Utilization of Glycosaminoglycans/Proteoglycans as Carriers for Targeted Therapy Delivery

Abstract

The outcome of patients with cancer has improved significantly in the past decade with the incorporation of drugs targeting cell surface adhesive receptors, receptor tyrosine kinases, and modulation of several molecules of extracellular matrices (ECMs), the complex composite of collagens, glycoproteins, proteoglycans, and glycosaminoglycans that dictates tissue architecture. Cancer tissue invasive processes progress by various oncogenic strategies, including interfering with ECM molecules and their interactions with invasive cells. In this review, we describe how the ECM components, proteoglycans and glycosaminoglycans, influence tumor cell signaling. In particular this review describes how the glycosaminoglycan hyaluronan (HA) and its major receptor CD44 impact invasive behavior of tumor cells, and provides useful insight when designing new therapeutic strategies in the treatment of cancer.

Figure 1

Structures of repeating disaccharides of glycosaminoglycans.

Figure 2

Diagram of part of an aggrecan aggregate. G1, G2, and G3 are globular, folded regions of the central core protein. Proteoglycan aggrecan showing the noncovalent binding of proteoglycan to HA with the link proteins.

Figure 3

Proteoglycans act as coreceptors for growth factor receptor (GFR) signaling, thus influencing cell signaling and cell behavior. GAGs present as a part of proteoglycans on the cell surface and in ECM, bind to numerous proteins, and modulate their function.

Figure 4

Alternative splicing in CD44 pre-mRNA. CD44 pre-mRNA is encoded by 20 exons. The common CD44s (hematopoietic) form contains no extra exons, and the protein may have a serine motif encoded in exon 5 that initiates synthesis of a chondroitin sulfate or dermatan sulfate chain. Alternative splicing of CD44 predominantly involves variable insertion of 10 extra exons with combinations of exons 6–15 and spliced in v1–v10 into the stem region, of which v3 encodes a substitution site for a heparan sulfate chain. Variable numbers of the v exons can be spliced in epithelial cells, endothelial cells, and inflammatory monocytes and also upregulated commonly on neoplastic transformation depending on the tissue.

Figure 5

Schematic illustration of cellular uptake of plasmid DNA/Tf-PEG-PEI (nanoparticles) polyplexes, their shielding from nonspecific interaction, and the mechanism of action of shRNA (adapted from [43]). Internalization of PEG-shielded and Tf-R-targeted polyplexes into target cells occurs by receptor-mediated endocytosis after association of polyplex ligand Tf to Tf-R present on the target cell plasma membrane. Internalized particles are trafficked to endosomes followed by endosomal release of the particles and/or the nucleic acid into cytoplasm. Released siRNA will form a RNA-induced silencing complex and will be guided for cleavage of complementary target mRNA in the cytoplasm. siRNA (antisense) guide strand will direct the targeted RNAs to be cleaved by RNA endonuclease. Finally plasmid/Tf-PEG-PEI-nanoparticles delivery in the target cell shows reporter gene expression and activity.

Figure 6

Model for delivery of shRNA (adapted from [18]). This illustration depicts cellular uptake of plasmid Tf-PEG-PEI nanoparticles and the mechanism of action of shRNA. First, a pSico vector containing a U6 promoter-loxP-CMV-GFP-STOP signal-loxP-CD44vshRNA (gene of interest) is made. Second, an expression vector with the Cre-recombinase gene controlled by the tissue specific promoter is created. Third, the two vectors are packaged in transferrin (Tf) coated-PEG-PEI nanoparticles that bind with Tf-receptors (Tf-R) present at high levels in the targeted tumor cells. Delivery of the vectors in normal and malignant cells from the targeted tissue results in deletion of the Stop signal and transcription of Cre-recombinase driven by the tissue specific promoter. The target gene (CD44vshRNA) is then unlocked and transcribed through the strong U6 promoter for high expression. The normal tissue cells are not affected because they do not make the targeted CD44 variant. Tf-PEG-PEI nanoparticle coated plasmids (pSico-CD44v6shRNA/pFabpl-Cre) circulating in blood accumulate at tumor regions enhanced by the EPR effect. Endocytosis mediated by ligand-receptor interactions occurs because the nanoparticles are coated with the Tf-ligand for the Tf-R receptor on the tumor cell surface.

