Phase I study of imatinib in combination with gemcitabine and capecitabine

e13523

Background: Imatinib-mediated inhibition of platelet-derived growth factor receptor lowers tumor interstitial pressure allowing for improved intratumoral antineoplastic drug concentration. A phase I study of imatinib (Im) with the synergistic combination of gemcitabine (Gem) and capecitabine (Cape) was undertaken. Methods: Eligibility requirements included refractory solid tumors, ECOG 0/1 and adequate organ function. A 3-week treatment cycle was used with the dose levels (DL) 0 and -1 as outlined in the table. Dose limiting toxicity (DLT) was defined as occurring within the first 2 cycles of therapy. Patients remained on therapy unless DLT occurred or disease progression. Results: Twelve patients with a median age of 59.5 (range 44 - 77) were evaluable. Baseline characteristics included ECOG PS 0/1: 6/6; prior systemic therapies: median 3 (range 1–6); tumor types: renal (4), melanoma (2), prostate, esophageal, pancreatic, small cell lung, breast, unknown primary. At DL 0, 2 of 6 patients experienced DLT (gr. 3 thrombocytopenia; gr. 4 leucopenia). At DL -1, 1 of 6 patients experienced DLT (gr. 3 thrombocytopenia). No patient missed a dose; one patient in DL -1 completed only 1 cycle. Median cycles administered was 2 (range, 1 - 19). At cycle 2 evaluation, 7 pts had stable disease, 4 had progressive disease and 1 was not evaluable. Grade 3 or 4 toxicity included thrombocytopenia, leucopenia, hyperglycemia and weakness. All hematologic grade 3/4 toxicity was seen in patients having received ≥3 cytotoxic regimens previously. Most common grade 1/2 toxicities included anemia, nausea/emesis and fatigue. One patient with renal cell had stable disease (SD) for 15 cycles and one patient with melanoma had SD for 19 cycles. Conclusions: Im in combination with Gem and Cape is well tolerated in patients without extensive exposure to cytotoxic therapy. Activity is seen in various tumor types particularly melanoma and renal cell. The suggested dose for phase II studies is Im 400 mg/d, Gem 400 mg/m2 and Cape 400 mg/m2 in the dose schedule as described above.

[Table: see text]

[Table: see text]

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

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.

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.

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.

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

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.

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.

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

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.

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

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.

Radiolabeled iododeoxyuridine: safety evaluation

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.

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

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.

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

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 potential of radioiodinated iododeoxyuridine in bladder cancer

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.

Colon-specific prodrugs of 5-radioiodo-2'-deoxyuridine

Two glycoside-based prodrugs, 125IUdR-5'-beta-D-glucopyranoside and 125IUdR-5'-beta-D-galactopyranoside, were synthesized. This selection was dictated by the abundance of appropriate enzymes in the GI tract of mice and similar levels of beta-D-glycosidases in human and rodent large intestine. Studies to establish the ability of colonic microflora to release 125IUdR were conducted in vitro and in Swiss Webster mice. Both prodrugs released 125IUdR in the presence of the corresponding enzymes or the GI content homogenates in vitro, and in vivo. Luminal enzymes in the proximal and distal small intestine in mice degraded less than 10% of each prodrug whereas enzymes from the colonic/caecal lumen of mice released nearly 100% of 125IUdR. 125IUdR freed by bacterial glycosidases was stable in the GI content. No significant amounts of other metabolites or deiodination products were observed. Total radioactivity recovered as by-products was less than 10%. The efflux of prodrugs from the GI tract after oral administration in mice was slow and limited. Unlike 125IUdR, prodrugs were not dehalogenated in vivo as indicated by biodistribution and imaging studies.

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.

