Biomedical subjects

Lawrence E Williams

Publications and source records attributed to Lawrence E Williams.

17 recordsLinked to original sources

PubMed2006

A phase I trial of (90)Y-DOTA-anti-CEA chimeric T84.66 (cT84.66) radioimmunotherapy in patients with metastatic CEA-producing malignancies.

PURPOSE/OBJECTIVE: Previous radioimmunotherapy (RIT) clinical trials at this institution with (90)Y-labeled cT84.66 anti-CEA (carcinoembryonic antigen) evaluated the antibody conjugated to diethylenetriaminepentaacetic acid (DTPA). The aim of this phase I therapy trial was to evaluate cT84.66 conjugated to the macrocyclic chelate (90)Y-DOTA and labeled with (90)Y in a comparable patient population. EXPERIMENTAL DESIGN: Patients with metastatic CEA-producing cancers were entered in this trial. If antibody targeting to tumor was observed after the administration of (111)In-DTPA cT84.66, the patient then received the therapy infusion of (90)Y-DOTA-cT84.66 1 week later. Serial nuclear scans, blood and urine collections, and computed tomography (CT) scans were performed to assess antibody biodistribution, pharmacokinetics, toxicities, and antitumor effects. RESULTS: Thirteen (13) patients were treated in this study. Dose-limiting hematologic toxicity was experienced at initial starting activity levels of 12 and 8 mCi/m(2). Subsequent patients received systemic Ca-DTPA at 125 mg/m(2) every 12 hours for 3 days post-therapy to allow for a dose escalation to 16 mCi/m(2), where hematologic toxicity was observed with an associated maximum tolerated dose (MTD) of 13.4 mCi/m(2). Tumor doses ranged from 4.4 to 569 cGy/mCi, which translated to 97-12,500 cGy after a single infusion of (90)Y-DOTA-cT84.66. Human anti-chimeric antibody (HACA) response developed in 8 of 13 patients and prevented additional therapy in 4 patients. CONCLUSIONS: This study demonstrates the feasibility of using (90)Y-DOTA-cT84.66 for antibody-guided radiation therapy. Immunogenicity of the DOTA-conjugated cT84.66 antibody was not appreciably greater than that observed with (90)Y-DTPA-cT84.66 in previous trials. Dose-limiting hematopoietic toxicity with (90)Y-DOTA-cT84.66 decreased with Ca-DTPA infusions post-therapy and appears to be comparable to previously published results for (90)Y-DTPA-cT84.66. The highest antibody uptake and tumor doses were to small nodal lesions, which supports the predictions from preclinical and clinical data that RIT may be best applied in the minimal tumor burden setting.

Adult↗

PubMed2006

AAPM Task Group 108: PET and PET/CT shielding requirements.

The shielding of positron emission tomography (PET) and PET/CT (computed tomography) facilities presents special challenges. The 0.511 MeV annihilation photons associated with positron decay are much higher energy than other diagnostic radiations. As a result, barrier shielding may be required in floors and ceilings as well as adjacent walls. Since the patient becomes the radioactive source after the radiopharmaceutical has been administered, one has to consider the entire time that the subject remains in the clinic. In this report we present methods for estimating the shielding requirements for PET and PET/CT facilities. Information about the physical properties of the most commonly used clinical PET radionuclides is summarized, although the report primarily refers to fluorine-18. Typical PET imaging protocols are reviewed and exposure rates from patients are estimated including self-attenuation by body tissues and physical decay of the radionuclide. Examples of barrier calculations are presented for controlled and noncontrolled areas. Shielding for adjacent rooms with scintillation cameras is also discussed. Tables and graphs of estimated transmission factors for lead, steel, and concrete at 0.511 MeV are also included. Meeting the regulatory limits for uncontrolled areas can be an expensive proposition. Careful planning with the equipment vendor, facility architect, and a qualified medical physicist is necessary to produce a cost effective design while maintaining radiation safety standards.

Positron-Emission Tomography↗

PubMed2006

Cortisol metabolism in the Bolivian squirrel monkey (Saimiri boliviensis boliviensis).

