Health-Related Quality-of-Life Outcomes with Actinium-225-Prostate-Specific Membrane Antigen-617 Therapy in Patients with Heavily Pretreated Metastatic Castration-Resistant Prostate Cancer

Design of 225Ac-PSMA for targeted alpha therapy in prostate cancer

The first alpha emitting radiopharmaceutical, 223RaCl2, radium dichloride, was approved 10 years ago into the clinical armament of treating bone metastases in metastatic castration-resistant prostate cancer (mCRPC). In addition to this, the first beta-emitting radionuclide Lu-177 chelated with a prostate-specific membrane antigen (PSMA) compound, got last year its marketing approval for the third line treatment of mCRPC. Therefore, there is great excitement about combining alpha-emitters and prostate cancer targeting PSMA compounds. This review describes the clinical history of alpha-emitting PSMA in treating mCRPC. Here, we present the potential, current status, and opportunities for 225Ac-PSMA therapy. The work reviews the basic concepts, current treatment outcome, and toxicity, and areas requiring further investigations such as dosimetric aspects in clinical studies covering more than 400 patients. In general, approximately two-thirds of the patients benefit from this third-line therapy. There is also successful evidence of using 225Ac-PSMA in the second-line of prostate cancer management. The future potential of 225Ac-PSMA therapy and targeted alpha therapy (TAT) of cancer in general is enormous. According to our overview the clinical experience with 225Ac-PSMA therapy to date has shown great benefit and physicians dedicated to theragnostics are anxiously waiting for new applications. Hopefully, this review helps in deeper understanding of the strengths and limitations of TAT and may help in creating effective therapy protocols.

Deescalated 225Ac-PSMA-617 Versus 177Lu/225Ac-PSMA-617 Cocktail Therapy: A Single-Center Retrospective Analysis of 233 Patients

The aim of this work is to evaluate our clinical real-world data obtained with 225Ac-PSMA-617 (AcPSMA), which were acquired under compassionate care regulations in patients with advanced-stage prostate cancer. The objective parameters that could be derived from this evaluation are compared with previous literature about AcPSMA and 177Lu-PSMA-617 (LuPSMA). Methods: The medical files of all patients who had received AcPSMA on an individual patient basis at the Heidelberg University Hospital since January 2014 were analyzed retrospectively. Previously published patients were excluded. The remaining patients were tailored into 2 subgroups with different treatment strategies: group 1 received AcPSMA as a deescalated monotherapy, and group 2 received LuPSMA plus AcPSMA as a cocktail regimen. Baseline characteristics, serum prostate-specific antigen (PSA) response, and overall survival were compared with the most appropriate historical controls. Results: Of 287 patients treated, 54 were excluded because of previous publication and 233 were evaluated, 104 of whom received AcPSMA monotherapy (median, 6 MBq). In this group, 55 patients (53%) presented with a best PSA response of at least 50%. The other 129 patients received a cocktail therapy of AcPSMA (median, 4 MBq) plus LuPSMA (4 GBq). In this group, a best PSA response of at least 50% was observed in 74 patients (57%). The median overall survival in the monogroup was 9 mo and in the cocktail group was 15 mo. If adjusted for prognostic baseline characteristics, the efficacy of both regimens was not significantly different. Conclusion: Deescalated treatment activities of AcPSMA or AcPSMA and LuPSMA cocktail regimens present better tolerability with regard to xerostomia than previous regimens of at least 100 kBq/kg while retaining high antitumor activity in poor-prognosis prostate cancer patients.

225 Ac-PSMA-617 Augmentation in High-Risk mCRPC Undergoing 177 Lu-PSMA-617 Radioligand Therapy : Pilot Experience From a Prospective Registry

PURPOSE

This pilot study investigates the efficacy and safety profile as well as predictive biomarkers of 225 Ac-PSMA-617-augmented 177 Lu-PSMA-617 radioligand therapy (RLT) in a cohort of high-risk patients with metastatic castration-resistant prostate cancer (mCRPC), enrolled in a prospective registry (NCT04833517).

