Vitamin D could help fight deadly breast cancer

How BRCA1-mutated cells are able to form tumors has been a long-standing question. Investigators recently showed that loss of another DNA repair factor, 53BP1, allows proliferation and survival of BRCA1-deficient cells. In addition, decreased levels of 53BP1 were observed in triple-negative breast cancers, and correlated with resistance to drugs at the forefront of cancer treatment, such as PARP inhibitors.

Gonzalo’s team has found a pathway responsible for the loss of 53BP1 in breast cancers with poor prognosis, specifically BRCA1 mutated and triple-negative. It turns out that loss of BRCA1 increases the expression of a protease, known as cathepsin L (CTSL), which causes the degradation of 53BP1. Cells that have lost both BRCA1 and 53BP1 have the ability to repair DNA, maintain the integrity of the genome, and proliferate. Thus, the protease helps cells with faulty BRCA1 to survive.

If lowering the levels of 53BP1 allows BRCA1 deficient cells to thrive and do their worst, increasing the levels of the protein offers a promising strategy for treatment of breast tumors.

In previous research, Gonzalo’s team showed that vitamin D inhibits CTSL-mediated degradation of 53BP1 in non-tumor cells, as efficiently as specific CTSL inhibitors. This time, they found that treatment of BRCA1-deficient tumor cells with vitamin D restores high levels of 53BP1, which results in increased genomic instability and reduced proliferation.

Importantly, their evidence suggests that vitamin D treatment might restore the sensitivity to PARP inhibitors in patients who become resistant. Thus, a

... contd.