225Ac-PSMA-617 radioligand therapy of de novo metastatic hormone-sensitive prostate carcinoma (mHSPC): preliminary clinical findings.

PURPOSE: 225Ac-PSMA-617 has demonstrated good anti-tumor effect as a treatment option for metastatic castration-resistant prostate cancer (mCRPC) patients. No study has previously assessed treatment outcome and survival following 225Ac-PSMA-617 treatment of de novo metastatic hormone-sensitive prostate carcinoma (mHSPC) patients. Based on the potential side effects that are known and explained to the patients by the oncologist, some of the patients refused the standard treatment and are seeking alternative therapies. Thus, we report our preliminary findings in a retrospective series of 21 mHSPC patients that refused standard treatment options and were treated with 225Ac-PSMA-617. METHODS: We retrospectively reviewed patients with histologically confirmed de novo treatment-naïve bone ± visceral mHSPC that were treated with 225Ac-PSMA-617 radioligand therapy (RLT). Inclusion criteria included an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2, treatment-naive bone ± visceral mHSPC, and patients refusal for ADT ± docetaxel, abiraterone acetate, or enzalutamide. We evaluated the response to treatment using prostate-specific antigen (PSA) response and the progression-free survival (PFS) and overall survival (OS) as well as the toxicities. RESULTS: Twenty-one mHSPC patients were included in this preliminary work. Following treatment, twenty patients (95%) had any decline in PSA and eighteen patients (86%) presented with a PSA decline of ≥ 50% including 4 patients in whom PSA became undetectable. A lower percentage decrease in PSA following treatment was associated with increased mortality and shorter progression-free survival. Overall, administration of 225Ac-PSMA-617 was well tolerated. The commonest toxicity seen was grade I/II dry mouth observed in 94% of patients. CONCLUSIONS: Given these favorable results, randomized prospective multicenter trials assessing the clinical value of 225Ac-PSMA-617 as a therapeutic agent for mHSPC administered either as monotherapy or administered concomitant with ADT are of interest.

Initial clinical experience performing sialendoscopy for salivary gland protection in patients undergoing 225Ac-PSMA-617 RLT.

PURPOSE: The main side effect of prostate-specific membrane antigen targeting alpha therapy (PSMA TAT) is dry mouth syndrome. Inflammation of the salivary glands and consequent reduced salivary function have been reported in patients after radioiodine therapy. The beneficial effects of sialendoscopy on radiation-induced inflammation in tissue are well known. Thus sialendoscopy with dilatation, saline irrigation and steroid injections (prednisolone) was performed before and after 225Ac-PSMA-617 TAT to reduce inflammatory effects in the salivary glands and to improve or prevent xerostomia. METHODS: Eleven men with metastatic castration-resistant prostate cancer (mean age 68.5 years, range 58-80 years) underwent sialendoscopy, dilatation, saline irrigation and steroid injection of both submandibular and both parotid glands before or after every cycle of 225Ac-PSMA-617 TAT. Sialendoscopy and steroid injection were performed by a senior ENT physician. Quality of life was evaluated using two health-related quality of life (HRQOL) questionnaires, the Xerostomia Questionnaire (XQ) and the Xerostomia Inventory (XI) before and 3 months after the intervention. RESULTS: In all 11 patients both parotid and both submandibular glands were affected by radiation sialadenitis and sialendoscopy was performed. The patients experienced no complications after sialendoscopy, and showed a significant improvement in HRQOL as measured using the XQ and XI. After sialendoscopy the XQ score decreased significantly from 77.7 ± 13.6 to 42.7 ± 14.8 (p = 0.003) and the XI score decreased from 44.5 ± 6.9 to 25.8 ± 12.8 (p = 0.003). Due to the limited number of patients we only report tendencies. CONCLUSION: Sialendoscopy with dilatation, saline irrigation and steroid injection had beneficial effects on salivary gland function and HRQOL in patients undergoing 225Ac-PSMA-617 RLT. However, even with sialadenoscopic support after multiple cycles of TAT, salivary gland function was reduced and xerostomia was present. Therefore, not only inflammation but also the direct effect of radiation is a putative cause of dry mouth. Further research is necessary to determine the main side effects of PSMA TAT.

Branched amphiphilic peptide capsules: cellular uptake and retention of encapsulated solutes.

Branched amphiphilic peptide capsules (BAPCs) are peptide nano-spheres comprised of equimolar proportions of two branched peptide sequences bis(FLIVI)-K-KKKK and bis(FLIVIGSII)-K-KKKK that self-assemble to form bilayer delimited capsules. In two recent publications we described the lipid analogous characteristics of our BAPCs, examined their initial assembly, mode of fusion, solute encapsulation, and resizing and delineated their capability to be maintained at a specific size by storing them at 4°C. In this report we describe the stability, size limitations of encapsulation, cellular localization, retention and, bio-distribution of the BAPCs in vivo. The ability of our constructs to retain alpha particle emitting radionuclides without any apparent leakage and their persistence in the peri-nuclear region of the cell for extended periods of time, coupled with their ease of preparation and potential tune-ability, makes them attractive as biocompatible carriers for targeted cancer therapy using particle emitting radioisotopes. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.

