Phase II study of ecteinascidin 743 in heavily pretreated patients with recurrent osteosarcoma

Abstract

BACKGROUND

Recurrent osteosarcoma is a drug-resistant disease with a dismal prognosis. The objective of this Phase II study was to evaluate the activity of ecteinascidin 743 (ET-743) as a salvage therapy in these patients.

METHODS

Patients with recurrent osteosarcoma who had received standard chemotherapeutic agents were eligible. ET-743 was administered at a dose of 1500 μg/m² as a 24-hour infusion every 3 weeks. Pharmacokinetic studies were performed during the first cycle.

RESULTS

Twenty-five patients were enrolled, 23 of whom were assessable for response (median age of 18 years; range, 12–67 years). The median number of previous chemotherapeutic agents was five (range, three to eight previous agents). Sixty-one cycles were administered (median number of cycles per patient was 2; range, 1–9 cycles per patient). Three patients (12%) achieved minor responses (49% 36% and 25%, respectively). Fifteen patients (60%) developed a transient elevation of hepatic transaminases (Grade 3 or 4 [according to the National Cancer Institute Common Toxicity Criteria]), which was not cumulative. Grade 3 or 4 neutropenia and thrombocytopenia were observed in 12 patients (48%) and 6 patients (24%), respectively. The mean area under the curve (AUC) in 4 patients experiencing Grade 4 toxicity (76.4 ± 29.3 ng × hr/mL) was significantly greater (P = 0.034) than that in those for whom the most severe toxicity was Grade 3 (39.5 ± 17.2 ng × hr/mL [n = 12]) or Grade 1-2 (52.6 ± 15.6 ng × hr/mL [n = 5]). There were no other significant correlations found between pharmacokinetic variables and patient characteristics, toxicity, or therapeutic response.

CONCLUSIONS

ET-743 was found to be well tolerated in heavily pretreated osteosarcoma patients but had limited antitumor activity as a single agent. The combination of ET-743 with cisplatin or doxorubicin should be considered. Cancer 2003;98:832–40. © 2003 American Cancer Society.

DOI 10.1002/cncr.11563

Osteosarcoma patients who develop disease recurrence after standard chemotherapy and surgery have a very grave prognosis.1 The overall survival rate after recurrence is < 30%, which includes mainly patients with focal and resectable lung metastasis. The outcome of patients with unresectable disease is dismal and the benefits of salvage chemotherapy are controversial.1–10 Novel therapies therefore are needed for these patients.

Ecteinascidin 743 (ET-743) is a tetrahydroisoquinoline alkaloid isolated from the Caribbean marine tunicate Ecteinascidia turbinata.11, 12 Preclinical studies have revealed potent activity of ET-743 against several solid tumor cell lines and human tumor xenografts including melanoma, soft tissue sarcoma, Ewing sarcoma, nonsmall cell lung carcinoma, ovarian carcinoma, renal carcinoma, prostate carcinoma, and breast carcinoma.13–19 Cytotoxicity is observed in vitro at nanomolar concentrations.14–19 A recent in vitro study in osteosarcoma cell lines demonstrated that ET-743 is very potent against both drug-sensitive and drug-resistant (methotrexate- and cisplatin-resistant) osteosarcoma cells.17

To our knowledge, the precise mechanism of antitumor activity of ET-743 has not been completely elucidated. Initial studies indicated that ET-743 binds to the DNA minor groove by alkylating the N₂ amino group of guanine at specific sequences.20–21 The ET-743 adducts induce a bend toward the DNA major groove, altering the interactions of DNA with transcription factors.22–25 As an example, ET-743 inhibits transcriptional activation of the multidrug resistance (MDR-1) gene by multiple inducers.26–28 A recent report confirmed that ET-743 precisely inhibits activated transcription.29 ET-743 also blocks the cell cycle in late S- and G₂-phases, leading to subsequent apoptosis,30, 31 and affects the organization and assembly of the microtubule network.32 Recent data strongly suggest that the cytotoxicity of ET-743 is mediated mainly by the transcription-coupled nucleotide excision repair (NER) pathway.33–37

Four Phase I trials of ET-743 have been conducted to date in patients with solid tumors. Among 20 patients with advanced pretreated sarcomas who received the recommended dose (RD) or the maximum tolerated dose (MTD), 1 complete response (CR) and 3 partial responses (PRs) were noted.38–41 One of the PRs was observed in a patient with a bulky recurrent osteosarcoma.38

