Can taxanes provide benefit in patients with CNS tumors and in pediatric patients with tumors? An update on the preclinical development of cabazitaxel.

PURPOSE: While first-generation taxanes are valuable treatment options for many solid tumors, they are limited by an inability to cross the blood-brain barrier (BBB) and by limited efficacy in pediatric patients. Following promising preclinical data for the next-generation taxane cabazitaxel, including activity in tumor models fully sensitive, poorly sensitive or insensitive to docetaxel, and its ability to cross the BBB, further preclinical studies of cabazitaxel relevant to these two clinical indications were performed. METHODS: Cabazitaxel brain distribution was assessed in mice, rats and dogs. Cabazitaxel antitumor activity was assessed in mice bearing intracranial human glioblastoma (SF295; U251) xenografts, and subcutaneous cell line-derived human pediatric sarcoma (rhabdomyosarcoma RH-30; Ewing's sarcoma TC-71 and SK-ES-1) or patient-derived pediatric sarcoma (osteosarcoma DM77 and DM113; Ewing's sarcoma DM101) xenografts. The activity of cabazitaxel-cisplatin combination was evaluated in BALB/C mice bearing the syngeneic murine colon adenocarcinoma, C51. RESULTS: Cabazitaxel penetrated rapidly in the brain, with a similar brain-blood radioactivity exposure relationship across different animal species. In intracranial human glioblastoma models, cabazitaxel demonstrated superior activity to docetaxel both at early (before BBB disruption) and at advanced stages, consistent with enhanced brain penetration. Compared with similar dose levels of docetaxel, cabazitaxel induced significantly greater tumor growth inhibition across six pediatric tumor models and more tumor regressions in five of the six models. Therapeutic synergism was observed between cisplatin and cabazitaxel, regardless of administration sequence. CONCLUSIONS: These preclinical data suggest that cabazitaxel could be an effective therapy in CNS and pediatric tumors, supporting ongoing clinical evaluation in these indications.

[Rhythm of expression of BCL-2 protein of MA13/C mammaryadenocarcinoma bearing-mice]. / Rythme d'expression de la protéine BCL-2 chez la souris porteuse de l'adénocarcinome mammaire MA13/C.

We previously demonstrated a circadian rhythm in response to docetaxel chemotherapy in C3H/HeN mice bearing MA13/C mammary adenocarcinoma. We investigated the relation between this rhythm and the expression of BCL-2 in bone marrow and in tumor tissues. A circadian rhythm characterized BCL-2 expression in the bone marrow, which was hardly modified in tumor-bearing animals. BCL-2 acrophase coincided with the time of highest docetaxel tolerability and efficacy in this model. This suggests that BCL-2 protects the bone marrow from the drug toxicity, especially during the light phase.

Circadian optimisation of irinotecan and oxaliplatin efficacy in mice with Glasgow osteosarcoma.

The relevance of circadian rhythms in irinotecan and oxaliplatin tolerability was investigated with regard to antitumour activity. Mice bearing Glasgow osteosarcoma (GOS) received single agent irinotecan (50 or 60 mg kg(-1) per day) or oxaliplatin (4 or 5.25 mg kg(-1) per day) at one of six dosing times expressed in hours after light onset (3, 7, 11, 15, 19 or 23 hours after light onset). Irinotecan (50 mg kg(-1) per day) and oxaliplatin (4 or 5.25 mg kg(-1) per day) were given 1 min apart at 7 or 15 hours after light onset, or at their respective times of best tolerability (7 hours after light onset for irinotecan and 15 hours after light onset for oxaliplatin) or worst tolerability (15 hours after light onset for irinotecan and 7 hours after light onset for oxaliplatin). Tumour growth rate was nearly halved and per cent increase in estimated life span (% ILS) was - doubled in the mice receiving irinotecan at 7 hours after light onset as compared to 15 hours after light onset (P<0.05). Results of similar magnitude were obtained with oxaliplatin for both endpoints, yet with 7 hours after light onset corresponding to least efficacy and 15 hours after light onset to best efficacy (P<0.05). Irinotecan addition to oxaliplatin proved therapeutic benefit only if the schedule consisted of irinotecan administration at 7 hours after light onset and oxaliplatin delivery at 15 hours after light onset, i.e. when both drugs were given near their respective "best" circadian times. These would correspond to the middle of the night for irinotecan and the middle of the day for oxaliplatin in humans.

