Dermanyssus gallinae and chicken egg production: impact, management, and a predicted compatibility matrix for integrated approaches.

The poultry red mite, Dermanyssus gallinae, is a worldwide threat to egg production and animal and human welfare. This mite is also a potential vector for several significant diseases. EU regulation that forbids the use of conventional cages for egg-laying hens may favour the growth of D. gallinae, a species known to thrive in more complex housing systems. Current control measures emphasize the use of chemical acaricides, which may have limited efficacy on D. gallinae considering its temporary blood-feeding behaviour. In integrated pest management (IPM), two or more compatible measures targeting physical, environmental, and/or biological aspects could be judiciously combined to enhance the effectiveness against D. gallinae infestation. To inform current and future IPM for D. gallinae, a compatibility matrix is proposed to guide the selection of control measures for field application.

The genome of the simian and human malaria parasite Plasmodium knowlesi.

Plasmodium knowlesi is an intracellular malaria parasite whose natural vertebrate host is Macaca fascicularis (the 'kra' monkey); however, it is now increasingly recognized as a significant cause of human malaria, particularly in southeast Asia. Plasmodium knowlesi was the first malaria parasite species in which antigenic variation was demonstrated, and it has a close phylogenetic relationship to Plasmodium vivax, the second most important species of human malaria parasite (reviewed in ref. 4). Despite their relatedness, there are important phenotypic differences between them, such as host blood cell preference, absence of a dormant liver stage or 'hypnozoite' in P. knowlesi, and length of the asexual cycle (reviewed in ref. 4). Here we present an analysis of the P. knowlesi (H strain, Pk1(A+) clone) nuclear genome sequence. This is the first monkey malaria parasite genome to be described, and it provides an opportunity for comparison with the recently completed P. vivax genome and other sequenced Plasmodium genomes. In contrast to other Plasmodium genomes, putative variant antigen families are dispersed throughout the genome and are associated with intrachromosomal telomere repeats. One of these families, the KIRs, contains sequences that collectively match over one-half of the host CD99 extracellular domain, which may represent an unusual form of molecular mimicry.

Radiolabeled anti-CD33 monoclonal antibody M195 for myeloid leukemias.

M195, a mouse monoclonal antibody reactive with the early myeloid antigen CD33, has been shown to target leukemia cells in patients and to reduce large leukemic burdens when labeled with 131I. A complementarity-determining region-grafted, humanized version (HuM195) has demonstrated similar targeting of leukemia cells without immunogenicity. We have studied two applications of therapy with 131I-M195. First, to intensify therapy prior to bone marrow transplantation (BMT), we combined 131I-M195 with busulfan and cyclophosphamide. Fifteen patients received first BMT for relapsed or refractory acute myelogenous leukemia or accelerated or blastic chronic myelogenous leukemia; four received second BMT for relapsed chronic or accelerated chronic myelogenous leukemia. Doses of 131I-M195 ranged from 120 to 230 mCi/m2. Few toxicities could be attributed to 131I-M195 therapy, and all patients engrafted. Eighteen patients achieved complete remission. Among those patients receiving first BMT, three have remained in unmaintained remission for 18+ to 29+ months. Six patients relapsed, including one with isolated central nervous system disease 32 months after BMT. Ten patients died in complete remission of transplant-related complications. Second, we studied whether 131I-M195 could reduce minimal residual disease and prolong remission and survival durations safely in patients with relapsed acute promyelocytic leukemia after they attained remission with all-trans-retinoic acid. Seven patients were treated with either 50 or 70 mCi/m2 131I-M195. Toxicity was limited to myelosuppression. As a measure of minimal residual disease, we monitored PML/RAR-alpha mRNA by reverse transcription PCR. Six patients had positive reverse transcription PCR assays prior to receiving 131I-M195; two converted transiently to negative. Median disease-free survival and overall survival of the seven patients were 8 (range, 3-14.5) months and 28 (range, 5.5-43+) months, respectively. This regimen compares favorably with others for relapsed acute promyelocytic leukemia. In an effort to avoid nonspecific cytotoxicity associated with 131I in future trials for minimal residual disease, we have conjugated short-range, alpha particle-emitting radioisotopes to HuM195 using a bifunctional chelate, 2-(p-isothiocyanatobenzyl)-cyclohexyldiethyl-enetriaminep entaacetic acid, with high efficiency and specific activities. 212Bi-HuM195 has demonstrated dose- and specific activity-dependent killing of HL60 cells in vitro. Injection of 213Bi-HuM195 into healthy BALB/c mice produced no effects on weight or viability.

Imaging brain tumor proliferative activity with [124I]iododeoxyuridine.

