Research Projects

• Rationale. Photosensitizer (PS) delivery to tumors for photodynamic therapy (PDT) relies on enhanced permeation and retention (EPR), and while this is definitely cost-effective, such passive delivery can lead to inefficient tumoral PS uptake, resulting in poor generation of reactive oxygen species (ROS) at the tumor. Also, due to their small size (less than 6 nm), PS molecules are quickly eliminated from the body through renal clearance, thereby reducing their circulation half-life. Although active delivery using anti-cancer antibodies helps in specific PS delivery, antibody treatment is expensive, and endocytosis-driven internalization of the PS-antibody conjugate can lead to its rapid lysosomal degradation, thereby necessitating its repeated dosage in high concentrations. Furthermore, commercial PS such as chlorin E6 (Ce6) are activated by short wavelength (500 - 650 nm) light, which is mostly absorbed within 3 mm under the skin, reducing ROS generation in deeper tissues. This restricts the application of PDT only to skin diseases such as melanoma and renders it ineffective against deeper tumors like breast cancer. • Scientific Goal. To expand the utility of PDT to breast cancers, novel PS delivery systems are required that will not only facilitate its direct internalization into the cells, bypassing the endocytosis pathway, but also lead to enhanced ROS generation at the tumor. Therefore, in this project, we propose to develop a delivery cum therapeutic platform against highly aggressive triple-negative breast cancer (TNBC) by conjugating cell-penetrating peptides (CPP) to PS-linked upconversion nanoparticles (UCNPs). CPPs, due to their net positive charge, allow for better cytosolic access of the conjugated small molecules via direct membrane transport. UCNPs, on the other hand, are novel lanthanide-based materials that absorb near infrared (NIR) light and emit ultraviolet to visible (UV-VIS) light, which can then be used to activate PS. • OBJECTIVE 1. We will be developing ytterbium (Yb), erbium (Er) doped sodium yttrium fluoride (NaYF4) based core-shell UCNPs (NaYF4:Yb,Er@NaYF4) and chemically conjugating them to cyclic deca-arginine (cR10)-based CPP and Ce6 photosensitizer via well-established click chemistry, resulting in a novel, one-of-its-kind nanoparticle conjugate, UCNP-cR10-Ce6. Hypothesis. The UCNP-cR10-Ce6 will not only demonstrate superior uptake in TNBC cells, via direct penetration by the CPPs, but when irradiated with 980 nm NIR light, can also initiate higher ROS formation via the 680 nm emission of the UCNPs to activate Ce6. • OBJECTIVE 2. The UCNP-cR10-Ce6 nano-conjugate will be incubated with MDA-MB-468 TNBC cells, followed by NIR irradiation, and its cellular uptake, consequent ROS generation, cancer cytotoxicity, and its biomarkers will be investigated in vitro. Hypothesis. This nano-conjugate would allow for better light penetration, leading to more efficient tumor irradiation, resulting in significantly improved killing efficiency of cancer cells due to the localized photodynamic effect. • OBJECTIVE 3. The TNBC cells will first be injected into immunocompromised mice for tumor growth, followed by the injection of UCNP-cR10-Ce6 (+)NIR, and its tumor cytotoxicity will be examined against these in vivo models, in terms of tumor growth rate and overall survival. Hypothesis. The UCNP-cR10-Ce6 nanoconjugate will not only demonstrate effective PDT against a simple, easy-to-replicate 2D monolayer of cells but will also lead to tumor reduction on in vivo mouse models, which better capture tumor heterogeneity. • Significance. If the above objectives are successful, such mouse tumor models can then be used for understanding key areas in drug delivery, such as transport mechanisms involved in such nanoparticle-carcinoma interactions. This is because these in vivo models better mimic the tumor micro-environment, such as the tumor stroma, while being easy to make, repeat, and reproduce.