BBC News today reported on research that “prevented breast cancer spreading to other organs in mice by blocking a chemical”. The researchers reportedly said that their findings provided "a ‘fantastic drug target’ and were ‘highly likely’ to be used in a clinical setting”.
These researchers analysed tumour cells from women with a type of breast cancer called oestrogen receptor negative (ER-) breast cancer. They found that the presence of higher amounts of a protein called LOXL2 was associated with a poorer prognosis.
In mice, the researchers lowered the amount of LOXL2 produced in cancer cells using either genetic engineering techniques or a chemical inhibitor. They found that this did not alter the rate at which the breast cancer tumour grew, but it did reduce the spread of the cancer to the liver and lungs.
This preliminary research was conducted in cell cultures and mice. This limits its direct relevance to humans at this stage. It has identified a potential target for treatment, however, and breast cancer charities have said that it shows “great promise”.
Where did the story come from?
The study was carried out by researchers from the Institute of Cancer Research. Funding was provided by the Institute of Cancer Research, the Breast Cancer Campaign and Cancer Research UK. The study was published in the peer-reviewed medical journal Cancer Research .
The Daily Express and BBC both reported that this was laboratory-based research in human cells and mice, but the Daily Mail did not mention this.
What kind of research was this?
The researchers were interested in proteins that may be involved in the spread of breast cancer to other parts of the body. They were particularly concerned with a protein called LOXL2, which belongs to a family of five similar proteins, all of which have been implicated in cancer progression. They said previous studies showed that human breast cancer cells that were likely to spread had high levels of LOXL2. Other studies found that samples from more advanced breast cancer tumours generally had higher levels of LOXL2.
This research was in oestrogen receptor negative tumours. There are different types of breast cancer. Some breast cancer tumour cells are positive for a receptor that is activated by oestrogen (ER+). Treatments for that type of cancer may involve preventing the action of oestrogen on this receptor (hormone therapy).
The researchers said their report is the first to have investigated the relationship between LOXL2 and metastasis (cancer spread) in breast cancer patients.
What did the research involve?
The researchers first investigated how levels of LOXL2 might be associated with cancer development. To do this, they compared the level of LOXL2 in tissue taken from 295 breast tumours with 13 normal breast tissue samples from women having breast reduction surgery and normal tissue from cancer patients. They identified those tumours that were oestrogen receptor negative (72) and measured the levels of LOXL2 in them.
The medical records of the women who had donated the tumour samples were also examined to look for an association between the amount of LOXL2 the tumour cells made and the severity of the cancer.
To investigate the role of LOXL2 in breast cancer metastasis, the researchers used two breast cancer cell lines. One of the cell lines was derived from human breast cancer cells and one from mouse tumours. The cell lines from both human and mouse cancer cells made high levels of LOXL2, and both were also oestrogen receptor negative. The researchers “knocked down” (inhibited) the activity of the LOXL2 gene in the cancer cell lines, reducing the amount of LOXL2 protein that was made. They then examined how this affected how the cancer cells divided (how cancer grows). In further experimentation, they also inhibited the activity of LOXL2 with a chemical called D-Penicillamine.
To assess the role of LOXL2 in the formation of tumours, the researchers injected live mice with either of the two breast cancer cell lines to induce the formation of tumours in the mice’s breast tissue. They also injected other mice with the genetically modified cell lines where LOXL2 was knocked down. When the tumours reached the maximum permitted size, the researchers looked at whether the cancer had spread to other parts of the mouse’s body. They also compared the degree of spread in mice that had been injected with tumour cell lines that produced high or low levels of LOXL2.
The researchers also used another mouse model of breast cancer, in which mice were genetically modified to produce breast tumours by five to six weeks of age and lung metastases by eight to nine weeks of age. They compared the outcome in mice given twice-weekly injections of D-penicillamine from four weeks of age with those left untreated.
What were the basic results?
The researchers found that women with oestrogen receptor negative tumours that made high levels of LOXL2 had a poorer prognosis than women whose tumours made low levels of LOXL2.
They found that knocking down LOXL2 had no effect on the rate at which the breast cancer cell lines divided. Tumours also grew at a similar rate in mice that had been injected with tumour cell lines that produced LOXL2 and those that had been knocked down. There was no difference in tumour size in mice who had received twice-weekly doses of the LOXL2 inhibitor D-penicillamine compared to those which had not. Based on these results, the researchers concluded that LOXL2 is not required for tumour growth.
However, the researchers found that mice injected with tumour cell lines that had LOXL2 knocked down or inhibited with D-penicillamine had fewer secondary lung or liver tumours than mice injected with cell lines that made high levels of LOX2L. They found that inhibiting LOX2L with an antibody that was targeted to bind to it reduced cancer spread in this mouse model.
When mice that were genetically modified to develop tumours were treated with D-penicillamine, their primary breast tumour grew at a similar rate to mice that had not received this treatment. However, they had fewer secondary lung tumours at 10 weeks. Delaying treatment with D-penicillamine until five weeks resulted in no difference in the number of secondary lung tumours in these mice. The researchers suggest this means that LOXL2 is required for the early stages of metastasis.
How did the researchers interpret the results?
The researchers say that LOXL2 is associated with the spread of cancer in patients with aggressive, oestrogen receptor negative breast cancer.
They suggest the amount of LOXL2 that a cell produces may predict which patients are most likely to develop a metastatic disease. They say their mouse models show that LOXL2 is not essential for primary tumour growth, but that it does affect the size and number of tumours formed in other areas. Given these results, they suggest that “LOXL2 inhibitors should be considered in the development of new therapies of metastatic breast cancer”.
The researchers presented experimental evidence that the LOXL2 protein may be involved in cancer spread in mouse models of breast cancer. It should be noted that this research was in oestrogen receptor negative tumours, so the results may not apply to other types of breast cancer. Further research is needed to see if LOXL2 plays a role in other breast cancer sub-types.
This was very preliminary research conducted in mice, which limits its direct relevance to humans at this stage. However, it has identified a potential target for treatment. Further research is warranted to assess the role of LOXL2 in human breast cancer and whether LOXL2 inhibitors could be safe to use and have any beneficial effect in humans.