Hsp90 inhibitors deplete key anti-apoptotic proteins in pediatric solid tumor cells and demonstrate synergistic anticancer activity with cisplatin

Drugs that inhibit the function of heat shock protein 90 (Hsp90) are of interest in the treatment of pediatric cancers because these agents deplete the cellular levels of signaling molecules that are important for the growth and survival of many childhood tumors. To generate preclinical data in anticipation of clinical trials of Hsp90 inhibitors in children, we evaluated the effects of the Hsp90 inhibitor geldanamycin (GA) alone and in combination with cis-platinum (II)-diamine dichloride (cisplatin) in pediatric tumor cells. Immunoblotting demonstrated depletion of the Hsp90 client proteins AKT and the type 1 insulin-like growth factor receptor (IGF1R) in a panel of pediatric tumor cell lines after exposure to GA. Drug exposure also led to a dramatic decrease in cell survival/proliferation in MYCN-amplified and non-amplified neuroblastoma cells. Moderate inhibition of survival/proliferation was observed in RB-deficient and wild-type osteosarcoma cells. Treatment of neuroblastoma and osteosarcoma cell lines with GA in combination with cisplatin resulted in greater than additive inhibition of survival/proliferation based on median dose analysis. Exposure to this drug combination also resulted in a marked increase in nuclear fragmentation as assessed by terminal deoxynucleotide transferase-mediated UTP nick end labeling (TUNEL) analysis. Combined exposure also abrogated the ability of GA to induce a cytoprotective heat shock response and resulted in Hsp90 adduct formation. Our findings suggest that Hsp90 inhibitors may prove useful either alone or as a component of multi-drug regimens in the treatment of neuroblastoma and osteosarcoma.

Hormone-refractory breast cancer remains sensitive to the antitumor activity of heat shock protein 90 inhibitors

PURPOSE

The antiestrogen tamoxifen (Tam) has been used as therapy against estrogen receptor (ER)-positive breast cancer for decades. Most tumors respond initially, but resistance frequently develops. The ER exists in a multiprotein complex containing the molecular chaperone heat shock protein (Hsp) 90, which is known to regulate the stability and activity of this receptor. Therefore, we investigated a ligand-independent approach to hormonal therapy that depletes cellular levels of the receptor by inhibiting the function of Hsp90.

EXPERIMENTAL DESIGN

The activity of the Hsp90 inhibitor geldanamycin (GA) and its clinically relevant derivative, 17-allylamino-17-demethoxygeldanamycin (17AAG), was examined at the molecular and cellular levels using Tam-resistant MCF-7 breast cancer cells both in vitro and in tumor xenografts.

RESULTS

The ER was depleted by GA in several Tam-resistant cell lines, as were other Hsp90 client proteins such as Akt and Raf-1. Unexpectedly, Tam inhibited ER depletion by GA but had no effect on destabilization of Akt or Raf-1. When SCID mice supplemented with Tam were treated with 17AAG, their tumors also showed no decrease in ER levels as measured by immunofluorescent staining and laser scanning cytometry. In these same tumors, however, decreased Akt and Raf-1 levels were observed. Drug administration also led to inhibition of tumor xenograft growth. The mechanism by which Tam inhibits GA-mediated ER depletion is unclear, but immunoprecipitation experiments showed that Tam does not inhibit the ability of GA to alter the ER-chaperone complex.

CONCLUSIONS

Based on its ability to deplete the ER as well as other critical signaling molecules in Tam-resistant breast cancer, 17AAG may provide a useful alternative treatment for patients with recurrent, hormone-refractory breast cancer that should be explored further in Phase II trials. In this context, combined treatment with 17AAG and Tam should be avoided because Tam may inhibit the ability of 17AAG to deplete the ER, potentially reducing its anticancer activity.

