Potential roles for preclinical pharmacology in phase I clinical trials

Concepts elucidated from preclinical pharmacology studies have made a substantial impact on the clinical use of anticancer drugs. However, the majority of animal pharmacology results have not been available until after drugs have entered clinical trials. Since clinical pharmacokinetic measurements are already part of many phase I trials, human data could be directly compared with mouse data if mouse pharmacology studies were completed before clinical trials were initiated. Once the starting dose in a phase I clinical trial has been evaluated, subsequent doses are escalated until the maximum tolerated dose is reached. The rate of escalation is empirically defined by a modified Fibonacci series. This universal escalation scheme is applied to all drugs, with no modifications based upon pharmacology or other factors. If the starting dose is far removed from the maximum tolerated dose, a large number of dose escalations are required. Consequently, most patients receive subtherapeutic doses, and the amount of resources allocated to each drug increases. We are exploring potential strategies for controlling the rate of dose escalation based upon pharmacokinetic determinations in mouse and man. Retrospective analyses indicate that 20%-50% savings in the total number of dose escalations are possible.

Phase II study of AMSA and doxorubicin to treat metastatic breast cancer

Twenty-two evaluable patients with metastatic breast cancer were treated with a combination of 4-(acridinylamino)methanesulfon-m-anisidide (AMSA) and doxorubicin. All patients but one had received prior therapy with fluorouracil, cyclophosphamide, and methotrexate. Eight patients had partial responses (36%) with a median time to treatment failure of 6 months. Two patients (9%) showed minor responses, and their times to progression were 4 and 6 months. The response rates obtained with this drug combination were similar to those observed in earlier studies using doxorubicin alone.

Potentiation of 4'-(9-acridinylamino)methanesulphon-m-anisidine) action by verapamil

Verapamil was shown to increase growth inhibition and decrease viability of PY815 mastocytoma cells treated with the anti-cancer drug mAMSA 4'-(9-acridinylamino)methanesulphon-m-anisidide (mAMSA) or its normally inactive congener, 4'-(9-acridinylamino)methanesulphon-o-anisidide (oAMSA). Verapamil also potentiated the effect of sub-optimal concentrations of mAMSA or oAMSA on DNA scission in intact cells. Uptake of [14C]mAMSA by PY815 cells was considerably enhanced, while efflux of [14C]mAMSA from precharged cells was inhibited by verapamil. It is concluded that verapamil potentiates the action of mAMSA on PY815 cells in culture by reducing efflux of drug from the cells. The possibility that verapamil may affect systems that sequester or metabolize AMSA drugs is suggested.

Effects of the DNA intercalators 4'-(9-acridinylamino)methanesulfon-m-anisidide and 2-methyl-9-hydroxyellipticinium on topoisomerase II mediated DNA strand cleavage and strand passage

DNA topoisomerase II is believed to be the enzyme that produces the protein-associated DNA strand breaks observed in mammalian cell nuclei treated with various intercalating agents. Two intercalators--4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA, amsacrine) and 2-methyl-9-hydroxyellipticinium (2-Me-9-OH-E+)--differ in their effects on protein-associated double-strand breaks in isolated nuclei. m-AMSA stimulates their production at all concentrations, whereas 2-Me-9-OH-E+ stimulates at low concentrations and inhibits at high concentrations. We have reproduced these differential effects in experiments carried out in vitro with purified L1210 DNA topoisomerase II, and we have found that concentrations of 2-Me-9-OH-E+ above 5 microM prevent the trapping of DNA-topoisomerase II cleavable complexes irrespective of the presence of m-AMSA. It also stimulated topoisomerase II mediated DNA strand passage, again with or without inhibitory amounts of m-AMSA (this result suggests that extensive intercalation by 2-Me-9-OH-E+ destabilized the cleavable complexes). From these data, it is concluded that intercalator-induced protein-associated DNA strand breaks observed in intact eukaryotic cells and isolated nuclei are generated by DNA topoisomerase II and that intercalators can affect mammalian DNA topoisomerase II in more than one way. They can trap cleavable complexes and inhibit DNA topoisomerase II mediated DNA relaxation (m-AMSA and low concentrations of 2-Me-9-OH-E+) or destabilize cleavable complexes and stimulate DNA relaxation (high concentrations of 2-Me-9-OH-E+).

