Radioactive drugs in drug development research: quality assurance issues.

Increasing number of new drugs, drug formulations and drug delivery systems is evaluated using noninvasive imaging methods. A successful use of new drugs and radiopharmaceuticals depends on their proven quality. This review provides a brief outline of the quality control procedures required for radiolabeled drugs within the context of the existing regulations.

99mTc-labeled divalent and tetravalent CC49 single-chain Fv's: novel imaging agents for rapid in vivo localization of human colon carcinoma.

UNLABELLED: Radioimmunopharmaceutical agents enabling rapid high-resolution imaging, high tumor-to-background ratios, and minimal immunogenicity are being sought for cancer diagnosis and imaging. Genetic engineering techniques have allowed the design of single-chain Fv's (scFv's) of monoclonal antibodies (mAbs) recognizing tumor-associated antigens. These scFv's show good tumor targeting and biodistribution properties in vivo, indicating their potential as imaging agents when labeled with a suitable radionuclide. METHODS: Divalent (sc(Fv)(2)) and tetravalent ([sc(Fv)(2)](2)) scFv's of mAb CC49 were evaluated for radioimmunolocalization of LS-174T colon carcinoma xenografts in athymic mice. scFv's were radiolabeled with (99m)Tc by way of the bifunctional chelator succinimidyl-6-hydrazinonicotinate hydrochloride using tricine as the transchelator. The immunoreactivity and in vitro stability of the scFv's were analyzed after radiolabeling. Biodistribution and pharmacokinetic studies were performed to determine the tumor-targeting potential of the radiolabeled scFv's. Whole-mouse autoradiography illustrated the possible application of these (99m)Tc-labeled multivalent scFv's for imaging. RESULTS: The radiolabeling procedure gave > or =95% radiometal incorporation, with a specific activity of >74 MBq/mg scFv. In solid-phase radioimmunoassay, both sc(Fv)(2) and [sc(Fv)(2)](2) exhibited 75%-85% immunoreactivity, with nonspecific binding between 0.8% and 1.2%. Size-exclusion high-performance liquid chromatography showed sc(Fv)(2) as a 60-kDa protein and [sc(Fv)(2)](2) as a 120-kDa protein. Blood clearance studies showed the elimination half-life of (99m)Tc-labeled sc(Fv)(2) as 144 min and that of [sc(Fv)(2)](2) as 307 min. Whole-body clearance studies confirmed the rapid elimination of scFv's, with half-lives of 184 +/- 19 min for sc(Fv)(2) and 265 +/- 39 min for [sc(Fv)(2)](2) (P < 0.001). At 6 h after administration, the tumor localization was 7.2 +/- 0.7 percentage injected dose per gram of tumor (%ID/g) for (99m)Tc-sc(Fv)(2). (99m)Tc-[sc(Fv)(2)](2) showed a tumor uptake of 19.1 +/- 1.1 %ID/g at the same time; the amount of radioactivity in the tumors was 4-fold higher than in the spleen and kidneys and 2-fold higher than in the liver. Macroautoradiography performed at 6 and 16 h after administration clearly detected the tumor with both scFv's. CONCLUSION: (99m)Tc-labeled multivalent scFv's show good tumor-targeting characteristics and high radiolocalization indices (tumor-to-background ratio). These reagents, therefore, have the potential for use in clinical imaging studies of cancer in the field of nuclear medicine.

Single-Dose versus fractionated radioimmunotherapy of human colon carcinoma xenografts using 131I-labeled multivalent CC49 single-chain fvs.

