Elizabeth Carswell Richards

Enhanced in vivo growth and resistance to rejection of tumor cells expressing dominant negative IFNγ receptors

Using a neutralizing monoclonal antibody specific for murine IFN gamma we show that endogenously produced IFN gamma plays an obligate role in mediating LPS-induced rejection of the Meth A fibrosarcoma tumor in syngeneic BALB/c mice. To examine the cellular targets of IFN gamma action, we generated IFN gamma-insensitive tumor cells by stably overexpressing in Meth A a truncated dominant negative form of the murine IFN gamma receptor alpha chain. When implanted in BALB/c mice, IFN gamma-insensitive Meth A cells displayed enhanced tumorigenicity compared with control Meth A cells and were not rejected when tumor-bearing mice were treated with concentrations of LPS that eliminated control tumors. In Meth A immune mice, IFN gamma-insensitive Meth A did not establish tumors while IFN gamma-insensitive tumors grew in a progressive manner. In addition, the IFN gamma-insensitive tumor cells were unable to elicit strong protective immunity to subsequent wild-type tumor challenge. These results show that IFN gamma has direct effects on tumor cell immunogenicity and thus plays an important role in promoting tumor cell recognition and elimination.

Phase I/II study of iodine 125-labeled monoclonal antibody A33 in patients with advanced colon cancer.

PURPOSE A phase I/II study was designed to determine the maximum-tolerated dose (MTD) of iodine 125-labeled monoclonal antibody A33 (125I-mAb A33), its limiting organ toxicity, and the uptake and retention of radioactivity in tumor lesions. PATIENTS AND METHODS Patients (N = 21) with advanced chemotherapy-resistant colon cancer who had not received prior radiotherapy were treated with a single 125I-mAb A33 dose. 125I doses were escalated from 50 to 350 mCi/m2 in 50-mCi/m2 increments. Radioimmunoscintigrams were performed for up to 6 weeks after 125I-mAb A33 administration. RESULTS All 20 patients with radiologic evidence of disease showed localization of 125I to sites of disease. Twelve of 14 patients, who underwent imaging studies 4 to 6 weeks after antibody administration, had sufficient isotope retention in tumor lesions to make external imaging possible. No major toxicity was observed, except in one patient with prior exposure to mitomycin who developed transient grade 3 thrombocytopenia. Although the isotope showed variable uptake in the normal bowel, gastrointestinal symptoms were mild or absent, and in no case did stools become guaiac-positive. The MTD was not reached at 125I doses up to 350 mCi/m2. However, cytotoxicity assays demonstrated that patients treated with the highest dose had sufficiently high serum levels of 125I-mAb A33 to lyse colon cancer cells in vitro. Among 21 patients, carcinoembryonic antigen (CEA) levels returned to normal in one patient and decreased by 35% and 23%, respectively, in two patients; one additional patient had a mixed response on computed tomography. Additional, significant responses were observed in those patients treated with chemotherapy [carmustine [BCNU], vincristine, flourouracil, and streptozocin [BOF-Strep]) after completion of the 125I-mAb A33 study. CONCLUSION Low-energy emission radioimmunotherapy with doses of up to 350 mCi/m2 of 125I-mAb A33 did not cause bowel or bone marrow toxicity. The modest antitumor activity in these heavily pretreated patients is encouraging because of lack of toxicity at the doses studied. The long radioactivity retention in tumors suggests that isotopes with a long half-life may have a therapeutic advantage, based on calculated dose delivery to tumor versus normal tissue. Due to the low bone marrow dose, further 125I trials with humanized mAb A33 are warranted, and controlled studies must be conducted to evaluate the combination of radioimmunotherapy and chemotherapy.

A Phase I Trial of Humanized Monoclonal Antibody A33 in Patients with Colorectal Carcinoma: Biodistribution, Pharmacokinetics, and Quantitative Tumor Uptake

Purpose: To determine the in vivo characteristics of huA33, a CDR-grafted humanized antibody against the A33 antigen, we have conducted an open-label, dose escalation, biopsy-based phase I trial of huA33 in patients with colorectal carcinoma. Experimental Design: Patients with colorectal carcinoma were infused with [131I]huA33 (400 MBq: 10 mCi) and [125I]huA33 (40 MBq: 1 mCi) 1 week before surgery. There were four huA33 dose levels (0.25, 1.0, 5.0, and 10 mg/m2). Adverse events, pharmacokinetics, biodistribution, tumor biopsies, and immune responses to huA33 were evaluated. Results: There were 12 patients entered into the trial (6 males and 6 females; age range, 39-66 years). No dose-limiting toxicity was observed. The biodistribution of huA33 showed excellent uptake of [131I]huA33 in metastatic colorectal carcinoma. Pharmacokinetic analysis showed no significant difference in terminal half-life (T1/2β) between dose levels (mean ± SD, 86.92 ± 22.12 hours). Modeling of colon uptake of huA33 showed a T1/2 of elimination of 32.4 ± 8.1 hours. Quantitative tumor uptake ranged from 2.1 × 10−3 to 11.1 × 10−3 %ID/g, and tumor/normal tissue and tumor/serum ratios reached as high as 16.3:1 and 4.5:1, respectively. Biosensor analysis detected low-level human anti-human antibody responses in four patients following huA33 infusion. Conclusions: huA33 shows selective and rapid localization to colorectal carcinoma in vivo and penetrates to the center of large necrotic tumors, and colon elimination half-life of huA33 is equivalent to basal colonocyte turnover. The excellent targeting characteristics of this humanized antibody indicate potential for the targeted therapy of metastatic colorectal cancer in future trials.

Pharmacokinetics and microdistribution of polyethylene glycol-modified humanized A33 antibody targeting colon cancer xenografts

Therapeutic proteins have been conjugated with polyethylene glycol (PEGylation) to reduce immunogenicity and enhance circulating dose. Here we have investigated the effect of PEGylation on immunogenicity, pharmacokinetics, and histologic microdistribution of tumor‐targeting antibodies with humanized A33 antibody (huA33) as a model system. Conjugation of huA33 with methoxy‐PEG of Mr 5,000 (32%–34% of primary amines modified) or Mr 20,000 (16%–18% modification) preserved >50% of native huA33 binding to SW1222 colon cancer cells. In mice, both PEGylated forms cleared from serum moderately slower than native huA33. After repeated immunization with PEG‐huA33, antiantibody titers in immunocompetent mice were <5% of those in huA33‐treated controls. Both PEG‐huA33 forms reached approx. 75% of the maximum tumor dose of huA33 in SW1222‐xenografted mice, but their tumor:blood ratios were considerably reduced. To demonstrate immunologic specificity of PEG‐huA33 targeting in SW1222 tumor‐bearing mice, antigenic sites were presaturated by injecting excess native huA33. This reduced subsequent uptake of PEG‐huA33 by up to 80%, whereas presaturation with hu3S193 control antibody had no significant effect. To assess the microdistribution of antibody uptake in the same xenograft model, tumor tissue resected at different time points after antibody administration was examined for human IgG by immunohistochemistry. Both PEG preparations achieved the same peak staining intensity and homogeneity as native huA33 with a delay of several hours. Given the measured reduction in immunoreactivity in vitro, these results demonstrate that the tumor targeting potential of huA33 in vivo is preserved at PEGylation levels sufficient to suppress immunogenicity. Int. J. Cancer 87:382–390, 2000.