EphrinA1-EphA2 interaction-mediated apoptosis and FMS-like tyrosine kinase 3 receptor ligand-induced immunotherapy inhibit tumor growth in a breast cancer mouse model.

Background: The receptor tyrosine kinase EphA2 is overexpressed in several types of cancers and is currently being pursued as a target for breast cancer therapeutics. The EphA2 ligand EphrinA1 induces EphA2 phosphorylation and intracellular internalization and degradation, thus inhibiting tumor progression. The hematopoietic growth factor, FMS-like tyrosine kinase 3 receptor ligand (Flt3L), promotes expansion and mobilization of functional dendritic cells.

Methods: We tested the EphrinA1-EphA2 interaction in MDA-MB-231 breast cancer cells focusing on the receptor-ligand-mediated apoptosis of breast cancer cells. To determine whether EphrinA1-EphA2 interaction-associated apoptosis and Flt3L-mediated immunotherapy would have an additive effect in inhibiting tumor growth, we used an immunocompetent mouse model of breast cancer to evaluate intratumoral (i.t.) inoculation strategies with human adenovirus (HAd) vectors expressing either EphrinA1 (HAd-EphrinA1-Fc), Flt3L (HAd-Flt3L) or a combination of EphrinA1-Fc + Flt3L (HAd-EphrinA1-Fc + HAd-Flt3L).

Results: In vitro analysis demonstrated that an EphrinA1-EphA2 interaction led to apoptosis-related changes in breast cancer cells. In vivo, three i.t. inoculations of HAd-EphrinA1-Fc showed potent inhibition of tumor growth. Furthermore, increased inhibition in tumor growth was observed with the combination of HAd-EphrinA1-Fc and HAd-Flt3L accompanied by the generation of an anti-tumor adaptive immune response.

Conclusions: The results obtained in the present study, indicating the induction of apoptosis and inhibition of mammary tumor growth, show the potential therapeutic benefits of HAd-EphrinA1-Fc. In combination with HAd-Flt3L, this represents a promising strategy for effectively inducing mammary tumor regression by HAd vector-based therapy.