Freeze-dried multi-dose kits for the fast preparation of 177Lu-Tyr3-octreotide and 177Lu-PSMA(inhibitor) under GMP conditions

Improving Overall Survival and Quality of Life in Patients with Prostate Cancer and Neuroendocrine Tumors Using 177Lu-iPSMA and 177Lu-DOTATOC: Experience after 905 Treatment Doses

¹⁷⁷Lu-iPSMA is a novel radioligand developed at ININ-Mexico with a high affinity for the PSMA protein heavily expressed in cancer cells of approximately 95% of patients with metastatic castration-resistant prostate cancer (mCRPC). ¹⁷⁷Lu-DOTATOC is a patent-free radioligand, molecularly recognized by somatostatin receptors (SSTR-2) overexpressed in cancer cells of about 80% of patients with metastatic gastroenteropancreatic neuroendocrine tumors (GEP-NET). This translational research aimed to determine the efficacy and safety of ¹⁷⁷Lu-iPSMA and ¹⁷⁷Lu-DOTATOC developed as GMP pharmaceutical formulations for treating progressive and advanced mCRPC and NET. One hundred and forty-five patients with mCRPC and one hundred and eighty-seven subjects with progressive NET (83% GEP-NET and 17% other NET), treated with ¹⁷⁷Lu-iPSMA and ¹⁷⁷Lu-DOTATOC, respectively, were evaluated. Patients received a mean dose of 7.4 GBq per administration of ¹⁷⁷Lu-iPSMA (range 1-5 administrations; 394 treatment doses) or ¹⁷⁷Lu-DOTATOC (range 2-8 administrations; 511 treatment doses) at intervals of 1.5-2.5 months. Efficacy was assessed by SPECT/CT or PET/CT. Results were stratified by primary tumor origin and number of doses administered. Patients with mCRPC showed overall survival (OS) of 21.7 months with decreased radiotracer tumor uptake (SUV) and PSA level in 80% and 73% of patients, respectively. In addition, a significant reduction in pain (numerical scale from 10-7 to 3-1) was observed in 88% of patients with bone metastases between one and two weeks after the second injection. In the GEP-NET population, the median progression-free survival was 34.7 months, with an OS of >44.2 months. The treatments were well tolerated. Only ten patients experienced grade ≥ 3 myelosuppression (3% of all patients). The observed safety profiles and favorable therapeutic responses demonstrated the potential of ¹⁷⁷Lu-iPSMA and ¹⁷⁷Lu-DOTATOC to improve overall survival and quality of life in patients with progressive and advanced mCRPC and NET.

Preparation of Patient Doses of [177Lu]Lu-DOTATATE and [177Lu]Lu-PSMA-617 with Carrier Added (CA) and No Carrier Added (NCA) 177Lu

Purpose

[177Lu]Lu-DOTATATE and [177Lu]Lu-PSMA-617 used for targeted radionuclide therapy are very often prepared in the hospital radiopharmacy. The preparation parameters vary depending upon the specific activity of the 177Lu used. The aim of this study was to develop optimized protocols to be used in the nuclear medicine department for the preparation of patient doses of the above radiopharmaceuticals.

Method

177Lu (CA and NCA) were used for radiolabeling DOTATATE and PSMA-617. Parameters studied are 177Lu of different specific activity and different peptide concentrations and two different buffer systems. Paper and thin layer chromatography systems were used for estimating the radiochemical yield as well as radiochemical purity. Solid-phase extraction was used for the purification of the labeled tracers.

Results

[177Lu]Lu-DOTATATE was prepared with CA 177Lu (n = 13) and NCA177Lu (n = 6). Four batches each of [177Lu]Lu-PSMA-617 were prepared using CA and NCA 177Lu. Radiochemical yields > 80% and final product with less than < 1% radiochemical impurity could be obtained in all batches which were used for therapy.

Conclusion

Robust protocols for the preparation of clinical doses of [177Lu]Lu-DOTATATE and [177Lu]Lu-PSMA-617 were developed and used for the preparation of clinical doses. The quality of the SPECT images of both the tracers are consistent with the expected uptake in respective diseases.

Preparation of 177Lu-PSMA-617 in Hospital Radiopharmacy: Convenient Formulation of a Clinical Dose Using a Single-Vial Freeze-Dried PSMA-617 Kit Developed In-House

Objective

In the recent time, endoradionuclide therapy for metastatic castration-resistant prostate carcinoma employing ¹⁷⁷Lu-PSMA-617 has yielded encouraging results and several clinical trials with the agent are currently ongoing. Routine preparation of ¹⁷⁷Lu-PSMA-617 patient doses can be made simpler and convenient, if the ingredients essential for radiolabeling are made available in a ready-to-use lyophilized form.

