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A series of stilbenes, based on combretastatin A-4, were synthesised. A structure-activity study was carried out to characterise the interaction of these agents with tubulin. The substitution of small alkyl substituents for the 4'-methoxy group of combretastatin A-4 and the loss of the 3'-hydroxyl group does not have a major effect on the interaction with tubulin. trans-Stilbenes were shown to bind tubulin, but do not inhibit microtubule assembly. This work, together with previous studies, has been used to propose an idealised structure for a tubulin-binding agent of this type.

A number of different alkylating chemotherapeutic agents--busulphan, dimethylbusulphan (DMB), isopropylmethane sulphonate (IMS), melphalan, cyclophosphamide (CY) and bischloroethylnitrosourea (BCNU)--were investigated for their cytotoxic effects on different haemopoietic cell populations in host mice and for their ability to induce short- and long-term engraftment of transplanted bone marrow. At 24 h after drug treatment the femoral content of transient and permanent repopulating stem cell subsets was assessed, respectively, from the frequency of early- (day 5-15) and late- (day 25-35) developing cobblestone area-forming cells (CAFCs), growing in vitro in long-term bone marrow cultures (LTBMCs). At this time a fixed complement of 10(7) congenically marked donor bone marrow cells (B6-Gpi-1a-->B6-Gpi-1b) was infused in the drug-treated mice and erythroid engraftment was followed over 36 weeks. Diverse effects on early- and late-developing CAFC frequencies were found for the different drugs; these were generally related to the pattern of donor bone marrow engraftment in treated recipients. Melphalan was more toxic to early-developing than to late-developing CAFC subsets, and the transplant only offered an early wave of blood chimerism followed by return of host cells. CY and BCNU had minimal to moderate effects on CAFC content and engraftment with no apparent preference for any particular haemopoietic cell subset. IMS also had a relatively low toxic effect on host marrow CAFC frequencies but appeared exceptional in its ability to allow for more donor-type engraftment. The dimethane sulphonate compounds busulphan and DMB were especially potent at depleting late CAFC subsets and ensured high and lasting levels of donor bone marrow engraftment. These studies support the value of CAFC measurements for predicting the fate and growth of transplanted bone marrow cells in recipients pretreated with a variety of cytotoxic agents.

Bryostatin 1 is a novel macrocyclic lactone activator of protein kinase C (PKC) which has clinical potential as an anti-cancer agent. The mechanism of action of this agent is unknown, but protein kinase C has been implicated. In order to investigate this possibility, we have developed P388 sublines resistant to bryostatin 1, by continuous challenge of the parent cell line with increasing incremental concentrations of the drug over 4 months. Cell lines were established at monthly intervals yielding four sublines: P388/BR/A, which were removed at 1 month; P388/BR/B, obtained after 2 months; P388/BR/C, obtained after 3 months; and P388/BR/D, which were established after 4 months. All four P388/BR sublines show an equal degree of resistance to the growth inhibitory effects of bryostatin 1, with a relative resistance ratio (RR) IC50 of approximately 4,000. The ability of the cytosol of cells to phosphorylate PKC-specific substrate is decreased by 41% for BR/A, 57% for BR/B 80% for BR/C and 94% for BR/D compared with the parental cell line, even when grown in the absence of bryostatin 1 for up to 4 weeks. Similar decreases are seen for cytosolic phorbol ester binding and whole-cell PKC isoenzyme expression. All four P388/BR sublines show high and equal levels of cross-resistance to the PKC activatory phorbol ester, phorbol 12-myristate 13-acetate (PMA). There is no loss of resistance to either bryostatin 1 or PMA up to 3 months after termination of exposure of the sublines to bryostatin 1. There was no significant degree of cross-resistance to daunorubicin in the bryosatin 1-resistant cell lines, P388/BR/A, B, C or D, when compared with the parent cell line, P388.

