Aaron C. Spalding

Preclinical Targeting of the Type I Insulin-Like Growth Factor Receptor in Adrenocortical Carcinoma

CONTEXT Drug therapy for adrenocortical carcinoma (ACC), a rare and lethal malignancy, is largely empirical and ineffective. New treatments directed at molecular targets critical to the pathophysiology of ACC may prove more efficacious. OBJECTIVE The objective of the study was to profile human adrenal tumors and ACC cell lines to assess activated IGF signaling and determine the efficacy of two IGF receptor (IGF-1R) antagonists alone and in combination with mitotane. EXPERIMENTAL DESIGN ACC cell lines that display or lack activated IGF signaling are used to assess the effects of two IGF-1R antagonists in cultured cells and ACC xenograft tumors. RESULTS Transcriptional profiling data derived from DNA microarray analysis of human adrenal tumors implicate IGF2 as the single highest up-regulated transcript in the vast majority of carcinomas. We show that the majority of ACC cell lines tested display constitutive IGF ligand production and activation of downstream effector pathways. Both IGF-1R antagonists cause significant dose-dependent growth inhibition in ACC cell lines. Furthermore, we observe that mitotane, the first-line adrenolytic drug used in patients with ACC, results in enhanced growth inhibition when used in combination with the IGF-1R antagonists. We next examined the activity of IGF-1R antagonists against ACC xenografts in athymic nude mice. IGF inhibition markedly reduced tumor growth greater than that observed with mitotane treatment, and combination therapy with mitotane significantly enhanced tumor growth suppression. CONCLUSION These findings establish a critical role of IGF signaling in ACC pathophysiology and provide rationale for use of targeted IGF-1R antagonists to treat adrenocortical carcinoma in future clinical trials.

Mechanism of Epinephrine-Induced Platelet Aggregation

We report that a genetic polymorphism of the alpha2-adrenergic receptor (A2AR) encoded by chromosome 10 is associated with hypertension and an increase in epinephrine-mediated platelet aggregation in humans. The mechanism responsible for this heritable contrast in sensitivity to epinephrine is unknown. We tested our hypothesis that epinephrine-induced platelet aggregation is mediated by activation of chloride transport. We measured epinephrine-mediated increases in optical density of gel-filtered platelets suspended in a bicarbonate-buffered physiological salt solution. Compared with platelets incubated in the control buffer (130 mmol/L NaCl), platelets incubated with either bumetanide, a Na/K/2Cl cotransport inhibitor; anthracene-9-carboxylic acid, a chloride channel blocker; or acetazolamide, an agent that blocks ATP-dependent chloride transport had significantly decreased aggregation responses to epinephrine. When measured fluorometrically, epinephrine significantly increased intraplatelet chloride concentrations. Chloride-dependent modifications of epinephrine-induced platelet aggregation were not attributable to changes in A2AR ligand binding characteristics or to the concentration of platelet cAMP. Finally, subthreshold concentrations of epinephrine also potentiated thrombin-induced platelet aggregation, and blockade of chloride transport diminished this synergistic action of epinephrine on thrombin-stimulated platelet aggregation. Heritable differences in epinephrine-mediated platelet aggregation may be attributable to genetic differences in chloride transport in platelets. Furthermore, because we observed a necessary role for chloride transport in epinephrine-mediated platelet aggregation, pharmacological agents that block chloride transport, such as diuretics, may provide salutary protection against vascular thrombosis in patients with hypertension independent of the effect of these drugs on blood pressure.

Potential for dose-escalation and reduction of risk in pancreatic cancer using IMRT optimization with lexicographic ordering and gEUD-based cost functions