The Stress Response: Implications for the Clinical Development of Hsp90 Inhibitors

In their role as molecular chaperones, heat shock proteins serve as central integrators of protein homeostasis within cells. As part of this function, they guide the folding, assembly, intracellular disposition and proteolytic turnover of many key regulators of cell growth, differentiation and survival. Not surprisingly then, heat shock proteins are over expressed in many types of cancer, and induction of the stress response may actually be required for cells to tolerate the genetic disarray characteristic of malignant transformation. Regulation of heat shock protein levels via the stress response is complex, but recent data indicate that the molecular chaperone Hsp90 plays a key role. Specifically, Hsp90 inhibitors alter the multi-chaperone complexes associated with Heat Shock Factor 1 (HSF1), the dominant transcription factor controlling induction of the stress response, and stimulate HSF1-activated heat shock gene expression. Induction of this heat shock response has now emerged as an important consideration in the further clinical development of Hsp90 inhibitors for several reasons. First, tumors in which the stress response is compromised appear particularly sensitive to Hsp90 inhibition. Second, induction of the stress response by Hsp90 inhibitors provides a sensitive pharmacodynamic endpoint with which to monitor drug action in individual patients. Third, Hsp90 inhibitors display important therapeutic interactions with both conventional DNA-targeted chemotherapeutics and newer molecularly targeted agents. These interactions are, at least in part, due to modulation of the stress response by these drugs. Lastly, stress response induction by Hsp90 inhibitors may have therapeutic benefits in non-neoplastic disorders such as heart disease, stroke and neurodegenerative diseases. These benefits are just beginning to be explored.

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

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 microg/m(2) 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 x 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 x hr/mL [n = 12]) or Grade 1-2 (52.6 +/- 15.6 ng x 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.

Low-dose tissue plasminogen activator thrombolysis in children

PURPOSE

To compare results of low-dose tissue plasminogen activator (TPA) in children with arterial and venous thrombi relative to standard published dosing.

METHODS

Subjects consisted of all consecutive children with objectively confirmed thrombi for whom TPA thrombolysis was clinically ordered by the authors. Initial dosing used published standard dose (0.1-0.5 mg/kg per hour). With experience, a low-dose regimen (0.01-0.06 mg/kg per hour) was given in an attempt to derive a minimal effective dose.

RESULTS

Thirty-five children were treated with TPA. Either standard or low-dose infusions of TPA resulted in complete thrombolysis of 28 of 29 (97%) acute thrombi, while all 6 chronic thrombi had a partial response. In contrast to the recommended adult-derived dosages of 0.1 to 0.5 mg/kg per hour, the authors found that initial doses of less than 0.01 mg/kg per hour were effective in 12 of 17 patients with acute thrombosis. Neonates required 0.06 mg/kg per hour. Route of administration (local or systemic) did not affect efficacy. Major bleeding occurred in only one extremely preterm infant. Minor bleeding, primarily oozing at intravenous sites, occurred in 27% of children during TPA infusions. Prophylactic unfractionated or low-molecular-weight heparin was infused concomitant with TPA in 42% of the children and did not increase the risk of bleeding.

CONCLUSIONS

TPA in very low doses appears to be safe and effective for thrombolysis of acute thromboses in most children, given appropriate patient selection.

Femoral central venous catheter-associated deep venous thrombosis in children with diabetic ketoacidosis

OBJECTIVE

To describe the incidence of clinical deep venous thrombosis associated with femoral central venous catheters (CVC-DVT) in children with diabetic ketoacidosis (DKA).

DESIGN

Retrospective case-matched control series.

SETTING

Pediatric intensive care units of two university-affiliated hospitals.

PATIENTS

All eight pediatric DKA patients with femoral central venous catheters between 1998 and 2001, and 16 age-matched control patients with femoral central venous catheters and circulatory shock.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The records of all children with DKA and the control patients were reviewed. CVC-DVT was defined as persistent ipsilateral leg swelling after removal of a femoral central venous catheter. Control patients with coagulopathies, thrombocytopenia, cancer, and hyperglycemia were excluded. Four of eight patients with DKA developed CVC-DVT compared with none of the 16 control patients (p = .007, Fisher's exact test). All four patients with DKA and CVC-DVT were <3 yrs old. Doppler ultrasound examination was performed on three of the four patients with clinical CVC-DVT, confirming the diagnosis in each case.