Bryostatin 1 is a novel antitumour agent derived from Bugula neritina of the marine phylum Ectoprocta. Nineteen patients with advanced solid tumours were entered into a phase I study to evaluate the toxicity and biological effects of bryostatin 1. Bryostatin 1 was given as a one hour intravenous infusion at the beginning of each 2 week treatment cycle. A maximum of three treatment cycles were given. Doses were escalated in steps from 5 to 65 micrograms m-2 in successive patient groups. The maximum tolerated dose was 50 micrograms m-2. Myalgia was the dose limiting toxicity and was of WHO grade 3 in all three patients treated at 65 micrograms m-2. Flu-like symptoms were common but were of maximum WHO grade 2. Hypotension, of maximum WHO grade 1, occurred in six patients treated at doses up to and including 20 micrograms m-2 and may not have been attributable to treatment with bryostatin 1. Cellulitis and thrombophlebitis occurred at the bryostatin 1 infusion site of patients treated at all dose levels up to 50 micrograms m-2, attributable to the 60% ethanol diluent in the bryostatin 1 infusion. Subsequent patients treated at 50 and 65 micrograms m-2 received treatment with an intravenous normal saline flush and they did not develop these complications. Significant decreases of the platelet count and total leucocyte, neutrophil and lymphocyte counts were seen in the first 24 h after treatment at the dose of 65 micrograms m-2. Immediate decreases in haemoglobin of up to 1.9g dl-1 were also noted in patients treated with 65 micrograms m-2, in the absence of clinical evidence of bleeding or haemodynamic compromise. No effect was observed on the incidence of haemopoietic progenitor cells in the marrow. Some patients' neutrophils demonstrated enhanced superoxide radical formation in response to in vitro stimulation with opsonised zymosan (a bacterial polysaccharide) but in the absence of this additional stimulus, no bryostatin 1 effect was observed. Lymphocyte natural killing activity was decreased 2 h after treatment with bryostatin 1, but the effect was not consistently seen 24 h or 7 days later. With the dose schedule examined no antitumour effects were observed. We recommend that bryostatin 1 is used at a dose of 35 to 50 micrograms m-2 two weekly in phase II studies in patients with malignancies including lymphoma, leukaemia, melanoma or hypernephroma, for which pre-clinical investigations suggest antitumour activity.

Amphethinile is a new spindle poison with a novel structure that has shown activity in the L1210, ADJ/PC6 and Walker carcinoma rodent tumours. In addition the agent appeared to have an improved therapeutic ratio compared to existing spindle poisons and is well absorbed when administered orally. The starting dose for the phase I study was 40 mg m-2 (1/10th mouse LD10) and further patients were studied at 200, 400, 800 and 1200 mg m-2, dose escalation being based on pharmacological monitoring. Significant toxic effects were seen only at 800 and 1200 mg m-2. At these doses patients experienced nausea and vomiting, light headedness during the infusion and varying degrees of lethargy following therapy. Two of six patients at 800 mg m-2 developed severe pain in the tumour bearing area 1-2 h after treatment and one experienced colicky abdominal pain. At 1200 mg m-2 two patients died within 48 h of treatment from what appeared to be vascular causes. Following these episodes the trial was discontinued. Neutropenia and alopecia occurred in two patients, one at 800 and one at 1200 mg m-2. These patients achieved the highest drug exposure in terms of area under the concentration x time curve. It was not possible to achieve an AUC consistently high enough to produce cytotoxic effects due to the occurrence of dose limiting toxicities thus amphethinile cannot at present be recommended for phase II testing by the i.v. route. The dose escalation scheme based on pharmacological monitoring resulted in a considerable saving in the duration of the trial. Further evaluation of this methodology is recommended.

The novel agent amphethinile is shown to inhibit tubulin assembly in vitro. This agent is capable of displacing colchicine but not vinblastine from tubulin and causes a stimulation in GTPase activity in vitro. The affinity constant for the association of this drug with tubulin has been determined (Ka = 1.3 x 10(6) M-1). It is concluded that amphethinile belongs to the class of agents which share a common binding site with colchicine on the tubulin molecule.

A new antitumour agent is described, which has been shown to induce a G2/M block in murine leukaemia cells in vitro. In addition this agent has been shown to be equally toxic toward parental and daunorubicin-resistant P388 cells in vitro. These resistant cells are highly cross-resistant to the established anti-mitotic agents vincristine and vinblastine. Drug accumulation studies in cells have shown that whereas resistance in this cell line is associated with decreased drug accumulation in the case of daunorubicin, vincristine and vinblastine, this effect is much less pronounced for amphethinile. It is proposed that amphethinile is a poor substrate for the drug efflux process associated with the pleiotropic resistance mechanism operating in these cells. The data suggest that cell sensitivity towards amphethinile differs qualitatively from that of the vinca alkaloids and anthracycline. Pharmacokinetic studies in male mice were undertaken. Area under the curve values (AUC), show that levels of approximately 313 micrograms l-1 h-1 were attained at doses equivalent to the LD10. The alpha half life is approximately 8 min after a bolus intravenous injection. The beta half life was approximately 100 min and relatively independent of dose level.