Targeted expression of a toxin gene to D1 dopamine receptor neurons by cre-mediated site-specific recombination

Idiopathic Parkinson's disease involves the loss of midbrain dopaminergic neurons, resulting in the presynaptic breakdown of dopaminergic transmission in the striatum. Huntington's disease and some neurodegenerative diseases with Parkinsonian features have postsynaptic defects caused by striatal cell death. Mice were generated in which an attenuated form of the diphtheria toxin gene (tox-176) was expressed exclusively in D1 dopamine receptor (D1R)-positive cells with the aim of determining the effect of this mutation on development of the basal ganglia and on the locomotor phenotype. Transgenic mice expressing Cre, a site-specific DNA recombinase, were crossed with a second line in which a transcriptionally silenced tox-176 gene was inserted into the D1R gene locus by homologous recombination. Young doubly transgenic mutant mice expressing the tox-176 gene displayed bradykinesia, dystonia, and had falls caused by myoclonic jerks. The mutant brain had evidence of apoptosis and reactive gliosis and, consistent with the D1R expression pattern, the striatum was reduced in volume, and the Islands of Calleja were absent. In contrast, the cortex was of normal thickness. D1Rs were not detectable in mutants by in situ hybridization or ligand autoradiography, whereas D2 dopamine receptor (D2R) mRNA and protein was present in the striatum. In addition, substance P and dynorphin, neuropeptides known to be expressed in D1R-positive striatonigral projection neurons were not detectable. Enkephalin, a marker found in D2-positive striatopallidal projection neurons was expressed in the mutant brain. The mutant represents a novel neurodegenerative disease model with a dramatic extrapyramidal phenotype.

Dose escalation trial of indium-111-labeled anti-carcinoembryonic antigen chimeric monoclonal antibody (chimeric T84.66) in presurgical colorectal cancer patients

Chimeric T84.66 (cT84.66) is a high-affinity (1.16x10(11) M(-1)) IgG1 monoclonal antibody against carcinoembryonic antigen (CEA). The purpose of this pilot trial was to evaluate the tumor-targeting properties, biodistribution, pharmacokinetics and immunogenicity of 111In-labeled cT84.66 as a function of administered antibody protein dose.

METHODS

Patients with CEA-producing colorectal cancers with localized disease or limited metastatic disease who were scheduled to undergo definitive surgical resection were each administered a single intravenous dose of 5 mg of isothiocyanatobenzyl diethylenetriaminepentaacetic acid-cT84.66, labeled with 5 mCi of 111In. Before receiving the radiolabeled antibody, patients received unlabeled diethylenetriaminepentaacetic acid-cT84.66. The amount of unlabeled antibody was 0, 20 or 100 mg, with five patients at each level. Serial blood samples, 24-hr urine collections and nuclear images were collected until 7 days postinfusion. Human antichimeric antibody response was assessed up to 6 mo postinfusion.

RESULTS

Imaging of at least one known tumor site was performed in all 15 patients. Fifty-two lesions were analyzed, with an imaging sensitivity rate of 50.0% and a positive predictive value of 76.9%. The antibody detected tumors that were not detected by conventional means in three patients, resulting in a modification of surgical management. Interpatient variations in serum clearance rates were observed and were secondary to differences in clearance and metabolic rates of antibody and antibody:antigen complexes by the liver. Antibody uptake in primary tumors, metastatic sites and regional metastatic lymph nodes ranged from 0.4% to 134% injected dose/kg, resulting in estimated 90Y-cT84.66 radiation doses ranging from 0.3 to 193 cGy/mCi. Thirteen patients were evaluated 1-6 mo after infusion for human antichimeric antibody, and none developed a response. No major differences in tumor imaging, tumor uptake, pharmacokinetics or organ biodistribution were observed with increasing protein doses, although a trend toward increasing blood uptake and decreasing liver uptake was observed with increasing protein dose.

