Validation of a model predicting enrollment status in a chemoprevention trial for breast cancer.

We evaluated the performance of a regression model in predicting enrollment status in a chemoprevention trial for breast cancer using a population independent of that from which the model was derived. In years 1 and 2 of recruitment, questionnaires were completed by eligible participants following attendance at informational meetings about the Breast Cancer Prevention Trial. The variables in the original model, based on women recruited in year 1, included not being able to take estrogen replacement therapy (ERT), concern about the side effects of tamoxifen, the possibility of getting a placebo, the out-of-pocket expenses associated with the trial, and disagreement with the statement "significant others would be reassured if the respondent was taking tamoxifen." These variables were used to predict enrollment status of women newly recruited to the trial in year 2. Among the 89 women in the study population who responded to the questionnaire, 66% did not enroll in the trial. By applying the original logistic regression model, enrollment status in the trial was correctly predicted for 72% of year 2 questionnaire respondents. Age and risk scores, as binary variables, were used in a derived logistic model to determine whether they provided additional predictive information on enrollment status. The resulting four-factor model, which predicted nonenrollment, included: age of > or = 50 years, not being able to take ERT, expressed concern that significant others would not be reassured if the respondent was taking tamoxifen, and concern about out-of-pocket expenses associated with the trial. This model correctly classified 76% of the respondents. The logistic regression models performed reasonably well in predicting enrollment status. Not being able to take ERT remained the strongest factor predicting nonenrollment. More research is needed to evaluate factors that motivate persons to seek participation in primary chemoprevention trials in culturally diverse populations.

Reduced immunogenicity and improved pharmacokinetics of humanized anti-Tac in cynomolgus monkeys.

The anti-Tac mAb has been shown to bind to the p55 chain of the IL-2R, block IL-2 binding and inhibit T cell proliferation. A humanized form of anti-Tac (HAT) has been constructed that retains the binding properties of murine anti-Tac (MAT). These two mAb were evaluated in cynomolgus monkeys to compare relative immunogenicity and pharmacokinetic properties. Monkeys treated with HAT daily for 14 days exhibited anti-HAT antibody titers which were 5- to 10-fold lower than their MAT-treated counterparts and these antibodies developed later than in the MAT-treated monkeys. Two of four monkeys receiving a single injection of MAT developed anti-MAT antibodies, whereas none of four monkeys developed antibodies after a single treatment with HAT. In monkeys injected with either HAT or MAT daily for 14 days, the anti-antibody titers induced were inversely related to the amount of anti-Tac administered. Antibodies that developed against MAT were both anti-isotypic and anti-idiotypic, whereas those developed against HAT appeared to be predominantly anti-idiotypic. The pharmacokinetic properties, that is the half-life and area under the curve values, of HAT were also significantly different from those of MAT. The area under the curve values for HAT in naive monkeys were approximately twofold more than those for MAT, and the mean serum half-life of HAT was 214 h, approximately four- to fivefold more than MAT. These pharmacokinetic values were reduced in monkeys previously sensitized with HAT or MAT suggesting that the presence of anti-antibodies altered these parameters.

Application of receptor-affinity chromatography to bioaffinity purification.

Receptor-affinity chromatography based upon the receptor-ligand interactions has been utilized for the purification of recombinant human interleukin-2 (rIL-2) from microbial and mammalian sources. The receptor-affinity purification process of rIL-2 is used as a model system to demonstrate the utility of this approach for the purification of recombinant proteins. The receptor-affinity purified biomolecule is shown to be biochemically and biologically more homogeneous than the immunoaffinity purified material.

Purification of the IL-2 receptor (TAC) by ligand-affinity chromatography and utilization of the immobilized receptor for receptor-affinity chromatography (RAC) purification of IL-2, mutant IL-2, and IL-2 fusion proteins.

Recombinant technology has facilitated the production of two soluble forms of human p55 interleukin-2 receptor (IL-2R) in Chinese hamster ovary cells. We have developed a ligand-affinity method for the medium-scale purification of these two soluble forms of the IL-2R, based on the biochemical interactions between the matrix-bound ligand (interleukin-2) and its soluble receptor. The affinity-purified IL-2R is further purified by anion-exchange chromatography followed by gel filtration. This method has provided enough highly pure IL-2R for structure and function studies and for use in practical applications such as high-flux drug-screening assays. The purified IL-2R subsequently has been immobilized on silica gel and employed for the purification of recombinant IL-2. Receptor-affinity-chromatography-purified IL-2 contains only a highly active monomeric form of the lymphokine, in contrast to immunoaffinity chromatography where several molecular forms of IL-2 with varying degrees of biologic activity are recovered. Receptor-affinity chromatography has been successfully applied to the purification of several mutant IL-2 as well as an IL-2-Pseudomonas exotoxin (IL2-PE40) fusion protein that is a 54.5-kDa chimeric protein in which the cell recognition domain is replaced by IL-2. The IL-2-PE40 is a potential cytotoxic agent for cells bearing the IL-2 receptor.

