Targeted Tumor Therapy


Current Research

The following research focuses on experiments that have been conducted to design tumor targeted devices.  The data has been published and the PubMed links to the respective papers can be found in the Resources section.


W. Arap, E. Ruoslahti, "Targeting the prostate for destruction through a vascular address"

Current surgical therapies to remove prostate cancer are associated with side effects such as incontinence and impotence.  This group is developing a strategy to provide a less traumatic treatment to a prostate cancer patient by specifically targeting the prostate.  The selection of a homing peptide was carried out through phage screening as documented in the Phage Selection Process on this website.  The screening found that phages expressing two peptides selectively homed to the prostate:  SMSIARL and VSFLEYR (single letter amino acid codes) at a selectively of 15 times and 10 times more than a control phage, respectively.  The study proceeded to use SMSIARL to conduct in vivo tests to target the prostate of rats.  The SMSIARL peptide was isolated and cloned into a T7 phage and it showed similar selectivity to the prostate.  Figure 1 shows the selectivity of the SMSIARL peptide seen during the phage screening process.  The SMSIARL is believed to target the vasculature of the prostate.  Immunohistochemical staining in Figure 2 shows that the phage localizes around prostate vasculature but not around that of the brain.  The next part of this study evaluated the ability of the SMSIARL peptide to deliver a biologically active drug.  p(KLAKLAK)2 is a drug that kills bacteria but is nontoxic to eukaryotic cells since it cannot cross the eukaryotic membrane.  When the SMSIARL peptide is conjugated to p(KLAKLAK)2 through a G-G linker, it is competent at destroying prostate tissue.  Figure 3 shows light microscopy histology of mouse prostate being destroyed by the conjugated drug.  When the two peptides are uncoupled and injected, the prostate does not show any destruction which suggests that the SMSIARL peptide can be coupled with other drugs to selectively kill prostate tumors in future studies.

Fig. 1: (a) Selectivity of SMSIARL phage for the prostate.  Injection of the SMSIARL along with the SMSIARL phage effectively inhibited the binding to the prostate compared to a control peptide.  This is perhaps the result of competitive binding.  (b) Prostate tissue and brain tissue (control) were tested for incorporation of the T7 phage cloned with the SMSIARL peptide.  Phage was extracted with either a PBS buffer or a lysis detergent.  PCR was run on the extracted phage colonies to screen for the SMSIARL sequence and in both conditions, incorporation was higher in the prostate than in the brain.  This high amount recovered in the lysis detergent suggest that much of the phage incorporates into the prostate cells.

Fig. 2: (a-c) are representative staining of the prostate. (d-f) are staining of brain tissue.  (a & d) are stained with an antibody against the T7 phage and visualized with FITC which shows green as positive.  CD31, a marker of vascular endothelial cells, was targeted by an antibody and is shown as a positive red (b, c, e, f).  DAPI was used to stain for nucleus (c & f) for comparison.  Similar tests were done for kidney, spleen, and lung tissue; data not shown).

Fig. 3: (a) Mouse prostate cross section after delivery of conjugated SMSIARL-p(KLAKLAK)2.  Massive grandular destruction  with nearly complete shedding of epithelial cells into lumen.  (b) shows the normal prostate after injection of SMSIARL and p(KLAKLAK)2 not conjugated.  (c) shows the necrosis of single epithelial cell from the conjugated group and (d) is that of the unconjugated group. (e) is a cross section of bladder tissue from the conjugate group which shows no damage.  The same goes for heart (f), kidney (g), and liver (h).


M. Akerman, S. Bhatia, E. Ruoslahti, "Nanocrystal targeting in vivo"

This study used peptides that homed to lung endothelial (LE), tumor vasculature, and human breast carcinoma MDA-MD-435 cells.  The peptides are named GFE, F3, and LyP-1 respectively.  These peptides were adsorbed to the surface of quantum dots (Qdots) through a thiol-exchange reaction.  Qdots have the unique ability to luminesce when excited at a certain wavelength of light.  The Qdots coated with F3 showed that the F3 tended to aggregate, due to the interactions of ionic residues, and was ineffective as a homing device.  To compensate for this, polyethylene glycol (PEG) was co-adsorbed onto the Qdots to space out the F3.  Figure 1 shows a variety of graphics which show the preferential binding of the three peptides to their respective targets and their non-binding to other cells.  The study also found that coating the surface of the Qdot with PEG alongside the peptide reduces its affinity to be taken up by the reticuloendothelial system relative to Qdots coated with just peptide.  The results for this are shown in Figure 2 where Qdots coated with LyP-1 are compared with Qdots coated with LyP-1 and PEG.  This result is beneficial in allowing the drug to stay in circulation longer and reducing the dose needed.  One of the problems with using Qdots is that fluorescence is not seen incorporated within the cells.  This is possible due to the large size of the Qdot-peptide conjugate or due to the fact that the Qdots were not stable enough to luminesce within cells and tissue.  There is also a possibility that the pH of the microenvironment causes a quenching of the Qdot fluorescence.

