Location: Engineering Library- RS122.2.N36 2016

Radiolabeled small-molecule DOTA-haptens can be combined with antitumor/anti-DOTA bispecific antibodies (BsAbs) for pretargeted radioimmunotherapy (PRIT). For optimized delivery of the theranostic - and β-emitting isotope ¹⁷⁷Lu with DOTA-based PRIT (DOTA-PRIT), bivalent Gemini (DOTA-Bn-thiourea-PEG4-thiourea-Bn-DOTA, aka (3,6,9,12-tetraoxatetradecane-1,14-diyl)bis(DOTA-benzyl thiourea)) was developed. Methods: Gemini was synthesized by linking 2 S-2-(4-isothiocyanatobenzyl)-DOTA molecules together via a 1,14-diamino-PEG4 linker. [¹⁷⁷Lu]Lu-Gemini was prepared with no-carrier-added ¹⁷⁷LuCl₃ to a molar-specific activity of 123 GBq/μmol and radiochemical purity of more than 99%. The specificity of BsAb-¹⁷⁷Lu-Gemini was verified in vitro. Subsequently, we evaluated biodistribution and whole-body clearance for [¹⁷⁷Lu]Lu-Gemini and, for comparison, our gold-standard monovalent [¹⁷⁷Lu]Lu-S-2-(4-aminobenzyl)-DOTA ([¹⁷⁷Lu]Lu-DOTA-Bn) in naïve (tumor-free) athymic nude mice. For our proof-of-concept system, a 3-step pretargeting approach was performed with an established DOTA-PRIT regimen (anti-GPA33/anti-DOTA IgG-scFv BsAb, a clearing agent, and [¹⁷⁷Lu]Lu-Gemini) in mouse models. Results: Initial in vivo studies showed that [¹⁷⁷Lu]Lu-Gemini behaved similarly to [¹⁷⁷Lu]Lu-DOTA-Bn, with almost identical blood and whole-body clearance kinetics, as well as biodistribution and mouse kidney dosimetry. Pretargeting [¹⁷⁷Lu]Lu-Gemini to GPA33-expressing SW1222 human colorectal xenografts was highly effective, leading to absorbed doses of [¹⁷⁷Lu]Lu-Gemini for blood, tumor, liver, spleen, and kidneys of 3.99, 455, 6.93, 5.36, and 14.0 cGy/MBq, respectively. Tumor–to–normal tissue absorbed-dose ratios (i.e., therapeutic indices [TIs]) for the blood and kidneys were 114 and 33, respectively. In addition, we demonstrate that the use of bivalent [¹⁷⁷Lu]Lu-Gemini in DOTA-PRIT leads to improved TIs and augmented [¹⁷⁷Lu]Lu-Gemini tumor uptake and retention in comparison to monovalent [¹⁷⁷Lu]Lu-DOTA-Bn. Finally, we established efficacy in SW1222 tumor-bearing mice, demonstrating that a single injection of anti-GPA33 DOTA-PRIT with 44 MBq (1.2 mCi) of [¹⁷⁷Lu]Lu-Gemini (estimated tumor-absorbed dose, 200 Gy) induced complete responses in 5 of 5 animals and a histologic cure in 2 of 5 (40%) animals. Moreover, a significant increase in survival compared with nontreated controls was noted (maximum tolerated dose not reached). Conclusion: We have developed a bivalent DOTA-radiohapten, [¹⁷⁷Lu]Lu-Gemini, that showed improved radiopharmacology for DOTA-PRIT application. The use of bivalent [¹⁷⁷Lu]Lu-Gemini in DOTA-PRIT, as opposed to monovalent [¹⁷⁷Lu]Lu-DOTA-Bn, allows curative treatments with considerably less administered ¹⁷⁷Lu activity while still achieving high TIs for both the blood (>100) and the kidneys (>30).