Iododeoxyuridine (IUdR) uptake and retention was imaged by positron emission tomography (PET) at 0-48 min and 24 h after administration of 28.0-64.4 MBq (0.76-1.74 mCi) of [124I]IUdR in 20 patients with brain tumors, including meningiomas and gliomas. The PET images were directly compared with gadolinium contrast-enhanced or T2-weighted magnetic resonance images. Estimates for IUdR-DNA incorporation in tumor tissue (Ki) required pharmacokinetic modeling and fitting of the 0-48 min dynamically acquired data to correct the 24-h image data for residual, nonincorporated radioactivity that did not clear from the tissue during the 24-h period after IUdR injection. Standard uptake values (SUVs) and tumor:brain activity ratios (Tm:Br) were also calculated from the 24-h image data. The Ki, SUV, and Tm/Br values were related to tumor type and grade, tumor labeling index, and survival after the PET scan. The plasma half-life of [124I]IUdR was short (2-3 min), and the arterial plasma input function was similar between patients (48 +/- 12 SUV*min). Plasma clearance of the major radiolabeled metabolite ([124I]iodide) varied somewhat between patients and was markedly prolonged in one patient with renal insufficiency. It was apparent from our analysis that a sizable fraction (15-93%) of residual nonincorporated radioactivity (largely [124I]iodide) remained in the tumors after the 24-h washout period, and this fraction varied between the different tumor groups. Because the SUV and Tm:Br ratio values reflect both IUdR-DNA incorporated and exchangeable nonincorporated radioactivity, any residual nonincorporated radioactivity will amplify their values and distort their significance and interpretation. This was particularly apparent in the meningioma and glioblastoma multiforme groups of tumors. Mean tumor Ki values ranged between 0.5 +/- 0.9 (meningiomas) and 3.9 +/- 2.3 microl/min/g (peak value for glioblastoma multiforme, GBM). Comparable SUV and Tm:Br values at 24 h ranged from 0.13 +/- 0.03 to 0.29 +/- 0.19 and from 2.0 +/- 0.6 to 6.1 +/- 1.5 for meningiomas and peak GBMs, respectively. Thus, the range of values was much greater for Ki (approximately 8-fold) compared with that for SUV (approximately 2.2-fold) and Tm:Br (approximately 3-fold). The expected relationships between Ki, SUV, and Tm:Br and other measures of tumor proliferation (tumor type and grade, labeling index, and patient survival) were observed. However, greater image specificity and significance of the SUV and Tm:Br values would be obtained by achieving greater washout and clearance of the exchangeable fraction of residual (background) radioactivity in the tumors, i.e., by increased hydration and urinary clearance and possibly by imaging later than 24 h after [124I]IUdR administration.

An alpha-particle emitting antibody ([213Bi]J591) for radioimmunotherapy of prostate cancer.

A novel alpha-particle emitting monoclonal antibody construct targeting the external domain of prostate-specific membrane antigen (PSMA) was prepared and evaluated in vitro and in vivo. The chelating agent, N-[2-amino-3-(p-isothiocyanatophen-yl)propyl]-trans-cyclohexane-1, 2-diamine-N,N',N',N'',N''-pentaacetic acid, was appended to J591 monoclonal antibody to stably bind the 213Bi radiometal ion. Bismuth-213 is a short-lived (t 1/2 = 46 min) radionuclide that emits high energy alpha-particles with an effective range of 0.07-0.10 mm that are ideally suited to treating single-celled neoplasms and micrometastatic carcinomas. The LNCaP prostate cancer cell line had an estimated 180,000 molecules of PSMA per cell; J591 bound to PSMA with a 3-nM affinity. After binding, the radiolabeled construct-antigen complex was rapidly internalized into the cell, carrying the radiometal inside. [213Bi]J591 was specifically cytotoxic to LNCaP. The LD50 value of [213Bi]J591 was 220 nCi/ml at a specific activity of 6.4 Ci/g. The potency and specificity of [213Bi]J591 directed against LNCaP spheroids, an in vitro model for micrometastatic cancer, also was investigated. [213Bi]J591 effectively stopped growth of LNCaP spheroids relative to an equivalent dose of the irrelevant control [213Bi]HuM195 or unlabeled J591. Cytotoxicity experiments in vivo were carried out in an athymic nude mouse model with an i.m. xenograft of LNCaP cells. [213Bi]J591 was able to significantly improve (P < 0.0031) median tumor-free survival (54 days) in these experiments relative to treatment with irrelevant control [213Bi]HuM195 (33 days), or no treatment (31 days). Prostate-specific antigen (PSA) was also specifically reduced in treated animals. At day 51, mean PSA values were 104 ng/ml +/- 54 ng/ml (n = 4, untreated animals), 66 ng/ml +/- 16 ng/ml (n = 6, animals treated with [213Bi]HuM195), and 28 ng/ml +/- 22 ng/ml (n = 6, animals treated with [213Bi]J591). The reduction of PSA levels in mice treated with [213Bi]J591 relative to mice treated with [213Bi]HuM195 and untreated control animals was significant with P < 0.007 and P < 0.0136, respectively. In conclusion, a novel [213Bi]-radiolabeled J591 has been constructed that selectively delivers alpha-particles to prostate cancer cells for potent and specific killing in vitro and in vivo.