Fig. 1: (a) Qdots coated with GFE (green) bind to LE cells (blue) through the membrane dipeptidase receptor, but is inhibited when free GFE (b) or cilastatin (an inhibitor of membrane dipeptidase) (c).  (d) shows a bar graph representation of the amount of Qdot-GFE incorporation into LE cells.  Column A is the Qdot-GFE conjugate, Column B is when free GFE is added, and Column C is when cilastatin is added.  Column D shows that binding to membrane dipeptidase by Qdot-GFE is not inhibited when a control peptide is added.  Column E shows that Qdot-LyP-1 does not bind to LE cells.  (e) shows that Qdot-F3 bind to MDA-MB-435 breast carcinoma cells while it is inhibited when free F3 is added (f).  (g) shows Qdot-LyP1 binding to MDA-MB-435 cells.  (h) shows Qdot-GFE does not bind to MDA-MB-435 cells and (i) shows Qdot-LyP1 does not bind to LE cells.

Fig. 2: Green Qdots coated with LyP-1 and either with or without PEG were injected into the tail vein of a mouse and the incorporation into the liver and spleen were examined by fluorescence microscopy. Qdot-LyP-1 is incorporated into the liver (a) and spleen (b).  Qdot-LyP-1-PEG shows significant reduced incorporation in the liver (c) and spleen (d).


Y. Chau, R. Langer, "Antitumor efficacy of a novel polymer-peptide-drug conjugate in human tumor xenograft models"

Tumors possess unique pathophysiology including highly permeable vasculature and poor lymphatic drainage.  A high molecular weight polymer-drug conjugate could then in theory extravasate into tumor tissues but not into normal tissue with low permeability.  Once the conjugate is inside the tumor tissue, it cannot readily exit because of the poor lymphatics.  This phenomenon is known as enhanced permeation and retention (EPR).  Langer's study is designed to create a drug/polymer conjugate that targets releases drug in the presence of matrix-metalloproteinase-2 and matrix-metalloproteinase-9 (MMP-2 & MMP-9, respectively).  The two enzymes are key in tumor metastasis and are utilized for targeted tumor therapy.  Dextran was used as the polymer in this study due to its high molecular weight and its hydrophilic nature and also due to its established biocompatibility and biodegradibility.  The drug chosen was methotrexate (MTX) which is a folic acid analog that inhibits dihydrofolate reductase and retards the synthesis of RNA and DNA.  The MTX is linked to the Dextran by a peptide which can be cleaved by MMP-2 and MMP-9 (Figure 1).  Through this, the drug will be released in the presence of the tumor and not in a healthy tissue site.  Three human tumor cell lines were used and tested for MMP-2 & MMP-9 expression (Figure 2).  The tumor lines are HT-1080, U-87, and RT-112.  Tumor lines HT-1080 and U-87 showed strong expression of the two MMPs while RT-112 showed relatively no expression of either MMP.  In vivo tests were done in mice grafted with these tumor lines.  Mice grafted with HT-1080 or U-87 showed an inhibition of tumor growth when the Dextran-MTX conjugate was administered relative to the control and free MTX.  Mice that had the RT-112 line grafted showed no retardation of tumor growth when the conjugate was administered relative to the control and free MTX (Figure 3).  This study validates that the Dextran-MTX conjugate is an effective drug delivery device to target tumors that express MMP-2 and MMP-9, which are characteristic of malignant, metastasizing tumors.  Further studies are being conducted to determine the severe and acute drug-related toxicity of the conjugate.  This study shows that tumor growth can be stopped but does not prove that the tumor can be eliminated altogether.

Fig. 1: Chemical structure of the Dextran-MTX conjugate.  The peptide linker is designed so that MMP-2 and MMP-9 cleave the linker thereby releasing the MTX in the presence of the tumor.

Fig. 2: Top panel is a staining for MMP-2 and bottom panel is staining for MMP-9.  Tumor lines HT-1080 (a), U-87 (b), and RT-112 (c).  In both panels, a brown indicates a positive stain for the respective MMP.  HT-1080 and U-87 show strong expression of MMP-9 and sparse expression of MMP-2 while RT-112 shows low expression levels for both MMPs.  Both panels are magnified at 20X.

Fig. 3: In vivo tumor progression of the three tumor lines.  (a) HT-1080, (b) U-87, and (c) RT-112.  Control group was treated with PBS (line with X through it).  Free MTX group (line with filled black boxes).  Dextran-MTX group (line with filled triangles).  No retardation of tumor growth in RT-112 line due to lack of MMP-2 and MMP-9 expression (Figure 2).


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University of California, Irvine
BME 240
June 2006

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