Quantitative intratumoural microdistribution and kinetics of 131I-huA33 antibody in patients with colorectal carcinoma

Abstract

BackgroundThe ability of recombinant antibodies to adequately penetrate into tumours is a key factor in achieving therapeutic effect; however, the behaviour of antibodies at a cellular level in tumours is poorly understood. The purpose of this study was to investigate those factors that influence the macroscopic and microscopic intratumoural distribution of an IgG1-humanized antibody, huA33, in colorectal tumours.MethodsTwelve patients were infused with radiolabelled huA33 at 7 days prior to elective surgery for colorectal carcinoma. Macroscopic huA33 uptake was determined by both gamma well counter and autoradiography measurements of the resected tumour specimens. Microscopic uptake was then quantitated at a cellular level and compared to vascular penetrance. The impact of variation in tumour antigen (GPA33) expression, tumour size, specimen type (primary vs metastatic), presence of macroscopic necrosis, and tumour vasculature on huA33 uptake were examined.ResultsThe I-huA33 uptake in whole tumour sections was (mean ± SD) 5.13 ± 2.71 × 10−3% injected dose per gram (ID/g). GPA33 was expressed in all viable tumour cells, and huA33 uptake was excellent regardless of tumour size and specimen type. In tumours with macroscopically evident central necrosis (n = 5), huA33 uptake in tumour necrotic centres was lower than in viable peripheries (0.606 ± 0.493 vs 2.98 ± 2.17 × 10−3%ID, p = 0.06). However, when corrected for low cell viability in necrotic centres, uptake of huA33 at the cellular level was highly comparable to that in the more viable tumour periphery (7.10 ± 5.10 × 10−9 vs 3.82 ± 3.67 × 10−9%ID/cell, p = 0.4). In the five patients who exhibited macroscopic necrosis in their tumours, huA33 showed excellent tissue penetration, with a maximum penetration distance of 26 μm in peripheral tumour regions and 118 μm in central regions. No correlation was observed between 131I-huA33 uptake in tumour on a cellular basis and tumour vascularity.ConclusionsIn patients with colorectal carcinoma, monoclonal antibody huA33 effectively targets viable tumour cells in all cellular milieus examined, including effective penetration into necrotic tumour centres, a novel and therapeutically important finding.

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Autoradiography techniques and quantification of drug distribution

“…Another recent study coupled the use of histochemical staining and an attempt at quantitative MARG to study the micro-distribution and kinetics of 131 I-huA33 antibody in patients with colorectal cancer (Ciprotti et al 2014). These investigators infused patients with 131 I-huA33 and obtained tumor samples for analysis by gamma counting, x-ray autoradiography, and histochemical staining for GPA33 expression and CD31-positive blood vessels.…”

Preparation of an engineered safer immunotoxin against colon carcinoma based on the ribotoxin hirsutellin A

“…In this regard, the use of the variable fragment of mAbA33 (scFvA33), which retains its binding specificity, could allow a better penetration into the tumor, as reported previously . However, the ability of a 131I‐huA33 antibody to penetrate into the necrotic centres of large tumors was not reduced . Thus, mAbA33 antibody or scFvA33 immunoconjugates would demonstrate similar penetration into a tumor.…”