Discovery of naphthacemycins as a novel class of PARP1 inhibitors.

Poly (ADP-ribose) polymerase-1 (PARP-1) is an abundant nuclear protein that plays important roles in a variety of nuclear processes, and it has been proved a prominent target in oncology for its key function in DNA damage repair. In this study, we discovered a series of naphthacemycins as a new class of PARP1 inhibitors from a microbial metabolites library via high-throughput screening. Compound I, one of this series of compounds, could reduce cellular poly (ADP-ribose) level, trap PARP1 on the damaged DNA and elevate the level of γ-H2AX, and showed the selective cytotoxicity against BRCA1-deficient cell line. Our study provided a potential scaffold for the development of new PARP1 inhibitors in cancer therapy.

Tetracenomycin X Exerts Antitumour Activity in Lung Cancer Cells through the Downregulation of Cyclin D1.

Tetracenomycin X (Tcm X) has been reported to have antitumour activity in various cancers, but there have not been any studies on its activity with respect to lung cancer to date. Therefore, this study aims to investigate the anti-lung cancer activity of Tcm X. In this study, we found that tetracenomycin X showed antitumour activity in vivo and selectively inhibited the proliferation of lung cancer cells without influencing lung fibroblasts. In addition, apoptosis and autophagy did not contribute to the antitumour activity. Tetracenomycin X exerts antitumour activity through cell cycle arrest induced by the downregulation of cyclin D1. To explore the specific mechanism, we found that tetracenomycin X directly induced cyclin D1 proteasomal degradation and indirectly downregulated cyclin D1 via the activation of p38 and c-JUN proteins. All these findings were explored for the first time, which indicated that tetracenomycin X may be a powerful antimitotic class of anticancer drug candidates for the treatment of lung cancer in the future.

Effects on leukemic clonogenic cells in murine myeloid leukemia of 1-beta-D-arabinofuranosylcytosine and the anthracyclines adriamycin, daunomycin, aclacinomycin A, and 4'-epidoxorubicin.

M-3 murine myeloid leukemic cells undergo terminal divisions making colonies in methylcellulose culture and also renew themselves in methylcellulose and suspension; leukemic clonogenic cells are characteristic as stem cells. The effects of 1-beta-D-arabinofuranosylcytosine and four anthracyclines (Adriamycin, daunomycin, aclacinomycin A, and 4'-epidoxorubicin) on M-3 leukemic clonogenic cells were studied. 1-beta-D-Arabinofuranosylcytosine was effective in reducing primary and secondary colonies in methylcellulose and the growth of clonogenic cells in suspension. In contrast, the anthracyclines were not so effective in reducing secondary colonies in methylcellulose or clonogenic cells in suspension as to suppress primary colonies in methylcellulose. The results suggest that 1-beta-D-arabinofuranosylcytosine but not the anthracyclines is effective for not only terminal divisions but also self-renewal of leukemic clonogenic cells. The study will be used as a practical screening test to examine the effects of antitumor agents on leukemic blast progenitors.

Therapeutic and pharmacological studies of tetrachloro(d,l-trans)1,2-diaminocyclohexane platinum (IV) (tetraplatin), a new platinum analogue.

