Zhengxing Qu

Characterization of a New Humanized Anti-CD20 Monoclonal Antibody, IMMU-106, and Its Use in Combination with the Humanized Anti-CD22 Antibody, Epratuzumab, for the Therapy of Non-Hodgkin’s Lymphoma

Purpose: A new humanized anti-CD20 monoclonal antibody (MAb), IMMU-106, was evaluated to elucidate its action as an antilymphoma therapeutic, as a single agent, and in combination with the anti-CD22 MAb, epratuzumab. Experimental Design: Antiproliferative effects, apoptotic effects, and the ability of IMMU-106 to mediate complement-mediated cytotoxicity and antibody-dependent cellular cytotoxicity on a panel of non-Hodgkin’s lymphoma (NHL) cell lines were compared with the chimeric anti-CD20 MAb, rituximab, and evaluated in light of the various levels of antigen expression by the cell lines. In vivo therapy studies were performed in SCID mice bearing disseminated Raji lymphoma. Results: The mechanisms of cytotoxicity of IMMU-106 were found to be similar to rituximab, and include direct apoptosis, antibody-dependent cellular cytotoxicity, and complement-mediated cytotoxicity. IMMU-106 was also found to be very similar to rituximab in terms of antigen-binding specificity, binding avidity, and dissociation constant. Treatment of Raji-bearing SCID mice with IMMU-106 yielded median survival increases of up to 4.2-fold compared with control mice. Survival in mice treated with IMMU-106 plus epratuzumab was compared with IMMU-106 treatment alone. Although the combined treatment did not improve median survival, an increased proportion of long-term survivors was observed. An enhanced antiproliferative effect was also observed in vitro in SU-DHL-6 cells when IMMU-106 was combined with epratuzumab. These findings are consistent with the up-regulation of CD22 expression observed after pretreatment of NHL cells in vitro with CD20 MAb (IMMU-106). Conclusions: It is expected that in humans IMMU-106 should be at least as effective as rituximab and, due to its human framework construction, it may exhibit different pharmacokinetic, toxicity, and therapy profiles. In addition, it may be possible to enhance efficacy by combination therapy comprised of anti-CD20 and other B-cell lineage targeting MAbs, such as epratuzumab. The current results emphasize that in vitro as well as in vivo studies with many of the NHL cell lines were generally predictive of the known activity of anti-CD20 MAbs in NHL patients, as well as the enhanced efficacy of epratuzumab combined with rituximab observed in early clinical trials.

Anti-CD74 Antibody-Doxorubicin Conjugate, IMMU-110, in a Human Multiple Myeloma Xenograft and in Monkeys

Purpose: IMMU-110 is a drug immunoconjugate composed of doxorubicin conjugated to the humanized anti-CD74 monoclonal antibody, hLL1, at a doxorubicin/monoclonal antibody ratio of ∼8:1 (mol/mol). CD74 is a rapidly internalizing molecule associated with HLA-DR, which has high expression by several tumor types. Here, we describe safety evaluations of IMMU-110 in mice and monkeys as well as efficacy studies in a xenograft model of the human multiple myeloma cell line, MC/CAR. Experimental Design:In vitro binding of IMMU-110 was determined by a cell-based ELISA and cytotoxicity of IMMU-110 assayed with a tetrazolium assay. Pharmacokinetics and biodistribution of radiolabeled IMMU-110 were examined in tumor-free BALB/c mice, and the therapeutic effectiveness was evaluated in severe combined immunodeficient mice bearing MC/CAR cells. Acute toxicity of IMMU-110 was studied in CD74-positive cynomolgus monkeys (Macaca fascicularis). Results:In vitro, IMMU-110 specifically binds to CD74 and is cytotoxic against MC/CAR cells. In vivo, IMMU-110 displayed a pharmacokinetic and biodistribution profile identical to that of unconjugated hLL1 monoclonal antibody, except for higher kidney uptake. Treatment with a single dose of IMMU-110 as low as 50 μg antibody/mouse (or 1.4 μg doxorubicin/mouse), 5 days postinjection of the multiple myeloma cells, resulted in cure of most mice. In mice, no host toxicity of IMMU-110 was observed at the highest protein dose tested (125 mg/kg). In cynomolgus monkeys, bone marrow toxicity was observed at 30 and 90 mg/kg doses. Conclusions: The excellent safety and efficacy profile of IMMU-110 supports clinical testing of this immunoconjugate in the treatment of CD74-positive B-cell malignancies.