New World squirrel monkeys (Saimiri spp.) have high circulating cortisol levels but normal electrolytes and blood pressures. The goal of the present study was to gain insight into adaptive mechanisms used by Bolivian squirrel monkeys to minimize the effects of high cortisol on mineralocorticoid receptor (MR) activity and electrolyte and water balance. Aldosterone levels in serum from 10 squirrel monkeys were 17.7 +/- 3.4 ng/dl (normal range in humans, 4 to 31 ng/dl), suggesting that squirrel monkeys do not exhibit a compensatory increase in aldosterone. The squirrel monkey MR was cloned and expressed in COS-7 cells and found to have similar responsiveness to cortisol and aldosterone as human MR, suggesting that squirrel monkey MR is not inherently less responsive to cortisol. To determine whether altered metabolism of cortisol might contribute to MR protection in squirrel monkeys, serum and urinary cortisol and cortisone were measured, and a comprehensive urinary corticosteroid metabolite profile was performed in samples from anesthetized and awake squirrel monkeys. The levels of cortisone exceeded those of cortisol in serum and urine, suggesting increased peripheral 11beta-hydroxysteroid dehydrogenase 2 activity in squirrel monkeys. In addition, a significant fraction (approximately 20%) of total corticosteroids excreted in the urine of squirrel monkeys appeared as 6beta-hydroxycortisol, compared with that in man (1%). Therefore, changes in cortisol metabolism likely contribute to adaptive mechanisms used by Bolivian squirrel monkeys to minimize effects of high cortisol.

Amino Acid Sequence↗

PubMed2005

Optimizing radiolabeled engineered anti-p185HER2 antibody fragments for in vivo imaging.

We have recently described the in vivo properties of an iodinated anti-p185HER2 engineered antibody fragment [minibody (scFv-C(H)3)2; 80 kDa], made from the internalizing 10H8 monoclonal antibody. Although the 10H8 minibody showed excellent binding to the target in vitro, only modest tumor uptake [5.6 +/- 1.7% injected dose per gram (ID/g) of tissue] was achieved in nude mice bearing MCF7/HER2 breast cancer tumors. Here, in an attempt to improve targeting, the 10H8 minibody was conjugated to 1,4,7,10-tetraazacyclododecane-N, N', N'', N'''-tetraacetic acid (DOTA), radiometal labeled, and evaluated in vivo. The tumor uptake of 111In-DOTA 10H8 minibody was 5.7 +/- 0.1% ID/g, similar to the radioiodinated 10H8 minibody. However, in addition to the expected liver clearance, the kidneys had unexpectedly high activity (34.0 +/- 4.0% ID/g). A minibody derived from a second anti-p185(HER2) antibody (trastuzumab; hu4D5v8) was also made. Tumor uptakes, evaluated by quantitative microPET using 64Cu-DOTA hu4D5v8 minibody, were 4.2 +/- 0.5% ID/g. Furthermore, in non-tumor-bearing mice, 111In-DOTA hu4D5v8 minibody exhibited similar elevated uptake in the kidneys (28.4 +/- 6.5% ID/g). Immunohistochemical staining of kidneys from non-tumor-bearing mice showed strong specific staining of the proximal tubules, and Western blot analysis of kidney lysate confirmed the presence of cross-reactive antigen. To further improve tumor uptake and normal tissue distribution, a larger hu4D5v8 fragment [(scFv-C(H)2-C(H)3)2; 105 kDa] was made, engineered to exhibit rapid clearance kinetics. This fragment, when evaluated by microPET, exhibited improved tumor targeting (12.2 +/- 2.4% ID/g) and reduced kidney uptake (13.1 +/- 1.5% ID/g). Thus, by manipulating the size and format of anti-p185(HER2) antibody fragments, the kidney activity was reduced and high or low expression of p185HER2 in xenografts could be distinguished by microPET imaging.

Animals↗

PubMed2005

Tailoring the pharmacokinetics and positron emission tomography imaging properties of anti-carcinoembryonic antigen single-chain Fv-Fc antibody fragments.