Phase I dose-finding and pharmacokinetic study of docetaxel and vinorelbine as first-line chemotherapy for metastatic breast cancer.

BACKGROUND AND PURPOSE: Anthracycline-containing regimens are widely used in advanced breast cancer. However, there is a need for new, non-anthracycline regimens that are active in patients for whom anthracyclines are contraindicated. The aim of this study was to determine the maximum tolerated dose (MTD), the dose-limiting toxicities (DLTs) and recommended doses of docetaxel and vinorelbine as first-line chemotherapy in patients with metastatic breast cancer. The pharmacokinetics of both drugs was also evaluated. PATIENTS AND METHODS: Thirty-four women with first-line metastatic breast cancer were treated with docetaxel, 60-100 mg/m2 (day 1), and vinorelbine, 20-22.5 mg/m2 (days 1 and 5), repeated every three weeks and administered on an outpatient basis. RESULTS: Two MTDs were determined: MTD1 was defined at the dose level using docetaxel 75 mg/m2, and vinorelbine 22.5 mg/m2 DLT being a grade 3 stomatitis that was more related to the dose of vinorelbine than that of docetaxel. Therefore, the study continued with a fixed dose of vinorelbine, 20 mg/m2, and docetaxel 85-100 mg/m2. MTD2 was defined at the dose level combining docetaxel, 100 mg/m2, and vinorelbine, 20 mg/m2; DLTs were grade 3 stomatitis and severe asthenia. Fluid retention was observed in 41% of patients but was never severe or a reason for patient discontinuation. In comparison with historical experience, Daflon 500 did not seem to increase the efficacy of the three-day corticosteroid premedication by further reducing the incidence or severity of fluid retention. No significant neurotoxicity was observed and no patient discontinued the study due to this site effect. Activity was observed at all dose levels and at all metastatic sites, with an overall response rate of 71% (95% CI: 52.0%-85.8%). The median time to progression was 31.4 weeks (95% CI: 12-48 weeks) and median survival was 15.6 months (95% CI: 2.6-26.6 months). The pharmacokinetics of docetaxel and vinorelbine were not modified between day 1 and day 3 when the two drugs were combined with the day 1 administration schedule used in this study. CONCLUSION: The recommended doses for phase II studies are docetaxel, 75 mg/m2 (day 1), plus vinorelbine, 20 mg/m2 (days 1 and 5), repeated every three weeks. At these doses, the combination was found to be active and well tolerated.

Preclinical evaluation of new taxoids.

Paclitaxel and docetaxel are two key molecules in the treatment of a variety of cancers with major impact in the treatment of breast, lung and ovarian cancers. A number of taxoids have then been synthesized in an effort to improve some of the features of the existing drugs. Although the literature is still scant of preclinical data due to the highly competitive field, several compounds are already in clinical trials. Most of these will be reviewed and have, either improved water solubility or reduced cross-resistance with marketed taxoids or reduced interaction with P-glycoprotein. In addition, the reduced recognition of several compounds by multi-drug-resistance related transport systems has yielded some orally bioavailable compounds with marked in vivo antitumor activity. It is likely that these additional properties should lead to an expanded spectrum of clinical activity compared to that of clinically available taxoids.

Experimental chronotherapy of mouse mammary adenocarcinoma MA13/C with docetaxel and doxorubicin as single agents and in combination.

