225Ac-Macropatate: A Novel Alpha Particle Peptide Receptor Radionuclide Therapy for Neuroendocrine Tumors

Neuroendocrine tumors (NETs) express somatostatin receptors (SSTRs) 2 and 5. Modified variants of somatostatin, the cognate ligand for SSTR2 and SSTR5, are used in treatment for metastatic and locoregional disease. Peptide receptor radionuclide therapy with ¹⁷⁷Lu-DOTATATE (DOTA-octreotate), a β-particle-emitting somatostatin derivative, has demonstrated survival benefit in patients with SSTR-positive NETs. Despite excellent results, a subset of patients has tumors that are resistant to treatment, and alternative agents are needed. Targeted α-particle therapy has been shown to kill tumors that are resistant to targeted β-particle therapy, suggesting that targeted α-particle therapy may offer a promising treatment option for patients with ¹⁷⁷Lu-DOTATATE-resistant disease. Although DOTATATE can chelate the clinically relevant α-particle-emitting radionuclide ²²⁵Ac, the labeling reaction requires high temperatures, and the resulting radioconjugate has suboptimal stability. Methods: We designed and synthesized MACROPATATE (MACROPA-octreotate), a novel radioconjugate capable of chelating ²²⁵Ac at room temperature, and assessed its in vitro and in vivo performance. Results: MACROPATATE demonstrated comparable affinity to DOTATATE (dissociation constant, 21 nM) in U2-OS-SSTR2, a SSTR2-positive transfected cell line. ²²⁵Ac-MACROPATATE demonstrated superior serum stability at 37°C over time compared with ²²⁵Ac-DOTATATE. Biodistribution studies demonstrated higher tumor uptake of ²²⁵Ac-MACROPATATE than of ²²⁵Ac-DOTATATE in mice engrafted with subcutaneous H69 NETs. Therapy studies showed that ²²⁵Ac-MACROPATATE exhibits significant antitumor and survival benefit compared with saline control in mice engrafted with SSTR-positive tumors. However, the increased accumulation of ²²⁵Ac-MACROPATATE in liver and kidneys and subsequent toxicity to these organs decreased its therapeutic index compared with ²²⁵Ac-DOTATATE. Conclusion: ²²⁵Ac-MACROPATATE and ²²⁵Ac-DOTATATE exhibit favorable therapeutic efficacy in animal models. Because of elevated liver and kidney accumulation and lower administered activity for dose-limiting toxicity of ²²⁵Ac-MACROPATATE, ²²⁵Ac-DOTATATE was deemed the superior agent for targeted α-particle peptide receptor radionuclide therapy.

Intraperitoneal Pretargeted Radioimmunotherapy for Colorectal Peritoneal Carcinomatosis

Peritoneal carcinomatosis (PC) is considered incurable, and more effective therapies are needed. Herein we test the hypothesis that GPA33-directed intracompartmental pretargeted radioimmunotherapy (PRIT) can cure colorectal peritoneal carcinomatosis. Nude mice were implanted intraperitoneally with luciferase-transduced GPA33-expressing SW1222 cells for aggressive peritoneal carcinomatosis (e.g., resected tumor mass 0.369 ± 0.246 g; n = 17 on day 29). For GPA33-PRIT, we administered intraperitoneally a high-affinity anti-GPA33/anti-DOTA bispecific antibody (BsAb), followed by clearing agent (intravenous), and lutetium-177 (Lu-177) or yttrium-86 (Y-86) radiolabeled DOTA-radiohapten (intraperitoneal) for beta/gamma-emitter therapy and PET imaging, respectively. The DOTA-radiohaptens were prepared from S-2-(4-aminobenzyl)-1,4,7, 10-tetraazacyclododecane tetraacetic acid chelate (DOTA-Bn). Efficacy and toxicity of single- versus three-cycle therapy were evaluated in mice 26-27 days post-tumor implantation. Single-cycle treatment ([177Lu]LuDOTA-Bn 111 MBq; tumor dose: 4,992 cGy) significantly prolonged median survival (MS) approximately 2-fold to 84.5 days in comparison with controls (P = 0.007). With three-cycle therapy (once weekly, total 333 MBq; tumor dose: 14,975 cGy), 6/8 (75%) survived long-term (MS > 183 days). Furthermore, for these treated long-term survivors, 1 mouse was completely disease free (microscopic "cure") at necropsy; the others showed stabilized disease, which was detectable during PET-CT using [86Y]DOTA-Bn. Treatment controls had MS ranging from 42-52.5 days (P < 0.001) and 19/20 mice succumbed to progressive intraperitoneal disease by 69 days. Multi-cycle GPA33 DOTA-PRIT significantly prolongs survival with reversible myelosuppression and no chronic marrow (929 cGy to blood) or kidney (982 cGy) radiotoxicity, with therapeutic indices of 12 for blood and 12 for kidneys. MTD was not reached.