Pretargeting of Carcinoembryonic Antigen–Expressing Cancers with a Trivalent Bispecific Fusion Protein Produced in Myeloma Cells

Purpose: To characterize a novel trivalent bispecific fusion protein and evaluate its potential utility for pretargeted delivery of radionuclides to tumors. Experimental Design: hBS14, a recombinant fusion protein that binds bispecifically to carcinoembryonic antigen (CEA) and the hapten, histamine-succinyl-glycine (HSG), was produced by transgenic myeloma cells and purified to near homogeneity in a single step using a novel HSG-based affinity chromatography system. Biochemical characterization included size-exclusion high-performance liquid chromatography (SE-HPLC), SDS-PAGE, and isoelectric focusing. Functional characterization was provided by BIAcore and SE-HPLC. The efficacy of hBS14 for tumor pretargeting was evaluated in CEA-expressing GW-39 human colon tumor–bearing nude mice using a bivalent HSG hapten (IMP-241) labeled with 111In. Results: Biochemical analysis showed that single-step affinity chromatography provided highly purified material. SE-HPLC shows a single protein peak consistent with the predicted molecular size of hBS14. SDS-PAGE analysis shows only two polypeptide bands, which are consistent with the calculated molecular weights of the hBS14 polypeptides. BIAcore showed the bispecific binding properties and suggested that hBS14 possesses two functional CEA-binding sites. This was supported by SE-HPLC immunoreactivity experiments. All of the data suggest that the structure of hBS14 is an 80 kDa heterodimer with one HSG and two CEA binding sites. Pretargeting experiments in the mouse model showed high uptake of radiopeptide in the tumor, with favorable tumor-to-nontumor ratios as early as 3 hours postinjection. Conclusions: The results indicate that hBS14 is an attractive candidate for use in a variety of pretargeting applications, particularly tumor therapy with radionuclides and drugs.

Preclinical Therapy of Breast Cancer with a Radioiodinated Humanized Anti-EGP-1 Monoclonal Antibody: Advantage of a Residualizing Iodine Radiolabel

AbstractBackground. A humanized monoclonal antibody (MAb), hRS7, labeled with 131I-IMP-R4, was evaluated for the preclinical radioimmunotherapy (RAIT) of breast cancer. 131I-IMP-R4 is an improved residualizing form of 131I that overcomes the short tumor residence time associated with conventionally radioiodinated MAbs. RS7, an internalizing MAb, recognizes epithelial glycoprotein-1, which is highly expressed in the carcinomas of breast, lung, ovary, and prostate. Methods. A humanized version of RS7 was generated by CDR-grafting and transfection. In vivo experiments were carried out in nude mice bearing subcutaneous MDA-MB-468 human breast cancer xenografts. Therapy experiments were performed using established tumors with mean tumor volume (MTV) of 0.3 cm3, and single administrations, at ∼70% of the estimated maximum tolerated doses (MTD), of the residualizing 131I-IMP-R4-hRS7 and 131I-hRS7 prepared by the conventional chloramine-T method [131I-hRS7 (CT)]. Therapeutic specificity was determined by comparison with untreated and non-specific MAb controls. Results. hRS7 was functionally very similar to murine and chimeric RS7. A biodistribution study using 125I-IMP-R4-hRS7 and 131I-hRS7 (CT) indicated a dosimetric advantage for the former. The MTVs 8 weeks post-treatment were 20, 163, and 280% of the starting MTVs of 131I-IMP-R4-hRS7-treated, 131I-hRS7 (CT)-treated, and untreated groups, respectively. Complete remissions were seen in 5 of 11 [and 6 of 8] mice treated with 131I-IMP-R4-hRS7, and in 1 of 11 mice treated with 131I-hRS7(CT). 131I-IMP-R4-hRS7 was significantly more efficacious than 131I-hRS7 (CT) [P = 0.01 for AUC] and the control 131I-IMP-R4-MAb. Conclusion. 131I-IMP-R4-hRS7 is a promising new agent for RAIT, providing significant therapeutic advantage in comparison to the conventionally 131I-labeled antibody.

Carbohydrates engineered at antibody constant domains can be used for site-specific conjugation of drugs and chelates.

To improve the efficiency of site-specific conjugation of chelates and drugs to antibodies, and to minimize the incidence of immunoreactivity perturbation to the resultant immunoconjugates, Asn-linked oligosaccharide moieties were designed and engineered into the constant domains of a humanized anti-CD22 monoclonal antibody, hLL2. From 10 potential glycosylation mutants, two CH1 domain glycosylation sites, HCN1 and HCN5, were identified that were positioned favorably for glycosylation. The carbohydrate (CHO) chains attached at these sites were differentially processed so that HCN5-CHOs were physically larger than HCN1-CHOs. Although both the CH1-appended CHOs, and the LL2 Vkappa-appended CHOs conjugated efficiently with small chelates, the HCN5-CHOs, due to the structural and positional superiority, appear to be a better conjugation site for large drug complexes, such as 18 kDa doxorubicin (DOX)-dextran.

Generation of a high-producing clone of a humanized anti-B-cell lymphoma monoclonal antibody (hLL2)†

LL2 is a murine immunoglobulin (Ig)G2a‐kappa anti‐B‐cell monoclonal antibody with proven targeting and therapeutic efficacy in the management of non‐Hodgkins lymphoma (NHL). The authors had previously generated a humanized LL2 (hLL2) that demonstrated binding properties identical to those of LL2. Nevertheless, the productivity of the cell line was insufficient for large‐scale production of the antibody for clinical studies. Therefore, the authors chose an amplifiable system for the generation of hLL2.