Targeting DDX3 in cancer: personalized drug development and delivery

Abstract

Cancer begins when a cell in an organ of our body starts to grow uncontrollably. Only recently has it become clear that targeting the cancer cells’ dependency on specific proteins, rather than their origin, has greater therapeutic potential. The vast majority of potential targets for cancer therapy are proteins that are hijacked by the tumor; this concept is referred to as non-oncogene addiction (Solimini et al., 2007). In our quest to characterize cellular pathways that are essential for the oncogenic state, we have identified DDX3, a member of an RNA helicase family that is disregulated in many cancer types. We describe the subcellular expression of DDX3 helicase in breast and lung carcinogenesis and progression. High expression of cytoplasmic DDX3 was mainly observed in ductal, high grade, high mitotic index, and HER2-driven breast cancer and was associated with a reduced survival rate. The 5-year survival rate was 87.4% in low cytoplasmic DDX3 expressing tumors compared to 78.9% in tumors with high DDX3 [removed]p=0.042). In lung cancer, patients with high levels of DDX3 died an average of 18 months earlier than patients with low DDX3 expression. The hazard ratio for death was 2.14 (95% CI; 1.08 to 4.23), independent of tumor size and histological type. Mechanistically, DDX3 can mediate a protective role during cellular stress by assembling stress granules in an ATP-independent manner. In invasive breast cancer, expression of DDX3 was indeed correlated with overexpression of HIF-1α and many other hypoxia-related proteins, suggesting a distinct role for DDX3 as a hypoxic stress regulator. Moreover, DDX3 bound to β-catenin in order to facilitate canonical Wnt-signaling and DDX3 facilitates DNA repair by non-homologous end-joining. We rationally designed small molecule inhibitors that fit into the ATP binding domain of DDX3 to abrogate its activity. RK-33 was the most potent of the synthesized molecules which binds to DDX3 and abrogates its helicase activity. RK-33 caused a cell cycle arrest, induced apoptosis, and promoted radiation sensitization, specifically in DDX3 overexpressing cells. More importantly, RK-33 in combination with radiation therapy induced tumor regression in two different mouse models. Functionally, RK-33 reduced DNA damage repair by impeding non-homologous end-joining. Thus, inhibition of DDX3 by RK-33 may lead to new treatment strategies or improvement of current therapies. Furtthermore, we generated RK-33 slow release PLGA-based nanoparticles of about 200nm to improve the bioavailability and effectiveness of RK-33. To reduce aggregation, these nanoparticles were coated with PVA and PEG-PPG-PEG. RK-33 was slowly released from the loaded NP’s both in vitro and in vivo.