The therapeutic index of docetaxel, doxorubicin and their combination may be improved by an adequate selection of the circadian time of administration. The present study constitutes a prerequisite to testing the clinical relevance of chronotherapy in human breast cancer. Three experiments were performed in C3H/HeN mice. Each treatment modality was administered i.v. once a week for 3 weeks at one of six circadian stages, during the light span, when the mice were resting: 3, 7, and 11 h after light onset (HALO), or during darkness, when the mice were active: 15, 19, and 23 HALO. The circadian time dependency of single agent tolerability was investigated in healthy mice using four dose levels for docetaxel (38.8, 23.3, 14, and 8.4 mg/kg/injection) and for doxorubicin (13.8, 8.3, 5 and 3 mg/kg/injection; experiment 1). The circadian time dependency of each single agent efficacy was studied in MA13/C-bearing mice, using two dose levels of docetaxel (38.8 or 23.3 mg/kg/injection) or doxorubicin (8.3 or 5 mg/kg/injection; experiment 2). The toxicity and the efficacy of the simultaneous docetaxel-doxorubicin combination were assessed as a function of dosing time in experiment 3. Two combinations were tested (A, 16.3 mg/kg/injection of docetaxel and 2.5 mg/kg/injection of doxorubicin; and B, 11.6 and 3.5 mg/kg/injection, respectively) at each of the above six circadian times. Mortality, body weight change, and tumor size were recorded for 60-70 days in each experiment. Single agent docetaxel or doxorubicin was significantly best tolerated near the middle of the rest span (7 HALO) and most toxic in the middle of the activity phase (19 HALO). Docetaxel or doxorubicin as a single drug were also most effective at 7 HALO, irrespective of dose. Treatment at 7 HALO produced highest rates of complete tumor inhibition (81% versus 11% at 3 HALO for docetaxel, p from chi2 <0.001, and 69% versus 44% at 11 HALO for doxorubicin, not significant) and highest day 60 survival rate (100% versus 28% at 3 HALO for docetaxel, p from chi2 <0.001 and 89% versus 69% at 15 HALO for doxorubicin, not significant). Docetaxel-doxorubicin combinations were most effective following dosing in the beginning of the rest span or short after the onset of the activity span, with regard to the rates of both complete tumor inhibitions (45% at 3 HALO versus 15% at 19 HALO) and day 70 survival rates (85% and 80% at 3 and 7 HALO respectively, versus 20% at 19 HALO). The efficacy of single agent docetaxel or doxorubicin and that of their combination varied largely as a function of circadian dosing time. Single agent docetaxel at 7 HALO was the best treatment option in this model with regard to both tolerability and efficacy. This timing may correspond to the middle of the night in cancer patients.

Proteolysis of microtubule associated protein 2 and sensitivity of pancreatic tumours to docetaxel.

We have studied the state of microtubule associated protein 2 (MAP2) in the pancreatic ductal adenocarcinomas P03 and P02 (sensitive and refractory to docetaxel respectively) since they express the corresponding mRNA and MAP2-related peptides. Immunohistochemical localization showed that in tumour P03 the MAP2-related peptides are highly expressed and confined to the epithelial malignant cells while in P02 the Intensity of the immunostaining is lower. However, anti alpha-tubulin staining followed a similar pattern suggesting that the net amount of macromolecular structures in the sensitive tumour is higher than in the refractory one. This may explain its higher sensitivity to docetaxel, because tubulin assembled into microtubules is the target of the drug. We found that protein extracts from both tumours differed in their proteolytic activity on rat brain MAP2. Since the proteolysis pattern obtained was similar to the one produced by Cathepsin D, we studied the effect of MAP2 proteolysed by this enzyme on microtubule formation in vitro. Proteolysis was found to increase the tendency of tubulin to assemble into macromolecular structures (microtubules and aggregates) in the presence of docetaxel. This suggests that in vivo proteolysis of MAP2 might increase microtubule alterations and potentiate the antitumour effect of docetaxel.

A novel human gene, encoding a potential membrane protein conserved from yeast to man, is strongly expressed in testis and cancer cell lines.

We have characterized a novel human gene (C14orf1) which codes for a polypeptide homologous to the yeast protein Yer044c. Both the human and yeast proteins are predicted to be highly basic and to present several potential, evolutionarily conserved, transmembrane domains. C14orf1 mRNA was found to be particularly abundant in the adult testis and in several cancer cell lines. The gene maps to chromosome band 14q24. Further investigations should be performed to understand the role of C14orf1 in the testis and the significance of its strong expression in the cell lines studied here.

Tau expression in model adenocarcinomas correlates with docetaxel sensitivity in tumour-bearing mice.

