Biomarkers to personalize treatment with 177Lu-PSMA-617 in men with metastatic castration-resistant prostate cancer - a state of the art review

Real-world Outcomes and Predictive Biomarkers for 177Lutetium Prostate-specific Membrane Antigen Ligand Treatment in Metastatic Castration-resistant Prostate Cancer: A European Association of Urology Young Academic Urologists Prostate Cancer Working Group Multi-institutional Observational Study

BACKGROUND

The European Association of Urology guidelines include the lutetium-177 (177Lu) PSMA-617 prostate-specific membrane antigen (PSMA) ligand as a therapy option for metastatic castration-resistant prostate cancer (mCRPC). A major challenge in clinical practice is to pursue a personalized treatment approach based on robust predictive biomarkers.

OBJECTIVE

To assess the performance of 177Lu PSMA in real-world practice and to elaborate clinical biomarkers for evaluating treatment responses.

DESIGN, SETTING, AND PARTICIPANTS

We conducted a retrospective observational study including 233 patients with mCRPC treated with 177Lu PSMA in eight high-volume European centers.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Baseline characteristics and clinical parameters during and after 177Lu PSMA treatment were documented. Correlations to treatment response were analyzed using χ2 and log-rank tests, with differences between groups with and without disease progression calculated using a Mann-Whitney U test. Univariate and multivariate-adjusted hazard ratios (HRs) were measured using Cox proportional hazards models.

RESULTS AND LIMITATIONS

A prostate-specific antigen (PSA) decrease of ≥30% was observed in 41.7%, 63.5%, and 77.8% of patients after the first, second, and third treatment cycle, respectively. Restaging performed via PSMA positron emission tomography-computed tomography revealed that 33.7% of patients had an imaging-based response, including two patients with a complete response, while 13.4% had stable disease. The median time to progression was 5 mo and the median time until the start of a consecutive antineoplastic therapy was 8.5 mo. Of importance, a PSA decrease ≥30% after the first two cycles of 177Lu PSMA (1 cycle: p = 0.0003; 2 cycles: p = 0.004), absolute PSA after the first three cycles (1 cycle: p = 0.011; 2 cycles: p = 0.0005; 3 cycles: p = 0.002), and a PSA doubling time >6 mo (p = 0.009) were significantly correlated to treatment response. Furthermore, gamma-glutamyl transferase ≤31 U/L at the start of 177Lu PSMA therapy was correlated with 1.5 times higher risk of progression for patients without but not with visceral metastases (p = 0.046).

CONCLUSIONS

177Lu PSMA is an effective treatment option in mCRPC in the real-world setting. A PSA decrease ≥30% after the first two cycles is an early marker of response that can be easily implemented in clinical practice.

PATIENT SUMMARY

177Lu PSMA is a radioactive agent approved for treatment of advanced prostate cancer. We reviewed its use outside of clinical trials for patients treated at eight European centers. We found that 177Lu PSMA is an effective treatment option in real-world practice. A PSA (prostate-specific antigen) decrease of ≥30% after the first two therapy cycles is an early indicator of response to treatment and can be used in personalizing treatments for patients.

Quantification of biochemical PSA dynamics after radioligand therapy with [177Lu]Lu-PSMA-I&T using a population pharmacokinetic/pharmacodynamic model

BACKGROUND

There is an unmet need for prediction of treatment outcome or patient selection for [177Lu]Lu-PSMA therapy in patients with metastatic castration-resistant prostate cancer (mCRPC). Quantification of the tumor exposure-response relationship is pivotal for further treatment optimization. Therefore, a population pharmacokinetic (PK) model was developed for [177Lu]Lu-PSMA-I&T using SPECT/CT data and, subsequently, related to prostate-specific antigen (PSA) dynamics after therapy in patients with mCRPC using a pharmacokinetic/pharmacodynamic (PKPD) modelling approach.

METHODS

A population PK model was developed using quantitative SPECT/CT data (406 scans) of 76 patients who received multiple cycles [177Lu]Lu-PSMA-I&T (± 7.4 GBq with either two- or six-week interval). The PK model consisted of five compartments; central, salivary glands, kidneys, tumors and combined remaining tissues. Covariates (tumor volume, renal function and cycle number) were tested to explain inter-individual variability on uptake into organs and tumors. The final PK model was expanded with a PD compartment (sequential fitting approach) representing PSA dynamics during and after treatment. To explore the presence of a exposure-response relationship, individually estimated [177Lu]Lu-PSMA-I&T tumor concentrations were related to PSA changes over time.

