BJA/RCoA International Collaborative Grants

The hypothesis that the anaesthetic and/or pain relief technique given during cancer surgery might influence whether cancer recurs or spreads (metastasis) was proposed by the international applicant 11 years ago, and has become a research priority for the specialty.

Experiments with isolated cancer cells in the laboratory suggest that local anaesthetics (which make you numb while still awake, example lidocaine), might stop cancer cells from spreading and might improve their sensitivity to chemotherapy. Propofol, commonly used general anaesthetic, might also resist cancer cell spreading properties. Steroids are known to modify the body's stress response to surgery under general anaesthesia and recent evidence in patients suggests this improves recovery, but steroid effects on cancer cell function in the context of cancer surgery are unknown. All this knowledge comes from isolated cell experiments in a laboratory setting. This model has obvious limitations when interpreting the findings for human cancer patients.

The next step is to obtain live animal (in vivo) data, essential to securing funding for the prospective, randomised controlled clinical trials (RCT), which is the ultimate tool to deliver definitive evidence on this question. The main applicant has just completed a series of experiments on mice which indicate that lidocaine resists cancer spread when given with one type of general anaesthetic but not with another.

We propose a collaborative, two-centre programme simultaneously delivering:

• A series of experiments on live rodents will be carried out to evaluate the effect of perioperative lidocaine, propofol and steroids with and without chemotherapy on breast cancer metastasis using a mouse model of breast cancer.
  
• We will test blood from the above experimental subjects for chemicals which signal inflammation and which are known to be linked to switching on and switching off metastasis processes in cancer cells.
  
• A joint of clinical-laboratory study: Ongoing RCT NCT00418457 is randomising patients to receive either of two distinct anaesthetic-pain relief techniques for breast cancer surgery. Forty consented patients have donated 10 ml venous blood before and 24 hr after surgery and a sample of their excised breast cancer tissue. We will take this patient material back to Dr. Ma's laboratory and test it for how much expression of genetic signals for cancer spread it shows, and whether the difference in anaesthetic technique the patients received makes any difference to these genetic signals.

Introduction of general anaesthesia over 170 years ago allowed patients to endure painful surgical procedures, and physicians are now able to perform longer and more complex procedures. Anaesthetics are thus indispensable to modern medicine. Clinical endpoints of anaesthesia include reversible loss of consciousness, amnesia and immobility. Despite their widespread clinical use, little is known about how they work. They are believed to alter function of specific proteins located in the cell membrane of neurones. These proteins include ion channels, which conduct ions across the membrane and are crucial for cell-to-cell communication by initiating and transmitting electrical signals. Modern inhaled anaesthetics, based on the original anaesthetic ether, interact with voltage-gated sodium ion channels by reducing the amount of sodium ions passing through the channel, thus reducing overall neuronal electrical excitability. How these anaesthetics interact with sodium channels is not known, and more detailed information regarding potential binding sites for anaesthetics on sodium channels should have a significant impact on the development of more specific anaesthetics with fewer undesirable effects. This would improve patient safety by increasing the specificity of general anaesthetics, which have a number of undesirable side effects (such as cardiovascular and respiratory depression) due to their effects on targets not critical to the state of anaesthesia.

We propose to address the question of how general anaesthetics inhibit sodium channels through synergistic structural and functional approaches using state-of-the-art molecular biophysical and electrophysiological techniques perfected in our respective laboratories through a developing collaboration. We will use the bacterial sodium channel NavMs as a model, which is an evolutionarily related ion channel that is simpler than the more complex mammalian forms. It provides a validated model for studying sodium channel structure, physiology and pharmacology.

The structural approach will use circular dichroism (CD) spectroscopy for studying protein movements, structure, folding and drug interactions. We will perform CD spectroscopy on the full-length bacterial sodium channel NavMs in the absence or presence of the modern inhaled anaesthetics desflurane and sevoflurane to identify potential drug binding sites.

The functional approach involves expression of NavMs in mammalian cells, from which sodium currents will be recorded in the absence or presence of the anaesthetics using single cell electrophysiology through glass microelectrodes. This 'patch-clamp electrophysiology' technique will allow us to examine the function of NavMs to determine channel opening and closing. In addition to expressing wild-type NavMs, we will examine the effects of various point mutations (single amino acid changes in the protein) at critical sites involved in channel opening and closing, and at putative anaesthetic binding sites identified by CD spectroscopy for example.

Use of this combined structural and functional approach will allow us to identify sites at which anaesthetics interact with NavMs. These findings will then be translated into our studies of mammalian sodium channels.