Tetrachloro(d,l-trans)1,2-diaminocyclohexane platinum (IV) (tetraplatin), a new platinum analogue, showed greater therapeutic efficacy after i.p. administration than either cis-dichlorodiammineplatinum (II) (cisplatin) or cis-diammine-1,1-cyclobutanedicarboxylate platinum (II) (carboplatin) in mice bearing i.p. implanted L1210 leukemia. At an optimal dose of 5.7 mg/kg/injection given as a single dose on days 1, 5, and 9, tetraplatin increased the median life span over controls by more than 566% with 5 of 8 long-term (50-day) survivors. In contrast, cisplatin at the same optimal dose increased survival by 186% with 2 of 8 long-term survivors, and carboplatin at an optimal dose of 75.6 mg/kg/injection increased survival by only 120% with no long-term survivors. Tetraplatin also was more effective than cisplatin when treatment was delayed until days 3, 7, and 11 after i.p. implant. A combination of tetraplatin and Adriamycin in mice bearing i.p. implanted L1210 leukemia produced more long-term survivors over a wider range of doses than could be achieved with either drug alone. Tetraplatin at 5.7 mg/kg/injection and Adriamycin at 3 mg/kg/injection on days 1, 5, and 9 increased survival by more than 566% with 8 of 8 50-day survivors. Using the same treatment schedule, combinations of tetraplatin with either cisplatin, carboplatin, daunomycin, or 5-fluorouracil did not produce therapeutic efficacy greater than that seen with tetraplatin alone. The in vitro cellular uptake of platinum by L1210 cells at 37 degrees C was about 4-fold higher after exposure to tetraplatin compared to cisplatin following a 2-h incubation at the two concentrations examined (2.5 and 5 micrograms/ml). Comparative pharmacological studies were performed in rats at a single dose of 3 mg/kg i.v. The t1/2 beta for total platinum in plasma was 29.10 h (7.47 h for unbound platinum) after the administration of tetraplatin and 23.70 h (13.09 h for unbound platinum) after cisplatin. By 48 h the urinary excretion of platinum after tetraplatin and cisplatin was 30.1% and 41.4%, respectively. Tissue distribution of platinum was similar after either complex. Thus, tetraplatin has similar pharmacological properties to cisplatin and like cisplatin is a candidate for combination chemotherapy. However, tetraplatin may be superior to cisplatin in some therapeutic situations based on its greater efficacy against selected tumors.

Markedly reduced levels of anthracycline-induced DNA strand breaks in resistant P388 leukemia cells and isolated nuclei.

DNA single-strand and double-strand breaks produced by doxorubicin and two anthracycline derivatives (4-demethoxy-daunorubicin and 4'-deoxy-4'-iododoxorubicin) were measured in doxorubicin-sensitive and -resistant P388 leukemia cell lines, using filter elution methods, and compared with cellular drug accumulation to account for major differences in their cytotoxic activities and cross-resistance. The increased cytotoxic potency of the two derivatives reflects at least in part the enhanced drug accumulation by cells that results from their increased lipophilicity. However, the level of protein-linked DNA breaks was not directly related to cellular accumulation of drug analogues. It is possible that enhanced cytotoxicity may also be the consequence of the greatly enhanced ability of analogues to cause DNA strand breaks. The resistant line showed only a modest degree of resistance to both anthracycline derivatives compared with the high degree of resistance to doxorubicin. Although for all the anthracyclines tested drug accumulation was reduced in the resistant line, this did not correlate with the degree of resistance. A differential sensitivity of resistant and parental cell lines to DNA cleavage activity was consistently found for all three drugs tested. However, in contrast to a lack of effect of doxorubicin, the derivatives caused appreciable DNA strand breakage in resistant cells. The enhanced ability of these analogues to break DNA in resistant cells is consistent with the slight cross-resistance with doxorubicin. DNA double-strand breaks produced in isolated nuclei from these cells paralleled the pattern found in whole cells, thus indicating that a nuclear alteration, presumably involving DNA topoisomerases, is associated with anthracycline resistance. Our findings strongly support the hypothesis that anthracycline resistance in these cell variants may be mediated by multiple mechanisms, involving alterations of plasma membrane and changes of nuclear enzymatic activities responsible for DNA strand breaks.

In vitro sensitivity of myeloblast clonogenic cells to doxorubicin, aclacinomycin A, and 4'-O-tetrapyranyl-doxorubicin: correlations with clinical responses.

The in vitro sensitivity of peripheral blood myeloblast clonogenic cells (CFU-MLs) to doxorubicin (DOX), aclacinomycin (ACL), and 4'-O-tetrapyranyl-doxorubicin (THP-DOX) was studied to evaluate the individual chemosensitivity of CFU-MLs. CFU-MLs from untreated patients were sensitive to the three tested anthracyclines (in 60% to 69% of the patients). Conversely, CFU-MLs from relapsed patients previously treated with DOX-containing regimens were sensitive to ACL and THP-DOX (in 71% and 75% of the patients, respectively) but resistant to DOX. Six of ten patients who entered complete remission with a combination of DOX, vincristine, and cytosine arabinoside had CFU-MLs in vitro which were sensitive to DOX. Conversely, none of the 13 patients resistant to this chemotherapy regimen displayed CFU-MLs which were sensitive in vitro to DOX. Nine of ten patients who responded to ACL as well as one of three resistant patients had CFU-MLs sensitive to ACL in vitro. No clinical responses were observed with THP-DOX in five of seven patients with CFU-MLs sensitive to this drug. The results indicate that myeloblast clonogenic assays can be used to predict the in vitro sensitivity of CFU-MLs to compounds with established antileukemic activity (ie, DOX, ACL). However, the discrepancy between in vitro and in vivo sensitivity to THP-DOX underlines the importance of knowledge of drug pharmacokinetics and the difficulty of using the CFU-ML test for screening new drugs.