RESULTS

The population PK model adequately described observed data in all compartments (based on visual inspection of goodness-of-fit plots) with adequate precision of parameters estimates (< 36.1% relative standard error (RSE)). A significant declining uptake in tumors (k14) during later cycles was identified (uptake decreased to 73%, 50% and 44% in cycle 2, 3 and 4-7, respectively, compared to cycle 1). Tumor growth (defined by PSA increase) was described with an exponential growth rate (0.000408 h-1 (14.2% RSE)). Therapy-induced PSA decrease was related to estimated tumor concentrations (MBq/L) using both a direct and delayed drug effect. The final model adequately captured individual PSA concentrations after treatment (based on goodness-of-fit plots). Simulation based on the final PKPD model showed no evident differences in response for the two different dosing regimens currently used.

CONCLUSIONS

Our population PK model accurately described observed [177Lu]Lu-PSMA-I&T uptake in salivary glands, kidneys and tumors and revealed a clear declining tumor uptake over treatment cycles. The PKPD model adequately captured individual PSA observations and identified population response rates for the two dosing regimens. Hence, a PKPD modelling approach can guide prediction of treatment response and thus identify patients in whom radioligand therapy is likely to fail.

Spatiotemporal modeling of radiopharmaceutical transport in solid tumors: Application to 177Lu-PSMA therapy of prostate cancer

BACKGROUND AND OBJECTIVE

177Lu-labeled prostate-specific membrane antigen (PSMA) radiopharmaceutical therapy (RPT) represents a pivotal advancement in addressing prostate cancer. However, existing therapies, while promising, remain incompletely understood and optimized. Computational models offer potential insights into RPTs, aiding in clinical drug delivery enhancement. In this study, we investigate the impact of various physiological parameters on the delivery of 177Lu-PSMA-617 RPT using the convection-diffusion-reaction (CDR) model.

METHODS

Our investigation encompasses tumor geometry and surrounding tissue, characterized by well-defined boundaries and initial conditions. Utilizing the finite element method, we solve governing equations across a range of parameters: dissociation constant KD (1, 0.1, 0.01 [nM]), internalization rate (0.01-0.0001 [min-1]), diverse tumor shapes, and variable necrotic zone sizes. This model can provide an accurate analysis of radiopharmaceutical delivery from the injection site to the tumor cell, including drug transport in the vascular, interstitial, and intracellular spaces, and considering important parameters (e.g., drug extravasation from microvessels or to lymphatic vessels, the extracellular matrix, receptors, and intracellular space).

RESULTS

Our findings reveal significant enhancements in tumor-absorbed doses as KD decreases. This outcome can be attributed to the higher affinity of radiopharmaceuticals for PSMA receptors as KD diminishes, facilitating a more efficient binding and retention of the therapeutic agent within the tumor microenvironment. Additionally, tumor-absorbed doses for KD ∼ 1 [nM] show an upward trend with higher internalization rates. This observation can be rationalized by considering that a greater internalization rate would result in a higher proportion of radiopharmaceuticals being taken up by tumor cells after binding to receptors on the cell surface. Notably, tumor shape and necrotic zone size exhibit limited influence on tumor absorbed dose.

CONCLUSIONS

The present study employs the CDR model to explore the role of physiological parameters in shaping 177Lu-PSMA-617 RPT delivery. These findings provide insights for improving prostate cancer therapy by understanding radiopharmaceutical transport dynamics. This computational approach contributes to advancing our understanding of radiopharmaceutical delivery mechanisms and has implications for enhancing treatment efficacy.

Current role of PSMA-PET imaging in the clinical management of prostate cancer

Despite the developments of the last few years, metastatic castration-resistant prostate cancer (PC) remains a deadly disease. Until recently, almost all guidelines recommended magnetic resonance imaging (MRI) or computed tomography (CT) for the initial staging and local/systematic recurrence. Positron emission tomography/computed tomography (PET/CT) with prostate-specific membrane antigen (PSMA) at the present stage, emerged as a promising diagnostic imaging tool for PC. PSMA PET/CT alone or in combination with multiparametric magnetic resonance imaging (mpMRI) can improve the detection of clinically significant PC, especially for Prostate Imaging Reporting & Data System (PI-RADS) = 3 lesions. In addition, PSMA PET/CT is more accurate than CT and bone scan for intermediate to high-risk disease at the initial staging. Contrariwise, a negative PET is not useful for surgeons to avoid a pelvic nodal dissection. PET-PSMA imaging is appropriate for prostate-specific antigen (PSA) persistence or PSA rise from undetectable level after radical prostatectomy or for PSA rise above nadir after definitive radiotherapy. Also, it is recommended for patients fit for curative salvage treatment. It should be noted that in patients, candidates for radionuclide therapy with Lutetium-177 (117Lu), a PSMA strong expression from PET/CT at baseline is considered necessary. This review summarizes the evolution of PSMA PET/CT and its current role in the management of PC.