The prospects of radiolabeled antibodies in cancer detection and therapy remain promising. However, efforts to achieve cures, especially of solid tumors, with the systemic administration of radiolabeled monoclonal antibodies (MAbs) have met with limited success. Using genetic engineering techniques, MAbs have been tailored to improve the therapeutic index (tumor:normal tissue ratio) in clinical radioimmunotherapy. In the present study, we investigated the potential of tetravalent ([sc(Fv)2]2) and divalent [sc(Fv)2] single chain Fvs of MAb CC49 for therapy in athymic mice bearing s.c. LS-174T human colon carcinoma xenografts. Mice received 1,000 microCi of 131I-labeled [sc(Fv)2]2 or 131I-labeled sc(Fv)2, either as a single injection on day 6 or as four injections (250 microCi each) on days 6, 7, 8, and 9; the day of tumor implantation was taken as day 0. The median survival for the control group was 26 days. Comparisons of single and fractionated therapeutic regimens showed median survival as 32 (P < 0.001) and 53 days (P < 0.0001), respectively for [sc(Fv)2]2 and 26 (P > 0.5) and 38 days (P < 0.0001), respectively for sc(Fv)2 when compared with the control groups. The time for the quadrupling of tumor volume for single and fractionated therapeutic treatments were: 9.0 +/- 0.8 and 21.1 +/- 2.9 days respectively for sc(Fv)2; 16.6 +/- 1.9 and 32.9 +/- 2.7 days respectively for [sc(Fv)2]2; and 8.3 +/- 0.7 and 8.4 +/- 0.6 days respectively for the control group. No 131I-labeled systemic toxicity was observed in any treatment groups. The results show that radioimmunotherapy delivery for sc(Fv)2 and [sc(Fv)2]2 in a fractionated schedule clearly presented a therapeutic advantage over single administration. The treatment group receiving tetravalent scFv showed a statistically significant prolonged survival with both single and fractionated administrations suggesting a promising prospect of this reagent for cancer therapy and diagnosis in MAb-based radiopharmaceuticals.

High-dose therapy with 90Yttrium-labeled monoclonal antibody CC49: a phase I trial.

A Phase I trial of increasing administered activities of 90yttrium (90Y)-labeled monoclonal antibody (MAb) CC49 was conducted to determine whether extrahematopoietic toxicity occurred with this radioimmunoconjugate. Twelve patients with various gastrointestinal tract cancers were administered a tracer dose of 111In-labeled MAb CC49 for biodistribution and pharmacokinetic studies. Patients then underwent a single treatment with increasing administered activities of 90Y-labeled MAb CC49 (0.3, 0.4, and 0.5 mCi/kg). Biodistribution studies, using 111In-labeled MAb CC49 as a surrogate, were determined using planar and single photon emission computed tomography imaging. Pharmacokinetic studies were performed by measuring radioactivity in blood samples taken at intervals after radioimmunoconjugate infusions. Tissue biopsies of tumor metastases and related normal tissues (liver and bone marrow) were obtained for radioactivity measurements. Radiation dosimetry estimates were calculated using these data. Toxicity was evaluated using the National Cancer Institute Common Toxicity Criteria. No dose limiting extrahematopoietic toxicity was identified in the range of administered activities used in this study. Radioimmunolocalization based on planar and single photon emission computed tomography images 111In-labeled MAb CC49 showed heterogeneous (nonspecific) liver and splenic uptake. Liver metastases were usually photopenic, and extrahepatic metastases showed faint to moderate uptake. The alpha and beta half-lives of 111In-labeled MAb CC49 and 90Y-labeled MAb CC49 in the blood were similar. Absorbed radiation dose estimates in metastatic tumor sites ranged from 180 to 3000 cGy. The percentage of injected dose/kg of tumor ranged from 1.12 to 18.14; however, tumor:normal liver ratios were consistently <1. No objective responses were observed. Doses of up to 0.5 mCi/kg could be administered with reversible grade IV myelotoxicity. Absorbed radiation dose in tumor was suboptimal, even at the highest administered activity level. Deposition of 90Y in liver was high, and estimates of absorbed dose in liver equaled or exceeded that which could be achieved in metastatic tumor sites. Strategies to enhance access of radioimmunoconjugates in tumor and diminish deposition in the liver need to be developed for effective treatment using MAb CC49 with chelated radiometals.

Divalent forms of CC49 single-chain antibody constructs in Pichia pastoris: expression, purification, and characterization.