A fluorimetric method for the detection of copper-mediated hydroxyl free radicals in the immediate proximity of DNA

An optical method to detect copper-mediated hydroxyl free radicals generated close to DNA and other biomolecules has been developed. Low-molecular-weight polylysines were labeled with SECCA, a derivative of coumarin that generates the fluorescent 7-OH-SECCA following its interaction with hydroxyl free radicals in aqueous solution. These polylysines were then complexed with DNA to place the detector molecule SECCA in the vicinity of the nucleic acid. Following addition of copper sulfate (0-10 mumol dm-3), free radicals were generated by incubation with ascorbic acid (0-1 mmol dm-3) and hydrogen peroxide (0-1 mmol dm-3). A rapid increase in the induced fluorescence was observed corresponding to the formation of the fluorescent 7-OH-SECCA in the polylysine-nucleic acid complex. This fluorescence was not decreased significantly by addition of high concentrations of hydroxyl free-radical scavengers (DMSO, methanol, ethanol and tert-butanol), but was diminished by addition of relatively low concentrations of EDTA (0.1 mmol dm-3), histidine (0.1 mmol dm-3) or catalase (8.3 x 10(-5) mmol dm-3). On the other hand, when such reaction mixtures were incubated with SECCA molecules that were free in solution or SECCA-labeled polylysine in the absence of DNA, the induced fluorescence was diminished by all hydroxyl free-radical scavengers. The efficiency by which the scavengers reduce the fluorescence increases as their hydroxyl rate constant increases. The data indicate that the detector molecule SECCA can be used to detect copper-mediated hydroxyl free radicals generated close to DNA.

The effects of indium-111 decay on pBR322 DNA

We have compared the effectiveness in causing DNA strand breaks of 111In bound to DNA or free in aqueous solution with that of gamma rays. Supercoiled DNA from pBR322 plasmid labeled with [3H]thymidine was purified and mixed with 111InCl3 in the absence or presence of diethylenetriaminepentaacetic dianhydride (DTPA), a metal chelator which prevents the binding of indium to DNA. The reaction mixtures were stored at 4 degrees C to accumulate radiation dose from the decay of 111In. The DNA was then resolved by gel electrophoresis into supercoiled, nicked circular and linear forms, representing undamaged DNA, single-strand breaks (SSBs) and double-strand breaks (DSBs), respectively. The D0 values of pBR322 DNA exposed to gamma radiation from an external 137Cs source and the decay of 111In dispersed in solution (+DTPA) are 3.1 +/- 0.1 and 2.8 +/- 0.1 Gy, respectively. In terms of accumulated 111In disintegrations cm-3 of plasmid DNA solution, the D0 value is 15.3 (+/- 0.7) x 10(10) disintegrations in the absence of DTPA and 38.2 (+/- 1.1) x 10(10) disintegrations in its presence. Since only 14.6 +/- 5% of the 111In was bound to DNA in the absence of DTPA, an effective D0 for bound 111In of 3.4 (+/- 1.1) x 10(10) disintegrations is obtained. The 11-fold (range 9- to 17-fold) increased effectiveness of this Auger electron emitter when in proximity to DNA appears to be due mainly to the higher yield of SSBs.

Accessibility of nucleic acid-complexed biomolecules to hydroxyl radicals correlates with their conformation: a fluorescence polarization spectroscopy study

A fluorescence methodology has been developed to examine the relationship between the conformational state of specific biomolecules in simple chromatin models and their accessibility to hydroxyl radicals (OH). Polylysine and histone H1 were labelled with SECCA, the succinimidyl ester of coumarin-3-carboxylic acid, which generates the fluorescent derivative 7-OH-SECCA following its interaction with radiation-induced OH in aqueous solution. The fluorescence induced per unit gamma-ray dose reflecting the accessibility of OH to such SECCA-conjugated biomolecules was recorded. The biomolecules were also labelled with the fluorescent derivative 7-OH-SECCA in trace amounts to study their conformation under identical conditions via fluorescence polarization spectroscopy. When these biomolecules were complexed with a polynucleotide or DNA, a major increase in polarization anisotropy was recorded. Upon salt-induced dissociation of these biomolecules from the nucleic acids, the increase in anisotropy was reversed. The histone H1-DNA complexes also exhibited an initial increase in anisotropy with increasing NaCl concentration (maximum at 100 mmol dm-3) indicating the possible formation of a more compact conformation. The fluctuations in anisotropy were inversely proportional to the recorded fluorescence/Gy. The data indicate a direct correlation between the accessibility of OH to polylysine or histone H1 complexed with nucleic acids and the conformation of these biomolecules.

