Self-Assembly of Mitochondria-Targeted Photosensitizer to Increase Photostability and Photodynamic Therapeutic Efficacy in Hypoxia.

The development of photosensitizers for cancer photodynamic therapy has been challenging due to their low photostability and therapeutic inefficacy in hypoxic tumor microenvironments. To overcome these issues, we have developed a mitochondria-targeted photosensitizer consisting of an indocyanine moiety with triphenylphosphonium arms, which can self-assemble into spherical micelles directed to mitochondria. Self-assembly of the photosensitizer resulted in a higher photostability by preventing free rotation of the indoline ring of the indocyanine moiety. The mitochondria targeting capability of the photosensitizer allowed it to utilize intramitochondrial oxygen. We found that the mitochondria-targeted photosensitizer localized to mitochondria and induced apoptosis of cancer cells both normoxic and hypoxic conditions through generation of ROS. The micellar self-assemblies of the photosensitizer were further confirmed to selectively localize to tumor tissues in a xenograft tumor mouse model through passive targeting and showed efficient tumor growth inhibition.

Dual Binding to Orthosteric and Allosteric Sites Enhances the Anticancer Activity of a TRAP1-Targeting Drug.

The molecular chaperone TRAP1 is the mitochondrial paralog of Hsp90 and is overexpressed in many cancer cells. The orthosteric ATP-binding site of TRAP1 has been considered the primary inhibitor binding location, but TRAP1 allosteric modulators have not yet been investigated. Here, we generated and characterized the Hsp90 inhibitor PU-H71, conjugated to the mitochondrial delivery vehicle triphenylphosphonium (TPP) with a C10 carbon spacer, named SMTIN-C10, to enable dual binding to orthosteric and allosteric sites. In addition to tight binding with the ATP-binding site through the PU-H71 moiety, SMTIN-C10 interacts with the E115 residue in the N-terminal domain through the TPP moiety and subsequently induces structural transition of TRAP1 to a tightly packed closed form. The data indicate the existence of a druggable allosteric site neighboring the orthosteric ATP pocket that can be exploited to develop potent TRAP1 modulators.

Mitochondrial heat shock protein-guided photodynamic therapy.

Mitochondria targeting sensitizers are continuing to gain importance in photodynamic therapy (PDT). Members of the 90 kDa heat shock protein (Hsp90) family, including TRAP1 (Hsp75), are overexpressed in cancer cells and help to control the antiapoptotic protein activity. The present work introduces an Hsp90 inhibitor-mitochondria targeting indocyanine dye conjugate (IR-PU) for high PDT efficacy.

Cancer-mitochondria-targeted photodynamic therapy with supramolecular assembly of HA and a water soluble NIR cyanine dye.

Mitochondria-targeted cancer therapies have proven to be more effective than other similar non-targeting techniques, especially in photodynamic therapy (PDT). Indocyanine dye derivatives, particularly IR-780, are widely known for their PDT utility. However, poor water solubility, dark toxicity, and photobleaching are limiting factors for these dyes, which otherwise show promise based on their good absorption in the near-infrared (NIR) region and mitochondria targeting ability. Herein, we introduce an indocyanine derivative (IR-Pyr) that is highly water soluble, exhibiting higher mitochondrial targetability and better photostability than IR-780. Furthermore, electrostatic interactions between the positively charged IR-Pyr and negatively charged hyaluronic acid (HA) were utilized to construct a micellar aggregate that is selective towards cancer cells. The cancer mitochondria-targeted strategy confirms high PDT efficacy as proved by in vitro and in vivo experiments.

Noncovalent Surface Locking of Mesoporous Silica Nanoparticles for Exceptionally High Hydrophobic Drug Loading and Enhanced Colloidal Stability.

Advances in water-insoluble drug delivery systems are limited by selective delivery, loading capacity, and colloidal and encapsulation stability. We have developed a simple and robust hydrophobic-drug delivery platform with different types of hydrophobic chemotherapeutic agents using a noncovalent gatekeeper's technique with mesoporous silica nanoparticles (MSNs). The unmodified pores offer a large volume of drug loading capacity, and the loaded drug is stably encapsulated until it enters the cancer cells owing to the noncovalently bound polymer gatekeeper. In the presence of polymer gatekeepers, the drug-loaded mesoporous silica nanoparticles showed enhanced colloidal stability. The simplicity of drug encapsulation allows any combination of small chemotherapeutics to be coencapsulated and thus produce synergetic therapeutic effects. The disulfide moiety facilitates decoration of the nanoparticles with cysteine containing ligands through thiol-disulfide chemistry under mild conditions. To show the versatility of drug targeting to cancer cells, we decorated the surface of the shell-cross-linked nanoparticles with two types of peptide ligands, SP94 and RGD. The nanocarriers reported here can release encapsulated drugs inside the reducing microenvironment of cancer cells via degradation of the polymer shell, leading to cell death.

Development of a mitochondria-targeted Hsp90 inhibitor based on the crystal structures of human TRAP1.

The mitochondrial pool of Hsp90 and its mitochondrial paralogue, TRAP1, suppresses cell death and reprograms energy metabolism in cancer cells; therefore, Hsp90 and TRAP1 have been suggested as target proteins for anticancer drug development. Here, we report that the actual target protein in cancer cell mitochondria is TRAP1, and current Hsp90 inhibitors cannot effectively inactivate TRAP1 because of their insufficient accumulation in the mitochondria. To develop mitochondrial TRAP1 inhibitors, we determined the crystal structures of human TRAP1 complexed with Hsp90 inhibitors. The isopropyl amine of the Hsp90 inhibitor PU-H71 was replaced with the mitochondria-targeting moiety triphenylphosphonium to produce SMTIN-P01. SMTIN-P01 showed a different mode of action from the nontargeted PU-H71, as well as much improved cytotoxicity to cancer cells. In addition, we determined the structure of a TRAP1-adenylyl-imidodiphosphate (AMP-PNP) complex. On the basis of comparative analysis of TRAP1 structures, we propose a molecular mechanism of ATP hydrolysis that is crucial for chaperone function.

Meso-tetrakis(p-sulfonatophenyl)N-confused porphyrin tetrasodium salt: a potential sensitizer for photodynamic therapy.

A water-soluble derivative of N-confused porphyrin (NCP) was synthesized, and the photodynamic therapeutic (PDT) application was investigated by photophysical and in vitro studies. High singlet oxygen quantum yield in water at longer wavelength and promising IC(50) values in a panel of cancer cell lines ensure the potential candidacy of the sensitizer as a PDT drug. Reactive oxygen species (ROS) generation on PDT in MDA-MB 231 cells and the apoptotic pathway of cell death was illustrated using different techniques.