The treatment of acute myelogenous leukemia in adults.

An uncompromisingly optimistic approach must now be taken to the future of the treatment of acute myelogenous leukemia. This view can be justified on two grounds. First, understanding of the biology of the disease is increasing, resulting for example in the demonstration of the prognostic significance of the behavior of the leukemic blast cells in culture and their chromosomal pattern. It seems most likely that individualization of treatment will follow from such observations, with obvious benefit to the patients. Second it has been shown that a modest proportion of patients is cured with the manipulations of chemotherapy with or without radiotherapy and bone marrow transplantation practised in the mid-1970s. Selected results reflecting a personal bias have been presented allowing speculation that very intensive chemotherapy, possibly of short duration may be able to increase this proportion. At the same time, advances in the techniques of preparation of both patient and bone marrow for transplantation are being made and may increase the potential pool of patients who may benefit from the procedure. Even within the limitations of the treatment available now, it is possible that a flexible attitude to the precise manipulation of cytotoxic drugs, radiotherapy and transplantation may result in cure for the majority, rather than the minority, of patients.

Experimental basis and clinical experience with non-cross-resistant combinations in solid tumours.

Experimental studies on anticancer drug resistance have shown that cisplatin and alkylating agents have a very low level of cross resistance towards heterocyclic agents such as anthracyclines, podophyllotoxins and vinca alkaloids. Based on this and on the model of Goldie and Coldman protocols using sequentially alternating non-cross-resistant combinations were given in testicular cancer, sarcomas and small cell bronchogenic carcinomas. Preliminary clinical results are presented here.

Predictive value of the CFU-C assay in acute nonlymphocytic leukemia.

A double-layer agar culture assay for granulopoietic progenitor cell (CFU-C) was employed to study the in vitro growth pattern of bone marrow or peripheral blood cells from 37 patients at diagnosis of acute nonlymphocytic leukemia. The patients were classified as having type A growth if there were greater than 50 colonies (A1), or greater than one colony and greater than 50 clusters was observed after 14 days in culture (A2). Type B growth was defined as no growth (B1), less than 50 colonies and less than 50 clusters (B2) or cluster growth only (B3). Agar cultures containing marrow cells from 10 patients were stained in situ, and the colonies and clusters revealed abnormal cellular maturation. Treatment with cytosine arabinoside and an anthracycline resulted in a complete remission of leukemia in one of 15 patients with type A growth and 17 of 22 patients with type B growth. The subtype of growth pattern did not correlate with the mechanism (i.e., drug resistance versus kinetic resistance) for the failure to achieve a complete remission. The subtype of type B growth (B1, B2 or B#) did not correlate with the duration of complete remission. Nonetheless, the growth patterns observed in cultures of cells obtained from patients with acute nonlymphocytic leukemia appear to be excellent predictors of the success of achieving complete remission with induction therapy.

7-Deoxydaunomycinone quinone methide reactivity with thiol nucleophiles.

Under anaerobic conditions and with NADPH as a reducing agent, daunomycin is reduced in the presence of spinach ferredoxin: NADP+ oxidoreductase as the enzyme catalyst to its hydroquinone, from which intramolecular elimination of the C-7 glycoside proceeds to provide a quinone methide intermediate. This quinone methide is capable of bimolecular reaction with the thiolate nucleophiles N-acetyl-L-cysteine, N-(tert-butoxycarbonyl)-L-cysteine, and 1-thio-beta-D-glucose, providing a pair of C-7 diastereomers, when the reaction is carried out under the autocatalytic conditions offered by substoichiometric quantities of NADPH. With 0.4 equiv of NADPH, optimal yields of the adducts are obtained of approximately 65%. In each case, the 7S adduct is the major product, with the observed stereoselectivities (7S to 7R) ranging from 2.6 to 1 for N-acetyl-L-cysteine to 4 to 1 for both the N-(tert-butoxycarbonyl)-L-cysteine and 1-thio-beta-D-glucose as nucleophiles. By standard blocking and deblocking procedures, the complete set of complementary functionalized (7S)- and (7R)-N-acetyl and O-methyl 7-L-cysteinyl-7-deoxydaunomycinones is prepared. All efforts to extend this quinone methide trapping reaction to additional nucleophiles (such as I- or N3-), including the use of Fe(III) chelation, are unsuccessful. The Fe(III) chelate of daunomycin is however reduced by ferredoxin reductase and NADPH to the Fe(III) chelate of 7-deoxydaunomycinone, suggesting that quinone reduction of the chelate to the quinone methide has occurred. Of the new compounds prepared, only (7R)-7-S-(beta-D-glucopyranosyl)-7-thio-7-deoxydaunomycinone has biological activity. As an in vitro inhibitor of P388 cell growth, it has a 50% inhibitory concentration 25 times greater than that of daunomycin.