CONCLUSION

Chimeric T84.66 demonstrated tumor targeting comparable to other radiolabeled intact anti-CEA monoclonal antibodies. Its immunogenicity after single administration was lower than murine monoclonal antibodies. These properties make 111In-cT84.66, or a lower molecular weight derivative, attractive for further evaluation as an imaging agent. Yttrium-90 dosimetry estimates predict potentially cytotoxic radiation doses to select tumor sites, which makes 90Y-cT84.66 also appropriate for further evaluation in Phase I radioimmunotherapy trials. Although clinically important changes in biodistribution, pharmacokinetics and tumor targeting with increasing protein doses of 111In-cT84.66 were not demonstrated, the results do suggest that antibody clearance from the blood is driven by hepatic uptake and metabolism, with more rapid blood clearance seen in patients with liver metastases. These patients with rapid clearance and potentially unfavorable biodistribution for imaging and therapy may, therefore, be a more appropriate subset in which to evaluate the role of administering higher protein doses. This underscores the need to further identify, characterize and understand those factors that influence the biodistribution and clearance of radiolabeled anti-CEA antibodies, to allow for better selection of patients for therapy and rational planning of radioimmunotherapy.

Structural studies of polymer-cushioned lipid bilayers

The structure of softly supported polymer-cushioned lipid bilayers, prepared in two different ways at the quartz-solution interface, were determined using neutron reflectometry. The polymer cushion consisted of a thin layer of branched, cationic polyethyleneimine (PEI), and the bilayers were formed by adsorption of small unilamellar dimyristoylphosphatidylcholine (DMPC) vesicles. When vesicles were first allowed to adsorb to a bare quartz substrate, an almost perfect bilayer formed. When the polymer was then added to the aqueous solution, it appeared to diffuse beneath this bilayer, effectively lifting it from the substrate. In contrast, if the polymer layer is adsorbed first to the bare quartz substrate followed by addition of vesicles to the solution, there is very little interaction of the vesicles with the polymer layer, and the result is a complex structure most likely consisting of patchy multilayers or adsorbed vesicles.

A neutron reflectivity study of polymer-modified phospholipid monolayers at the solid-solution interface: polyethylene glycol-lipids on silane-modified substrates

The structure of polymer-decorated phospholipid monolayers at the solid-solution interface was investigated using neutron reflectometry. The monolayers were composed of distearoylphosphatidylethanolamine (DSPE) matrixed with varying amounts of DSPE-PEG (DSPE with polyethylene glycol covalently grafted to its headgroup). Mixed lipid monolayers were Langmuir-Blodgett deposited onto hydrophobic quartz or silicon substrates, previously hydrophobized by chemically grafting a robust monolayer of octadecyltrichlorosilane (OTS). We show that this method results in homogeneous and continuous phospholipid monolayers on the silanated substrates and determine that the grafted PEG chains extend away from the monolayers into the solvent phase as a function of their density, as expected from scaling theories. In addition, ligands were coupled to the end of the PEG chains and selective binding was demonstrated using fluorescence microscopy. Our results demonstrate that these constructs are ideal for further characterization and studies with well-defined monomolecular films.

Monte Carlo-assisted voxel source kernel method (MAVSK) for internal beta dosimetry

A method is described for the determination of patient-specific organ beta doses given a known cumulated internal radioactivity distribution. A voxel source kernel for 90Y analogous to the point source function was simulated. Dose to each organ of interest could then be estimated by convolving the voxel source kernel with the patient's 3-D volume with known radioactivity assigned to each voxel. The dose calculation on eight organs took less than 1 min per patient using a Sun Sparc10 workstation.

Estimating residence times and their associated errors in patient absorbed-dose calculation

OBJECTIVE

An approach for estimating organ residence times (tau) and their errors in patient internal emitter radiation dosage calculations has been determined.

METHODS

Using a modeling algorithm and its associated parameters, chimeric anti-CEA monoclonal antibody (cT84.66) patient organ uptake data and residence times of source organ activity were calculated. Through the covariance matrix of the model's parameters and subsequent Monte Carlo simulations, errors in organ residence time (gamma tau) also were estimated

RESULTS

These relative tau errors were found to be model-dependent; increasing as the number of organs being simultaneously modeled in a set of two patients being considered for 90Y-cT84.66 radioimmunotherapy.

