Development of Bispecific NT-PSMA Heterodimer for Prostate Cancer Imaging: A Potential Approach to Address Tumor Heterogeneity

A novel androgen-independent radiotracer with dual targeting of NTSR1 and PSMA for PET/CT imaging of prostate cancer

A substantial proportion of patients with prostate cancer (PCa) develop treatment resistance or mortality after androgen deprivation therapy (ADT). Current methods for identifying and locating recurrent lesions using prostate-specific membrane antigen (PSMA)-based positron emission tomography (PET) imaging, which relies on androgen levels, often result in diagnostic delays. Therefore, the development of an androgen-independent radiotracer is critical for the early identification of recurrent lesions. The neurotensin receptor 1 (NTSR1) is highly expressed in androgen-independent PCa lesions. Here, we synthesized a bispecific ligand targeting PSMA and NTSR1 by solid-phase peptide synthesis and formulated a68Ga-labeled bispecific radiotracer, ([68Ga]Ga-NT-PSMA). This radiotracer exhibited a high radiochemical yield (71.27 % ± 1.58 %) and demonstrated an affinity for NTSR1 (39.32 ± 2.98 nM) and PSMA (63.47 ± 5.14 nM) in vitro. Small animal PET imaging showed comparable uptake of [68Ga]Ga-NT-PSMA and the monomeric radiotracer [68Ga]Ga-DOTA-NT20.3 in mice bearing androgen-independent PC3 (3.64 ± 0.49 %ID/g vs. 5.60 ± 1.42 %ID/g, nonsignificant [ns]) and DU145 tumors (2.49 ± 0.20 %ID/g vs. 2.34 ± 0.18 %ID/g, ns) at 90 min post-injection. In androgen-dependent 22Rv1 xenografts, [68Ga]Ga-NT-PSMA uptake was lower (1.94 ± 0.29 %ID/g) than [68Ga]Ga-PSMA-11 (3.94 ± 0.26 %ID/g, P < 0.001). Nevertheless, [68Ga]Ga-NT-PSMA effectively imaged all three xenograft types with high contrast, an achievement not possible with monomeric radiotracers alone. These results indicate that imaging with [68Ga]Ga-NT-PSMA is independent of the androgen dependence of the model, highlighting its potential as a promising nuclear medicine diagnostic tool for the early identification and localization of castration-resistant PCa lesions.

Neurotensin and Its Involvement in Female Hormone-Sensitive Cancers

Neurotensin (NT) is a peptide involved in digestion, neuromodulation, and cancer progression. NT and its receptors (NTR1 and SORT1 mainly) have been widely studied in oncology. Data show that NT expression is under the control of sex steroid hormones, in particular estradiol. We focused on its involvement in three main female hormone-sensitive cancers, breast, ovarian, and endometrial cancer, in a narrative review. NT, NTR1, and SORT1 are mostly expressed in these three cancers, and their involvement in oncologic processes such as proliferation and invasion seems to match, as does their impact on prognosis for most. The development of NT receptor-targeted therapies, including theranostics and radioligand treatments, presents a promising avenue for personalized cancer treatment.

Rational design of NT-PSMA heterobivalent probes for prostate cancer theranostics

Targeting the prostate-specific membrane antigen (PSMA) with radiopharmaceuticals for imaging and/or therapy has demonstrated significant advancement in the management of prostate cancer patients. However, PSMA targeting remains unsuccessful in prostate cancers with low expression of PSMA, which account for 15% of cases. The neurotensin receptor-1 (NTS1) has been highlighted as a suitable oncotarget for imaging and therapy of PSMA-negative prostate cancer lesions. Therefore, heterobivalent probes targeting both PSMA and NTS1 could improve the prostate cancer management. Herein, we report the development of a branched hybrid probe (JMV 7489) designed to target PSMA and/or NTS1 bearing relevant pharmacophores and DOTA as the chelating agent. The new ligand was synthesized with a hybrid approach, which includes both syntheses in batch and in the solid phase. Saturation binding experiments were next performed on HT-29 and PC3-PIP cells to derive K d and B max values. On the PC3-PIP cells, [68Ga]Ga-JMV 7489 displayed good affinity towards PSMA (K d = 53 ± 17 nM; B max = 1393 ± 29 fmol/106 cells) in the same range as the corresponding reference monomer. A lower affinity value towards NTS1 was depicted (K d = 157 ± 71 nM; B max = 241 ± 42 fmol/106 cells on PC3-PIP cells; K d = 246 ± 1 nM; B max = 151 ± 44 fmol/106 cells on HT-29 cells) and, surprisingly, it was also the case for the corresponding monomer [68Ga]Ga-JMV 7089. These results indicate that the DOTA macrocycle and the linker are critical elements to design heterobivalent probes targeting PSMA and NTS1 with high affinity towards NTS1.

