Preparation of patient doses of (177)Lu-DOTA-TATE using indigenously produced (177)Lu: the Indian experience

The efficacy, toxicity and survival of salvage retreatment PRRT with 177Lu-DOTATATE in patients with progressive NET following initial course of PRRT

OBJECTIVE

To evaluate the efficacy, toxicity and survival of salvage peptide receptor radionuclide therapy (PRRT) with indigenous, direct-route 177Lu-labelled-DOTATATE in metastatic Nueroendocrine tumor (NET) patients who showed an objective response or disease stabilization following initial course of 177Lu-DOTATATE PRRT cycles and eventually developed progressive disease after a time-interval of more than 1 year; the variables influencing survival and response of salvage PRRT were also examined.

METHODS

A total of 26 progressive metastatic NET patients who received salvage PRRT with indigenous 177Lu-DOTATATE, were evaluated. Response was assessed under three broad categories as clinical symptomatic, biochemical and imaging (both molecular and morphological imaging). The Kaplan-Meier product-limit method was used to calculate progression-free survival (PFS) and overall survival (OS). Toxicity of salvage PRRT was evaluated by NCI-CTCAE v. 5.0 criteria (included complete blood counts, renal and liver function tests). Association between various variables and response and survival were analyzed using the χ2 test.

RESULTS

Out of the 26 patients, the complete follow-up data were not available for four patients, where only survival information was available. Thus, a total of 22 patients (median age: 55 years, range: 38-68 years, 12 men and 10 women) were included and analyzed retrospectively in study. The cumulative dose of initial course of PRRT (I-PRRT) with indigenous 177Lu-DOTATATE ranged from 800 mCi (29.6 GBq) to 1231 mCi (45.54 GBq) per patient {mean administered cumulative dose of 964 mCi (35.66 GBq) per patient}, and the salvage PRRT with indigenous 177Lu-DOTATATE comprised of a mean dose of 170 mCi (6.29GBq) per patient. The disease control rate of 68.1%, 77.3%, 63.6% and 63.6% were observed after salvage PRRT on clinical symptomatic, biochemical, molecular and morphological imaging response respectively. The median PFS after salvage PRRT was 17 months. The median OS was not attained after I-PRRT (OS-i) and salvage PRRT (OS-s). Estimated OS-i rate was 68% at 108 months and OS-s rate was 82% at 18 months. None of the patients developed Grade 3/4 hematotoxicity, nephrotoxicity and hepatotoxicity or AML/MDS after I-PRRT and salvage PRRT at median follow-up of 72 months and 12 months respectively. The highest level of toxicity was Grade 2 [seen as reversible anemia, thrombocytopenia and nephrotoxicity in 3 (13.5%), 1 (4.5%) and 2 patients (9%) respectively]. The significant p-value was not observed for any variable association.

CONCLUSION

With limited therapeutic options available for progressive NET after I-PRRT and in the absence of high-grade toxicity after 177Lu-DOTATATE salvage PRRT, retreatment with PRRT may be considered as a relatively safe therapeutic option for these patients.

ADVANCES IN KNOWLEDGE

This study examined salvage retreatment PRRT with indigenous "direct-route" 177Lu-DOTATATE and registered its safety and survival benefits, indicating this could be an effective therapeutic option in this clinical setting.

Estimation of Absorbed Doses of Indigenously Produced "Direct-route" Lutetium-177-Labeled DOTA-TATE PRRT in Normal Organs and Tumor Lesions in Patients of Metastatic Neuroendocrine Tumors: Comparison with No-Carrier-Added [177Lu]Lu-DOTA-TATE and the Trend with Multiple Cycles