CONCLUSION

Use of modeling and Monte Carlo methods provide a general, direct procedure for calculating the degree of accuracy of activity integrals and other mathematical functions of kinetic variables.

Effect of proparacaine on tropicamide-induced mydriasis

PURPOSE

The use of a topical anesthetic before the instillation of a mydriatic is recommended in order to enhance both the rate and magnitude of pupillary dilation. However, there is a paucity of data supporting the prior use of topical anesthetics with tropicamide, the most commonly used mydriatic agent in optometric practice. Therefore, we conducted a study to determine the clinical effect of proparacaine on tropicamide-induced pupillary dilation.

METHODS

We investigated the effects of prior instillation of 0.5% proparacaine (Ophthetic) on pupillary dilation with 0.5% tropicamide (Mydriacyl) using a double-blind, placebo-controlled protocol on two groups of young adult subjects. Thirty subjects, aged between 18 and 30 years, were divided into 2 groups of 15, based on whether they had light- or dark-colored irides. The pupils of both eyes of each subject were dilated with tropicamide, but only one eye, chosen at random, received proparacaine (experimental condition), whereas the other was administered a saline placebo (control condition). Pupil diameter was measured using a ruler and magnifying loupe.

RESULTS

Subjects with light-colored irides had a greater average pupil dilation than subjects with dark-colored irides. There was a small, statistically significant difference in pupil diameter between the control and experimental conditions, but only for subjects with light-colored irides. The rate of pupillary dilation to peak pupil diameter and the rate of decrease in pupil diameter after peak pupil diameter was reached did not differ between experimental conditions or subject groups.

CONCLUSIONS

Although prior instillation of topical proparacaine produced a statistically significant difference in pupil diameter for subjects with light-colored irides, the result was not clinically significant. Therefore, we do not recommend the use of a topical anesthetic before tropicamide-induced mydriasis for young adult patients.

Clinical evaluation of indium-111-labeled chimeric anti-CEA monoclonal antibody

Chimeric T84.66 (cT84.66) is a high-affinity (1.16 x 10[11] M[-1]) IgG1 monoclonal antibody (MAb) against carcinoembryonic antigen (CEA). This pilot trial evaluated the tumor-targeting properties, biodistribution, pharmacokinetics and immunogenicity of 111In-labeled cT84.66.

METHODS

Patients with CEA-producing metastatic malignancies were administered a single intravenous dose of 5 mCi 111In-diethylenetriaminepentaacetic acid-cT84.66. Serial blood samples, 24-hr urine collections and nuclear images were collected up to 7 days postinfusion. Human antichimeric antibody response was assessed up to 6 mo postinfusion.

RESULTS

Imaging of at least one known tumor site was observed in 14 of 15 (93%) patients. Seventy-four lesions were analyzed with an imaging sensitivity rate of 45.1% and a positive predictive value of 94.1%. In one patient, two additional bone metastases developed within 6 mo of antibody administration at sites initially felt to be falsely positive on scan. One patient developed a human antichimeric antibody response predominantly to the murine portion of the antibody. The antibody cleared serum with a median T(1/2alpha) of 6.53 hr and a T(1/2beta) of 90.87 hr. Interpatient variations in serum clearance rates were observed and were secondary to differences in clearance and metabolic rates of antibody-antigen complexes by the liver. One patient demonstrated very rapid clearance of antibody by the liver, which compromised antibody localization to the primary tumor. Antibody uptake in primary and metastatic tumors ranged from 0.5% to 10.5% injected dose/kg, resulting in estimated radiation doses ranging from 0.97 to 21.3 cGy/mCi 90Y. Antibody uptake in regional lymph nodes ranged from 1.3% to 377% injected dose/kg, resulting in estimated radiation doses ranging from 2.0 to 617 cGy/mCi 90Y.