Quantification of radiation-induced hydroxyl radicals within nucleohistones using a molecular fluorescent probe

We present a method that specifically records .OH formation within histones and possibly at other sites in irradiated nucleohistone. The approach uses the radiation-induced fluorescence emissions from a chromatin-conjugated .OH detector, SECCA (a succinylated derivative of coumarin), that is converted to a fluorescent derivative, 7-hydroxy-SECCA (7-OH-SECCA), after interaction with .OH in neutral aqueous solutions. It is shown that (a) the fluorescent product 7-OH-SECCA cannot be generated by direct radiation effects after gamma or neutron irradiation of SECCA; (b) when SECCA-labeled histone is complexed with DNA to form nucleohistone, the physical properties of the modified nucleohistone are similar to those of unlabeled nucleoprotein; and (c) after irradiation of SECCA-labeled nucleohistone, a linear induction of the fluorescence signal is observed within the radiation doses examined (0.3-30 Gy). Since the sample remains available for further studies after registration of the optical signal, the current approach should permit the investigator to correlate in a single sample the localization and frequency of .OH formation with the results of other assays.

Tumor targeting potential and metabolism of 5-[125I]iodo-2'-deoxyuridine injected intratumorally in patients with breast cancer

We have previously demonstrated the high tumor targeting potential of the thymidine analogue 125IUdR in experimental animal models following direct intratumoral or locoregional (intracavitary) administration. The aim of the present work was to evaluate the metabolism and selectivity (based on differential cell proliferation kinetics) of 125IUdR incorporation in patients with breast cancer following a similar approach. 125IUdR (4-8 MBq) was injected intratumorally by ultrasound-guided percutaneous injection in 7 patients with breast cancer 24 hours before ablative surgery. Blood and urine samples were collected up to 72 hours after injection and analyzed by HPLC using a C18 reversed-phase column and methanol:water (20:80) as the mobile phase. Following resection, the radioactivity of the tumor and the surrounding tissues was measured in a gamma counter, and microautoradiography was performed on semithin tissue sections to determine the site of tracer incorporation at the cellular level. Activity in plasma peaked at 0.5 to 1 hour after 125IUdR injection (4.96 +/- 1.08% of injected dose/liter), declining thereafter with a mean T1/2 of 11.24 +/- 2.78 hours. By HPLC analysis, undegraded 125IUdR was about 15-30% of total plasma activity, with a biphasic pattern peaking at both 1-3 hours and approximately 12 hours. In addition to free 125I-, about 10% of early plasma activity was constituted by a labeled metabolite (tentatively identified as radio-iodouracil), rising to about 50-60% at later time points. About 70-90% of urinary radioactivity was 125I-, and 5-20% was undegraded 125IUdR in the first 24-hour samples, while the remainder was iodouracil. High tumor/nontumor ratios were obtained (mean 147.4 +/- 125.2, range 27-397) with average tumor/blood ratios at the time of surgery equal to 32.7 +/- 18.6 (range 5-56). An average 0.0244 +/- 0.0189% of the injected dose was present per gram of tumor (range 0.001-0.061% ID/g). Microautoradiography confirmed the high values of tumor/nontumor incorporation ratios and demonstrated the specificity of 125IUdR incorporation mostly in the tumor cell nuclei, with only occasional incorporation by normal-appearing tubular cells. These results suggest the potential of radiolabeled IUdR for tumor targeting in humans, to be used whenever a satisfactory route of locoregional administration allowing for homogeneous tracer distribution within the tumor mass is accessible and in the presence of favorable tumor cell proliferations kinetics.

Labeling of immunoglobulins with bifunctional, sulfhydryl-selective, and photoreactive coumarins

4-(Bromomethyl)-6,7-dimethoxy-2-oxo-2H-benzopyran (1a) and 4-(bromomethyl)-7-methoxy-2-oxo-2H-benzopyran (1b) and their iodo analogs (2) reacted selectively with the sulfhydryl groups generated in a limited reduction of the hinge disulfide bonds of an immunoglobulin G (IgG) giving proteins labeled with a fluorescent and/or radioactive moiety. Quantitative alkylation of free thiol groups was obtained with 1 and 125/127I-2. Photodimerization of these adducts produced IgG with covalently joined heavy chains.