Five Phase II studies of ET-743 in patients with soft tissue sarcomas have been reported in adult populations.42–46 The response rate of soft tissue sarcoma was 10% for previously treated patients and that in untreated patients (first-line trial) was 18%.42 The best responses were noted in patients with liposarcoma and leiomyosarcoma. The median duration of response was 17 months.42

In a group of 55 pretreated sarcoma patients who had access to a worldwide compassionate-use program of ET-743, the objective response rate was 11%. Two PRs were observed among 10 osteosarcoma patients, including 1 response that lasted 14 months.47

The current study was an open-label, Phase II, nonrandomized trial, for which the objective was to determine the activity of ET-743 as a salvage therapy in patients with recurrent osteosarcoma and to define the toxicity of ET-743. We report the response rate, the toxicity observed during the treatment, and data from pharmacokinetic studies.

MATERIALS AND METHODS

Patient Eligibility

Patients with histologically proven, high-grade, recurrent osteosarcoma who had received prior chemotherapy with the standard agents (methotrexate, doxorubicin, cisplatin, and ifosfamide) were eligible. Patients who had received other investigational drugs for recurrence were not excluded. There was no limitation with regard to the number of previous chemotherapeutic agents received. Written informed consent was obtained from all patients prior to participation in the study. The protocol was approved by the Institutional Review Board at each participating institution. Eligibility criteria included the following: no previous chemotherapy for 4 weeks, at least 1 bidimensionally measurable lesion (spiral computed tomography [CT] scan > 10 mm, clinically > 20 × 20 mm) in a nonirradiated area, full recovery from the toxic effects of prior therapies, age ≥ 12 years, World Health Organization (WHO) performance status (PS) ≤ 1, a life expectancy ≥ 3 months, adequate bone marrow reserve as well as renal and liver function (normal bilirubin and alkaline phosphatase), and a negative pregnancy test in women of childbearing potential.

ET-743 Treatment

ET-743 was administered at the dose of 1500 μg/m² as a 24-hour intravenous continuous infusion, which was repeated every 3 weeks on an outpatient basis. The drug was delivered through a central venous catheter using a CADD-1 Model 5100 or CADD-PLUS Model 5400 programmable ambulatory infusion pump (SIMS Deltec, St. Paul, MN). No dose escalation was permitted. Steroid premedication was allowed. No prophylactic hematopoietic growth factor support was allowed. Follow-up evaluations during the treatment were comprised of a clinical examination every 3 weeks. Complete blood count, dosage of hepatic transaminases, alkaline phosphatase, bilirubin, and creatine kinase were assessed weekly.

Subsequent courses of ET-743 were not administered until the granulocyte count was > 1500/μL, the platelet count was > 100,000/μL, and the patient had recovered fully from any nonhematologic toxicity. Dose modification by 20% was based on nadir Grade 4 platelet toxicity (count < 25,000/μL), Grade 4 neutrophil toxicity (count < 500/μL), or any nonhematologic toxicity of ≥ Grade 3. The drug was supplied by PharmaMar, S.A. (Tres Cantos, Spain).

Assessment of Response and Toxicity

Response to therapy was assessed every two cycles using CT scan measurements. The WHO definitions of clinical response, which were commonly used at the time of the study,48 were as follows. A CR indicated total disappearance of tumors, a PR indicated a decrease of at least 50% in the sum of the products of the greatest perpendicular dimensions of all measurable lesions, a minor response (MR) indicated a decrease of ≥ 25% but < 50% in the sum of the products of the greatest perpendicular dimensions of measurable lesions, stable disease (SD) indicated a decrease of < 25% or increase of < 25% in the sum of the products of the greatest perpendicular dimensions of all measurable lesions, and progressive disease (PD) indicated an increase of ≥ 25% in the sum of the products of the greatest perpendicular dimensions of measurable lesions or the appearance of disease at a new site.

Toxicity was graded according to the National Cancer Institute Common Toxicity Criteria, Version 2.0. Grade 3 indicates severe toxicity and Grade 4 indicates unacceptable or life-threatening toxicity.