Single-chain variable fragments (scFvs) are tumor-recognition units that hold enormous potential in antibody-based therapeutics. Their clinical applications, however, require the large scale production and purification of biologically active recombinant scFvs. In the present study, we engineered and expressed divalent non-covalent [(scFv)(2)-His(6)] and covalent [sc(Fv)(2)-His(6)] scFvs of a tumor-associated monoclonal antibody (MAb) CC49 in Pichia pastoris. The purity and immunoreactivity of the scFvs were analyzed by SDS-PAGE, HPLC, and competitive ELISA. The binding affinity constant (K(A)), determined by surface plasmon resonance analysis using BIAcore, was 4.28 x 10(7), 2.75 x 10(7), and 1.14 x 10(8) M(-1) for (scFv)(2)-His(6), sc(Fv)(2)-His(6), and CC49 IgG, respectively. The expression of scFvs in P. pastoris was 30 to 40-fold higher than in Escherichia coli. Biodistribution studies in athymic mice bearing LS-174T human colon carcinoma xenografts showed equivalent tumor-targeting of CC49 dimers generated in yeast (scFv)(2)-His(6) and bacteria (scFv)(2) with 12.52% injected dose/gram (%ID/g) and 11. 42%ID/g, respectively, at 6 h post-injection. Interestingly, the pharmacokinetic pattern of dimeric scFvs in xenografted mice exhibited a slower clearance of His-tagged scFvs from the blood pool than scFvs lacking the His-tag (0.1 >/= p >/= 0.05). In conclusion, improved yields of divalent scFvs were achieved using the P. pastoris expression/secretion system. The in vitro and in vivo properties of these scFvs suggest possible therapeutic applications.

Genetically engineered tetravalent single-chain Fv of the pancarcinoma monoclonal antibody CC49: improved biodistribution and potential for therapeutic application.

Failure of radiolabeled monoclonal antibodies (MAbs) in the treatment of solid tumors, for the most part, is a result of undesirable pharmacokinetics that lead to significant radiation exposure of normal tissues and an inadequate delivery of radiation doses to tumors. Using genetic engineering, antitumor MAbs can be optimized for desirable clinical applications. In the present study, we report the generation of a tetravalent single-chain Fv [[sc(Fv)2]2] of the murine MAb CC49 that recognizes the tumor-associated glycoprotein, TAG-72. [Sc(Fv)2]2 was expressed as a secreted soluble protein in Pichia pastoris under the regulation of alcohol oxidase 1 promoter. The in vitro binding properties of the tetravalent construct were analyzed by solid-phase RIA and surface plasmon resonance studies using BIAcore. The binding affinity constant (K(A)) for the [sc(Fv)2]2 and CC49 IgG were similar, i.e., 1.02 x 10(8) M(-1) and 1.14 x 10(8) M(-1), respectively, and were 4-fold higher than its divalent scFv [sc(Fv)2; 2.75 x 10(7) M(-1)]. At 6 h postadministration, the percentage of injected dose accumulated/g of LS-174T colon carcinoma xenografts was 21.3+/-1.3, 9.8+/-1.3, and 17.3+/-1.1 for radioiodinated [sc(Fv)2]2, sc(Fv)2, and IgG, respectively. Pharmacokinetic analysis of blood clearance studies showed the elimination half-life for [sc(Fv)2]2, sc(Fv)2, and IgG as 170, 80, and 330 min, respectively. The gain in avidity resulting from multivalency along with an improved biological half-life makes the tetravalent construct an important reagent for cancer therapy and diagnosis in MAb-based radiopharmaceuticals.

Tumor localization and systemic absorption of intravesical instillation of radio-iodinated iododeoxyuridine in patients with bladder cancer.

PURPOSE: We evaluated tumor uptake and systemic distribution of intravesically instilled iododeoxyuridine (IUdR) in patients with superficial bladder cancer. MATERIALS AND METHODS: We performed 24 intravesical instillation studies in 11 patients with a mean age of 71 years. Radio-iodinated IUdR was administered through a Foley catheter. Gamma camera imaging was done after instillation and after 5 to 7 bladder irrigations. Tumor uptake was estimated by region of interest analysis. Bladder biopsy samples and surgical tumor specimens were tested for acid insoluble (deoxyribonucleic acid incorporated) radioactivity. Blood samples were obtained and analyzed for systemic absorption. RESULTS: Imaging was positive in all patients with bladder cancer. Average tumor uptake plus or minus standard deviation was 0.185+/-0.120% of the instilled dose. Preferential uptake of IUdR in the tumor was observed in all 6 patients undergoing tissue analysis. The tumor-to-normal bladder ratio ranged from 3.2 to 74,000 (median 202). Systemic absorption of IUdR was minimal. Blood sample analysis performed after intravesical instillation in all 11 cases revealed an average uptake of 3.2x10(-5)% instilled dose per ml. (range 0.69x10(-5) to 6.7x10(-5)) in the systemic circulation. Instillation within 24 hours after transurethral bladder tumor resection in 5 cases resulted in a higher but not dangerous average systemic uptake of 7.3x10(-4)% instilled dose per ml. (range 1.3x10(-5) to 2.6x10(-3)). Instillation 1 to 4 weeks after transurethral surgery in 8 cases resulted in no increased systemic absorption with an average blood level of 3.4+/-1.8x10(-5)% instilled dose per ml. There was no detectable distribution of radioactivity into other organs, including the thyroid. We noted no evidence of systemic toxicity in the study. CONCLUSIONS: Intravesical instillation of radio-iodinated IUdR achieves selective localization in the bladder tumor with minimal uptake by the normal bladder and minimal systemic absorption. The use of intravesical IUdR therapy for bladder cancer appears to be promising and requires further study.