Theranostics of Primary Prostate Cancer: Beyond PSMA and GRP-R

The imaging of Prostate-Specific Membrane Antigen (PSMA) is now widely used at the initial staging of prostate cancers in patients with a high metastatic risk. However, its ability to detect low-grade tumor lesions is not optimal.

METHODS

First, we prospectively performed neurotensin receptor-1 (NTS₁) IHC in a series of patients receiving both [⁶⁸Ga]Ga-PSMA-617 and [⁶⁸Ga]Ga-RM2 before prostatectomy. In this series, PSMA and GRP-R IHC were also available (n = 16). Next, we aimed at confirming the PSMA/GRP-R/NTS₁ expression profile by retrospective autoradiography (n = 46) using a specific radiopharmaceuticals study and also aimed to decipher the expression of less-investigated targets such as NTS₂, SST₂ and CXCR4.

RESULTS

In the IHC study, all samples with negative PSMA staining (two patients with ISUP 2 and one with ISUP 3) were strongly positive for NTS₁ staining. No samples were negative for all three stains-for PSMA, GRP-R or NTS₁. In the autoradiography study, binding of [¹¹¹In]In-PSMA-617 was high in all ISUP groups. However, some samples did not bind or bound weakly to [¹¹¹In]In-PSMA-617 (9%). In these cases, binding of [¹¹¹n]In-JMV 6659 and [¹¹¹In]In-JMV 7488 towards NTS₁ and NTS₂ was high.

CONCLUSIONS

Targeting PSMA and NTS₁/NTS₂ could allow for the detection of all intraprostatic lesions.

Clinical advancement of precision theranostics in prostate cancer

Theranostic approaches with positron emission tomography/computed tomography (PET/CT) or PET/magnetic resonance imaging (PET/MRI) molecular imaging probes are being implemented clinically in prostate cancer (PCa) diagnosis and imaging-guided precision surgery. This review article provides a comprehensive summary of the rapidly expanding list of molecular imaging probes in this field, including their applications in early diagnosis of primary prostate lesions; detection of lymph node, skeletal and visceral metastases in biochemical relapsed patients; and intraoperative guidance for tumor margin detection and nerve preservation. Although each imaging probe shows preferred efficacy in some applications and limitations in others, the exploration and research efforts in this field will eventually lead to improved precision theranostics of PCa.

Synthesis and Preclinical Evaluation of Three Novel 68Ga-Labeled Bispecific PSMA/FAP-Targeting Tracers for Prostate Cancer Imaging

Tumor heterogeneity limits the efficacy and reliability of monospecific radiopharmaceuticals in prostate cancer diagnosis and therapy. To overcome this limitation and improve lesion detection sensitivity, we developed and evaluated three bispecific radiotracers that can target both prostate-specific membrane antigen (PSMA) and fibroblast activation protein (FAP), which are the two key proteins overexpressed in prostate cancer. Three FAP-targeting ligands with various linker lengths were synthesized through multistep organic synthesis, and then connected to the PSMA-targeting motif. IC₅₀(PSMA) and IC₅₀(FAP) values of Ga-complexed bispecific ligands, Ga-AV01017, Ga-AV01030, and Ga-AV01038 were 25.2-71.6 and 1.25-2.74 nM, respectively. The uptake values in PSMA-expressing LNCaP tumor xenografts were 4.38 ± 0.55, 5.17 ± 0.51, and 4.25 ± 0.86 %ID/g for [⁶⁸Ga]Ga-AV01017, [⁶⁸Ga]Ga-AV01030, and [⁶⁸Ga]Ga-AV01038, respectively, which were lower than the monospecific PSMA-targeting tracer [⁶⁸Ga]Ga-HTK03041 (23.1 ± 6.11 %ID/g). The uptake values in FAP-expressing HEK293T:hFAP tumor xenografts were 2.99 ± 0.37, 3.69 ± 0.81, 3.64 ± 0.83 %ID/g for [⁶⁸Ga]Ga-AV01017, [⁶⁸Ga]Ga-AV01030, and [⁶⁸Ga]Ga-AV01038, respectively, which were also lower than the monospecific FAP-targeting tracer, [⁶⁸Ga]Ga-FAPI-04 (12.5 ± 2.00 %ID/g). We observed that the bispecific tracers had prolonged blood retention, in which tracers with a longer linker tend to have a higher blood uptake and lower tumor uptake. Further investigations are needed to optimize the linker selection to generate promising bispecific PSMA/FAP-targeting tracers for prostate cancer imaging.