Pharmacokinetic Studies

The pharmacokinetics of ET-743 were characterized during the first cycle of therapy using a minimally intensive sampling schedule.49 All procedures used for the collection, processing, and storage of the pharmacokinetic specimens were the same as previously described.49 The concentration of ET-743 in plasma was determined by high-performance liquid chromatography with electrospray ionization mass spectrometric detection, as previously reported, without modification.39 All methods used for analyzing the pharmacokinetic data and statistical evaluations also have been described in detail elsewhere.49

Statistical Analysis

Prior to the initiation of the study, it was determined that a response rate of at least 10% would be considered evidence for further exploration of this drug. This study used a 2-stage design with a maximum accrual of 35 patients to determine the objective response rate achieved with ET-743 in patients with recurrent osteosarcoma. It was determined that 25 patients, 23 of whom were expected to be eligible, would be entered and treated. If no responses were observed in these patients, the study would be terminated. If one or more responses were observed, an additional eight patients, seven of whom were expected to be eligible, would be treated. With these criteria, the probability of accepting the agent if it had minimal activity (response rate of 1%) was approximately 3.5% and the probability of rejecting the agent if it had significant activity (response rate of 10%) was approximately 20%.

RESULTS

Patients Characteristics

The baseline characteristics of the patients are summarized in Table 1. The study accrued a total of 25 patients treated in 4 different cancer centers between January 2000 and July 2001. The median age of the patients was 18 years (range, 12–67 years). The distribution by gender was 19 males (76%) and 6 females (24%). The most frequent primary sites of osteosarcoma were the femur (9 patients; 36%), tibia (8 patients; 32%), and humerus (5 patients; 20%). Eleven patients (44%) had metastatic disease at the time of presentation. At the beginning of the study, 22 patients (88%) had lung metastases. The median number of previous regimens received by these patients was three (range of one to five regimens) and the median number of chemotherapeutic agents received was five (range of three to eight agents). The median number of advanced regimens (defined as any treatment administered after disease recurrence) was two (range of none to five advanced regimens). Six patients had received trimetrexate as salvage chemotherapy before the initiation of this study.

Table 1. Patient Characteristics (n = 25)

a Advanced chemotherapy indicates any treatment administered after disease recurrence.
Male:female ratio	19:6
Age (yrs), median (range)	18	(12–67)
Primary site at diagnosis
Femur	9	(36%)
Tibia	8	(32%)
Humerus	5	(20%)
Other sites	3	(12%)
Stage at presentation
Localized	14	(56%)
Metastatic	11	(44%)
Metastatic site at study entry
Lung	22	(88%)
Lymph node	3	(12%)
Bone	2	(8%)
Other sites	8	(32%)
Prior chemotherapy, median (range)
No. of regimens, overall	3	(1–5)
No. of regimens, advanceda	2	(0–5)
No. of chemotherapeutic agents	5	(3–8)
Interval between diagnosis of progressive disease and first ET-743 administration
Median (mos) (range)	0.6 month	(0–1.4)
No. of cycles of ET-743
Total	61
Per patient, median (range)	2	(1–9)

A total of 61 cycles were administered. A median number of two cycles per patient (range of one to nine cycles) were given.

Response

Twenty-three patients were assessable for response. Two patients were not assessable for response because, although they were formally enrolled on the study, they were retrospectively found to have initial disease that was evaluable but not measurable (below the threshold defined for measurable lesion). Because they were formally enrolled on the study, their toxicity and pharmacokinetics data nevertheless are presented. No CRs or PRs were noted but 3 patients achieved MRs (49%, 36%, and 25%, respectively) for an MR rate of 12%. The median duration of response was 3 months (range, 2–4 months). Table 2 shows the characteristics of the three responders. One patient (Patient 208) achieved a very good MR (49%) of 3 months' duration and another patient (Patient 219) achieved an MR (25%) of 4 months' duration, both for their lung metastasis. These patients were found to have PD at the time of evaluation after the sixth cycle of ET-743. Prior to receiving ET-743, Patient 208 had received doxorubicin as a single agent at the time of disease recurrence and had PD. For Patient 219, the best response to salvage chemotherapy after disease recurrence, prior to ET-743, was SD while receiving octreotide pamoate (OncoLAR®^M, Novartis Pharmaceuticals, East Hanover, NJ) and tamoxifen. A third patient (Patient 307) experienced an objective response (36%) after 2 cycles of ET-743, which was maintained up to 2 months. Thereafter, the patient elected to discontinue the therapy for personal reasons that were not related to adverse events. Her best response to previous salvage chemotherapy (doxorubicin and cisplatin) had been the achievement of SD. Patients 208 and 307 died of PD and Patient 219 was alive with PD at the time of last follow-up.