Antibody fragments are recognized as promising vehicles for delivery of imaging and therapeutic agents to tumor sites in vivo. The serum persistence of IgG1 and fragments with intact Fc region is controlled by the protective neonatal Fc receptor (FcRn) receptor. To modulate the half-life of engineered antibodies, we have mutated the Fc-FcRn binding site of chimeric anti-carcinoembryonic antigen (CEA) antibodies produced in a single-chain Fv-Fc format. The anti-CEA T84.66 single-chain Fv-Fc format wild-type and five mutants (I253A, H310A, H435Q, H435R, and H310A/H435Q, Kabat numbering system) expressed well in mammalian cell culture. After purification and characterization, effective in vitro antigen binding was shown by competition ELISA. Biodistribution studies in BALB/c mice using (125)I- and (131)I-labeled fragments revealed blood clearance rates from slowest to fastest as follows: wild-type > H435R > H435Q > I253A > H310A > H310A/H435Q. The terminal half-lives of the mutants ranged from 83.4 to 7.96 hours, whereas that of the wild-type was approximately 12 days. Additionally, (124)I-labeled wild-type, H435Q, I253A, H310A, and H310A/H435Q variants were evaluated in LS174T xenografted athymic mice by small animal positron emission tomography imaging, revealing localization to the CEA-positive xenografts. The slow clearing wild-type and H435Q constructs required longer to localize to the tumor and clear from the circulation. The I253A and H310A fragments showed intermediate behavior, whereas the H310A/H435Q variant quickly localized to the tumor site, rapidly cleared from the animal circulation and produced clear images. Thus, attenuating the Fc-FcRn interaction provides a way of controlling the antibody fragment serum half-life without compromising expression and tumor targeting.

Animals↗

PubMed2005

Population modeling for a captive squirrel monkey colony.

Population modeling for a squirrel monkey colony breeding in a captive laboratory environment was approached with the use of two different mathematical modeling techniques. Deterministic modeling was used initially on a spreadsheet to estimate future census figures for animals in various age/sex classes. Historical data were taken as input parameters for the model, combined with harvesting policies to calculate future population figures in the colony. This was followed by a more sophisticated stochastic model that is capable of accommodating random variations in biological phenomena, as well as smoothing out measurement errors. Point estimates (means) for input parameters used in the deterministic model are replaced by probability distributions fitted into historical data from colony records. With the use of Crystal Ball (Decisioneering, Inc., Denver, CO) software, user-selected distributions are embedded in appropriate cells in the spreadsheet model. A Monte Carlo simulation scheme running within the spreadsheet draws (on each cycle) random values for input parameters from the distribution embedded in each relevant cell, and thus generates output values for forecast variables. After several thousand runs, a distribution is formed at the output end representing estimates for population figures (forecast variables) in the form of probability distributions. Such distributions provide the decision-maker with a mathematical habitat for statistical analysis in a stochastic setting. In addition to providing standard statistical measures (e.g., mean, variance, and range) that describe the location and shape of the distribution, this approach offers the potential for investigating crucial issues such as conditions surrounding the plausibility of extinction.

Animals↗

PubMed2005

Age-related diffuse chronic telogen effluvium- type alopecia in female squirrel monkeys (Saimiri boliviensis boliviensis).

We investigated the diffuse alopecia affecting some female squirrel monkeys (Saimiri boliviensis boliviensis) housed in a breeding facility. We randomly selected 100 female and 10 male animals and performed a complete physical exam and a hair assessment on all animals; blood tests, trichograms, hair density; and skin biopsies in representative cases; and a dominance behavioral assessment of 50 animals. Hair coat was normal in 35 female monkeys and all 10 male animals. Of the 65 females with diffuse alopecia, 17 had mild, 22 moderate, and 26 severe hair loss. The alopecia group had a mean age of 9.6 +/- 0.6 years, whereas that of the normal group was 4.7 +/- 0.6 years (P < 0.05). The parity in the alopecia group was 4.2 +/- 0.6 but 2.0 +/- 0.6 (P < 0.05) in the normal group. There were no statistically significant differences in body weight, hemoglobin, blood urea nitrogen, serum glucose, liver aspartate aminotransaminase, or free thyroxine. The trichogram demonstrated 20.8% +/- 1.6% (mean +/- standard error) of telogen hairs in the alopecia group compared with 9.5% +/- 2.8% of the control group (P < 0.05). The hair density in the alopecia group was 52.8 +/- 4.1/cm2 and 79.6 +/- 14.3/cm2 in the control group. Skin biopsies in affected monkeys demonstrated increased telogen follicles, with no fibrosis or inflammation. There were no statistically significant differences in the dominance behavioral analysis. The findings are consistent with chronic telogen effluvium (CTE). A number of organic, behavioral, and dominance-related stress causes of CTE were excluded. CTE appears to be predominantly age-related in this population. CTE in female squirrel monkeys may serve as an animal model for human diffuse alopecia.

