<p>Supplementary Figures S1-4. Figure S1. 89Zr-J591 versus bone scan comparison of lesion positivity. Figure S2. Patient with metastatic prostate cancer (PSA of 10.1) with 89Zr-J591+ lesions that were not seen on MDP. Figure S3. Patient with metastatic prostate cancer (PSA of 0.62). Figure S4. Uniform prior distribution.</p>
Clearing agents (CAs) can rapidly remove nonlocalized targeting biomolecules from circulation for hepatic catabolism, thereby enhancing the therapeutic index (TI), especially for blood (marrow), of the subsequently administered radioisotope in any multistep pretargeting strategy. Herein we describe the synthesis and in vivo evaluation of a fully synthetic glycodendrimer-based CA for DOTA-based pretargeted radioimmunotherapy (DOTA-PRIT). The novel dendron–CA consists of a nonradioactive yttrium-DOTA-Bn molecule attached via a linker to a glycodendron displaying 16 terminal α-thio-N-acetylgalactosamine (α-SGalNAc) units (CCA α-16-DOTA-Y3+; molecular weight: 9059 Da). Pretargeting [177Lu]LuDOTA-Bn with CCA α-16-DOTA-Y3+ to GPA33-expressing SW1222 human colorectal xenografts was highly effective, leading to absorbed doses of [177Lu]LuDOTA-Bn for blood, tumor, liver, spleen, and kidneys of 11.7, 468, 9.97, 5.49, and 13.3 cGy/MBq, respectively. Tumor-to-normal tissues absorbed-dose ratios (i.e., TIs) ranged from 40 (e.g., for blood and kidney) to about 550 for stomach.
Although a large body of literature exists on the potential use of nanoparticles for medical applications, the number of probes translated into human clinical trials is remarkably small. A major challenge of particle probe development and their translation is the elucidation of safety profiles associated with their structural complexity, not only in terms of size distribution and heterogeneities in particle composition but also their effects on biological activities and the relationship between particle structure and pharmacokinetics. Here, we report on the synthesis, characterization, and long-term stability of ultrasmall (<10 nm diameter) dual-modality (optical and positron emission tomography) and integrin-targeting silica nanoparticles (cRGDY–PEG–Cy5–C′ dots and 124I-(or 131I-) cRGDY–PEG–Cy5–C′dots) and the extent to which their surface ligand density differentially modulates key in vitro and in vivo biological activities in melanoma models over a range of ligand numbers (i.e., ∼6–18). Gel permeation chromatography, established as an important particle characterization tool, revealed a two-year shelf life for cRGDY–PEG–Cy5–C′ dots. Radiochromatography further demonstrated the necessary radiochemical stability for clinical applications. The results of subsequent ligand density-dependent studies elucidate strong modulations in biological response, including statistically significant increases in integrin-specific targeting and particle uptake, cellular migration and adhesion, renal clearance, and tumor-to-blood ratios with increasing ligand number. We anticipate that nanoprobe characteristics and a better understanding of the structure–function relationships determined in this study will help guide identification of other lead nanoparticle candidates for in vitro and in vivo biological assessments and product translation.
We conducted a phase I dose-escalation study with 89Zr-desferrioxamine-IAB2M (89Zr-IAB2M), an anti-prostate-specific membrane antigen minibody, in patients with metastatic prostate cancer.Patients received 185 MBq (5 mCi) of 89Zr-IAB2M and Df-IAB2M at total mass doses of 10 (n = 6), 20 (n = 6), and 50 mg (n = 6). Whole-body and serum clearance, normal-organ and lesion uptake, and radiation absorbed dose were estimated, and the effect of mass escalation was analyzed.Eighteen patients were injected and scanned without side effects. Whole-body clearance was monoexponential, with a median biologic half-life of 215 h, whereas serum clearance showed biexponential kinetics, with a median biologic half-life of 3.7 (12.3%/L) and 33.8 h (17.9%/L). The radiation absorbed dose estimates were 1.67, 1.36, and 0.32 mGy/MBq to liver, kidney, and marrow, respectively, with an effective dose of 0.41 mSv/MBq (1.5 rem/mCi). Both skeletal and nodal lesions were detected with 89Zr-IAB2M, most visualized by 48-h imaging.89Zr-IAB2M is safe and demonstrates favorable biodistribution and kinetics for targeting metastatic prostate cancer. Imaging with 10 mg of minibody mass provides optimal biodistribution, and imaging at 48 h after injection provides good lesion visualization. Assessment of lesion targeting is being studied in detail in an expansion cohort.
