Antisense pharmaceutical research has sought to provide drugs that would yield effective therapies for dis-
Antisense pharmaceutical research has sought to strategieases resulting from the production of deleterious procally design drugs that would predictably yield safe and effecteins. The original concept was straightforward: tive therapies. It is now clear that a broad knowledge of nueliminate production of unwanted proteins, such as oncleic acid biochemistry will be needed to attain this goal and cogenic proteins, by blocking the function of their other related objectives. As originally conceived, antisense mRNAs; and block their mRNAs by adding ''antisense'' strategies were to offer a general and rational approach for nucleic acids that bind them through complementary designing treatments for all diseases resulting from the probase pairing. However, it has proven difficult to develop duction of deleterious proteins, such as viral, oncogenic, cytoclinically useful antisense strategies. Conventional antitoxic, misfolded, or overly abundant proteins (including pepsense nucleic acids are large, highly charged, complex tide hormones). Figure 1 illustrates one type of antisense molecules that interact with a wide variety of uninapproach. In this model, the therapeutic molecule is an antitended cellular and microbial components, often caussense DNA oligonucleotide. It is composed of sequences coming ''nonantisense effects.'' It is now clear that a broad plementary to its target, a messenger (mRNA). The mRNA knowledge of nucleic acid biochemistry will be needed contains genetic information in the functional, or sense, orito optimize antisense molecules for use in patients. The entation. In the ideal strategy, binding of the antisense oligoefficacy of naturally occurring antisense molecules and nucleotide inactivates the intended mRNA and prevents its the success of antisense agricultural strategies prove translation into protein, while leaving all other RNAs unafthat antisense approaches can be powerful and specific. fected. 5 Antisense strategies are based on biochemical experi-Pharmaceutical antisense research can be expected to ments showing 1) that proteins are translated from specific yield many valuable products once sufficient informa-RNAs; 2) that once the sequence of an RNA is known, it is tion about antisense mechanisms has been gathered and possible to design an antisense molecule that will bind to it applied. This article explains the biochemical events through complementary Watson-Crick base pairs; and 3) that that give rise to both antisense and nonantisense effects by manipulating conditions in vitro, it is possible to obtain and provides guidelines for designing and evaluating sequence-specific binding, albeit under conditions that are antisense experiments. (HEPATOLOGY 1996;24:1517-1529.) often far outside the physiological range.
Several factors make it difficult to develop clinical applications of the classical antisense model presented in Fig. 1.
PREAMBLE
First, conventional antisense nucleic acids are too large and Acting upon a suggestion from a reviewer, I am honored highly charged to readily pass into the nucleus and cytoplasm to dedicate this article to the memory of Dr. Harold Weinof cells. Second, they are complex molecules that interact traub, an innovator whose work paved the way for the develwith a wide variety of unintended cellular and microbial comopment of the antisense field. [1][2][3][4] Dr. Weintraub died on March ponents. Third, many of the tricks used to obtain specific 28, 1995. I first heard about him in 1972 from my best friend binding in vitro, such as raising the temperature, cannot be who was having a great time working with ''a very smart and used in living cells, making it difficult to design antisense incredibly nice post doc called Hal Weintraub.'' As the years approaches that discriminate between closely related RNAs. passed, Dr. Weintraub became widely admired for his in-Finally, in many diseases, continuous degradation of the tarsights into the regulation of gene expression, for his love of get RNA is needed to counteract transcription, which soon science, and for the goodwill he extended to his colleagues. I replenishes the supply of the undesirable RNA. Ingenious try to be guided by his example as I study pathogens that approaches have been developed to surmount these chalinfect the liver and as I investigate new ways to treat liver lenges. Consult reviews of both the successes and the issues diseases.
that remain to be resolved. [5][6][7][8][9][10][11][12][13][14] The results of early conventional antisense strategies have prompted a mixture of satisfaction, frustration, and amaze-Abbreviations: mRNA, messenger RNA; ODN, oligodeoxynucleotide; RNase H, ribo-ment. What is the current thinking about the state of antinuclease H; HBV, hepatitis B virus; HIV, human immunodeficiency virus; HCV, hepatitis sense therapy? ''Many people are worried that a lot of the C virus; dsRNA, double-stranded RNA; PKR, protein kinase activated by dsRNA; tRNA, positive effects reported are not just antisense but other nontransfer RNA, IRES, internal ribosome entry site.
antisense mechanisms as well,'' according to Dr. Cy Stein.