PDGFbeta receptor blockade inhibits intimal hyperplasia in the baboon

BACKGROUND

We have evaluated the use of a mouse/human chimeric anti-platelet-derived growth factor-beta receptor antibody in combination with heparin to inhibit intimal hyperplasia in the saphenous artery of the baboon after balloon angioplasty.

METHODS AND RESULTS

The study evaluated lesion development in sequential injuries made 28 days apart. Each animal received control treatment after the first injury and antibody/heparin therapy after the second injury to the contralateral artery. The antibody was administered by bolus intravenous injections (10 mg/kg) on study days 1, 4, 8, 15, and 22 and heparin coadministered by continuous intravenous infusion at a dose of 0.13 mg/kg per hour. Morphometric analysis of tissue sections showed a 53% decrease in intimal area after antibody/heparin treatment (P=0.005), corresponding to a 40% decrease in the intima-to-media ratio (P=0.005). Smooth muscle cell proliferation in the injured wall, measured at both 4 and 29 days after balloon injury, were similar in the control and antibody/heparin-treated animals.

CONCLUSIONS

These data suggest that platelet-derived growth factor plays a key role in the development of intimal lesions at sites of acute vascular injury in the nonhuman primate.

Generation and characterization of a recombinant/chimeric B72.3 (human gamma 1)

We report here the generation and characterization of a recombinant/chimeric construct of murine gamma 1 monoclonal antibody (MAb) B72.3, containing the murine variable region and a human gamma 1 constant region [designated cB72.3(gamma i)]. cB72.3(gamma 1) was generated by first isolating functionally rearranged VH and VL genes of B72.3 from partial genomic libraries in phage vectors. Construction of mouse-human chimeric heavy and light chain genes was performed by inserting restriction fragments carrying VL and VH regions of B72.3 into unique sites of expression vectors which contains sequences encoding constant regions of human kappa and gamma 1, respectively. The expression constructs were subsequently electroporated into SP2/0 cells. The transfected SP2/0 murine cell line has been shown to synthesize cB72.3(gamma 1) at a level of 10-20 micrograms/ml. Reciprocal competition radioimmunoassays demonstrated that cB72.3(gamma 1), a previously described cB72.3(gamma 4), and native B72.3 (designated nB72.3) competed similarly. A rat anti-idiotype MAb made against nB72.3 was shown to bind equally well to cB72.3(gamma 1) and to the nB72.3. Immunochemical studies of the nB72.3, cB72.3(gamma 4), and cB72.3(gamma 1) revealed slight differences in size among the three MAb forms on sodium dodecyl sulfate gels and revealed a higher isoelectric point for the cB72.3(gamma 1). Antibody-dependent cell-mediated cytotoxicity experiments using human lymphokine-activated killer effector cells indicated better tumor cell killing by the cB72.3(gamma 1) than the nB72.3 or cB72.3(gamma 4). Dual label studies of coinjected cB72.3(gamma 1) and nB72.3 revealed that both MAbs could efficiently localize human tumor xenografts in athymic mice. Pharmacokinetic studies, analyzing the blood clearance of cB72.3(gamma 1), cB72.3(gamma 4), and nB72.3 in mice, showed that the nB72.3 beta phase of clearance was slower than that of other MAb forms. However, when the pharmacokinetic patterns of these three MAbs forms were analyzed in monkeys, the cB72.3(gamma 1) and the nB72.3 showed similar clearance curves, while the cB72.3(gamma 4) showed a much slower plasma clearance. In view of the binding properties of nB72.3 and its ability to localize a range of carcinomas in clinical trials, the studies reported here demonstrate that the cB72.3(gamma 1) may serve as a potentially useful diagnostic and/or therapeutic reagent.

Characterization and biodistribution of recombinant and recombinant/chimeric constructs of monoclonal antibody B72.3

B72.3 is a murine monoclonal antibody (IgG1) that recognizes a tumor-associated glycoprotein, termed TAG-72. B72.3 has been shown, using a variety of methodologies, to have a high degree of selective reactivity for colorectal, ovarian, lung, and breast carcinomas. Radiolabeled B72.3 has been administered both i.v. and i.p. in patients with colorectal and ovarian cancer as well as other carcinomas and has been shown to selectively bind to approximately 70-80% of metastatic lesions. Greater than 50% of the patients that have been treated with B72.3 have developed an immunological response to murine IgG after a single injection. In an attempt to minimize the immune response of these patients to the administered murine monoclonal antibody, we developed a recombinant form of the murine B72.3 as well as a recombinant/chimeric antibody, using the variable regions of the murine B72.3 and human heavy chain (gamma 4) and light chain (kappa) constant regions. We report here that both the recombinant B72.3 [rB72.3] and the recombinant/chimeric B72.3 [cB72.3(gamma 4)] IgGs maintain the tissue binding and idiotypic specificity of the native murine IgG. The native B72.3, rB72.3, and cB72.3(gamma 4) IgGs were radiolabeled and the biodistribution of these IgGs was studied in athymic mice bearing human colon carcinoma xenografts (LS-174T). Differences were observed between the cB72.3(gamma 4) and the native B72.3 in the percentage of injected dose/g that localized in the tumor. The somewhat lower absolute amounts of the cB72.3(gamma 4) in the tumor are mostly likely due to the observed more rapid clearance from the blood and body of the mouse as compared to the native B72.3 and rB72.3. All three forms [native B72.3, rB72.3, and cB72.3(gamma 4)] of the IgG, however, were able to localize the colon tumor with similar radiolocalization indices [percentage of injected dose/g in tumor divided by the percentage of injected dose/g in normal tissue].

Codon usage can affect efficiency of translation of genes in Escherichia coli

By inserting synthetic oligonucleotides into a highly expressed gene in E. coli it has been shown that unfavourable codon usage can reduce the maximum translation rate of a protein. However, in the case of the codon used (AGG), a significant effect on translation was only seen at very high transcription rates from a gene containing multiple copies of the unfavourable codon.