The use of proteolysis and direct N-terminal sequence analysis to study human interleukin-2/receptor interaction on solid support.

An immobilized interleukin-2 receptor which is capable of binding interleukin-2 and suitable for direct N-terminal sequence analysis was employed to study interleukin-2/receptor interactions. Sensitive tryptic sites on the immobilized receptor and its interleukin-2 complex were identified by sequence analyses and compared. The results have revealed that the N-terminal region of interleukin-2 is not involved in receptor binding and the peptide segment covering residues 36-39 in the receptor is probably near or involved in the interleukin-2 binding site. The rapidity and simplicity make this solid phase sequence approach a good method for analyzing interleukin-2/receptor interaction and may be suitable for studying other protein-ligand interactions.

Medium-scale ligand-affinity purification of two soluble forms of human interleukin-2 receptor.

Recombinant technology has facilitated the production of two soluble forms of human interleukin-2 receptor (IL-2R) in Chinese hamster ovary cells. We have developed a ligand-affinity method for the medium-scale purification of these two IL-2Rs, based on the biochemical interactions between the matrix-bound ligand (interleukin-2) and its soluble receptor. The affinity-purified IL-2R is further purified by anion-exchange chromatography followed by gel filtration. This method has provided enough highly pure IL-2R for structure and function studies and for use in practical applications such as high-flux drug screening assays and the receptor-affinity purification of human recombinant interleukin-2.

Structural analysis of recombinant soluble human interleukin-2 receptor. Primary structure, assignment of disulfide bonds and core IL-2 binding structure.

A purified soluble and functional form of recombinant human interleukin-2 receptor, engineered and expressed in Chinese hamster ovary cells, was structurally characterized. The primary sequence of this 224 amino acid recombinant protein which lacks most of the carboxy-terminal transmembrane and cytoplasmic portions of the intact protein was established by sequence analyses. The disulfide bonds were assigned by comparative peptide mapping of the reduced and non-reduced peptide digests. As in the case of natural interleukin-2 receptor they occur between cysteines 3-147, 46-104, 131-163, and 28/30-59/61. Based on assignment of the disulfide bonds, a structural model of the interleukin-2 receptor for interleukin-2 binding is proposed.

Hematologic studies during isolated ultrafiltration.

The effect of negative-pressure isolated ultrafiltration on leucocytes, platelets, and clotting factors was evaluated in maintenance hemodialysis patients. A significant decrease in the number of leucocytes was observed during the first 45 minutes of ultrafiltration. However, by one hour, leucocyte counts had returned to pre-ultrafiltration values. A slight, of haptoglobin, free hemoglobin, or fibrinogen after one hour of isolated ultrafiltration. Levels of fibrin degradation products and fibrin monomers similarly showed no change. Heparin administration alone had no effect on the above hematologic values. We suggest that isolated ultrafiltration, as clinically practised, has little acute effect on the coagulation system, and does not cause detectable hemolysis. The transient decrease in leucocyte count, and the modest fall in platelet count that were found are in keeping with changes previously reported to occur during hemodialysis.

Urinary saturation measurements in calcium nephrolithiasis.

Urinary saturation with respect to calcium oxalate monohydrate was measured in 111 consecutive patients with calcium nephrolithiasis. Each patient also was evaluated by a detailed conventional metabolic protocol. Patients with idiopathic hypercalciuria produced abnormally oversaturated urine more frequently than normal subjects and normocalciuric patients, but normocalciuric patients had unexpectedly high levels of urine saturation. Measuring levels of calcium concentration, oxalate concentration, or the chemical concentration product of calcium and oxalate in urine did not predict oversaturation. During thiazide treatment, saturation level tended to fall if it was initially elevated, whether the patient was hypercalciuric or not. Patients whose urine was not remarkably oversaturated showed no tendency to elaborate even less saturated urine during thiazide treatment; instead, the average calcium oxalate saturation level remained constant. Direct urine saturation measurements can detect a small but significant number of normocalciuric patients who have marked oversaturation with respect to calcium oxalate and appear to benefit from treatment.