Activity and Adverse Events of Actinium-225-PSMA-617 in Advanced Metastatic Castration-resistant Prostate Cancer After Failure of Lutetium-177-PSMA.

BACKGROUND: Beta-emitting Lu-177-labeled prostate-specific membrane antigen (PSMA) radioligand therapy (RLT) is a new option for metastatic castration-resistant prostate cancer (mCRPC), but its antitumor effect can decrease over time. OBJECTIVE: To report the safety and activity of alpha-emitting Ac-225-PSMA-617 RLT in mCRPC that has progressed after Lu-177-PSMA. DESIGN, SETTING, AND PARTICIPANTS: Twenty-six patients were treated under a compassionate use protocol. The eligibility criteria included previous treatment with abiraterone or enzalutamide, previous taxane-based chemotherapy, progression after Lu-177-PSMA, and positive PSMA-ligand uptake. The median number of previous mCRPC regimens was 6. Ac-225-PSMA-617 was given every 8 wk until progression/intolerable side effects. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Prostate-specific antigen (PSA) decline, PSA progression-free survival (PSA-PFS), clinical progression-free survival (cPFS), overall survival (OS), and toxicity were measured. RESULTS AND LIMITATIONS: Sixty-one cycles of Ac-225-PSMA-617 (median number of cycles 2; median activity 9 MBq) were administered. A PSA decline of ≥50% was achieved in 17/26 patients. The median PSA-PFS, cPFS, and OS periods were 3.5 (95% confidence interval [CI] 1.8-11.2), 4.1 (95% CI 3-14.8), and 7.7 (95% CI 4.5-12.1) mo, respectively. Liver metastases were associated with shorter PSA-PFS (median 1.9 vs 4.0 mo; p = 0.02), cPFS (median 1.8 vs 5.2 mo; p = 0.001), and OS (median 4.3 vs 10.4 mo; p = 0.01). Hematological grade 3/4 toxicities were anemia (35%), leucopenia (27%), and thrombocytopenia (19%). All patients experienced grade 1/2 xerostomia. Two and six patients stopped due to hematological toxicity and xerostomia, respectively. A limitation is the retrospective design. CONCLUSIONS: Ac-225-PSMA-617 showed measurable antitumor effect after Lu-177-PSMA failure in late-stage mCRPC. Grade 3/4 hematological side effects were observed in up to one-third of patients, and xerostomia led to treatment halt in a relevant number of patients. PATIENT SUMMARY: Ac-225-labeled prostate-specific membrane antigen (PSMA)-617 therapy showed substantial antitumor effect in late metastatic castration-resistant prostate cancer after Lu-177-PSMA failure. However, dry mouth is a common side effect that caused about a quarter of patients to stop therapy.

Uptake and subcellular distribution of radiolabeled polymersomes for radiotherapy.

Polymersomes have the potential to be applied in targeted alpha radionuclide therapy, while in addition preventing release of recoiling daughter isotopes. In this study, we investigated the cellular uptake, post uptake processing and intracellular localization of polymersomes. Methods: High-content microscopy was used to validate polymersome uptake kinetics. Confocal (live cell) microscopy was used to elucidate the uptake mechanism and DNA damage induction. Intracellular distribution of polymersomes in 3-D was determined using super-resolution microscopy. Results: We found that altering polymersome size and concentration affects the initial uptake and overall uptake capacity; uptake efficiency and eventual plateau levels varied between cell lines; and mitotic cells show increased uptake. Intracellular polymersomes were transported along microtubules in a fast and dynamic manner. Endocytic uptake of polymersomes was evidenced through co-localization with endocytic pathway components. Finally, we show the intracellular distribution of polymersomes in 3-D and DNA damage inducing capabilities of 213Bi labeled polymersomes. Conclusion: Polymersome size and concentration affect the uptake efficiency, which also varies for different cell types. In addition, we present advanced assays to investigate uptake characteristics in detail, a necessity for optimization of nano-carriers. Moreover, by elucidating the uptake mechanism, as well as uptake extent and geometrical distribution of radiolabeled polymersomes we provide insight on how to improve polymersome design.

Development and evaluation of peptidic ligands targeting tumour-associated urokinase plasminogen activator receptor (uPAR) for use in alpha-emitter therapy for disseminated ovarian cancer.

