Antibody drug conjugates, targeting cancer-expressed EGFR, exhibit potent and specific antitumor activity

The monoclonal antibody '40H3 ' binds to EGFRvIII and to full-length EGFR when it is overexpressed on cancer cells. To generate candidate cytotoxic antibody-drug conjugates (ADCs), 40H3 was modified by the addition of small molecular weight payloads that included two tubulin-modifying agents, two topoisomerase inhibitors and a pyrrolobenzodiazepine (PBD) dimer. Conjugates retained antigen binding activity comparable to the unmodified 40H3 antibody. The cytotoxicity of five distinct ADCs was evaluated on a variety of EGFR-expressing cells including three triple negative breast cancer (TNBC) lines. Generally, the 40H3 conjugate with the PBD dimer (40H3-Tesirine) was the most active killing agent. The killing of EGFR-positive cells by 40H3-Tesirine correlated with the number of surface binding sites for 40H3. However, bystander killing was also evident in experiments with antigen-negative cells. In vivo tumor xenograft experiments were conducted on two TNBC tumor lines. Three treatments with the 40H3-Tesirine ADC at 1 mg/kg were sufficient to achieve complete remissions without evidence of mouse toxicity. Data support the development of ADCs derived from the 40H3 antibody for the treatment of cancers that express EGFRvIII or high levels of EGFR.

Automated summary

The monoclonal antibody '40H3' can bind to both EGFRvIII and full-length EGFR when overexpressed on cancer cells. By modifying 40H3 with small molecular weight payloads, including tubulin-modifying agents, topoisomerase inhibitors, and a PBD dimer, candidate cytotoxic antibody-drug conjugates (ADCs) were generated. Among the five evaluated ADCs, the 40H3-Tesirine conjugate showed the highest cytotoxicity against EGFR-positive cells. In vivo experiments on TNBC tumor lines demonstrated that three treatments with 40H3-Tesirine ADC achieved complete remissions without mouse toxicity. These findings support the development of ADCs derived from the 40H3 antibody for treating EGFRvIII-expressing or high EGFR-expressing cancers.