Abstract 13400: STAT3 ASO-Loaded Microbubbles With Pulsed Ultrasound for Enhanced Therapeutic Effect in Head and Neck Tumors

Abstract

Introduction: Signal transducer and activator of transcription 3 ( STAT3 ) is an oncogenic transcription factor implicated in carcinogenesis, tumor progression, and drug resistance in many cancers, including head and neck squamous cell carcinoma ( HNSCC ). STAT3 antisense oligonucleotide ( ASO ) specifically targeting the nucleotide sequence of STAT3 has therapeutic promise, but effective delivery remains challenging. We developed microbubble ( MB ) delivery vehicles loaded with STAT3 ASO and hypothesized that compared to intravenous ( i.v. ) delivery, ultrasound-targeted microbubble cavitation ( UTMC )-mediated ASO delivery confers superior tumor growth inhibition. Methods: Lipid MBs loaded with STAT3 ASO (S3MB) or mutant ASO (Mut-MB) were prepared. First, murine squamous carcinoma cells (SCC-7) in contact with MBs were exposed to pulsed ultrasound (1 MHz, 0.5 MPa, 100 μs pulse duration, 1 ms pulse interval) for 10 sec to establish efficacy with respect to cytotoxicity, apoptosis, and gene knockdown. Thereafter, the anti-tumor effect of 3 treatments with STAT3 ASO (10 μg) delivered i.v. or via UTMC x 15 min ( f= 1MHz, 0.7MPa, 100 cycles x 5 every 2 sec) was compared in vivo in a murine SCC-7 xenograft model followed up to 17 days. Results: S3MB + UTMC conferred more cytoxocitiy, apoptosis, and downregulation of transcripts for STAT3 and its target genes (Bcl-xL and Cyclin D1) compared to Mut-MB + UTMC in vitro (p<0.05). In tumor bearing mice, compared to i.v. STAT3 ASO (n=8), Mut-MB+UTMC (n=5) or no treatment (n=8), S3MB + UTMC (n=9) significantly attenuated tumor burden, prolonged doubling time, and improved survival (p<0.05). While i.v. STAT3 ASO had no effect on tumor expression of STAT3, Bcl-x, and cyclin D1 at the transcript and protein levels, its delivery via UTMC significantly reduced tumor expression of these genes (p<0.01). Conclusion: At a dose of 10 μg, STAT3 ASO significantly inhibited murine HNSCC tumor growth and downregulated STAT3 and its target genes when delivered via UTMC, compared with intravenous administration alone. Our platform offers a promising imaged-guided, targeted delivery strategy for nucleotide-based therapeutics in cancer applications.