Docetaxel is a new taxoid with clinical activity in breast and lung cancer. Using docetaxel-sensitive and -refractory mammary and pancreatic murine tumours, as well as human-derived neoplasms, we investigated if a determinant of docetaxel sensitivity could be found at the level of its mechanism of action. Because microtubules represent the cellular targets of the drug, we studied their heterogeneity in the tumour models to try to explain the differences in drug sensitivity. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of the expression of microtubular components showed that levels of Mbeta4-tubulin and Tau mRNAs were higher in the murine sensitive neoplasms than in the refractory ones. It was also found that Tau protein levels differed markedly among the tumours. In the human-derived sensitive neoplasm, beta-tubulins and some Tau isoforms were found to be more abundant than in the resistant one. Western blot analysis of MAP2 revealed the presence of several immunoreactive species. Some of these polypeptides were also found in higher amounts in the docetaxel-sensitive tumours. The possible meaning of these correlations is discussed in connection with the regulation of microtubule dynamics.

Docetaxel chronopharmacology in mice.

Docetaxel tolerance and antitumor efficacy could be enhanced if drug administration was adapted to circadian rhythms. This hypothesis was investigated in seven experiments involving a total of 626 male B6D2F1 mice, synchronized with an alternation of 12 h of light and 12 h of darkness (12:12), after i.v. administration of docetaxel. In experiment (Exp) 1, the drug was given once a week (wk) for 6 wks (20 mg/kg/wk) or for 5 wks (30 mg/kg/wk) at one of six circadian times, during light when mice were resting [3, 7, or 11 hours after light onset (HALO)], or during darkness, when mice were active (15, 19, or 23 HALO). Endpoints were survival and body weight change. In Exp 2 and 3, docetaxel (30 mg/kg/wk) was administered twice, 1 wk apart, at one of four circadian stages (7, 11, 19, or 23 HALO). Endpoints were hematological and intestinal toxicities. In Exp 4, circadian changes in cell cycle phase distribution and BCL-2 immunofluorescence were investigated in bone marrow as possible mechanisms of docetaxel tolerability rhythm. In Exp 5 to 7, docetaxel was administered to mice bearing measurable P03 pancreatic adenocarcinoma (270-370 mg), with tumor weight and survival as endpoints. Mice from Exp 5 and 6 received a weekly schedule of docetaxel at one of six circadian stages (20 or 30 mg/kg/wk at 3, 7, 11, 15, 19, or 23 HALO). In Exp 7, docetaxel (30 mg/kg) was given every 2 days (day 1, 3, 5 schedule) at 7, 11, 19, or 23 HALO. Docetaxel dosing in the second half of darkness (19 or 23 HALO) resulted in significantly worse toxicity than its administration during the light span (3, 7, or 11 HALO). The survival rate ranged from 56.3% in the mice treated at 23 HALO to 93.8 or 87.5% in those injected at 3 or 11 HALO, respectively (Exp 1, P < 0.01). Granulocytopenia at nadir was -49 +/- 14% at 7 HALO compared with -84 +/- 3% at 19 HALO (Exp 2 and 3, P < 0.029), and severe jejunal mucosa necrosis occurred in 5 of 8 mice treated at 23 HALO as opposed to 2 of 18 receiving docetaxel at 7, 11, or 19 HALO (Exp 2 and 3, P < 0.02). The time of least docetaxel toxicity corresponded to the circadian nadir in S or G2-M phase and to the circadian maximum in BCL-2 immunofluorescence in bone marrow. Docetaxel increased the median survival of tumor-bearing mice in a dose-dependent manner (controls: 24 days; 20 mg/kg weekly, 33 days; 30 mg/kg weekly or day 1, 3, 5 schedule, 44 or 46 days, respectively; Exp 5-7). Survival curves of treated mice differed significantly according to dosing time for each dose and schedule (P from log rank <0.003 to P < 0.03). In Exp 5 and 6, the percentage of increase in life span was largest if docetaxel was administered weekly at 7 HALO (20 mg/kg, 220%; 30 mg/kg, 372%) and lowest after docetaxel dosing at 19 HALO (80% with 20 mg/kg) or at 15 HALO (78% with 30 mg/kg). In Exp 7, (day 1, 3, 5 schedule), docetaxel was most active at 11 HALO (percentage increase in life span, 390%) and least active at 23 HALO (210%). Docetaxel tolerability and antitumor efficacy were simultaneously enhanced by drug dosing in the light span, when mice were resting. Mechanisms underlying the tolerability rhythm likely involved the circadian organization of cell cycle regulation. Docetaxel therapeutic index may be improved with an administration at night in cancer patients, when fewest bone marrow cells are in S or G2-M phase.