PURPOSE: Among gynecologic malignancies, ovarian cancer has the highest mortality due to rapid peritoneal dissemination. Treatment failure particularly arises from failure to eliminate disseminated cells. Our aim was to develop peptidic radioligands targeting tumour cell-associated urokinase receptor (uPAR, CD87) for alpha-emitter therapy for advanced ovarian cancer. METHODS: DOTA-conjugated, uPAR-directed ligands were synthesised on solid-phase. Binding of peptides to human cells expressing uPAR was assayed by flow cytofluorometry or, in case of (213)Bi-labelled peptides, by measuring cell-bound radioactivity. Bio-distribution of the (213)Bi-labelled peptide P-P4D was analysed in nude mice 28 days after intraperitoneal inoculation of OV-MZ-6 ovarian cancer cells in the absence or presence of the plasma expander gelofusine. RESULTS: uPAR-selective ligands were developed based on published high-affinity uPAR-binding peptides. For preparation of N-terminally cross-linked divalent ligands, a novel solid-phase procedure was developed. Specific binding of (213)Bi-labelled peptides to monocytoid U937 and OV-MZ-6 cells was demonstrated using the natural ligand of uPAR, pro-uPA, or a soluble form of uPAR, suPAR, as competitors. The pseudo-symmetrical covalent dimer (213)Bi-P-P4D displayed superior binding to OV-MZ-6 cells in vitro. Accumulation of (213)Bi-P-P4D in tumour tissue was demonstrated by bio-distribution analysis in nude mice bearing intraperitoneal OV-MZ-6-derived tumours. Gelofusine reduced kidney uptake of (213)Bi-P-P4D by half. CONCLUSION: Ovarian cancer cells overexpressing uPAR were specifically targeted in vitro and in vivo by (213)Bi-P-P4D. Kidney uptake of (213)Bi-P-P4D was distinctly reduced using gelofusine. Thus, this radiopeptide may represent a promising option for therapy for disseminated ovarian cancer.

Alpha-particle radiotherapy: For large solid tumors diffusion trumps targeting.

Diffusion limitations on the penetration of nanocarriers in solid tumors hamper their therapeutic use when labeled with α-particle emitters. This is mostly due to the α-particles' relatively short range (≤100 µm) resulting in partial tumor irradiation and limited killing. To utilize the high therapeutic potential of α-particles against solid tumors, we designed non-targeted, non-internalizing nanometer-sized tunable carriers (pH-tunable liposomes) that are triggered to release, within the slightly acidic tumor interstitium, highly-diffusive forms of the encapsulated α-particle generator Actinium-225 (225Ac) resulting in more homogeneous distributions of the α-particle emitters, improving uniformity in tumor irradiation and increasing killing efficacies. On large multicellular spheroids (400 µm-in-diameter), used as surrogates of the avascular areas of solid tumors, interstitially-releasing liposomes resulted in best growth control independent of HER2 expression followed in performance by (a) the HER2-targeting radiolabeled antibody or (b) the non-responsive liposomes. In an orthotopic human HER2-negative mouse model, interstitially-releasing 225Ac-loaded liposomes resulted in the longest overall and median survival. This study demonstrates the therapeutic potential of a general strategy to bypass the diffusion-limited transport of radionuclide carriers in solid tumors enabling interstitial release from non-internalizing nanocarriers of highly-diffusing and deeper tumor-penetrating molecular forms of α-particle emitters, independent of cell-targeting.

Anti-prostate-specific membrane antigen liposomes loaded with 225Ac for potential targeted antivascular α-particle therapy of cancer.