Methods

PSMA-617 freeze-dried kit was formulated and used for the preparation of ¹⁷⁷Lu-PSMA-617 clinical dose with high radiochemical purity using low/medium specific activity ¹⁷⁷Lu. Detailed radiochemical studies were performed to determine the maximum activity and volume of ¹⁷⁷LuCl₃, which can be added in the kit for the formulation of ¹⁷⁷Lu-PSMA-617. Studies were also performed to determine the shelf life of the kit to ensure its long-term usage. Studies were performed in buffer as well as human serum medium to determine the stability of the ¹⁷⁷Lu-PSMA-617 complex after storing in respective media up to 7 days postpreparation. About ten patient doses of ¹⁷⁷Lu-PSMA-617 were administered, and posttherapy scans were acquired.

Results

The formulated freeze-dried kit of PSMA-617 could be radiolabeled with an average percentage radiochemical purity > 98.53 ± 0.38. The freeze-dried kit was found suitable for tolerating up to 0.5 mL of ¹⁷⁷LuCl₃ (in 0.01 N HCl) and specific activity of 555 MBq/μg (15 mCi/μg) for the preparation of the patient dose of ¹⁷⁷Lu-PSMA-617. The ¹⁷⁷Lu-PSMA-617 complex prepared using the freeze-dried kit of PSMA-617 was observed to maintain % radiochemical purity (RCP) of 96.74 ± 0.87 and 94.81 ± 2.66, respectively, even after storing up to 7 days in buffer and human serum, respectively. ¹⁷⁷Lu-PSMA-617 prepared using the in-house formulated freeze-dried kit of PSMA-617 exhibited accumulation in metastatic lesions picked up in a pretherapy PET scan. Reduction in number as well as size of lesions was observed in posttherapy scans acquired after two months of administering the first therapeutic dose of ¹⁷⁷Lu-PSMA-617.

Conclusions

The freeze-dried kit of PSMA-617 could be used for the preparation of ¹⁷⁷Lu-PSMA-617 with high radiochemical purity (>98%) in a reproducible manner. ¹⁷⁷Lu-PSMA-617 prepared using the developed kit was successfully evaluated in patients suffering from metastatic prostate cancer.

Preclinical dosimetric studies of 177 Lu-scFvD2B and comparison with 177 Lu-PSMA-617 and 177 Lu-iPSMA endoradiotherapeutic agents

PURPOSE

Internal dosimetry has become a very important tool to evaluate the risks and benefits of new endoradiotherapeutic agents. Nowadays, some of the most successful targeted radionuclide therapy (TRT) agents are ¹⁷⁷ Lu-DOTA conjugates based on low molecular weight (LMW) Glu-ureido PSMA inhibitors. It has, however, been demonstrated that the DOTA chelating moiety reduces the internalization of the LMW-PSMA agent and its radiation dose to the tumor. Previously, we reported that ¹⁷⁷ Lu-scFvD2B, an antibody-based construct, demonstrated statistically significant higher cell uptake and internalization in LNCaP prostate cancer (PCa) cells (PSMA-positive) when compared to the LMW-PSMA agents, ¹⁷⁷ Lu-PSMA-617 and ¹⁷⁷ Lu-iPSMA, two of the endoradiotherapeutic agents which currently are the most used in PCa therapy. The aim of this study is to estimate the preclinical ¹⁷⁷ Lu-scFvD2B organ and tumor-absorbed doses, and to compare the values with those of ¹⁷⁷ Lu-PSMA-617 and ¹⁷⁷ Lu-iPSMA.

METHODS

¹⁷⁷ Lu-scFvD2B, ¹⁷⁷ Lu-PSMA-617, and ¹⁷⁷ Lu-iPSMA were prepared and their radiochemical purity determined. Biodistribution studies of each radiopharmaceutical were then carried out in healthy mice to define the main source organs (SO) and to calculate the number of disintegrations in each source organs per unit of administered activity (N_SO ). Absorbed dose in the main organs were then calculated for each ¹⁷⁷ Lu-conjugate by means of OLINDA/EXM 2.1.1 software, using the calculated N_SO for both the adult male and the mouse phantoms as program inputs. Images of mice bearing micropulmonary tumors injected with ¹⁷⁷ Lu-conjugates were also obtained. Tumor standardized uptake values (SUV) for the different conjugates, obtained from the 3D SPECT image reconstruction of these mice, were used as the number of disintegrations in a tumor site per unit of administered activity (N_T ). The tumor-absorbed dose was calculated using the published electron dose S-values for sphere models with diameters ranging from 10 µm to 10 mm and considering a uniform activity distribution and tumor density equivalent to water density.