Phase I/II study of iodine 131-labeled monoclonal antibody A33 in patients with advanced colon cancer.

PURPOSE: A phase I/II study was designed to determine the maximum-tolerated dose (MTD) of iodine 131-labeled monoclonal antibody (mAb) A33 (131I-mAb A33) administered intravenously, its limiting organ toxicity, and its radioisotope retention in tumors, and to develop preliminary evidence of antitumor activity. PATIENTS AND METHODS: Patients (N = 23) with colorectal cancer who had failed to respond to conventional chemotherapy but had not received prior radiotherapy were treated with escalating doses of 131I-mAb A33. Three or more patients were entered at each dose level, starting at 30 mCi/m2, with increments of 15 mCi/m2 to a maximal dose of 90 mCi/m2. Radiolabeling was performed to maintain a specific activity of 30 mCi/m2/4 mg mAb A33 (projected maximum, 15 mCi/mg). Patients were under strict isolation precautions until whole-body radiation levels decreased to less than 5 mrem/h at 1 m. Serial radioimmunoscintigrams were performed in some cases for up to 3 weeks after 131I-mAb A33 administration. RESULTS: All 20 patients with radiologic evidence of disease showed localization of radioisotope to sites of disease. Two patients with elevated carcinoembryonic antigen (CEA) levels and negative radiologic tests did not have positive antibody scans. One patient with a small-bowel cancer also had a negative antibody scan. The major toxicity was hematologic and was more pronounced in patients with compromised bone marrow due to prior chemotherapy. Of five patients who received 78 to 84 mCi/m2 131I-mAb A33, one had grade 3 and one grade 4 toxicity; of six patients treated with 86 to 94 mCi/m2 131I-mAb A33, two had grade 4 and one grade 1 toxicity. The MTD was determined to be 75 mCi/m2 in these heavily pretreated patients. Although the isotope showed variable uptake in the normal bowel, gastrointestinal symptoms were mild (n = 8) or absent. No major responses were observed; however, three patients had evidence of mixed responses, and CEA levels decreased in two patients without clinical or radiologic measurable disease. Immunoreactivity of radiolabeled mAb A33 decreased at the highest dose levels in preparations in which specific activity exceeded 18 mCi/mg. CONCLUSION: The A33 antigen appears to be a promising target for radioimmunotherapy of colon cancer. The modest antitumor activity of 131I-mAb A33 in heavily pretreated patients is encouraging because of its lack of toxicity in the bowel, the only antigen-positive normal tissue.

A phase I trial of monoclonal antibody M195 in acute myelogenous leukemia: specific bone marrow targeting and internalization of radionuclide.

Ten patients with myeloid leukemias were treated in a phase I trial with escalating doses of mouse monoclonal antibody (mAb) M195, reactive with CD33, a glycoprotein found on myeloid leukemia blasts and early hematopoietic progenitor cells but not on normal stem cells. M195 was trace-labeled with iodine-131 (131I) to allow detailed pharmacokinetic and dosimetric studies by serial sampling of blood and bone marrow and whole-body gamma-camera imaging. Total doses up to 76 mg were administered safely without immediate adverse effects. Absorption of M195 onto targets in vivo was demonstrated by biopsy, pharmacology, flow cytometry, and imaging; saturation of available sites occurred at doses greater than or equal to 5 mg/m2. The entire bone marrow was specifically and clearly imaged beginning within hours after injection; optimal imaging occurred at the lowest dose. Bone marrow biopsies demonstrated significant dose-related uptake of M195 as early as 1 hour after infusion in all patients, with the majority of the dose found in the marrow. Tumor regressions were not observed. An estimated 0.33 to 1.0 rad/mCi 131I was delivered to the whole body, 1.1 to 6.1 rad/mCi was delivered to the plasma, and up to 34 rad/mCi was delivered to the red marrow compartment. 131I-M195 was rapidly modulated, with a majority of the bound immunoglobulin G (IgG) being internalized into target cells in vivo. These data indicate that whole bone marrow ablative doses of 131I-M195 can be expected. The rapid, specific, and quantitative delivery to the bone marrow and the efficient internalization of M195 into target cells in vivo also suggest that the delivery of other isotopes such as auger or alpha emitters, toxins, or other biologically important molecules into either leukemia cells or normal hematopoietic progenitor cells may be feasible.

