Membrane targets in cancer chemotherapy

Effects of 4-alkylmorpholine N-oxides on ATP-producing processes in Ehrlich ascites and L1210 leukaemia cells

The main purpose of the present investigation was to study the effect of the homologous series of 4-alkylmorpholine N-oxides on ATP-producing processes in Ehrlich ascites and L1210 murine leukaemia cells. The effects on aerobic glucose consumption, lactic acid formation, content of total (T-SH) and non-protein thiol groups (NP-SH), endogenous and exogenous respiration and the level of ATP in tumour cells incubated in vitro were investigated. 4-Dodecylmorpholine N-oxide (DMNO), one of the most active compounds, decreased the level of ATP immediately after addition to the suspension of Ehrlich cells in an ice bath. After 2 h incubation at 37 degrees C the drop in the ATP level was much lower. A possible explanation for the decrease in the ATP level might be interaction of the amine oxide with the cell membrane.

Cytoxicity of 1-alkylperhydroazepine N-oxides and quantitative structure-activity relationships

A new class of nonaromatic amine oxides was tested for cytotoxic activity. The main aim of the present investigation was to screen a series of 1-alkylperhydroazepine N-oxides for in vitro cytotoxicity and to find out whether there is a quantitative structure-activity correlation (QSAR) between cytotoxic effect and structure (as a structural parameter the number of carbon atoms m in the alkyl chain was used). Cytotoxicity was determined here by inhibition of incorporation of [14C]adenine into nucleic acid or [14C]valine into proteins in Ehrlich ascites carcinoma (EAC) cells. On the basis of primary screening, one of the most active compounds, namely 1-tetradecylperhydroazepine N-oxide (TPNO), was chosen for further biochemical study. The drug inhibited the incorporation rate of [14C] labeled precursors (adenine, thymidine, uridine, valine) into appropriate macromolecules of Ehrlich cells. The extent of inhibition was dependent on both time and drug concentration. The lengthening of the alkyl chain in 1-alkylperhydroazepine N-oxides positively affected their cytotoxic activity in EAC cells. For these compounds the optimal m value is 12-14.

Increases in leucocyte and platelet counts induced by the alkyl phospholipid hexadecylphosphocholine

Hexadecylphosphocholine (HePC) is a new alkyl phospholipid that has been shown to have antitumour activity in vitro and in vivo. In vivo studies have shown absence of bone marrow toxicity at therapeutic doses. In addition, at the highest dosage group in rats, an increase in white blood cell counts (WBC) was observed. To study the presence of a similar phenomenon in man, frequent measurements of haematological parameters were performed in a series of phase II studies. 70 patients were treated with daily doses of 100-200 mg of the oral formulation of HePC. WBC and platelet counts were performed weekly. In a subgroup of 23 patients serum levels of haemopoietic growth factors were measured before and during treatment. A significant increase in WBC and platelet counts was seen in 74 and 73% of the patients, respectively. In 4 patients, bone marrow showed normal cellularity, and in 1 patient, bone marrow culture showed normal numbers and sizes of colony forming units. No abnormal levels or trends over time of cytokines were observed. We conclude that oral HePC induces an increase in WBC and platelet counts in the majority of those treated.

Biochemical basis of cytotoxic activity of some new N'-oxides of N',N'-dimethylaminoalkylamides of dodecanoic acid

The objective of the present investigation was to screen a series of new N'-oxides of N',N'-dimethylaminoalkylamides of dodecanoic acid for activity in vitro and to investigate the biochemical mode of action. On the basis of primary screening, one of the most active compounds, namely the N'-oxide of 10-(N',N'-dimethylaminodecyl)amide of dodecanoic acid (n = 10) was chosen for detailed biochemical study. This compound inhibited the incorporation of 14C-precursors (adenine, valine, thymidine, uridine) into appropriate macromolecules of P388 murine leukemia and Ehrlich ascites carcinoma cells. The amine oxide also interfered with energy-yielding processes (aerobic glycolysis, endogenous respiration). Cytotoxicity is a consequence of the cytolytic activity of the compounds mentioned above. Membranous effects were demonstrated by the measuring of the release of cytoplasmic materials absorbing at 260 and 280 nm, marker enzyme activities (LDH, MDH), release of protein from the cells into the culture medium, as well as by morphological examination. It is evident that the site of action of the amine oxides investigated was the biological membrane which, after interaction with the amine oxides, showed changes in molecular organization and osmotic and permeability characteristics.

Relationships between the chemical structure and cytotoxicity of 4-alkylmorpholine N-oxides

The main objective of the present investigation was to screen a series of 4-alkylmorpholine N-oxides for in vitro cytotoxicity and to find out whether there is a quantitative structure-activity correlation (QSAR) between cytotoxic effect represented here by inhibition of incorporation of [14C]adenine into nucleic acid or [14C]valine into proteins in Ehrlich ascites carcinoma (EAC) cells and structure (as a structural parameter the number of carbon atoms m in the alkyl chain was used). On the basis of primary screening, one of the most active compounds, namely 4-dodecylmorpholine N-oxide, was chosen for further biochemical study. The drug inhibited the incorporation rate of [14C] precursors (adenine, thymidine, uridine, valine) into appropriate macromolecules of Ehrlich cells, the extent of inhibition being dependent on both time and concentration of the compound in the incubation medium. The lengthening of the alkyl chain in 4-alkyl-morpholine N-oxides positively affected their cytotoxic activity in Ehrlich cells. For these compounds the optimal m-value is 15-16.

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)