Effects of DNA intercalating agents on topoisomerase II induced DNA strand cleavage in isolated mammalian cell nuclei

Intercalator-induced DNA double-strand breaks (DSB) presumably represent topoisomerase II DNA cleavage sites in mammalian cells. Isolated L1210 cell nuclei were used to determine the saturability of this reaction at high drug concentrations. 4'-(9-Acridinylamino)methanesulfon-m-anisidide (m-AMSA) and 5-iminodaunorubicin (5-ID) both produced DSB in a concentration-dependent manner, and the production of these breaks leveled off above 10 microM. Addition of m-AMSA to 5-ID-treated nuclei did not raise the plateau level. Thus, both drugs seemed to interact similarly on identical targets. The ellipticine derivative 2-methyl-9-hydroxyellipticinium (2-Me-9-OH-E+) had two effects on the production of DSB. Below 10 microM, 2-Me-9-OH-E+ produced DSB as did ellipticine, m-AMSA, or 5-ID. Above 10 microM, 2-Me-9-OH-E+ did not induce DSB and inhibited the DSB induced by m-AMSA, 5-ID, or ellipticine. 2-Me-9-OH-E+ and m-AMSA competed with each other to produce either double-strand break formation (m-AMSA-induced reaction) or double-strand break inhibition (2-Me-9-OH-E+-induced reaction at concentrations greater than 10 microM). Because these results were reproduced in experiments using DNA topoisomerase II isolated from L1210 nuclei, it is likely that the intercalator-induced protein-associated DNA breaks detected by alkaline elution in nuclei represent DNA topoisomerase II-DNA complexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Transport of AMSA drugs into cells

The uptake and efflux of radioactive 4'-(9-acridinylamino)methanesulphon-m-anisidide (mAMSA) and its inactive congener 4'-(9-acridinylamino)methanesulphon-o-anisidide (oAMSA) by PY815 mastocytoma cells were investigated. Both drugs were readily taken up by intact cells although only mAMSA caused DNA scission and is actively cytotoxic to PY815 cells. The microsomal enzyme inhibitors cimetidine or SKF525A increased drug uptake and decreased drug efflux suggesting that drug metabolism could explain the different activities of oAMSA and mAMSA.

m-AMSA in refractory lymphoma. A phase II trial of the Eastern Cooperative Oncology Group

m-AMSA (4'-[9'-acridinylamino]-methansulfon-m-anisidide) is an acridine derivative which has shown a wide spectrum of activity in preclinical testing. The mechanism of action is thought to be via interference with synthesis and integrity of DNA chains by intercalation between base pairs and external binding. Initial phase I clinical trials revealed granulocytopenia to be the dose limiting toxicity with occasional thrombocytopenia. Phlebitis, liver function abnormalities, and cardiac abnormalities have also been noted. Early reports suggested activity in leukemia and lymphoma. Based on these results ECOG evaluated m-AMSA in a phase II trial of Hodgkin's disease and non-Hodgkin's lymphoma.

Calmodulin inhibitor trifluoperazine selectively enhances cytotoxic effects of strong vs weak DNA binding antitumor drugs in doxorubicin-resistant P388 mouse leukemia cells

Doxorubicin-resistant P388 mouse leukemia cells are cross-resistant to anthracycline and non-anthracycline DNA intercalators as well as to natural and semisynthetic anthracyclines which bind weakly or not at all to DNA. In the presence of a non-lethal concentration of 5 microM trifluoperazine cytotoxic effects of the strong DNA binding drugs actinomycin-D, mitoxantrone and m-AMSA were enhanced less than 2 fold in doxorubicin-sensitive cells and up to 50 fold in doxorubicin-resistant cells. Additionally, trifluoperazine induced a greater than 2-fold enhancement in the cytotoxic effects (but not accumulation and retention) of the strong DNA binder N,N-dimethyladriamycin-14-valerate only in doxorubicin resistant cells. In contrast, cell kill, drug accumulation and retention in P388/S and P388/DOX cells treated with the weak DNA binders N-benzyl-adriamycin-14-valerate and 7(R)-O-methylnogarol, and DNA-nonbinding N,N-dibenzyldaunorubicin was similar with or without trifluoperazine treatment. The study demonstrates that the calmodulin inhibitor trifluoperazine induces a specific and marked enhancement in the cytotoxic effects of strong vs weak DNA binding antitumor drugs in doxorubicin-resistant cells.