Radiotherapy for pancreatic cancer is limited by the tolerance of local organs at risk (OARs) and frequent overlap of the planning target volume (PTV) and OAR volumes. Using lexicographic ordering (LO), a hierarchical optimization technique, with generalized equivalent uniform dose (gEUD) cost functions, we studied the potential of intensity modulated radiation therapy (IMRT) to increase the dose to pancreatic tumors and to areas of vascular involvement that preclude surgical resection [surgical boost volume (SBV)]. We compared 15 forward planned three-dimensional conformal (3DCRT) and IMRT treatment plans for locally advanced unresectable pancreatic cancer. We created IMRT plans optimized using LO with gEUD-based cost functions that account for the contribution of each part of the resulting inhomogeneous dose distribution. LO-IMRT plans allowed substantial PTV dose escalation compared with 3DCRT; median increase from 52 Gy to 66 Gy (a=-5,p<0.005) and median increase from 50 Gy to 59 Gy (a=-15,p<0.005). LO-IMRT also allowed increases to 85 Gy in the SBV, regardless of a value, along with significant dose reductions in OARs. We conclude that LO-IMRT with gEUD cost functions could allow dose escalation in pancreas tumors with concomitant reduction in doses to organs at risk as compared with traditional 3DCRT.

TW-37, a small-molecule inhibitor of Bcl-2, mediates S-phase cell cycle arrest and suppresses head and neck tumor angiogenesis.

Members of the Bcl-2 family play a major role in the pathobiology of head and neck cancer. We have shown that Bcl-2 orchestrates a cross talk between tumor cells and endothelial cells that have a direct effect on the progression of head and neck squamous cell carcinoma (HNSCC). Notably, Bcl-2 is significantly up-regulated in the tumor-associated endothelial cells compared with the endothelial cells of normal oral mucosa in patients with HNSCC. Here, we evaluated the effect of TW-37, a small-molecule inhibitor of Bcl-2, on the cell cycle and survival of endothelial cells and HNSCC and on the progression of xenografted tumors. TW-37 has an IC50 of 1.1 μmol/L for primary human endothelial cells and averaged 0.3 μmol/L for head and neck cancer cells (OSCC3, UM-SCC-1, and UM-SCC-74A). The combination of TW-37 and cisplatin showed enhanced cytotoxic effects for endothelial cells and HNSCC in vitro, compared with single drug treatment. Notably, whereas cisplatin led to an expected G2-M cell cycle arrest, TW-37 mediated an S-phase cell cycle arrest in endothelial cells and in HNSCC. In vivo, TW-37 inhibited tumor angiogenesis and induced tumor apoptosis without significant systemic toxicities. Combination of TW-37 and cisplatin enhanced the time to tumor failure (i.e., 4-fold increase in tumor volume), compared with either drug given separately. Collectively, these data reveal that therapeutic inhibition of Bcl-2 function with TW-37 is sufficient to arrest endothelial cells and HNSCC in the S phase of the cell cycle and to inhibit head and neck tumor angiogenesis.[Mol Cancer Ther 2009;8(4):893–903]

New and Emerging Radiosensitizers and Radioprotectors

The combination of chemotherapy and radiation has led to clinical breakthroughs in several disease sites, and current work continues to define optimum combinations of proven chemotherapy as well as more recently available, noncytotoxic agents. Administration of systemic therapies allows modulation of radiation response to improve tumor control (radiosensitization) or to prevent normal tissue toxicity (radioprotection). Substantial progress has been made in identifying the targets of standard chemotherapeutic radiation sensitizers and protectors as well as in the introduction of a new generation of molecularly targeted therapies in combination with radiation. We have reviewed the most recent, predominantly early phase clinical trials combining systemic agents with radiation. Although the proof of an improved schedule ultimately needs to come from well-run Phase III trials, the search among schedules could be shortened by the use of surrogate endpoints such as presence of active drug metabolites in the tumor. This has been accomplished only in a few cases and needs to become a more standard part of radiation sensitizer and protector trials.

Inhibition of Protein Kinase Cβ by Enzastaurin Enhances Radiation Cytotoxicity in Pancreatic Cancer