Single-Time-Point Imaging for Dosimetry After [177Lu]Lu-DOTATATE: Accuracy of Existing Methods and Novel Data-Driven Models for Reducing Sensitivity to Time-Point Selection

Estimation of the time-integrated activity (TIA) for dosimetry from imaging at a single time point (STP) facilitates the clinical translation of dosimetry-guided radiopharmaceutical therapy. However, the accuracy of the STP methods for TIA estimation varies on the basis of time-point selection. We constructed patient data-driven regression models to reduce the sensitivity to time-point selection and to compare these new models with commonly used STP methods. Methods: SPECT/CT performed at time period (TP) 1 (3-5 h), TP2 (days 1-2), TP3 (days 3-5), and TP4 (days 6-8) after cycle 1 of [177Lu]Lu-DOTATATE therapy involved 27 patients with 100 segmented tumors and 54 kidneys. Influenced by the previous physics-based STP models of Madsen et al. and Hänscheid et al., we constructed an STP prediction expression, TIA = A(t) × g(t), in a SPECT data-driven way (model 1), in which A(t) is the observed activity at imaging time t, and the curve, g(t), is estimated with a nonparametric generalized additive model by minimizing the normalized mean square error relative to the TIA derived from 4-time-point SPECT (reference TIA). Furthermore, we fit a generalized additive model that incorporates baseline biomarkers as auxiliary data in addition to the single activity measurement (model 2). Leave-one-out cross validation was performed to evaluate STP models using mean absolute error (MAE) and mean square error between the predicted and reference TIA. Results: At days 3-5, all evaluated STP methods performed very well, with an MAE of less than 7% (between-patient SD of <10%) for both kidneys and tumors. At other TPs, the Madsen method and data-driven models 1 and 2 performed reasonably well (MAEs < 17% for kidneys and < 32% for tumors), whereas the error with the Hänscheid method was substantially higher. The proof of concept of adding baseline biomarkers to the prediction model was demonstrated and showed a moderate enhancement at TP1, especially for estimating kidney TIA (MAE ± SD from 15.6% ± 1.3% to 11.8% ± 1.0%). Evaluations on 500 virtual patients using clinically relevant time-activity simulations showed a similar performance. Conclusion: The performance of the Madsen method and proposed data-driven models is less sensitive to TP selection than is the Hänscheid method. At the earliest TP, which is the most practical, the model incorporating baseline biomarkers outperforms other methods that rely only on the single activity measurement.

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.

Joint EANM/SNMMI procedure guideline for the use of 177Lu-labeled PSMA-targeted radioligand-therapy (177Lu-PSMA-RLT)

Prostate-specific membrane antigen (PSMA) is expressed by the majority of clinically significant prostate adenocarcinomas, and patients with target-positive disease can easily be identified by PSMA PET imaging. Promising results with PSMA-targeted radiopharmaceutical therapy have already been obtained in early-phase studies using various combinations of targeting molecules and radiolabels. Definitive evidence of the safety and efficacy of [177Lu]Lu-PSMA-617 in combination with standard-of-care has been demonstrated in patients with metastatic castration-resistant prostate cancer, whose disease had progressed after or during at least one taxane regimen and at least one novel androgen-axis drug. Preliminary data suggest that 177Lu-PSMA-radioligand therapy (RLT) also has high potential in additional clinical situations. Hence, the radiopharmaceuticals [177Lu]Lu-PSMA-617 and [177Lu]Lu-PSMA-I&T are currently being evaluated in ongoing phase 3 trials. The purpose of this guideline is to assist nuclear medicine personnel, to select patients with highest potential to benefit from 177Lu-PSMA-RLT, to perform the procedure in accordance with current best practice, and to prepare for possible side effects and their clinical management. We also provide expert advice, to identify those clinical situations which may justify the off-label use of [177Lu]Lu-PSMA-617 or other emerging ligands on an individual patient basis.

Prostate cancer and novel pharmacological treatment options-what's new for 2022?

INTRODUCTION

Androgen deprivation therapy (ADT) plus Androgen Receptor Target Agents (ARTAs) or docetaxel are the actual standard of care in prostate cancer (PC). Several therapeutic options are available for pretreated patients: cabazitaxel, olaparib, and rucaparib for BRCA mutations, Radium-223 for selected patients with symptomatic bone metastasis, sipuleucel T, and 177 LuPSMA-617.