RESULTS

All ¹⁷⁷ Lu-labeled agents were obtained in high yield (98%). Dosimetric studies carried out using mouse phantoms demonstrated that organ absorbed doses of ¹⁷⁷ Lu-scFvD2B were from 1.4 to 2.3 times higher than those for ¹⁷⁷ Lu-iPSMA and from 1.5 to 2.6 times higher than those for ¹⁷⁷ Lu-PSMA-617. However, the ¹⁷⁷ Lu-scFvD2B values of tumor-absorbed doses for all investigated tumor sizes were from 2.8 to 3.0 times greater than those calculated for ¹⁷⁷ Lu-iPSMA and ¹⁷⁷ Lu-PSMA-617, respectively. Moreover, ¹⁷⁷ Lu-scFvD2B showed the highest tumor/kidney ratio when compared to those reported for ¹⁷⁷ Lu-albumin conjugates.

CONCLUSIONS

In this preclinical study, we demonstrated the potential of ¹⁷⁷ Lu-scFvD2B as a therapeutic agent for PSMA-expressing tumors, due to its higher tumor-absorbed dose when compared with ¹⁷⁷ Lu-LMW agents.

Development of 177Lu-scFvD2B as a Potential Immunotheranostic Agent for Tumors Overexpressing the Prostate Specific Membrane Antigen

The clinical translation of theranostic ¹⁷⁷Lu-radiopharmaceuticals based on inhibitors of the prostate-specific membrane antigen (PSMA) has demonstrated positive clinical responses in patients with advanced prostate cancer (PCa). However, challenges still remain, particularly regarding their pharmacokinetic and dosimetric properties. We developed a potential PSMA-immunotheranostic agent by conjugation of a single-chain variable fragment of the IgGD2B antibody (scFvD2B) to DOTA, to obtain a ¹⁷⁷Lu-labelled agent with a better pharmacokinetic profile than those previously reported. The labelled conjugated ¹⁷⁷Lu-scFvD2B was obtained in high yield and stability. In vitro, ¹⁷⁷Lu-scFvD2B disclosed a higher binding and internalization in LNCaP (PSMA-positive) compared to PC3 (negative control) human PCa cells. In vivo studies in healthy nude mice revealed that ¹⁷⁷Lu-scFvD2B present a favorable biokinetic profile, characterized by a rapid clearance from non-target tissues and minimal liver accumulation, but a slow wash-out from kidneys. Micro-SPECT/CT imaging of mice bearing pulmonary microtumors evidenced a slow uptake by LNCaP tumors, which steadily rose up to a maximum value of 3.6 SUV at 192 h. This high and prolonged tumor uptake suggests that ¹⁷⁷Lu-scFvD2B has great potential in delivering ablative radiation doses to PSMA-expressing tumors, and warrants further studies to evaluate its preclinical therapeutic efficacy.

Radiolabeled Protein-inhibitor Peptides with Rapid Clinical Translation towards Imaging and Therapy

Protein interactions are the basis for the biological functioning of human beings. However, many of these interactions are also responsible for diseases, including cancer. Synthetic inhibitors of protein interactions based on small molecules are widely investigated in medicinal chemistry. The development of radiolabeled protein-inhibitor peptides for molecular imaging and targeted therapy with quickstep towards clinical translation is an interesting and active research field in the radiopharmaceutical sciences. In this article, recent achievements concerning the design, translational research and theranostic applications of structurally-modified small radiopeptides, such as prostate-specific membrane antigen (PSMA) inhibitors, fibroblast activation protein (FAP) inhibitors and antagonists of chemokine-4 receptor ligands (CXCR-4-L), with high affinity for cancer-associated target proteins, are reviewed and discussed.

Synthesis and preclinical evaluation of the 177Lu-DOTA-PSMA(inhibitor)-Lys3-bombesin heterodimer designed as a radiotheranostic probe for prostate cancer

BACKROUND

Human tumors show intrinsic heterogeneity and changes in phenotype during disease progression, which implies different expression levels of cell surface receptors. The research on new heterodimeric lutetium-177 (Lu)-radiopharmaceuticals interacting with two different targets on tumor cells is a strategy for improvement of radiotheranostic performance. This study aimed to synthesize and characterize the Lu-DOTA-PSMA(inhibitor)-Lys-bombesin (Lu-DOTA-iPSMA-Lys-BN) heterodimer and to evaluate its potential to target prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPr) overexpressed in prostate cancer.