²²⁶Ac (t_1/2 = 29.37 h) has been proposed as a theranostic radioisotope leveraging both its diagnostic -emissions and therapeutic α-emissions. ²²⁶Ac emits 158 and 230 keV -photons ideal for quantitative SPECT imaging and acts as an in vivo generator of 4 high-energy α-particles. Because of these nuclear decay properties, ²²⁶Ac has potential to act as a standalone theranostic isotope. In this proof-of-concept study, we evaluated a preclinical ²²⁶Ac-radiopharmaceutical for its theranostic efficacy and present the first ²²⁶Ac-targeted α-therapy study. Methods: ²²⁶Ac was produced at TRIUMF and labeled with the chelator-peptide bioconjugate crown-TATE. [²²⁶Ac]Ac-crown-TATE was selected to target neuroendocrine tumors in male NRG mice bearing AR42J tumor xenografts for SPECT imaging, biodistribution, and therapy studies. A preclinical SPECT/CT scanner acquired quantitative images reconstructed from both the 158 and the 230 keV emissions. Mice in the biodistribution study were euthanized at 1, 3, 5, 24, and 48 h after injection, and internal radiation dosimetry was derived for the tumor and organs of interest to establish appropriate therapeutic activity levels. Mice in the therapy study were administered 125, 250, or 375 kBq treatments and were monitored for tumor size and body condition. Results: We present quantitative SPECT images of the in vivo biodistribution of [²²⁶Ac]Ac-crown-TATE, which showed agreement with ex vivo measurements. Biodistribution studies demonstrated high uptake (>30%IA/g at 5 h after injection) and retention in the tumor, with an estimated mean absorbed dose coefficient of 222 mGy/kBq. [²²⁶Ac]Ac-crown-TATE treatments significantly extended the median survival from 7 d in the control groups to 16, 24, and 27 d in the 125, 250, and 375 kBq treatment groups, respectively. Survival was prolonged by slowing tumor growth, and no weight loss or toxicities were observed. Conclusion: This study highlights the theranostic potential of ²²⁶Ac as a standalone therapeutic isotope in addition to its demonstrated diagnostic capabilities to assess dosimetry in matched ²²⁵Ac-radiopharmaceuticals. Future studies will investigate maximum dose and toxicity to further explore the therapeutic potential of ²²⁶Ac-radiopharmaceuticals.

Her blood-testing startup claimed to revolutionise testing by detecting hundreds of medical conditions from just a few drops of blood 

Objectives: Lutetium-177 (¹⁷⁷Lu)-PSMA-617 (LuPSMA) is a radioligand with high affinity for prostate specific membrane antigen (PSMA) enabling targeted beta-irradiation of prostate cancer. We have previously reported favorable activity with low toxicity in a prospective phase II trial involving 30 men with metastatic castrate-resistant prostate cancer (mCRPC). We now report their longer-term outcomes including a 20 patient extension cohort and outcomes of subsequent systemic treatments following completion of trial therapy. Methods: 50 patients with PSMA-avid mCRPC who had progressed after standard therapies received up to 4 cycles of LuPSMA every 6 weeks. Endpoints included PSA response (PCWG2), toxicity (CTCAE v4.03), imaging response, patient-reported health-related quality of life (QoL), progression-free and overall survival. We also describe, as a novel finding, outcomes of men who subsequently progressed and had further systemic therapies, including LuPSMA. Results: 75 men were screened to identify 50 patients eligible for treatment. Adverse prognostic features of the cohort included short median PSA doubling time (2.3 months) and extensive prior treatment including prior docetaxel (84%), cabazitaxel (48%), and abiraterone and/or enzalutamide (90%). The mean administered radioactivity was 7.5 GBq/cycle. PSA decline ≥ 50% was achieved in 32 of 50 patients (64%, 95% CI 50-77%), including 22 patients (44%, 95% CI 30-59%) with ≥ 80% decrease. Of 27 patients with measurable soft tissue disease, 15 (56%) achieved an objective response by RECIST 1.1. The most common toxicities attributed to LuPSMA were self-limiting G1-2 dry mouth (66%), transient G1-2 nausea (48%), G3-4 thrombocytopenia (10%) and G3 anemia (10%). Brief pain inventory severity and interference scores decreased at all time points including at the 3 month follow-up with a decrease of -1.2 (95% CI -0.5 to -1.9, P = 0.001) and 1.0 (95% CI -0.2 to -0.18, P = 0.013), respectively. At a median follow-up of 31.4 months, median OS was 13.3 months (95% CI 10.5-18.7) with a significantly longer survival of 18.4 months (95% CI 13.8-23.8) in patients achieving a PSA decline ≥ 50%. At progression following prior response, further LuPSMA was administered to 15 (30%) patients (median 2 cycles commencing 359 days from enrolment) with PSA decline ≥ 50% in 11 patients (73%). 4 of 21 patients (19%) receiving other systemic therapies upon progression experienced PSA decline ≥ 50%. There were no unexpected adverse events with LuPSMA re-treatment. Conclusion: This expanded 50 patient cohort of men with extensive prior therapy confirms our earlier report of high response rates, low toxicity and improved QoL with LuPSMA radioligand therapy. Upon progression, re-challenge LuPSMA demonstrated higher response rates than other systemic therapies.

