Identification of key factors and genes involved in breast cancer metastasis to the bone and development of scaffolds incorporating germanium nanowires for biological applications

Metastasis is the main cause of death for most cancer patients and approximately 70% of metastatic breast cancer patients develop bone metastasis. In spite of screening programs and improvement in therapeutic strategies, breast cancer is still one of the most common causes of death in Ireland. Our work has focussed on discovering essential growth factors and genes involved in progression of breast cancer to the bone and development of a novel biomaterial that incorporates bioactive germanium nanowires, which may prove beneficial in biological applications such as targeted drug delivery and tissue repair.

We hypothesized that the establishment and growth of cancer cells at distant sites is dependent on critical interactions between the tumour cells and the host microenvironment. To mimic physiological loading conditions, we mechanically stimulated the bone cells to release essential factors that may play a role in mediating metastasis. To investigate this mechanism, we cultured MCF-7 breast cancer cells with conditioned media derived from mechanically stimulated osteocyte bone cells to mimic physiological loading conditions in the bone microenvironment. Our results displayed significant increase in the proliferation and migration of breast cancer cells when they were maintained in media derived from mechanically stimulated bone cells in contrast to the static media. To further elucidate, essential cytokines and growth factors which may be driving these mechanisms, we harnessed the cytokine array comprising of ninety-seven different targets to obtain a list of dysregulated cytokines, when bone cells are mechanically stimulated. We selected CXCL1 and CXCL2 from our cytokine array results and further characterized their role in enhancing migration of breast cancer.

Subsequently, we used a clinical approach to establish a gene signature to identify breast cancer patients at high risk of developing bone metastasis so that an effective and timely treatment may prevent development of metastasis. To achieve our objective, we used the Chipster software to integrate and analyse data from publicly available gene expression repositories to study dysregulated genes in a wide range of patient population. Using this approach, we have been able to identify a set of ten dysregulated genes namely NAT1, TFF1, TFF3, AGR2, CYP2B6, IGHG1, SCUBE2, RARRES1, MSMB and ROPN1 in breast cancer patients that are highly likely to develop bone metastasis. To elucidate differential expression of these genes, we studied the expression pattern of these genes in an Irish patient study using the Chipster software. We further quantified gene expression and examined protein expression in a sub-set of genes in cell models to correlate and validate our results.

Nanotechnology has shown huge benefits in delivering effective and targeted treatments to breast cancer patients with minimal side effects. The development of germanium nanowires has shown promising results in promoting cell adhesion and proliferation with essential benefits over existing alternative products. Therefore, we developed a protocol by selecting appropriate parameters and technique to develop collagen scaffolds that incorporates these nanowires. We further characterized the physical properties of the newly synthesized material and confirmed that these scaffolds allowed adhesion and proliferation of bone cells with no toxic effects. This work has paved a way towards the application of germanium nanowires in diverse ranges of biomedical platforms such bone tisue engineering and targeted drug delivery.

In conclusion, we have identified essential growth factors and genes that play a crucial role in development of bone metastasis in breast cancer patients along with development of novel biomaterial incorporating germanium nanowires. This work may potentially help to identify breast cancer patients that are highly likely to develop bone metastasis and help in developing novel targets for treating breast cancer patients with bone metastasis.