5-[125I]iodo-2'-deoxyuridine in the radiotherapy of brain tumors in rats.

UNLABELLED: Glial neoplasms of the human central nervous system have defied treatment, in part because of the limited selectivity of available cytotoxic agents. The thymidine analog 5-iodo-2'-deoxyuridine radiolabeled with the Auger electron emitter 125I (125IUdR) is highly toxic to dividing cells when it is deoxyribonucleic acid incorporated, but it is relatively innocuous when located outside the nucleus. Previous studies have shown that 125IUdR has significant antineoplastic potential against mammalian cells in vitro and direct administration of 125IUdR is effective therapy for ovarian ascites tumors in mice and neoplastic meningitis in rats. Studies using external gamma imaging and autoradiography have also shown that direct intratumoral administration of 123IUdR/125IUdR into intracerebral 9L gliosarcomas in rats results in selective uptake of the radionuclide into tumor cells. Based on these encouraging results, we have evaluated the therapeutic potential of 125IUdR in rats bearing intracerebral 9L gliosarcomas. METHODS: Iodine-125-IUdR was infused intracerebrally over a 2-day period into rats bearing 1-day-old 9L tumors and over a 6-day period into animals with 9-day-old 9L tumors; equimolar concentrations of 127IUdR were infused into control animals. Tumor growth was monitored by contrast-enhanced 1H MRI and animal survival was followed over time. RESULTS: Intracerebral tumors (3-7 mm) were readily detected by MRI. Tumor-bearing rats treated with 127IUdR succumbed within 17-24 days, whereas tumor-bearing animals treated with 125IUdR survived significantly longer, and 10%-20% of the animals were cured of tumors. CONCLUSION: These data substantiate the antineoplastic potential of 5-[125I]iodo-2'-deoxyuridine and indicate that it may be a useful agent for the therapy of solid tumors that are accessible to direct radiopharmaceutical administration.

Stabilization of vasoactive intestinal peptide by lipids.

An anionic phospholipid, phosphatidylglycerol (PG), induced vasoactive intestinal peptide (VIP) to adopt a helical conformation, determined by circular dichroism studies. PG inhibited the trypsin-catalyzed, antibody-catalyzed and uncatalyzed cleavage of VIP, measured by radiometric and HPLC methods. Phosphatidylcholine, a neutral lipid, did not alter the circular dichroism spectra of VIP, and it was without detectable effect on the rates of VIP cleavage. Trypsin-catalyzed cleavage of Boc-Ile-Glu-Arg-methylcoumarinamide, a substrate unrelated in sequence to VIP, proceeded at equivalent rates in the absence and presence of PG, which suggests that the phospholipid did not exert a nonspecific inhibitory effect on the enzyme. Study of the kinetics of antibody-catalyzed VIP cleavage indicated that the inhibition by PG was due to decreased affinity for VIP, suggested by observations of increased K(m) values and unaltered Vmax values. Incorporation of VIP in the liposomes and the liposomal surface permitted maintenance of the peptide in essentially undegraded form at 37 degrees C for 8 days. The longevity of liposomal VIP administered i.v. to mice was increased by about 5-fold compared with aqueous VIP. These observations indicate that certain phospholipids and liposomes can be applied to circumvent the rapid loss of VIP in vitro and in vivo due to degradative processes.