Potent therapeutic activity of irinotecan (CPT-11) and its schedule dependency in medulloblastoma xenografts in nude mice.

The anti-tumor activity of irinotecan (CPT-11), a DNA-topoisomerase 1 inhibitor, was evaluated in 5 advanced stage subcutaneous medulloblastoma xenografts in nude mice, using different schedules of administration. With a 5-day schedule, the highest i.v. dose tested (40 mg kg-1 day-1) induced complete regressions in all xenografts but 1, and delays in tumor growth always exceeded 30 days. Two xenografts, IGRM11 and IGRM33, were highly sensitive, and animals survived tumor-free beyond 120 days after treatment. CPT-11 clearly retained its anti-tumor activity at a lower dosage (27 mg kg-1 day-1). CPT-11 was significantly more active than cyclophosphamide, thiotepa and etoposide against the 3 xenografts evaluated. To study the schedule dependency of its anti-tumor activity, CPT-11 was given i.v. at the same total doses over the same period (33 days) using either a protracted or a sequential schedule in IGRM34-bearing mice. With a dose of 10 mg kg-1 day-1 given on days 0-4, days 7-11, days 21-25 and days 28-32 (total dose, 200 mg kg-1), 3 of 6 animals were tumor free on day 378. The same total dose given with a sequential schedule, i.e., 20 mg kg-1 day-1 on days 0-4 and days 28-32, failed to induce complete regression. The plasma pharmacokinetics of CPT-11 and SN-38 were studied in IGRM34-bearing animals after a single i.v. dose of 10 and 40 mg kg-1. The plasma clearance rate of CPT-11 was dose dependent. The ratio between the SN-38 and CPT-11 area under the curve in plasma was 0.4-0.65, i.e., significantly higher than that observed in humans at the maximum tolerated dose (0.01-0.05). Conversely, this ratio was 10-fold lower in tumor than in plasma. Clinical development of irinotecan is warranted in pediatric malignancies.

Syntheses and structure-activity relationships of the second-generation antitumor taxoids: exceptional activity against drug-resistant cancer cells.

A series of new 3'-(2-methyl-1-propenyl) and 3'-(2-methylpropyl) taxoids with modifications at C-10 was synthesized by means of the beta-lactam synthon method using 10-modified 7-(triethylsilyl)-10-deacetylbaccatin III derivatives. The new taxoids thus synthesized show excellent cytotoxicity against human ovarian (A121), non-small-cell lung (A549), colon (HT-29), and breast (MCF-7) cancer cell lines. All but one of these new taxoids possess better activity than paclitaxel and docetaxel in the same assay, i.e., the IC50 values of almost all the taxoids are in the subnanomolar level. It is found that a variety of modifications at C-10 is tolerated for the activity against normal cancer cell lines, but the activity against a drug-resistant human breast cancer cell line expressing MDR phenotype (MCF7-R) is highly dependent on the structure of the C-10 modifier. A number of the new taxoids exhibit remarkable activity (IC50 = 2.1-9.1 nM) against MCF7-R. Among these, three new taxoids, SB-T-1213 (4a), SB-T-1214 (4b), and SB-T-1102 (5a), are found to be exceptionally potent, possessing 2 orders of magnitude better activity than paclitaxel and docetaxel. The observed exceptional activity of these taxoids may well be ascribed to an effective inhibition of P-glycoprotein binding by the modified C-10 moieties. The new taxoid SB-T-1213 (4a) shows an excellent activity (T/C = 0% at 12.4 and 7.7 mg/kg/dose, log10 cell kill = 2.3 and 2.0, respectively) against B16 melanoma in B6D2F1 mice via intravenous administration.

Therapeutic activity of CPT-11, a DNA-topoisomerase I inhibitor, against peripheral primitive neuroectodermal tumour and neuroblastoma xenografts.