Epithelial ovarian cancer (EOC) is often asymptomatic and presents clinically in an advanced stage as widespread peritoneal microscopic disease that is generally considered to be surgically incurable. Targeted α-therapy with the α-particle–emitting radionuclide 225Ac (half-life, 9.92 d) is a high-linear-energy-transfer treatment approach effective for small-volume disease and even single cells. Here, we report the use of human epidermal growth factor receptor 2 (HER2) 225Ac-pretargeted radioimmunotherapy (PRIT) to treat a mouse model of human EOC SKOV3 xenografts growing as peritoneal carcinomatosis (PC). Methods: On day 0, 105 SKOV3 cells transduced with a luciferase reporter gene were implanted intraperitoneally in nude mice, and tumor engraftment was verified by bioluminescent imaging (BLI). On day 15, treatment was started using 1 or 2 cycles of 3-step anti-HER2 225Ac-PRIT (37 kBq/cycle as 225Ac-Proteus DOTA), separated by a 1-wk interval. Efficacy and toxicity were monitored for up to 154 d. Results: Untreated PC-tumor–bearing nude mice showed a median survival of 112 d. We used 2 independent measures of response to evaluate the efficacy of 225Ac-PRIT. First, a greater proportion of the treated mice (9/10 1-cycle and 8/10 2-cycle; total, 17/20; 85%) survived long-term compared with controls (9/27, 33%), and significantly prolonged survival was documented (log-rank [Mantel–Cox] P = 0.0042). Second, using BLI, a significant difference in the integrated BLI signal area to 98 d was noted between controls and treated groups (P = 0.0354). Of a total of 8 mice from the 2-cycle treatment group (74 kBq total) that were evaluated by necropsy, kidney radiotoxicity was mild and did not manifest itself clinically (normal serum blood urea nitrogen and creatinine). Dosimetry estimates (relative biological effectiveness–weighted dose, where relative biological effectiveness = 5) per 37 kBq administered for tumors and kidneys were 56.9 and 16.1 Gy, respectively. One-cycle and 2-cycle treatments were equally effective. With immunohistology, mild tubular changes attributable to α-toxicity were observed in both therapeutic groups. Conclusion: Treatment of EOC PC-tumor–bearing mice with anti-HER2 225Ac-PRIT resulted in histologic cures and prolonged survival with minimal toxicity. Targeted α-therapy using the anti-HER2 225Ac-PRIT system is a potential treatment for otherwise incurable EOC.
Abstract Purpose: Many cancer treatments suffer from dose-limiting toxicities to vital organs due to poor therapeutic indices. To overcome these challenges we developed a novel multimerization platform that rapidly removes tumor-targeting proteins from the blood to substantially improve therapeutic index. Experimental Design: The platform was designed as a fusion of a self-assembling and disassembling (SADA) domain to a tandem single-chain bispecific antibody (BsAb, anti-ganglioside GD2 × anti-DOTA). SADA–BsAbs were assessed with multiple in vivo tumor models using two-step pretargeted radioimmunotherapy (PRIT) to evaluate tumor uptake, dosimetry, and antitumor responses. Results: SADA–BsAbs self-assembled into stable tetramers (220 kDa), but could also disassemble into dimers or monomers (55 kDa) that rapidly cleared via renal filtration and substantially reduced immunogenicity in mice. When used with rapidly clearing DOTA-caged PET isotopes, SADA–BsAbs demonstrated accurate tumor localization, dosimetry, and improved imaging contrast by PET/CT. When combined with therapeutic isotopes, two-step SADA-PRIT safely delivered massive doses of alpha-emitting (225Ac, 1.48 MBq/kg) or beta-emitting (177Lu, 6,660 MBq/kg) S-2-(4-aminobenzyl)-1,4,7,10-tetraazacyclododecane tetraacetic acid (DOTA) payloads to tumors, ablating them without any short-term or long-term toxicities to the bone marrow, kidneys, or liver. Conclusions: The SADA–BsAb platform safely delivered large doses of radioisotopes to tumors and demonstrated no toxicities to the bone marrow, kidneys, or liver. Because of its modularity, SADA–BsAbs can be easily adapted to most tumor antigens, tumor types, or drug delivery approaches to improve therapeutic index and maximize the delivered dose. See related commentary by Capala and Kunos, p. 377
Antibodies and antibody-drug conjugates targeting the cell surface protein 6 transmembrane epithelial antigen of prostate 1 (STEAP1) are in early clinical development for the treatment of castration-resistant prostate cancer (PCa). In general, antigen expression directly affects the bioactivity of therapeutic antibodies, and the biologic regulation of STEAP1 is unusually complicated in PCa. Paradoxically, STEAP1 can be induced or repressed by the androgen receptor (AR) in different human PCa models, while also expressed in AR-null PCa. Consequently, there is an urgent need to translate diagnostic strategies to establish which regulatory mechanism predominates in patients to situate the appropriate therapy within standard of care therapies inhibiting AR. Methods: To this end, we prepared and evaluated 89Zr-labeled MSTP2109A (89Zr-2109A), a radiotracer for PET derived from a fully humanized monoclonal antibody to STEAP1 in preclinical PCa models. Results:89Zr-2109A specifically localized to the STEAP1-positive human PCa models CWR22Pc, 22Rv1, and PC3. Moreover, 89Zr-2109A sensitively measured treatment-induced changes (∼66% decline) in STEAP1 expression in CWR22PC in vitro and in vivo, a model we showed to express STEAP1 in an AR-dependent manner. Conclusion: These findings highlight the ability of immuno-PET with 89Zr-2109A to detect acute changes in STEAP1 expression and argue for an expansion of ongoing efforts to image PCa patients with 89Zr-2109A to maximize the clinical benefit associated with antibodies or antibody-drug conjugates to STEAP1.