Labeling of sulfhydryl groups in intact mammalian cells with coumarins

4-(Bromomethyl)-6,7-dimethoxy-2-oxo-2H-benzopyran (1) and its 3-[125I]iodo derivative (2) were reacted with sulfhydryl groups of proteins in viable Chinese hamster V79 lung fibroblasts. Pretreatment of cells with dithiothreitol (DTT) as the reducing agent was necessary to give detectable levels of fluorescence. In the absence of DTT, V79 cells incorporated about 1 x 10(-3) pCi/cell of the radioiodinated, no-carrier-added derivative; following incubation of cells with 320 microM DTT the uptake was nearly doubled (1.87 x 10(-3) pCi/cell).

Tumor targeting in vivo and metabolic fate of 5-[iodine-125]iodo-2'-deoxyuridine following intratumoral injection in patients with colorectal cancer

Previous studies have demonstrated the tumor-targeting potential of radioiodinated 5-iodo-2'-deoxyuridine (IUdR) in experimental animal models following direct intratumoral or intracavitary administration. The aim of this study was to measure the tumor uptake and metabolic fate of 5-[125I]iodo-2'-deoxyuridine ([125I]UdR) in humans after a single intratumoral injection. Ten patients with colorectal cancer were injected intratumorally with [125I]UdR) (0.24-3.9 MBq) during endoscopy 24 hr before ablative surgery. Blood and urine samples were collected up to 72 hr after [125I]UdR injection. Following resection, the radioactivity in the tumor and the surrounding tissues was measured in a gamma counter, and microautoradiography was performed on semi-thin tissue sections to assess localization of the radiopharmaceutical at the cellular level. An average of 0.234% of the injected dose was present per gram of tumor (range 0.009-0.918, median value 0.147), and tumor-to-nontumor radioactivity incorporation ratios were high for colonic mucosa when the nontumor tissue was taken at 1 cm (mean 629, range 27-2391) and 15 cm (mean 2387, range 122-12674) from the injection site. Microautoradiography confirmed these high tumor-to-nontumor ratios and demonstrated localization of [125I]UdR in the tumor cell nuclei. These results suggest that radioiodinated IUdR might have potential as a tumor-targeting agent in humans, provided homogeneous intratumoral distribution of the radiopharmaceutical by a suitable route of loco-regional administration can be achieved.

A method for detection of hydroxyl radicals in the vicinity of biomolecules using radiation-induced fluorescence of coumarin

A novel method is described to quantitate radiation-induced hydroxyl radicals in the vicinity of biomolecules in aqueous solutions. Coumarin-3-carboxylic acid (CCA) is a non-fluorescent molecule that, upon interaction with radiation in aqueous solution, produces fluorescent products. CCA was derivatized to its succinimidyl ester (SECCA) and coupled to free primary amines of albumin, avidin, histone-H1, polylysine, and an oligonucleotide. When SECCA-biomolecule conjugates were irradiated, the relationship between induced fluorescence and dose was linear in the dose range examined (0.01-10 Gy). The fluorescence excitation spectrum of irradiated SECCA-biomolecule conjugates was very similar to that of 7-hydroxy-SECCA-biomolecule conjugates, indicating the conversion of SECCA to 7-hydroxy-SECCA following irradiation. Control studies in environments that excluded certain radiation-induced water radicals for both the conjugated and unconjugated forms of irradiated SECCA demonstrated that: (1) the induction of fluorescence is mediated by the hydroxyl radical; (2) the presence of oxygen enhances induced fluorescence by a factor of about 1.4, and (3) other primary water radicals and secondary radicals caused by interaction of primary water radicals with biomolecules do not significantly influence the induced fluorescence. The data indicate that the induction of fluorescence on SECCA-biomolecule conjugates records specifically the presence of the hydroxyl radical in the immediate vicinity of the irradiated biomolecule. The method is rapid and sensitive, uses standard instrumentation, and the sample remains available for further studies.