Age Factors↗

PubMed2004

Humanization of the anti-CEA T84.66 antibody based on crystal structure data.

Chimeric T84.66 (cT84.66) is a monoclonal antibody (mAb) of high specificity and affinity for the tumor-associated carcinoembryonic antigen (CEA). Radiolabeled cT84.66 has demonstrated utility in the clinic as a reagent for the radioimmunoscintigraphy and radioimmunotherapy of CEA-positive colorectal and breast malignancies. To extend the therapeutic efficacy of T84.66, humanization by complementary determining region (CDR) grafting was employed. CDR grafting is a well-established technique, though often a series of framework back-mutations is required to restore high affinity. Recently, the crystal structure of the T84.66 diabody (scFv dimer) derived from the murine T84.66 mAb was determined, facilitating the humanization process by the availability of crystal structure data for both the graft donor and graft acceptor. A search of the Protein Data Bank revealed close structural similarity (r.m.s.d. of 1.07 A) between the Fv of T84.66 and the Fv of 4D5v8, a humanized anti-p185HER2 antibody marketed as Herceptin (Trastuzumab). This resulted in two humanized versions of the T84.66 M5A and M5B mAbs that differed only in the number of murine residues present in the C-terminal half of CDR-H2. Biochemical analysis and animal biodistribution studies were conducted to evaluate the humanized mAbs. The M5A, M5B and cT84.66 mAbs showed sub-nanomolar affinity for CEA and as radiolabeled mAbs exhibited specific tumor localization in tumor bearing mice. The T84.66 M5A mAb was selected for clinical development due to a slightly higher tumor uptake and a larger content of human residues, and was renamed hT84.66. A limited-scale production and animal imaging study have demonstrated hT84.66's ability to support clinical trials. Planned clinical trials will determine the effective utilization of this structure-based approach in the development of a promising new therapeutic.

Amino Acid Sequence↗

PubMed2004

Pilot trial evaluating an 123I-labeled 80-kilodalton engineered anticarcinoembryonic antigen antibody fragment (cT84.66 minibody) in patients with colorectal cancer.

PURPOSE: The chimeric T84.66 (cT84.66) minibody is a novel engineered antibody construct (V(L)-linker-V(H)-C(H)3; 80 kDa) that demonstrates bivalent and high affinity (4 x 10(10) m(-1)) binding to carcinoembryonic antigen (CEA). The variable regions (V(L) and V(H)) assemble to form the antigen-combining sites, and the protein forms dimers through self-association of the C(H)3 domains. In animal models, the minibody demonstrated high tumor uptake, approaching that of some intact antibodies, substantially faster clearance than intact chimeric T84.66, and superior tumor-to-blood ratios compared with the cT84.66 F(ab')(2) fragment, making it attractive for further evaluation as an imaging and therapy agent. The purpose of this pilot clinical study was to determine whether (123)I-cT84.66 minibody demonstrated tumor targeting and was well tolerated as well as to begin to evaluate its biodistribution, pharmacokinetics, and immunogenicity in patients with colorectal cancer. EXPERIMENTAL DESIGN: Ten patients with biopsy-proven colorectal cancer (6 newly diagnosed, 1 pelvic recurrence, 3 limited metastatic disease) were entered on this study. Each received 5-10 mCi (1 mg) of (123)I-labeled minibody i.v. followed by serial nuclear scans and blood and urine sampling over the next 48-72 h. Surgery was performed immediately after the last nuclear scan. RESULTS: Tumor imaging was observed with (123)I-labeled minibody in seven of the eight patients who did not receive neoadjuvant therapy before surgery. Two patients received neoadjuvant radiation and chemotherapy, which significantly reduced tumor size before surgery and minibody infusion. At surgery, no tumor was detected in one patient and only a 2-mm focus was seen in the second patient. (123)I-labeled minibody tumor targeting was not seen in either of these pretreated patients. Mean serum residence time of the minibody was 29.8 h (range, 10.9-65.4 h). No drug-related adverse reactions were observed. All 10 patients were evaluated for immune responses to the minibody, with no significant responses observed. CONCLUSION: This pilot study represents one of the first clinical efforts to evaluate an engineered intermediate-molecular-mass radiolabeled antibody construct directed against CEA. cT84.66 minibody demonstrates tumor targeting to colorectal cancer and a faster clearance in comparison with intact antibodies, making it appropriate for further evaluation as an imaging and therapy agent. The mean residence time of the minibody in patients is longer than predicted from murine models. We therefore plan to further evaluate its biodistribution and pharmacokinetic properties with minibody labeled with a longer-lived radionuclide, such as (111)In.

