NIR Fluorescent Imaging and Photodynamic Therapy with a Novel Theranostic Phospholipid Probe for Triple-Negative Breast Cancer Cells

(Nano)platforms in breast cancer therapy: Drug/gene delivery, advanced nanocarriers and immunotherapy

Breast cancer is the most malignant tumor in women, and there is no absolute cure for it. Although treatment modalities including surgery, chemotherapy, and radiotherapy are utilized for breast cancer, it is still a life-threatening disease for humans. Nanomedicine has provided a new opportunity in breast cancer treatment, which is the focus of the current study. The nanocarriers deliver chemotherapeutic agents and natural products, both of which increase cytotoxicity against breast tumor cells and prevent the development of drug resistance. The efficacy of gene therapy is boosted by nanoparticles and the delivery of CRISPR/Cas9, Noncoding RNAs, and RNAi, promoting their potential for gene expression regulation. The drug and gene codelivery by nanoparticles can exert a synergistic impact on breast tumors and enhance cellular uptake via endocytosis. Nanostructures are able to induce photothermal and photodynamic therapy for breast tumor ablation via cell death induction. The nanoparticles can provide tumor microenvironment remodeling and repolarization of macrophages for antitumor immunity. The stimuli-responsive nanocarriers, including pH-, redox-, and light-sensitive, can mediate targeted suppression of breast tumors. Besides, nanoparticles can provide a diagnosis of breast cancer and detect biomarkers. Various kinds of nanoparticles have been employed for breast cancer therapy, including carbon-, lipid-, polymeric- and metal-based nanostructures, which are different in terms of biocompatibility and delivery efficiency.

Cancer Cell-Specific Fluorescent Prodrug Delivery Platforms

Targeting cancer cells with high specificity is one of the most essential yet challenging goals of tumor therapy. Because different surface receptors, transporters, and integrins are overexpressed specifically on tumor cells, using these tumor cell-specific properties to improve drug targeting efficacy holds particular promise. Targeted fluorescent prodrugs not only improve intracellular accumulation and bioavailability but also report their own localization and activation through real-time changes in fluorescence. In this review, efforts are highlighted to develop innovative targeted fluorescent prodrugs that efficiently accumulate in tumor cells in different organs, including lung cancer, liver cancer, cervical cancer, breast cancer, glioma, and colorectal cancer. The latest progress and advances in chemical design and synthetic considerations in fluorescence prodrug conjugates and how their therapeutic efficacy and fluorescence can be activated by tumor-specific stimuli are reviewed. Additionally, novel perspectives are provided on strategies behind engineered nanoparticle platforms self-assembled from targeted fluorescence prodrugs, and how fluorescence readouts can be used to monitor the position and action of the nanoparticle-mediated delivery of therapeutic agents in preclinical models. Finally, future opportunities for fluorescent prodrug-based strategies and solutions to the challenges of accelerating clinical translation for the treatment of organ-specific tumors are proposed.

Establishing a Robust and Reliable Response from a Potent Osmium-Based Photosensitizer Via Lipid Nanoformulation†

Osmium (Os) based photosensitizers (PSs) are a unique class of nontetrapyrrolic metal-containing PSs that absorb red light. We recently reported a highly potent Os(II) PS, rac-[Os(phen)2 (IP-4T)](Cl)2 , referred to as ML18J03 herein, with light EC50 values as low as 20 pm. ML18J03 also exhibits low dark toxicity and submicromolar light EC50 values in hypoxia in some cell lines. However, owing to its longer oligothiophene chain, ML18J03 is not completely water soluble and forms 1-2 μm sized aggregates in PBS containing 1% DMSO. This aggregation causes variability in PDT efficacy between assays and thus unreliable and irreproducible reports of in vitro activity. To that end, we utilized PEG-modified DPPC liposomes (138 nm diameter) and DSPE-mPEG2000 micelles (10.2 nm diameter) as lipid nanoformulation vehicles to mitigate aggregation of ML18J03 and found that the spectroscopic properties important to biological activity were maintained or improved. Importantly, the lipid formulations decreased the interassay variance between the EC50 values by almost 20-fold, with respect to the unformulated ML18J03 when using broadband visible light excitation (P = 0.0276). Herein, lipid formulations are presented as reliable platforms for more accurate in vitro photocytotoxicity quantification for PSs prone to aggregation (such as ML18J03) and will be useful for assessing their in vivo PDT effects.