Purpose: Aberrant activation of protein kinase Cβ (PKCβ) by pancreatic cancer cells facilitates angiogenesis and tumor cell survival. Targeting PKCβ with enzastaurin, a well-tolerated drug in clinical trials, would be expected to radiosensitize pancreatic tumors through direct antitumor and antivascular effects. Experimental Design: We tested the hypothesis that enzastaurin radiosensitizes pancreatic cancer cells in culture and in vivo through inhibition of PKCβ. We analyzed pancreatic cancer xenografts for growth delay and microvessel density after treatment with enzastaurin, radiation, or both. We determined the effect of radiation and enzastaurin on glycogen synthase kinase 3β, a mediator of cell death in culture and in vivo. Results: At concentrations attained in patients, enzastaurin reduced levels of active PKCβ measured by phosphorylation at Thr500 in culture and in xenografts. Enzastaurin alone did not affect pancreatic cancer cell survival, proliferation, or xenograft growth. However, enzastaurin radiosensitized pancreatic cancer cells in culture by colony formation assay. Enzastaurin alone decreased microvessel density of pancreatic cancer xenografts without appreciable effects on tumor size. When combined with radiation, enzastaurin increased radiation-induced tumor growth delay with a corresponding decrease in microvessel density. Enzastaurin inhibited radiation-induced phosphorylation of glycogen synthase kinase 3β at Ser9 in pancreatic cancer cells in culture and in tumor xenografts, suggesting a possible mechanism for the observed radiosensitization. Conclusions: Enzastaurin inhibits PKCβ in pancreatic cancer cells in culture, enhancing radiation cytotoxicity. Additional antivascular effects of enzastaurin were observed in vivo, resulting in greater radiosensitization. These results provide the rationale for a clinical trial in locally advanced pancreatic cancer combining enzastaurin with radiation.

The Metabolic Syndrome: A Modern Plague Spread by Modern Technology

Malnutrition and infectious disease represent the most common health threats facing the developing world. However, increasing technological developments and the expansion of western culture have contributed to the increasing prevalence of the metabolic syndrome. The epidemiologic significance and potential costs to governmental health care systems of an increasing incidence of metabolic syndrome could become high. The role of environmental influences that lead to the development of the metabolic syndrome needs to be explored. Because the metabolic syndrome becomes more common as nations develop, investigations into the ramifications of this disease often come too late.

Chloride increases adrenergic receptor-mediated platelet and vascular responses.

BACKGROUND We postulated that increasing intracellular chloride concentration ([Cl-]i) in human platelets would potentiate alpha2 adrenergic receptor (A2AR)-mediated platelet aggregation, and that vascular reactivity would also be increased by raising [Cl-]i in blood vessels. We further hypothesized that ligands binding to the A2AR would increase [Cl-]i by stimulating carbonic anhydrase-dependent chloride/bicarbonate exchange. Because diuretics are potent inhibitors of carbonic anhydrase, we speculated that these agents inhibit platelet aggregation and vascular contractility through inhibition of chloride influx by decreasing carbonic anhydrase activity, and subsequently, chloride/bicarbonate exchange. The aim of this study was to test these hypotheses. METHODS Platelet aggregation was measured by determining changes in optical density of platelet-rich plasma. Contractile responses to A2AR agonists were recorded in isolated vascular smooth muscle. The substances [Cl-]i and intracellular pH (pHi) were measured using microfluorometric methods. Carbonic anhydrase activity and chloride/bicarbonate exchange were determined by an in vitro assay based on the Stewart cycle. RESULTS Increasing [Cl-]i potentiated platelet aggregation and vascular contractility, and epinephrine raised [Cl-]i by stimulating carbonic anhydrase-dependent chloride/bicarbonate exchange. Furthermore, diuretic-dependent inhibition of carbonic anhydrase activity decreased chloride/bicarbonate exchange. CONCLUSIONS Our data support the concept that diuretics inhibit carbonic anhydrase activity and chloride/bicarbonate exchange in platelets and vascular smooth muscle. The ensuing reduction in [Cl-]i that is induced by diuretics in these tissues could play a role in reducing the effect of catecholamines on precipitating thrombotic stroke or myocardial infarction.

Metronomic small molecule inhibitor of Bcl-2 (TW-37) is antiangiogenic and potentiates the antitumor effect of ionizing radiation.

