Clinical outcomes and treatment patterns in REASSURE: planned interim analysis of a real-world observational study of radium-223 in metastatic castration-resistant prostate cancer

Increase of prostate-specific antigen doubling time predicts survival in metastatic castration-resistant prostate cancer patients undergoing radium therapy

OBJECTIVE

Radium-223 (Ra-223) is an important treatment modality for bone-dominant metastatic castration-resistant prostate cancer (mCRPC). However, there is currently a lack of effective markers to monitor treatment response during treatment. We aim to investigate the response in prostate-specific antigen doubling time (PSADT) as a potential marker for assessing Ra-223 treatment in mCRPC patients.

METHODS

We retrospectively collected data from mCRPC patients who underwent radium treatment at our institution between August 2020 and June 2023. Prostate-specific antigen (PSA) measurements prior to treatment and during treatment were collected. Baseline PSADT was calculated from PSA measurements prior to Ra-223 treatment; interim PSADT was calculated from PSA measurements before Ra-223 treatment and prior to the fourth course injection. Overall survival was calculated from the start of treatment to the date of death. Univariable and multivariable analysis using the Cox proportional hazards model were performed to examine the association of factors with overall survival.

RESULTS

We included 35 patients from our institution, with a median overall survival of 13.3 months. Eighteen (51.4%) completed all six courses of treatment. PSA dynamic response (interim PSADT > baseline PSADT or decreased PSA) was observed in 20 patients. Overall survival was associated with a PSA dynamic response (HR = 0.318, 95% CI 0.133-0.762, p = 0.010) when compared to patients without response.

CONCLUSIONS

Dynamic changes in PSADT were associated with survival in mCRPC patients receiving radium therapy. Comparing interim and baseline PSADT could serve as a valuable marker for determining treatment benefits.

The Role of Extracellular Vesicles in the Treatment of Prostate Cancer

Prostate cancer (PCa) has become a public health concern in elderly men due to an ever-increasing number of estimated cases. Unfortunately, the available treatments are unsatisfactory because of a lack of a durable response, especially in advanced disease states. Extracellular vesicles (EVs) are lipid-bilayer encircled nanoscale vesicles that carry numerous biomolecules (e.g., nucleic acids, proteins, and lipids), mediating the transfer of information. The past decade has witnessed a wide range of EV applications in both diagnostics and therapeutics. First, EV-based non-invasive liquid biopsies provide biomarkers in various clinical scenarios to guide treatment; EVs can facilitate the grading and staging of patients for appropriate treatment selection. Second, EVs play a pivotal role in pathophysiological processes via intercellular communication. Targeting key molecules involved in EV-mediated tumor progression (e.g., proliferation, angiogenesis, metastasis, immune escape, and drug resistance) is a potential approach for curbing PCa. Third, EVs are promising drug carriers. Naïve EVs from various sources and engineered EV-based drug delivery systems have paved the way for the development of new treatment modalities. This review discusses the recent advancements in the application of EV therapies and highlights EV-based functional materials as novel interventions for PCa.

Safety and effectiveness of the radium-223-taxane treatment sequence in patients with metastatic castration-resistant prostate cancer in a global observational study (REASSURE)

BACKGROUND

Radium-223 and taxane chemotherapy each improve survival of patients with metastatic castration-resistant prostate cancer (mCRPC). Whether the radium-223-taxane sequence could extend survival without cumulative toxicity was explored.

METHODS

The global, prospective, observational REASSURE study (NCT02141438) assessed real-world safety and effectiveness of radium-223 in patients with mCRPC. Using data from the prespecified second interim analysis (data cutoff, March 20, 2019), hematologic events and overall survival (OS) were evaluated in patients who were chemotherapy-naive at radium-223 initiation and subsequently received taxane chemotherapy starting ≤90 days ("immediate") or >90 days ("delayed") after the last radium-223 dose.

