules with increasing amounts of injected activity. In vivo SPECT measurement of (99m)Tc-DMSA uptake was highly accurate to grade renal tubular damage after PRRT.

Amifostine protects rat kidneys during peptide receptor radionuclide therapy with [177Lu-DOTA0,Tyr3]octreotate

PURPOSE

In peptide receptor radionuclide therapy (PRRT) using radiolabelled somatostatin analogues, the kidneys are the major dose-limiting organs, because of tubular reabsorption and retention of radioactivity. Preventing renal uptake or toxicity will allow for higher tumour radiation doses. We tested the cytoprotective drug amifostine, which selectively protects healthy tissue during chemo- and radiotherapy, for its renoprotective capacities after PRRT with high-dose [(177)Lu-DOTA(0),Tyr(3)]octreotate.

METHODS

Male Lewis rats were injected with 278 or 555 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate to create renal damage and were followed up for 130 days. For renoprotection, rats received either amifostine or co-injection with lysine. Kidneys, blood and urine were collected for toxicity measurements. At 130 days after PRRT, a single-photon emission computed tomography (SPECT) scan was performed to quantify tubular uptake of (99m)Tc-dimercaptosuccinic acid (DMSA), a measure of tubular function.

RESULTS

Treatment with 555 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate resulted in body weight loss, elevated creatinine and proteinuria. Amifostine and lysine treatment significantly prevented this rise in creatinine and the level of proteinuria, but did not improve the histological damage. In contrast, after 278 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate, creatinine values were slightly, but not significantly, elevated compared with the control rats. Proteinuria and histological damage were different from controls and were significantly improved by amifostine treatment. Quantification of (99m)Tc-DMSA SPECT scintigrams at 130 days after [(177)Lu-DOTA(0),Tyr(3)]octreotate therapy correlated well with 1/creatinine (r(2)=0.772, p<0.001).

CONCLUSION

Amifostine and lysine effectively decreased functional renal damage caused by high-dose [(177)Lu-DOTA(0),Tyr(3)]octreotate. Besides lysine, amifostine might be used in clinical PRRT as well as to maximise anti-tumour efficacy.

Long-term toxicity of [(177)Lu-DOTA (0),Tyr (3)]octreotate in rats

PURPOSE AND METHODS

Studies on peptide receptor radionuclide therapy (PRRT) using radiolabelled somatostatin analogues have shown promising results with regard to tumour control. The efficacy of PRRT is limited by uptake and retention in the proximal tubules of the kidney, which might lead to radiation nephropathy. We investigated the long-term renal toxicity after different doses of [(177)Lu-DOTA(0),Tyr(3)]octreotate and the effects of dose fractionation and lysine co-injection in two tumour-bearing rat models.

RESULTS

Significant renal toxicity was detected beyond 100 days after start of treatment as shown by elevated serum creatinine and proteinuria. Microscopically, tubules were strongly dilated with flat epithelium, containing protein cylinders. Creatinine levels rose significantly after 555 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate, but were significantly lower after 278 MBq (single injection) or two weekly doses of 278 MBq. Renal damage scores were maximal after 555 MBq and significantly lower in the 278 and 2x278 MBq groups. Three doses of 185 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate with intervals of a day, a week or a month significantly influenced serum creatinine (469+/-18, 134+/-70 and 65+/-15 micromol/l, respectively; p<0.001). Renal histological damage scores were not significantly influenced by dose fractionation. Lysine co-administration with three weekly treatments of 185 MBq significantly lowered serum creatinine and proteinuria.

CONCLUSION

Injection of high doses of [(177)Lu-DOTA(0),Tyr(3)]octreotate resulted in severe renal damage in rats as indicated by proteinuria, elevated serum creatinine and histological damage. This damage was dose dependent and became overt between 100 and 200 days after treatment. Dose fractionation had significant beneficial effects on kidney function. Also, lysine co-injection successfully prevented functional damage.

A stylized computational model of the rat for organ dosimetry in support of preclinical evaluations of peptide receptor radionuclide therapy with (90)Y, (111)In, or (177)Lu

The therapeutic effects of peptide receptor-based radionuclide therapy are extensively being investigated in rats bearing tumors. Both the dose to the tumor and the therapy-limiting dose to normal tissues, such as kidneys and bone marrow, are of interest for these preclinical studies. The aim of this work was to develop a generalized computational model for internal dosimetry in rats.