PATIENTS AND METHODS

A group of n = 33 high-risk mCRPC patients received 177 Lu-PSMA-617 RLT, augmented by 1 or more cycles of 225 Ac-PSMA-617. Response was assessed by prostate-specific antigen (PSA) serum value after 2 cycles of treatment. Overall survival (OS) and PSA-based progression-free survival were evaluated using Kaplan-Meier analysis. To assess the side effect profile, Common Terminology Criteria for Adverse Events were applied. In total, 12 potential pretherapeutic biomarkers were tested for association with OS.

RESULTS

The median decrease in serum PSA value was -49.1%, and 16/33 (48.5%) patients experienced a partial response after 2 cycles RLT. The median PSA-based progression-free survival and median OS was 7.2 and 14.8 months, respectively. Alkaline phosphatase ( P < 0.001), lactate dehydrogenase ( P = 0.035), Eastern European Oncology Group Performance Score ( P = 0.037), and the presence of visceral metastases ( P = 0.029) revealed significant association with OS in Kaplan-Meier analysis (log-rank test). Most of the recorded adverse events were rated as mild or moderate. Higher-grade adverse events were very limited with only 1 case (3.0%) of grade 3 anemia. Treatment-related mild xerostomia was recorded in 6/33 (18.2%) patients.

CONCLUSIONS

225 Ac-PSMA-617 augmentation in high-risk mCRPC undergoing 177 Lu-PSMA-617 RLT appears to be an effective treatment option with a favorable safety profile. The pretherapeutic values of alkaline phosphatase, lactate dehydrogenase, the Eastern European Oncology Group Performance Score, and the presence of visceral metastases may be appropriate biomarkers predicting survival outcome of this treatment regimen.

Prostate-specific Membrane Antigen: Alpha-labeled Radiopharmaceuticals

Novel prostate-specific membrane antigen (PSMA) ligands labeled with α-emitting radionuclides are sparking a growing interest in prostate cancer treatment. These targeted alpha therapies (TATs) have attractive physical properties that deem them effective in progressive metastatic castrate-resistant prostate cancer (mCRPC). Among the PSMA TAT radiopharmaceuticals, [225Ac]Ac-PSMA has been used extensively on a compassionate basis and is currently undergoing phase I trials. Notably, TAT has the potential to improve quality of life and has favorable antitumor activity and outcomes in multiple scenarios other than in mCRPC. In addition, resistance mechanisms to TAT may be amenable to combination therapies.

Targeted Radiopharmaceutical Therapy for Bone Metastases

Radiopharmaceutical approaches for targeting bone metastasis have traditionally focused on palliation of pain. Several agents have been clinically used over the last several decades and have proven value in pain palliation providing pain relief and improving quality of life. The role is well established across several malignancies, most commonly used in osteoblastic prostate cancer patients. These agents have primarily based on targeting and uptake in bone matrix and have mostly included beta emitting isotopes. The advent alpha emitter and FDA approval of 223Ra-dichloride has created a paradigm shift in clinical approach from application for pain palliation to treatment of bone metastasis. The approval of 223Ra-dichloride given the survival benefit in metastatic prostate cancer patients, led to predominant use of this alpha emitter in prostate cancer patients. With rapid development of radiopharmaceutical therapies and approval of other targeted agents such as 177Lu-PSMA the approach to treatment of bone metastasis has further evolved and combination treatments have increasingly been applied. Novel approaches are needed to improve and expand the use of such therapies for treatment of bone metastasis. Combination therapies with different targeting mechanisms, combining chemotherapies and cocktail of alpha and beta emitters need further exploration.

Targeted Alpha Therapy: All We Need to Know about 225Ac's Physical Characteristics and Production as a Potential Theranostic Radionuclide

The high energy of α emitters, and the strong linear energy transfer that goes along with it, lead to very efficient cell killing through DNA damage. Moreover, the degree of oxygenation and the cell cycle state have no impact on these effects. Therefore, α radioisotopes can offer a treatment choice to individuals who are not responding to β- or gamma-radiation therapy or chemotherapy drugs. Only a few α-particle emitters are suitable for targeted alpha therapy (TAT) and clinical applications. The majority of available clinical research involves 225Ac and its daughter nuclide 213Bi. Additionally, the 225Ac disintegration cascade generates γ decays that can be used in single-photon emission computed tomography (SPECT) imaging, expanding the potential theranostic applications in nuclear medicine. Despite the growing interest in applying 225Ac, the restricted global accessibility of this radioisotope makes it difficult to conduct extensive clinical trials for many radiopharmaceutical candidates. To boost the availability of 225Ac, along with its clinical and potential theranostic applications, this review attempts to highlight the fundamental physical properties of this α-particle-emitting isotope, as well as its existing and possible production methods.

