2011 UGA Conference on Drug Discovery: anti-HIV RNAs, enhanced DNA vaccines, and adenosine ligands
The real highlight of the 2011 UGA Conference on Drug Discovery (sponsored by the University of Georgia Center for Drug Discovery) was the food. After all the free soda, scones, biscuits, fried chicken and rice, strawberry shortcake, malt balls, and gummy worms, I feel a little sick to my stomach.
In addition to all the good food, there were some good talks, including “Small RNAs: their biology and therapeutic applications in HIV and cancer” by John Rossi, PhD, “Synthetic DNA vaccines for treatment or prophylaxis of difficult pathogens” by David Weiner, PhD, and “Drug discovery based on G protein-coupled receptors for extracellular nucleosides and nucleotides” by Kenneth Jacobson, PhD. These talks are summarized below.
Small RNAs: their biology and therapeutic applications in HIV and cancer
John Rossi’s group works on RNA-based therapies. For therapy of HIV, they have developed 3 different RNAs:
- nucleolar localizing TAR decoy (Michienzi et. al. 2002, 2006)
This therapeutic small RNA works by binding to Tat, an HIV protein that enhances HIV gene expression, thereby preventing Tat binding to the transactivation response (TAR) element in the HIV-1 LTR, and subsequent transcription from the HIV-1 LTR.
- chimeric VA1CCR5 ribozyme (Cagnon et. al. 2000)
This is a ribozyme that targets CCR5 mRNA, reducing expression of this HIV coreceptor.
- anti tat/rev shRNA (Lee et. al. 2002)
This siRNA targets tat/rev, which regulate HIV gene expression.
These RNAs were delivered to AIDS/lymphoma patients in combination, using a gene therapy approach – a lentiviral vector encoding the RNAs was transduced into patient CD34+ cells, which were then re-introduced to the patient (DiGuisto et. al. 2010). Expression of these RNAs has been observed for up to 2 years in treated individuals, demonstrating the feasibility of this approach (DiGuisto et. al.). This is not the only study suggesting that gene therapy could work as a functional cure for HIV. In a 2009 study, Hutter et. al. were able to cure an HIV patient by transplanting stem cells from a CCR5 delta32 homozygous individual into this patient (Hutter et. al. 2009). Currently, Rossi aims to further optimize delivery of anti-HIV RNAs such that they will better control HIV replication, will only need to be delivered once (at a cost of $100,000), and will possibly replace HAART ($20,000/yr) one day.
This group has also tried aptamers (“in vitro evolved nucleic acids that bind to selected ligands”) as a means of delivering anti-HIV siRNAs. Aptamer-based delivery of anti-HIV siRNAs was tested in RAG-hu mice, was nontoxic, and resulted in decreased HIV replication (Neff et. al. 2011).
Synthetic DNA vaccines for treatment or prophylaxis of difficult pathogens
David Weiner, one of the founding fathers of DNA vaccines, started his talk by discussing the importance of vaccines in general, showing a life expectancy graph from 1200-2000 AD, with a major increase around 1800-1900 as a result of antibiotics and vaccination (Fig. 1, Akbar et. al. 2004).
DNA vaccine work started around 1992 with multiple mouse studies. To quote Weiner (slightly paraphrased), “DNA vaccines have eliminated all mouse diseases. We could start a mouse hospital and set it up next to the roach motel.” Unfortunately, DNA vaccines have not yet done this for human diseases due to an initial lack of immune potency in humans. A data slide from Merck shows that early DNA vaccines were not very potent compared to other vaccine vectors, especially Ad5.
I say an initial lack of immune potency, because Weiner has continued working to optimize the immune potency of DNA vaccines in humans. His enhanced DNA vaccines have done the following:
- increased the amount of antigen produced per cell
- increased the number of cells transfected in vivo
- increased the response to antigens delivered by use of IL-12 as an adjuvant
Now, data from a more recent trial shows that enhanced DNA vaccines are able to perform better than Ad5.
For a review of DNA vaccines, see Kutzler and Weiner (2008). DNA Vaccines: Ready for Prime Time? Nature Reviews Genetics Vol.9:1-13.
Drug discovery based on G protein-coupled receptors for extracellular nucleosides and nucleotides
Adenosine is a neuromodulator. As such, adenosine receptor agonists and antagonists are desired for treating various diseases, especially inflammatory conditions (see Jacobson et. al. for a review). Interestingly, adenosine A3 receptor (A3AR) is highly expressed on inflammatory cells (e.g. PBMN cells), and A3AR agonists are in clinical trials for several inflammatory diseases, including rheumatoid arthritis, psoriasis, and Crohn’s disease.
Jacobson went into structure-based drug discovery at length as it relates to adenosine receptors. However, this portion of the talk was over my head.
Michienzi, A. (2002). A nucleolar TAR decoy inhibitor of HIV-1 replication Proceedings of the National Academy of Sciences, 99 (22), 14047-14052 DOI: 10.1073/pnas.212229599
Michienzi A, De Angelis FG, Bozzoni I, & Rossi JJ (2006). A nucleolar localizing Rev binding element inhibits HIV replication. AIDS research and therapy, 3 PMID: 16712721
Cagnon L, & Rossi JJ (2000). Downregulation of the CCR5 beta-chemokine receptor and inhibition of HIV-1 infection by stable VA1-ribozyme chimeric transcripts. Antisense & nucleic acid drug development, 10 (4), 251-61 PMID: 10984119
Lee NS, Dohjima T, Bauer G, Li H, Li MJ, Ehsani A, Salvaterra P, & Rossi J (2002). Expression of small interfering RNAs targeted against HIV-1 rev transcripts in human cells. Nature biotechnology, 20 (5), 500-5 PMID: 11981565
DiGiusto, D., Krishnan, A., Li, L., Li, H., Li, S., Rao, A., Mi, S., Yam, P., Stinson, S., Kalos, M., Alvarnas, J., Lacey, S., Yee, J., Li, M., Couture, L., Hsu, D., Forman, S., Rossi, J., & Zaia, J. (2010). RNA-Based Gene Therapy for HIV with Lentiviral Vector-Modified CD34+ Cells in Patients Undergoing Transplantation for AIDS-Related Lymphoma Science Translational Medicine, 2 (36), 36-36 DOI: 10.1126/scitranslmed.3000931
Hütter G, Nowak D, Mossner M, Ganepola S, Müssig A, Allers K, Schneider T, Hofmann J, Kücherer C, Blau O, Blau IW, Hofmann WK, & Thiel E (2009). Long-term control of HIV by CCR5 Delta32/Delta32 stem-cell transplantation. The New England journal of medicine, 360 (7), 692-8 PMID: 19213682
Neff CP, Zhou J, Remling L, Kuruvilla J, Zhang J, Li H, Smith DD, Swiderski P, Rossi JJ, & Akkina R (2011). An aptamer-siRNA chimera suppresses HIV-1 viral loads and protects from helper CD4(+) T cell decline in humanized mice. Science translational medicine, 3 (66) PMID: 21248316
Akbar AN, Beverley PC, & Salmon M (2004). Will telomere erosion lead to a loss of T-cell memory? Nature reviews. Immunology, 4 (9), 737-43 PMID: 15343372
Kutzler MA, & Weiner DB (2008). DNA vaccines: ready for prime time? Nature reviews. Genetics, 9 (10), 776-88 PMID: 18781156
Jacobson, K., & Gao, Z. (2006). Adenosine receptors as therapeutic targets Nature Reviews Drug Discovery, 5 (3), 247-264 DOI: 10.1038/nrd1983