When Thomas Cech of the University of Colorado announced alittle over a decade ago that he had discovered a self-splicingintron, a little piece of non-coding RNA that splices itself out ofthe transcript prior to translation, it seemed about as esotericas research can get. (When proteins are made, DNA is"transcribed" to "messenger RNA," which is "translated" toprotein.)
Earlier, Sidney Altman of Yale University had discovered thatthe catalytic activity of a splicing enzyme, RNase P, resides inthe RNA, not the protein, of this 7-1 mix of RNA to protein.
This shattered the common belief that only proteins can beenzymes, and led to implications for theories of how life gotstarted. The two scientists eventually won the 1989 NobelPrize.
But 10 years ago, no one would have guessed that biotechcompanies would be developing therapeutics from RNAenzymes. Two months ago, Innovir Laboratories Inc. andAltman were granted a patent for a novel targeting techniqueinvolving RNase P. And just last week, 5-month-old RibozymePharmaceuticals Inc. of Boulder, Colo., where Cech is a boardmember, announced a second round of venture capital fundingof $12 million.
All together, seven companies are putting eggs in the ribozyme(RNA enzyme) basket, including Johnson & Johnson and twoforeign companies -- in Australia and France. Three of thesecompanies are devoted exclusively to ribozymes.
In scientific literature, references to ribozymes have exploded,from the low tens to the low hundreds, according to JamesHawkins, editor of the journal Antisense Research andDevelopment.
The overall method underlying ribozyme therapeutics is to useribozymes to cleave some crucial piece of RNA in the targetmicrobe, disabling the pathogen. The technique covered by theInnovir/Altman patent, No. 5,168,053, is potentially useful fortreating a wide range of diseases of viral, bacterial and cellularorigin, including cancer, said Allan R. Goldberg, the company'schairman and chief scientific officer.
One strategy uses a synthetic piece of RNA, called the externalguide sequence (EGS) is a hybrid molecule composed of asequence that RNase P recognizes and cleaves, and partlycomplementary to the target RNA. For example, in the case of atherapy for hepatitis B, part of the EGS is complementary to acrucial messenger RNA (the RNA from which proteins aretranslated) coded for by one of the genes in that virus. RNase P,which exists naturally in the nucleus of the cell, recognizes itsusual target, which the EGS has fastened onto the targetmessenger RNA, and through its own inability to distinguishthe target RNA from its natural target, it slices the former.
Another strategy uses a genetically engineered virus encodinga synthetic gene for the EGS to produce the EGS inside of thecell. This technique ensures continuous production of largequantities of EGS. Goldberg expects to have animal experimentsunder way some time this year.
At Ribozyme Pharmaceuticals, the big effort is toward a proof-of-concept therapy for herpes infection of the eye. But thecompany is also working with John Rossi, chairman of thedivision of biology at Beckman Research Institutes of the Cityof Hope in Duarte, Calif., on a ribozyme for blocking HIVinfectivity in T cells, that would prevent the virus fromspreading throughout the body. "Probably we would make thegene for the ribozyme, put it into a retrovirus vector, and putthat into human bone marrow cells," said Rossi. They wouldthen produce T cells expressing the ribozyme against HIV.
The ribozyme would go after the tat gene, which produces aprotein that activates transcription of the virus.
Hawkins said that ribozymes pose a variety of technicalproblems. For example, RNA enzymes function slowlycompared to proteins. However, new techniques allow chemiststo modify the ribozymes for greater speed.
In basic research, the discovery of RNA enzymes has pointed toa way around the chicken-and-egg question concerning thebeginning of life: Which came first, protein or DNA? RNA couldhave served both as genetic material and as enzymes.
Lately, the scientific funding establishment is becomingimpatient with basic research, and there has been some flow offunds toward applied research. This is short-sighted, saidWalter Gilbert, chairman of cellular and developmental biologyat Harvard University and founder of Biogen Inc. of Cambridge,Mass.
The ribozyme "is a perfect example of how all of moderntechnology flows from our increase in basic understanding," hesaid. "The biotechnology companies that were created in theearly '80s and the late '70s developed from the basic researchof the 1960s and '70s."
Ribozymes were developed "from the most basic kind ofresearch that involved pursuing totally unforeseen lines ofresearch in organisms that no one would have thought wouldyield anything novel," Gilbert said.
Other companies involved in developing ribozymes are GeneShears of Sydney, Australia; Genset of Paris; Hybridon Inc. ofWorcester, Mass.; Lynx Therapeutics Inc. of Foster City, Calif.
-- David C. Holzman Special to BioWorld
(c) 1997 American Health Consultants. All rights reserved.