Structure-activity relationship studies of prostate-specific membrane antigen (PSMA) inhibitors derived from α-amino acid with (S)- or (R)-configuration at P1′ region

A Prostate-Specific Membrane Antigen-Targeting Small Molecule-Drug Conjugate Strategy to Overcome the Hematological Toxicity of Olaparib

PARP inhibitors have gained attention in the treatment of metastatic castration-resistant prostate cancer, but approximately half of patients have to abort treatment due to severe hematological toxicity. Herein, we proposed a prostate-specific membrane antigen (PSMA)-targeting small molecule-drug conjugate (SMDC) strategy to address this issue. This led to CQ-16, which achieved its targeting to prostate tumor cells through binding to PSMA. Also, CQ-16 retained the PARP inhibitory activity and exhibited highly selective antiproliferative activities between PSMA-positive and PSMA-negative prostate cells. Moreover, the hematological toxicity observed in Olaparib was not showing in the group of CQ-16 even at a high dose of 390 mg/kg. Moreover, oral administration of CQ-16 exerted significant tumor growth inhibition in the 22Rv1 xenograft mouse model. These above findings not only highlight the potential of CQ-16 to overcome the hematological toxicity associated with PARP inhibitors but also provide a strategy to develop an SMDC with enhanced safety profiles.

Halogen Replacement on the Lysine Side Chain of Lys-Urea-Glu-Based PSMA Inhibitors Leads to Significant Changes in Targeting Properties

PURPOSE

Investigate the impact of various halogens on pharmacokinetics, biodistribution, and micro positron emission tomography/computed tomography (PET/CT) imaging of Glu-urea-Lys-based prostate-specific membrane antigen (PSMA) inhibitors.

PROCEDURES

Based on the modification of SC691, a small molecule inhibitor of PSMA previously developed by our group, we synthesized ⁶⁸Ga-labeled compounds by modifying the lysine terminal amino with different halogenated phenyl substituents. After complete characterization, in vitro and in vivo properties were studied.

RESULTS

The [⁶⁸Ga]Ga-DOTA-SC691-R possesses a high radiochemical yield (98-99%). The internalization values of [⁶⁸Ga]Ga-DOTA-SC691-H, [⁶⁸Ga]Ga-DOTA-SC691-Cl, and [⁶⁸Ga]Ga-DOTA-SC691-Br in LNCaP cells all displayed time-dependent pattern enhanced with time. The results of in vitro competitive inhibition assay showed that the affinity of ^natGa-DOTA-SC691-R for PSMA had a trend of H < F < Cl < Br < I. The blocking imaging and dynamic imaging on micro-PET/CT of male non-obese diabetic/severe combined immunodeficiency mice with LNCaP tumors showed the rapid tumor targeting properties of [⁶⁸Ga]Ga-DOTA-SC691-R with specificity for PSMA. Static imaging of micro-PEC/CT of these compounds could rapidly localize LNCaP tumors with decent image quality (except for [⁶⁸Ga]Ga-DOTA-SC691-H). Biodistribution data showed that [⁶⁸Ga]Ga-DOTA-SC691-R were metabolized via the kidney and tumor accumulation followed the order of H ≈ F ≈ Cl < I < Br uptake values at 1 h. [⁶⁸Ga]Ga-DOTA-SC691-Br showed the highest tumor accumulation and retention (15.21 ± 5.57%ID/g at 30 min, 20.39 ± 4.38%ID/g at 60 min, and 13.30 ± 4.39%ID/g at 120 min), which is consistent with the results of the competitive inhibition assay and cell binding assay.

CONCLUSIONS

It was demonstrated that the halogen substituent on the lysine terminal amino group on the Glu-urea-Lys backbone did positively affect the binding of [⁶⁸Ga]Ga-DOTA-SC691-R to PSMA. The bulkier and less electronegative Br (or I) elements are preferred for structural modifications here.

Synthesis and development of seven-membered constrained cyclic urea based PSMA inhibitors via RCM

Intramolecular ring-closing metathesis on an N,N-diallyl Glu-urea-Gly substrate affords 7-membered cyclic ureas as inhibitors of prostrate specific membrane antigen (PMSA).

PSMA-Targeting Radiopharmaceuticals for Prostate Cancer Therapy: Recent Developments and Future Perspectives

Simple Summary

One of the most frequently diagnosed cancer in men is adenocarcinoma of the prostate. Once the disease is metastatic, only very limited treatment options are available, resulting in a very short median survival time of 13 months; however, this reality is gradually changing due to the discovery of prostate-specific membrane antigen (PSMA), a protein that is present in cancerous prostate tissue. Researchers have developed pharmaceuticals specific for PSMA, ranging from antibodies (mAb) to low-molecular weight molecules coupled to beta minus and alpha-emitting radionuclides for their use in targeted radionuclide therapy (TRT). TRT offers the possibility of selectively removing cancer tissue via the emission of radiation or radioactive particles within the tumour. In this article, the major milestones in PSMA ligand research and the therapeutic developments are summarised, together with a future perspective on the enhancement of current therapeutic approaches.

Abstract

Prostate cancer (PC) is the second most common cancer among men, with 1.3 million yearly cases worldwide. Among those cancer-afflicted men, 30% will develop metastases and some will progress into metastatic castration-resistant prostate cancer (mCRPC), which is associated with a poor prognosis and median survival time that ranges from nine to 13 months. Nevertheless, the discovery of prostate specific membrane antigen (PSMA), a marker overexpressed in the majority of prostatic cancerous tissue, revolutionised PC care. Ever since, PSMA-targeted radionuclide therapy has gained remarkable international visibility in translational oncology. Furthermore, on first clinical application, it has shown significant influence on therapeutic management and patient care in metastatic and hormone-refractory prostate cancer, a disease that previously had remained immedicable. In this article, we provide a general overview of the main milestones in the development of ligands for PSMA-targeted radionuclide therapy, ranging from the firstly developed monoclonal antibodies to the current state-of-the-art low molecular weight entities conjugated with various radionuclides, as well as potential future efforts related to PSMA-targeted radionuclide therapy.

Inhibitors of prostate-specific membrane antigen in the diagnosis and therapy of metastatic prostate cancer - a review of patent literature

INTRODUCTION

Prostate-specific membrane antigen (PSMA), also known as glutamate carboxypeptidase II, is a potential target protein for imaging and treatment of patients with prostate cancer because of its overexpression during metastasis. Various PSMA-targeted imaging and therapeutic probes have been designed and synthesized based on the Lys-urea-Glu motif. Structural modifications have been made exclusively in the linker region, while maintaining the Lys-urea-Glu structure that interacts with S1 and S1' pockets.

AREA COVERED

This review includes WIPO-listed patents (from January 2017 to June 2020) reporting PSMA-targeted probes based on the Lys-urea-Glu or Glu-urea-Glu structure.

EXPERT OPINION

: PSMA-targeted imaging agents labeled with radionuclides such as fluorine-18, copper-64, gallium-68, and technetium-99m have been successfully translated into clinical phase for the early diagnosis of metastatic prostate cancer. Recently, PSMA-targeted therapeutic agents labeled with iodine-131, lutetium-177, astatine-211, and lead-212 have also been developed with notable progress. Most PSMA-targeted agents are based on the Lys-urea-Glu or Glu-urea-Glu structure, demonstrate strong PSMA-binding affinity in nanomolar range, and achieve diverse structural modifications in the non-pharmacophore pocket. By exploiting the S1 accessory pocket or the tunnel region of the PSMA active site, the in vivo efficacy and pharmacokinetic profiles of the PMSA-targeted agents can be effectively modulated.