The anti-tumour activity of CPT-11, a topoisomerase I inhibitor, was evaluated in four human neural-crest-derived paediatric tumour xenografts; one peripheral primitive neuroectodermal tumour (pPNET) (SK-N-MC) and three neuroblastomas. Two models, SK-N-MC and IGR-N835, were established in athymic mice from a previously established in vitro cell line. Two new neuroblastoma xenograft models, IGR-NB3 and IGR-NB8, were derived from previously untreated non-metastatic neuroblastomas. They exhibited the classic histological features of immature neuroblastoma along with N-myc amplification, paradiploidy, chromosome 1p deletions and overexpression of the human mdr 1 gene. These tumour markers have been shown to be poor prognostic factors in children treated for neuroblastoma. CPT-11 was tested against advanced stage subcutaneous tumours. CPT-11 was administered i.v. using an intermittent (q4d x 3) and a daily x 5 schedule. The optimal dosage and schedule was 40 mg kg-1 daily for 5 days. At this highest non-toxic dose, CPT-11 induced 100% tumour-free survivors on day 121 in mice bearing the pPNET SK-N-MC xenograft. For the three neuroblastoma xenografts, 38-100% complete tumour regressions were observed with a tumour growth delay from 38 to 42 days, and anti-tumour activity was clearly sustained at a lower dosage (27 mg kg-1 day-1). The efficacy of five anti-cancer drugs commonly used in paediatric oncology or in clinical development was evaluated against SK-N-MC and IGR-N835. The sensitivity of these two xenografts to cyclophosphamide, thiotepa and cisplatin was of the same order of magnitude as that of CPT-11, but they were refractory to etoposide and taxol. In conclusion, CPT-11 demonstrated significant activity against pPNET and neuroblastoma xenografts. Further clinical development of CPT-11 in paediatric oncology is warranted.

Experimental antitumor activity and pharmacokinetics of the camptothecin analog irinotecan (CPT-11) in mice.

Irinotecan (CPT-11) is a semi-synthetic derivative of camptothecin currently in clinical trials. In vitro, CPT-11 presented preferential cytotoxicity toward some solid tumor cells (mouse colon 38 and pancreas 03; human pancreas MIA PaCa-2) as compared to leukemia cells (L1210), whereas SN-38, a metabolite of CPT-11, was not solid tumor selective. In vivo, schedule of administration studies in P388 leukemia and mammary adenocarcinoma 16/C (MA16/C) showed that CPT-11 was not markedly schedule dependent. In order to determine its spectrum of anticancer activity, CPT-11 was evaluated against a variety of mouse and human tumors. The end points used were total log cell kill (Lck) for solid tumors and increase in life span (% ILS) for leukemia. Intravenous CPT-11 was found highly active against both early and advanced stage pancreatic ductal adenocarcinoma 03 (P03), with 60% long-term survivors and 100% complete regressions, respectively. Other responsive tumors included: colon adenocarcinomas 38 and 51 (both 1.0 Lck); MA16/C (3.4 Lck); MA13/C (1.0 Lck); human Calc18 breast adenocarcinoma (2.8 Lck); Glasgow osteogenic sarcoma (1.8 Lck); Lewis lung carcinoma (1.4 Lck); B16 melanoma (1.4 Lck); P388 leukemia (170% ILS) and L1210 leukemia (64% ILS). Of interest, CPT-11 was active against tumors with acquired resistance to vincristine (P388/Vcr), to doxorubicin (P388/Dox) and to docetaxel (Calc18/TXT). CPT-11 was also found highly active after oral administration in mice bearing P03 and MA16/C tumors. Pharmacokinetic evaluations performed i.v. at the highest non-toxic dosage in mice bearing P03 tumors revealed CPT-11 peak plasma concentrations (Cmax) of 8.9 micrograms/ml and a terminal half-life of 0.6 h. The metabolite SN-38 plasma concentrations presented a Cmax of 1.6 micrograms/ml and a terminal half-life of 7.4 h. Although the CPT-11 tumor levels were similar to the plasma concentrations for early time points, drug levels decreased more slowly in the tumor compared to plasma (half-life, 5.0 h). SN-38 tumor levels reached concentrations in the range of 0.32-0.34 micrograms/g and decayed with a half-life of 6.9 h. No significant difference in plasma or tumor pharmacokinetics of either CPT-11 or SN-38 were noted after one or five daily i.v. injections. Overall, these data show that CPT-11 has good activity in experimental models, when administered both by the i.v. and the oral routes. Compared to humans, a similar schedule of administration independence was observed and similar CPT-11 levels could be reached at efficacious dosages although metabolite SN-38 levels were found higher in mice.