Adult↗

PubMed2004

Characterization of engineered anti-p185HER-2 (scFv-CH3)2 antibody fragments (minibodies) for tumor targeting.

An engineered antibody fragment (minibody; scFv-C(H)3gamma(1) dimer, M(r) 80 000) specific for carcinoembryonic antigen (CEA) has previously demonstrated excellent tumor targeting coupled with rapid clearance in vivo. In this study, variable (V) genes from the anti- p185(HER-2) 10H8 antibody were similarly assembled and expressed. Four constructs were made: first, the V genes were assembled in both orientations (V(L)-linker-V(H) and V(H)-linker-V(L)) as single chain Fvs (scFvs). Then each scFv was fused to the human IgG1 C(H)3 domain, either by a two amino acid linker (ValGlu) that resulted in a non-covalent, hingeless minibody, or by IgG1 hinge and a GlySer linker peptide to produce a covalent, hinge-minibody. The constructs, expressed in NS0 mouse myeloma cells at levels of 20-60 mg/l, demonstrated binding to the human p185(HER-2) overexpressing breast cancer cell line, MCF7/HER2. Binding affinities (K(D) approximately 2-4 nM) were equivalent to that for the parental 10H8 mAb (K(D) approximately 1.6 nM). Radioiodinated 10H8 hinge-minibody was evaluated in athymic mice, bearing MCF7/HER2 xenografts. Maximum tumor uptake was 5.6 (+/-1.65)% injected dose/g (ID/g) at 12 h, which was lower than that of the anti-CEA minibody, whereas the blood clearance (beta-phase, 5.62 h) was similar. Thus, minibodies with different specificities display similar pharmacokinetics, while tumor uptake may vary depending on the antigen-antibody system.

Amino Acid Sequence↗

PubMed2004

Covalent disulfide-linked anti-CEA diabody allows site-specific conjugation and radiolabeling for tumor targeting applications.

An engineered anti-carcinoembryonic antigen (CEA) diabody (scFv dimer, 55 kDa) was previously constructed from the murine anti-CEA T84.66 antibody. Tumor targeting, imaging and biodistribution studies in nude mice bearing LS174T xenografts with radiolabeled anti-CEA diabody demonstrated rapid tumor uptake and fast blood clearance, which are favorable properties for an imaging agent. Current radiolabeling approaches result in random modification of the protein surface, which may impair immunoreactivity especially for smaller antibody fragments. Site-specific conjugation approaches can direct modifications to reactive groups located away from the binding site. Here, cysteine residues were introduced into the anti-CEA diabody at three different locations, to provide specific thiol groups for chemical modification. One version (with a C-terminal Gly-Gly-Cys) existed exclusively as a disulfide-bonded dimer. This cysteine-modified diabody (Cys-diabody) retained high binding to CEA and demonstrated tumor targeting and biodistribution properties identical to the non-covalent diabody. Furthermore, following reduction of the disulfide bond, the Cys-diabody could be chemically modified using a thiol-specific bifunctional chelating agent, for radiometal labeling. Thus, the Cys-diabody provides a covalently linked alternative to conventional diabodies, which can be reduced and modified site-specifically. This format will provide a versatile platform for targeting a variety of agents to CEA-positive tumors.

Animals↗

PubMed2003

A Phase I trial of 90Y-anti-carcinoembryonic antigen chimeric T84.66 radioimmunotherapy with 5-fluorouracil in patients with metastatic colorectal cancer.