CONCLUSIONS

This study suggests that young children with DKA have an increased incidence of clinical DVT associated with the placement of femoral central venous catheters.

Increased Expression of the Hsp70 Cochaperone HspBP1 in Tumors

Hsp70 levels are elevated in a number of different tumors. The Hsp70 cochaperone heat shock protein-binding protein 1 (HspBP1) has been shown to bind to Hsp70, inhibit its activity and promote dissociation of nucleotide from the Hsp70 ATPase domain. The purpose of this study was to determine if the levels of HspBP1 are altered in tumor cells. In this report, we show that HspBP1 levels are elevated in two mouse tumor models, 3LL cells (Lewis Lung carcinoma) and neuroblastoma tumors. The amounts of HspBP1 and Hsp70 in selected tissues, tumors and a rabbit reticulocyte lysate were determined using Western blots. It was found that the molar ratio of these two proteins was within a small range (0.21-0.42) in the normal and tumor tissues examined. This ratio was considerably below the HspBP1 to Hsp70 ratio of 4.0 needed for 50% inhibition of Hsp70-mediated refolding of a partially denatured protein in rabbit reticulocyte lysate. The ratio of HspBP1 to Hsp70 in these tissues is too low to inhibit Hsp70 globally in the cell, but is high enough to provide a pool of HspBP1 that could inhibit Hsp70 in a localized fashion. These studies have shown that HspBP1 is elevated in the tumors examined and therefore could be a new cancer marker.

When children die: a seminar series for pediatric residents

OBJECTIVE

Our goals were to assist residents in acquiring skills needed to care for children at the end of life and to increase their comfort level regarding critical aspects of caring for dying children.

METHODS

We designed and implemented a 6-part seminar series for pediatric residents in their postgraduate year-2 at the University of Arizona Pediatric Residency Program. The series consisted of small group sessions regarding medical and legal issues facing physicians at the time of a pediatric patient's death, symptom management in dying children, approaches to limitation of care and discussion of impending death of a child, cultural and developmental factors impacting on the care of children at the end of life, parent and sibling bereavement after the death of a child, and physician's personal responses to the death of pediatric patients. The sessions were conducted on weekday evenings away from patient care settings and included input from community-based individuals as well as academic pediatric subspecialists. To promote active discussion, size was limited to 12 participants. Pretests and posttests were used to evaluate the success of this program. Residents' level of comfort with important issues in end-of-life care was measured using a 5-point Likert scale.

RESULTS

Although most of the residents taking part in the seminar series had previously participated in discussions of limitation of care of a child and/or had performed advanced life support measures on a child, few had any previous training in end-of-life care. Responses of the 8 participants who completed both the pretests and posttests were evaluated for assessment of changes in comfort level in areas pertinent to end-of-life care. We found that on completion of this program, residents were significantly more comfortable with logistic issues and symptom management, discussing death and limitation of medical care with families, discussing end-of-life care with colleagues and families, handling conflicts within the health care team, working with families of varying ethnic backgrounds, guiding developmentally appropriate discussions of death, identifying and seeking out advice from a role model regarding end-of-life care, and coping with their own responses to a child's death. Costs of this seminar series were minimal.

CONCLUSIONS

An inexpensive, discussion-based seminar series successfully provided pediatric residents with basic information regarding end-of-life care and significantly increased their confidence as clinicians caring for seriously ill and dying children.

Two cases of pediatric neuroblastoma with tumor thrombus in the inferior vena cava

The authors describe two children with abdominal neuroblastoma with radiographic evidence of tumor extension into the inferior vena cava. Imaging studies were suggestive of Wilms tumor, but histologic analysis revealed neuroblastoma. In one patient a pulmonary embolus developed after initiation of cytotoxic therapy; the second patient was prophylactically anticoagulated and had no embolic event.