Conjugates of Tetrapyrrolic Macrocycles as Potential Anticancer Target-Oriented Photosensitizers

Photodynamic therapy is a minimally invasive treatment of tumors using photosensitizers, light, and reactive oxygen species, which can destroy cellular structures. With the development of photodynamic therapy, significant efforts have been made to create new efficient photosensitizers with improved delivery to cells, stability, and selectivity against cancer tissues. Naturally occurring tetrapyrrolic macrocycles, such as porphyrins and chlorins, are very attractive as photosensitizers, and their structural modification and conjugation with other biologically active molecules are promising approaches for creating new photosensitizers specifically targeting cancer cells. The present review aims to highlight recent developments in the design, preparation, and investigation of complex conjugates of tetrapyrrolic macrocycles, which can potentially be used as sensitizers for target-oriented photodynamic therapy of cancer. In this review, we discuss the structure, photodynamic effect, and anticancer activity of the following conjugates of tetrapyrrolic macrocycles: (1) conjugates obtained by modifying peripheral substituents in porphyrins and chlorins; (2) conjugates of porphyrins and chlorins with lipids, carbohydrates, steroids, and peptides; (3) conjugates of porphyrins and chlorins with anticancer drugs and some other biologically active molecules; (4) metal-containing conjugates. The question of how the conjugate structure affects its specificity, internalization, localization, and photoinduced toxicity within cancer cells is the focus of this review.

Enabling In Vivo Optical Imaging of an Osmium Photosensitizer by Micellar Formulation

Osmium (Os)-based photosensitizers (PSs) exhibit unique broad, red-shifted absorption, favoring PDT activity at greater tissue depths. We recently reported on a potent Os(II) PS, rac-[Os(phen)₂(IP-4T)](Cl)₂ (ML18J03) with submicromolar hypoxia activity. ML18J03 exhibits a low luminescence quantum yield of 9.8 × 10^-5 in PBS, which limits its capacity for in vivo luminescence imaging. We recently showed that formulating ML18J03 into 10.2 nm DSPE-mPEG₂₀₀₀ micelles (Mic-ML18J03) increases its luminescence quantum yield by two orders of magnitude. Here, we demonstrate that Mic-ML18J03 exhibits 47-fold improved accumulative luminescence signals in orthotopic AT-84 head and neck tumors. We show, for the first time, that micellar formulation provides up to 11.7-fold tumor selectivity for ML18J03. Furthermore, Mic-ML18J03 does not experience the concentration-dependent quenching observed with unformulated ML18J03 in PBS, and formulation reduces spectral shifting of the emission maxima during PDT (variance = 6.5 and 27.3, respectively). The Mic-ML18J03 formulation also increases the production of reactive molecular species 2-3-fold. These findings demonstrate that micellar formulation is a versatile and effective approach to enable in vivo luminescence imaging options for an otherwise quenched, yet promising, PS.

Development of Nucleoside Diphosphate-Bearing Fragile Histidine Triad-Imaging Fluorescence Probes with Well-Tuned Hydrophobicity for Intracellular Delivery

Fluorescence-guided cancer surgery can dramatically improve recurrence rates and postoperative quality of life of patients by accurately distinguishing the boundary between normal and cancer tissues during surgery, thereby minimizing excision of normal tissue. One promising target in early stage cancer is fragile histidine triad (FHIT), a cancer suppressor protein with dinucleoside triphosphate hydrolase activity. In this study, we have developed fluorescence probes containing a nucleoside diphosphate moiety, which dramatically improves the reactivity and specificity for FHIT, and a moderately lipophilic ester moiety to increase the membrane permeability. The ester moiety is cleaved by ubiquitous intracellular esterases, and then, FHIT in the cells specifically cleaves nucleoside monophosphate. The remaining phosphate moiety is rapidly cleaved by ubiquitous intracellular phosphatases to release the fluorescent dye. We confirmed that this probe can detect FHIT activity in living cells. A comprehensive evaluation of the effects of various ester moieties revealed that probes with CLogP = 5-7 showed good membrane permeability and were good substrates of the target enzyme; these findings may be helpful in the rational design of other multiple phosphate-containing probes targeting intracellular enzymes.