Clinical Experience with [225Ac]Ac-PSMA Treatment in Patients with [177Lu]Lu-PSMA-Refractory Metastatic Castration-Resistant Prostate Cancer

For patients with advanced-stage metastatic castration-resistant prostate cancer (mCRPC) who do not respond to [177Lu]Lu-PSMA therapy, there are limited treatment options. Clinical results obtained with [225Ac]Ac-PSMA are promising. We retrospectively analyzed the outcomes of patients treated with [225Ac]Ac-PSMA between December 2018 and October 2022. Methods: We evaluated the treatment results of 23 patients (mean age, 70.3 ± 8.8 y) with mCRPC who were refractory to treatment with [177Lu]Lu-PSMA (2-9 cycles). The safety profile was assessed according to Common Technology Criteria for Adverse Events version 5.0. Treatment efficacy was assessed using prostate-specific membrane antigen PET progression criteria and prostate-specific antigen (PSA) response according to Prostate Cancer Working Group 2 criteria after the first cycle of [225Ac]Ac-PSMA treatment. Results: All patients received androgen-deprivation therapy, whereas 22 (96%) and 19 (83%) patients received chemotherapy and second-generation antiandrogen therapy, respectively. One patient received 4 cycles, 2 received 3 cycles, 8 received 2 cycles, and 12 received 1 cycle of [225Ac]Ac-PSMA. The median interval between cycles was 13 wk (range, 8-28 wk). [225Ac]Ac-PSMA was administered with a mean activity of 7.6 MBq (range, 6.2-10.0 MBq) in each cycle. Patients were at an advanced stage of disease, and tumor burden was very high. Although the best PSA response was observed in 5 patients (26%) after [225Ac]Ac-PSMA treatment, there was at least some level of decline in PSA observed in 11 patients (58%; n = 19). Treatment response was assessed in patients who underwent [68Ga]Ga-PSMA PET/CT imaging. After the first cycle of treatment (n = 18), 50% of patients (n = 9) showed disease progression according to prostate-specific membrane antigen PET progression criteria, and the disease control rate was calculated to be 50%. Median progression-free survival was 3.1 mo, and median overall survival was 7.7 mo. Grade 3 hematologic toxicity occurred in 1 patient, and grade 3 nephrotoxicity was observed in another patient. Parotid SUVmax decreased by 33%, although all patients complained of dry mouth before treatment. Conclusion: We observed that [225Ac]Ac-PSMA therapy was safe and showed potential even in cases with advanced-stage mCRPC in which all other treatment options were completed.