Dose-escalation trial of M195 labeled with iodine 131 for cytoreduction and marrow ablation in relapsed or refractory myeloid leukemias.

PURPOSE: Mouse monoclonal antibody (mAb) M195 (anti-CD33) is reactive with most myeloid leukemia cells, monocytes, and hematopoietic progenitors, but not with other hematopoietic cells or stem cells nor with nonhematopoietic human tissues. A therapeutic dose-escalation study of M195 labeled with iodine 131 was conducted in patients with relapsed or refractory myeloid leukemias. METHODS: Twenty-four patients (16 relapsed or refractory acute myeloid leukemias, five blastic myelodysplastic syndromes [MDS], two chemotherapy-related secondary leukemias, and one blastic chronic myelogenous leukemia [CML]), including seven who had failed to respond to prior bone marrow transplantation (BMT), received from 50 mCi/m2 to 210 mCi/m2 of 131I-M195 in divided doses. RESULTS: In 22 patients, whole-body gamma-imaging demonstrated marked uptake of antibody into all areas of bone marrow. Twenty-three patients (96%) demonstrated decreases in peripheral-blood cell counts, with decreased percentage of bone marrow blasts seen in 83% of cases. Eighty-nine percent of bone marrow biopsies examined quantitatively demonstrated substantial decreases in the number of blasts, with greater than 99% of blasts killed in some patients. The two cases that failed to demonstrate leukemic cytoreduction occurred in the first two dose levels. For 131I doses of 135 mCi/m2 or greater, pancytopenia was profound and lasted for at least 12 days. Eight patients had sufficient marrow cytoreduction to proceed to BMT. Three of these achieved marrow remission, one of 6+, and one of 9 months' duration. Two patients in blastic phase temporarily reverted to their original myelodysplastic states. Thirty-seven percent of assessable patients developed human anti-mouse antibody (HAMA). In two patients with HAMA who were re-treated, plasma 131I-M195 levels could not be maintained and no therapeutic effect resulted. Significant nonhematologic toxicity (hepatic) was seen in one patient and the maximum-tolerated dose (MTD) was not reached. CONCLUSION: These data suggest that safe leukemic cytoreduction can be achieved with 131I-M195 even in multiply relapsed or chemotherapy-refractory leukemias. This agent may be useful as part of a preparative regimen for BMT.

Antibody targeting in metastatic colon cancer: a phase I study of monoclonal antibody F19 against a cell-surface protein of reactive tumor stromal fibroblasts.

PURPOSE: To define the toxicity, imaging, and biodistribution characteristics of iodine 131-labeled monoclonal antibody F19 (131I-mAbF19). MAbF19 recognizes the fibroblast activation protein (FAP), a cell-surface glycoprotein not present in most normal tissues, but abundantly expressed by reactive stromal fibroblasts of epithelial cancers, including more than 95% of primary and metastatic colorectal carcinomas. PATIENTS AND METHODS: 131I-mAbF19 was administered intravenously to 17 patients with hepatic metastases from colorectal carcinoma who were scheduled for resection of localized metastases or insertion of hepatic artery catheter for regional chemotherapy. Seven to 8 days before surgery, patients received 131I-mAbF19 at three dose levels, with at least four patients entered at each level. RESULTS: No toxicity associated with intravenous 131I-mAbF19 administration was observed. Tumor images were obtained on planar and single-photon emission tomography (SPECT) scans in 15 of 17 patients with hepatic metastases, tumor-infiltrated portal lymph nodes, and/or recurrent pelvic disease. The smallest lesion visualized was 1 cm in diameter. The optimal time for tumor imaging was 3 to 5 days after 131I-mAbF19 administration. The use of image registration techniques allowed precise anatomic localization of 131I-mAbF19 accumulation. Immunohistochemical analysis of biopsy tissues showed expression of FAP in the tumor stroma (but not in normal liver) in all patients studied and confirmed that the FAP-positive tumor stromal fibroblasts were interposed between the tumor capillaries and the malignant colon epithelial cells. At the time of surgery, tumor-to-liver ratios up to 21:1 and tumor-to-serum ratios up to 9:1 were obtained. The fraction of the injected 131I-mAbF19 dose per gram tumor (%ID/g tumor) localized to hepatic metastases at the time of surgery ranged from 0.001% to 0.016%. CONCLUSION: The FAP tumor fibroblast antigen is highly expressed in primary and metastatic colorectal carcinomas and shows limited expression in normal adult tissues. This highly selective expression pattern allows imaging of colorectal carcinoma lesions as small as 1 cm in diameter on 131I-mAbF19 scans. Because of the consistent presence of FAP in the stroma of epithelial cancers and the accessibility of FAP-positive tumor stromal fibroblasts to circulating monoclonal antibodies (mAbs), this study suggests possible diagnostic and therapeutic applications of humanized mAbF19 and mAbF19 constructs with novel immune and nonimmune effector functions.

