Spreading Knowledge is a great Legacy. MMG

1. GT FOR MULTIFACTORIAL
GENETIC DISEASES

2. Colorectal cancer
 2nd most common malignancy
 Tumor can be visualized and sampled
 Carcinomas develop from adenomas
 Monoclonal
 4-5 chromosomal losses per carcinoma cell

4. Hereditary colorectal cancers
 One germline abnormality, second during
lifetime
 Familial adenomatous polyposis
 HNPCC
 Sporadic cases

5. Genetic alterations in oncogenes
 Protooncogenes
 Point mutations altering the product
 Gene amplification
 Overexpression
 Gene rearrangements
 Mutant K-ras oncogene

6.  Allelic losses
 Loss of chromosomal regions
 LOH (17p, 18q, 17q21)
 Presence of 2nd gene copy and its malfunctioning
Genetic alterations in oncogenes

7.  DNA hypomethylation
 Inhibition of chromosomal condensation
 Lead to non-disjunction
Genetic alterations in oncogenes

8. Cancer GT
Which target gene?
What delivery method?
 Tumor suppressor gene replacement
 Oncogenic inactivation by antisense technology
 Genetic prodrug activation therapy
 Immunotherapy
 MDR genes
 Vascular and stromal targetting

9. Oncogenic inactivation by antisense
technology
 Use of a nucleic acid (antisense nucleic acid)
complementary to a part of DNA/RNA
 Hybridization causes silencing of that
DNA/RNA
 Suitable for genes overexpressed in tumor
tissues
 Antisense nucleic acid can
 Form irreversible triple helix with DNA
 Form Double helix with RNA to block translation
 Complex with transcription associated proteins
 Be a ribozyme itself

10. Tumor suppressor gene replacement
 Replacement of tumor suppressor function
 Some correction-vector inefficiency
 Use of E1B attenuated adenovirus
 Replication of virus in tumor cells causing
cytolysis, normal cells are protected
 Research is still in progress

11. Genetic prodrug activation therapy
 Targetting a specific cytotoxic agent to tumor
cells
 Delivery of a gene encoding a drug
metabolizing enzyme to tumor cells
 A non toxic prodrug is given to thepatient
 The prodrug is converted to a toxic
metabolite only in tumor cells because of the
presence of drug metabolizing enzyme only
in tumor cells

12. Immunotherapy
 Tumor cells are poorly Immunogenic
 Use of direct cytokine administration-toxic
 Need is to produce small levels of cytokine
only in the tumor cells
 By transferring cytokine genes to tumor
infiltrating lymphocytes (TIL), tumor
associated lymphocytes andlymphokine
activated killer cells ex vivo and injecting back
into the patient
 Or doing the same with patient tumor cells

13. Multidrug resistance genes
 Tumors develop resistance to many drugs
 Mechanism is drug efflux by membrane
pumps by MDR1 protein
 Transfer of MDR1 gene to normal marrow
cells
 Normal cells will be thus resistant and higher
drug doses can be given
 Marrow cells transduced with dihydrofolate
reductase are resistant to methotrexate

14. Vascular and Stromal Targetting
 Suppression of positive regulators
 Induction of negative regulators
 Suppression of receptor expression on
endothelial cells
Less vascular supply to tumor tissues result in
tumor cell killing