AIDS TREATMENT NEWS Issue #187, November 19, 1993
Dave Gilden
Isis 2922, for which the company filed an Investigational New Drug application with the FDA on October 27, is one of the furthest developed of a new class of medications -- antisense RNA. These compounds are synthetic creations that are exactly complementary to the RNA sequences produced by viral (or cancer) genes within a cell. The function of RNA is to convey instructions to the rest of the cell from any of the multitude of DNA-based genes in the cell nucleus. RNA encodes the structure of individual enzymes and other proteins necessary for cell function.
Antisense RNA locks onto the RNA produced by the disease- provoking genes, thus preventing the "bad" RNA from directing undesired protein production within the cell. It is hoped that antisense RNA will be so specific that it will nullify the disease process while leaving cells' natural chemical machinery alone.
The Isis drug blocks the functioning of CMV's IE2 gene. This gene encodes instructions for a protein that regulates the production of new CMV virus particles. Since Isis 2922 does not kill cells already infected with CMV, it is a long-term maintenance therapy and not a cure. Isis plans to try the drug by injecting it directly into volunteers' eyes on a weekly or biweekly basis. The initial 12-week safety trial will involve 25 people with CMV retinitis who are failing on standard therapies. This trial is not available to the general public. The volunteers will come from the practices of four physicians, whose identities have not been disclosed.
If the first trial is promising, Isis will conduct larger trials in the future. It is also considering some kind of expanded access program for people outside the official trials. Future development plans include trying Isis 2922 as first line therapy for CMV retinitis and as a treatment for CMV infections elsewhere in the body.
Antisense is a new and speculative field. In the past the use of antisense drugs has run into problems with unthinkably high cost, finding a critical target gene, delivering the drug to the proper tissues and cells, stability within the body, and low effectiveness. Whether antisense drugs really leave normal body processes alone also remains open to question. The local injection method Isis is using for CMV retinitis minimizes most of these concerns. Similarly. the company's other antisense drug in human trials is an anti- genital wart medicine that is administered directly to the warts.
Isis is considered among the leading companies in antisense technology. However, another company, Hybridon, of Worcester, Massachusetts, is embarking on human trials of an antisense compound aimed at HIV. (See AIDS TREATMENT NEWS #185.)
Isis has set up a voice mail line for inquiries about its CMV therapy. Questions can be left by calling (619) 929-3898.
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