PURPOSE: Targeted systemic radiation therapy using radiolabeled antibodies results in tumor doses sufficient to produce significant objective responses in the radiosensitive hematological malignancies. Although comparable doses to tumor are achieved with radioimmunotherapy (RIT) in solid tumors, results have been modest primarily because of their relative lack of radiosensitivity. For solid tumors, as with external beam radiotherapy, RIT should have a more important clinical role if combined with other systemic, potentially radiation-enhancing chemotherapy agents and if used as consolidative therapy in the minimal tumor burden setting. The primary objective of this trial was to evaluate the feasibility and toxicities of systemic 90Y-chimeric T84.66 (cT84.66) anti-carcinoembryonic antigen RIT in combination with continuous infusion 5-fluorouracil (5-FU). EXPERIMENTAL DESIGN: Patients with chemotherapy-refractory metastatic colorectal cancer were entered. The study was designed for each patient to receive 90Y-cT84.66 anti-carcinoembryonic antigen at 16.6 mCi/m2 as an i.v. bolus infusion combined with 5-FU delivered as a 5-day continuous infusion initiated 4 h before antibody infusion. Cohorts of patients were entered at 5-FU dose levels of 700, 800, 900, and 1000 mg/m2/day. Upon reaching the highest planned dose level of 5-FU, a final cohort received 90Y-cT84.66 at 20.6 mCi/m2 and 5-FU at 1000 mg/m2/day. For all patients, Ca-diethylenetriaminepentaacetic acid at 125 mg/m2 every 12 h was administered for the first 72 h after 90Y-cT84.66. Patients were eligible to receive up to three cycles of 90Y-cT84.66/5-FU every 6 weeks. RESULTS: Twenty-one patients were treated on this study. All had been heavily pretreated with 19 having previously received 5-FU and 16 having failed two to four chemotherapy regimens. A maximum-tolerated dose of 16.6 mCi/m2 90Y-cT84.66 combined with 1000 mg/m2/day 5-FU was reached. These dose levels are comparable with maximum-tolerated dose levels of each agent alone. Thirteen patients received one cycle and 8 patients two cycles of therapy. Hematopoietic toxicity was dose-limiting and reversible. RIT did not appear to increase nonhematopoietic toxicities associated with 5-FU. Two of 19 patients assayed developed a human anti-chimeric antibody immune response after the first cycle of therapy, which is significantly less than that observed in a previous trial evaluating 90Y-cT84.66 alone. No objective responses were observed. However, 11 patients with progressive disease entering the study demonstrated radiological stable disease of 3-8 months duration and 1 patient demonstrated a mixed response. CONCLUSIONS: Results from this trial are encouraging and demonstrate the feasibility and possible advantages of combining continuous infusion 5-FU with 90Y-cT84.66 RIT. The addition of 5-FU does not appear to significantly enhance hematological toxicities of the radiolabeled antibody. In addition, 5-FU reduces the development of human anti-chimeric antibody response, permitting multicycle therapy in a larger number of patients. Future efforts should continue to focus on integrating radiation therapy delivered by radiolabeled antibodies into established 5-FU regimens.

Antibodies, Monoclonal↗

PubMed2003

124I-labeled engineered anti-CEA minibodies and diabodies allow high-contrast, antigen-specific small-animal PET imaging of xenografts in athymic mice.