CONCLUSION

Chimeric T84.66 demonstrated tumor targeting that was comparable to that of other radiolabeled intact anti-CEA Mabs. Its immunogenicity after single administration was lower than murine Mabs. These properties make cT84.66 or a lower molecular weight derivative attractive for further evaluation as an imaging agent. These same properties also make it appropriate for future evaluation in Phase I therapy trials. Finally, a wide variation in the rate of antibody clearance was observed, with one patient demonstrating very slow clearance, resulting in the highest estimated marrow dose of the group, and one patient demonstrating unusually rapid clearance, resulting in poor antibody localization to tumor. Data from this study suggest that serum CEA levels, antibody-antigen complex clearance and, therefore, antibody clearance are influenced by both the production and clearance rates of CEA. This underscores the need to further identify, characterize and understand those factors that influence the biodistribution and clearance of radiolabeled anti-CEA antibodies to allow for better selection of patients for therapy and rational planning of radioimmunotherapy.

Expression of brain-derived neurotrophic factor and TrkB neurotrophin receptors after striatal injury in the mouse

Brain-derived neurotrophic factor (BDNF) promotes the survival and differentiation of nigral dopaminergic neurons and supports the activity of dopaminergic cells grafted into the striatum. However, little attention has been given to the physiological role of endogenous BDNF and its receptor TrkB within the nigrostriatal dopamine system. We know that striatal injury is followed by long-term stimulation of dopaminergic activity in the striatum, could BDNF play a role in this phenomenon? One week after physical injury to the striatum of C57/Black mice, just before dopaminergic activation becomes obvious, in situ hybridization on coronal sections through mouse striatum reveals that BDNF mRNA expression increases significantly before returning to basal levels within 1 month. Expression of mRNA for TrkB follows a very different pattern. No change of expression of the full-length and catalytically competent TrkBTK+ receptor is seen. However, expression of the truncated form of the receptor TrkTK-, which lacks the catalytic tyrosine kinase domain, does increase and stays elevated for at least 2 months after injury. When combined with observations of dopaminergic activation after striatal injury and the neuroprotective effects of BDNF introduced into the striatum, our findings suggest that BDNF and TrkBTK- do indeed play a role in dopaminergic regeneration and repair.

Proteolytic degradation of host hemoglobin by schistosomes

Schistosomes acquire amino acids for growth, development, and reproduction by catabolizing hemoglobin obtained from ingested host erythrocytes. While the biochemical pathway(s) involved has not been determined definitively, a number of proteases including schistosome legumain and cathepsin L-, D-, B- and C-like enzymes have been ascribed roles in the degradation of hemoglobin to diffusible peptides. Transcripts encoding these schistosome proteases, which appear to be expressed in the gastrodermis and cecum of the schistosome, have been reported. Because these enzymes are candidate targets at which to direct novel anti-schistosomal therapies, the comparative biochemistry of these and their counterpart mammalian proteases is now the focus of research in a number of laboratories. This paper reviews reports dating from 40 years ago to the present on how schistosomes digest host-derived hemoglobin, and interprets apparent anomalies in some earlier compared to later reports, the latter having benefited from the availability of PCR and gene cloning technologies. More specifically, the review concentrates on five proteolytic enzymes, and their associated genes, which have been ascribed key roles in the pathway of hemoglobin degradation.

Expression of glial cell line-derived neurotrophic factor (GDNF) mRNA following mechanical injury to mouse striatum

Although glial cell line-derived neurotrophic factor (GDNF) expression is low in the adult brain, its administration protects dopaminergic neurons against a range of insults, leading to the suggestion of a role in dopaminergic regeneration. If locally produced GDNF is to fulfil a role in dopaminergic regeneration after injury, it seems reasonable to hypothesize that its expression will increase after mechanical trauma. We have demonstrated that GDNF mRNA expression increases within 6 h of using a wire knife to injure adult mouse striatum. Expression doubles after 1 week and remains elevated for at least 1 month. Most GDNF expression is associated with haemosiderin-containing cells, indicating production by brain macrophages. GDNF production by macrophages may be essential for neural regeneration following CNS trauma.