Glypican-3-Targeted Alpha Particle Therapy for Hepatocellular Carcinoma

Glypican-3 (GPC3) is expressed in 75% of hepatocellular carcinoma (HCC), but not normal liver, making it a promising HCC therapeutic target. GC33 is a full-length humanized monoclonal IgG1 specific to GPC3 that can localize to HCC in vivo. GC33 alone failed to demonstrate therapeutic efficacy when evaluated in patients with HCC; however, we posit that cytotoxic functionalization of the antibody with therapeutic radionuclides, may be warranted. Alpha particles, which are emitted by radioisotopes such as Actinium-225 (Ac-225) exhibit high linear energy transfer and short pathlength that, when targeted to tumors, can effectively kill cancer and limit bystander cytotoxicity. Macropa, an 18-member heterocyclic crown ether, can stably chelate Ac-225 at room temperature. Here, we synthesized and evaluated the efficacy of [²²⁵Ac]Ac–Macropa–GC33 in mice engrafted with the GPC3-expressing human liver cancer cell line HepG2. Following a pilot dose-finding study, mice (n = 10 per group) were treated with (1) PBS, (2) mass-equivalent unmodified GC33, (3) 18.5 kBq [²²⁵Ac]Ac–Macropa–IgG1 (isotype control), (4) 9.25 kBq [²²⁵Ac]Ac–Macropa–GC33, and (5) 18.5 kBq [²²⁵Ac]Ac–Macropa–GC33. While significant toxicity was observed in all groups receiving radioconjugates, the 9.25 kBq [²²⁵Ac]Ac–Macropa–GC33 group demonstrated a modest survival advantage compared to PBS (p = 0.0012) and 18.5 kBq [²²⁵Ac]Ac–IgG1 (p = 0.0412). Hematological analysis demonstrated a marked, rapid reduction in white blood cells in all radioconjugate-treated groups compared to the PBS and unmodified GC33 control groups. Our studies highlight a significant disadvantage of using directly-labeled biomolecules with long blood circulation times for TAT. Strategies to mitigate such treatment toxicity include dose fractionation, pretargeting, and using smaller targeting ligands.

Imaging quiz: elbow pain in a cyclist

A 40-year-old man presented with left elbow pain in his nondominant arm and inability to pronate the left forearm. He had purchased a mountain bike 6 months earlier and had been riding approximately 30 miles per week over mostly flat terrain. He complained of gradually increasing left elbow and forearm pain during the previous month, with pain and stiffness on pronation that was worse the morning after biking. He sought medical attention when his inability to pronate the forearm interfered with daily activities, such as combing hair and brushing teeth.