UNLABELLED: This study evaluates targeted liposomes loaded with the α-particle generator (225)Ac to selectively kill prostate-specific membrane antigen (PSMA)-expressing cells with the aim to assess their potential for targeted antivascular radiotherapy. METHODS: In this study, PEGylated liposomes were loaded with (225)Ac and labeled with the mouse antihuman PSMA J591 antibody or with the A10 PSMA aptamer. The targeting selectivity, extent of internalization, and killing efficacy of liposomes were evaluated on monolayers of prostate cancer cells intrinsically expressing PSMA (human LNCaP and rat Mat-Lu cells) and on monolayers of HUVEC induced to express PSMA (induced HUVEC). RESULTS: The loading efficiency of (225)Ac into preformed liposomes ranged from 58.0% ± 4.6% to 85.6% ± 11.7% of introduced radioactivity. The conjugation reactions resulted in approximately 17 ± 2 J591 antibodies and 9 ± 2 A10 aptamers per liposome. The average size of liposomes, 107 ± 2 nm in diameter, was not affected by conjugation or loading. LNCaP cells exhibit 2:1:0.5 relative PSMA expression, compared with MatLu and induced HUVEC, respectively, based on flow cytometry detecting association of the J591 antibody. J591-labeled liposomes display higher levels of total specific binding to all cell lines than A10 aptamer-labeled liposomes. Specific cell association of targeted liposomes increases with incubation time. Cytotoxicity studies demonstrate that radiolabeled J591-labeled liposomes are most cytotoxic, with median lethal dose values, after 24 h of incubation, equal to 1.96 (5.3 × 10(-5)), 2.92 × 10(2) (7.9 × 10(-3)), and 2.33 × 10(1) Bq/mL (6.3 × 10(-4) µCi/mL) for LNCaP, Mat-Lu, and induced HUVEC, respectively, which are comparable to the values for the radiolabeled J591 antibody. For A10 aptamer-labeled liposomes, the corresponding values are 3.70 × 10(1) (1.0 × 10(-3)), 1.85 × 10(3) (5.0 × 10(-2)), and 4.07 × 10(3) Bq/mL (1.1 × 10(-1) µCi/mL), respectively. CONCLUSION: Our studies demonstrate that anti-PSMA-targeted liposomes loaded with (225)Ac selectively bind, become internalized, and kill PSMA-expressing cells including endothelial cells induced to express PSMA. These findings-combined with the unique ability of liposomes to be easily tuned, in terms of size and surface modification, for optimizing biodistributions-suggest the potential of PSMA-targeting liposomes encapsulating α-particle emitters for selective antivascular α radiotherapy.

Immunoliposomal delivery of 213Bi for alpha-emitter targeting of metastatic breast cancer.

Current treatment for late-stage metastatic breast cancer is largely palliative. alpha-Particles are highly potent, short-range radiation emissions capable of sterilizing individual cells with one to three traversals of the cell nucleus. The alpha-emitter, (213)Bi (T(1/2) = 45.6 min), was conjugated to a 100-nm diameter liposomal-CHX-A''-DTPA construct, upon which the rat HER2/neu reactive antibody, 7.16.4, was grafted. A conjugation time of 10 minutes was achieved giving a specific activity corresponding to 0.1 (213)Bi atom per liposome; stability in vitro and in vivo was confirmed. Efficacy in a rat/neu transgenic mouse model of metastatic mammary carcinoma was investigated. Three days after left cardiac ventricular injection of 10(5) rat HER-2/neu-expressing syngeneic tumor cells, macrophage-depleted Neu-N mice were treated by i.v. injection with (a) 19.2 MBq (520 muCi) of liposome-CHX-A''-DTPA-(213)Bi, (b) 19.2 MBq of liposome-CHX-A''-DTPA-(213)Bi-7.16.4, (c) 4.44 MBq (120 muCi) of (213)Bi-7.16.4, and (d) cold (nonradioactive) liposome-CHX-A''-DTPA-7.16.4 as control. Treatment with (a) increased median survival time to 34 days compared with 29 days for the untreated controls (P = 0.013) and 27 days for treated cold controls. Treatment with the radiolabeled antibody-conjugated liposome (b) increased median survival time to 38 days (P = 0.0002 relative to untreated controls). The radiolabeled antibody-treated group (c) gave a median survival of 39 days, which was similar to that for the radiolabeled antibody-conjugated liposome-treated group (P = 0.5). We have shown that the (213)Bi radiolabeled immunoliposomes are effective in treating early-stage micrometastases, giving median survival times similar to those obtained with antibody-mediated delivery of (213)Bi in this animal model.

Interim analysis of toxicity and response in phase 1 trial of systemic targeted alpha therapy for metastatic melanoma.

PURPOSE: The aim is to assess toxicity and response of systemic alpha therapy for metastatic melanoma. EXPERIMENTAL DESIGN: This is an open-labelled Phase 1 dose escalation study to establish the effective dose of the alpha-immunoconjugate (213)Bi-cDTPA-9.2.27 mAb (AIC). Tools used to investigate the effects were physical examination; imaging of tumors; pathology; GFR; CT and changes in tumor marker. Responses were assessed using RECIST criteria. RESULTS AND DISCUSSION: Twenty-two patients with stage IV melanoma/in-transit metastasis were treated with activities of 55-947 MBq. Using RECIST criteria 50% showed stable disease and 14% showed partial response. One patient (6%) showed near complete response and was retreated because of an excellent response to the initial treatment. Another patient showed response in his tumor on mandible and reduction in lung lesions. Overall 30% showed progressive disease. The tumor marker melanoma inhibitory activity protein (MIA) showed reductions over eight weeks in most of the patients. The disparity of dose with responders is discussed. No toxicity was observed over the range of administered activities. CONCLUSION: Observation of responses without any toxicity indicates that targeted alpha therapy has the potential to be a safe and effective therapeutic approach for metastatic melanoma.