Discovery of non-substrate, environmentally sensitive turn-on fluorescent probes for imaging HDAC8 in tumor cells and tissue slices

Histone deacetylase 8 (HDAC8) is overexpressed in multiple cancers and lack of effective chemical probes which could detect and visualize HDAC8 in tumor cells and tissues remains unsolved. In this work, three novel turn-on HDAC8 fluorescent probes 17-19 derived from solvatochromic fluorophore 4-sulfamonyl-7-aminobenzoxadiazole (SBD) conjugating with a potent HDAC8 inhibitor PCI-34051 (IC₅₀ = 10 nM) as the recognition group were fabricated. The probes exhibited much stronger fluorescence when they transfer from hydrophilic environment (Φ < 8%) to hydrophobic environment (Φ > 46%). Compared with PCI-34051 (K_D = 9.16 × 10^-6 M), probes 17 (K_D = 5.37 × 10^-6 M), 18 (K_D = 3.57 × 10^-6 M) and 19 (K_D = 8.89 × 10^-6 M) possessed slightly better affinity for HDAC8. Probe 19 was selected for cell imaging and it showed significantly enhanced fluorescence only after binding into the cavity of HDAC8 in SH-SY5Y and MDA-MB-231 tumor cells. Co-localization results demonstrated that HDAC8 is expressed in cytoplasm and nucleus. Furthermore, probe 19 was successfully utilized to distinguish the expression level of HDAC8 in SH-SY5Y tumor and normal tissue slices.

Chemical Probes and Activity-Based Protein Profiling for Cancer Research

Chemical probes can be used to understand the complex biological nature of diseases. Due to the diversity of cancer types and dynamic regulatory pathways involved in the disease, there is a need to identify signaling pathways and associated proteins or enzymes that are traceable or detectable in tests for cancer diagnosis and treatment. Currently, fluorogenic chemical probes are widely used to detect cancer-associated proteins and their binding partners. These probes are also applicable in photodynamic therapy to determine drug efficacy and monitor regulating factors. In this review, we discuss the synthesis of chemical probes for different cancer types from 2016 to the present time and their application in monitoring the activity of transferases, hydrolases, deacetylases, oxidoreductases, and immune cells. Moreover, we elaborate on their potential roles in photodynamic therapy.

Near-infrared (NIR) fluorescence-emitting small organic molecules for cancer imaging and therapy

We discuss recent advances made in the development of NIR fluorescence-emitting small organic molecules for tumor imaging and therapy.

Metal-organic framework-encapsulated nanoparticles for synergetic chemo/chemodynamic therapy with targeted H2O2 self-supply

Nanocatalytic cancer therapy based on chemodynamic therapy, which converts hydrogen peroxide (H₂O₂) into toxic reactive oxygen species via the Fenton-like reaction, is regarded as a promising therapeutic strategy due to its specific response toward the tumor microenvironment (TME). However, the H₂O₂ concentration in TME (100 μM to 1 mM) is insufficient and introducing enough H₂O₂ or H₂O₂-generating agents is challenging. In view of this, we report a drug delivery system, CaO₂/DOX@Cu/ZIF-8@HA (CDZH), which is capable of targeted H₂O₂ self-supply and exhibits outstanding chemo/chemodynamic synergetic therapy capability. CaO₂/DOX@Cu/ZIF-8@HA is synthesized by fabricating biodegradable Cu/ZIF-8 shell-encapsulated CaO₂ nanoparticles, loading chemotherapy drug doxorubicin, and coating a hyaluronic acid shell. In an acidic tumor microenvironment, the CDZH nanostructures targeted the release of doxorubicin, Cu²⁺, and CaO₂. Doxorubicin affects chemotherapy and bioimaging, and CaO₂ supplies H₂O₂ through a Cu-Fenton-like reaction to generate hydroxyl radicals with high oxidation activity for chemodynamic therapy. In brief, the drug delivery system combined targeted H₂O₂ self-supply and targeted bioimaging possess the potential of an efficient synergistic strategy for chemodynamic therapy and chemotherapy.