PSMA-targeted low-molecular double conjugates for diagnostics and therapy

This review presents data on dual conjugates of therapeutic and diagnostic action for targeted delivery to prostate cancer cells. The works of the last ten years on this topic were analyzed. The mail attention focuses on low-molecular-weight conjugates directed to the prostate-specific membrane antigen (PSMA); the comparison of high and low molecular weight PSMA-targeted conjugates was made. The considered conjugates were divided in the review into two main classes: diagnostic bimodal conjugates (which are containing two fragments for different types of diagnostics), theranostic conjugates (containing both therapeutic and diagnostic agents); also bimodal high molecular weight therapeutic conjugates containing two therapeutic agents are briefly discussed. The data of in vitro and in vivo studies for PSMA-targeted double conjugates available by the beginning of 2021 have been analyzed.

Image-guided selection of Gd@C-dots as sensitizers to improve radiotherapy of non-small cell lung cancer

BACKGROUND

Recently, gadolinium-intercalated carbon dots (Gd@C-dots) have demonstrated potential advantages over traditional high-Z nanoparticles (HZNPs) as radiosensitizers due to their high stability, minimal metal leakage, and remarkable efficacy.

RESULTS

In this work, two Gd@C-dots formulations were fabricated which bore carboxylic acid (CA-Gd@C-dots) or amino group (pPD-Gd@C-dots), respectively, on the carbon shell. While it is critical to develop innovative nanomateirals for cancer therapy, determining their tumor accumulation and retention is equally important. Therefore, in vivo positron emission tomography (PET) was performed, which found that 64Cu-labeled pPD-Gd@C-dots demonstrated significantly improved tumor retention (up to 48 h post injection) compared with CA-Gd@C-dots. Indeed, cell uptake of 64Cu-pPD-Gd@C-dots reached close to 60% of total dose compared with ~ 5% of 64Cu-CA-Gd@C-dots. pPD-Gd@C-dots was therefore further evaluated as a new radiosensitizer for non-small cell lung cancer treatment. While single dose radiation plus intratumorally injected pPD-Gd@C-dots did lead to improved tumor suppression, the inhibition effect was further improved with two doses of radiation. The persistent retention of pPD-Gd@C-dots in tumor region eliminates the need of reinjecting radiosensitizer for the second radiation.

CONCLUSIONS

PET offers a simple and straightforward way to study nanoparticle retention in vivo, and the selected pPD-Gd@C-dots hold great potential as an effective radiosensitizer.

Ditelluride-Bridged PEG-PCL Copolymer as Folic Acid-Targeted and Redox-Responsive Nanoparticles for Enhanced Cancer Therapy

The development of the nanosized delivery systems with targeting navigation and efficient cargo release for cancer therapy has attracted great attention in recent years. Herein, a folic acid (FA) modified PEGylated polycaprolactone containing ditelluride linkage was synthesized through a facile coupling reaction. The hydrophobic doxorubicin (DOX) can be encapsulated into the polymeric micelles, and such nanoparticles (F-TeNPDOX) exhibited redox-responsive drug release under abundant glutathione (GSH) condition due to the degradation of ditelluride bonds. In addition, flow cytometric analyses showed that the FA ligands on F-TeNPDOX could facilitate their cellular uptake in 4T1 breast cancer cells. Therefore, F-TeNPDOX led to the promoted drug accumulation and enhanced growth inhibition on 4T1 tumor in vivo. The obtained results suggest F-TeNPDOX excellent potential as nanocarriers for anticancer drug delivery.