Background: Lutetium-177-labeled somatostatin analogue, [¹⁷⁷Lu]Lu-DOTA-TATE is most commonly used across the world for peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors (NETs). The primary objective of this study was to estimate the absorbed doses in organs and tumor lesions in NET patients treated with indigenously produced "direct-route" [¹⁷⁷Lu]Lu-labeled DOTA-TATE and impact of multiple treatment cycles on absorbed doses, and compare with those treated with no-carrier-added [¹⁷⁷Lu]Lu-labeled DOTA-TATE. Materials and Methods: Sixty patients of NET were enrolled in this prospective study. These patients received up to 6 cycles of PRRT with [¹⁷⁷Lu]Lu-DOTA-TATE (total 232 cycles) at 10- to 12-week intervals between the two successive therapy cycles. The patients were administered 5.55-7.4 GBq (150-200 mCi) of [¹⁷⁷Lu]Lu-DOTA-TATE in 100 mL of normal saline over a period of 30 min. Postadministration whole-body planar scintigraphy were acquired at five time points 0.5 (prevoid), 2, 12, 24, and 72 h (postvoid) and one SPECT scan at 24 h (postvoid). Number of disintegrations was determined from time-activity curves generated by drawing regions of interests (ROIs) on the images. Tumor masses were derived from computed tomography (CT) data. The absorbed doses for normal organs and tumor lesions were calculated using OLINDA 2.1.1 software. The same were also estimated in a group of 22 patients who were treated with no-carrier-added [¹⁷⁷Lu]Lu-labeled DOTA-TATE. Results: The mean absorbed organ doses (mean ± SD) in Gy/GBq received by normal organs were as follows: kidneys 0.64 ± 0.21, liver 0.10 ± 0.05, spleen 0.88 ± 0.35, bone marrow 0.04 ± 0.02, urinary bladder 0.26 ± 0.06, heart wall 0.04 ± 0.02, and whole-body 0.06 ± 0.02. Tumor dosimetry was performed in a total of 410 tumor lesions, the mean absorbed dose to the tumor lesions was 4.79 ± 4.23 Gy/GBq. Large variations were observed in absorbed doses received by these lesions (range: 0.15-21.26 Gy/GBq). With no-carrier-added [¹⁷⁷Lu]Lu-DOTA-TATE, the mean absorbed organ doses (mean ± SD) in Gy/GBq received by normal organs were as follows: kidneys 0.76 ± 0.16, liver 0.10 ± 0.05, spleen 1.14 ± 0.31, bone marrow 0.05 ± 0.02, urinary bladder 0.27 ± 0.05, heart wall 0.06 ± 0.02, whole-body 0.07 ± 0.02, and tumor dose 5.87 ± 5.74. Conclusions: There was no statistically significant difference in the dosimetry data of patients treated with no-carrier-added (indirect route) [¹⁷⁷Lu]Lu-labeled DOTA-TATE and the dosimetry data of patients treated with [¹⁷⁷Lu]Lu-labeled with DOTA-TATE formulated using ¹⁷⁷Lu produced through "Direct-route" and were comparable with the data reported.

Prospective evaluation of organ-specific dose and lesional doses following therapeutic [177Lu]Lu-EDTMP administration in patients with multiple skeletal metastases and its correlation with clinical hematological toxicity

AIM

In patients with multiple skeletal metastases, accurate estimation of absorbed doses to radiosensitive bone marrow in bone-directed systemic radionuclide therapies (RNT) is critically important from clinical dose determination standpoint. The primary aim of the present study was to estimate the radiation absorbed doses of therapeutic [177Lu]Lu-EDTMP to bone marrow by two methods viz. Medical Internal Radiation Dose (MIRD) schema and using OLINDA software and correlate with hematological toxicity.

METHODS

A total of 15 patients diagnosed to have multiple painful skeletal metastases being treated with [177Lu]Lu-EDTMP for palliation of pain, were enrolled for this prospective study. For all patients, urine was collected immediately after infusion of [177Lu]Lu-EDTMP up to 24 h post-administration and cumulative activity excreted from body via urine was calculated. For dosimetry, patients underwent post-administration whole-body scintigraphy at five-time points: 0.5 (pre-void), 2, 24, 48 and 120 h (post-void). From the time-activity curves generated by drawing regions of interest (ROIs) on the images, number of disintegrations was determined. Absorbed doses for organs and bone lesions were calculated using OLINDA 2.2.0 software. For bone marrow dose estimates, in addition to OLINDA 2.2.0 software, MIRD schema was also adopted. Hematological profile was monitored in all patients during the treatment and post-treatment follow-up (estimating complete blood counts, every 15 d for 3 months after therapy).

