Drug development of RK-33 for breast cancer treatment

Triple-negative breast cancers (TNBCs) are breast cancers that lack expression of estrogen receptor alpha, progesterone receptor, and HER2. They constitute approximately 10-25% of all breast cancers and primarily affect younger women and African-American women. Even though the majority of patients with TNBC respond to neoadjuvant chemotherapy, they have a higher rate of distant recurrence and poor prognosis. The current treatment of TNBC is inadequate due to a lack of targetable biomarkers and the heterogeneous nature of the disease. To overcome the current treatment limitations, we need to uncover the mechanisms underlying TNBC biogenesis to generate targeted therapies. We found that a member of the RNA helicase family, DDX3, is dysregulated in breast tumors and is implicated in cancer establishment and metastasis. Importantly, we found DDX3 to be overexpressed in a significantly high percentage in breast cancer metastases, indicating that there is a dependency on DDX3 to maintain their malignant properties (non-oncogene addiction) and high DDX3 expression may help cells adapt to the metastatic microenvironment. Natsar Pharmaceuticals, Inc. (Natsar) was founded to commercialize RK-33 as a therapeutic candidate for treating TNBC. We used a rational drug design approach to develop a small molecule inhibitor of DDX3, designated as RK-33, which showed robust killing of TNBC cancer cells and was able to reduce metastatic load in a preclinical model of breast cancer. RK-33 exhibited high specificity towards DDX3 and was safe as per ICH S9 scientific guidelines for non-clinical evaluation for anti-cancer pharmaceuticals. Also, 28 days repeated toxicity studies in Wistar rats, as per FDA ICH MS (R2) and ICH S3A guidelines, showed No Observed Adverse Effect Level (NOAEL). Mechanistically, RK-33 induced caspase activation, inhibited non-homologous end joining (NHEJ) activity, and perturbed Wnt- signaling. Moreover, in combination with radiotherapy, there was a synergistic reduction of tumors in multiple preclinical models of cancer. The objectives of this SBIR proposal are to prepare trial materials using Good Laboratory Practice (GLP) and conduct safety, pharmacokinetics, and toxicity studies using the formulated RK- 33 needed for filing an Investigational New Drug (IND) application to the FDA. Three Aims are proposed for this SBIR Direct Phase II proposal. Aim 1: To synthesize GMP-grade RK-33 and develop analytical validation protocols for safety studies; Aim 2: To generate large-scale active pharmaceutical product of RK-33 nanosuspension formulation for therapeutic use and Aim 3: To evaluate the safety profile of RK-33 nanosuspension in IND-enabling GLP canine studies. The impact of this SBIR grant is high, and the targeted approach is novel. It should increase overall survival and quality of life for TNBC patients due to RK-33’s very low toxicity. Upon completing this SBIR study, Natsar will validate using RK-33 as a front-line chemotherapeutic agent for primary and metastatic TNBC lesions. Furthermore, Natsar will raise additional investments to conduct clinical trials and IND clearance application.