Recovery of left ventricular function following discontinuation of anthracycline chemotherapy in children.

Echocardiographic evaluation of left ventricular (LV) performance was performed in 41 children during and following anthracycline chemotherapy. Prior to treatment LV function was normal in all patients; LV shortening fraction was 35.2 +/- 0.7% and percent of predicted velocity of circumferential fiber shortening was 110 +/- 20%. However, the indices measured concurrent with the final anthracycline dose (mean = 308 +/- 16 mg/sq m) demonstrated a significant decline in LV function. The LV shortening fraction had decreased to 29.5 +/- 0.8% and percent of predicted velocity of circumferential fiber shortening decreased to 94 +/- 4% (P less than .01). Four of the eight patients with evidence of significant LV dysfunction had received thoracic or upper abdominal irradiation. Following cessation of anthracycline therapy, LV function improved within one to six months and had returned to normal in all but two patients, both of whom received irradiation. Echocardiography is useful for the identification of anthracycline-induced LV dysfunction. With discontinuation of further anthracycline administration the functional decline in LV performance appears to be reversible.

Clinical and morphologic cardiac findings after anthracycline chemotherapy. Analysis of 64 patients studied at necropsy.

The relation between clinical evidence of and histologic signs of anthracycline cardiotoxicity was evaluated by reviewing the clinical and morphologic findings in 64 patients studied at necropsy, all of whom had received doxorubicin or daunorubicin chemotherapy during life. Of the 64 patients, 20 (31%) had documented clinical toxicity consisting of impaired left ventricular systolic performance; in 7 (35%) of these 20 patients, histologic signs of toxicity were absent. In the remaining 13 patients with clinical toxicity, histologic signs of toxicity ranged from mild to severe. Of the 44 (69%) patients without clinical signs of drug toxicity, 21 (48%) had no histologic sign of cardiotoxicity; in 23 (52%) of the patients without clinical toxicity, however, morphologic signs of cardiotoxicity were nevertheless present--mild in most patients, but extensive in 4. Signs of extensive histologic toxicity (19 [30%] of 64 patients) were associated with large doses (greater than 450 mg/m2) of the drug, mediastinal irradiation, and age greater than 70 years. This study suggests that attempts to monitor cardiotoxicity by serial evaluation of cardiac histology in patients undergoing anthracycline chemotherapy may be seriously limited by the fact that clinical evidence of toxicity may be present without histologic signs of toxicity; likewise, histologic signs of anthracycline toxicity may be present without clinical evidence of toxicity.

The design of cytotoxic-agent-antibody conjugates.

The rationale for the use of antibodies as carriers of cancer chemotherapeutic agents is based upon: the presence on cells of tumor-associated cell surface antigens (TAA); the ability to obtain specific polyclonal or monoclonal antibodies against them; and the availability of methods for binding appropriate toxic agents or radionuclides with retention of activity of both antibody and agents. The general finding so far has been that both conventional polyclonal and hybridoma-derived monoclonal antibodies can deliver cytocidal amounts of toxic agents to target tumor cells both in vitro and in vivo. Moreover, various agents with different modes of antitumor activity (e.g., DNA intercalation or alkylation, enzyme inhibition, and cell surface modification) have all produced superior tumor inhibition in conjugate form compared to the individual or synergistic inhibition produced by agent and antibody. Recent studies are contributing to the understanding of the mechanism of action of drug-antibody conjugates and are thus establishing guidelines for this approach to cancer therapy.

