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Heat shock protein 32 (Hsp32), also known as heme oxygenase 1 (HO-1), has recently been identified as a potential target in various hematologic malignancies. We provide evidence that Hsp32 is constitutively expressed in primary leukemic cells in patients with acute myeloid leukemia (AML) and in various AML cell lines (HL60, U937, KG1). Expression of Hsp32 mRNA was demonstrable by qPCR, and expression of the Hsp32 protein by immunocytochemistry and Western blotting. The stem cell-enriched CD34+/CD38+ and CD34+/CD38- fractions of AML cells were found to express Hsp32 mRNA in excess over normal CD34+ progenitor cells. Two Hsp32-targeting drugs, pegylated zinc-protoporphyrin (PEG-ZnPP) and styrene-maleic-acid-copolymer-micelle-encapsulated ZnPP (SMAZnPP), were found to inhibit cytokine-dependent and spontaneous proliferation in all 3 AML cell lines as well as in primary AML cells. Growth inhibitory effects of SMA-ZnPP and PEG-ZnPP were dose-dependent with IC50 values ranging between 1 and 20 μM, and were accompanied by apoptosis as evidenced by light- and electron microscopy, Tunel assay, and caspase-3 activation. Finally, we were able to demonstrate that SMA-ZnPP inhibits cytokine-dependent proliferation of CD34+/CD38+ and CD34+/CD38- AML progenitor cells in vitro in all patients as well as leukemiainitiation of AML stem cells in NOD-SCID IL-2Rγ(-/-) (NSG) mice in vivo. Together, our data suggest that Hsp32 plays an important role as a survival factor in leukemic stem cells and as a potential new target in AML.

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Xanthine oxidase (XO) is the major source of superoxide anion (O(2)(-)) that is associated with various reactive oxygen species (ROS) related diseases. 4-amino-6-hydroxypyrazolo[3,4-d]pyrimidine (AHPP) is a potent XO inhibitor discovered in Maeda's laboratory, which is now being developed for the treatment of ischemia reperfusion injury and inflammatory diseases. However, the poor aqueous solubility of AHPP at physiological pH hampers its clinical development. To overcome this drawback, in the present study water soluble polyethyleneglycol conjugated AHPP (AHPP-PEG) was synthesized via two different approaches, which resulted in two derivatives of AHPP-PEG, namely, mono-AHPP-PEG and bis-(AHPP)-PEG depending on the number of AHPP on PEG chain. We characterized both conjugates by UV, FTIR spectroscopy and elemental analysis. Dynamic light scattering and Sephadex G-100 chromatography studies revealed mean particle size of 164.1 and 218.8 nm and Mw. equivalent to 107 and 126 kDa for mono-AHPP-PEG and bis-(AHPP)-PEG, respectively. Further, XO inhibitory activity for mono-AHPP-PEG and bis-(AHPP)-PEG were found with Ki of 0.23±0.03 and 0.21±0.03 μM, respectively. In vivo pharmacokinetic study showed longer circulation time of AHPP-PEG conjugates compared to free AHPP. These results indicate AHPP-PEG conjugates have better potentials with supramolecular assemblies in aqueous medium and may become a good candidate for the treatment of ROS related diseases.

Targeted therapy by using nanomedicines based on the enhanced permeability and retention (EPR) effect is becoming a promising anticancer strategy. Many nano-designed photosensitizers (PSs) for photodynamic therapy (PDT) have been developed which show superior therapeutic potentials than free PS. To further understand the advantages of nano-designed PS, in this study, we used styrene-co-maleyl telomer (SMA) as a polymer platform to prepare a micellar type of PS with two well-characterized PSs—rose bengal (RB) and methylene blue (MB)—and evaluated the outmatching benefits of SMA-PS micelles, especially focusing on the singlet oxygen (1O2) generation capacity and intracellular uptake profiles. In aqueous solutions, SMA-PS self-assembles to form micelles by non-covalent interactions between PS and SMA. SMA-PS micelles showed discrete distributions by dynamic light scattering having a mean particle size of 18–30 nm depending on the types of SMA and different PSs. The hydrodynamic size of SMA-PS was evaluated by Sephadex chromatography and it found to be 30–50 kDa. In the presence of human serum albumin, the sizes of SMA-PS remarkably increased, suggesting the albumin-binding property. 1O2 generation from the SMA-PS micelle was determined by electron spin resonance, in which the SMA-PS micelle showed comparatively more photo-stable, and consequently a more durable and constant, 1O2 generation capability than free PS. Moreover, intracellular uptake of SMA-PS micelles was extensively faster and higher than free PS, especially in tumor cells. Taken together, SMA-PS micelles appear highly advantageous for photodynamic therapy in addition to its capacity in utilizing the EPR effect for tumor targeted delivery.