RESULTS

The mean ± standard deviation activity of [177Lu]Lu-EDTMP administered per patient per cycle was 2.08 ± 0.45 GBq. The results demonstrated higher uptake of [177Lu]Lu-EDTMP in bone metastases compared to normal bones. Within 2 and 24 h of administration of [177Lu]Lu-EDTMP, [177Lu]Lu activity excreted from the body was 24 ± 9% and 39 ± 14%, respectively. The mean absorbed organ doses (mean ± SD) in Gy/GBq were as follows: osteogenic cells 3.15 ± 1.85, bone marrow 0.57 ± 0.31, kidneys 0.08 ± 0.05, urinary bladder 0.32 ± 0.04, and bone lesions 2.91 ± 1.88. Strong correlation was found between (a) MIRD schema and OLINDA 2.2.0 software method for estimation of bone marrow doses (r = 0.96; P = <0.0001) and (b) Bone marrow absorbed dose and hematological toxicity (r = 0.81, P = 0.0027).

CONCLUSION

Radiation absorbed doses to the bone marrow and skeletal metastatic lesions, following therapeutic [177Lu]Lu-EDTMP were estimated using a convenient and non-invasive quantitative imaging method. The estimated bone marrow absorbed dose, either by MIRD schema or the OLINDA 2.2.0 software method, demonstrated strong correlation. Strong correlation was also observed between bone marrow absorbed dose and hematological toxicity.

Long-term outcome of indigenous 177Lu-DOTATATE PRRT in patients with Metastatic Advanced Neuroendocrine Tumours: a single institutional observation in a large tertiary care setting

OBJECTIVES

Assessment of long-term outcome and toxicity of indigenous ¹⁷⁷Lu-DOTATATE PRRT in patients of metastatic/advanced NETs in a large tertiary-care PRRT setting.

METHODS

A total of 468 metastatic/advanced NET patients (wide range of primary sites including CUP-NETs), who underwent at least two cycles of ¹⁷⁷Lu-DOTATATE PRRT with available follow-up information, were included and analysed retrospectively in this study. In-house labelling of DOTATATE with ¹⁷⁷Lu (direct route produced) was carried out in the hospital radiopharmacy and treatment administered in cycles (dose: 5.55 to 7.4 GBq per patient), at 10-12 weeks interval. The assessment of long-term outcome was undertaken under three broad headings: (a) Therapeutic response, (b) Survival outcome and (c) Toxicity assessment. The median point estimate with 95% CI for progression free survival (PFS) and overall survival (OS) were calculated by Kaplan-Meier method. Prognostic covariates for association with PFS and OS was investigated by Cox proportional hazards model (univariate and multivariate Hazard Ratios) and with disease control rate (DCR) by Chi-square test, with significant P value defined as <0.05.

RESULTS

Long-term outcome (follow-up ranging from 4 to 97.6 months; median period:46 months following first ¹⁷⁷Lu-DOTATATE PRRT) results showed, (i) on symptomatic response evaluation scale, complete response (CR) in 214 patients (45.7%), partial response (PR) in 108 (23.1%), stable disease (SD) in 118 (25.2%), progressive disease (PD) in 28 (6%). (ii) Biochemical response evaluation showed CR in 52 (12%), PR in 172 (40%), SD in 161 (38%), and PD in 42 patients (10%). (iii) Molecular imaging response (by PERCIST criteria) showed CR in 29 (6%), PR in 116 (25%), SD in 267 (57%) and PD in 56 (12%) patients. (iv) On RECIST 1.1 criteria, CR was observed in 14 patients (3%), PR in 126 patients (27%), SD in 282 patients (60%) and PD in 46 patients (10%). The median PFS and OS were not reached at a median follow-up of 46 months. Observed PFS and OS at 7 years were 71.1% 95% CI (62.4-79.7%) and 79.4% 95% CI (71.4-86.9%) respectively. PFS was dependent on previous history of chemotherapy, baseline ⁶⁸Ga-DOTATATE and ¹⁸F-FDG uptake, site of primary tumour, total cumulative dose and number of PRRT cycles on univariate analysis, whereas multivariate analysis showed significant association for previous history of chemotherapy, baseline ⁶⁸Ga-DOTATATE and ¹⁸F-FDG uptake and number of PRRT cycles. The OS was dependent on baseline ⁶⁸Ga-DOTATATE uptake, site of primary tumour, presence of bony metastatic disease, total cumulative dose and number of PRRT cycles on univariate analysis, whereas multivariate analysis showed significant association for bony metastatic disease and number of PRRT cycles. Transient haematological toxicity of Grade 1, Grade 2, and Grade 3 was found in 8 (1.7%), 1 (0.2%) and one patient (0.2%), respectively. Nephrotoxicity of Grade 1, Grade 2, Grade 3, and Grade 4 were seen in 16 (3.5%), 3 (0.6%), 2 (0.4%) and one patient (0.2%), respectively. On a separate sub-analysis of 322 NET patients with progressive disease at the initiation point of PRRT, overall response rates (CR + PR + SD) were 93.5%, 88.5%, 89.1 and 87.9% on symptomatic, biochemical, RECIST 1.1 and PERCIST criteria and PFS and OS at 7 years 68.3% and 79.2%, respectively.

