Myriam E. Rodriguez

Delivery of the photosensitizer Pc 4 in PEG–PCL micelles for in vitro PDT studies

The silicon phthalocyanine Pc 4 is a second-generation photosensitizer that has several properties superior to other photosensitizers currently approved by the FDA, and it has shown significant promise for photodynamic therapy (PDT) in several cancer cells in vitro and model tumor systems in vivo. However, because of the high hydrophobicity of Pc 4, its formulation for in vivo delivery and favorable biodistribution become challenging. To this end, we are studying encapsulation and delivery of Pc 4 in block copolymer micelles. Here, we report the development of biocompatible PEG-PCL micelle nanoparticles, encapsulation of Pc 4 within the micelle core by hydrophobic association with the PCL block, and in vitro PDT studies of the micelle-formulated Pc 4 in MCF-7c3 human breast cancer cells. Our studies demonstrate efficient encapsulation of Pc 4 in the micelles, intracellular uptake of the micelle-formulated Pc 4 in cells, and significant cytotoxic effect of the formulation upon photoirradiation. Quantitative estimation of the extent of Pc 4 loading in the micelles and the photocytotoxicity of the micelle-incorporated Pc 4 demonstrate the promise of our approach to develop a biocompatible nanomedicine platform for tumor-targeted delivery of Pc 4 for site-selective PDT.

Structural factors and mechanisms underlying the improved photodynamic cell killing with silicon phthalocyanine photosensitizers directed to lysosomes versus mitochondria.

The phthalocyanine photosensitizer Pc 4 has been shown to bind preferentially to mitochondrial and endoplasmic reticulum membranes. Upon photoirradiation of Pc 4‐loaded cells, membrane components, especially Bcl‐2, are photodamaged and apoptosis, as indicated by activation of caspase‐3 and cleavage of poly(ADP‐ribose) polymerase, is triggered. A series of analogs of Pc 4 were synthesized, and the results demonstrate that Pcs with the aminopropylsiloxy ligand of Pc 4 or a similar one on one side of the Pc ring and a second large axial ligand on the other side of the ring have unexpected properties, including enhanced cell uptake, greater monomerization resulting in greater intracellular fluorescence and three‐fold higher affinity constants for liposomes. The hydroxyl‐bearing axial ligands tend to reduce aggregation of the Pc and direct it to lysosomes, resulting in four to six times more killing of cells, as defined by loss of clonogenicity, than with Pc 4. Whereas Pc 4‐PDT photodamages Bcl‐2 and Bcl‐xL, Pc 181‐PDT causes much less photodamage to Bcl‐2 over the same dose–response range relative to cell killing, with earlier cleavage of Bid and slower caspase‐3‐dependent apoptosis. Therefore, within this series of photosensitizers, these hydroxyl‐bearing axial ligands are less aggregated than is Pc 4, tend to localize to lysosomes and are more effective in overall cell killing than is Pc 4, but induce apoptosis more slowly and by a modified pathway.

Targeting of mitochondria by 10-N-alkyl acridine orange analogues: Role of alkyl chain length in determining cellular uptake and localization

10-N-Nonyl acridine orange (NAO) is used as a mitochondrial probe because of its high affinity for cardiolipin (CL). Targeting of NAO may also depend on mitochondrial membrane potential. As the nonyl group has been considered essential for targeting, a systematic study of alkyl chain length was undertaken; three analogues (10-methyl-, 10-hexyl-, and 10-hexadecyl-acridine orange) were synthesized and their properties studied in phospholipid monolayers and breast cancer cells. The shortest and longest alkyl chains reduced targeting, whereas the hexyl group was superior to the nonyl group, allowing very clear and specific targeting to mitochondria at concentrations of 20-100 nM, where no evidence of toxicity was apparent. Additional studies in wild-type and cardiolipin-deficient yeast cells suggested that cellular binding was not absolutely dependent upon cardiolipin.

A requirement for bid for induction of apoptosis by photodynamic therapy with a lysosome- but not a mitochondrion-targeted photosensitizer.