A chemical perspective on the anthracycline antitumor antibiotics.

The anthracycline antitumor antibiotics occupy a central position in the chemotherapeutic control of cancer. They remain, however, antibiotics of the last resort and thus exhibit toxicity both to the neoplasm and to the host organism. As part of the continuing effort to dissociate the molecular processes responsible for these two separate toxicities, attention has been drawn to the intrinsic redox capacity of their tetrahydronapthacenedione aglycone moiety, and to the possible expression of this redox activity against those biomolecules for which anthracyclines have a particular affinity (polynucleotides and membranes). This review is a synopsis of the present trends and thoughts concerning this relationship, written from the point of view of the intrinsic chemical competence of the anthracyclines and their metabolites. While our ignorance is profound--the precise molecular locus of the antitumor expression of the anthracyclines remains unknown--there is now evidence that the relationship of the anthracyclines to the DNA (possibly requiring enzymatic cooperation) and to the membranes, with neither event requiring redox chemistry, may comprise the core of the antitumor effects. The adventitious expression of the redox activity under either aerobic conditions (in which circumstances molecular oxygen is reduced) or anaerobic conditions (in which circumstances potentially reactive aglycone tautomers are obtained) is therefore thought to contribute more strongly to the host toxicity. Yet little remains proven, and the understanding of the intrinsic chemical competence can do little more than lightly define the boundaries within which are found these and numerous other working hypotheses.

Treatment of four patients with myelodysplastic syndrome with a small dose of aclacinomycin-A.

The effect of a small dose of aclacinomycin-A (ACR) was examined in two patients with refractory anemia (RA) and two with refractory anemia with excess of blasts in transformation (RAEB-t). ACR (7 or 14 mg/m2) was given for 10 days in a 2-h per day drip infusion. Clinical symptoms and laboratory data improved in 3 of these 4 patients. In a patient with RA, marked increase in reticulocytes and elevation of the hemoglobin level from 6 to 9 g/dl was observed after two courses of ACR therapy. In two with RAEB-t, Auer's rod bearing cells disappeared in the bone marrow and megaloblastic change of the erythroblasts was diminished in one patient. Hemoglobin levels rose from 4.7 to 10 g/dl in one, and platelets and WBC increased in another. No effect was seen in a patient with RA. The cytoreductive effect of ACR was minor compared to the therapy with small dose of cytosine arabinoside (Ara-C). Therefore, ACR warrants further consideration for the treatment of patients with MDS.

Phase II trial of aclacinomycin A in acute leukemia and various solid tumors.

Aclacinomycin A (ACM) is a new anthracycline antibiotic with a reduced cardiac toxicity in animal models. A phase II study was performed in a total of 25 patients, 23 of whom are evaluable for response. All suffered from recurrent and advanced tumors. Pretreatment consisted of at least four different chemotherapeutic agents (range: 4-9). Lung cancer patients (3/9) were irradiated to the mediastinum. Eighteen patients were pretreated with doxo- or daunomycin. The dose for solid tumors was 2-3 mg/kg given on 3 consecutive days every 3 weeks. Leukemia patients received a daily dose of 20 mg/m2, and standard response criteria were used. Marked reductions of leukocyte counts were achieved in leukemia patients. The overall response rate was about 15% in solid tumors, but major objective responses (CR + PR) have not been observed. Myelosuppression was commonly moderate in solid tumor patients, nausea and vomiting were rare, and alopecia was not induced. Cumulative cardiotoxicity was not evaluated in this trial. Treatment with ACM requires further investigation in acute leukemias and solid tumors, not pretreated with anthracycline antibiotics.

Phase I study of pirarubicin.

A Phase I trial of pirarubicin (4'-O-tetrahydropyranyl-doxorubicin) was undertaken to study its toxicity and to gain preliminary knowledge of its efficacy. The dose was escalated by increments of 10 from 30 to 70 mg/m2. Out of 20 patients, 19 were evaluable for toxicity and response to treatment. Hematologic toxicity was dose limiting and dose related. Other adverse effects included nausea and vomiting, hair loss, and stomatitis. No acute cardiotoxicity was encountered. In 2 patients with metastatic breast cancer who had not been pretreated with cytostatic agents, a partial remission was achieved lasting for 5 months. In 6 patients, tumor parameters did not change for a median of 3 months, and 11 patients suffered progressive disease.

