Abstract 586: Targeted cancer gene-therapy using second-generation HIF-activated oncolytic adenoviruses with increased replication, oncolytic, and anti-tumor efficacy.

A clinically important target for anti-tumor therapy is hypoxia-inducible factor (HIF). HIF is a transcription factor that is expressed in a wide range of primary tumors, metastases, and cancer stem cells, whereas it is undetectable in normal healthy tissues. HIF expression in tumors is associated with (i) resistance to apoptosis, chemotherapy, and radiotherapy and (ii) increased invasion/metastasis, angiogenesis, and patient mortality. Oncolytic adenoviruses (Ad) are a cancer therapy which utilize the cytolytic replication cycle of the virus to specifically kill tumor cells (oncolysis). A wild-type Ad cannot be used for cancer therapy because it lacks tumor-specificity and is toxic to normal healthy tissues. We exploited the differential activation of HIF-dependent gene expression in tumors versus normal tissue for the design of targeted HIF-activated oncolytic Ads. In the first-generation HIF-activated oncolytic Ad called HYPR-Ad, we placed the E1A gene which is essential for Ad replication under the regulation of a HIF-inducible promoter. Our published studies with HYPR-Ad provided critical proof that a HIF-activated oncolytic Ad can specifically kill HIF-active tumor cells and inhibit tumor growth. While therapeutically efficacious, HYPR-Ad exhibited attenuated replication and oncolytic activity when compared to a wild-type Ad in vitro. To overcome these deficiencies and improve anti-tumor efficacy, we created a second-generation HIF-activated oncolytic Ad, called HIF-Ad, which has two key changes: (i) a modified HIF-responsive promoter to regulate the E1A replication gene and (ii) insertion of the E3 gene region. To augment the anti-tumor activity of HIF-Ad beyond the killing of HIF-active tumor cells, it was modified to express interleukin-4 (HIF-Ad-IL4). The IL4 cytokine was selected because it has potent multimodal anti-tumorigenic activities. Using normal and tumor cell lines in vitro, we found that the HIF-Ads have HIF-dependent E1A expression, replication, and oncolytic activity. Importantly, the replication and oncolytic efficacy of the HIF-Ads was similar to a wild-type Ad and superior to the HYPR-Ads. The HIF-Ads demonstrated strong anti-tumor activity against subcutaneous human tumor xenografts. Notably, HIF-Ad-IL4 treatment led to tumor regressions and its anti-tumor efficacy was up to 6-fold greater than HYPR-Ad-IL4, HIF-Ad, and wild-type Ad treatment. These studies demonstrate that the HIF-Ads have improved anti-tumor activity compared to the HYPR-Ads and that treatment with a HIF-activated oncolytic Ad leads to a measurable therapeutic response. The novel design of the HIF-Ads represents a significant improvement compared to first-generation oncolytic Ads and has great potential to increase the anti-tumor efficacy of this cancer therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 586.