Antibody localization in human renal cell carcinoma: a phase I study of monoclonal antibody G250.

PURPOSE: To define the imaging and biodistribution characteristics of iodine 131-labeled monoclonal antibody (mAb) G250 (131I-mAbG250), which recognizes a cell-surface antigen expressed by human renal cell carcinoma (RCC). PATIENTS AND METHODS: G250 is a cell-surface antigen recognized by mAbG250 expressed by RCC but not detected in normal kidney. Clear-cell RCC, the most frequent form of RCC, shows homogeneous expression of G250, whereas non-clear-cell RCC and cancers derived from other organs generally do not express G250. Expression in normal tissues is highly restricted and limited to large bile ducts and gastric epithelium. 131I-mAbG250 was administered intravenously (IV) to 16 patients with RCC 7 to 8 days before surgery at five dose levels, with at least three patients entered at each dose level. RESULTS: Clear tumor images were observed in 12 patients with G250-positive tumors and in one of three patients with G250-negative tumors. Imaged lesions in the peritoneal cavity were confirmed at surgery. The smallest lesion visualized was 8 mm in diameter. The specificity of 131I-mAbG250 localization to tumor tissue was established by radioactivity measurements, autoradiography, and immunohistochemistry of biopsied tissues, and technetium 99-human serum albumin blood-flow studies. The fraction of the injected 131I-mAbG250 dose per gram tumor (%ID/g tumor) localized in G250-positive tumors showed a broad range, but reached levels as high as 0.02% to 0.12%. CONCLUSION: 131I-mAbG250 localized specifically to G250 antigen-positive RCC and seems to have considerable potential as an imaging agent in RCC patients. 131I-mAbG250 uptake in the tumors, relative as well as absolute, are among the highest reported for tumor biopsies obtained 8 days after IV mAb administration. Based on the specific localization and high accumulation, mAb G250 may have therapeutic potential.

Phase I/II study of iodine 125-labeled monoclonal antibody A33 in patients with advanced colon cancer.

PURPOSE: A phase I/II study was designed to determine the maximum-tolerated dose (MTD) of iodine 125-labeled monoclonal antibody A33 (125I-mAb A33), its limiting organ toxicity, and the uptake and retention of radioactivity in tumor lesions. PATIENTS AND METHODS: Patients (N = 21) with advanced chemotherapy-resistant colon cancer who had not received prior radiotherapy were treated with a single 125I-mAb A33 dose. 125I doses were escalated from 50 to 350 mCi/m2 in 50-mCi/m2 increments. Radioimmunoscintigrams were performed for up to 6 weeks after 125I-mAb A33 administration. RESULTS: All 20 patients with radiologic evidence of disease showed localization of 125I to sites of disease. Twelve of 14 patients, who underwent imaging studies 4 to 6 weeks after antibody administration, had sufficient isotope retention in tumor lesions to make external imaging possible. No major toxicity was observed, except in one patient with prior exposure to mitomycin who developed transient grade 3 thrombocytopenia. Although the isotope showed variable uptake in the normal bowel, gastrointestinal symptoms were mild or absent, and in no case did stools become guaiac-positive. The MTD was not reached at 125I doses up to 350 mCi/m2. However, cytotoxicity assays demonstrated that patients treated with the highest dose had sufficiently high serum levels of 125I-mAb A33 to lyse colon cancer cells in vitro. Among 21 patients, carcinoembryonic antigen (CEA) levels returned to normal in one patient and decreased by 35% and 23%, respectively, in two patients; one additional patient had a mixed response on computed tomography. Additional, significant responses were observed in those patients treated with chemotherapy [carmustine [BCNU], vincristine, flourouracil, and streptozocin [BOF-Strep]) after completion of the 125I-mAb A33 study. CONCLUSION: Low-energy emission radioimmunotherapy with doses of up to 350 mCi/m2 of 125I-mAb A33 did not cause bowel or bone marrow toxicity. The modest antitumor activity in these heavily pretreated patients is encouraging because of lack of toxicity at the doses studied. The long radioactivity retention in tumors suggests that isotopes with a long half-life may have a therapeutic advantage, based on calculated dose delivery to tumor versus normal tissue. Due to the low bone marrow dose, further 125I trials with humanized mAb A33 are warranted, and controlled studies must be conducted to evaluate the combination of radioimmunotherapy and chemotherapy.

