ANTISENSE RNA and DNA

By: Dr. Erin A. Sharkawy

Basic Science:-Genes contain the information necessary to

produce proteins.

-Protein production occurs in two phases called transcription and translation .

-In the transcription phase, the DNA strand is used as a template for manufacturing an mRNA molecule .

-mRNA is responsible for communicating the genetic message in the DNA to the cell so that protein production can take place .

-In the translation phase, the mRNA travels to the ribosome, and carry out protein synthesis.

Normally only one of the two DNA strands in a given portion of double helix is transcribed into RNA and always the strand for a given gene (sense DNA ).

if a cloned gene is engineered so that the

only opposite (antisense DNA)is transcribed , the result will be antisense RNA with a sequence complementary to the

normal RNA transcript .

Antisense RNA . When synthesized in large enough amounts will often hybridize with the sense RNA made by normal genes and therapy inhibit the synthesis of the corresponding protein.

Based on this conception , a versatile new approach for shutting off an endogenous cellular gene targets the gene’s mRNA

rather than the gene itself .

Overview:-Currently, a total of ~4,000 genetic

disorders are known.

-The mutated genes produce proteins that cannot function properly, leading to the occurrence of the diseases.

-Examples: Sickle-cell anemia, Cystic fibrosis, Color blindness

How to stop genetic disorder using DNA drugs?

-Design a short DNA sequence that matches the sequence of mRNA that is transcribed from the mutated gene (which causes diseases).

-The DNA drug binds to the mRNA

-The mRNA cannot be translated to protein

-Because no disease-causing protein, disease is cured

Antisense TechnologyAntisense technology interrupts the translation phase of the protein production process by:

1-Preventing the mRNA instructions from

reaching the ribosome .2-Inhibiting the protein synthesis.

Antisense drugs Antisense drugs are short, chemically

modified complementary nucleotide chains that hybridize to a specific complementary area of mRNA.

Antisense drugs are being researched to treat a variety of diseases such as cancers (including lung cancer, colorectal carcinoma, pancreatic carcinoma , and malignant melanoma), diabetes, muscular dystrophy and diseases such as asthma, arthritis.

The idea is to introduce into cell an RNA or single stranded DNA molecule that is complementary to the mRNA of the target gene .

* several strategies have been used to

introduce antisense nucleic acids into cells:

1 -antisense RNA was synthesized into vitro using bacteriophage RNA polymerase and then microinjected into cells.

2 -introducing antisense NA into cells using synthetic single stranded DNA oligonucleotides.

when short nucleotides complementary to the sequence around the transitional initiation site (the AUG codon) of a mRNA enter cells ,they hybridize to the mRNA and prevent the initiation of the translation.

simply adding high conc. of such nucleotides to cell culture is sometimes sufficient to prompt cells to take them in or we can modify the oligonucleotides chemically

to increase the efficiency entering the cells and their stability inside.

* this method has been used to turn off oncogene function.

* Antisense oligonucleotides directed

against viral RNA can protect cells against viral infection.

* Antisense technology offers hope for new therapies for cancer and for viral diseases , such as AIDS .

MECHANISM OF ANTISENSE THERAPY

- Most potential therapies have not yet produced significant clinical results

though two antisense drugs have been approved by the U.S. FDA :

- - one of them is:

* Fomivirsen -marketed as Vitravene as a treatment for cytomegalovirus retinitis.

Thank you