UNLABELLED: Prolonged clearance kinetics have hampered the development of intact antibodies as imaging agents, despite their ability to effectively deliver radionuclides to tumor targets in vivo. Genetically engineered antibody fragments display rapid, high-level tumor uptake coupled with rapid clearance from the circulation in the athymic mouse/LS174T xenograft model. The anticarcinoembryonic antigen (CEA) T84.66 minibody (single-chain Fv fragment [scFv]-C(H)3 dimer, 80 kDa) and T84.66 diabody (noncovalent dimer of scFv, 55 kDa) exhibit pharmacokinetics favorable for radioimmunoimaging. The present work evaluated the minibody or diabody labeled with (124)I, for imaging tumor-bearing mice using a high-resolution small-animal PET system. METHODS: Labeling was conducted with 0.2-0.3 mg of protein and 65-98 MBq (1.7-2.6 mCi) of (124)I using an iodination reagent. Radiolabeling efficiencies ranged from 33% to 88%, and immunoreactivity was 42% (diabody) or >90% (minibody). In vivo distribution was evaluated in athymic mice bearing paired LS174T human colon carcinoma (CEA-positive) and C6 rat glioma (CEA-negative) xenografts. Mice were injected via the tail vein with 1.9-3.1 MBq (53-85 microCi) of (124)I-minibody or with 3.1 MBq (85 microCi) of (124)I-diabody and imaged at 4 and 18 h by PET. Some mice were also imaged using (18)F-FDG 2 d before imaging with (124)I-minibody. RESULTS: PET images using (124)I-labeled minibody or diabody showed specific localization to the CEA-positive xenografts and relatively low activity elsewhere in the mice, particularly by 18 h. Target-to-background ratios for the LS174T tumors versus soft tissues using (124)I-minibody were 3.05 at 4 h and 11.03 at 18 h. Similar values were obtained for the (124)I-diabody (3.95 at 4 h and 10.93 at 18 h). These results were confirmed by direct counting of tissues after the final imaging. Marked reduction of normal tissue activity, especially in the abdominal region, resulted in high-contrast images at 18 h for the (124)I-anti-CEA diabody. CEA-positive tumors as small as 11 mg (<3 mm in diameter) could be imaged, and (124)I-anti-CEA minibodies, compared with (18)F-FDG, demonstrated highly specific localization. CONCLUSION: (124)I labeling of engineered antibody fragments provides a promising new class of tumor-specific probes for PET imaging of tumors and metastases.

Animals↗

PubMed2003

Studies of heart disease and failure in aged female squirrel monkeys (Saimiri sp.).

Lesions consistent with heart failure were found in 23 of 88 adult squirrel monkeys that died between 1995 and 1999 at the Squirrel Monkey Breeding and Research Resource (SMBRR). This provided a rationale for a study surveying aged animals in the SMBRR for normal cardiac characteristics, using echocardiography (ECHO) and electro-cardiogram. In the pilot study, ECHO and electrocardiography were performed on 59 healthy female squirrel monkeys aged 10 years or older and 39 five-year-old monkeys. Parameters were heart rate, P-wave duration and amplitude, and PR, QRS, and QT intervals (electrocardiography), and ejection fraction. Two animals with cardiomyopathy were identified and received similar testing. Advanced-study animals had the same measurements, plus left ventricular internal diameter-systole (LVIDs) and -diastole (LVIDd), left atrial diameter-diastole (LADd) and aortic root diameter-diastole (AoRDd) by use of ECHO. Significant differences were found between groups in LADd, and P-wave and QRS interval durations. In a clinical context, these differences were not considered to be substantial. Normal aged female squirrel monkeys had significant increases in heart dimension and longer P- and QRS-wave durations than did monkeys of a five-year-old control group, although the increases were not considered clinically relevant. This study documents myocardial dynamics in healthy saimiri and those with cardiomyopathy.

Aging↗

PubMed2002

The two types of correction of absorbed dose estimates for internal emitters.

BACKGROUND: Two types of correction for absorbed dose (D) estimates are described for clinical applications of internal emitters. The first is appropriate for legal and scientific reasons involving phantom-based estimates; the second is patient-specific and primarily intended for radioimmunotherapy (RIT). METHODS: The Medical Internal Radiation Dose (MIRD) relationship (D) = S A is used, where S is a geometric matrix factor and A is the integral of source organ activities. Internal consistency of the data and the size of organ systems in the humanoid phantom must be assured in both types of estimation. RESULTS: The first dose estimate correction (I) is one whereby computations refer to one or another standard (e.g., MIRD-type) phantom. In this case the S value remains as given, but the measured patient A data must be standardized. The correction factor is the phantom's ratio of organ mass to whole-body mass divided by the same ratio for the volunteer or patient. The second dose estimate correction (II) is patient-specific. While the A value is unchanged for this application, a correction term is provided for the phantom-derived S matrix. The dominant (nonpenetrating radiation) component of this correction factor can be obtained via the ratio of the patient to phantom organ masses. In both corrections, we recommend that true organ sizes, necessary in each method of estimation, be determined in a separate sequence of anatomic images. CONCLUSIONS: In both dose estimation corrections, true sizes of the patient's or volunteer's internal organs must be obtained. Correction due to organ mass size can be severalfold and is probably the dominant uncertainty in the internal emitter absorbed dose calculation process.