Schistosomes express two forms of cathepsin D

We report here a cDNA and its deduced amino acid sequence encoding a cathepsin D-like, aspartic protease expressed by adult stages of the human blood fluke Schistosoma mansoni. The cDNA encodes a short signal peptide, a pro-enzyme peptide of 37 amino acid residues, and a mature enzyme of 377 residues which has strong homology with mammalian cathepsins D. This aspartic protease, although 84% identical in amino acids of the mature enzyme region to the previously reported cathepsin D from the Asian schistosome S. japonicum, differs remarkably from the S. japonicum enzyme in having a carboxyl terminal extension of 43 amino acid residues. These cathepsins D of schistosomes may play pivotal roles in the degradation of hemoglobin obtained by the parasites from ingested host erythrocytes.

Direct measurement of a tethered ligand-receptor interaction potential

Many biological recognition interactions involve ligands and receptors that are tethered rather than rigidly bound on a cell surface. A surface forces apparatus was used to directly measure the force-distance interaction between a polymer-tethered ligand and its receptor. At separations near the fully extended tether length, the ligands rapidly lock onto their binding sites, pulling the ligand and receptor together. The measured interaction potential and its dynamics can be modeled with standard theories of polymer and colloidal interactions.

Dopaminergic responses to striatal damage

The improvements obtained by grafting dopamine-rich tissues into the striatum of patients with Parkinson's disease are generally attributed to production and release of dopamine by the graft. However, it is becoming increasingly clear that grafting also stimulates the host dopaminergic system. We provide evidence in a mouse model of striatal damage that surgical cavitation induces a concerted response from the dopaminergic system with proliferation of striatal presynaptic dopamine uptake sites, increased tyrosine hydroxylase activity, increased concentrations of dopamine, dihydroxyphenylacetic acid and homovanillic acid. The response increases with time and ultimately includes contralateral stimulation of striatal tyrosine hydroxylase activity and elevation of dihydroxyphenylacetic acid and homovanillic acid concentrations. The time course and extent of the host dopaminergic response suggests that it may make a significant contribution to observed clinical improvements after intrastriatal transplantation in human parkinsonism.

Minibody: A novel engineered anti-carcinoembryonic antigen antibody fragment (single-chain Fv-CH3) which exhibits rapid, high-level targeting of xenografts

A novel engineered antibody fragment (VL-VH-CH3, or "minibody") with bivalent binding to carcinoembryonic antigen (CEA) was produced by genetic fusion of a T84.66 (anti-CEA) single-chain antibody (scFv) to the human IgG1 CH3 domain. Two designs for the connecting peptide were evaluated. In the T84.66/212 LD minibody, a two-amino acid linker (generated by fusion of restriction sites) was used to join VH and CH3. In the T84.66/212 Flex minibody, the human IgG1 hinge plus an additional 10 residues were used as the connecting peptide. Size exclusion chromatography of purified minibodies demonstrated that both proteins had assembled into Mr80,000 dimers as expected. Furthermore, analysis by SDS-PAGE under nonreducing conditions was consistent with disulfide bond formation in the hinge of the T84.66 Flex minibody. Purified minibodies retained high affinity for CEA (KA, 2 x 10(9) M(-1)) and demonstrated bivalent binding to antigen. Tumor targeting properties were evaluated in vivo using athymic mice bearing LS174T human colon carcinoma xenografts. 123I-labeled T84.66 minibodies demonstrated rapid, high tumor uptake, reaching 17% injected dose/gram (%ID/g) for the LD minibody and 33%ID/g for the Flex minibody at 6 h following injection. Radioiodinated minibody also cleared rapidly from the circulation, yielding high tumor:blood uptake ratios: 44.5 at 24 h for the LD minibody and 64.9 at 48 h for the Flex minibody. Rapid localization by the T84.66/212 Flex minibody allowed imaging of xenografts at 4 and 19 h after administration.