Influence of microtubule-associated proteins on the differential effects of paclitaxel and docetaxel.

Microtubules are complex structures arising in part from the polymerization of tubulin dimers. Tubulin binds to a wide range of drugs which have been used as probes for tubulin conformation and assembly properties. There is some evidence that taxol and taxotere have differing effects on tubulin conformation. Previous work has shown that MAP2 and Tau, although they both induce microtubule assembly, have qualitatively different effects on tubulin's behavior. Since most microtubules in vivo are likely to be associated with MAPs, we decided to characterize the differential effects of MAP2, Tau, taxol, and taxotere on tubulin polymerization with the aim of understanding the mechanisms through which these agents stimulate microtubule assembly. Furthermore, the inhibitive effect of calcium has been used to elucidate the ability of the two drugs to force tubulin assembly. These observations suggest that docetaxel, in addition to its greater efficiency in tubulin assembly, may have the capacity to differently alter certain classes of microtubules. Tau and MAP2 accessory proteins may represent important cofactors modulating the effects of taxoids.

Preclinical evaluation of CPT-11 and its active metabolite SN-38.

CPT-11 (irinotecan) is a water-soluble analogue of camptothecin (CPT), an antitumor drug extracted from the Chinese tree Camptotheca acuminata. SN-38 is an active metabolite of CPT-11 that contributes significantly to its activity. The antitumor effects of CPT-11 and SN-38 are exerted through a novel mechanism of action; inhibition of DNA topoisomerase I. CPT-11 and its metabolite have demonstrated potent inhibitory activity against a variety of cancer cell lines in vitro and against several murine and human tumors grafted in mice in vivo, including those that express multidrug resistance. CPT-11 has also shown synergistic activity in combination with 5-fluorouracil and cisplatin in vitro. No irreversible or unusual toxicities were observed with CPT-11 in animal toxicity studies. In summary, the preclinical profile of CPT-11 confirmed this drug to be an attractive candidate for clinical development.

Phase I and pharmacology study of intoplicine (RP 60475; NSC 645008), novel topoisomerase I and II inhibitor, in cancer patients.