Table 2. Characteristics of Responding Patients

Patient no.	Age (yrs)	Primary site at diagnosis	Metastatic site at study entry	No. of regimens prior to ET-743	Prior chemotherapeutic agents	No. of cycles of ET-743	Overall response to ET-743	Reason off study
ET-743: ecteinascidin 743; ifos: ifosfamide; doxo: doxorubicin; CDDP: cisplatin; MTX: methotrexate; bleo: bleomycin; MR: minor response; PD: progressive disease.
208	55	Femur, lymph node	Lung	2	ifos, doxo, and CDDP	6	MR of −49% (lung)	PD
219	32	Buttock (gluteal region)	Lung	4	ifos, doxo, MTX, CDDP, bleo, and tamoxifen	6	MR of −25% (lung)	PD
307	60	Femur	Lung	2	ifos, doxo, and CDDP	4	MR of −36% (lung)	Refusal

Fourteen patients (56%) had PD and 6 patients (24%) demonstrated early progression of disease (progression occurring before the first scheduled disease evaluation). The median time to progression of disease was 1.3 months (range, 0.5–5.4 months).

Toxicity

All 25 patients in the current study were assessable for toxicity. There were no treatment-related deaths reported. Table 3 summarizes the toxicity observed for all cycles of therapy. Grade 3 and 4 neutropenia were observed in 28% and 20% of patients, respectively. Approximately 24% of patients developed Grade 3 thrombocytopenia and none had thrombocytopenia of Grade 4. A total of 60% of patients developed a transient and noncumulative elevation of hepatic transaminases of Grade 3 (56%) or Grade 4 (4%).

Table 3. Toxicity Observed for All Cycles of Therapy (n = 25)

	Grade 1a	Grade 2	Grade 3	Grade 4
AST: aspartate aminotransferase; ALT: alanine aminotransferase; ALK: alkaline. a Toxicity was graded according to the National Cancer Institute Common Toxicity Criteria.
Hematology
Leukocyte count	8 (32%)	5 (20%)	11 (44%)	1 (4%)
Absolute neutrophil count	8 (32%)	5 (20%)	7 (28%)	5 (20%)
Platelets	16 (64%)	3 (12%)	6 (24%)
Hemoglobin	14 (56%)	9 (36%)	2 (8%)
Hepatic
AST	6 (24%)	6 (24%)	12 (48%)
ALT	3 (12%)	6 (24%)	14 (56%)	1 (4%)
ALK phosphatase	10 (40%)	1 (4%)	4 (16%)	1 (4%)
Renal
Creatinine	8 (32%)
Creatine kinase	5 (20%)		1 (4%)
Adverse events
Anorexia	5 (20%)	1 (4%)
Asthenia	7 (28%)	4 (16%)	1 (4%)
Constipation	2 (8%)	2 (8%)
Dehydration			1 (4%)
Flushing	5 (20%)
Nausea	11 (44%)	4 (16%)	3 (12%)
Emesis	1 (4%)	1 (4%)	2 (8%)
Other	16 (64%)	1 (4%)

A total of 61 cycles of ET-743 were administered. For patients who received more than 1 cycle, the median dose intensity was 429 μg/m²/week (range, 300–512 μg/m²/week). The relative dose intensity was 86% (range, 60–102%). A total of 19 of 36 cycles (53%) had to be delayed. Of these, 5 cycles were delayed because of hematologic toxicity, 11 cycles were delayed because of nonhematologic toxicity (all cases of liver toxicity), and 3 cycles were delayed for other reasons. Approximately 22% of the cycles (8 of 36 cycles) required dose reductions. The reasons for dose reductions were increased transaminases (four cycles), alkaline phosphatase (three cycles), and creatine kinase (one cycle).