Sequential targeted therapy for relapsed acute promyelocytic leukemia with all-trans retinoic acid and anti-CD33 monoclonal antibody M195.

Acute promyelocytic leukemia (APL) provides a model to examine the sequential use of selective oncogene product-targeted and lineage-targeted agents. All-trans retinoic acid (RA) has been shown to produce brief remissions by a novel differentiating mechanism in most patients with APL. M195, a mouse monoclonal antibody (moAb) reactive with the cell-surface antigen CD33, can target myeloid leukemia cells in patients and reduce large leukemic burdens when labeled with 131I. We studied whether 131I-M195 could safely reduce minimal residual disease and prolong remission and survival durations in patients with relapsed APL after they had attained remission with all-trans RA. Seven patients with relapsed APL in second remission were treated with either 70 (n = 2) or 50 (n = 5) mCi/m2 of 131I-M195. As a measure of minimal residual disease, we serially monitored PML/RAR-alpha mRNA by a reverse transcription polymerase chain reaction (RT-PCR) assay. There was no immediate toxicity. Late toxicity was limited to myelosuppression, but no episodes of febrile neutropenia were seen. Six patients had detectable PML/RAR-alpha mRNA after all-trans RA therapy; two had single negative RT-PCR determinations following 131I-M195. Median disease-free survival of the seven patients was 8 months (range 3-14.5). Four patients with median follow-up of 24 months remain alive, and median overall survival exceeds 21+ months (range 5.5-33+). This regimen based on targeted therapy compares favorably to other approaches for the treatment of relapsed APL, including that used in the immediately preceding trial in which patients were induced into remission and maintained with all-trans RA, as well as other chemotherapy-based regimens. These data support further study of moAb-based therapy for minimal residual disease in acute leukemia.

Pilot radioimmunotherapy trial with 131I-labeled murine monoclonal antibody CC49 and deoxyspergualin in metastatic colon carcinoma.

An antimouse immune response is invariable following administration of murine monoclonal antibody (mAb), precluding effective multidose therapy. In advanced colorectal cancer patients, we carried out a pilot study with multiple doses of 131I-labeled CC49 administered with deoxyspergualin (DSG), an immunomodulator, to determine its effect on immune response. Cumulative toxicity and efficacy were also evaluated. Six patients with tumor-associated glycoprotein 72-expressing colorectal cancer were treated i.v. with 15 mCi/m2 131I-labeled to 20 mg mAb CC49 biweekly, along with concurrent DSG 200 mg/m2 daily for 5 days, for a maximum of four courses. None had received prior murine mAbs. All patients had targeting of radioactivity to known tumor sites following initial infusion. Four of six patients received all four courses of therapy, three without any acute side effects. In these patients, there was no change in serum clearance with variable tumor targeting following repeat infusions. Two patients had

Distribution of radiolabeled monoclonal antibody MX35 F(ab')2 in tissue samples by storage phosphor screen image analysis: evaluation of antibody localization to micrometastatic disease in epithelial ovarian cancer.

Our objective was to quantify the targeting of the monoclonal antibody (mAb) MX35 F(ab')2 to micrometastatic epithelial ovarian cancer. This mAb detects a Mr 95,000 glycoprotein with homogeneous distribution on 80% of ovarian tumor specimens. Six patients with minimal residual disease from an imaging trial were injected with 2 or 10 mg of 131I- and 125I-labeled mAb MX35 F(ab')2. Biopsied samples were removed at second-look laparotomy 1-5 days post-i.v. or -i.p. infusion of antibody. Serial cryostat sections were stained by indirect immunoperoxidase method for antigen distribution and exposed to storage phosphor screens for quantitative autoradiography. Coregistration of tumor histology, antigen expression, and radionuclide distribution demonstrated specific localization in micrometastatic tumor foci (50 micrometer to 1 mm) found within tissue stroma. The radiolabeled antibody uptake determined by well scintillation counts ranged between 5.2 and 223.5 x 10(-4) percentage of injected dose/g of tumor tissue for 131I. Specific localization of mAb in tumor was determined by tumor:normal tissue (fat) ratios ranging from 0.9:1 to 35.9:1 for 131I. The high resolution and linear response of the storage phosphor screen imager was used to estimate the radionuclide activity localized in each micrometastatic site. Quantitation of phosphor screen response revealed microCi/g values of 0.026-0.341 for normal tissue and 0.184-6.092 for tumor biopsies, evaluated 4 or 5 days post-antibody injection. The tumor:normal tissue (adjacent to tumor) ratios were between 1 and 4 times greater using the phosphor screen method than well counter measurements, but even larger variations of ratios up to 20:1 were observed between tumor cell foci and stromal cells within the same tissue section. This study has demonstrated that mAb MX35 F(ab')2 localizes to the micrometastatic ovarian carcinoma deposits within the peritoneal cavity. The dosimetry results suggest a therapeutic potential for this antibody in patients with minimal residual disease (<5 mm).