Prodrugs in site-selective delivery of radiopharmaceuticals.

This paper reviews basic rules for the design of site-selective prodrugs and various modes of their activation with particular emphasis on the applications of prodrugs to targeted delivery of radiopharmaceuticals. Although many radiopharmaceuticals are "targeted" to specific tissues or organs, we will discuss only agents that are either chemically or metabolically transformed producing an active form that is retained by its target. Site-specific prodrugs of diagnostic radiopharmaceuticals are routine in the nuclear medicine applications, but the instances of targeting of radiotherapeutic prodrugs are surprisingly rare. We have concentrated on our own efforts to design and synthesize site-selective prodrugs of 5-[125I]iodo-2'-deoxyuridine (125IUdR) for cancer radiotherapy. The prodrugs of 125IUdR for targeted delivery include several derivatives with altered permeability, 3',5'-dioctanoyl, 3',5'-dioleoyl, 3'- and 5'-N-alkyl-dihydropyridyl, 3'- and 5'-N-alkyl-dihydroisoquinolyl, and 3'- and 5'-N-alkyl-dihydroacridinyl esters of 125IUdR; polymeric and macromolecular prodrugs of 125IUdR for a carrier-mediated or local delivery; metabolically trapped 125IUdR prodrugs; and glycoconjugate prodrugs for oral colon-specific delivery of 125IUDR, 125IUDR-5'-beta-d-cellobioside, 125IUDR-5'-beta-D-glucopyranoside, 125IUDR-5'-beta-D-galactopyranoside and 125IUDR-5'-beta-D-glucuronide. We also describe prodrugs of several diagnostic agents in the context of the metabolic trapping as the primary targeting modality. For various diagnostic agents the prodrug target-associated enzymes are discussed and examples of the site-specific release of the active agent are given. A brief overview of an emerging role of residualizing labels in radioimmunotherapy is included.

Patient-specific dosimetry of indium-111- and yttrium-90-labeled monoclonal antibody CC49.

UNLABELLED: The objective of this work was to develop patient-specific dosimetry for patients with metastatic gastrointestinal tract cancers who received 111In-CC49 IgG for imaging before therapy with 90Y-CC49 IgG. METHODS: Whole-body imaging of 12 patients, who received 111-185 MBq (3-5 mCi) of 111In-CC49, commenced in < 2 hr postinfusion and was continued daily for 4-5 days. SPECT data were acquired at 24 and 72 hr to determine the range of 111In-CC49 activity concentrations in tumors and normal organs. Time-activity curves were generated from the image data and scaled from 111In-CC49 to 90Y-CC49 for dosimetric purposes. Absorbed-dose calculations for 90Y-CC49 included the mean and range in tumor and normal organs. Computed 90Y-CC49 activity concentrations were compared with measurements on 10 needle biopsies of normal liver and four tumor biopsies. RESULTS: In 9 of 10 normal liver samples, the range of computed 90Y-CC49 activity concentrations bracketed measured values. This was also the case for 3 of 4 tumor biopsies. Absorbed-dose calculations for 90Y-CC49 were based on patients' images and activities in tissue samples and, hence, were patient-specific. CONCLUSION: For the radiolabeled antibody preparations used in this study, quantitative imaging of 111In-CC49 provided the data required for 90Y-CC49 dosimetry. The range of activities in patients' SPECT images was determined for a meaningful comparison of measured and computed values. Knowledge of activity distributions in tumors and normal organs was essential for computing mean values and ranges of absorbed dose and provided a more complete description of the absorbed dose from 90Y-CC49 than was possible with planar methods.

Strand breaks after the decay of iodine-125 in proximity to plasmid pBR322 DNA.