DNA damage produced in V79 cells by DNA-incorporated iodine-123: a comparison with iodine-125

The neutral elution technique (pH 9.6) has been used to compare the damage produced in the DNA of V79 cells following the decay of the Auger-electron emitters 123I and 125I incorporated into DNA in the form of 5-[123I/125I]iodo-2'-deoxyuridine (123IdU, 125IdU) or after 60Co gamma irradiation. Elution profiles of retained radioactivity versus eluted volume were generally found to be nonlinear and partially dependent on the cell treatment prior to elution. Plots of a suitable function of radioactivity retention on the filters versus total decays for 123I or 125I and dose (Gy) for gamma radiation were linear. Assuming that each 125I decay produces one double-strand break (DSB), the 60Co efficiency in DSB production was found to be 53.4 DSBs/Gy/cell (or 17.8 DSBs/Gy/10(12) Da), in agreement with values reported previously. The decay of 123I led to 0.74 DSB/decay/cell if decays occurring only during nonrepair conditions were counted. This DSB production efficiency is in agreement with Monte Carlo semiempirical models of the action of radiation on DNA.

5-[123I]iodo-2'-deoxyuridine in the radiotherapy of an early ascites tumor model

The extreme biological toxicity of Auger emitters is caused by the decay-associated, highly localized deposition of energy. The antineoplastic capability of an Auger-electron emitter, iodine-123, incorporated into the thymidine analog, 5-iodo-2'-deoxyuridine (IUdR) was evaluated in an intraperitoneal (i.p.) murine ovarian tumor (MOT) in female C3HeB/FeJ mice. Total doses of 0.37 to 8.88 MBq (10-240 microCi) 123IUdR were administered i.p. in five equally divided fractions at 24, 28, 32, 36, and 40 hr after the i.p. inoculation of 0.5 to 1.6 x 10(6) tumor cells per mouse. Control tumor-bearing animals were injected with identical volumes of saline at 4-hr intervals. Biodistribution studies demonstrated a distinct and localized uptake of 123IUdR in the MOT cells (1% of the injected dose was associated with MOT cells 24 hr after the last injection), whereas in animals without tumor there was no radioactivity associated with the peritoneal cells. Analogous results were obtained from scintigraphic images where the focal area of abdominal activity persisted only in MOT-bearing mice while it cleared from the abdomen of the controls. The 50% survival (median survival) of the control group was 19 days for an inoculum of 1.6 x 10(6) MOT cells per animal, whereas the median survival of MOT-bearing animals treated with 123IUdR increased by 11 days for the highest administered dose (8.88 MBq, 240 microCi) and resulted in a 20% absolute survival at 7 weeks. Statistically significant absolute survival prolongation was found with all of the total administered doses. The prolongation of both median and absolute survival time of the tumor-bearing animals treated with 123IUdR conclusively indicates the substantial antineoplastic activity of the Auger-electron emitter iodine-123.

Capping and internalization of a monoclonal antibody-surface antigen complex: a possible mode of interaction of monoclonal antibodies and tumor cells

Our results demonstrate that upon incubation of 125I-3G5 (a monoclonal IgM against a membrane ganglioside antigen on RINm5F cells) with rat insulinoma RINm5F cell monolayers at 37 degrees C, the IgM is rapidly internalized. Cell-bound radioactivity, detectable within 10 to 15 minutes, reaches a peak at 4 hours. By 24 hours the intracellular radioactivity has decreased to about 37.5% of the 4-hour value, accompanied by an increase in free 125I in the incubation medium. The incubation of 125I-3G5 with RINm5F cell monolayers at 4 degrees C shows that this series of events is inhibited by low temperature. Microautoradiography confirms these events indicating the presence of radiolabeled antibody on the plasma membrane as well as distinct capping processes and diffuse radioactive deposits within the cells as early as 5 to 10 minutes after initiating incubation at 37 degrees C. Electron microscopy autoradiography provides a detailed demonstration of the capping phenomenon and of endocytic vacuoles, followed at later times by the distribution of radioactive deposits throughout the cell. This model constituted by the capping of the 125I-3G5-ganglioside complex on rat insulinoma RINm5F cells may be useful in elucidating a possible mode of interaction of monoclonal antibodies and tumor cells.

Potential for tumor therapy with iodine-125 labeled immunoglobulins

Because of the high intranuclear toxicity of Auger-electron emitters, the use of radioiodinated (123I, 125I) 5-iodo-2'-deoxyuridine (IUdR)-antibody conjugates for cancer therapy has been examined. The results have demonstrated that all the conditions necessary for labeling DNA in vivo are present: uptake of the radiolabeled immunoglobulin by target cells, its subsequent internalization, the degradation of the IUdR-protein conjugate by lysosomal enzymes, and the incorporation of the radionucleoside into DNA.