Destabilization of steroid receptors by heat shock protein 90-binding drugs: a ligand-independent approach to hormonal therapy of breast cancer

Steroid hormone receptors have become an important target in the management of breast cancers. Despite a good initial response rate, however, most tumors become refractory to current hormonal therapies within a year of starting treatment. To address this problem, we evaluated the effects of agents that bind the molecular chaperone heat shock protein 90 (Hsp90) on estrogen receptor function in breast cancer. Unstimulated estrogen and progesterone receptors exist as multimolecular complexes consisting of the hormone-binding protein itself and several essential molecular chaperones including Hsp90. We found that interaction of the Hsp90-binding drugs geldanamycin and radicicol with the chaperone destabilizes these hormone receptors in a ligand-independent manner, leading to profound and prolonged depletion of their levels in breast cancer cells cultured in vitro. Consistent with these findings, in vivo administration of the geldanamycin derivative 17-allylaminogeldanamycin (17AAG; NSC330507) to estrogen-supplemented, tumor-bearing SCID mice resulted in marked depletion of progesterone receptor levels in both uterus and tumor. Drug administration also delayed the growth of established, hormone-responsive MCF-7 and T47D human tumor xenografts for up to 3 weeks after the initiation of therapy. We conclude that in light of their novel mechanism of anti-hormone action, consideration should be given to examining the activity of 17AAG and other Hsp90-binding agents in patients with refractory breast cancer in future clinical trials, either alone or in combination with conventional hormone antagonists.

Induction of a heat shock factor 1-dependent stress response alters the cytotoxic activity of hsp90-binding agents

In addition to its classic role in the cellular stress response, heat shock protein 90 (Hsp90) plays a critical but less well appreciated role in regulating signal transduction pathways that control cell growth and survival under basal, nonstress conditions. Over the past 5 years, the antitumor antibiotics geldanamycin and radicicol have become recognized as selective Hsp90-binding agents (HBA) with a novel ability to alter the activity of many of the receptors, kinases, and transcription factors involved in these cancer-associated pathways. As a consequence of their interaction with Hsp90, however, these agents also induce a marked cellular heat shock response. To study the mechanism of this response and assess its relevance to the anticancer action of the HBA, we verified that the compounds could activate a reporter construct containing consensus binding sites for heat shock factor 1 (HSF1), the major transcriptional regulator of the vertebrate heat shock response. We then used transformed fibroblasts derived from HSF1 knock-out mice to show that unlike conventional chemotherapeutics, HBA increased the synthesis and cellular levels of heat shock proteins in an HSF1-dependent manner. Compared with transformed fibroblasts derived from wild-type mice, HSF1 knock-out cells were significantly more sensitive to the cytotoxic effects of HBA but not to doxorubicin or cisplatin. Consistent with these in vitro data, we found that systemic administration of an HBA led to marked increases in the level of Hsp72 in both normal mouse tissues and human tumor xenografts. We conclude that HBA are useful probes for studying molecular mechanisms regulating the heat shock response both in cells and in whole animals. Moreover, induction of the heat shock response by HBA will be an important consideration in the clinical application of these drugs, both in terms of modulating their cytotoxic activity as well as monitoring their biological activity in individual patients.

Inhibition of oncogene expression using vector-generated RNA antisense

Antisense RNA expression vectors have been developed relatively recently as a means to study the role of specific oncogenes in malignant transformation. In this paper, strategies for the construction of antisense plasmid vectors from commercially available reagents are described. Techniques for the introduction of these vectors into cell lines and tumors are also described and preferred methods for the evaluation of biological effects are presented. Lastly, using specific examples, the limitations and potential artifacts associated with antisense vector use in the study of tumorigenesis are discussed.