The current status of prostate cancer treatment and PSMA theranostics

In the treatment of cancer, understanding the disease status, or accurate staging, is extremely important, and various imaging techniques are used. Computed tomography (CT), magnetic resonance imaging, and scintigrams are commonly used for solid tumors, and advances in these technologies have improved the accuracy of diagnosis. In the clinical practice of prostate cancer, CT and bone scans have been considered especially important for detecting metastases. Nowadays, CT and bone scans are called conventional methods because positron emission tomography (PET), especially prostate-specific membrane antigen (PSMA)/PET, is extremely sensitive in detecting metastases. Advances in functional imaging, such as PET, are advancing the diagnosis of cancer by allowing information to be added to the morphological diagnosis. Furthermore, PSMA is known to be upregulated depending on the malignancy of the prostate cancer grade and resistance to therapy. Therefore, it is often highly expressed in castration-resistant prostate cancer (CRPC) with poor prognosis, and its therapeutic application has been attempted for around two decades. PSMA theranostics refers to a type of cancer treatment that combines both diagnosis and therapy using a PSMA. The theranostic approach uses a radioactive substance attached to a molecule that targets PSMA protein on cancer cells. This molecule is injected into the patient's bloodstream and can be used for both imaging the cancer cells with a PET scan (PSMA PET imaging) and delivering radiation directly to the cancer cells (PSMA-targeted radioligand therapy), with the aim of minimizing damage to healthy tissue. Recently, in an international phase III trial, the impact of ¹⁷⁷Lu-PSMA-617 therapy was studied in patients with advanced PSMA-positive metastatic CRPC who had previously been treated with specific inhibitors and regimens. The trial revealed that ¹⁷⁷Lu-PSMA-617 significantly extended both progression-free survival and overall survival compared to standard care alone. Although there was a higher incidence of grade 3 or above adverse events with ¹⁷⁷Lu-PSMA-617, it did not negatively impact the patients' quality of life. PSMA theranostics is currently being studied and used primarily for the treatment of prostate cancer, but it has the potential to be applied to other types of cancers as well.

Recent Innovations and Nano-Delivery of Actinium-225: A Narrative Review

The actinium-225 (²²⁵Ac) radioisotope exhibits highly attractive nuclear properties for application in radionuclide therapy. However, the ²²⁵Ac radionuclide presents multiple daughter nuclides in its decay chain, which can escape the targeted site, circulate in plasma, and cause toxicity in areas such as kidneys and renal tissues. Several ameliorative strategies have been devised to circumvent this issue, including nano-delivery. Alpha-emitting radionuclides and nanotechnology applications in nuclear medicine have culminated in major advancements that offer promising therapeutic possibilities for treating several cancers. Accordingly, the importance of nanomaterials in retaining the ²²⁵Ac daughters from recoiling into unintended organs has been established. This review expounds on the advancements of targeted radionuclide therapy (TRT) as an alternative anticancer treatment. It discusses the recent developments in the preclinical and clinical investigations on ²²⁵Ac as a prospective anticancer agent. Moreover, the rationale for using nanomaterials in improving the therapeutic efficacy of α-particles in targeted alpha therapy (TAT) with an emphasis on ²²⁵Ac is discussed. Quality control measures in the preparation of ²²⁵Ac-conjugates are also highlighted.

Efficacy and Safety of Actinium-225 Prostate-Specific Membrane Antigen Radioligand Therapy in Metastatic Prostate Cancer: A Systematic Review and Metanalysis

BACKGROUND

Actinium-225 (Ac-225) labelled PSMA RLT has been tested recently in metastatic castration-resistant prostate cancer (mCRPC), with encouraging results. Ac-225, being an alpha emitter, is expected to have higher efficacy and fewer side effects compared to the beta-emitters such as Lutetium-177. We have performed a meta-analysis to assess the therapeutic responses, survival effects, and significant side effects of Ac-225 PSMA RLT in patients with mCRPC.

METHODOLOGY

Systematic literature search was carried out from five electronic databases PubMed/MEDLINE, SCOPUS, EMBASE, Web of Science, and Cochrane Library until March 2021. Eight studies were found to be eligible for this metanalysis.

RESULTS

Eight studies with 226 patients were analyzed in this metanalysis. 81% (95% CI 73-89) patients had a decline in PSA levels. 60% of the patients showed more than 50% PSA decline. Two studies assessed survival effects of radioligand naïve patients compared to patients who had received Lu-PSMA therapy previously and the pooled HR for radioligand naïve patients is 0.22. The most common toxicity reported was xerostomia in 167 patients out of 226 patients (73.9%, 95% CI 67.6-79.5%); however, most of them were confined to grade I and II levels. Other reported side effects include hematologic toxicity and nephrotoxicity.

CONCLUSION

Ac-PSMA RLT is a safe and potentially effective treatment option for patients with mCRPC.