AREAS COVERED

This review the new potential therapeutic approaches and the most impacting recent published trials to provide an overview on the future management of PC.

EXPERT OPINION

Currently, there is a growing interest in the potential role of triplet therapies encompassing ADT, chemotherapy, and ARTAs. These strategies, explored in different settings, appeared to be particularly promising in metastatic hormone-sensitive PC. Recent trials investigating ARTAs plus poly(adenosine diphosphate-ribose) polymerase (PARPi) inhibitor provided helpful insights for patients with metastatic castration resistant disease, regardless of homologous recombination genes status. Otherwise, the publication of the complete data is awaited, and more evidence is required. In advanced settings, several combination approaches are under investigation, to date with contradictory results, such as immunotherapy plus PARPi or chemotherapy. The radionuclide ¹⁷⁷Lu-PSMA-617 proved successful outcomes in pretreated mCRPC patients. Additional studies will better clarify the appropriate candidates to each strategy and the correct treatments' sequence.

Costs of radium-223 and the pharmacy preparation 177Lu-PSMA-I&T for metastatic castration-resistant prostate cancer in Dutch hospitals

OBJECTIVE

The radiopharmaceuticals radium-223 and the pharmacy preparation ¹⁷⁷Lu-PSMA-I&T are reimbursed in the Netherlands for metastatic castration-resistant prostate cancer (mCRPC) treatment. Although shown to be life-prolonging in patients with mCRPC, the treatment procedures associated with these radiopharmaceuticals can be challenging for both patients and hospitals. This study investigates the costs of mCRPC treatment in Dutch hospitals for currently reimbursed radiopharmaceuticals with a demonstrated overall survival benefit.

METHODS

A cost model that calculated the direct medical per-patient costs of radium-223 and ¹⁷⁷Lu-PSMA-I&T was developed, following clinical trial regimens. The model considered six 4-weekly administrations (i.e. ALSYMPCA regimen) of radium-223. Regarding ¹⁷⁷Lu-PSMA-I&T, the model used both the VISION regimen (i.e. five 6-weekly administrations) and the SPLASH regimen (i.e. four 8-weekly administrations). Based on health insurance claims, we also estimated the coverage a hospital would receive for providing treatment. No fitting health insurance claim for ¹⁷⁷Lu-PSMA-I&T is currently available; therefore, we calculated a break-even value for a potential health insurance claim that would exactly counterbalance the per-patient costs and coverage.

RESULTS

Radium-223 administration is associated with per-patient costs of €30,905, and these costs are fully covered by the coverage a hospital receives. The per-patient costs of ¹⁷⁷Lu-PSMA-I&T range between €35,866 and €47,546 per administration period, depending on the regimen. Current healthcare insurance claims do not fully cover the costs of providing ¹⁷⁷Lu-PSMA-I&T: hospitals must pay €4,414-€4,922 for each patient out of their own budget. The break-even value for the potential insurance claim covering ¹⁷⁷Lu-PSMA-I&T administration with a VISION (SPLASH) regimen is €1,073 (€1,215).

CONCLUSION

This study shows that, without consideration of the treatment effect, radium-223 treatment for mCRPC leads to lower per-patient costs than treatment with ¹⁷⁷Lu-PSMA-I&T. The detailed overview of the costs associated with radiopharmaceutical treatment provided by this study is relevant for both hospitals and healthcare insurers.

Status of PSMA-targeted radioligand therapy in prostate cancer: current data and future trials

Metastatic prostate cancer continues to be an incurable disease. Despite all the novel therapies approved in the past two decades, overall patient outcomes remain relatively poor, and these patients die on a regular basis. Clearly, improvements in current therapies are needed. Prostate-specific membrane antigen (PSMA) is a target for prostate cancer given its increased expression on the surface of the prostate cancer cells. PSMA small molecule binders include PSMA-617 and PSMA-I&T and monoclonal antibodies such as J591. These agents have been linked to different radionuclides including beta-emitters such as lutetium-177 and alpha-emitters such as actinium-225. The only regulatory-approved PSMA-targeted radioligand therapy (PSMA-RLT) to date is lutetium-177-PSMA-617 in the setting of PSMA-positive metastatic castration-resistant prostate cancer that has failed androgen receptor pathway inhibitors and taxane chemotherapy. This approval was based on the phase III VISION trial. Many other clinical trials are evaluating PSMA-RLT in various settings. Both monotherapy and combination studies are underway. This article summarizes pertinent data from recent studies and provides an overview of human clinical trials in progress. The field of PSMA-RLT is rapidly evolving, and this therapeutic approach will likely play an increasingly important role in the years to come.