Studies on the fluorescence labeling of human red blood cell membrane ghosts with 4'-(9-acridinylamino)methanesulfon-m-anisidide

4'-(9-Acridinylamino)methanesulfon-m-anisidide (mAMSA) interacts with red cell membranes, resulting in the formation of fluorescent protein adducts. The mAMSA-membrane protein adducts exhibited an emission fluorescence maximum at 445 nm, with two shoulders at approximately 425 and 470 nm. The major labeled proteins were identified as spectrins 1 and 2 and bands 3, 4.1, 4.2 and 5. The fluorescence intensity increased with increasing mAMSA concentrations (0.03 to 1.5 mM), time (15-120 min), and temperature of the reaction. Results from sodium dodecyl sulfate gel electrophoresis show that mAMSA caused no detectable change in the molecular weight of membrane proteins. This indicates that mAMSA is a monofunctional, noncrosslinking agent. Other acridine analogs, 9-aminoacridine and acridine, did not fluorescently label membrane proteins, suggesting that the presence of the acridine nucleus is not sufficient for labeling. Addition of 2-mercaptoethanol to the mAMSA-membrane reaction mixtures reversed the fluorescence labeling. Furthermore, pretreatment of membrane proteins with N-ethylmaleimide or iodoacetamide prevented the formation of fluorescent mAMSA-membrane protein adducts. These data suggest that mAMSA interacts with sulfhydryl groups of the membrane proteins. When the membrane sulfhydryl groups were assayed by labeling with N-[ethyl-2-3H]ethylmaleimide, it was shown that the accessible membrane sulfhydryl groups were reduced after the mAMSA treatment. The above results suggest that mAMSA covalently binds to the sulfhydryl groups in the red cell membrane, with the production of fluorescent mAMSA-protein adducts.

Phase II study with amsacrines (m-AMSA and m-AMSA lactate) in refractory lymphomas

A total of 70 patients with malignant lymphomas refractory to one or more chemotherapeutic regimens were treated with iv amsacrines (m-AMSA and m-AMSA lactate). Of 58 evaluable patients, 12 had Hodgkin's disease and 46 had non-Hodgkin's lymphoma. Twenty-nine of the evaluable patients received m-AMSA and 29 received m-AMSA lactate. The amsacrines were recycled every 3 weeks. The doses of m-AMSA were 90-120, 70, and 25-30 mg/m2/day for 3 days, respectively. All patients treated with m-AMSA lactate received a single dose of 225 mg/m2. In Hodgkin's disease, the response rate was 58.3% (one complete response among 12 patients), and in non-Hodgkin's lymphoma, the response rate was 30.4% (six complete responses among 46 patients). The median duration of response was 3 and 5 months, respectively. The response rate was unfavorably affected by the presence of extra-nodal disease and a Karnofsky performance status less than 80. There was no important difference in the incidence and duration of response between m-AMSA and m-AMSA lactate. After vomiting, myelosuppression was the most frequent observed toxic effect. One patient showed an unexpected fatal bone marrow aplasia following the first course of 90 mg/m2. This study indicates that m-AMSA and m-AMSA lactate are active and moderately toxic in previously treated malignant lymphomas. Thus, amsacrines could be effectively incorporated into salvage polydrug regimens.

Amsacrine in refractory acute leukemia

Thirty-two patients with heavily pretreated, relapsed acute leukemia were treated with amsacrine (120 mg/m2/day X 5). The 32 patients received a total of 41 courses of therapy, and 31 patients were evaluable for response. There were no complete remissions and only one partial remission (3 months) in an adult patient with acute lymphoblastic leukemia. Toxic effects included myelosuppression (100% of the patients), hyperbilirubinemia (41%), nausea and vomiting (41%), stomatitis (9%), and cardiac dysrhythmia (3%). We conclude that amsacrine as a single agent is not a useful treatment for relapsed, heavily pretreated adult and pediatric acute leukemia.

Chromosomol DNA fragments from mouse cells exposed to an intercalating agent contain a 175-kdalton terminal polypeptide

A 175 kdalton (kDa) polypeptide is bound covalently to the chromosomal DNA fragments from mouse cells exposed to the intercalating agent 4'-[(9-acridinyl)-amino]methansulphon-m-anisidide. Electron microscopy shows a terminal protein on the DNA fragments, whose 5'-termini are blocked. Since the relative molecular mass of topoisomerase II polypeptide chains is also about 175 kDa and topoisomerase II inhibitors prevent intercalator-induced DNA fragmentation, we propose that the polypeptide bound covalently to the 5'-terminus of the DNA fragments is a polypeptide derived from frequently integrated topoisomerase II operating to normalize torsional stress resulting from intercalation.