Phase I/II radioimmunotherapy trial with iodine-131-labeled monoclonal antibody G250 in metastatic renal cell carcinoma.

This Phase I/II radioimmunotherapy study was carried out to determine the maximum tolerated dose (MTD) and therapeutic potential of 131I-G250. Thirty-three patients with measurable metastatic renal cell carcinoma were treated. Groups of at least three patients received escalating amounts of 1311I (30, 45, 60, 75, and 90 mCi/m2) labeled to 10 mg of mouse monoclonal antibody G250, administered as a single i.v. infusion. Fifteen patients were studied at the MTD of activity. No patient had received prior significant radiotherapy; one had received prior G250. Whole-body scintigrams and single-photon emission computed tomography images were obtained in all patients. There was targeting of radioactivity to all known tumor sites that were > or =2 cm. Reversible liver function test abnormalities were observed in the majority of patients (27 of 33 patients). There was no correlation between the amount of 131I administered or hepatic absorbed radiation dose (median, 0.073 Gy/mCi) and the extent or nature of hepatic toxicity. Two of the first six patients at 90 mCi/m2 had grade > or =3 thrombocytopenia; the MTD was determined to be 90 mCi/m2 131I. Hematological toxicity was correlated with whole-body absorbed radiation dose. All patients developed human antimouse antibodies within 4 weeks posttherapy; retreatment was, therefore, not possible. Seventeen of 33 evaluable patients had stable disease. There were no major responses. On the basis of external imaging, 131I-labeled mouse monoclonal antibody G250 showed excellent localization to all tumors that were > or =2 cm. Seventeen of 33 patients had stable disease, with tumor shrinkage observed in two patients. Antibody immunogenicity restricted therapy to a single infusion. Studies with a nonimmunogenic G250 antibody are warranted.

Impact of the high tyrosine fraction in complementarity determining regions: measured and predicted effects of radioiodination on IgG immunoreactivity.

Although iodine-131 is the most widely used radionuclide for radioimmunotherapy, direct radiolabeling methods yield decreased immunoreactivity of the antibody as a function of increased iodine incorporation. We have studied the amino acid sequences of a therapeutic IgG (HuM195), and in particular its complementarity determining regions (CDR), in order to correlate the iodination of tyrosine residues in the antigen binding site with changes in immunoreactivity. The CDR contained an overabundance of tyrosines relative to an expected random distribution of amino acids. In contrast, lysine residues that can be used for ligand attachment were evenly distributed throughout the IgG. HuM195 was first trace labeled with 111In and then labeled with stable 127I at various specific activities. The immunoreactivity of each product was determined using the 111In tracer. The immunoreactivity measured after varying levels of iodination fit a theoretical curve that was generated based on the assumption that a single iodine incorporation anywhere on a tyrosine residue in a CDR destroys the immunoreactivity of the antibody. Similar theoretical curves for antibody fragments (Fab, Fv) suggest an even faster decrease in immunoreactivity with increasing iodination. A review of the sequences of other therapeutic IgG shows that a similar overabundance of tyrosine residues is found in the CDRs. Using enzyme digestion, the distribution of iodine on different parts of the antibody was also studied. The iodinated residues were distributed non uniformly throughout the IgG, with the heavy chain variable region tyrosines having a higher propensity for iodine incorporation than tyrosines in the other regions of the IgG. The common abundance of tyrosine in the CDR of IgG and its correlation with loss of function have important implications for therapeutic use of high specific activity radioiodinated monoclonal antibodies or fragments.

[18F]-2-fluoro-2-deoxy-D-glucose positron emission tomography localizes residual thyroid cancer in patients with negative diagnostic (131)I whole body scans and elevated serum thyroglobulin levels.