Genomic characterization of metastatic castration-resistant prostate cancer patients undergoing PSMA radioligand therapy: A single-center experience

BACKGROUND

Genomic defects in DNA-damage repair (DDR) mechanisms have been proposed to affect the radiosensitivity of prostate cancers. In this study, we intended to evaluate the prevalence of genetic alterations in a cohort of metastatic castration-resistant prostate cancer (mCRPC) patients undergoing radioligand therapy (RLT) with prostate-specific membrane antigen (PSMA)-inhibitors as well as the impact of such mutations on treatment outcomes.

METHODS

Data of consecutive mCRPC patients from 2017 to 2021 who were treated with PSMA-RLT and underwent next-generation sequencing (NGS) were collected and analyzed for response and survival outcomes.

RESULTS

In 95 patients of mCRPC treated with PSMA-RLT, 15 patients (median age: 66 years, range: 50-73 years; [¹⁷⁷ Lu]Lu-PSMA-617, n = 12; [²²⁵ Ac]Ac-PSMA-617, n = 3) underwent NGS. The median progression-free survival (PFS) of this cohort was 3 months (95% confidence interval: 1.6-4.4 months). On NGS, 21 genetic alterations were reported in 10/15 (67%) patients, of which 13 were DDR-associated alterations involving the genes: ATM (n = 3), BRCA2 (n = 3), TP53 (n = 2), PTEN (n = 2), FANCD2 (n = 1), FANCM (n = 1), and NBN (n = 1). Overall, 5/15 (33%) patients harbored six pathogenic variants (BRCA2, n = 2; ATM, n = 1; TP53, n = 1; PTEN, n = 2). No significant difference was noted for the biochemical response, radiological response, PFS, and overall survival between the patients with and without genetic alterations.

CONCLUSIONS

Patients of mCRPC undergoing PSMA-RLT were frequently seen to harbor DDR-associated aberrations, albeit with no significant impact on treatment outcomes. Large prospective trials comparing PSMA-RLT-related outcomes in DDR-deficient and -proficient patients are required to bring out the differences, if any, in a more observable manner.

Advances in 177Lu-PSMA and 225Ac-PSMA Radionuclide Therapy for Metastatic Castration-Resistant Prostate Cancer

For patients with metastatic castration-resistant prostate cancer (mCRPC), the survival benefit of classic treatment options with chemotherapy and drugs targeting androgen signaling is limited. Therefore, beta and alpha radionuclide therapy (RNT) have emerged as novel treatment options for patients with mCRPC. Radioligands target the prostate-specific membrane antigen (PSMA) epitopes, which are upregulated up to a thousand times more in prostate cancer cells compared to the cells in normal tissues. For this reason, PSMA is an excellent target for both imaging and therapy. Over the past years, many studies have investigated the treatment effects of lutetium-177 labeled PSMA (177Lu-PSMA) and actinium-225 labeled PSMA (225Ac-PSMA) RNT in patients with mCRPC. While promising results have been achieved, this field is still in development. In this review, we have summarized and discussed the clinical data of 177Lu-PSMA and 225Ac-PSMA RNT in patients with mCRPC.

Delayed Nephrotoxicity After 225Ac-PSMA-617 Radioligand Therapy

ABSTRACT

177Lu-PSMA-617 radioligand therapy (RLT) has evolved as a suitable alternative to existing therapeutic options in patients with metastatic castration-resistant prostate cancer. With the emergence of α-emitters such as 225Ac, the efficacy of PSMA-RLT has further improved. Xerostomia and myelosuppression are common early treatment-emergent adverse events in patients receiving this therapy; however, data on long-term toxicity are relatively scarce. In this report, we describe a 76-year-old man with metastatic castration-resistant prostate cancer, who after having an initial excellent response to 2 cycles of 225Ac-PSMA-617 RLT, developed delayed nephrotoxicity in the form of tubulointerstitial nephritis.

Efficacy and Safety of 225Ac-PSMA-617-Targeted Alpha Therapy in Metastatic Castration-Resistant Prostate Cancer: A Systematic Review and Meta-Analysis

Objective

To conduct a meta-analysis of the efficacy and safety of ²²⁵Ac-PSMA-617 in the treatment of metastatic castration-resistant prostate cancer based on existing clinical evidence.

