The cell membrane and cell signals: new targets for novel anticancer drugs.

In the concluding Discussion session, emphasis focussed on the potential for interfering selectively with cell membranes and cell signalling in tumour as against normal tissues. There could be no doubt that tremendous advances are being made in our understanding of the molecular changes associated with malignancy and that the information available for the rational design of inhibitors of particular signalling pathways is increasingly sophisticated. There was a consensus that we need more information on the qualitative and quantitative differences in the structure and function of membranes and the signalling machinery in various normal tissues as compared to their cancerous counterparts. Ideally we will develop drug against, for example, specific forms of, let us say, protein kinase C or tyrosine kinase which are found to be predominantly active in neoplastic cells. This may well prove possible, at least in some instances, in which case a safe therapeutic margin will be assured. But differences may in other situations turn out to be in the level of expression rather than purely qualitative in nature, and the scale of the disparate expression may not always be great. Even in such situations, adequate therapeutic selectivity may still be achieved. This may derive from a "damping down" of signalling in the hyperactive tumour. Although there are legitimate concerns regarding the possible toxic effects of administering signal-wrecking molecules in man, we should not be pessimistic as there are clear precedents elsewhere in medicine for drugs acting on membrane signals proving to be safe and effective against expectation informed by hindsight. There may also be concerns about new forms of drug resistance. But this will be so for any new agent or novel target. And with mechanism of action clearly to the fore we should be able to predict resistance pathways in advance and devise appropriate circumvention strategies or targeted second line therapies. There was a palpable buzz at the meeting that this is a valid, different and above all rational approach. Not only that, but the new therapeutic molecules which we discover will themselves prove to be valuable tools with which to probe further into the mechanisms of malignancy and signal transduction. We had expected to see a bewildering amount of new information from the basic sciences of molecularbiology and cell physiology, and we got it. But it was also impressive to witness the number of new compounds coming through which look like real drugs or at least exciting lead compounds. The membrane-active ether lipids are in clinical trial. Bryostatin 1 will shortly join them.(ABSTRACT TRUNCATED AT 400 WORDS)