Purpose: This prospective study evaluated the imaging performance of a novel immunological pretargeting positron-emission tomorgraphy (immuno-PET) method in patients with HER2-negative, carcinoembryonic antigen (CEA)-positive, metastatic breast cancer (BC), compared to computed tomography (CT), bone magnetic resonance imaging (MRI), and ¹⁸Fluorodeoxyglucose PET (FDG-PET). Patients and Methods: Twenty-three patients underwent whole-body immuno-PET after injection of 150 MBq ⁶⁸Ga-IMP288, a histamine-succinyl-glycine peptide given following initial targeting of a trivalent anti-CEA, bispecific, anti-peptide antibody. The gold standards were histology and imaging follow-up. Tumor standard uptake values (SUV_max and SUVmean) were measured, and tumor burden analyzed using Total Tumor Volume (TTV) and Total Lesion Activity (TLA). Results: Total lesion sensitivity of immuno-PET and FDG-PET was 94.7% (1116/1178) and 89.6% (1056/1178), respectively. Immuno-PET had a somewhat higher sensitivity than CT and FDG-PET in lymph nodes (92.4% vs 69.7% and 89.4%, respectively) and liver metastases (97.3% vs 92.1% and 94.8%, respectively), whereas sensitivity was lower for lung metastases (48.3% vs 100% and 75.9%, respectively). Immuno-PET showed higher sensitivity than MRI and FDG-PET for bone lesions (95.8% vs 90.7% and 89.3%, respectively). In contrast to FDG-PET, immuno-PET disclosed brain metastases. Despite equivalent tumor SUV_max, SUVmean, and TTV, TLA was significantly higher with immuno-PET compared to FDG PET (P = 0.009). Conclusion: Immuno-PET using anti-CEA/anti-IMP288 bispecific antibody, followed by ⁶⁸Ga-IMP288, is a potentially sensitive theranostic imaging method for HER2-negative, CEA-positive, metastatic BC patients, and warrants further research.

Fibroblast activation protein (FAP), which promotes tumor growth and progression, is overexpressed in cancer-associated fibroblasts of many human epithelial cancers. Because of its low expression in normal organs, FAP is an excellent target for theranostics. In this study, we used radionuclides with relatively long half-lives, ⁶⁴Cu (half-life, 12.7 h) and ²²⁵Ac (half-life, 10 d), to label FAP inhibitors (FAPIs) in mice with human pancreatic cancer xenografts. Methods: Male nude mice (body weight, 22.5 ± 1.2 g) were subcutaneously injected with human pancreatic cancer cells (PANC-1, n = 12; MIA PaCa-2, n = 8). Tumor xenograft mice were investigated after the intravenous injection of ⁶⁴Cu-FAPI-04 (7.21 ± 0.46 MBq) by dynamic and delayed PET scans (2.5 h after injection). Static scans 1 h after the injection of ⁶⁸Ga-FAPI-04 (3.6 ± 1.4 MBq) were also acquired for comparisons using the same cohort of mice (n = 8). Immunohistochemical staining was performed to confirm FAP expression in tumor xenografts using an FAP-α-antibody. For radioligand therapy, ²²⁵Ac-FAPI-04 (34 kBq) was injected into PANC-1 xenograft mice (n = 6). Tumor size was monitored and compared with that of control mice (n = 6). Results: Dynamic imaging of ⁶⁴Cu-FAPI-04 showed rapid clearance through the kidneys and slow washout from tumors. Delayed PET imaging of ⁶⁴Cu-FAPI-04 showed mild uptake in tumors and relatively high uptake in the liver and intestine. Accumulation levels in the tumor or normal organs were significantly higher for ⁶⁴Cu-FAPI-04 than for ⁶⁸Ga-FAPI-04, except in the heart, and excretion in the urine was higher for ⁶⁸Ga-FAPI-04 than for ⁶⁴Cu-FAPI-04. Immunohistochemical staining revealed abundant FAP expression in the stroma of xenografts. ²²⁵Ac-FAPI-04 injection showed significant tumor growth suppression in the PANC-1 xenograft mice, compared with the control mice, without a significant change in body weight. Conclusion: This proof-of-concept study showed that ⁶⁴Cu-FAPI-04 and ²²⁵Ac-FAPI-04 could be used in theranostics for the treatment of FAP-expressing pancreatic cancer. α-therapy targeting FAP in the cancer stroma is effective and will contribute to the development of a new treatment strategy.

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Wall Street Journal investigative reporter John Carreyrou recounts some of the more unusual experiences he had while uncovering the story of Theranos's business practices.

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