MARCH 2014 HighlightsPreventing cancer, or even reversing its earliest stages, would be hugely preferable to treating more advanced cases. Now, Dana-Farber researcher Michael Goldberg, PhD, has contributed to research that demonstrates one way this might work.
"Conventional wisdom holds that we must kill cancer cells in order to resolve cancer, but this may not be the case," says Goldberg, of Dana-Farber's Department of Cancer Immunology and AIDS, where his lab focuses on delivering molecular agents that decrease, or "knock down," the activity level of culprit gene in cancer cells.
A multidisciplinary collaboration
Goldberg was involved in a collaboration led by researchers at the Wyss Institute of Biologically Inspired Engineering at Harvard University. They used a gene-knockdown strategy to partially reverse an early non-invasive breast cancer called ductal carcinoma in situ (DCIS) in laboratory cells and to prevent breast cancer in cancer-prone mice. The results were published in Science Translational Medicine.
The Wyss Institute team asked Goldberg to devise a delivery system that could smuggle gene-silencing snippets called siRNAs (short interfering RNAs) into breast cells to turn off a gene that the researchers had pinpointed as a ringleader in DCIS growth. This tool, more broadly known as RNAi (RNA interference), is part of a natural biological system for reducing gene activity.
DCIS is marked by the presence of non-invasive cancer cells inside the milk ducts; the cells are not life-threatening until they escape the ducts and invade the breast and other tissues. About 25 percent of new breast cancer diagnoses in the United States are DCIS. It's estimated that around half of these cases will never become invasive breast cancer, but without any way to predict which ones will, many women opt for a lumpectomy or mastectomy and may receive radiation as well.
The Wyss Institute scientists, led by Donald Ingber, MD, PhD, founding director of the Wyss and a pathologist at Boston Children's Hospital, sought another way to manage this condition. What if it were possible to hunt through networks of genes to identify kingpins in breast cancer – abnormally active genes that order other genes to misbehave – and then block them with targeted molecular agents?
Ingber, working with Jim Collins, PhD, a Wyss core faculty member and professor at Boston University, and Hu Li, a postdoctoral fellow on Collins' team, used computers to search through complex networks of genes that act suspiciously just before milk-duct cells in the breast begin to overgrow.
From 100 initial candidates, they identified a prime suspect – a gene called HoxA1 – that had a strong statistical link to breast cancer but hadn't previously been tied to the disease. They also confirmed that the gene was overproduced in some human breast tumors.
When Amy Brock, PhD, a postdoctoral fellow on Ingber's team, treated cancerous mouse and human breast cells with siRNAs that muted the HoxA1 gene, the cells reversed their march to malignancy. They stopped their runaway growth, and formed hollow balls, as healthy cells do. What's more, they became specialized as if they were growing in healthy tissue.
Ingber and his colleagues wanted to test the preventive potential of siRNA in mice that were genetically susceptible to breast cancer. They faced a roadblock – the lack of a means to safely and effectively deliver siRNAs to the milk ducts of living animals, as siRNAs do not readily cross the cell membrane. So they turned to Goldberg.
A Trojan horse approach
At MIT, where he earned his doctorate, Goldberg had synthesized molecules called "lipidoids" and employed them as delivery vehicles for siRNA, like a molecular Trojan horse. For this study, he used that approach to construct lipidoids containing siRNA that targets HoxA1. The technique caused genes to be silenced for weeks inside the body.
The researchers then injected these siRNA-loaded nanoparticles directly through the nipples into the milk ducts of the cancer-prone mice, using a new method developed by Silva Krause, PhD, another postdoctoral fellow on Ingber's team. The treated mice remained healthy, while untreated mice developed breast cancer.
"Through a tremendous multidisciplinary collaboration, our team successfully prevented the development of breast cancer in mice that are genetically predisposed to develop the disease," says Goldberg. Although taking this concept to the clinic is years away, the researchers suggest that it might be possible to administer the siRNAs to the breasts of women who are considered to be at high risk for breast cancer as a strategy for keeping breast cancer from getting started in the first place by converting DCIS into healthy tissue.