Researchers have reported a discovery that they hope would lead to the development of a powerful new way of treating an aggressive form of breast cancer.

The breast cancer subtype in question is commonly called “HER2-positive”; it’s a subset of the disease affecting about one patient in four, in which tumor cells overexpress a signaling protein called HER2.

The blockbuster drug Herceptin is a treatment of choice for many women with HER2-positive breast cancer, but in most cases, resistance to the treatment develops within several years. The prognosis for HER2-positive breast cancer patients is worse than for those with other subtypes of the illness.

A multi-institution team led by CSHL Professor Nicholas Tonks reported that it has found a means of inhibiting another protein, called PTP1B, whose expression is also upregulated in HER2-positive breast cancer.
PTP1B has been shown to play a critical role in the development of tumors in which HER2 signaling is aberrant.

When they treated mice modeling HER2-positive breast cancer with a PTP1B inhibitor called MSI-1436 (also called trodusquemine), Tonks and colleagues inhibited signaling by HER2 proteins.

Dr. Tonks discovered PTP1B some 25 years ago. It is an enzyme – one in a “superfamily” of 105 called protein tyrosine phosphatases (PTPs) — that perform the essential biochemical task of removing phosphate groups from amino acids called tyrosines in other proteins. Adding and removing phosphate groups is one of the means by which signals are sent among proteins.

The new paper by Tonks and collaborators importantly reveals an alternative binding site, called an allosteric site, that does not present the biochemical difficulties that the active, or “catalytic,” binding site does. This allosteric site is a target of the candidate drug trodusquemine.

The paper has been published online in the journal Nature Chemical Biology

Source: Yahoo news