Progressive dedifferentiation of thyroid cancer cells leads to a loss of iodine-concentrating ability, with resultant false negative, whole body radioactive iodine scans in approximately 20% of all differentiated metastatic thyroid cancer lesions. We tested the hypothesis that all metastatic thyroid cancer lesions that did not concentrate iodine, but did produce thyroglobulin (Tg), could be localized by [18F]2-fluoro-2-deoxy-D-glucose (FDG)-positron emission tomography (PET). We performed FDG-PET on 37 patients with differentiated thyroid cancer after surgery and radioiodine ablation who had negative diagnostic 131I whole body scans during routine follow-up. Serum Tg, Tg autoantibodies, neck ultrasounds, and other clinically indicated imaging procedures were performed to detect residual disease. In those with elevated Tg levels, FDG-PET localized occult disease in 71%, was false positive in one, and was false negative in five patients. The majority of false negative FDG-PET occurred in patients with minimal cervical adenopathy. Surgical resections, biopsies, 131 therapy, and differentiation therapy were performed based on the PET results. The FDG-PET result changed the clinical management in 19 of the 37 patients. In patients with elevated Tg levels, FDG-PET had a positive predictive value of 92%. In patients with low Tg levels, FDG-PET had a negative predictive value of 93%. No FDG-PET scans were positive in stage I patients; however, they were always positive in stage IV patients with elevated Tg levels. An elevated TSH level (i.e. hypothyroidism) did not increase the ability to detect lesions. FDG-PET is able to localize residual thyroid cancer lesions in patients who have negative diagnostic 131I whole body scans and elevated Tg levels, although it was not sensitive enough to detect minimal residual disease in cervical nodes.

Measurement of cerebral blood flow in the rat with intravenous injection of [11C]butanol by external coincidence counting: a repeatable and noninvasive method in the brain.

No method has been reported for measuring CBF, repeatedly and noninvasively, in the rat brain. A new method is described, which is noninvasive to the brain, skull, or cervical large vessels. Two pairs of coincidence detectors were positioned, one over the rat brain and the other at the loop of a catheter inserted into the femoral artery. The coincidence head curve and arterial curve were recorded after intravenous injection of 1-[11C]butanol in 15 rats. CBF was calculated by one-compartment curve fitting ( CBFo ) from 1-min data and with the recirculation corrected height/area method from 3-min data ( CBFh X 3 min) and 5-min data ( CBFh X 5 min). CBFo agreed well with CBFh X 5 min, although a slight overestimation was observed in CBFh X 3 min. The normal CBFo in the normocapnic group (n = 6, paCO2 36.7 +/- 2.3 mm Hg) was 1.76 +/- 0.49 ml/g min (mean +/- SD). A good correlation was observed between CBFo (y) and PaCO2 (x), and the regression line was y = 0. 0629x -0.715 (r = 0.88, p less than 0.0001). We concluded that this method gives the stable blood flow values noninvasively and with a minimum loss of blood (less than 0.28 ml per measurement). Applications of this method include activation studies, studies on the effect of drugs and treatments, and water and oxygen extraction fraction studies using different tracers in the same rat.

A simplified in vivo autoradiographic strategy for the determination of regional cerebral blood flow by positron emission tomography: theoretical considerations and validation studies in the rat.

A simplified mathematical model is described for the measurement of regional cerebral blood flow by positron emission tomography in man, based on a modification of the autoradiographic strategy originally developed for experimental animal studies. A modified ramp intravenous infusion of radiolabeled tracer is used; this results in a monotonically increasing curvilinear arterial activity curve that may be accurately described by a polynomial of low degree (= zeta). Integrated cranial activity CB is measured in regions of interest during the latter portion of the tracer infusion period (times T1 to T2). It is shown that (See formula: text) where each of the terms A chi is a readily evaluated function of the blood flow rate constant kappa, the brain:blood partition coefficient for the tracer, the cranial activity integration limits T1 and T2, the coefficients of the polynomial describing the arterial curve, and an iteration factor n that is chosen to yield the desired degree of precision. This relationship permits generation of a table of CB vs. kappa, thus facilitating on-line computer solution for blood flow. This in vivo autoradiographic paradigm was validated in a series of rats by comparing it to the classical autoradiographic strategy developed by Kety and associates. Excellent agreement was demonstrated between blood flow values obtained by the two methods: CBF in vivo = CBF classical X 0.99 - 0.02 (units in ml g-1 min-1; correlation coefficient r = 0.966).

11C-carbon dioxide fixation and equilibration in rat brain: effects on acid-base measurements.

The positron-emitting isotope 11C was used to label CO2 for studies of metabolic fixation and equilibration after a single-breath inhalation by rats. Metabolic fixation and loss of the label via exhalation caused the metabolized fraction of the label in the brain to rise to 30.1 +/- 0.7% within 30 minutes. The T12 for equilibration of the label between blood and brain was 1.95 minutes. When the label was 95% equilibrated, 12% was metabolically trapped by brain, and when only 5% was trapped, the blood-brain equilibration process was only 50% complete. Labeled CO2 thus has limited usefulness as an acid-base or metabolic tracer for positron-emission tomography.