Methods

Search for retrospective studies about ²²⁵Ac-PSMA-617 in the treatment of metastatic castration-resistant prostate cancer from establishment to July 2021 in PubMed and EMBASE. The primary endpoint was ²²⁵Ac-PSMA-617 biochemical response evaluation criteria after treatment [any prostate specific antigen (PSA) decrease and PSA decrease >50% from baseline] to evaluate the treatment effect. Secondary endpoints included assessment of overall survival (OS), progression-free survival (PFS), molecular response, and toxicity for all studies. Two researchers conducted literature screening, data extraction and quality evaluation according to the inclusion and exclusion criteria. Use stata16.0 software for analysis, fixed-effects model for data merging and forest plots for display.

Results

A total of 6 retrospective studies, namely, 201 patients, were included in the final analysis. The pooled proportions of patients with decreased PSA and PSA decreased by more than 50% were 87.0% (95% confidence interval, 0.820 to 0.920) and 66.1% (95% confidence interval, 0.596 to 0.726), respectively. The pooled proportions of OS and PFS were 12.5 months (95%CI: 6.2–18.8 months) and 9.1 months (95%CI: 2.6–15.7 months). The patients showing molecular responses were 54% (95% confidence interval: 25–84%). In all studies, the most common side effect of ²²⁵Ac-PSMA-617 TAT was xerostomia, with any degree of xerostomia occurring in 77.1% (155 out of 201), and grade III only accounted for 3.0%. The second was 30.3% (61 out of 201) anemia of any degree, and grade III accounts for 7.5% (15 out of 201). Grade III leukopenia and thrombocytopenia were 4.5% (9 out of 201) and 5.5% (11 out of 201), respectively. Only 6 (3.0%) of 201 patients had Grade III nephrotoxicity.

Conclusion

²²⁵Ac-PSMA-617 is an effective and safe treatment option for mCRPC patients, and the toxicity caused by it is relatively low. However, future randomized controlled trials and prospective trials are required in the future to judge the therapeutic effects and survival benefits compared with existing clinical treatments.

Systematic Review Registration

PROSPERO: CRD42021281967.

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.

Effects of 225Ac-labeled prostate-specific membrane antigen radioligand therapy in metastatic castration-resistant prostate cancer: A meta-analysis

Prostate-specific membrane antigen (PSMA), overexpressed in prostate cancer, has become a popular target for radionuclide-based theranostic applications in the advanced stages of prostate cancer. We conducted a meta-analysis of the therapeutic effects of PSMA-targeting alpha therapy [²²⁵Ac-PSMA radioligand therapy (RLT)] in patients with metastatic castration-resistant prostate cancer (mCRPC). Methods: A systematic search was performed using the keywords "mCRPC," "²²⁵Ac-PSMA," and "alpha therapy". Therapeutic responses were analyzed as the pooled proportions of patients with more than 50% of prostate-specific antigen (PSA) decline and any PSA decline. Survival outcomes were analyzed by estimating summary survival curves for progression-free survival (PFS) and overall survival (OS). Adverse events were analyzed as the pooled proportions of patients with xerostomia and severe hematotoxicity (anemia, leukocytopenia, and thrombocytopenia). Results: Nine studies with 263 patients were included in our meta-analysis. The pooled proportions of patients with more than 50% of PSA decline and any PSA decline were 60.99% [95% confidence interval (CI) = 54.92-66.83%] and 83.57% (95% CI = 78.62-87.77%), respectively. The estimated mean PFS and mean OS were 9.15 months (95% CI = 6.69-11.03 months) and 11.77 months (95% CI = 9.51-13.49 months), respectively. The pooled proportions of patients with adverse events were 62.81% (95% CI = 39.34-83.46%) for xerostomia, 14.39% (95% CI = 7.76-22.63%) for anemia, 4.12% (95% CI = 0.97-9.31%) for leukocytopenia, and 7.18% (95% CI = 2.70-13.57%) for thrombocytopenia. Conclusion: In our study, around 61% of patients had more than 50% of PSA decline and 84% of patients had any PSA decline after ²²⁵Ac-PSMA RLT. The common adverse events in ²²⁵Ac-PSMA RLT were xerostomia in 63% of patients and severe hematotoxicity in 4-14% of patients.