A phase I clinical trial of aclacinomycin A administered on a five-consecutive-day schedule.

In the Phase I study, the new anthracycline aclacinomycin A was given to 22 advanced cancer patients on a schedule of daily intravenous administration for five days repeated every four weeks. The limiting toxicity was myelosuppression, which was severe at a dose of 30 mg/m2 per day for five days. Platelet nadirs were more marked than those of white cells and occurred at day 21. Some patients had moderate nausea and vomiting. No hepatic or renal toxicity was observed, and alopecia was minimal. Cardiac function was monitored prospectively, using radionuclide left ventricular ejection fractions and serial ECGs. One patient developed transient atrial fibrillation; and one other, who had previously received 380 mg/m2 doxorubicin, developed congestive heart failure. Otherwise there was no evidence of cardiac toxicity. No tumor regressions were seen. We conclude that 1509 mg/m2 given in five daily 30 mg/m2 fractions is a maximum tolerated dose of aclacinomycin A. This is higher than the reported MTD of 120 mg/m2 for single bolus injection. We recommend a Phase II starting dose of 25 mg/m2 per day for good-risk patients and 20 mg/m2 per day for poor-risk patients when the drug is given on this schedule.

Phase I and II agents in cancer therapy: I. Anthracyclines and related compounds.

Anthracycline antibiotics remain among the most potent anticancer drugs, but their efficacy is limited by the development of a dose-dependent irreversible cardiomyopathy and by the emergence of clones of tumor cells resistant to the effects of the drug. Modifications of the basic anthracycline structure have resulted in molecules that may share the activity of the parent compound, with amelioration of some toxicities, absence of cross-resistance, or activity against tumors insensitive to the parent drug. Epirubicin has a unique metabolic pathway, glucuronidation, that may result in more rapid plasma clearance and reduced toxicity as compared with doxorubicin. Epirubicin has demonstrated comparable activity to doxorubicin in breast cancer, with possibly reduced toxicity. Idarubicin is of interest because of its cytotoxic activity when given orally. Idarubicin has prolonged retention in the plasma and has equal cytotoxic activity to the parent compound. Idarubicin has demonstrated activity against acute leukemia and breast cancer; in the latter tumor category, some doxorubicin-resistant tumors have responded. Esorubicin is of interest because of its nearly absent cardiac toxicity. This agent has some activity against solid tumors and is currently being clinically tested. Aclacinomycin A is an anthracycline in which a trisaccharide is substituted for the aminosugar. Aclacinomycin A and the related compound marcellomycin are of interest as both cytotoxic and differentiating agents. Menogaril is an anthracycline with the aminosugar on the D ring; it does not exhibit cross-resistance with doxorubicin or cardiotoxicity. Mitoxantrone is a compound that is related to the anthracyclines but has a different mechanism of action. This agent has significant activity against acute leukemia and breast cancer and is currently being compared with doxorubicin. Amsacrine is another compound related to the anthracyclines that possesses major activity against acute leukemias. Minor modifications of the anthracycline molecule have had major impact on the biologic activity of these drugs. New anthracycline analogues with up to 100 times the potency of currently available anthracyclines are being developed for clinical testing, and these complex molecules retain a nearly unlimited potential for structural modification.

Preliminary results of a phase II trial of aclacinomycin in acute leukaemia and lymphosarcoma. An oncostatic anthracyclin that is rarely cardiotoxic and induces no alopecia.

A phase II trial of which preliminary results are available for 22 patients indicates that aclacinomycin applied in a continuous modality induced complete and partial remission in four of nine patients with acute lymphoid leukaemia that was resistant to all previously available drugs, and in four of eight patients with stage V lymphosarcoma (leukaemic). Bone-marrow toxicity was the major side-effect. Only one patient of 20 suffered from cardiac toxicity; no one had alopoecia. This very low incidence of myocardial lesions and the absence of hair loss had been predicted, respectively, by our electron microscope study of the myocardium and the light electron microscope study of the skin of golden hamsters [7], a test that detects frequent severe myocardium and skin toxicities for adriamycin and some anthracyclin analogues such as detorubicin, which was found to be toxic in a high percentage of patients in a clinical trial conducted by the E.O.R.T.C. Clinical Screening Group [8].