Seroreactivity of Salmonella-infected cattle herds against a fimbrial antigen in comparison with lipopolysaccharide antigens

The IgG seroreaction of Salmonella-infected cattle herds against a fimbrial antigen (SEF14) was compared with that against lipopolysaccharide (LPS) antigens. Sera from 23 dairy herds (n = 205) from an island with no occurrence of salmonellosis, four herds (n = 303) with recent outbreaks of S. dublin and four herds (n = 168) with recent outbreaks of S. typhimurium, were tested in a SEF14-ELISA, S. dublin LPS (0:1, 9, 12) ELISA and S. typhimurium LPS (0:1, 4, 5, 12) ELISA. At a cut-off OD of 0.5, only one of the animals tested from the salmonellosis-free island showed significant seroreaction against the SEF14 antigen, which was confirmed in a Western-blot analysis. Three out of the four S. dublin-infected herds had several seroreactors in the SEF14-ELISA, whereas all the four herds were positive in the 0:1, 9, 12-ELISA. All but two samples (both from the same herd) in the four S. typhimurium-infected herds, positive in the 0:1, 4, 5, 12-ELISA, had OD values below 0.5 in the SEF14-ELISA. The results indicate that cattle can produce detectable specific antibodies against fimbrial antigens which may be used for screening of S. dublin-infected herds, particularly in areas with low prevalence of salmonellosis, increasing the predictive value of serology.

Development and application of enzyme-linked immunosorbent assay for specific detection of Salmonella enteritidis infections in chickens based on antibodies to SEF14 fimbrial antigen

A double-antibody sandwich enzyme-linked immunosorbent assay (ELISA) was developed to detect antibodies to the SEF14 fimbrial antigen (SEF14-DAS ELISA) and was evaluated for its use in the specific detection of chicken flocks infected with Salmonella enteritidis. The SEF14-DAS ELISA successfully discriminated between chickens experimentally infected with S. enteritidis and those infected with S. panama or S. typhimurium, although the SEF14 responses in adult birds infected with S. enteritidis were detectable but low. In contrast, ELISAs used to detect antibodies to lipopolysaccharide (LPS) and flagella were unable to discriminate between the infected groups of chicks and adult birds infected with different Salmonella serotypes. LPS and flagellar responses were low and variable in chicks, whereas in adult hens they were found to be consistently strong. When flocks naturally infected with S. enteritidis were tested by the SEF14-DAS ELISA and ELISAs to detect LPS and flagellar antibodies, it was found that they could all identify the infected flocks, although there was little correlation between individual serum samples. The study shows that the SEF14-DAS ELISA may offer advantages over existing assays with comparable sensitivities coupled with higher specificities for the serological detection of S. enteritidis-infected chicken flocks.

Five-year experience with exercise stress testing in a family practice program

OBJECTIVE

This study describes the implementation of exercise stress testing at a family practice residency program, looking at safety and the feasibility of having family practice faculty serve as instructors.

METHODS

Results from the first 5 years of testing were collected, and residency graduates were polled about their experience with treadmill testing during and after residency.

RESULTS

A total of 202 treadmill tests were performed, all without serious complications. Family practice faculty provided the instruction. One quarter of graduates were performing treadmill tests in their practices, and most of the others felt the training was beneficial.

CONCLUSIONS

It is both feasible and safe for family practice faculty to provide training in exercise treadmill testing to residents.

