An antibody blocked one route aggressive prostate cancer uses to spread

A receptor at the cell surface is meant to relay signals inward. In aggressive prostate cancer cells, however, a piece of that receptor can be cut free, enter the nucleus and push the tumour toward a more mobile, invasive state.

Researchers have developed an antibody that shields the receptor from this cut. In cell experiments and mouse models, the targeted intervention suppressed tumour growth and metastasis without shutting down the receptor’s normal signalling functions.

A useful pathway with a dangerous second role

Transforming growth factor beta, or TGF-β, helps regulate tissue repair, immune activity and normal cell behaviour. It transmits its signals through a membrane receptor called TβRI.

In advanced cancer, the same pathway can be repurposed. An enzyme called ADAM17 cuts the receptor, releasing an intracellular fragment that travels into the nucleus. There it interacts with proteins that regulate gene activity and promotes epithelial-to-mesenchymal transition, a cellular programme that makes tumour cells less tightly connected and more capable of invading surrounding tissue.

Blocking all TGF-β signalling has proved difficult because the pathway also supports healthy functions in the heart, blood vessels, immune system and other tissues. The researchers therefore targeted the abnormal receptor-cleavage step rather than disabling the entire pathway.

An antibody that acts as a protective shield

The team first mapped the site on TβRI that ADAM17 cuts. They then developed a fully human monoclonal antibody, mAbF11, that binds near this site and physically obstructs the enzyme.

In castration-resistant prostate cancer cells, mAbF11 reduced production of the receptor fragment and prevented its accumulation in the nucleus. It also lowered the activity of genes associated with invasive cell behaviour and reduced the cells’ ability to cross a laboratory barrier.

Crucially, the antibody did not block conventional TGF-β signalling through SMAD proteins. Preserving this physiological branch of the pathway is what distinguishes the strategy from compounds that broadly inhibit the receptor.

What happened in mice

For the main animal experiment, human aggressive prostate cancer cells were implanted directly into the prostates of immunodeficient mice. One week later, 72 animals were assigned to six groups receiving a control antibody, one of three mAbF11 doses, a vehicle control or the chemotherapy drug docetaxel.

Treatment was given twice weekly for four weeks. At doses of 10 and 30 milligrams per kilogram, mAbF11 significantly reduced primary tumour growth and metastatic involvement of regional lymph nodes. Treated tumours also contained less nuclear TβRI fragment and showed lower markers of proliferation and invasive cell identity.

A separate safety experiment involved 24 mice. After four weeks, the researchers detected no differences in ascending aortic diameter or measures of left-ventricular filling between the antibody and control groups. They also observed no notable loss of body weight. This was a limited preclinical safety assessment, not evidence that the antibody is safe in humans.

Docetaxel reduced tumour size as well, but its experiment had to be stopped after roughly two and a half weeks because 8 of the 16 treated mice developed severe weight loss. The study therefore does not provide a clean, equal-duration comparison between the antibody and chemotherapy.

The human evidence remains indirect

The team also analysed tumour-biopsy data from two independent cohorts of patients with metastatic castration-resistant prostate cancer: 158 patients in one dataset and 94 in the other. Higher TGFBR1 expression was associated with poorer survival, and TGFBR1 expression correlated with that of ADAM17.

Those findings support the relevance of the biological target, but none of the patients received mAbF11. The study cannot show whether the antibody slows disease, extends survival or is safe in people. Its therapeutic findings come from cell systems and immunodeficient mice, which cannot reveal the full effect of the treatment on the immune response.

The broader lesson is not simply that another powerful signalling pathway might be blocked. By identifying the precise point at which a normal receptor acquires a tumour-promoting function, the researchers found a way to interfere with the harmful branch while leaving much of the useful biology intact.