Liposomal siRNA — Genetic On/Off Switches That Target Ovarian Cancer Through the Trojan Horse Effect

Use of Liposomal siRNA to Target Ovarian Cancer Protein Known as “Interleukin-8 (IL-8)”

“A protein that stimulates blood vessel growth worsens ovarian cancer, but its production can be stifled by a tiny bit of RNA wrapped in a fatty nanoparticle, a research team led by scientists at The University of Texas M. D. Anderson Cancer Center reports in the Journal of the National Cancer Institute.

The protein IL-8 is a potential therapeutic target in ovarian cancer,’ said senior author Anil Sood, M.D., professor in the M. D. Anderson Departments of Gynecologic Oncology and Cancer Biology.

The paper demonstrates that high IL-8 expression in tumors is associated with advanced tumor stage and earlier death for ovarian cancer patients. Lab experiments and research in a mouse model show that short interfering RNA (siRNA) can cut IL-8 expression, reducing tumor size by attacking its blood supply.

‘This comprehensive analysis – with human data, animal data and lab experiments to highlight the molecular mechanisms involved – helps us develop the new targets needed for a more effective approach against ovarian cancer,’ Sood said.

Interleukin-8 is overexpressed in many types of cancer and has previously been shown to promote tumor growth, new blood vessel growth known as angiogenesis, and metastasis, the spread of cancer to other organs. ‘In the long run, this research will have applications in other cancers as well,’ Sood said.

His research focuses on ovarian cancer, for example, while senior co-author Menashe Bar-Eli, Ph.D., professor in M. D. Anderson’s Department of Cancer Biology, examines IL-8’s role in melanoma.

Impact on survival

Ovarian cancer is often detected in late stages. Initial treatment includes surgery and taxane- or platinum-based chemotherapy regimens that keep the cancer at bay for a time in most patients. Recurrence is common and often lethal.

To examine IL-8’s role in ovarian cancer, the researchers analyzed tumors from 102 patients diagnosed and treated between 1988 and 2006 at M. D. Anderson and the University of Iowa. Of those, 43 had tumors with high levels of IL-8 and 59 had low levels. The median survival of those with high IL-8 tumors was 1.62 years, compared with 3.79 years for those with low expression of the protein.

All 43 tumors with high expression of IL-8 were of high grade and 42 of 43 were advanced, either stage III or IV tumors. By comparison, 10 of 59 tumors with low IL-8 expression were early stage tumors and six were of low grade.

Shrinking tumors

Genes transcribe single strands of RNA that in turn are ‘read’ by ribosomes to produce proteins. siRNAs are short, double-stranded bits of RNA capable of halting that process. The team confirmed in a lab experiment that a specific siRNA silences IL-8 and then tested it against two lines of ovarian cancer in a mouse model.

Sood, Gabriel Lopez-Berestein, M.D., professor in M. D. Anderson’s Department of Experimental Therapeutics, and colleagues are building an arsenal of siRNAs capable of silencing genes that produce cancer-promoting proteins. They packaged siRNA that stymies IL-8 into a small ball of fat known as a liposome, a combination they developed to overcome a problem – siRNA is hard to deliver to tumors.

Tumors shrank by a median of 32 percent and 52 percent in the two cancer lines among mice that received injections of the IL-8 siRNA liposome compared to those receiving control siRNA or empty liposomes.

Mice that got both the IL-8 siRNA plus the taxane-based chemotherapy drug docetaxel [Taxotere®] had median tumor weight reduction of 90 percent and 98 percent in the two cell lines. Mice with control siRNA plus docetaxel saw reductions of 67 and 84 percent.

Finally, they tested the approach in mice with an ovarian cancer cell line known to be resistant to taxane-based drugs such as docetaxel. IL-8 siRNA alone reduced the size of these tumors by 47 percent, and when combined with docetaxel reduced tumor size by 77 percent, suggesting that the combination re-sensitizes a resistant tumor to taxanes.

The team gauged the impact of IL-8 siRNA on tumor blood supply by measuring the density of blood vessels in the tumor. The IL-8 siRNA alone reduced blood vessel density by 34 percent and 39 percent in two cancer lines.

Clinical Prospects

‘These are encouraging results. We want to move one of our siRNA agents into the clinic to test its potential for therapy,’ Sood said, ‘and then in the longer term, we’ll consider moving additional siRNA agents into the clinical arena.’