Immunomodulation of interleukin-2 by cyclophosphamide: a phase IB trial

The objective of this phase IB trial was to determine if cyclophosphamide (CY) could enhance the immune effects of interleukin-2 (IL-2), and if it could, was there an optimal immunomodulatory dosage. IL-2 alone at 30 million IU/m2 thrice weekly for 6 weeks or in combination with varying dosages of CY (300, 600, and 1,200 mg/m2) administered 3 days before IL-2 and repeated 3 weeks later was given to consecutive cohorts of patients (at least five per group) with advanced malignancies of varying types. To gauge the immune effects of the treatment, the variation in the amount of lymphokine-activated killer (LAK) cells generated in the peripheral blood mononuclear cells of patients and in a control group of normal volunteers was measured weekly over 7 consecutive weeks. Other immune parameters [natural killer cells (NK), peripheral blood eosinophils and lymphocytes, cell surface markers, soluble IL-2 receptor, and IL-2 antibodies] were also closely followed to study if they correlated with the degree of LAK activity. The group of patients that received low-dosage CY (300 mg/m2) and IL-2 produced the highest and most sustained levels of LAK and NK activity (p < 0.05) when compared with the cohorts receiving IL-2 alone or to those receiving the higher dosages of CY. No other immune parameter showed a significant difference between the groups. Although low-dosage CY does increase the LAK activity seen with IL-2, only randomized clinical trials can determine if this enhancement will improve tumor responses.

Development of monoclonal antibody ELISA for simultaneous detection of bovine coronavirus, rotavirus serogroup A, and Escherichia coli K99 antigen in feces of calves

A rapid ELISA was developed for simultaneous detection of bovine coronavirus (BCV), rotavirus (RV) serogroup A, and Escherichia coli K99 antigen in feces of calves. A mixture of 3 monoclonal antibodies specific for BCV, RV, or K99 was used successfully to capture the antigens; the same antibodies labeled with peroxidase were used to detect BCV, RV, or K99. The triple ELISA was compared with standard reference diagnostic methods by examining feces from experimentally and naturally infected and healthy calves. All the components of the test were highly specific (greater than 90%) and sensitive (BCV, 77%; K99, 93%; RV, 100%) when used in a format requiring short incubation steps at 20 C and visual recording of results.

Screening 1140 fifth graders for hypercholesterolemia: family history inadequate to predict results

Cholesterol screening was performed on 1140 fifth-grade students in Scottsdale, AZ, as part of a school-affiliated, health-education program. The goals were to determine whether family history of heart disease or high cholesterol can predict which children have high cholesterol levels and to examine the feasibility of screening large numbers of elementary school students. Among the children studied, the mean cholesterol level was 168.3 mg/dL (4.35 mmol/L), and 13 percent had cholesterol levels above 200 mg/dL (5.20 mmol/L). Fifty-four percent had a family member with high cholesterol or a heart attack before age 60 years, but 36 percent of the students with cholesterol levels greater than 200 mg/dL (5.20 mmol/L) had a negative family history. Family history was neither sensitive nor specific as a predictor of elevated cholesterol levels (sensitivity 0.64, specificity 0.47, and positive predictive value 0.16 for predicting cholesterol levels greater than 200 mg/dL [5.20 mmol/L]). Large numbers of children were screened safely and efficiently with good student and parental cooperation. Results of this study do not support the current recommendations to screen children for hypercholesterolemia based upon their family histories.

A peer review of a peer review organization

Under Medicare, one of the federally required objectives of peer review organizations is to reduce inappropriate and unnecessary admissions. We reevaluated 32 admissions approved and 32 denied by the Arizona peer review organization, Health Services Advisory Group (HSAG), in a "blind" manner to determine whether practicing physicians in the community agree with the local peer review organization. Overall, physicians at the Scottsdale Memorial Hospital (SMH) approved 72% of HSAG-approved and denied 61% of HSAG-denied admissions. Of the 64 admissions, 3 or 4 of 4 reviewers (2 physicians and 2 nurses) agreed with the HSAG decision in 38 (59%), but 2 or more reviewers disagreed in the other 26 (41%). Disagreement between the 2 physicians occurred in 48% of the cases and disagreement between the 2 nurses in 33%. Even among admissions denied by SMH physician reviewers, the physicians would have admitted 23% of those patients under similar circumstances. In 28% of the HSAG-denied admissions, the reviewing physicians thought that the patients' health care would have been compromised if the admissions had not taken place. Despite well-defined criteria for the appropriateness of hospital admissions, the review process remains subjective, with much disagreement between peer review organizations and practicing physicians.