Tumor localization of anti-CEA single-chain Fvs: improved targeting by non-covalent dimers

BACKGROUND

Genetic engineering can produce novel antibody fragments with improved properties for applications such as tumor targeting in vivo.

OBJECTIVES

To produce stable monomeric (27 kDa) and dimeric (55 kDa) forms of a single-chain Fv (scFv) from the anti-carcinoembryonic antigen (anti-CEA) antibody T84.66, and assess the targeting and biodistribution properties in an animal model.

STUDY DESIGN

ScFv were constructed with either a 28 or 14 amino acid connecting peptide and expressed by secretion from E. coli. Following affinity purification, proteins were characterized by gel electrophoresis and mass spectrometry. Binding properties were assessed by size exclusion HPLC after incubation with antigen, and affinities determined by surface plasmon resonance. The shorter linker favored formation of dimers (and higher multimers) which showed unusual stability. ScFv were radiolabeled with 125I for tumor targeting and biodistribution studies of monomeric or dimeric forms were conducted in athymic mice bearing LS174T human colorectal carcinoma xenografts.

RESULTS

125I-scFv monomers and dimers targeted exhibited rapid clearance kinetics in tumor-bearing mice. Nevertheless, the anti-CEA scFvs targeted very well to xenografts, leading to high tumor: normal organ ratios (greater than 20:1 at 24 h) for both forms. Tumor localization of the non-covalent dimers was much higher than monomers, reaching 10-15% injected dose per gram at 1 h.

CONCLUSION

Non-covalent dimers of scFv (also known as diabodies) are stable, easy to produce and show excellent targeting as compared to monomeric scFv, probably due to increased mass and valency.

Initial experience evaluating 90yttrium-radiolabeled anti-carcinoembryonic antigen chimeric T84.66 in a phase I radioimmunotherapy trial

Chimeric T84.66 (cT84.66) is a high-affinity (5 x 10(10) M-1) anti-carcino-embryonic antigen (CEA) IgG1. In a recently completed pretherapy imaging trial, 111In-labeled cT84.66 demonstrated targeting of CEA-producing metastatic sites and low immunogenicity, with human antichimeric antibody (HACA) response in only 1 of 15 patients after a single administration. The purpose of the present study was to evaluate cT84.66-diethylenetriaminepentaacetic acid labeled with 90Y in a dose-escalation Phase I trial. Patients with metastatic CEA-producing malignancies received imaging doses of 5 mCi 111In-labeled cT84.66 first, followed 1-2 weeks later by 5 mg cT84.66 labeled with the therapeutic dose of 90Y. Immediately following the therapeutic infusion, diethylenetriaminepentaacetic acid was administered by continuous i.v. infusion over 3 days at 250 mg/m2 body surface area/24 h. Biodistribution, tumor targeting, absorbed radiation dose estimates, antibody clearance, and HACA response were evaluated through blood samples, 24-h urine collections, and nuclear images performed at serial time points after infusion. To date, three patients with metastatic colorectal cancer have been evaluated at the first dose level of 5 mCi/m2. No side effects were associated with antibody administration. Localization of the antibody to nonhepatic metastatic sites was observed. Size-exclusion high-performance liquid chromatography demonstrated the formation of CEA:antibody complexes in serum in all three patients. A significant variation among patients in the clearance rate of the antibody and complexes from blood to liver was seen, which resulted in a reciprocal relationship between estimated liver dose and red marrow dose. Patients who demonstrated faster clearance to liver demonstrated greater excretion of a low-molecular-weight metabolite through the urine. Two patients developed HACA response, which persisted at 4 months after therapy. At this first dose level, no tumor responses were seen and reversible grade 1 thrombocytopenia was observed in 2 patients. cT84.66 demonstrated effective localization in CEA-producing tumors. Its low immunogenicity after a single administration makes it attractive for further evaluation as a radioimmunotherapeutic agent. However, further evaluation is needed to determine whether its immunogenicity will remain low after multiple administrations. Additionally, in two of the three patients, we identified rapid clearance of the antibody to the liver. This underscores the need to identify, characterize, and understand further those factors that influence the biodistribution and clearance of anti-CEA antibodies to allow for better selection of patients for therapy and rational planning of radioimmunotherapy.

