Receptor-Mediated DNA-Targeted Photoimmunotherapy

Tom C Karagiannis,Brenda K.Y Leung,Jonathan M White,Pavel N Lobachevsky,Roger F Martin

doi:10.1158/0008-5472.can-06-1853

Abstract

We show the efficacy of a therapeutic strategy that combines the potency of a DNA-binding photosensitizer, UV(A)Sens, with the tumor-targeting potential of receptor-mediated endocytosis. The photosensitizer is an iodinated bibenzimidazole, which, when bound in the minor groove of DNA and excited by UV(A) irradiation, induces cytotoxic lesions attributed to a radical species resulting from photodehalogenation. Although reminiscent of photochemotherapy using psoralens and UV(A) irradiation, an established treatment modality in dermatology particularly for the treatment of psoriasis and cutaneous T-cell lymphoma, a critical difference is the extreme photopotency of the iodinated bibenzimidazole, approximately 1,000-fold that of psoralens. This feature prompted consideration of combination with the specificity of receptor-mediated targeting. Using two in vitro model systems, we show the UV(A) cytotoxicity of iodo ligand/protein conjugates, implying binding of the conjugate to cell receptors, internalization, and degradation of the conjugate-receptor complex, with release and translocation of the ligand to nuclear DNA. For ligand-transferrin conjugates, phototoxicity was inhibited by coincubation with excess native transferrin. Receptor-mediated UV(A)-induced cytotoxicity was also shown with the iodo ligand conjugate of an anti-human epidermal growth factor receptor monoclonal antibody, exemplifying the potential application of the strategy to other cancer-specific targets to thus improve the specificity of phototherapy of superficial lesions and for extracorporeal treatments.

Highlights

The accumulation of examples of targeted cancer therapy indicates that the long-heralded potential of antitumor antibodies is being realized [1, 2]
Given the extreme photopotency of UVASens, we developed conjugates to direct the drug to specific target cells via receptor-mediated endocytosis, and we establish proof of principle in vitro using two model systems involving transferrin and epidermal growth factor receptor (EGFR) internalization
Human chronic myelogenous leukemia K562 cells, which express f1.5 Â 105 transferrin receptors per cell, were grown in suspension in RPMI 1640 supplemented with 20 mmol/L HEPES, 10% (v/v) fetal bovine serum (FBS; Commonwealth Serum Laboratories, Parkville, Victoria, Australia), 2 mmol/L L-glutamine, and 80 Ag/mL gentamicin

Summary

Introduction

The accumulation of examples of targeted cancer therapy indicates that the long-heralded potential of antitumor antibodies is being realized [1, 2]. Given the extreme photopotency of UVASens, we developed conjugates to direct the drug to specific target cells via receptor-mediated endocytosis, and we establish proof of principle in vitro using two model systems involving transferrin and epidermal growth factor receptor (EGFR) internalization. Two experimental systems were used to establish in vitro proof of principle of delivery of the halogenated ligand to the DNA of target cells via receptor-mediated endocytosis, involving human erythroleukemic K562 cells and human epidermoid carcinoma A431 cells, which overexpress transferrin and EGFRs, respectively.

Results

Conclusion