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Success of gene therapy

by- Nitin Kshirsagar

Outline

Introduction to gene therapyGlobal gene therapy marketSignificance in therapeuticsSuccess of gene therapyCurrent scenarioChallenges

“It's a history book - a narrative of the journey of our species through time. It's a shop manual, with an incredibly detailed blueprint for building every human cell.

It's a transformative textbook of medicine, with insights that will give health care providers immense new powers to treat, prevent and cure disease."

- Francis Collins

Introduction to Gene Therapy

I. Genome = approx. 3 billion base pairs II. One base pair is 0.00000000034 metersIII. DNA sequence in any two people is 99.9% identical – only

0.1% is unique!

Genetic disorders

Single gene disorders caused by a mistake in a single gene. Sickle cell, cystic fibrosis and Tay-Sachs

Chromosome disorders caused by an excess or deficiency of the genes. Down syndrome is caused by an extra copy of a chromosome (but no individual gene on the chromosome is abnormal)

Multifactorial inheritance disorders caused by a combination of small variations in genes, most cancers, Alzheimer's.

Gene therapy

In 1865 Mendel’s observations led to laws regarding the transmission of hereditary characteristics from generation to generation

1940s - Avery and colleagues 1953 –Watson and Crick 1990 - The first gene therapy journal published,

Human Gene Therapy 1990 - Ashanthi DeSilva, ADA-deficient Severe

Combined Immunodeficiency 2000 - The first cure Alain Fischer (Paris) totally

correcting children with SCID-X1

Global gene therapy market

The once abandoned gene therapy field has become a hotbed, with 11 different companies raising at least $618 million from venture capitalists and the public markets since the beginning of 2013, and one more, AGTC (Australasian Gene Therapy Society) plans a $50 million initial public offering soon. The iShares Nasdaq Biotechnology Index is up 65% in 12 months.

In March 2014 researchers at the University of Pennsylvania reported that 12 patients with HIV had been treated since 2009 in a trial with a genetically engineered virus with a rare mutation known to protect against HIV (CCR5 deficiency) top talent is being attracted to what was once seen as a lost cause

Cedars-Sinai Regenerative Medicine Institute has received a $2.5 million grant from the Department of Defense to conduct animal studies that, if successful, could provide the basis for a clinical trial of a gene therapy product for patients with Lou Gehrig's disease, also called amyotrophic lateral sclerosis(ability to initiate and control muscle movement is lost.)-

News medical, BBC 31.3.13

Significance in therapeutics

Means of gene therapy

Viruses- adenoviruses, retro viruses (unlike Ad, transfect by integrating the transgene into the target-cell chromosome)

Naked gene transfer- to elucidate mechanisms of gene expression and the role of genes and their cognate proteins in the pathogenesis of disease in animal models also being used in several human clinical trials like- genetic vaccines, Duchenne muscular dystrophy, peripheral limb ischemia, cardiac ischemia

Needle-free injection- gene gun, Intraject or Jetgun Electroporation - involves the application of a pulsed electric field enhance

cell permeability, resulting in the transit of exogenous polynucleotide across the cytoplasmic membrane performed by locally injecting DNA to the site of interest followed by the application of electric field

local injection < systemic injection Condensed DNA particles- polymers are heterogeneous polylysine,

polyethylene imine Liposomes

Burdette, Walter J. The Basis for Gene Therapy. Springfield: 2001

Path towards successful GT

Success of gene therapy

GT drugs as Anti-cancer

The increasing popularity of cancer therapeutics as a major interest for gene therapy applications led to it accounting for a dominant share of more than 60% in the overall number of clinical studies

Rexin-G A tumor-targeted retrovector bearing a cytocidal cyclin G1 construct, is the first targeted gene therapy vector to gain fast track designation and orphan drug priorities for multiple cancer indications in US

Gendicin Recombinant Ad-p53 gene therapy for head and neck squamous cell carcinoma (HNSCC)—a cancer that accounts for about 10% of the 2.5 million annual new cancer patients in China.

The reasons for cancer to become a preferred area of application for gene therapy are the significant unmet medical needs in cancer therapy, coupled with the large size of its market. Additionally, the ethical acceptance of gene therapy as a therapeutic solution also a contribution

CVS

Stem cell transplantation therapies that would accelerate natural processes of postnatal collateral vessel formation, an approach referred to as therapeutic angiogenesis

Coronary (CAD) and peripheral (PAD) artery disease Direct intramyocardial injection of VEGF DNA using an

adenovirus vector in patients with otherwise inoperable coronary artery disease and intractable angina pectoris

Rhumatoid arthritis- liposome, plasmid, RNAi

Alpha-1 antitrypsin (AAT) deficiency -is a hereditary disorder associated with mutations in the SERPINA1 gene

Over 100 different alleles have been identified however the most common disease-causing mutation

Others:-

RNA interference

RNA interference, also known as RNAi presents a new approach to gene therapy by targeting specific genes and down-regulating gene expression

One of the most potent forms of RNAi is small interfering RNA, or siRNA

Small fragments of double stranded RNA, specific for a particular gene target, are introduced to the cell

Specific hybridization between the naturally occurring transcript and the induced siRNA (antisense portion) instigates the destruction of the message.

directly on the transcriptional level of gene expression. Therapeutically speaking, siRNA efficacy would be

determined by percent knock-down BUT- this method is transient, requiring re-administration

Current scenario

The most promising gene-therapy concepts, at the

present time :

1. Direct killing of tumour cells with genes delivered by Ad vectors for local management of cancer;

2. Delivery of naked DNA by injection or by the gene gun for preventative vaccination against infectious diseases;

3. Naked DNA delivery of genes promoting angiogenesis for cardiovascular disorders; and

4. AV delivery for chronic disorders, such as haemophilia and anaemia

Challenges

Short Lived- Hard to rapidly integrate therapeutic DNA into genome and rapidly dividing nature of cells prevent gene therapy for long time

Immune Response- leads to immune responseIncreased response when a repeat offender enters

Viral Vectors- patient could have toxic, immune, inflammatory responsealso may cause disease once inside

Multigene Disorders- Heart disease, high blood pressure, Alzheimer’s, arthritis diabetes,etc. need to introduce more than one gene

May induce a tumor if integrated in a tumor suppressor gene because of insertional mutagenesis

Ethical and moral challenges

Thankk you…