Key differences in tumour vasculature Different flow characteristics / blood volume Microvasculature permeability Increased fractional volume of extravascular, extracellular space
Angiogenesis-overview Balance between inhibitory factors (endostatin) and angiogenic factors (VEGF, bFGF) angiogenic factors stimulate MMPs and plasminogen activators Degradation of basement membrane Invasion and differentiation of endothelial cells in surrounding tissues
MMPIs Disappointing results with matrix metalloproteinase inhibitors Disappointing results with matrix metalloproteinase inhibitors Poor survival rate in phase III clinical trials against renal cell carcinoma Poor survival rate in phase III clinical trials against renal cell carcinoma
Newer cancer therapies Gene therapy Severe Combined Immunodeficiency Disease (SCID)
Antisense therapy compensates for genetic mutations that produce destructive proteins Main strategies involved are 1) short stretches of synthetic DNA that target the mRNA transcripts of abnormal proteins preventing its translation OR small RNA molecules (siRNA) used to degrade aberrant RNA transcripts
Antisense therapy 2) provide a gene for a protein (intracellular antibody) that can block the activity of the mutant protein Tumor necrosis therapy utilizes monoclonal antibodies targeting intracellular tumor antigens on necrotic (dead) tissue. This method overcomes some of the limitations of current antibody-based therapeutic approaches 3)design hybrids of DNA / RNA that might direct repair of the mutant gene
Gene augmentation most therapies simply add a useful gene into a selected cell type to compensate for the missing or flawed version or even instil an entirely new version. Direct approach inducing cancer cells to make a protein that will kill the cell. Indirect approach stimulating an immune response against selected cells or eliminating the blood supply.
delivery 3 challenges in gene therapy deliverydelivery 1) Package the gene 2) Protect the gene 3) deliver to the nucleus and release in an active form Vectors ‘Trojan horses’ that sneak the gene into the cell
Carrier molecules designed specifically to enter cells & deposit therapeutic genes Vectors can be viral or non-viral Vectors
Viral vector strategy Replication & virulence genes can be substituted with therapeutic genes
designed to enter cell and deposit genes Problems of retroviral therapy include Lack of cell specificity: Promiscuous: depositing genes into several cell types resulting in reduced target efficiency and unwanted physiological effects Random splicing into host DNA resulting in normal gene disruption and/or alteration in gene function Retroviral vectors
Adenoviral vectors do not insert into genome temporary lack of specificity strong immune response
Adeno-associated viral vectors Nature Reviews Genetics 1; 91-99 (2000); Integrate into genome but small in size
Advantages non-toxic no immune response Non-viral Vectors
amino acid polymers: cationic polymers e.g. B-cyclodextrins Non-viral Vectors
naked DNA artificial human chromosomes Non-viral Vectors Gene gun
Successes Cancer and the p53 gene. Researchers used a virus to carry a normal copy of the p53 gene into the abdominal and pelvic areas of women with advanced ovarian cancer. Seven of 25 women tested in California and Iowa survived more than 2 years after the therapy, despite having a terminal diagnosis. Cancer and enzyme therapy. This type of therapy targets enzymes, or proteins, that are made by abnormal genes. Example: Gleevec, a new drug, targets an abnormal protein produced by a cancer-causing gene. The abnormal protein is necessary for some types of cancer to survive and reproduce. Gleevec blocks the action of the protein. Gleevec has been successful in chronic myeloid leukemia and in gastrointestinal stromal tumors. It is being tested in other types of cancer. Cancer and other therapies. Advances in identifying genes have helped researchers to target other therapies. Example: Herceptin targets the HER-2 gene. In 25%-35% of breast cancers, HER-2 produces too many copies of itself, causing breast cancer cells to reproduce out of control and spread throughout the body. Herceptin blocks excess HER-2 by binding to growth receptors on the surface of the cell, causing tumors to shrink.
Gleevec for chronic myeloid leukaemia (CML) CML results through a chromosomal rearrangement that fuses two genes together. This produces an oncogene that encodes an enzyme, a form of tyrosine kinase known as BCR-ABL. Unchecked production of that enzyme leads to excessive levels of white blood cells in the blood and bone marrow. that disrupts the normal production of white blood cells. CML results through a chromosomal rearrangement that fuses two genes together. This produces an oncogene that encodes an enzyme, a form of tyrosine kinase known as BCR-ABL. Unchecked production of that enzyme leads to excessive levels of white blood cells in the blood and bone marrow. that disrupts the normal production of white blood cells. Gleevec works specifically to block the activity of that form of tyrosine kinase. Gleevec works specifically to block the activity of that form of tyrosine kinase.