Leukaemia inhibitory factor prevents injury induced proliferation of striatal dopamine uptake sites

The injury associated with implantation of an inert gelatin matrix (gel foam) into normal mouse striatum induces a long-lived increase in binding of [3H]mazindol to presynaptic dopamine uptake sites, probably due to proliferation of striatal dopaminergic terminals. Because of the known effects of leukaemia inhibitory factor (LIF) on catecholaminergic cells, we tested the hypothesis that LIF may alter the striatal dopaminergic response to injury in vivo. Application of LIF to mouse striatum in a gel foam implant abolished the usual injury induced proliferation of dopamine uptake sites. The ability of LIF to prevent proliferation of dopamine terminals may have important implications for our understanding of neural regeneration, the aetiology of Parkinson's disease and its treatment by intrastriatal grafting.

Glutathione S transferase-theta (GSTT1) genetic polymorphism among Chinese, Malays and Indians in Singapore

Glutathione S-transferase-theta (GSTT1) is subject to a genetic polymorphism where approximately 50% of a Caucasian population are homozygous for the null allele. Because of the possible association of the polymorphism with increased cancer risk in individuals, we genotyped by polymerase chain reaction 187 normal Chinese, 167 normal Malays and 152 normal Indians from Singapore and Malaysia. The proportion of Chinese, Malays and Indians with the null genotype were 58%, 38% and 16% respectively and mirrored previously reported frequencies of the GSTM1 null genotype in these populations. The frequency of the combined GSTM1 and GSTT1 null genotypes among Chinese, Malays and Indians were 37%, 22% and 5% respectively. The similarity with predicted frequencies indicated no interaction between the two genetic polymorphisms.

Frequency of mutant CYP1A1, NAT2 and GSTM1 alleles in normal Indians and Malays

Several xenobiotic metabolizing enzymes, including CYP1A1, NAT2 and GSTM1, are subject to genetic polymorphisms. Because these enzymes are important for the detoxification and/or bioactivation of drugs and carcinogens, these polymorphisms have important implications in therapeutics and cancer susceptibility. The distributions of CYP1A1, NAT2 and GSTM1 genotype frequencies in unrelated individuals of the Indian (n = 139) and Malay (n = 146) populations were characterized by the polymerase chain reaction. The respective allelic frequencies of wild-type and mutant alleles of CYP1A1 were 0.82 and 0.18 for the Indians, and 0.69 and 0.31 for the Malays. The frequencies of wild-type, M1, M2 and M3 of NAT2 among Indians were 0.44, 0.20, 0.32 and 0.04 respectively. The corresponding NAT2 allelic frequencies in Malays were 0.41, 0.12, 0.38 and 0.09. The GSTM1*A allele could not be amplified in 33.1% of Indians and 61.6% of Malays. At least one GSTM1*B allele was detected in 7.2% and 7.5% of the respective populations. The allelic frequencies of CYP1A1, NAT2 and GSTM1 among Malays are similar to previously reported frequencies among Chinese in the region. These findings will be of importance in the determination of cancer risks in these populations.

On the correction for radioactive decay in pharmacokinetic modeling

The question of how to include radioactive decay during biological modeling with first-order differential equations was considered. Modeling may involve either experimental data y(t) or decay-corrected data z(t) [identical to exp(lambda t)y(t) where lambda is the decay constant] for each compartment. It is sometimes assumed that the latter are solutions to corresponding purely pharmacokinetic models (no decay). We primarily compared the two analyses in the case where the model did not require simultaneous consideration of both labeled and unlabeled material. A general theorem was found which limits the use of decay-corrected data to pharmacokinetic models containing linear, homogeneous differential equations. By way of verification, an example of this model type was analyzed for a chimeric monoclonal antibody biodistribution in man. Even in this case, statistically significant differences between the two solutions showed that one may find different model parameters depending upon which data set (y or z) was analyzed. For other mathematical forms, the analyst must include the physical decay in all relevant compartments. By analyzing an open, quadratic model, effects of not including decay were seen to be maximized if the biological rate constant was > or = lambda, the physical decay constant. Finally, using monoclonal antibody-antigen reactions, similar discrepancies between the z functions and the pharmacokinetic variables were demonstrated. This result was found to persist even if competitive molecules were included. We conclude that decay-corrected data may be shown, but should not be entered into the modeling equations unless the latter are of the linear, homogeneous form.

