Echogenic polymersomes for triggered contents release

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PROJECT SUMMARY Polymersomes are bilayer vesicles prepared from amphiphilic block copolymers. Although they have many advantages compared to other nanoparticles (such as longer circulation time, higher stability, ability to carry both hydrophilic and hydrophobic drugs), their applications as carriers for cytotoxic drugs and imaging agents remain under-developed. During the previous award (1R01 GM114080), we developed polymersomes for glutathione-triggered contents release. We rendered the polymersomes echogenic by a unique preparation protocol that encapsulated air bubbles in the system, allowing us to image them by a diagnostic ultrasound scanner. By conjugating appropriate ligands, we targeted the polymersomes to cancer cells and intracellular organelles such as the nucleus or mitochondria attaining their penetration at least 200 m in cultured spheroids. They also exhibited 50 dB and 25 dB enhancement in linear and nonlinear ultrasound signals and adequate stability. The previous award resulted in 25 peer-reviewed publications, two book chapters, one patent, and 5 students graduating with Ph.D. degree. In the renewal application, we will prepare targeted, deep-tissue-penetrating echogenic polymersomes responsive to varying degrees of hypoxia (2–10% oxygen) for drug delivery and concurrent ultrasound imaging. Hypoxia develops in many pathological conditions, including solid tumors, pulmonary hypertension, ischemia, altitude sickness, brain injury, stroke, etc. Hypoxia in solid tumors triggers remodeling of the extracellular matrix, epithelial-to-mesenchymal transition, cell survival, metastasis, the formation of the cancer stem cells, and significant resistance to chemo- and radiotherapy. Hypoxia further promotes the development of collagen-rich, fibrous extracellular stroma (desmoplasia), which increases the interstitial pressure and limits the diffusion and transport of the drugs. In this application, we will use triple-negative breast cancer as a surrogate for hypoxic solid tumors. We will conduct mechanistic studies on hypoxia-triggered contents release, echogenicity, ultrasound attenuation and scattering, and the cellular consequences of delivering an anticancer drug along with a stemness inhibitor in the hypoxic regions of solid tumors. We will conduct the proposed studies with three Specific Aims. (1) Synthesize hypoxia-responsive polymers, prepare tissue-penetrating polymersomes and perform mechanistic studies on triggered contents release. (2) Prepare echogenic hypoxia-responsive polymersomes, characterize echogenicity, investigate its mechanism, and optimize imaging to elucidate ultrasound induced content release. (3) Demonstrate the functional efficacy of the hypoxia-responsive echogenic polymersomes using cellular and mouse models of hypoxic niches. Our approach is innovative for the following reasons. It proposes (i) delivery of polymersomes deep into the solid tumors, including hypoxic niches, overcoming the desmoplastic barrier, which remained out of bounds due to diffusional limitations, (ii) hypoxia responsive drug release, which would be useful in many other diseases, (iii) delivery of transcription inhibitor, that can reach and kill cancer stem cells deep inside the tumors, and finally (iv) dual functionality of echogenic polymersomes allowing ultrasound imaging and ultrasound- induced release. The knowledge gained from our studies has the potential also to target other disease conditions where hypoxia-mediated worsening occur, including multiple solid tumors, pulmonary hypertension, ischemia, high-altitude mountain sickness, brain, kidney, and lung injury, especially following transplantation.