Targeting a Radiosensitizing Antibody-Drug Conjugate to a Radiation-Inducible Antigen

Purpose: We recently discovered that anti-TIP1 antibody activates endocytosis in Cancer cells, which facilitates retention of antibody and dissociation of a conjugated drug. To improve the pharmacokinetics and Cancer specificity of radiosensitizing drugs, we utilized antibody-drug conjugates (ADCs) that bind specifically to radiation-inducible antigen, TIP1, on non-small cell lung Cancer (NSCLC). This approach exploits the long circulation time of Antibodies to deliver a radiosensitizing drug to Cancer each day during radiotherapy.

Experimental design: Antibodies to TIP1 were prioritized based on affinity, cancer-specific binding, and internalization. The lead antibody, 7H5, was conjugated with a cytotoxic drug MMAE because of its ability to radiosensitize Cancer. Cytotoxicity, colony formation, and tumor growth studies were performed with 7H5-VcMMAE in combination with radiation.

Results: 7H5 showed a high affinity to recombinant TIP1 protein and radiation-inducible TIP1 on the Cancer cell surface. 7H5 undergoes endocytosis in NSCLC cells in vitro. We obtained an average drug-to-antibody ratio (DAR) of 4.25 for 7H5-VcMMAE. A 70% reduction in viable cells was observed following 7H5-VcMMAE treatment compared with 7H5 alone in both A549 and H1299 cells. 7H5-VcMMAE sensitized NSCLC cells to radiation, thereby significantly decreasing the surviving fraction. The ADC combined with radiation showed a prolonged delay in tumor growth and improved survival in A549 and H1299 tumor models.

Conclusions: Targeting radiation-inducible TIP1 with a radiosensitizing ADC is a promising strategy to enhance the therapeutic efficacy of NSCLC. This novel approach of targeting with ADCs to radiation-inducible antigens will lead to clinical trials in lung Cancer patients treated with radiotherapy.