Muscarinic inhibition of salivary glands with glycopyrronium bromide does not reduce the uptake of PSMA-ligands or radioiodine

PSMA-Targeted Radiopharmaceuticals for Prostate Cancer Diagnosis and Therapy

ABSTRACT

Prostate cancer (PCa) is the most common noncutaneous malignancy in men. Until recent years, accurate imaging of men with newly diagnosed PCa, or recurrent or low-volume metastatic disease, was limited. Further, therapeutic options for men with advanced, metastatic, castration-resistant disease were increasingly limited as a result of increasing numbers of systemic therapies being combined in the upfront metastatic setting. The advent of urea-based, small-molecule inhibitors of prostate-specific membrane antigen (PSMA) has partially addressed those shortcomings in diagnosis and therapy of PCa. On the diagnostic side, there are multiple pivotal phase III trials with several different agents having demonstrated utility in the initial staging setting, with generally modest sensitivity but very high specificity for determining otherwise-occult pelvic nodal involvement. That latter statistic drives the utility of the scan by allowing imaging interpreters to read with very high sensitivity while maintaining a robust specificity. Other pivotal phase III trials have demonstrated high detection efficiency in patients with biochemical failure, with high positive predictive value at the lesion level, opening up possible new avenues of therapy such as metastasis-directed therapy. Beyond the diagnostic aspects of PSMA-targeted radiotracers, the same urea-based chemical scaffolds can be altered to deliver therapeutic isotopes to PCa cells that express PSMA. To date, one such agent, when combined with best standard-of-care therapy, has demonstrated an ability to improve overall survival, progression-free survival, and freedom from skeletal events relative to best standard-of-care therapy alone in men with metastatic, castration-resistant PCa who are post chemotherapy. Within the current milieu, there are a number of important future directions including the use of artificial intelligence to better leverage diagnostic findings, further medicinal chemistry refinements to the urea-based structure that may allow improved tumor targeting and decreased toxicities, and the incorporation of new radionuclides that may better balance efficacy with toxicities than those nuclides that are available.

Advances in PSMA Alpha Theragnostics

Alpha theranostics offer an attractive alternative form of therapy, which has best been investigated and documented with 225Ac-PSMA in patients with prostate cancer. Advantages offered by targeted alpha therapy include overcoming radiation resistance, oxygen independence, effecting double-stranded DNA breakages within the tumors with anticipated improved clinical outcomes and an acceptable side effect profile. The previous Seminars article on this topic, published in 2020, had to rely mostly on published case reports and small observational studies. In the last few years, however, several meta-analyses have emerged that evaluate the safety and efficacy of 225Ac-PSMA in prostate cancer patients, followed most recently by a multi-center retrospective study initiated by WARMTH. The findings of these publications, together with the exploration of TAT offered in clinical conditions other than as a last resort, is the focus of this updated overview. Unresolved clinical issues that remain, include the appropriate selection of patients that would benefit most from treatment with 225Ac-PSMA, treatment timing within the disease landscape, optimal dosing schedule, dosimetry, when and how to best use combination therapies and minimization and treatment of side effects, particularly that of xerostomia.

A novel PSMA-targeting tracer with highly negatively charged linker demonstrates decreased salivary gland uptake in mice compared to [68Ga]Ga-PSMA-11

BACKGROUND

The current generation of radiolabeled PSMA-targeting therapeutic agents is limited by prominent salivary gland binding, which results in dose-limiting xerostomia from radiation exposure. JB-1498 is a urea-based small molecule with a highly negatively charged linker targeting prostate specific membrane antigen (PSMA). Prior work on a similar tracer with the same negatively charged linker demonstrated low normal organ/soft tissue background uptake compared to [68Ga]Ga-PSMA-11. The purpose of this study was to investigate if [68Ga]Ga-JB-1498 had reduced salivary gland uptake in mice compared to [68Ga]Ga-PSMA-11.

RESULTS

JB-1498 demonstrated high affinity for PSMA binding and tumor uptake in a murine tumor model. In an initial biodistribution study with low molar activity, [68Ga]Ga-JB-1498 demonstrated salivary gland uptake of 0.13 ± 0.01%ID/g. In a second biodistribution study in non-tumor-bearing mice with high molar activity, [68Ga]Ga-JB1498 demonstrated salivary gland uptake of 0.39 ± 0.24% ID/g and kidney activity of 10.12 ± 1.73% ID/g at one hour post IV injection. This salivary gland uptake is significantly less than the published uptake of [68Ga]Ga-PSMA-11. Micro-PET visually confirmed the findings of the biodistribution studies. Dynamic micro-PET imaging demonstrated gradually decreasing [68Ga]Ga-JB1498 activity in salivary glands and kidneys, compared to gradually increasing [68Ga]Ga-PSMA-11 activity in these two organs during the first hour.

CONCLUSION

Biodistribution and micro-PET imaging of [68Ga]Ga-JB-1498 demonstrate significantly decreased salivary gland uptake and different pharmacokinetic behavior in kidneys and salivary glands in mice compared to [68Ga]Ga-PSMA-11. Our findings suggest that constructing a PSMA-targeting molecule with a highly negatively charged linker is a promising strategy to reduce salivary gland uptake of GCP-II/PSMA ligands in theranostic applications.