The IL-8 siRNA liposome is the third developed by Sood’s and Lopez-Berestein’s team. Two others target the oncoproteins FAK and EphA2. The EphA2 siRNA liposome is closest to Phase I clinical trial, with required toxicology studies nearly complete. A clinical trial could begin within a year.

Methods used to inject siRNA in high volumes for research purposes are impractical for human therapy. Sood and Lopez-Berestein developed the liposomal approach to ensure that the siRNA reaches the cell intact so it can silence the targeted gene. Their research has shown that the liposome penetrates deeply into cells to deliver its siRNA.

Research reported in JNCI was funded by grants from the National Cancer Institute of the National Institutes of Health, including M. D. Anderson’s Specialized Program of Research Excellence in Ovarian Cancer; the Ovarian Cancer Research Fund, Inc.; and the Zarrow Foundation.”

Quoted Source: [“Researchers Identify and Shut Down Protein that Fuels Ovarian Cancer, M. D. Anderson-led team pinpoints blood vessel promoter’s role and targets it with siRNA,” M.D Anderson News Release, dated February 26, 2008]. See also “Effect of Interleukin-8 Gene Silencing With Liposome-Encapsulated Small Interfering RNA on Ovarian Cancer Cell Growth;” Merritt,W.M., Lin,Y.G., Spannuth,W.A., Fletcher,M.S., Kamat,A.A., Han,L.Y., Landen,C.N., Jennings,M., Geest,K., Langley,R.R., Villares,G., Sanguino,A., Lutgendorf,S.K., Lopez-Berestein,G., Bar-Eli,M.M., Sood, A.K.; Journal of the National Cancer Institute 2008 100(5):359-372.

Use of Liposomal siRNA to Target Ovarian Cancer Protein Known as “Focal-Adhesion Kinase (FAK)”

Recent work reported in October 2006 by Dr. Anil Sood at M.D. Anderson involved the use of a targeted “siRNAliposome in mice to identify and correct defective ovarian cancer cells. M. D. Anderson researchers used siRNA (which acts as a genetic “on/off” switch) to target an ovarian cancer protein known as focal-adhesion kinase (FAK), which is present in all ovarian cancer cells. FAK helps ovarian cancer cells survive and spread. The siRNA was rolled into a liposome – a ball of fat so small that its dimensions are measured in nanometers (billionths of a meter). Because of their tiny size, these liposomes have no problem traveling through the blood supply into cells that make up tumors through the so-called “Trojan Horse” effect. To test how well it worked, mice that were implanted with human ovarian tumors were given injections of the therapy for three to five weeks. The mice ovarian tumors experienced a 44% to 72% reduction in weight. Adding chemotherapy to the treatment boosted tumor weight reduction to the 94% to 98% range. The next step for the FAK siRNA liposome is testing for toxicity prior to studies in human patients.

Source: [ “Novel Therapy Shrinks Ovarian Tumors in Mice, Genetic Fragments Turn Off Cancer Growth Switch,” Cancer Newsline, October 2006, M.D. Anderson Cancer Center, University of Texas.]

Use of Liposomal siRNA to Target the Ovarian Cancer Kinase Known as “EphA2”

In an earlier in vitro studies, Anil Sood, M.D. et. al. demonstrated that when EphA2-targeting siRNA was combined with paclitaxel [Taxol®], tumor growth was dramatically reduced compared with treatment with paclitaxel and a nonsilencing siRNA. These studies show the feasibility of siRNA as a clinically applicable therapeutic modality.

Source: [“Therapeutic EphA2 Gene Targeting In vivo Using Neutral Liposomal Small Interfering RNA Delivery;” Landen,C.N., Chavez-Reyes, A., Bucana, C., Schmandt, R., T. Deavers, M., Lopez-Berestein, G. and Sood, A.K., The University of Texas M.D. Anderson Cancer Center, Houston, Texas; Cancer Research 65, 6910-6918, August 1, 2005.

Comment: The ultimate use of siRNA to treat ovarian cancer in humans holds future promise. Ovarian cancer survivors should monitor the development of this liposomal siRNA form of treatment because its use in human clinical trials could occur in the near future, assuming that pre-clinical trial toxicity tests demonstrate safety. Anil Sood, M.D. has developed the liposomal siRNA for IL-8, FAK, and EphA2. It is reported that human clinical trials with respect to the EphA2 siRNA treatment will begin within 12 months.

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