Figure 7

Uptake of pSV-β-galactosidase/Tf-PEG-PEI (nanoparticles) into target cell. Delivery of pSV-β-gal nanoparticles in colon cancer cells (adapted from [43]). (a) In situ   β-galactosidase expression in the target cell. The Apc10.1-HAS2 clone and the CT26 cells were treated for 48 h with the pSV-β-gal alone (panel 1), with the pSV-β-gal with liposome (panel 2), or with the pSV-β-gal/nanoparticles (35 nm average diameter, 8 μg of pSV-β-gal/mL) (panel 3). The average size of the pSV-β-gal/nanoparticles is ~35 nm ± 20 nm. The transfected cells were fixed in 0.2% glutaraldehyde in PBS and washed twice in PBS. The cells were treated with a β-galactosidase staining solution and digitally photographed. (b) Transferrin-dependent uptake and in situ   β-galactosidase expression in the target cell. The Apc 10.1-HAS2 cells were transfected with the pSV-β-gal with liposome (panel 1), treated with Tf-R antibody and followed by transfection with the pSV-β-gal/nanoparticles (8 μg pSV-β-gal/mL) (panel 2), or treated with the pSV-β-gal/nanoparticles (8 μg pSV-β-gal/mL) alone (panel 3). The transfected cells were fixed in 0.2% glutaraldehyde in PBS and washed twice in PBS. β-galactosidase expressions in the cells were digitally photographed. (c) Cell-free extracts of parallel cultures were prepared in 10 mM CHAPS buffer and assayed for β-galactosidase activity using o-nitrophenyl β-D-galactopyranoside as substrate. The results are expressed as micromoles of o-nitrophenol formed per min/mg protein and represent ± S.D. of triplicate assays from the untransfected, liposome-transfected, or nanoparticles-treated cultures for each cell type.

Figure 8

Systemic application of pSicoCD44v6shRNA plasmid in Apc Min/+ mice. Effect of plasmid/nanoparticle treatment on protein expression, RT-PCR analysis, and number of adenomas in Apc Min/+ mice (adapted from [43]). Thirty Apc Min/+ mice were randomly divided into three groups. Group 1 received pSV-β-galactosidase (100 μg/100 μL, intraperitoneally (i.p.)) alone, Group 2 received pSV-β-gal nanoparticles (100 μg/100 μL, i.p.) targeted to the Tf-R, and Group 3 received pSico-CD44v6shRNA (75 μg) plus pFabpl-Cre (25 μg)/nanoparticles i.p. every other day. 10 days after beginning treatment, the animals were sacrificed, and the large (>1 mm) and small (<1 mm) adenomas were counted (a). The tumor and adjacent normal tissues were subsequently processed for (b) western blots for CD44, pErbB2, TErbB2, COX-2, and β-actin and (c) RT-PCR analyses for CD44 variants from total RNA. Total ErbB2 remained unchanged in all the treatment groups (data not shown).

Figure 9

Exploitation of HA-CD44 interaction for anticancer therapy. Left panel represents the internalization of HA-drug conjugate that ultimately releases the drug that inhibits DNA synthesis of cancer cells. CD44 on the cell membrane binds the HA-drug conjugate and is internalized by endocytosis. The endosome formed is moved to the lysosome and fused. Here the HA in the conjugate is degraded first by hyaluronidase 1 (Hyal-1) into small HA oligosaccharides and next by lysosomal glycosidases to monosaccharides followed by release of the drug. The drug inhibits the DNA synthesis in the nucleus. Right panel exemplifies the steps that target the CD44v6mRNA in cancer cells by CD44v6shRNA. Plasmids producing CD44v6shRNA are coated with transferrin containing nanoparticles to target transferrin receptors of the cells. The particles are then internalized and form an endosome from which the plasmids are released to the nucleus where activation of DNA pol III occurs that results in CD44v6shRNA production. Through exportin, the newly produced CD44v6shRNA come out into cytoplasm where it is converted into CD44v6siRNA by dicer enzyme. One of the strands of siRNA will bind to CD44v6mRNA and forms RNA-induced silencing complex (RISC) which is ultimately degraded.