I read that solid tumours are unable to grow beyond a certain size because of hypoxia, which means "insufficient oxygen." What happens is that, as tumours grow, they need more and more nutrients and oxygen. At a certain point, though. the tumour microenvironment just can’t deal with this constant demand (if I got that right…) and becomes hypoxic. Under hypoxic conditions (less than 6% oxygen, I read), HIF-1 alpha, a transcription factor, becomes activated, and it in turn activates genes, dozens of them!, that keep tumours alive and well, via angiogenesis, glucose transport and whatnot. So tumour progression goes hand in hand with the increased activity of HIF-1 alpha.
Back to the Italian study on caffeine (see abstract): “Pretreatment of cells with caffeine significantly reduces adenosine-induced VEGF promoter activity and VEGF and IL-8 expression.” (Wait…adenosine? Uffa, another thing to look up…) Here we go: simply put, adenosine is a natural chemical, a neurotransmitter, released by brain cells to make us sleepy. The more we stay awake, the more adenosine gets released. But I should point out that adenosine is present also in all cells of the body, and, aha!, has the function of protecting cells from damage under conditions of hypoxia. And it protects solid tumours from the attacks of NK cells and T-lymphocytes, as can be seen in this abstract (“International Journal of Oncology,” March 2008): http://tinyurl.com/yu7o72. It seems to be involved in a lot of mischief! Well, ok, not all the time!, for instance it mediates the damage caused by strokes…
Enough. You can read more about the importance of adenosine on the Grouppe Kurosawa public blog (February 29 post): http://tinyurl.com/23fbgo. The main thing we need to know is that, when adenosine is released, HIF-1 alpha and VEGF, the very best friends of cancer cells, are activated.
- Hypoxic tumour cells are resistant to chemotherapy and radiotherapy. Eh!
- Hypoxia stimulates IL-8, which is involved with cancer progression (including myeloma progression, as we know from a previous post).
- HIF-1 “contributes to tumor progression and metastasis.”