Specific uptake of the auger electron-emitting thymidine analogue 5-[123I/125I]iodo-2'-deoxyuridine in rat brain tumors: diagnostic and therapeutic implications in humans

Glial neoplasms of the human central nervous system are malignancies that have defied treatment. Part of the problem lies in the limitations of current diagnostic techniques which are unable to identify small collections of neoplastic glia within normal parenchyma and in the difficulty of sterilizing these tumors because of limited selectivity of the cytotoxic agents available. The thymidine analogue 5-iodo-2'-deoxyuridine (IdUrd) radiolabeled with 123I and 125I was injected directly into an intracerebral rat 9L gliosarcoma and found to be a sensitive and specific agent for the detection of this neoplasm in rats. External gamma camera imaging (123I) visualized tumors as small as 0.5 mm in diameter. Autoradiography (125I) indicated that IdUrd was incorporated into the DNA of neoplastic glia only. Since 123I emits gamma-photons suitable for scintigraphy, [123I]IdUrd holds promise for the diagnosis of brain tumors in humans as well. Furthermore, since 123I and 125I are Auger electron emitters that have demonstrated antineoplastic effects, direct administration of [123I]IdUrd or [125I]IdUrd into tumors may also have potential for the treatment of central nervous system malignancies.

Inhomogeneous deposition of radiopharmaceuticals at the cellular level: experimental evidence and dosimetric implications

We have undertaken an experimental examination of the conventional internal dosimetry assumptions of homogeneity of radionuclide deposition in tissues. The distribution of radiolabeled Microlite has been quantitated in mouse liver at the millimeter (multicellular) and the micrometer (cellular) levels. Measurements of radioactivity in 1-mm3 tissue samples indicate homogeneous radionuclide distribution; those derived from autoradiographs of 0.5-micron tissue sections show that, relative to other cells, the colloid was concentrated 200- to 1000-fold in liver macrophages. The dosimetric implications of such inhomogeneous radionuclide distribution in human liver, where similar radionuclide distribution is expected, are discussed on the basis of a recently developed model for calculating the dose at the cellular level, and the estimates are compared to conventional internal dosimetry predictions. It is demonstrated that during routine diagnostic examinations with 99mTc-Microlite, conventional dosimetry underestimates the dose to labeled human liver cells by factors of 8-30.

Immunoradiometric assay for antibodies recognizing antigenic gangliosides

An immunoradiometric assay for monoclonal antibodies (MoAb) recognizing gangliosides as antigens (Ag) is described and exemplified by the determination of the immunoreactive fraction of 125I-radiolabeled monoclonal A2B5 and 3G5 IgM antibodies. The assay was performed in 96-well microtiter plates equipped with cellulose filter membranes, using the antigens extracted from cloned rat insulinoma cells (RINm5F). The selectivity of the assay was demonstrated by studying the interactions of A2B5 and 3G5 with specific Ag and irrelevant gangliosides. The binding of 125I-A2B5 and 125I-3G5 to the RINm5F extract containing Ag exceeded 35% of the total applied radioactivity and depended on the degree of protein damage caused by radiolabeling, whereas irrelevant glycolipids bound 0.4% (s.d. 0.3%) of total applied 125I-3G5 and 1.2% (s.d. 0.3%) of 125I-A2B5 regardless of the initial amount of the radiolabeled MoAb used. Additional support for the specificity of this method was acquired in experiments with the A1D2 IgG antibody that interacts with a glycoprotein expressed by RINm5F cells but not with the gangliosidic antigens present in the same cell line. 125I-A1D2 bound neither Ag (0.47%; s.d. 0.12%) nor brain extracts containing irrelevant gangliosides (0.32%; s.d. 0.17%). The data for the specific MoAb-Ag systems were analyzed using a modified Lineweaver-Burk graph. By plotting the reciprocal of the fraction of specifically bound MoAb versus the reciprocal of the antigen concentration, the immunoreactive fraction was determined. The present method is rapid, convenient, and independent of variability in antigen expression on the cell surface.

