Trojan Horse* For Ovarian Cancer–Nanoparticles Turn Immune System Soldiers Against Tumor Cells

In a feat of trickery, Dartmouth Medical School immunologists have devised a Trojan horse to help overcome ovarian cancer, unleashing a surprise killer in the surroundings of a hard-to-treat tumor. Using nanoparticles–ultra small bits– the team has reprogrammed a protective cell that ovarian cancers have corrupted to feed their growth, turning the cells back from tumor friend to foe. Their research, published online July 13 for the August Journal of Clinical Investigation, offers a promising approach to orchestrate an attack against a cancer whose survival rates have barely budged over the last three decades …

Hanover, N.H.—In a feat of trickery, Dartmouth Medical School immunologists have devised a Trojan horse to help overcome ovarian cancer, unleashing a surprise killer in the surroundings of a hard-to-treat tumor.

Using nanoparticles–ultra small bits– the team has reprogrammed a protective cell that ovarian cancers have corrupted to feed their growth, turning the cells back from tumor friend to foe. Their research, published online July 13 for the August Journal of Clinical Investigation, offers a promising approach to orchestrate an attack against a cancer whose survival rates have barely budged over the last three decades.

Dr. Jose Conejo-Garcia (right) with graduate student Juan Cubillos-Ruiz  (Photo Source:  Dartmouth Medical School News Release,

Dr. Jose Conejo-Garcia (right) with graduate student Juan Cubillos-Ruiz (Photo Source: Dartmouth Medical School News Release, 13 Jul. 09)

“We have modulated elements of the tumor microenvironment that are not cancer cells, reversing their role as accomplices in tumor growth to attackers that boost responses against the tumor,” said Dr. Jose Conejo-Garcia, assistant professor of microbiology and immunology and of medicine, who led the research. “The cooperating cells hit by the particles return to fighters that immediately kill tumor cells.”

The study, in mice with established ovarian tumors, involves a polymer now in clinical trials for other tumors. The polymer interacts with a receptor that senses danger to activate cells that trigger an inflammatory immune response.

The Dartmouth work focuses on dendritic cells–an immune cell particularly abundant in the ovarian cancer environment. It does take direct aim at tumor cells, so it could be an amenable adjunct to other current therapies.

“The cooperating cells hit by the particles return to fighters that immediately kill tumor cells.” —Dr. Jose Conejo-Garcia

“That’s the beautiful part of story–people usually inject these nanoparticles to target tumor cells. But we found that these dendritic cells that are commonly present in ovarian cancer were preferentially and avidly engulfing the nanoparticles. We couldn’t find any tumor cells taking up the nanoparticles, only the dendritic cells residing in the tumor,” explained Juan R. Cubillos-Ruiz, graduate student and first author.

Dendritic cells are phagocytes–the soldiers of the immune system that gobble up bacteria and other pathogens, but ovarian cancer has co-opted them for its own use, he continued. “So we were trying to restore the attributes of these dendritic cells–the good guys; they become Trojan horses.”

Cancer is more than tumor cells; many other circulating cells including the dendritic phagocytes converge to occupy nearby space. The dendritic cells around ovarian cancer scoop up the nanocomplexes, composed of a polymer and small interfering RNA (siRNA) molecules to silence their immunosuppressive activity.

Nanoparticle incorporation transforms them from an immunosuppressive to an immunostimulatory cell type at tumor locations, provoking anti-tumor responses and also directly killing tumor cells. The effect is particularly striking with an siRNA designed to silence the gene responsible for making an immune protein called PD-L.

The new findings also raise a warning flag about the use of gene silencing complexes in cancer treatment. Inflammation is a helpful immune response, but the researchers urge caution when using compounds that can enhance inflammation in a patient already weakened by cancer.

Ovarian cancer, which claims an estimated 15,000 US lives a year, is an accessible disease for nanoparticle delivery, according to the investigators. Instead of systemic administration, complexes can be put directly into the peritoneal cavity where the phagocytes take them up.

Samples of human ovarian cancer cells show similar responses to nanoparticle stimulation, the researchers observed, suggesting feasibility in the clinical setting. It could be part of a “multimodal approach,” against ovarian cancer, said Conejo-Garcia also a member of the Dartmouth’s Norris Cotton Cancer Center. “The prevailing treatment is surgical debulking, followed by chemotherapy. Our findings could complement those because they target not the tumor cells themselves, but different cells present around the tumor.”

Co-authors are Xavier Engle, Uciane K. Scarlett, Diana Martinez, Amorette Barber, Raul Elgueta, Li Wang, Yolanda Nesbeth and Charles Sentman of Dartmouth; Yvon Durant of University of New Hampshire, Andrew T Gewirtz of Emory, and Ross Kedl of University of Colorado.

The work was supported by grants from the National Institutes of Health, including the National Cancer Institute and National Center for Research Resources, a Liz Tilberis Award from the Ovarian Cancer Research Fund, and the Norris Cotton Cancer Center Nanotechnology Group Award.

Read an interview of Jose Conejo – Garcia with the Ovarian Cancer Research Fund.

Source: Trojan Horse for Ovarian Cancer–Nanoparticles Turn Immune System Soldiers against Tumor Cells, News Release, Dartmouth Medical School, July 13, 2009 (summarizing Cubillos-Ruiz JR, Engle X, Scarlett UK, et. al. Polyethylenimine-based siRNA nanocomplexes reprogram tumor-associated dendritic cells via TLR5 to elicit therapeutic antitumor immunity. J Clin Invest. 2009 Aug 3;119(8):2231-2244. doi: 10.1172/JCI37716. Epub 2009 Jul 13).

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* The Trojan Horse was a tale from the Trojan War, as told in Virgil’s Latin epic poem The Aeneid. The events in this story from the Bronze Age took place after Homer’s Iliad, and before Homer’s Odyssey. It was the strategy that allowed the Greeks finally to enter the city of Troy and end the conflict. In the best-known version, after a fruitless 10-year siege of Troy, the Greeks built a huge horse figure and hid a select force of men within it. The Greeks left the Horse at the city gates of Troy and pretended to sail away.  Thereafter, the Trojans pulled the Horse into their city as a victory trophy. That night the Greek force crept out of the Horse and opened the gates for the returning Greek army, which had sailed back to Troy under cover of night. The Greek army entered and destroyed the city, decisively ending the war. A “Trojan Horse” has come to mean any trick that causes a target to invite a foe into a securely protected bastion or place.

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