Intoplicine (RP 60475F; NSC 645008) is a novel 7H-benzo[e]pyrido[4,3-b]indole derivative which interacts with both topoisomerases I and II. Because of its high activity in preclinical cancer models, original mechanism of action and acceptable toxicity profile, intoplicine was further evaluated in a phase I and pharmacology study. Thirty-three (33) patients (24 men and nine women) meeting standard phase I eligibility criteria were included: median age was 56 years, performance status 0-1 in 28 patients and 2 in five patients. Tumor primary sites were head and neck (9), colon (6), lung (3) and various other sites (15). Thirty-one patients had received prior radiotherapy and/or chemotherapy. Sixty-nine coursed of intoplicine were administered as a 1 h i.v. infusion at dose levels ranging from 12 to 360 mg/m2. Dose-dependent and reproducible hepatotoxicity was dose limiting in three out of four patients at 360 mg/m2: this toxicity was reversible in two of three patients, but fatal in one. Two sudden deaths occurred in this study at 12 and 48 mg/m2, and the drug implication could not be excluded. No myelosuppression was noted. Hepatotoxicity is therefore dose limiting at 360 mg/m2, and the phase II recommended dose is 270 mg/m2 every 3 weeks with close monitoring of hepatic and cardiac functions. Intoplicine pharmacokinetics was determined in plasma (23 patients) and whole blood (18 patients) at doses ranging from 12 to 360 mg/m2. Intoplicine plasma concentration decay was either bi- or triphasic with the following pharmacokinetic values (mean +/- SEM): half-life alpha, 0.04 +/- 0.004 h; half-life beta, 0.61 +/- 0.13 h; terminal half-life, 19.4 +/- 4.0 h; mean residence-time (MRT), 11.3 +/- 2.4; total plasma clearance (CL), 74 +/- 5 l/h; volume of distribution beta (V beta), 1982 +/- 477 l: volume of distribution at steady state (Vss): 802 +/- 188 l. both the area under the plasma concentration versus time curves (AUC) and the maximum plasma concentrations (Cmax) increased linearly with the intoplicine dose, indicating linear pharmacokinetics (AUC: r = 0.937; slope = 0.01305; p < 0.001; Cmax: r = 0.847; slop = 0.01115; p < 0.001). Plasma AUC was also predicted very accurately by the Cmax values (r = 0.909; slope = 1.0701; p < 0.001). Other plasma pharmacokinetic parameter values increased significantly with dose, e.g. the terminal half-life (r = 0.748, p < 0.001) the MRT (r = 0.728, p < 0.001), the V beta (r = 0.809, p < 0.001), and the Vss (r = 0.804, p < 0.001). This was probably due to a longer detectability of the drug in plasma at higher doses. Blood pharmacokinetics was also evaluated in 18 patients since it was found that red blood cells represented a significant drug reservoir for intoplicine. Blood intoplicine disposition curves were either bi- or triphasic with the following pharmacokinetic parameter values (mean +/- SEM): half-life alpha, 0.04 +/- 0.01 h; half-life beta, 0.94 +/- 0.22 h; terminal half-life, 57.1 +/- 6.6 h; MRT, 82.2 +/- 9.9 h; CL, 18 +/- 3 l/h; V beta, 1188 +/- 147 I; Vss 1163 +/- 138 I. Blood pharmacokinetics was linear, since AUC and Cmax increased linearly with dose (AUC: r = 0.879; slop = 0.06884; p < 0.001; Cmax: r = 0.835, slop = 0.01223; p < 0.001). Blood AUC values could also be determined by the blood Cmax (r = 0.768; slop = 5.0206; p < 0.001). Other blood pharmacokinetic parameter values presented a dose dependence, e.g. the terminal half-life (r = 0.626, p = 0.005), the V beta (r = 0.682, p = 0.002) and the Vss (r = 0.555, p = 0.017). The plasma or blood intoplicine concentrations achieved in vivo in humans are potentially cytotoxic levels based on preclinical in vivo and in vitro data. In conclusion, the phase II recommended dose of intoplicine is 270 mg/m2 administered as a 1 h i.v. infusion every 3 weeks. Plasma and blood pharmacokinetics were linear within the dose range studied. Potentially cytotoxic concentrations were reached at clinically achievable doses.

Preclinical antitumor activity of CI-994.

CI-994 [aka: acetyldinaline; PD 123654; 4-acetylamino-N-(2'aminophenyl)-benzamide] (Figure 1) is a novel antitumor agent with a unique mechanism of action. It is the acetylated metabolite of dinaline, a compound previously identified as having cytotoxic and cytostatic activity against several murine and human xenograft tumor models. CI-994 had activity against 8/8 solid tumors tested (log cell kills at the highest non-toxic dose): pancreatic ductal adenocarcinoma #02 (4.7); pancreatic adenocarcinoma #03 (3.0; 1/6 cures); colon adenocarcinoma #38 (1.6); colon adenocarcinoma #51/A (1.1); mammary adenocarcinoma #25 (1.7); mammary adenocarcinoma #17/ADR (0.5); Dunning osteogenic sarcoma (4.0); and the human prostate carcinoma LNCaP (1.2). CI-994 had the same spectrum of activity in vivo as dinaline. It also behaved similarly in schedule comparison/toxicity trials. Prolonged administration with lower drug doses was more effective than short-term therapy at higher individual doses. If doses were kept between 40 and 60 mg/kg/injection, prolonged administration (> 50 days) was tolerated with no gross toxicity. Doses > or = 90 mg/kg/injection caused lethality after 4-5 days of administration. The maximum tolerated total dose was also increased with smaller individual doses administered for prolonged intervals. Clinical Phase I trials are ongoing with this agent.