Preclinical development of RAG1-40-31L: A novel small activating RNA-lipid conjugate targeting tumor suppressor gene p21 for treatment of non-muscle invasive bladder cancer.

Abstract

e16620 Background: Loss-of-function of tumor suppressor genes are the dominant driving force in tumorigenesis. Restoration in function and/or expression of these genes holds tremendous therapeutic potential in cancer treatment. Bladder cancer is the 9th leading cause of cancer-related deaths in the United States in which ~75% of all newly diagnosed cases are non-muscle invasive bladder cancer (NMIBC). Standard-of-care includes intravesical installation of Bacillus Calmette-Guerin following tumor resection with an expected failure rate of ~50% within 6 months for patients with high-grade tumors. RNA activation (RNAa) is a mechanism in which short RNA duplexes termed small activating RNA (saRNA) induce gene transcription by targeting non-coding regulatory sequence ( i.e., promoters) embedded in chromatin. Thus, saRNA-induced overexpression of p21WAF1/CIP1 (p21) – a tumor suppressor of several anti-growth pathways – may hold therapeutic potential in bladder cancer. Through conjugation of a novel lipid ( i.e., C5X5), we have created a p21-targeting saRNA drug candidate referred to as RAG01-40-31L for delivery to bladder cancer cells in vivo. The aim of this work was to characterize the intravesical administration of RAG01-40-31L on p21 induction and its anti-tumor potential in NMBIC models. Methods: In vitro expression analyses were performed to investigate p21 induction via saRNA in KU7 and T24 bladder cancer cell lines by RT-qPCR and immunoblot analysis. Cell cycle analysis and tumorigenicity assays examined impact of RAG1-40-31L on cancer cell growth. Orthotopic human bladder tumors were established in female BALB/c nude mice using the recombinant cell line KU7 engineered to overexpress luciferase reporter. Tumor growth was monitored in live animals via luciferase bioluminescence using an in vivo imaging system. Plasma and tissue were harvested for drug exposure and expression analytics. Results: In vitro analyses indicated RAG1-40-31L activated p21 expression by approximately 6-fold and inhibited bladder cancer cell growth ( i.e., cell cycle arrest, apoptosis, and senescence) in a dose-dependent manner with low nanomolar potency. Intravesical administration of RAG1-40-31L (3 times per week for 2 weeks) inhibited growth of orthotopic tumors by 65% in mouse bladder models. Single-dose pharmacokinetics demonstrated a half-life (t1/2) of ~114 h with minimal systemic exposure (~0.05% of that of bladder tissue). Conclusions: These data constitute a preclinical proof-of-concept for saRNA as a novel p21-targeting modality in the treatment of cancer. The C5X5 lipid conjugate appears to be a viable approach to enhance oligonucleotide delivery and activity in bladder cancer. Preclinical safety assessment studies to enable clinical trials of RAG01-40-31L are currently underway.