Optimized Therapeutic 177Lu-Labeled PSMA-Targeted Ligands with Improved Pharmacokinetic Characteristics for Prostate Cancer

Clinical trials have shown the significant efficacy of [¹⁷⁷Lu]Lu-PSMA-617 for treating prostate cancer. However, the pharmacokinetic characteristics and therapeutic performance of [¹⁷⁷Lu]Lu-PSMA-617 still need further improvement to meet clinical expectations. The aim of this study was to evaluate the feasibility and therapeutic potential of three novel ¹⁷⁷Lu-labeled ligands for the treatment of prostate cancer. The novel ligands were efficiently synthesized and radiolabeled with non-carrier added ¹⁷⁷Lu; the radiochemical purity of the final products was determined by Radio-HPLC. The specific cell-binding affinity to PSMA was evaluated in vitro using prostate cancer cell lines 22Rv1and PC-3. Blood pharmacokinetic analysis, biodistribution experiments, small animal SPCET imaging and treatment experiments were performed on normal and tumor-bearing mice. Among all the novel ligands developed in this study, [¹⁷⁷Lu]Lu-PSMA-Q showed the highest uptake in 22Rv1 cells, while there was almost no uptake in PC-3 cells. As the SPECT imaging tracer, [¹⁷⁷Lu]Lu-PSMA-Q is highly specific in delineating PSMA-positive tumors, with a shorter clearance half-life and higher tumor-to-background ratio than [¹⁷⁷Lu]Lu-PSMA-617. Biodistribution studies verified the SPECT imaging results. Furthermore, [¹⁷⁷Lu]Lu-PSMA-Q serves well as an effective therapeutic ligand to suppress tumor growth and improve the survival rate of tumor-bearing mice. All the results strongly demonstrate that [¹⁷⁷Lu]Lu-PSMA-Q is a PSMA-specific ligand with significant anti-tumor effect in preclinical models, and further clinical evaluation is worth conducting.

Prostate-specific membrane antigen-directed imaging and radioguided surgery with single-photon emission computed tomography: state of the art and future outlook

INTRODUCTION

Prostate-specific membrane antigen (PSMA) has emerged as a highly relevant target for prostate cancer (PC) diagnosis and therapy. PSMA inhibitors targeting PSMA-enzymatic domain have been successfully labeled with radionuclides emitting positrons or gamma-photons, thus obtaining tracers suitable for imaging with positron emission computed tomography (PET/CT) or single-photon emission tomography (SPECT).

AREAS COVERED

The different approaches for obtaining PSMA-ligands labeled with gamma-emitting nuclides (^99mTc or¹¹¹In) are reviewed. Furthermore, the applications of ^99mTc/¹¹¹In-PSMA SPECT for the imaging of PC patients in different clinical settings (staging or biochemical recurrence) are covered. Lastly, the employment of PSMA-targeted SPECT tracers for radioguided surgery (RGS) during primary or salvage lymphadenectomy is discussed.

EXPERT OPINION

RGS provided satisfying preliminary results in both primary and salvage lymphadenectomy, allowing to discriminate between pathological and non-pathological nodes with high accuracy, although prospective studies with larger cohorts are needed to further validate this surgical approach. The potential of PSMA-targeted SPECT/CT has not been fully explored yet, but it might represent a relatively cost-effective alternative to PSMA PET/CT in limited resource environments. In this perspective, the implementation of novel SPECT technologies or algorithms, such as semiconductor-ionization detectors or resolution recovery reconstruction, will be topic of future investigation.

Lutetium Lu 177 Vipivotide Tetraxetan: First Approval

Lutetium Lu 177 vipivotide tetraxetan (PLUVICTO™, formerly known as ¹⁷⁷Lu-PSMA-617) is a radioligand therapeutic agent that is being developed by Advanced Accelerator Applications (a subsidiary of Novartis) for the treatment of prostate-specific membrane antigen (PSMA)-expressing metastatic prostate cancer. The active part of the radiopharmaceutical is lutetium-177, which is linked to a ligand that binds to prostate-specific membrane antigen (PSMA), a transmembrane enzyme overexpressed in primary and metastatic prostate cancers. Based on efficacy results from the phase 3 VISION trial, lutetium Lu 177 vipivotide tetraxetan was approved in the USA on 23 March 2022 for the treatment of adult patients with PSMA-positive metastatic castration-resistant prostate cancer (mCRPC) who have been treated with androgen receptor (AR) pathway inhibition and taxane-based chemotherapy. Regulatory review in the EU and other countries is underway. This article summarizes the milestones in the development of Lutetium Lu 177 vipivotide tetraxetan leading to this first approval as a therapeutic radioligand for mCRPC.