Gene Therapy: A New Twist on an Old Helix – Genetic Engineering & Biotechnology News

Many Helpers Make Light Work

Targeting cancer cells that have spread to several organs of the body is difficult. Targeted radiation therapy or chemotherapy tends to destroy not only the cancer cells but also normal cells. Turning to gene therapy to selectively deliver therapeutic genes into these cancer cells on a larger scale and eliminating them in one fell swoop is the ultimate goal of Tocagen.

Using two products, Toca 511 and Toca FC, the company plans on developing an effective combination therapy that could hit the cancer hard. Toca 511 is an injectable retroviral replicating vector (RRV) that provides the genetic material to encode a prodrug activator enzyme, cytosine deaminase (CD), which is derived from yeast and has no human counterpart. It is selectively delivered to only cancer cells, thus producing the CD protein in each cell.

Part two of this therapy involves a pill called Toca FC, which contains 5-fluorocytosine (5-FC) that converts to the anticancer agent 5-FU in the presence of CD protein. Toca FC kills not only the cancer cells, but also the myeloid-derived suppressor cells (MDSCs), which suppress the immune system, and tumor-associated macrophages (TAMs).

Harry Gruber, M.D., cofounder and former CEO of Tocagen, talks about the use of gamma-retroviruses: The advantage of using a gamma-retrovirus (as opposed to the lentivirus) is that it cannot enter the nucleus on its own. This makes it selective to dividing cells only, and since cancer cells are rapidly dividing, [gamma-retroviruses] help in spreading the virus and its genetic information. They live in defective cells that lack an innate immunity, and due to this selectivity, they are designed to be universally geared toward only cancer cells.

Dr. Gruber also mentioned that Toca 511/FC received the FDAs Breakthrough therapy designation, which expedites drug development.

The field of gene therapy has come a long way since its inception. Early failures and setbacks forced researchers back to the drawing board to figure out how viral vectors could be accepted by the human body, which ordinarily rejects foreign particles. Researchers also had to learn how such vectors could reach specific targets and deliver foreign DNA that could be integrated into the genome. This dance between therapy and the innate immune system is getting more complex, but is also showing its true beauty within the complexity.

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Gene Therapy: A New Twist on an Old Helix - Genetic Engineering & Biotechnology News