To elucidate the kinetics of DNA strand breaks caused by low-energy Auger electron emitters in proximity to DNA molecules, we synthesized (125)I-labeled 2-iodoacridine (2-(125)IA), which intercalates with DNA, and 4-iodoacridine (4-(125)IA), which does not. Supercoiled DNA from pBR322 plasmid, labeled with 3H, was purified and incubated with 2-(125)IA or 4-(125)IA in aqueous solution. Reaction mixtures were stored at 4 degrees C to accumulate radiation dose from the decay of (125)I, and DNA was resolved by gel electrophoresis into supercoiled (DNA-I), nicked-circular (DNA-II) and linear (DNA-III) forms, representing undamaged DNA, single-strand breaks (SSBs) and double-strand breaks (DSBs), respectively. Gamma irradiation from an external (137)Cs source led to an exponential decrease in DNA-I with a D0 value of 10.8 +/- 0.3 Gy. Under identical conditions, the D0 values for 2-(125)IA and 4-(125)IA were 22.4 +/- 0.6 x 10(11) disintegrations and 4.7 +/- 0.4 x 10(11) disintegrations, respectively. External gamma irradiation and 4-(125)IA produced SSB/DSB ratios of 26.5 +/- 2.1 and 15.9 +/- 2, respectively, while that for 2-(125)IA was 0.6. The average number of DSBs from each decay of (125)I was 0.67 for 2-(125)IA and 0.27 for 4-(125)IA. The results indicate that the decay of (125)I bound to a DNA-intercalating compound produces DSBs 2.5-fold more efficiently than (125)I bound to a nonintercalating compound and support the theoretical expectations that predict a DSB yield that is highly dependent on the proximity of the Auger electron emitter to DNA.

Antiidiotypic response against murine monoclonal antibodies reactive with tumor-associated antigen TAG-72.

The immune response of 42 gastrointestinal and ovarian cancer patients at 1 month after exposure to murine monoclonal antibodies (B72.3 and CC49) reactive with the tumor-associated antigen TAG-72 was studied. The incidence of human anti-mouse antibody response was 89% to B72.3 and 70% to CC49. To evaluate the antiidiotypic immune response, we developed a serological assay based on affinity chromatography to remove the interference due to the presence of TAG-72, antiisotypic, and antiallotypic immunoglobulins in the serum. Seventy-eight percent of patients who received B72.3 developed an antiidiotypic response; in 33% of the patients, this was the only immune response detected. The antiidiotypic immune response after treatment with CC49 was present in 54% of the patients. Twelve percent of the patients who received CC49 developed an antiidiotypic response in the absence of antiisotypic or antiallotypic immune response. The lower immunogenicity of the variable region of CC49 is encouraging when considering the use of chimeric or humanized antibodies derived from the murine monoclonal antibody CC49 in clinical studies.

Tumor uptake and mitotic activity pattern of 5-[125I]iodo-2'- deoxyuridine after intravesical infusion in patients with bladder cancer.

UNLABELLED: In patients with bladder cancer, little is known about diffusion in the tumor mass of 5-iodo-2'-deoxyuridine (IUdR) administered intraluminally, although previous studies based on external scanning have shown promising tumor-targeting properties of IUdR instilled intravesically. This study compared the pattern of IUdR uptake by bladder cancer cells with the actual distribution of mitotic activity, as evaluated by incubation of ex vivo tumor specimens with tritiated thymidine. METHODS: The [125I]IUdR (2-13 MBq) was instilled over 1-3 hr in the bladder of four patients with bladder cancer scheduled for ablative surgery. Twenty-four hours later, surgical samples were assayed for radioactivity and processed for microautoradiography, while fresh tumor specimens were fragmented, incubated with [3H]thymidine and further processed for microautoradiography. The diffusion of labeled IUdR across the bladder wall was evaluated by blood sampling. RESULTS: Tumor incorporation of [125I]IUdR 24 hr after intravesical instillation was 0.002%-0.05% ID/g, while the average tumor-to-normal bladder ratio was about 20. Microautoradiography showed that [125I]IUdR incorporation was confined to tumor cells in the most superficial layers of the bladder, while incubation of the tumor fragments with [3H]thymidine demonstrated the presence of diffuse mitotic activity also in the deeper tumor mass. Diffusion of labeled IUdR in the general circulation was minimal. CONCLUSION: Poor diffusion in the tumor mass makes *IUdR unsuitable for intracavitary therapy of bladder cancer, but the role of such an approach in the postsurgical "sterilization" of cancer remnants floating in the bladder lumen after partial cystectomy should be explored.

Radiolabeled iododeoxyuridine: safety evaluation.