Absorption↗

PubMed2002

Choosing an optimal radioimmunotherapy dose for clinical response.

Clinical trials have documented the single-agent efficacy of radioimmunotherapy (RIT) in lymphoma, and several combination therapy studies are now in progress. RIT agents are currently becoming generally available for clinical use in lymphoma therapy. Solid tumors, which are notoriously less responsive to any single agent, have demonstrated clinically useful responses, albeit temporary, and multimodality studies have been instituted. However, a sincere debate continues regarding the basic parameters to be used to define appropriate therapeutic dosing when using this modality in clinical cancer care. It is a good time to reevaluate relevant dose response information from preclinical and clinical RIT. Preclinical studies have demonstrated abundant evidence of dose response in tumor and normal tissue in homogenous model systems; however, substantive variation occurs between the dose responses of tumors with low and variable (or shed) antigen expression, as well as between histologically different tumor models. Clinical studies of various heavily pretreated patient populations given several very different RIT pharmaceuticals have led to disparate conclusions regarding patient dosing methods and dosimetric predictions of toxicity and efficacy. Single-study data on previously untreated lymphoma patients with similar histology has demonstrated a correlation of imaging dosimetry with toxicity and tumor response. High-dose therapy with bone marrow support has also demonstrated a high tumor response rate and nonmarrow normal organ toxicities that correlate with the calculated dose to those organs from imaging. In iodine-131 ((131)I)--anti-CD20 studies, (131)I was demonstrated to have variable excretion, and estimated total-body radiation dose from tracer study proved a predictive surrogate for marrow toxicity. Yttrium-90 ((90)Y)--anti-CD20, which has little (90)Y excretion from the body, demonstrated the injected dose per body weight to be more predictive of marrow toxicity than indium-111 ((111)In) tracer dosimetry methods in heavily pretreated patients, and showed maximal safety with standard mCi/kg therapy dosing. Variations in clinical RIT choices, dosing methods, and dosimetry methods emphasize the need to review the relevant information to date. Future clinical trial designs, the sophistication of dosimetry, treatment planning, and clinical treatment decisions should all be focused on achieving the best benefit-risk relationship for each patient.

Decision Support Systems, Clinical↗

PubMedDate not supplied

Improved biodistribution and radioimmunoimaging with poly(ethylene glycol)-DOTA-conjugated anti-CEA diabody.

Diabodies are single chain antibody fragments (scFvs) that spontaneously form bivalent dimers of molecular size 50-55000. Radiolabeled diabodies are almost ideal tumor targeting agents due to their high avidity (bivalent) binding to tumor antigens and small size (50-55000) that leads to improved tumor-to-blood ratio compared to intact antibodies (150000). However, due to their high retention and metabolism in the kidney, radioiodine is the current radiolabel of choice for diabodies since radioiodine is rapidly excreted from the kidney once metabolized. We have previously shown that 111In-DOTA-diabody gives higher tumor uptake in nude mouse xenografts than 125I-diabody, but has extremely high kidney retention since its 111In-labeled metabolites are retained by and only slowly excreted from the kidney. When a diabody is conjugated to a bifunctional PEG-3400 derivative followed by reaction with cysteinyl-DOTA, the resulting product has an apparent molecular size of 75000 and a Stokes radius of 35 angstroms on size exclusion chromatography, compared to a Stokes radius of 25 angstroms for intact diabody. When radiolabeled, the conjugate gives high yields of 111In-labeled product, retains high immunoreactivity, and gives improved biodistributions (30-40%ID/g, 12-48 h) compared to 111In-DOTA-diabody (12-13%ID/g, 6-12 h). We show that the improved biodistribution is due to an increase in Stokes radius caused by the linear PEG-3400 since conjugation of diabody with multiple (PEG)12 linkers followed by reaction with cysteinyl-DOTA does not reduce kidney accumulation. We also show that 111In-cysteinyl-DOTA-PEG3400-diabody gives excellent tumor images in the nude mouse xenograft model and that 125I-PEG3400-diabody gives equivalent images to 125I-minibody (molecular size, 80000), but improved tumor-to-liver ratios, suggesting that this imaging agent can be used to image liver metastases.

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