Exploiting Bacterial Shuttles: Enhancing Deep Tissue Delivery of Nanoparticles for Targeted Cancer Therapy

Cancer, a leading cause of death, poses challenges for chemotherapy due to limited selective accumulation. Targeted approaches and nanoparticles exploit enhanced permeability but face obstacles in effective delivery. Bacteria, historically effective for cancer targeting, show promise as carriers for nanoparticles, overcoming deep tissue hindrances. Yet, conjugated forms often compromise selective accumulation and tissue penetration due to increased immunogenicity, limiting bacterial motility and proliferation. This study engineered bacteria with cancer-targeting abilities expressing strep tags for streptavidin binding. We evaluated their binding to Chlorin-e6 (Ce6) nanoparticles, a potential photosensitizer for photodynamic therapy, selecting strains with optimal performance. Validating enhanced delivery, we assessed bacterial tumor-selective colocalization and nanoparticle delivery in a fibrous tumor microenvironment in vitro. To address reduced delivery efficiency in vivo, bacteria were intravenously injected and induced to conjugate with peritumorally introduced nanoparticles, confirming effective delivery to hypoxic cancer tissue regions. This underscores bacteria’s role as cancer-targeting agents and shuttles enhancing deep tissue delivery.

I. Introduction

Cancer, despite extensive research over the years, remains a leading cause of death [1]. Conventional chemotherapy faces challenges due to limited selective accumulation in cancer, resulting in significant toxicity to normal cells [2]. Targeted chemotherapeutic approaches have been proposed to address this issue, utilizing antibodies, peptides, and small-molecule ligands with affinity for markers highly expressed in cancer tissues [3]. Nanoparticles within a specific range exploit the enhanced permeability and retention effect in cancer tissues due to their leaky vasculature structure, enhancing the accumulation of nano-chemotherapeutics [4]. However, challenges persist in achieving effective delivery beyond improved accumulation, attributed to various tumor microenvironment characteristics, such as adverse pressure gradient [5], elevated interstitial pressure [5], and congested structural arrangements [6]. Bacteria, validated for their targeting efficacy in cancer tissues since the late 1900s [7], emerged as potential candidates for anticancer agents. Intrinsic intracellular invasion [8], [9] and intercellular penetration [10] demonstrate their potential as carriers for anticancer nanoparticles, overcoming hindrances to deep tissue delivery.While there have been numerous studies on the delivery of nanoparticles to cancer tissues using bacterial binding, the conjugated form of bacteria-nanoparticles often exhibits essential compromises in the performance of selective cancer accumulation and tissue penetration. This is attributed to the increased immunogenicity due to substances attached to the bacterial surface, leading to decreased motility and proliferation of bacteria.