Pharmacokinetics

Data regarding the pharmacokinetics of ET-743 were obtained from 21 of the 25 patients during treatment with the first 1500 μg/m² dose of the drug given as a 24-hour continuous intravenous infusion. The mean ± standard deviation (SD) area under the curve (AUC) of ET-743 was 47.9 ± 22.3 ng × hr/mL (median, 46.2 ng × hr/mL; range, 24.5–133.6 ng × hr/mL) and the mean clearance (CL) was 31.3 ± 14.7 L/hr/m². The mean ± SD of the observed maximum concentration (C_max) of the drug was 1.26 ± 0.56 ng/mL. The relation between the most severe drug-related toxicity that occurred during the first cycle of therapy and the AUC is shown in Figure 1. The mean AUC for the 4 patients experiencing Grade 4 toxicity during the first cycle of therapy (76.4 ± 29.3 ng × hr/mL) was significantly greater (P = 0.034) than that in patients for whom the most severe toxicity was Grade 3 (39.5 ± 17.2 ng × hr/mL [n = 12]) or Grades 1-2 (52.6 ± 15.6 ng × hr/mL [n = 5]). However, the clinical relevance of this finding may be questionable because there was not only a substantial degree of overlap in AUC values between the groups, but the mean AUC of the drug for the 7 patients requiring a delay in the administration of the second cycle of therapy to permit recovery from treatment-related toxicity (51.2 ± 24.9 ng × hr/mL) was not significantly different (P = 0.67) from that of 14 patients who received the second dose as scheduled (46.4 ± 21.4 ng × hr/mL). There were no other significant correlations or differences noted between the AUC, C_max, or CL of ET-743 and patient characteristics, pretreatment serum chemistry tests, toxicity, or time to disease progression.

Figure 1. Area under the curve (AUC) of ecteinascidin 743 (ET-743) grouped according to the most severe grade of any drug-related toxicity observed during the first cycle of therapy. Solid points are the observed AUC values in individual patients and the horizontal bars represent the geometric mean values for each grade of toxicity.

DISCUSSION

Recurrent osteosarcoma is a drug-resistant disease for which the benefits of standard chemotherapeutic agents, even at high doses, are reported to be marginal.1, 3, 6, 8, 9 New therapeutic strategies therefore must be developed for this population of patients.

The 12% MR rate obtained in the current study reflects the limited antitumor activity of ET-743 as a single agent in patients with recurrent osteosarcoma. This is consistent with the results of another Phase II study that also was conducted in heavily pretreated adult and pediatric osteosarcoma patients,50 in which no objective response was noted among 11 patients. However, a total of three PRs of osteosarcoma patients to ET-743 have been reported in a Phase I study and the worldwide compassionate-use program.38, 47 Limited data in patients with Ewing sarcoma suggest the potential antitumor activity of ET-743. In a Phase I study of ET-743 in pediatric refractory solid tumors, one patient of three with refractory Ewing sarcoma achieved a CR51 and, in a Phase II study, two patients of nine achieved an objective response.50

It is notable that the patients participating in the current study had a median age of only 18 years and therefore were, to our knowledge, considerably younger than patients taking part in any other clinical trial of ET-743 reported to date. However, it is interesting to note that the three patients who achieved an MR were adults. The explanation of these results is unclear but, of these three patients, two received only three chemotherapeutic agents prior to ET-743 treatment, which is lower than the median of five agents for all patients.

The low response rate that we obtained might be an underestimate of the efficacy of ET-743 because the patients had been heavily pretreated. A study on recurrent osteosarcoma from the Pediatric Oncology Group assessed this issue. They observed that the efficacy of ifosfamide as a single chemotherapeutic agent in patients with recurrent osteosarcoma was underestimated in a heavily pretreated population, in comparison with the previously untreated patients with metastatic osteosarcoma.52 Therefore, we believe that it is worthwhile to perform another Phase II study in a less heavily pretreated osteosarcoma patient population. This could be performed as a window study in combination with other chemotherapeutic agents reported to be active in osteosarcoma.

Another issue in the evaluation of the current study is that we used conventional radiologic imaging to assess response in these patients. It is well known that osteosarcoma cells secrete a calcium-rich matrix that often is ossified. Therefore, the radiologic appearance of the osteosarcoma lesions does not always correlate with the degree of necrosis found in the lesion evaluated by pathologic assessment. We believe that it is possible that the true response rate of osteosarcoma to ET-743 is higher than what we observed by conventional imaging. In the current study, the presence of calcified pulmonary nodules in a patient with SD of 3 months' duration could support this hypothesis.

Overall, ET-743 was found to be well tolerated in this population of heavily pretreated patients. Hematologic toxicity was acceptable. Acute elevation of hepatic transaminases was common, as in other Phase I and II studies of ET-743, but it was always reversible and noncumulative. No case of hepatic failure, rhabdomyolysis, or toxic death was observed. Since the report of three toxic deaths in the first Phase I trials,53 normal baseline biliary function has been required to give a full dose of ET-743 at the beginning of each cycle. The safety profile is now better since this amendment.54 If ET-743 were to be studied in combination with high-dose methotrexate in less heavily pretreated osteosarcoma patients, liver function tests would have to be monitored closely because to our knowledge the interactions and potential additive hepatotoxicity are unknown.

