The Twin Evils of Concomitant Rare Pathology with Variant Anatomy: Superior Mesenteric Artery Aneurysm and a Replaced Right Hepatic Artery.

Aneurysmal degeneration of the superior mesenteric artery (SMA) is a rare clinical finding, estimated to affect <1% of the general population in postmortem studies. Due to the rare prevalence of aneurysms affecting the SMA, there are no clear or definitive published consensus guidelines for its management at presentation, with both surgical and endovascular options described. An aberrant or replaced right hepatic artery (RRHA) is thought to affect 10-15% of the population. The prevalence of both conditions presenting concomitantly is unknown, but undoubtedly even rarer. We describe the successful management of a symptomatic SMA aneurysm with an RRHA emerging from the aneurysmal sac presenting to our vascular unit. This was repaired via an open surgical approach with SMA aneurysmectomy and interposition grafting using reversed vein with preservation of RHA liver perfusion via a novel reconstruction option. This case highlights the challenge that visceral aneurysms pose, especially when simple or orthodox reconstruction options are limited due to rare or unusual anatomy.

Targeting of radiolabeled J591 antibody to PSMA-expressing tumors: optimization of imaging and therapy based on non-linear compartmental modeling.

BACKGROUND: We applied a non-linear immunokinetic model to quantitatively compare absolute antibody uptake and turnover in subcutaneous LNCaP human prostate cancer (PCa) xenografts of two radiolabeled forms of the humanized anti-prostate-specific membrane antigen (PSMA) monoclonal antibody J591 ((124)I-J591 and (89)Zr-J591). Using the model, we examined the impact of dose on the tumor and plasma positron emission tomography (PET)-derived time-activity curves. We also sought to predict the optimal targeting index (ratio of integrated-tumor-to-integrated-plasma activity concentrations) for radioimmunotherapy. METHODS: The equilibrium rates of antibody internalization and turnover in the tumors were derived from PET images up to 96 h post-injection using compartmental modeling with a non-linear transfer rate. In addition, we serially imaged groups of LNCaP tumor-bearing mice injected with (89)Zr-J591 antibody doses ranging from antigen subsaturating to saturating to examine the suitability of using a non-linear approach and derived the time-integrated concentration (in µM∙hours) of administered tracer in tumor as a function of the administered dose of antibody. RESULTS: The comparison of (124)I-J591 and (89)Zr-J591 yielded similar model-derived values of the total antigen concentration and internalization rate. The association equilibrium constant (k a) was twofold higher for (124)I, but there was a ~tenfold greater tumoral efflux rate of (124)I from tumor compared to that of (89)Zr. Plots of surface-bound and internalized radiotracers indicate similar behavior up to 24 h p.i. for both (124)I-J591 and (89)Zr-J591, with the effect of differential clearance rates becoming apparent after about 35 h p.i. Estimates of J591/PSMA complex turnover were 3.9-90.5 × 10(12) (for doses from 60 to 240 µg) molecules per hour per gram of tumor (20 % of receptors internalized per hour). CONCLUSIONS: Using quantitative compartmental model methods, surface binding and internalization rates were shown to be similar for both (124)I-J591 and (89)Zr-J591 forms, as expected. The large difference in clearance rates of the radioactivity from the tumor is likely due to differential trapping of residualizing zirconium versus non-residualizing iodine. Our non-linear model was found to be superior to a conventional linear model. This finding and the calculated activity persistence time in tumor have important implications for radioimmunotherapy and other antibody-based therapies in patients.

Theranostic pretargeted radioimmunotherapy of colorectal cancer xenografts in mice using picomolar affinity 86Y- or ¹77Lu-DOTA-Bn binding scFv C825/GPA33 IgG bispecific immunoconjugates.

PURPOSE: GPA33 is a colorectal cancer (CRC) antigen with unique retention properties after huA33-mediated tumor targeting. We tested a pretargeted radioimmunotherapy (PRIT) approach for CRC using a tetravalent bispecific antibody with dual specificity for GPA33 tumor antigen and DOTA-Bn-(radiolanthanide metal) complex. METHODS: PRIT was optimized in vivo by titrating sequential intravenous doses of huA33-C825, the dextran-based clearing agent, and the C825 haptens (177)Lu-or (86)Y-DOTA-Bn in mice bearing the SW1222 subcutaneous (s.c.) CRC xenograft model. RESULTS: Using optimized PRIT, therapeutic indices (TIs) for tumor radiation-absorbed dose of 73 (tumor/blood) and 12 (tumor/kidney) were achieved. Estimated absorbed doses (cGy/MBq) to tumor, blood, liver, spleen, and kidney for single-cycle PRIT were 65.8, 0.9 (TI 73), 6.3 (TI 10), 6.6 (TI 10), and 5.3 (TI 12), respectively. Two cycles of PRIT (66.6 or 111 MBq (177)Lu-DOTA-Bn) were safe and effective, with a complete response of established s.c. tumors (100 - 700 mm(3)) in nine of nine mice, with two mice alive without recurrence at >140 days. Tumor log kill in this model was estimated to be 2.1 - 3.0 based on time to 500-mm(3) tumor recurrence. In addition, PRIT dosimetry/diagnosis was performed by PET imaging of the positron-emitting DOTA hapten (86)Y-DOTA-Bn. CONCLUSION: We have developed anti-GPA33 PRIT as a triple-step theranostic strategy for preclinical detection, dosimetry, and safe targeted radiotherapy of established human colorectal mouse xenografts.