CONCLUSIONS

The present results demonstrate that ¹⁷⁷Lu-DOTATATE PRRT improved symptoms and biochemical markers substantially in most of the NET patients, with disease stabilisation on both anatomical and molecular imaging in majority and response in a sizeable fraction. Additionally, the therapeutic protocol with lesser dose per cycle (mean 5.92 GBq/cycle) and prolonged duration (over 5 cycles and 1.5 years) in a metastatic NET setting proved equally efficacious (with superior PFS and OS rates) and relatively better tolerated with minimal toxicity.

ADVANCES IN KNOWLEDGE

The present work critically examines the long-term results, survival outcome and toxicity profile of the indigenous ¹⁷⁷Lu-DOTATATE (produced through direct neutron activation of enriched ¹⁷⁶Lu) in metastatic progressive NETs across a wide range of primary sites and malignancies. Such long-term outcome data establishes the favourable impact of PRRT in a wide patient base and also the therapeutic efficacy of the product.

Long-term outcome of "Sandwich" chemo-PRRT: a novel treatment strategy for metastatic neuroendocrine tumors with both FDG- and SSTR-avid aggressive disease

OBJECTIVE

The primary aims of this study were to evaluate the long-term outcome of a "sandwich chemo-PRRT (SCPRRT)" regimen with regard to therapeutic response rate, progression-free survival (PFS), and overall survival (OS) rates in metastatic neuroendocrine tumors (NETs) with both somatostatin receptor (SSTR)- and fluorodeoxyglucose (FDG)-avid aggressive disease. Additionally, health-related quality of life (HRQoL) scales, clinical toxicity, and association of PFS and disease control rate (DCR) with various variables were also evaluated.

MATERIALS AND METHODS

A total of 38 patients of the aforementioned cohort, who received SCPRRT (at least 2 cycles of each PRRT and chemotherapy) at our institute between January 2012 and December 2018, were included and analyzed in this retrospective study. Between two cycles of ¹⁷⁷Lu-DOTATATE peptide receptor radionuclide therapy (PRRT), two cycles of oral capecitabine and temozolomide (CAPTEM) were sandwiched. Therapeutic responses following SCPRRT were assessed by using pre-defined criteria. PFS and OS after first SCPRRT were determined. Eastern Cooperative Oncology Group (ECOG) and Karnofsky score were used for evaluation of HRQoL before and after SCPPRT in all 38 patients. Any adverse events were graded according to the Common Terminology Criteria for Adverse Events version 5.0 (CTCAE v5.0) of the National Cancer Institute. Associations of PFS and DCR with various variables were evaluated.