The pharmacokinetic behavior of ET-743 in this younger cohort of patients was very similar to the findings of several other Phase I and II studies in which this same dosing regimen was employed.38, 49 This further substantiates the earlier observation that the CL of ET-743 is independent of patient age.49 In addition, CL (L/hr) was found to be poorly correlated with the body surface area of the patients (correlation coefficient [r] = 0.23), as initially reported for a larger cohort of adult patients with soft tissue sarcomas with a diverse range of characteristics.49 All but 2 of the 21 patients in whom the pharmacokinetics of ET-743 were determined received dexamethasone at doses of 10–20 mg just prior to initiation of the 24-hour infusion of chemotherapy. There was some suggestion in a collective analysis of pharmacokinetics data in 69 adult patients with soft tissue sarcoma who were treated with 1500 μg/m² of ET-743 as a 24-hour intravenous infusion that pretreatment with dexamethasone moderately enhanced the clearance of the drug, although the effect did not appear to achieve statistical significance.49 However, the mean AUC of ET-743 in these osteosarcoma patients (47.9 ± 22.3 ng × hr/mL) was more comparable to the value reported for soft tissue sarcoma patients who did not receive dexamethasone (48.5 ± 20.3 ng × hr/mL) than the value for those who did (38.1 ± 15.4 ng × hr/mL). Accordingly, it appears unlikely that the regimen of dexamethasone that has been adopted to control the nausea and emesis associated with the administration of ET-743 has a clinically relevant effect on its clearance. Finally, the AUC of the initial dose of the drug did not appear to be predictive of patient susceptibility to severe toxicity, including those requiring a delay in subsequent treatment to adequately recover from drug-related toxicity, nor was it found to be associated significantly with response as indicated by the time to disease progression (r = 0.037).

The combination of ET-743 with other chemotherapeutic agents recently was explored. An in vitro study in osteosarcoma cell lines demonstrated synergistic effects between ET-743 and doxorubicin and cisplatin, whereas subadditive effects were observed with methotrexate, vincristine, and actinomycin D.17 One study reported that ET-743 regulates MDR-1 transcription, particularly through the inhibition of the orphan nuclear receptor SXR, which plays an important role in the hepatic drug metabolism.55 The potential reduction of MDR-1 expression by ET-743 suggests that this agent could be useful against cell lines that overexpress MDR-1 and could increase the activity of drugs such as doxorubicin, which is a substrate for MDR-1.26 In vitro studies using soft tissue sarcoma cell lines demonstrated a synergistic interaction of ET-743 and doxorubicin when ET-743 was given for 24 hours before doxorubicin.19 In human sarcoma xenografts, the combination of ET-743 and doxorubicin also was found to be effective against cell lines that overexpressed MDR.56, 57

Recent reports emphasize the fact that ET-743 interacts with the NER system to induce lethal DNA strand breaks.33–37 This is supported by the observation that xeroderma pigmentosum cells, which are deficient in NER, are resistant to ET-743.33 Furthermore, cisplatin-resistant ovarian carcinoma cells with increased NER are reported to be very sensitive to ET-743.33, 58 An in vitro study using osteosarcoma cell lines found that the cisplatin-resistant cells were even more sensitive to ET-743 than the parental cell lines.17 The combination of ET-743 and cisplatin in in vitro studies using melanoma and ovarian cell lines was either synergistic or additive.58 In several xenograft models, this combination clearly was synergistic.37, 58 Given this synergy with cisplatin and considering the great sensitivity to ET-743 of cisplatin-resistant tumor cells, combination therapy is logical and Phase I clinical studies of the combination of ET-743 and cisplatin currently are ongoing.58, 59

The synergy of steroids with ET-743 also has been recently investigated. An in vivo study in osteosarcoma xenografts demonstrated a greater activity of ET-743 in combination with dexamethasone pretreatment than as a single agent.60 The inhibition of the orphan nuclear receptor SXR by ET-743 as described earlier could have a role in this synergy.55

ET-743 was found to be well tolerated in heavily pretreated osteosarcoma patients but had limited antitumor activity as a single agent. Trials in less pretreated patients or ET-743 in combination with cisplatin or doxorubicin should be considered.