UNLABELLED: The emphasis of radiolabeled iododeoxyuridine (*IUdR) research at our institution to date has been to assess its safety as a potential therapeutic agent. Toward this goal, we have performed preclinical and clinical studies, using various routes of administration, to detect adverse changes in normal tissues in both humans and animals. As IUdR is rapidly dehalogenated by the liver, the intravenous route is unlikely to be successful in therapeutic efforts. We have therefore focused our attention on more "protected" routes: intra-arterial and intravesicular administration. METHODS: Studies were performed in farm pigs after multiple administrations of [125I]IUdR into the aorta, carotid artery and bladder. IUdR and metabolites were measured in venous blood samples at appropriate time intervals after administration, after which histologic examination of tissues was performed. Studies in human have been performed after intra-arterial administration of [123I]IUdR in patients with liver metastases and intravesicular administration in patients with bladder carcinoma, initially using [123I]IUdR and currently using both [123I]IUdR and [125I]IUdR. Blood samples for pharmacokinetics and metabolite analysis and tissue for autoradiography (when feasible) have been obtained. RESULTS: To date, no evidence of adverse effects on normal tissue or alteration of hematologic or metabolic indices have been seen in pigs or humans. When instilled in the bladder, there is little leakage of IUdR in the circulation. CONCLUSION: When [125I]IUdR is used as a therapeutic agent, we anticipate little or no effect on normal tissues.

Intratumoral administration of 5-[123I]iodo-2'-deoxyuridine in a patient with a brain tumor.

UNLABELLED: We have initiated a study in which patients suspected of having primary gliomas are given a single intracerebral injection of the thymidine analog 5-[123I]iodo-2'-deoxyuridine ([123I]IUdR). The purpose of the study is to determine the biodistribution of the radiopharmaceutical and to calculate dose estimates to the tumor and normal tissues. METHODS: A patient with a cystic glioma was injected with [123I]IUdR. Whole-body scans and brain scans were obtained at various times after injection, and blood, urine and stools were collected and assayed for radioactivity to assess its biodistribution and clearance. RESULTS: Scintigraphic imaging demonstrated that the distribution of radiolabeled IUdR was mainly confined to the tumor (injection site), stomach and bladder. Disappearance from the tumor site and blood clearance were delayed probably due to collection in the cystic lesion. Eighty percent of the injected dose was recovered in the urine. CONCLUSION: The pharmacokinetics of [123I]IUdR locoregionally administered to a human glioma in situ resembled those observed in a rat glioma model where administration of the radiopharmaceutical radiolabeled with the Auger electron emitter 125I was therapeutically effective.

Tumor targeting by intra-arterial infusion of 5-[123I]iodo-2'-deoxyuridine in patients with liver metastases from colorectal cancer.

UNLABELLED: We previously showed the tumor-targeting potential of the 125I-labeled thymidine analog 5-iodo-2'-deoxyuridine (IUdR) injected intratumorally in patients with high tumor-cell kinetics. In this study, we evaluated the tumor incorporation of [123I]IUdR infused intra-arterially in patients with liver metastases from colorectal cancer. METHODS: Iodine-123-IUdR (110-300 MBq, 3-8 mCi, specific activity, 150-200 Ci/mumole) was infused into the hepatic artery of 16 patients with inoperable liver metastases over 30-45 min through a permanent intra-arterial catheter. A dynamic sequence during infusion, spot images, whole-body scans and SPECT acquisitions were recorded up to 42 hr. Blood and urine samples were obtained for biodistribution and HPLC analyses. RESULTS: In the 14 patients with adequate tumor perfusion patterns, tumor uptake reached 2%-17.6% ID at the end of infusion. After a washout phase that lasted 18-20 hr, incorporated radioactivity remained steadily associated with the tumor lesions until at least 42 hr after infusion (about 1.4%-11.1% ID). HPLC analysis indicated a virtually 100% first-pass hepatic deiodination of unincorporated [123I]IUdR (about 80%-95% ID recovered in the 42-hr urine). No significant uptake was detected in the bone marrow or in other normal dividing tissues. CONCLUSION: These results encourage further studies to enable dosimetric estimates, optimization of dose regimens, and examination of the therapeutic potential of Auger-electron-emitter-labeled IUdR in cancer therapy utilizing this type of approach.

Tumor-targeting potential of radioiodinated iododeoxyuridine in bladder cancer.