PURPOSE To investigate the effect of a metronomic (low-dose, high-frequency) small-molecule inhibitor of Bcl-2 (TW-37) in combination with radiotherapy on microvascular endothelial cells in vitro and in tumor angiogenesis in vivo. METHODS AND MATERIALS Primary human dermal microvascular endothelial cells were exposed to ionizing radiation and/or TW-37 and colony formation, as well as capillary sprouting in three-dimensional collagen matrices, was evaluated. Xenografts vascularized with human blood vessels were engineered by cotransplantation of human squamous cell carcinoma cells (OSCC3) and human dermal microvascular endothelial cells seeded in highly porous biodegradable scaffolds into the subcutaneous space of immunodeficient mice. Mice were treated with metronomic TW-37 and/or radiation, and tumor growth was evaluated. RESULTS Low-dose TW-37 sensitized primary endothelial cells to radiation-induced inhibition of colony formation. Low-dose TW-37 or radiation partially inhibited endothelial cell sprout formation, and in combination, these therapies abrogated new sprouting. Combination of metronomic TW-37 and low-dose radiation inhibited tumor growth and resulted in significant increase in time to failure compared with controls, whereas single agents did not. Notably, histopathologic analysis revealed that tumors treated with TW-37 (with or without radiation) are more differentiated and showed more cohesive invasive fronts, which is consistent with less aggressive phenotype. CONCLUSIONS These results demonstrate that metronomic TW-37 potentiates the antitumor effects of radiotherapy and suggest that patients with head and neck cancer might benefit from the combination of small molecule inhibitor of Bcl-2 and radiation therapy.

Radiation therapy reduces local failure and improves overall survival in sPNET

To the Editor: We applaud the study by Fangusaro et al. [1] on the treatment of young patients with sPNET which continues to be a challenging disease requiring multi-disciplinary management. However, we fear that with the authors’ focus on intensive chemotherapy and autologous transplant they have underestimated the curative value of radiation therapy in this disease. It is true that 12/20 survivors (60%) did not receive radiation therapy and, therefore, were spared the toxicity of this treatment. Unfortunately, 21/43 children enrolled on the trial died of progressive/recurrent disease, and only 8 of these received radiation. Therefore, more than 60% of patients who died did not receive a potentially curative treatment while another two patients (4.7%) died directly as a result of their intensive chemotherapy regimen. This seems a high price to pay in order to avoid the potential late toxicity of radiation therapy. Previous studies support the benefit of radiation therapy in the treatment of sPNET. The German HIT-SKK87 and HIT-SKK92 trials examined a cohort of 29 patients (all <38 months), and the only factor on multivariate analysis that predicted overall and progression-free survival was the use of radiation therapy [2]. The Canadian pediatric brain tumor consortium reported on 49 patients where both chemotherapy and radiation therapy predicted survival, but again only the use of radiation was associated with increased survival on multivariate analysis [3]. In addition, when looking at the patterns of failure analysis for Head Start I and II, it appears that at minimum local radiation therapy to the site of the primary tumor would have made a significant difference. For instance in those with progressive/ recurrent disease 17/25 (68%) experienced ‘‘local only’’ failure; 23/ 25 (92%) of all failures had a local component. This is in contrast to CCG-921, which included much less intensive chemotherapy in combination with local and cranial-spinal radiation, where the 5-year rate of ‘‘local only’’ failure was 22% and for any failure involving the primary site was 42% [4]. The importance of radiation treatment with any concern for residual disease left after surgical resection is a fact that was also born out by both the French [5] and German [6] infant medulloblastoma studies using chemotherapy alone. In these reports, following gross-total resection without evidence of metastases, there was impressive long-term event free and overall survival. However, if there was any residual or metastatic disease chemotherapy alone had significantly worse prognosis with EFS of <50% with residual disease and <20% with metastatic disease [5,6]. Certainly the use of any therapy with potential morbidity should be approached cautiously. However, given the clear benefit of radiation therapy and the fact that modern radiation treatment may be given in a fashion to decrease doses to normal tissues thus minimizing late sequalea of therapy [7–9], even in young children [7], we question the omission of this therapy from sPNET regimens, especially in those with any residual/metastatic disease or at the time of progression. Aaron C. Spalding, MD, PhD* Daniel A. Hamstra, MD, PhD Department of Radiation Oncology The University of Michigan Ann Arbor, Michigan 48109-0010 REFERENCES