ACS Chemistry for Life

Following undergraduate work in Chemistry at Dartmouth, Paul C. Zamecnik got his M.D. at Harvard, and then returned to intern at the Cleveland Clinic in his native Ohio during the late 1930s.  His professional concern with cancer patients led him to conduct basic studies in protein synthesis, first in at the Carlsberg labs Denmark, then returning to Harvard.  He developed the first laboratory methods to make protein in cell extracts as opposed to living cells.  Using radiolabeled amino acids, Zamecnik and coworkers identified transfer RNA as a carrier molecule involved in the protein synthesis process. They also made some of the first observations of amino acid selection based on RNA composition, where poly-adenosine added to the cell-free synthesis systems gave rise to polyphenylalanine.   (We now know that the DNA “codon” letters TTT gives rise to messenger RNA sequence AAA, which encodes one phenylalanine.)      

 In the 1970s, Zamecnik and coworkers were studying Rous sarcoma virus and found their RNA sequencing effort had become an “also-ran” effort in a race won by Maxam and Gilbert, and Fredrick Sanger.  His collaborators left the field, but Paul was struck by the fact that their effort had stalled at exactly the point where the structure of the RNA they were trying to sequence had the opportunity to stick to itself (“self-hybridize”).  He realized that binding a small “wrong molecule” had the potential to disrupt many biological processes, which became known as the “antisense” principle. Subsequently, many examples of “antisense” inhibition and regulation of biological processes were found in nature.    In seminars, he often included a still photo of Charlie Chaplin from “Modern Times” sticking a wrench into the massive machinery in the factory.      

In the 1980s, the number of known nucleic acid sequences increased dramatically just as (and primarily because) incredibly efficient synthetic methods for synthesis of short strands of DNA were being introduced.  This provided almost unlimited amounts of both the gene targets and the probes needed to perform antisense experiments. In principle all one would need to know in order to stop a biochemical process was a part of a protein’s gene sequence.  This was indeed shown to work in very many useful laboratory tests, making it far easier to prove that a particular protein or gene involved in a a disease or other biological process. Producing drugs based on the antisense principle proved far more difficult. After more than two decades of work by dozens of labs, only one antisense oligonucleotide has been approved by the FDA, though many more continue in development.  Much attention is currently going to the closely-related processes known as RNA silencing and the use of small-interfering RNAs (siRNAs).