Rochelle Bagatell

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.

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.

Phase I Pharmacokinetic and Pharmacodynamic Study of 17-N-Allylamino-17-Demethoxygeldanamycin in Pediatric Patients with Recurrent or Refractory Solid Tumors: A Pediatric Oncology Experimental Therapeutics Investigators Consortium Study

Purpose: Heat shock protein 90 (Hsp90) is essential for the posttranslational control of many regulators of cell growth, differentiation, and apoptosis. 17-N-Allylamino-17-demethoxygeldanamycin (17-AAG) binds to Hsp90 and alters levels of proteins regulated by Hsp90. We conducted a phase I trial of 17-AAG in pediatric patients with recurrent or refractory neuroblastoma, Ewings sarcoma, osteosarcoma, and desmoplastic small round cell tumor to determine the maximum tolerated dose, define toxicity and pharmacokinetic profiles, and generate data about molecular target modulation. Experimental Design: Escalating doses of 17-AAG were administered i.v. over 1 to 2 h twice weekly for 2 weeks every 21 days until patients experienced disease progression or toxicity. harmacokinetic and pharmacodynamic studies were done during cycle 1. Results: Fifteen patients were enrolled onto dose levels between 150 and 360 mg/m2; 13 patients were evaluable for toxicity. The maximum tolerated dose was 270 mg/m2. DLTs were grade 3 transaminitis and hypoxia. Two patients with osteosarcoma and bulky pulmonary metastases died during cycle 1 and were not evaluable for toxicity. No objective responses were observed. 17-AAG pharmacokinetics in pediatric patients were linear; clearance and half-life were 21.6 ± 6.21 (mean ± SD) L/h/m2 and 2.6 ± 0.95 h, respectively. Posttherapy increases in levels of the inducible isoform of Hsp70, a marker of target modulation, were detected in peripheral blood mononuclear cells at all dose levels. Conclusion: 17-AAG was well tolerated at a dose of 270 mg/m2 administered twice weekly for 2 of 3 weeks. Caution should be used in treatment of patients with bulky pulmonary disease.

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.

A phase I study of 17-allylaminogeldanamycin in relapsed/refractory pediatric patients with solid tumors: A children's oncology group study

Purpose: To determine the recommended phase 2 dose, dose-limiting toxicities (DLT), pharmacokinetic profile, and pharmacodynamics of the heat shock protein (Hsp) 90 inhibitor, 17-allylaminogeldanamycin (17-AAG). Experimental Design: 17-AAG was administered as a 60-min infusion, on days 1, 4, 8, and 11 of a 21-day cycle at dose levels of 150, 200, 270, and 360 mg/m2/dose. Pharmacokinetic studies and evaluations for Hsp72 and Akt levels in peripheral blood mononuclear cells were done during the first course of therapy. Results: Seventeen patients (7 males), median 7 years of age (range, 1-19 years), were enrolled using a standard dose escalation scheme. No DLTs were observed. Although there were no objective responses, three patients remain on therapy at 6+, 7+, and 9+ months with stable disease. One patient with hepatoblastoma had a reduction in α-fetoprotein and stable disease over three cycles. At 270 mg/m2/dose, the Cmax and areas under the plasma concentration-time curves of 17-AAG were 5,303 ± 1,591 ng/mL and 13,656 ± 4,757 ng/mL h, respectively, similar to the exposure in adults. The mean terminal half-life for 17-AAG was 3.24 ± 0.80 h. Induction of Hsp72, a surrogate marker for inhibition of Hsp90, was detected at the 270 mg/m2 dose level. Conclusions: Drug exposures consistent with those required for anticancer activity in preclinical models were achieved without DLT. Evidence for drug-induced modulation of Hsp90 systemically was also detected. The recommended phase II dose of 17-AAG is 360 mg/m2/d. Non-DMSO–containing formulations may improve acceptance of this drug by children and their families.

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

ObjectiveTo describe the incidence of clinical deep venous thrombosis associated with femoral central venous catheters (CVC-DVT) in children with diabetic ketoacidosis (DKA). DesignRetrospective case-matched control series. SettingPediatric intensive care units of two university-affiliated hospitals. PatientsAll 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. InterventionsNone. Measurements and Main ResultsThe 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. ConclusionsThis study suggests that young children with DKA have an increased incidence of clinical DVT associated with the placement of femoral central venous catheters.

Update on imaging and treatment of Ewing sarcoma family tumors: What the radiologist needs to know

This review article provides an update on multimodality imaging characteristics of Ewing sarcoma family tumors. Pathology of this tumor and current trends in medical and surgical treatment are briefly discussed.

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.

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.

The perfect storm: Torsades de Pointes in a child with leukemia.

Torsades de Pointes (TdP) is a life‐threatening ventricular arrhythmia that can be associated with metabolic abnormalities, exposure to arrhythmogenic medications, and congenital long‐QT syndrome. This report describes a patient with ALL and multiple complications of therapy who developed TdP. The patient had no evidence of congenital long‐QT syndrome, but a constellation of factors appears to have led to QT prolongation, ventricular ectopy, and TdP. Although the patient suffered cardiac arrest, rapid recognition of TdP and prompt defibrillation resulted in an excellent outcome. Pediatr Blood Cancer 2007;49:996–999.