METHODS

The heterodimeric conjugate was synthesized and characterized by infrarred, mass, and H-NMR spectroscopies. The ligand was labeled with Lu and the radiochemical purity was assessed by radio-high-performance liquid chromatography. PSMA/GRPr affinity and the heterobivalent effect on cell viability were evaluated in LNCaP and PC3 prostate cancer cell lines. The biodistribution profile (3 and 96 h) was assessed in athymic mice with induced prostate tumors. Using pulmonary LNCaP (PSMA-positive) and PC3 (GRPr-negative) micrometastasis models, the influence of heterobivalency and affinity on tumor uptake was quantified (micro-SPECT/CT).

RESULTS

Lu-iPSMA-BN (radiochemical purity>98%) showed specific recognition for PSMA and GRPr (IC50=5.62 and 3.49 nmol/l, respectively) with a significant decrease in cell viability (10.15% of cell viability in LNCaP and 40.10% in PC3 at 48 h), as well as high LNCaP and PC3 tumor uptake (5.21 and 3.21% ID/g at 96 h, respectively). Micro-SPECT/CT imaging showed the heterodimer ability to target the tumors (SUVmax of 1.93±0.30 and 1.76±0.10 in LNCaP and PC3, respectively), possibly influenced by the heterobivalent effect. Lu-DOTA-iPSMA-Lys-BN showed suitable affinity for PSMA and GRPr.

CONCLUSION

The results warrant further preclinical studies to establish the Lu-radiotracer theranostic efficacy.

Assessment of the radiation absorbed dose produced by 177Lu-iPSMA, 225Ac-iPSMA and 223RaCl2 to prostate cancer cell nuclei in a bone microenvironment model

This research aimed to assess the radiation absorbed dose produced by ¹⁷⁷Lu-iPSMA (¹⁷⁷Lu-prostate specific membrane antigen inhibitor), ²²⁵Ac-iPSMA and ²²³RaCl₂ to prostate cancer cell nuclei in a simplified model of bone by using an experimental in-vitro prostate cancer LNCaP cell biokinetic study and Monte Carlo simulation with the MCNPX code. Results showed that ²²⁵Ac-iPSMA releases a nine hundred-fold radiation dose greater than ¹⁷⁷Lu-iPSMA and 14 times more than ²²³RaCl₂ per unit of activity retained in bone. ²²⁵Ac-iPSMA could be the best option for treatment of bone metastases in prostate cancer.

177Lu-DOTA-HYNIC-Lys(Nal)-Urea-Glu: Biokinetics, Dosimetry, and Evaluation in Patients with Advanced Prostate Cancer

SPECT/CT images in patients have demonstrated the ability of [99mTc]Tc-EDDA/HYNIC-Lys(Nal)-Urea-Glu ([99mTc]Tc-iPSMA) to detect tumors and metastases of prostate cancer. Considering that theranostics combines the potential of therapeutic and diagnostic radionuclides in the same molecular probe, the aim of this research was to estimate the biokinetics and dosimetry of 177Lu-DOTA-HYNIC-Lys(Nal)-Urea-Glu (177Lu-iPSMA) in healthy subjects and analyze the response in patients receiving 177Lu-iPSMA therapeutic doses. 177Lu-iPSMA was obtained from lyophilized formulations with radiochemical purities >98%. Whole-body images from five healthy subjects were acquired at 20 min, 6, 24, 48, and 120 h after 177Lu-iPSMA administration (185 MBq). The image sequence was used to extrapolate the 177Lu-iPSMA time-activity curves of each organ to adjust the biokinetic model and calculate the total number of disintegrations (N) that occurred in the source regions. N data were the input for the OLINDA/EXM code to calculate internal radiation doses. Ten patients (median age: 68 y; range 58-86 y) received from 1 to 4 cycles of 177Lu-iPSMA (3.7 or 7.4 GBq) every 8-10 weeks. Response was evaluated using the 68Ga-PSMA-ligand-PET/CT or 99mTc-iPSMA-SPECT/CT diagnostic images and serum PSA levels before and after 177Lu-iPSMA treatment. The blood activity showed a half-life value of 1.1 h for the fast component (T 1/2 α = ln2/0.614), 9.2 h for the first slow component (T 1/2 β = ln2/0.075), and 79.6 h for the second slow component (T 1/2 γ = ln2/0.008). The average absorbed doses were 0.23, 0.28, 0.88, and 1.17 Gy/GBq for the spleen, liver, kidney, and salivary glands. A total of 18 cycles were performed in 10 patients. A PSA decrease and some reduction of the radiotracer uptake (SUV) in tumor lesions occurred in 60% and 70% of the patients, respectively. 177Lu-iPSMA obtained from kit formulations showed high tumor uptake with good response rates in patients. The results obtained in this study warrant further clinical studies to establish the optimal number of treatment cycles and for evaluating the effect of this therapeutic agent on survival of patients.