RESULTS

Response (complete response and partial response) to SCPRRT was seen in 28 patients (73%), 15 patients (39%), and 16 patients (42%) on symptomatic, biochemical, and molecular imaging response evaluation criteria respectively. A total of 17 patients (45%) had anatomical imaging response with DCR of 84% based upon the RECIST 1.1 criteria. Pre-therapy mean ECOG and KPS was 2.0 and 68, which changed to 1.0 and 75 respectively following SCPRRT. Long-term follow-up data was available and ranged from 12 to 65 months after the first SCPRRT. Median PFS and OS were not reached at a median follow-up of 36 months. An estimated PFS rate of 72.5% and OS rate of 80.4% was found at 36 months. Longer PFS was dependent upon high SSTR uptake and number of CAPTEM cycle (≥ 7 cycles), absence of skeletal metastasis, and no previous external beam radiotherapy (EBRT) exposure with significant P value. Higher DCR was dependent upon absence of skeletal metastasis with significant P value. SCPRRT was tolerated well with none developing grade 4 hematotoxicity and nephrotoxicity of any grade. Anemia (grade 3), thrombocytopenia (grade 3), and leukopenia (grade 3) were noticed in 1 patient (2.5%), 2 patients (5%), and 1 patient (2.5%) respectively in this study.

CONCLUSION

Thus, favorable response rates with effective control of symptoms and longer PFS and OS without high-grade or life-threatening toxicities were important observations in the present study following SCPRRT in NET patients with aggressive, both FDG- and SSTR-avid, metastatic progressive disease. The study results indicate the potential role of "sandwich chemo-PRRT" in future therapeutic algorithms of aggressive, both SSTR- and FDG-positive subset of neuroendocrine tumors.

Preparation of [177Lu]Lu-DOTA-Ahx-Lys40-Exendin-4 for radiotherapy of insulinoma: a detailed insight into the radiochemical intricacies

INTRODUCTION

[¹⁷⁷Lu]Lu-DOTA-Ahx-Lys40-Exendin-4 ([¹⁷⁷Lu]Lu-DOTA-Exendin-4) is a potential agent for radiotherapy of insulinomas owing to its specificity towards GLP-1 (Glucagon like peptide-1) receptors over-expressed on such cancers. The objective of the present study is to optimize the various radiochemistry parameters for the consistent formulation of the agent with high radiolabeling yield using carrier added [¹⁷⁷Lu]LuCl₃ and also to evaluate its biological behaviour in small animal model.

METHODS

In order to optimize the radiolabeling parameters, DOTA-Exendin-4 was radiolabeled with [¹⁷⁷Lu]LuCl₃ in two different buffer systems (sodium acetate and HEPES) at three different temperatures (45, 65 and 95 °C) using three different ligand to metal ratios (3:1, 4:1 and 5:1). The radiolabeled peptide was characterized by both paper chromatography and HPLC. The effect of addition of three different radio-protectors on complexation yield was also studied. Bio-distribution studies were carried out in healthy Swiss mice to evaluate the pharmacokinetic behaviour of the radiolabeled peptide as well as to determine the in vivo specificity of the radiotracer towards GLP-1 receptors (blocking studies). Urine and kidney lysate of the animals were analyzed at various post-administration time-points in order to determine the in vivo stability of the radiolabeled peptide.

RESULTS

The [¹⁷⁷Lu]Lu-DOTA-Exendin-4 complex could be prepared consistently with >95% radiolabeling yield using the optimized reaction conditions. Bio-distribution studies revealed early accumulation of [¹⁷⁷Lu]Lu-DOTA-Exendin-4 in pancreas along with fast clearance via renal pathway. Significantly high accumulation of the radiotracer was observed in kidneys. Analyses of urine and kidney lysate of the animals revealed in vivo stability of [¹⁷⁷Lu]Lu-DOTA-Exendin-4. Blocking studies showed displacement of significant amount of radiotracer from GLP-1 receptor-positive organs such as, pancreas and lungs (p <0.05) in presence of unlabeled peptide, indicating the specificity of the radiolabeled preparation towards GLP-1 receptors.

CONCLUSIONS

Present study shows that [¹⁷⁷Lu]Lu-DOTA-Exendin-4 could be formulated for radiotherapeutic application with high radiochemical purity and adequate in vivo stability using [¹⁷⁷Lu]LuCl₃ produced via direct neutron irradiation.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Findings of the present study will be helpful in preparing the patient dose of [¹⁷⁷Lu]Lu-labeled Exendin for radiotherapy of insulinoma using carrier added [¹⁷⁷Lu]LuCl₃, produced in a medium flux reactor, without the requirement of post-labeling purification.