Correlation between experimentally and clinically demonstrated activity of two new cytotoxic agents in breast cancer

Experimental evidence of the cytotoxic activity of two new agents was obtained using five lines of human breast carcinoma serially transplanted into immunosuppressed mice. Tumor growth delay was used to compare the effect of the new agents with that of cytotoxic drugs of known value in human breast cancer. The mean specific growth delay (number of tumor volume doubling times saved) for each agent against the five lines was: CL232/315 (mitoxantrone) 1.9; M-AMSA (4'[9 - acridinyl] amino-methane sulphon - M - ansidine) 0.5; cyclophosphamide, 1.9; adriamycin, 1.8; melphalan 2.2. There was no significant difference between the activity of mitoxantrone and the clinically useful drugs, but m-AMSA (amsacrine) was significantly less active than the other agents. A clinical trial of mitoxantrone at the Royal Marsden Hospital has confirmed the prediction of useful activity against breast cancer. Objective responses (CR + PR, UICC response criteria) were noted in 21 out of 70 (30%) patients with advanced breast cancer treated with the drug. The responses were of 4-7 months plus duration, and the 30% response rate compares favorably with other single agents. Although amsacrine is active in many forms of malignant disease, several Phase II studies have shown it to have little effect in breast cancer. By using panels of xenografts of different tumor types, it should be possible to select the most appropriate human tumors against which to test a new cytotoxic agent in Phase II studies.

Single- and double-strand DNA breakage and repair in human lung adenocarcinoma cells exposed to etoposide and teniposide

The anticancer agents 4'-demethylepipodophyllotoxin-4-(4,6-O-ethylidene-beta-D-glucopyra noside (etoposide) (VP16-213) and 4'-demethylepipodophyllotoxin-4-(4,6-O-thenylidene-beta-D-gl ucopyranoside (teniposide) (VM26) produce cytotoxicity by inhibiting type II topoisomerase, resulting in an accumulation of DNA breaks. By using alkaline elution techniques to assess in vivo DNA break frequencies, we have been able to follow formation and repair of both single- and double-strand DNA breaks induced by the exposure of A549 human lung adenocarcinoma cells to VP16-213 and VM26. Single-strand DNA breaks are detectable in cells within 2 min of drug exposure, increase in frequency to a maximum after as little as 15 min of exposure, and remain near maximum levels. Double-strand breaks accumulate more slowly, reaching a maximum after 1 to 2 h, and remaining constant thereafter upon continuous exposure to drug. Single-strand DNA breaks predominate at early incubation times and low drug concentrations, whereas the ratios between single- and double-strand DNA breaks decrease at higher drug concentrations. Changing to drug-free medium after 1-h drug exposure results in rapid exponential repair of both single- and double-strand DNA breaks with a time required for repair of one-half of the DNA breaks of 20 to 60 min. VM26 and VP16-213 have similar kinetics for DNA break formation and repair and similar relationships between DNA breakage and cytotoxicity, but VM26 is five to ten times more potent than VP16-213. Results indicate that DNA breakage plateaus may reflect a steady state equilibrium established between the drug and its nuclear target, possibly type II topoisomerase, and demonstrate unique properties of VP16-213- and VM26-induced DNA breakage.

Effects of AMSA, an antineoplastic agent, on spermatogenesis in the mouse

The stages of spermatogenic cells killed by the single and fractionated administration of AMSA, an acridine derivative used in cancer chemotherapy, have been identified in the mouse. A wide range of doses, up to a total of 30 mg/kg, which is the LD50 for AMSA given in three daily injections, was employed. Survival of differentiating (types A1 through Intermediate) and stem spermatogonia was measured by sperm counts performed 29 and 56 days after treatment, respectively. The sensitivity of germ cells to AMSA at other stages of differentiation was determined by semiquantitative histologic analysis at 11 days after treatment. Significant killing of differentiating spermatogonia, types A2 through B, but only minor killing of stem cells and no toxicity to post-spermatogonial stages were observed with all treatment schedules. This pattern of differential sensitivity can explain the temporary azoospermia observed in man during AMSA treatment, which was followed by a return to normal sperm counts after cessation of therapy.