UNLABELLED: Since bladder cancer arises in the superficial lining of the urothelium, it is a likely candidate for site-directed administration of 5-iodo-2'-deoxyuridine radiolabeled with the Auger electron emitter 123I or 125I (*IUdR). METHODS: We instilled *IUdR for 2 hr directly within the bladder lumen of rats bearing N-methyl-N-nitrosourea (NMU)-induced bladder cancer and conducted scintigraphic, biodistribution and autoradiography (ARG) studies 48 hr and 1 wk later. Control animals were not subjected to the carcinogen but were instilled with *IUdR. RESULTS: Two groups of animals were identified after instillation of MNU: Group A consisted of rats with hyperplasia and Group B of rats with papillary carcinoma (stages Ta and T1). Scintigraphic detection of carcinomas was achieved with high sensitivity and specificity, and increased tumor-to-normal tissue ratios were obtained in both groups. Moreover, ARG demonstrated that (1) the uptake of *IUdR was observed in the hyperplastic and carcinomatous urothelium but not in the normal urothelium; (2) uptake was detected at a very early stage of tumor development (hyperplasia stage); (3) *IUdR was able to penetrate deep within the bladder wall; and (4) other normal dividing tissues, such as the bone marrow, the small intestine and the large intestine, were free of silver grains (i.e., no DNA-incorporated *IUdR). CONCLUSION: Since this carrier of Auger electron emitters has antineoplastic effects ([123I]IUdR and [125I]IUdR) in addition to its scintigraphic potential ([123I]IUdR and [131I]IUdR), it holds promise for therapy and early diagnosis of bladder cancer.

On the safety of 5-[125I]iodo-2'-deoxyuridine--Preclinical evaluation in swine.

To increase tumor incorporation and minimize hepatic degradation of radio-IUdR, compartmental administration routes are being considered as an alternative to intravenous (i.v.) injections. Although there are significant data on the biodistribution and some reports on radiotoxicity of i.v.-administered 125IUdR, similar results for other routes of delivery are not available. We have undertaken a series of experiments intended to examine radiation effects of 125IUdR after intravesical (3 swine; eight 3 mCi doses at 4-day intervals), intracarotid (3 swine; two 10 mCi doses at 2-week intervals), and intra-aortic (5 swine, single dose of 10 mCi) administration in a swine model. Liver, renal functions, and complete blood counts were monitored throughout the duration of the experiment. Pharmacokinetics, systemic distribution of radioactivity and metabolites were measured. The normal tissue 125IUdR uptake and histology were determined after necropsy. No adverse systemic effects were identified. Clinical observations, laboratory data, and necropsy results were within normal range.

Biochemical modulation by 5-fluorouracil and 1-folinic acid of tumor uptake of intra-arterial 5-[123I]iodo-2'deoxyuridine in patients with liver metastases from colorectal cancer.

In previous studies we demonstrated a high tumor-targeting value of the 123I-labeled thymidine analogue 5-iodo-2'-deoxyuridine (IUdR) infused intra-arterially in patients with liver metastases from colorectal cancer. In the present study we have explored the possibility of enhancing tumor uptake of [123I]IUdR, by biochemical modulation with 5-fluorouracil (5-FU) and 1-folinic acid (FA), a drug combination known to inhibit thymidylate synthetase in tumor cells. The investigation was carried out employing diagnostic imaging doses of [123I]IUdR, much lower than possible therapeutic levels. In the baseline study, [123I]IUdR was infused into the hepatic artery of patients with inoperable liver metastases from colorectal cancer, and a second infusion was performed one week later, after intra-arterial administration of 5-FU and FA. The effect was evaluated by comparing tumor uptake of [123I]IUdR in the second study with that of the baseline study. The average tumor uptake immediately after [123I]IUdR infusion was 9.1% ID in the baseline study, increasing to 14.9% ID after pretreatment with 5-FU and FA. The average enhancement in early tumor uptake of [123I]IUdR induced by biochemical modulation was 72%. This enhancement was sustained at 18 and 42 hours after infusion (stable uptake). The results encourage the pretreatment of patients with 5-FU and FA prior to radioiodinated IUdR administration and suggest its inclusion in therapeutic protocols employing IUdR labeled with 123I or 125I as a source of highly cytotoxic Auger electrons.