Evolving role of 225Ac-PSMA radioligand therapy in metastatic castration-resistant prostate cancer-a systematic review and meta-analysis

BACKGROUND

Targeted radionuclide therapy with Actinium-225-labeled prostate-specific membrane antigen ligands (²²⁵Ac-PSMA) has emerged as a promising treatment modality in the management of metastatic castration-resistant prostate cancer (mCRPC). With its high linear energy transfer and short path length, ²²⁵Ac induces double-stranded DNA breaks and is expected to have excellent efficacy and safety profile. This systematic review was conducted to precisely evaluate the role of ²²⁵Ac-PSMA radioligand therapy (RLT) in mCRPC.

METHODS

This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. Searches were made using relevant keywords in the PubMed, Embase, and Scopus databases, and articles up to December 2020 were included. Data on efficacy and toxicity were extracted from the individual articles. Random-effects model was used for generating pooled estimates through meta-analysis.

RESULTS

Ten articles comprising 256 patients were included. Overall, 62.8% (95% confidence interval, CI: 53.4-71.7%) of the patients treated with ²²⁵Ac-PSMA RLT achieved biochemical response, i.e., ≥50% decline in the serum prostate-specific antigen levels from baseline. Molecular response on Gallium-68 PSMA positron emission tomography/computed tomography was noted in 74% (95% CI: 50.1-92.1%) of the patients. The pooled estimates of median progression-free survival and overall survival were 9.1 months (95% CI: 3.6-14.5 months) and 12.8 months (95% CI: 4.5-21.0 months), respectively. The most commonly reported adverse event was xerostomia, which was observed in 72.7% (95% CI: 50.5-90.1%) of the patients. However, clinically significant toxicity was limited with grade ≥3 xerostomia, anemia, leucopenia, thrombocytopenia, and nephrotoxicity occurring in 1.2%, 12.3%, 8.3%, 6.3%, and 3.8% of the patients, respectively. Treatment discontinuation due to adverse events was noted in 20/208 patients.

CONCLUSIONS

²²⁵Ac-PSMA RLT is an efficacious and safe treatment option for patients with mCRPC. Future randomized controlled trials are required to establish its therapeutic efficacy and survival benefit vis-à-vis other approved treatment modalities.

Efficacy and Safety of [225Ac]Ac-PSMA-617 Augmented [177Lu]Lu-PSMA-617 Radioligand Therapy in Patients with Highly Advanced mCRPC with Poor Prognosis

The use of ²²⁵Ac in prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT), either as monotherapy or in combination with ¹⁷⁷Lu, is a promising therapy approach in patients with metastatic castration-resistant prostate carcinoma (mCRPC). In this study, we report the efficacy and safety of [²²⁵Ac]Ac-PSMA-617 augmented [¹⁷⁷Lu]Lu-PSMA-617 RLT in ¹⁷⁷Lu-naive mCRPC patients (n = 15) with poor prognosis (presence of visceral metastases, high total tumor burden with diffuse bone metastases or a short PSA doubling time of <2 months). Biochemical (by PSA serum value) and molecular imaging response (by [⁶⁸Ga]Ga-PSMA-11 PET/CT) was assessed after two cycles of [¹⁷⁷Lu]Lu-PSMA-617 RLT, with at least one [²²⁵Ac]Ac-PSMA-617 augmentation. In addition, PSA-based progression-free survival (PSA-PFS), overall survival (OS) and toxicity (according to CTCAE) were analyzed. We observed a biochemical- and molecular imaging-based partial remission in 53.3% (8/15) and 66.7% (10/15) of patients, respectively. The median PSA-PFS and OS was 9.1 and 14.8 months, respectively. No serious acute adverse events were recorded. Two out of fifteen patients experienced grade 3 anemia. No other grade 3/4 toxicities were observed. RLT-related xerostomia (grade 1/2) was recorded in 2/15 patients. Our data showed a high clinical efficacy with a favorable side effects profile of [²²⁵Ac]Ac-PSMA-617 augmented [¹⁷⁷Lu]Lu-PSMA-617 RLT in this highly challenging patient cohort.