Photodynamic therapy (PDT) with lysosome‐targeted photosensitizers induces the intrinsic pathway of apoptosis via the cleavage and activation of the BH3‐only protein Bid by proteolytic enzymes released from photodisrupted lysosomes. To investigate the role of Bid in apoptosis induction and the role of damaged lysosomes on cell killing by lysosome‐targeted PDT, we compared the responses of wild type and Bid‐knock‐out murine embryonic fibroblasts toward a mitochondrion/endoplasmic reticulum‐binding photosensitizer, Pc 4, and a lysosome‐targeted sensitizer, Pc 181. Whereas apoptosis and overall cell killing were induced equally well by Pc 4‐PDT in both cell lines, Bid−/− cells were relatively resistant to induction of apoptosis and to overall killing following PDT with Pc 181, particularly at low PDT doses. Thus, Bid is critical for the induction of apoptosis caused by PDT with the lysosome‐specific sensitizers, but dispensable for PDT targeted to other membranes.

TLR2 engagement on CD4+ T cells enhances effector functions and protective responses to Mycobacterium tuberculosis

We have previously demonstrated that mycobacterial lipoproteins engage TLR2 on human CD4+ T cells and upregulate TCR‐triggered IFN‐γ secretion and cell proliferation in vitro. Here we examined the role of CD4+ T‐cell‐expressed TLR2 in Mycobacterium tuberculosis (MTB) Ag‐specific T‐cell priming and in protection against MTB infection in vivo. Like their human counterparts, mouse CD4+ T cells express TLR2 and respond to TLR2 costimulation in vitro. This Th1‐like response was observed in the context of both polyclonal and Ag‐specific TCR stimulation. To evaluate the role of T‐cell TLR2 in priming of CD4+ T cells in vivo, naive MTB Ag85B‐specific TCR transgenic CD4+ T cells (P25 TCR‐Tg) were adoptively transferred into Tlr2−/− recipient C57BL/6 mice that were then immunized with Ag85B and with or without TLR2 ligand Pam3Cys‐SKKKK. TLR2 engagement during priming resulted in increased numbers of IFN‐γ‐secreting P25 TCR‐Tg T cells 1 week after immunization. P25 TCR‐Tg T cells stimulated in vitro via TCR and TLR2 conferred more protection than T cells stimulated via TCR alone when adoptively transferred before MTB infection. Our findings indicate that TLR2 engagement on CD4+ T cells increases MTB Ag‐specific responses and may contribute to protection against MTB infection.

Photo-oxidation of Cardiolipin and Cytochrome c with Bilayer-Embedded Pc 4

Singlet oxygen, (1)O(2), is produced by absorption of red light by the phthalocyanine dye Pc 4, followed by energy transfer to dissolved triplet molecular oxygen, (3)O(2). In tissues, Pc 4 concentrates in lipid bilayers, and particularly in mitochondrial membranes, because of its positive charge. Illumination of cells and tissues with red light after uptake of Pc 4 results in cell death. The potential initial chemical steps that result in cellular dysfunction have been characterized in this study. Both unsaturated acyl chains of phospholipids and proteins are identified as targets of oxidation. Tetra-linoleoyl cardiolipin was oxidized in both liposomes and mitochondria after Pc 4-mediated (1)O(2) generation. Evidence for the formation of both mono- and bis-hydroperoxide adducts of single linoleoyl side chains is provided by ESI-MS and ESI-MS/MS. Similarly, illumination of Pc 4 in liposomes and mitochondria resulted in cytochrome c oxidation as detected by oxidation of His 26 in the peptide H(26)*KTGPNLHGLFGK, further supporting the potential use of this peptide as a biomarker for the presence of mitochondrial oxidative stress characteristic of (1)O(2) in vivo (J. Kim et al., Free Radic. Biol. Med. 44:1700-1711; 2008). These observations provide evidence that formation of lipid hydroperoxides and/or protein oxidation can be the initial chemical steps in Pc 4-mediated induction of apoptosis in photodynamic therapy.

Binding to and photo-oxidation of cardiolipin by the phthalocyanine photosensitizer Pc 4.