Plackett-Burman and face-centered composite designs for development and optimization of chromatographic method for the simultaneous determination of glycopyrronium, indacaterol and mometasone in their fixed dose combination inhaler - Green profile assessment

A novel simple, specific, sensitive, accurate and precise reversed phase high performance liquid chromatographic method (RP-HPLC/UV) was developed and validated for the simultaneous estimation of Glycopyrronium bromide (GLY), Indacaterol acetate (IND) and Mometasone furoate (MOF) in pure form, in laboratory prepared mixtures and in pharmaceutical dosage form. Experimental design methodology was applied by using Plackett-Burman and face-centered composite designs to achieve the best resolution with minimum experimental trials. The designed model was statistically analyzed, graphically presented by surface plots and the relationships between coefficients of the derived polynomial equations were interpreted. Chromatographic separation was achieved on Inertsil ODS C18 column (250 ×4.6 mm, 5 µm) at ambient temperature using a mobile phase composed of methanol: 0.1% glacial acetic acid (pH4) in a gradient elution at a flow rate 1 mL /min. UV detection was carried out at 233 nm. Response was found to be linear in the concentration range of 20-120 µg /mL with regression coefficient (r2 = 0.999) for GLY, 50-300 µg /mL with regression coefficient (r2 = 0.9995) for IND and 50-300 µg /mL with regression coefficient (r2 = 0.9998) for MOF. The method was validated as per ICH guidelines and satisfactory results were achieved. The method was successfully applied for the analysis of the cited drugs in their fixed dose combination (FDC) pharmaceutical formulation. Statistical comparison between the results obtained by the proposed method and the reference methods for GLY, IND and MOF showed no significant difference. The developed method could be implemented in quality control aspects of the cited drugs. Four green metrics were used to evaluate the new RP-HPLC/UV method's greenness and compare it to other published techniques.

Sublingual Atropine Administration as a Tool to Decrease Salivary Glands' PSMA-Ligand Uptake: A Preclinical Proof of Concept Study Using [68Ga]Ga-PSMA-11

Prostate Specific Membrane Antigen (PSMA)-directed radionuclide therapy has gained an important role in the management of advanced castration-resistant prostate cancer. Although extremely promising, the prolongation in survival and amelioration of disease-related symptoms must be balanced against the direct toxicities of the treatment. Xerostomia is amongst the most common and debilitating of these, particularly when using an alpha emitter. It is therefore of main importance to develop new preventive strategies. This preclinical study has evaluated the effect of α-adrenergic and anticholinergic drugs on [99mTc]TcO4− Single Photon Emission Computed Tomography/Computed Tomography (SPECT/CT) and [68Ga]Ga-PSMA-11 Positron Emission Tomography (PET/CT). Methods: The effects of phenylephrine, scopolamine, atropine, and ipratropium on salivary glands uptake were evaluated in non-tumor-bearing mice by [99mTc]TcO4− microSPECT/CT. The most efficient identified strategy was evaluated in non-tumor-bearing and xenografted mice by [68Ga]Ga-PSMA-11 PET/CT. Results: Scopolamine and atropine showed a significant decrease in the parotid glands’ uptake on SPECT/CT whereas phenylephrine and ipratropium failed. Atropine premedication (sublingual route), which was the most effective strategy, also showed a drastic decrease of [68Ga]Ga-PSMA-11 salivary glands’ uptake in both non-tumor-bearing mice (−51.6% for the parotids, p < 0.0001) and human prostate adenocarcinoma xenografted mice (−26.8% for the parotids, p < 0.0001). Conclusion: Premedication with a local administration of atropine could represent a simple, safe, and efficient approach for reducing salivary glands’ uptake.

Safety of High-Dose Botulinum Toxin Injections for Parotid and Submandibular Gland Radioprotection

Botulinum Toxin injections into salivary glands (SG) up to a total dose of 100 units IncobotulinumtoxinA (IncoA) represent the treatment of choice for sialorrhea. However, BTX might also protect SG against sialotoxic radioligand cancer therapies. The radioligand Actinium-225-PSMA effectively targets Prostate Cancer (PCa) metastases but inevitably destroys SG due to unintended gland uptake. A preliminary case series with regular-dose IncoA failed to reduce SG PSMA-radioligand uptake. We therefore increased IncoA dosage in combination with transdermal scopolamine until a clinically relevant SG PSMA-radioligand uptake reduction was achieved. Ten consecutive men with metastasized PCa refractory to all other cancer therapies received gradually increasing IncoA dosages as part of a compassionate use PSMA-radioligand-therapy trial. The parotid gland received six and the submandibular gland three injection points under ultrasound control, up to a maximum of 30 units IncoA per injection point. A maximum total dose of 250 units IncoA was applied with up to 170 units per parotid and 80 units per submandibular gland. Treatment was well tolerated and all side-effects were non-serious. The most frequent side-effect was dry mouth of mild severity. No dysphagia, facial weakness, chewing difficulties or systemic side-effects were observed. SG injections with IncoA up to a total dose of 250 units are safe when distributed among several injection-points under ultrasound control by an experienced physician. These preliminary findings lay the basis for future trials including BTX as major component for SG protection in established as well as newly emerging radioligand cancer therapies.

Global experience with PSMA-based alpha therapy in prostate cancer

PURPOSE

This review discusses the current state of prostate-specific membrane antigen (PSMA)-based alpha therapy of metastatic castration-resistant prostate cancer (mCRPC). With this in-depth discussion on the growing field of PSMA-based alpha therapy (PAT), we aimed to increase the interactions between basic scientists and physician-scientists in order to advance the field.

METHODS

To achieve this, we discuss the potential, current status, and opportunities for alpha therapy and strategies, attempted to date, and important questions that need to be addressed. The paper reviews important concepts, including whom to treat, how to treat, what to expect regarding treatment outcome, and toxicity, and areas requiring further investigations.

RESULTS

There is much excitement about the potential of this field. Much of the potential exists because these therapies utilize unique mechanisms of action, difficult to achieve with other conventional therapies.

CONCLUSION

A better understanding of the strengths and limitations of PAT may help in creating an effective therapy for mCRPC and design a rational combinatorial approach to treatment by targeting different tumor pathways.