Concomitant 177Lu-DOTATATE and capecitabine therapy in malignant paragangliomas

BACKGROUND

The role of concomitant peptide receptor radionuclide therapy (PRRT) and capecitabine therapy has shown benefit in gastroenteropancreatic neuroendocrine tumors. However, data reporting its role in paraganglioma (PGL) patients is lacking. The aim of this study was to evaluate the role of combined capecitabine and ¹⁷⁷Lu-DOTATATE in malignant PGL patients.

METHODS

In this retrospective, single-institutional, single-arm, observational study, data of consecutive advanced stage PGL patients treated with concomitant ¹⁷⁷Lu-DOTATATE-capecitabine therapy, between July 2009 and March 2017, were collected and analyzed.

RESULTS

Twenty-five PGL patients received an average dose of 22.86 ± 9.54 (14.43-50) GBq ¹⁷⁷Lu-DOTATATE and 1250 mg/m² capecitabine from days 0 to 14, commencing on the morning of PRRT. The median overall survival (OS) was not attained in this patient cohort; however, the median PFS was 32 months. Morphological response according to RECIST 1.1 criteria was achieved in 28% (7/25) patients. Biochemical response with > 50% reduction in chromogranin A levels was observed in 28% of the patients.

CONCLUSIONS

Our data confirm that ¹⁷⁷Lu-DOTATATE-capecitabine therapy is effective in achieving an objective response in 28% and symptomatic response in 43% patients. In comparison to published PRRT monotherapy outcomes in PGL, we did not observe any great advantage of concomitant therapy; however, it could be due to under-powered study. We recommend a large randomized trial to prove or disprove the utility of capecitabine as a radiosensitizer for PRRT in PGL patients.

Concomitant 177Lu-DOTATATE and Capecitabine Therapy in Patients With Advanced Neuroendocrine Tumors: A Long-term-Outcome, Toxicity, Survival, and Quality-of-Life Study

PURPOSE

The purpose of this study was to evaluate the outcome, toxicity, survival, and quality of life in patients with advanced neuroendocrine tumors.

METHODS

One hundred sixty-seven patients were enrolled in the study. All patients underwent baseline Ga-DOTANOC PET/CT scans. Lu-DOTATATE therapy was administered quarterly along with oral capecitabine therapy in group 1 patients (n = 88), whereas group 2 patients (n = 79) were treated only with Lu-DOTATATE. Hematologic, kidney function, liver function tests and chromogranin A levels were recorded before and after therapy at 2-week, 4-week, and 3-month intervals. Biochemical and morphological responses were assessed with the trend in chromogranin A levels and Response Evaluation Criteria in Solid Tumors 1.1 criteria, respectively.

RESULTS

There was no significant difference in the hemoglobin levels after Lu-DOTATATE therapy (P = 0.4892). In most patients, there was a decrease in the platelet levels; however, all the patients had platelet counts greater than 100,000/μL with no platelet toxicity. There was no toxicity related to leukocytes. Two patients showed renal insufficiencies. No hepatotoxicity was observed in any of the patients. According to Response Evaluation Criteria in Solid Tumors 1.1 criteria, in group 1 patients, the response was partial response in 34% of the patients, stable disease in 50.2%, and progressive disease in 6.8% versus partial response in 6.3%, stable disease in 60.9%, and progressive disease in 26.5% among group 2 patients. The median overall survival (OS) and progression-free survival (PFS) was not reached in group 1 patients. The median OS and PFS in group 2 patients were 48 months. Ki-67 tumor proliferation index was significantly associated with increased risk of disease progression.

CONCLUSIONS

Addition of capecitabine therapy with Lu-DOTATATE therapy lengthens the OS and PFS. Patients with aggressive disease may benefit from this synergetic therapeutic approach.

Estimation of Whole Body Radiation Exposure to Nuclear Medicine Personnel During Synthesis of 177Lutetium-labeled Radiopharmaceuticals

PURPOSE OF THE STUDY

With rapid development in the field of nuclear medicine therapy, radiation safety of the personnel involved in synthesis of radiopharmaceuticals has become imperative. Few studies have been done on estimating the radiation exposure of personnel involved in the radio labeling of 177Lu-compounds in western countries. However, data from the Indian subcontinent are limited. We have estimated whole body radiation exposure to the radiopharmacist involved in the labeling of: 177Lu-DOTATATE, 177Lu-PSMA-617, and 177Lu-EDTMP.