RESULTS

Following radium-223 therapy, 182 patients received docetaxel (172 [95%]) and/or cabazitaxel (44 [24%]); 34 patients (19%) received both. Seventy-three patients (40%) received immediate chemotherapy and 109 patients (60%) received delayed chemotherapy. Median time from last radium-223 dose to first taxane cycle was 3.6 months (range, 0.3-28.4). Median duration of first taxane was 3.7 months (range, 0-22.0). Fourteen patients (10 in the immediate and four in the delayed subgroup) had grade 3/4 hematologic events during taxane chemotherapy, including neutropenia in two patients in the delayed subgroup and thrombocytopenia in one patient in each subgroup. Median OS was 24.3 months from radium-223 initiation and 11.8 months from start of taxane therapy.

CONCLUSIONS

In real-world clinical practice settings, a heterogeneous population of patients who received sequential radium-223-taxane therapy had a low incidence of hematologic events, with a median survival of 1 year from taxane initiation. Thus, taxane chemotherapy is a feasible option for those who progress after radium-223.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT02141438.

PLAIN LANGUAGE SUMMARY

Radium-223 and chemotherapy are treatment options for metastatic prostate cancer, which increase survival but may affect production of blood cells as a side effect. We wanted to know what would happen if patients received chemotherapy after radium-223. Among the 182 men treated with radium-223 who went on to receive chemotherapy, only two men had severe side effects affecting white blood cell production (neutropenia) during chemotherapy. On average, the 182 men lived for 2 years after starting radium-223 and 1 year after starting chemotherapy. In conclusion, patients may benefit from chemotherapy after radium-223 treatment without increasing the risk of side effects.

Beyond Average: α-Particle Distribution and Dose Heterogeneity in Bone Metastatic Prostate Cancer

α-particle emitters are emerging as a potent modality for disseminated cancer therapy because of their high linear energy transfer and localized absorbed dose profile. Despite great interest and pharmaceutical development, there is scant information on the distribution of these agents at the scale of the α-particle pathlength. We sought to determine the distribution of clinically approved [223Ra]RaCl2 in bone metastatic castration-resistant prostate cancer at this resolution, for the first time to our knowledge, to inform activity distribution and dose at the near-cell scale. Methods: Biopsy specimens and blood were collected from 7 patients 24 h after administration. 223Ra activity in each sample was recorded, and the microstructure of biopsy specimens was analyzed by micro-CT. Quantitative autoradiography and histopathology were segmented and registered with an automated procedure. Activity distributions by tissue compartment and dosimetry calculations based on the MIRD formalism were performed. Results: We revealed the activity distribution differences across and within patient samples at the macro- and microscopic scales. Microdistribution analysis confirmed localized high-activity regions in a background of low-activity tissue. We evaluated heterogeneous α-particle emission distribution concentrated at bone-tissue interfaces and calculated spatially nonuniform absorbed-dose profiles. Conclusion: Primary patient data of radiopharmaceutical therapy distribution at the small scale revealed that 223Ra uptake is nonuniform. Dose estimates present both opportunities and challenges to enhance patient outcomes and are a first step toward personalized treatment approaches and improved understanding of α-particle radiopharmaceutical therapies.

Targeted Alpha-Particle Therapy: A Review of Current Trials

Radiopharmaceuticals are rapidly developing as a field, with the successful use of targeted beta emitters in neuroendocrine tumors and prostate cancer serving as catalysts. Targeted alpha emitters are in current development for several potential oncologic indications. Herein, we review the three most prevalently studied conjugated/chelated alpha emitters (²²⁵actinium, ²¹²lead, and ²¹¹astatine) and focus on contemporary clinical trials in an effort to more fully appreciate the breadth of the current evaluation. Phase I trials targeting multiple diseases are now underway, and at least one phase III trial (in selected neuroendocrine cancers) is currently in the initial stages of recruitment. Combination trials are now also emerging as alpha emitters are integrated with other therapies in an effort to create solutions for those with advanced cancers. Despite the promise of targeted alpha therapies, many challenges remain. These challenges include the development of reliable supply chains, the need for a better understanding of the relationships between administered dose and absorbed dose in both tissue and tumor and how that predicts outcomes, and the incomplete understanding of potential long-term deleterious effects of the alpha emitters. Progress on multiple fronts is necessary to bring the potential of targeted alpha therapies into the clinic.