5-iodo-2'-deoxyuridine-protein conjugates: synthesis and enzymatic degradation

Several halogenated analogs of thymidine and cytidine possess antineoplastic and antiviral activity. They are also powerful sensitizers of bacterial and mammalian cells to lethal effects of x-irradiation. An important factor limiting the effectiveness of these agents in therapy is their extremely short half-life in circulation due to rapid hepatic dehalogenation. An approach to this problem is to deliver the drug directly to its target using monoclonal antibodies. This study evaluates the lysosomotropic delivery systems of halogenated pyrimidines using 5-iodo-2'-deoxyuridine [IUdR] as a model. IUdR, derivatized and activated at either the 3'- or the 5'-position forms covalent adducts with the epsilon-amino groups of the lysine residues in proteins (bovine serum albumin [BSA], and immunoglobulins [IgG]). Two methods suitable for conjugation of IUdR to proteins involving either the formation of acyl-imidazoles in the reaction of IUdR succinates with N,N'-carbonyldiimidazole or the preparation of N-succinimidyl esters of IUdR succinates were established. Both derivatives express comparable reactivity toward proteins. The degree of IUdR incorporation is easily controlled by the ratio of reagents. The succinate "arm" linking IUdR to protein is susceptible to lysosomal hydrolysis in vitro releasing intact IUdR. The half-life of the IUdR-IgG conjugate in the presence of the lysosomal enzymes was shown to be approximately twice that of the IUdR-BSA conjugate.

Intermolecular engagement of estrogen receptors indicated by the formation of a high molecular weight complex during activation

After exposure to ligand at 0-4 degrees C, estrogen receptors from mouse uteri characteristically eluted between thyroglobulin (Mr 669,000) and ferritin (Mr 443,000) during size-exclusion HPLC. However, when preparations were warmed with ligand under mild activating conditions, most or all of the receptor was observed as a much larger complex, which eluted between dextran blue 2000 and thyroglobulin. Formation of the large complex required ligand, was inhibited by molybdate, and occurred even in 0.4 M KCl. Slower ligand dissociation characterized the large complex, indicating that activated receptors were included preferentially. This large complex did not form when charged cytosols were aged, concentrated, or precipitated, indicating that formation was not the result of random aggregation. After exposure to conditions commonly used for activation (25 degrees C, 60 min), most receptor existed as a very large, monodisperse complex of finite size, predicting an ordered structure for these large complexes that should be useful for defining the types of proteins which can interact with estrogen receptors. Formation of the large complex was not impeded or disrupted by EDTA, RNase, DNase I, thiourea, or mercaptoethanol; however, the capacity to form this large complex was not demonstrated by preparations that had been exposed to trypsin or by the small receptor forms obtained after salt extraction. Proteolytic sensitivity and lack of sensitivity to RNase or DNase indicate that interactions between receptors and other proteins are involved in peak A formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Radiotoxicity of 5-[123I]iodo-2'-deoxyuridine in V79 cells: a comparison with 5-[125I]iodo-2'-deoxyuridine

The toxic effects of the short-lived (T 1/2 = 13.2 h) Auger-electron-emitting isotope 123I, incorporated in the form of 123IUdR into the DNA of V79 cells in vitro, have been investigated and compared to those of 125IUdR. For the concentrations tested, the rate of incorporation of 123IUdR at any time is proportional to the concentration of extracellular radioactivity. The curve for survival of clonogenic cells decreases exponentially and exhibits no shoulder at low doses. The mean lethal dose (D37) to the nucleus is 79 +/- 9 cGy and is about the same as that obtained previously with 125IUdR. However, the total number of decays needed to produce this D37 with 123IUdR is about twice that required with 125IUdR, approximately equal to the ratio of the energy deposited in microscopic volumes by 125I and 123I, respectively. This correlation suggests that nuclear recoil, electronic excitation, and chemical transmutation are probably of minor importance to the observed biological toxicity with either isotope. The results also indicate that there are no saturation effects in the decay of 125IUdR in the DNA of V79 cells (i.e., all of the emitted energy is biologically effective) and that each of the two steps involved in the 125I decay is equally effective in causing biological damage.