METHODS

Mature rats were dissected and the relative positions, dimensions, and weights of all of their major organs were measured. A mathematic model was set up for the rat body and its internal organs to enable Monte Carlo radiation transport calculations to determine estimates for both tumor and organ self-doses as cross-organ doses for (90)Y, (111)In, and (177)Lu. The organs and body were mostly of ellipsoid shape with the axes given as the measured length, width, and height normalized to values that, together with the measured weights, are consistent with the recommended soft-tissue and bone densities. A spheric tumor of 0.25 g was positioned on the right femur. Calculations were performed with the Monte Carlo neutral particle transport code MCNP for the beta-emitters (maximum energy, 2.28 MeV) and (177)Lu (maximum energy, 0.497 MeV) and for the gamma-emissions from (177)Lu and from (111)In. The presented absorbed dose S values are used to calculate the absorbed dose estimates for the rat organs in a study on the biodistribution of (177)Lu-DOTA-Tyr(3)-octreotate (DOTA is 1,4,7,10-tetraazadodecane-N,N',N",N"'-tetraacetic acid). Three activity distributions were considered in the kidney: uniform in the whole kidney, in the cortex, or in the outer 1-mm-thick rim of the cortex. Isodose curves and dose volume histograms were calculated for the dose distribution to the kidneys.

RESULTS

Depending on the activity distribution in the kidneys, the renal dose for (177)Lu-DOTA-Tyr(3)-octreotate is 0.13-0.17 mGy/MBq.

CONCLUSION

The renal dose of 70-95 Gy for an injected activity of 555 MBq will likely cause radiation damage, although the higher amount of peptide with this activity may influence the dosimetry by partial receptor saturation. Dose volume histograms show that (111)In and (177)Lu are likely to have a higher threshold for renal damage than (90)Y.

Imaging expression of adenoviral HSV1-tk suicide gene transfer using the nucleoside analogue FIRU

Substrates for monitoring HSV1-tk gene expression include uracil and acycloguanosine derivatives. The most commonly used uracil derivative to monitor HSV1-tk gene transfer is 1-(2-fluoro-2-deoxy--D-arabinofuranosyl)-5-[*I]iodouracil (fialuridine; I*-FIAU), where the asterisk denotes any of the radioactive iodine isotopes that can be used. We have previously studied other nucleosides with imaging properties as good as or better than FIAU, including 1-(2-fluoro-2-deoxy--D-ribofuranosyl)-5-[*I]iodouracil (FIRU). The first aim of this study was to extend the biodistribution data of 123I-labelled FIRU. Secondly, we assessed the feasibility of detecting differences in HSV1-tk gene expression levels following adenoviral gene transfer in vivo with 123I-FIRU. 9L rat gliosarcoma cells were stably transfected with the HSV1-tk gene (9L-tk+). 123I-FIRU was prepared by radioiodination of 1-(2-fluoro-2-deoxy--D-ribofuranosyl)-5-tributylstannyl uracil (FTMRSU; precursor compound) and purified using an activated Sep-Pak column. Incubation of 9L-tk+ cells and the parental 9L cells with 123I-FIRU resulted in a 100-fold higher accumulation of radioactivity in the 9L-tk+ cells after an optimum incubation time of 4 h. NIH-bg-nu-xid mice were then inoculated subcutaneously with HSV1-tk (-) 9L cells or HSV1-tk (+) 9L-tk+ cells into both flanks. Biodistribution studies and gamma camera imaging were performed at 15 min and 1, 2, 4 and 24 h p.i. At 15 min, the tumour/muscle, tumour/blood and tumour/brain ratios were 5.2, 1.0 and 30.3 respectively. Rapid renal clearance of the tracer from the body resulted in increasing tumour/muscle, tumour/blood and tumour/brain ratios, reaching values of 32.2, 12.5 and 171.6 at 4 h p.i. A maximum specific activity of 22%ID/g tissue was reached in the 9L-tk+ tumours 4 h after 123I-FIRU injection. Two Ad5-based adenoviral vectors containing the HSV1-tk gene were constructed: a replication-incompetent vector with the transgene in the former E1 region, driven by a modified CMV promoter, and a novel replication-competent vector with the HSV1-tk gene in E3 driven by the natural E3 promoter. The human glioma cell lines U87MG and T98G were infected with a multiplicity of infection (m.o.i.) of 10. Forty-eight hours later the cells were incubated with 123I-FIRU and radioactivity was measured in a gamma counter. We found significantly higher levels of radioactivity in both cell lines following infection with the replication-competent vector (P<0.001). NIH-bg-nu-xid mice were then inoculated subcutaneously with U87MG cells. Tumours (approximately 1,000 mm3) were injected with 108 and 109 Infectious Units (I.U.) of either vector. After 48 h, the tracer was injected, followed by gamma camera imaging and direct measurement of radioactivity in the tumours at 4 h p.i. Images and direct measurements indicated increased uptake of tracer with higher I.U. and also demonstrated increased accumulation of tracer in the tumours treated with the replication-competent adenoviral vector (P=0.03). These results demonstrate that 123I-FIRU in combination with HSV1-tk is a valuable tracer for in vivo monitoring of adenoviral gene transfer.