Purpose: CD40 ligand (CD40L, CD154) plays a central role in immunoregulation and also directly modulates epithelial cell growth and differentiation. We previously showed that the CD40 receptor is commonly expressed in primary breast cancer tissues. In this proof-of-principle study, we examined the breast cancer growth-regulatory activities of an oncolytic adenoviral construct carrying the CD40L transgene (AdEHCD40L).
Experimental design: In vitro and in vivo evaluations were carried out on AdEHCD40L to validate selective viral replication and CD40L transgene activity in hypoxia inducing factor-1alpha and estrogen receptor-expressing human breast cancer cells.
Results: AdEHCD40L inhibited the in vitro growth of CD40+ human breast cancer lines (T-47D, MDA-MB-231, and BT-20) by up to 80% at a low multiplicity of infection of 1. Incorporation of the CD40L transgene reduced the effective dose needed to achieve 50% growth inhibition (ED50) by approximately 10-fold. In contrast, viral and transgene expression of AdEHCD40L, as well its cytotoxicity, was markedly attenuated in nonmalignant cells. Intratumoral injections with AdEHCD40L reduced preexisting MDA-MB-231 xenograft growth in severe combined immunodeficient mice by >99% and was significantly more effective (P<0.003) than parental virus AdEH (69%) or the recombinant CD40L protein (49%). This enhanced antitumor activity correlated with cell cycle blockade and increased apoptosis in AdEHCD40L-infected tumor cells.
Conclusions: These novel findings, together with the previously known immune-activating features of CD40L, support the potential applicability of AdEHCD40L for experimental treatment of human breast cancer.