[Combination of AMSA-high dose cytosine arabinoside in acute leukemia]

Forty patients with refractory and/or relapsing acute leukaemia were treated with AMSA (90-120 mg/sq m/day) for 5 days combined with high dose cytosine-arabinoside (HDARAC) (3 g/sq m/12 hours) during the first 2 days. Complete remission was obtained in 46% of the 26 cases of acute myelogenous leukaemia, and the complete remission rate was fair (44%) in the 20 patients refractory to conventional induction treatments. The results were less satisfactory in the few patients with other cytological types: there were 2 complete remissions in 10 patients with acute lymphoblastic leukaemia and none in 4 patients with blast crisis of chronic myelocytic leukaemia. Haematological toxicity was severe, and 6 patients died during the aplastic phase. No cardiac toxicity associated with AMSA was observed, nor did the ocular, cutaneous or cerebellar side-effects described after longer courses of HDARAC develop. Complete remissions were relatively short, and 11 of 14 remitters relapsed after 2 to 11 months (median 4 months). However, 3 remitters underwent allogenic bone marrow transplantation with 2 surviving. Another patient has a prolonged fourth complete remission with AMSA + HDARAC maintenance treatment. It is concluded that the AMSA-HDARAC combination seems to be one of the best salvage induction regimens in acute myelogenous leukaemia.

[AML-6 and AML-7 studies on the treatment of acute myelocytic leukemia. Cyclic alternating chemotherapy during remission, and induction of remission and survival of elderly patients]

Twenty-five institutions are participating in the AML-6-trial designed to improve remission incidence and to delay the time of relapse. Therefore, an intensive cyclic therapy is employed early after achievement of remission using either the same drugs of the induction regimen or rotating combinations of alternative drugs, e.g. AMSA, 5-AZA and HD-araC. So far, 266 patients entered the trial. The overall C.R. rate is 71%. 58 patients are randomized to 'maintenance' arm I, 54 to arm II, 79/112 patients are still being studied. Toxicity was in 7% and 3% respectively a reason to interrupt the study during induction or 'maintenance'. Since the intensity of modern protocols for remission induction of AML presents a major problem in elderly patients due to toxicity, and since most studies indicate low remission rates with an increasing death rate in this age group, the AML-7-study was initiated to prospectively compare survival and quality of life of two different therapeutic strategies: immediate intensive remission induction versus supportive care, 'wait and see' policy, and palliative cytoreduction with hydroxyurea and ara C when necessary. During the first 8 months after activating this study, 27 patients entered, 13 were randomized to branch I, and 14 to branch II.

[AMSA/etoposide (VP 16-213). A phase I/II study in refractory acute myeloid leukemia]

In a phase I/II study the tolerable doses and antileukemic efficacy of the combination AMSA and etoposide (VP 16-213) was assessed in 20 patients with refractory acute myeloid leukemia. The following 5 day treatment course was found tolerable and effective: AMSA 210 mg/m2/die on days 2, 3 and 4, and etoposide on days 1 and 5 as a 1 h infusion of 100 mg/m2 followed by a 23-h continuous infusion of 230 mg/m2. In 5 of 20 patients partial remissions were achieved; 4 of these patients were primarily resistant against two TAD induction cycles. Bone marrow aplasia without a residual blast population was achieved in 7 of the 8 patients with primary TAD resistance. AMSA/etoposide thus seems to express an antileukemic efficacy without cross-resistance against TAD.

In vivo mapping of DNA topoisomerase II-specific cleavage sites on SV40 chromatin

The antitumor drug, m-AMSA (4'-(9-acridinylamino)-methanesulfon-m-anisidide), is known to interfere with the breakage-reunion reaction of mammalian DNA topoisomerase II by blocking the enzyme-DNA complex in its putative cleavable state. Treatment of SV40 virus infected monkey cells with m-AMSA resulted in both single- and double-stranded breaks on SV40 viral chromatin. These strand breaks are unusual because they are covalently associated with protein. Immunoprecipitation results suggest that the covalently linked protein is DNA topoisomerase II. These results are consistent with the proposal that the drug action in vivo involves the stabilization of a cleavable complex between topoisomerase II and DNA in chromatin. Mapping of these double-stranded breaks on SV40 viral DNA revealed multiple topoisomerase II cleavage sites. A major topoisomerase II cleavage site was preferentially induced during late infection and was mapped in the DNAase I hypersensitive region of SV40 chromatin.