MATERIALS AND METHODS

Background radiation was measured by keeping a pocket dosimeter around the workbench when no radioactive work was conducted. The same pocket dosimeter was given to the radiopharmacist performing the labeling of 177Lu-compounds. All radiopharmaceuticals were synthesized by the same radiopharmacist with 3, 1 and 3 year experience, respectively, in radiolabeling the above compounds.

RESULTS

One Curie (1 Ci) of 177Lu was received fortnightly by our department. Data were collected for 12 syntheses of 177Lu-DOTATATE, 8 syntheses of 177Lu-PSMA-617, and 3 syntheses of 177Lu-EDTMP. Mean time required to complete the synthesis was 0.81, 0.65, and 0.58 h, respectively. Mean whole body radiation exposure was 0.023 ± 0.01 mSv, 0.01 ± 0.002 mSv, and 0.002 ± 0.0006 mSv, respectively. Overall mean radiation dose for all the three 177Lu-compounds was 0.014 mSv. Highest exposure was obtained during the synthesis of 177Lu-DOTATATE.

CONCLUSION

Our data suggest that the manual radiolabeling of 177Lu compounds is safe, and the whole body radiation exposure to the involved personnel is well within prescribed limits.

PLGA nanoparticles for peptide receptor radionuclide therapy of neuroendocrine tumors: a novel approach towards reduction of renal radiation dose

BACKGROUND

Peptide receptor radionuclide therapy (PRRT), employed for treatment of neuroendocrine tumors (NETs) is based on over-expression of Somatostatin Receptors (SSTRs) on NETs. It is, however, limited by high uptake and retention of radiolabeled peptide in kidneys resulting in unnecessary radiation exposure thus causing nephrotoxicity. Employing a nanocarrier to deliver PRRT drugs specifically to the tumor can reduce the associated nephrotoxicity. Based on this, (177)Lu-DOTATATE loaded PLGA nanoparticles (NPs) were formulated in the present study, as a potential therapeutic model for NETs.

METHODOLOGY AND FINDINGS

DOTATATE was labeled with Lutetium-177 ((177)Lu) (labeling efficiency 98%; R(f)∼0.8). Polyethylene Glycol (PEG) coated (177)Lu-DOTATATE-PLGA NPs (50:50 and 75:25) formulated, were spherical with mean size of 304.5±80.8 and 733.4±101.3 nm (uncoated) and 303.8±67.2 and 494.3±71.8 nm (coated) for PLGA(50:50) and PLGA(75:25) respectively. Encapsulation efficiency (EE) and In-vitro release kinetics for uncoated and coated NPs of PLGA (50:50 & 75:25) were assessed and compared. Mean EE was 77.375±4.98% & 67.885±5.12% (uncoated) and 65.385±5.67% & 58.495±5.35% (coated). NPs showed initial burst release between 16.64-21.65% with total 42.83-44.79% over 21 days. The release increased with coating to 20.4-23.95% initially and 60.97-69.12% over 21 days. In-vivo studies were done in rats injected with (177)Lu-DOTATATE and (177)Lu-DOTATATE-NP (uncoated and PEG-coated) by imaging and organ counting after sacrificing rats at different time points over 24 hr post-injection. With (177)Lu-DOTATATE, renal uptake of 37.89±10.2%ID/g was observed, which reduced to 4.6±1.97% and 5.27±1.66%ID/g with uncoated and coated (177)Lu-DOTATATE-NP. The high liver uptake with uncoated (177)Lu-DOTATATE-NP (13.68±3.08% ID/g), reduced to 7.20±2.04%ID/g (p = 0.02) with PEG coating.

CONCLUSION

PLGA NPs were easily formulated and modified for desired release properties. PLGA 50:50 NPs were a more suitable delivery vehicle for (177)Lu-DOTATATE than PLGA 75:25 because of higher EE and slower release rate. Reduced renal retention of (177)Lu-DOTATATE and reduced opsonisation strongly advocate the potential of (177)Lu-DOTATATE-PLGA-PEG NPs to reduce radiation dose in PRRT.