Bladder cancer is an insidious foe. About 70 percent of the time the condition is diagnosed while still confined to the bladder lining (in these cases, it's known as a "carcinoma in situ," or CIS). However, a subset of these localized cancers will go on to invade tissue surrounding the bladder and become much more deadly.
Now, developmental biologist Philip Beachy, PhD, a Howard Hughes Medical Institute investigator, and his colleagues have found that low doses of a drug called FK506 currently used to prevent the rejection of transplanted organs can prevent the progression of CIS into invasive bladder cancer in mice. Beachy collaborated with collaborated with urologist Joseph Liao, MD, and pulmonary specialist Edda Spiekerkoetter, MD, to conduct the research, which was published today in Cancer Cell. As Beachy explains in our release:
This could be a boon to the management of bladder cancer patients. Bladder cancer is the most expensive cancer to treat per patient because most patients require continual monitoring. The effective prevention of progression to invasive carcinoma would be a major advance in the treatment of this disease.
Beachy and Liao are members of the Stanford Cancer Institute. Together they're hoping to initiate clinical trials of FK506 in people with CIS to learn whether the drug can also prevent progression to invasive cancer in humans.
The findings of the current study build upon previous research into the disease in Beachy's laboratory and a long-time interest by Beachy in a molecular signaling pathway governed by a protein called sonic hedgehog. Beachy identified the first hedgehog protein in 1992; the protein (and the hedgehog pathway) have since been shown to play a vital role in embryonic developments and many types of cancers. Sonic hedgehog, Beachy has found, is produced by specialized stem cells in the bladder as a way to communicate with neighboring cells. They learned it's required for the formation of CIS, but that it must also be lost in order for the cancer cells to invade other tissues. As Beachy explained in our release:
This was a very provocative finding. It was clear that these [sonic-hedgehog-expressing] bladder stem cells were the source of the intermediate cancers, or carcinomas in situ, that remain confined to the bladder lining. However, it was equally clear that sonic hedgehog expression must then be lost in order for those cancer cells to be able to invade surrounding tissue. We wondered whether the loss of this expression leads to increased tumor cell growth.
The researchers found that sonic hedgehog expression works in a loop with another class of proteins called BMPs. (You can read more about this in our release.) FK506 works by activating the BMP portion of the pathway in the absence of sonic hedgehog. Ten out of ten mice with CIS who received a low dose of the drug (low enough not to cause immunosuppression) were protected from developing invasive bladder cancer after five months of exposure to the carcinogen. In contrast, seven of nine mice receiving a placebo did develop the invasive form of the disease within the same time period.
The finding is particularly important because the opposite has been shown to be true in many other types of solid cancers, including basal cell carcinoma and medulloblastoma,, which have been shown to respond well to compounds that block the sonic hedgehog signaling pathway. However, clinical trials of these pathway blocking compounds in pancreatic, colon or ovarian cancers have either shown no benefit, or been terminated early when accelerated cancer growth was observed.
Bladder cancer has one of the highest recurrence rates of all cancers and poses many challenges in its clinical management. These insights into the molecular mechanism of cancer progression in this clinically relevant animal model are truly exciting. As a urologist who cares for many bladder cancer patients, I feel the possibility of using an approved drug to curtail progression of early stage cancer to muscle-invasive disease, which typically requires complete removal of the bladder, could be a potential game changer.
Previously: Bladder infections -- How does your body repair the damage?, Cellular culprit identified for invasive bladder cancer, according to Stanford study, and Mathematical technique used to identify bladder cancer marker