Cardiolipin is a unique phospholipid of the mitochondrial inner membrane. Its peroxidation correlates with release of cytochrome c and induction of apoptosis. The phthalocyanine photosensitizer Pc 4 binds preferentially to the mitochondria and endoplasmic reticulum. Earlier Förster resonance energy transfer studies showed colocalization of Pc 4 and cardiolipin, which suggests cardiolipin as a target of photodynamic therapy (PDT) with Pc 4. Using liposomes as membrane models, we find that Pc 4 binds to cardiolipin-containing liposomes similarly to those that do not contain cardiolipin. Pc 4 binding is also studied in MCF-7c3 cells and those whose cardiolipin content was reduced by treatment with palmitate. Decreased levels of cardiolipin are quantified by thin-layer chromatography. The similar level of binding of Pc 4 to cells, irrespective of palmitate treatment, supports the lack of specificity of Pc 4 binding. Thus, factors other than cardiolipin are likely responsible for the preferential localization of Pc 4 in mitochondria. Nonetheless, cardiolipin within liposomes is readily oxidized by Pc 4 and light, yielding apparently mono- and dihydroperoxidized cardiolipin. If similar products result from exposure of cells to Pc 4-PDT, they could be part of the early events leading to apoptosis following Pc 4-PDT.

Mycobacterial phosphatidylinositol mannoside 6 (PIM6) up-regulates TCR-triggered HIV-1 replication in CD4+ T cells.

Tuberculosis (TB) is the leading cause of mortality among those infected with human immunodeficiency virus (HIV-1) worldwide. HIV-1 load and heterogeneity are increased both locally and systemically in active TB. Mycobacterium tuberculosis (MTB) infection supports HIV-1 replication through dysregulation of host cytokines, chemokines, and their receptors. However the possibility that mycobacterial molecules released from MTB infected macrophages directly interact with CD4+ T cells triggering HIV-1 replication has not been fully explored. We studied the direct effect of different MTB molecules on HIV-1 replication (R5-tropic strain Bal) in anti-CD3- stimulated CD4+ T cells from healthy donors in an antigen presenting cell (APC)-free system. PIM6, a major glycolipid of the mycobacterial cell wall, induced significant increases in the percent of HIV-1 infected T cells and the viral production in culture supernatants. In spite of structural relatedness, none of the other three major MTB cell wall glycolipids had significant impact on HIV-1 replication in T cells. Increased levels of IFN-γ in culture supernatants from cells treated with PIM6 indicate that HIV-1 replication is likely dependent on enhanced T cell activation. In HEK293 cells transfected with TLR2, PIM6 was the strongest TLR2 agonist among the cell wall associated glycolipids tested. PIM6 increased the percentage of HIV infected cells and viral particles in the supernatant in a T-cell-based reporter cell line (JLTRg-R5) transfected with TLR1 and TLR2 but not in the cells transfected with the empty vector (which lack TLR2 expression) confirming that PIM6-induced HIV-1 replication depends at least partially on TLR2 signaling.

Studies directed towards nonyl acridine orange analogues having the potential to act as FRET donors with the PDT drug Pc 4

A group of nonyl acridine orange analogues (NAO) was prepared which were designed to have the potential of possessing visible bands allowing them to act in cells as fluorescence resonance energy transfer (FRET) donors with the photodynamic therapy drug Pc 4. The existence of Pc 4-FRET with the analogues of NAO in MCF-7c3 cells was probed. The results suggest that NAO analogues giving strong FRET with Pc 4 in cells can be found.

Molecular factors in cell (and tumor) response to photodynamic therapy: the role of Bid

The phthalocyanine photosensitizer Pc 4 binds preferentially to mitochondrial and endoplasmic reticulum membranes. Upon photoirradiation of Pc 4-loaded cells, membrane components, including Bcl-2, are photodamaged and apoptosis is triggered. We recently prepared analogues of Pc 4 containing two axial ligands, one identical to the single ligand in Pc 4, and the other containing one or two hydroxyl groups on a dimethylsiloxy alkyl chain. Pc 181 is representative of this group of photosensitizers. In MCF-7 human breast cancer cells, the new analogues preferentially localized in lysosomes and were highly efficient in inducing apoptosis and overall cell death. The Bcl-2 family member Bid is required for signaling to mitochondria for apoptosis in response to primary lysosomal photodamage. To further evaluate the role of Bid, we compared the effects of PDT with Pc 4 or Pc 181 in wild-type murine embryonic fibroblasts and those knocked out for Bid. We find that the two cell lines are equally sensitive to killing by Pc 4-PDT, but the Bid-/- cells are significantly more resistant to killing and apoptosis induction by Pc 181-PDT than are the Bid+/+ cells. The data show that low levels of lysosomal photodamage are not alone lethal and that a specific defect in a factor required for apoptosis can severely compromise cell response to PDT.