gamma-Interferon administration after 90yttrium radiolabeled antibody therapy: survival and hematopoietic toxicity studies

PURPOSE

Hematopoietic toxicity is the dose-limiting factor for radioimmunotherapeutic regimens. Cytokines have been shown to decrease hematopoietic toxicity in animals exposed to whole-body irradiation. The purpose of this study was to investigate the effects of murine gamma-interferon (gamma-IFN) on survival and hematopoietic toxicity in mice treated with high dose 90yttrium labeled anticarcinoembryonic antigen (CEA) monoclonal antibody.

METHODS AND MATERIALS

Balb/c nu/nu mice were injected intravenously with 250 Ci 90Y-T84.66 (a murine anti-CEA monoclonal antibody). Thirty thousand units of gamma-IFN was administered i.v. 24 h later. Control mice received either 250 Ci 90Y-T84.66 alone or 30,000 units gamma-IFN alone. Survival, antibody biodistribution, and bone marrow histologic studies were then performed.

RESULTS

Only 7% of the animals treated with 90Y-T84.66 survived up to 40 days posttreatment, when the study was terminated. In contrast, 52% of the mice treated with both 90Y-T84.66 and gamma-IFN survived 40 days posttherapy. No toxic deaths were seen in the control group administered gamma-interferon alone. Histologic examination of the bone marrow of animals receiving 90Y-T84.66 and gamma-IFN showed cellular depletion of 40-70% of the hematopoietic cells by 48 h. Cell depletion was 50-70% and 20% by 72 h and 8 days posttherapy, respectively. The marrow of the 90Y-T84.66-treated control group was depleted to a level of 50-80% at 48 h, and remained depleted at 90% at 72 h and 8 days posttherapy. No marrow cell reduction was seen in the gamma-IFN-only treated group. Biodistribution studies showed no alterations in antibody biodistribution or kinetics that could account for the changes in bone marrow toxicity after gamma-IFN.

CONCLUSION

These results demonstrate that gamma-IFN can reduce the hematologic toxicity resulting from high dose radioimmunotherapy. Histologic studies of bone marrow suggest that gamma-IFN acts primarily to accelerate myelorestoration of the bone marrow. Further studies exploring the use of gamma-IFN as an adjunct to radioimmunotherapy are therefore warranted.

Electrically conducting polymers can noninvasively control the shape and growth of mammalian cells

Electrically conducting polymers are novel in that their surface properties, including charge density and wettability, can be reversibly changed with an applied electrical potential. Such properties might render conducting polymers unique for biological applications. However, the majority of research on conducting polymers has been carried out under nonbiological conditions. We synthesized optically transparent polypyrrole thin films and studied them in environments suitable for protein adsorption and mammalian cell culture. In vitro studies demonstrated that extracellular matrix molecules, such as fibronectin, adsorb efficiently onto polypyrrole thin films and support cell attachment under serum-free conditions. When aortic endothelial cells were cultured on fibronectin-coated polypyrrole (oxidized) in either chemically defined medium or the presence of serum, cells spread normally and synthesized DNA. In contrast, when the polymer was switched to its neutral state by applying an electrical potential, both cell extension and DNA synthesis were inhibited without affecting cell viability. Application of a similar electrical potential to cells cultured on indium tin oxide surfaces had no effect on cell shape or function. These data suggest that electrically conducting polymers may represent a type of culture substrate which could provide a noninvasive means to control the shape and function of adherent cells, independent of any medium alteration.