Amanda F. Baker

Phase II Trial of Erlotinib in Gastroesophageal Junction and Gastric Adenocarcinomas: SWOG 0127

PURPOSE A phase II trial of the oral epidermal growth factor receptor (EGFR) inhibitor erlotinib in patients with gastroesophageal adenocarcinomas stratified according to primary tumor location into two groups: gastroesophageal junction (GEJ)/cardia and distal gastric adenocarcinomas. PATIENTS AND METHODS Patients with a histologically proven diagnosis of adenocarcinoma of the GEJ or stomach (ST) that was unresectable or metastatic; presence of measurable disease; no prior chemotherapy for advanced or metastatic cancer; Zubrod performance status (PS) of 0 to 1; and adequate renal, hepatic, and hematologic function were treated with erlotinib 150 mg/d orally. Patient characteristics were median age, GEJ-63 years, ST-64 years; sex, GEJ-84% male and 16% female, ST-60 male and 40 female; Zubrod PS, GEJ-25 had a PS of 0 and 18 had a PS 1, ST-13 had a PS of 0 and 12 had a PS of 1. RESULTS Percentage of common toxicities were skin rash, 86% and 72%; fatigue, 51% and 44%; and AST/ALT elevation, 28% and 28%, respectively for GEJ and ST. There has been one confirmed complete response, three confirmed partial responses (PRs) and one unconfirmed PR for an overall response probability of 9% confirmed (95% CI, 3% to 22%), all occurring in GEJ stratum. No responses were observed in ST stratum. The median survival was 6.7 months in GEJ and 3.5 months in ST stratum. Neither intratumoral EGFR, transforming growth factor-alpha or phosphorylated Akt kinase expression nor plasma proteomic analyses were predictive of clinical outcome. No somatic mutations of the EGFR exons 18, 19, or 21 were detected and there was no gross amplification of EGFR by fluorescence in situ hybridization. CONCLUSION Erlotinib is active in patients with GEJ adenocarcinomas, but appears inactive in gastric cancers. The molecular correlates examined were not predictive of the patient therapeutic response.

Stability of Phosphoprotein as a Biological Marker of Tumor Signaling

Purpose: The purpose of the study was to evaluate the stability of phosphoprotein as a marker of signaling activity in human tumors using clinical samples and xenografts. Experimental Design: The expression of phospho-Ser473-Akt (p-Akt) was assessed by immunohistochemistry in paraffin-embedded samples from patients enrolled in a Southwest Oncology Group clinical trial of gastroesophageal junction tumors and by immunohistochemistry and Western blotting in human colon tumor xenografts at various times after removal from the animal. Results: Clinical samples had evaluable p-Akt staining only when obtained as biopsies (9 of 13) and no staining was observed in tumors obtained as surgically resected samples (0 of 15). In HT-29 colon cancer xenografts, p-Akt staining was present in fresh sample but not in tissue that had been allowed to stand for 30 minutes at room temperature. Western blotting of HT-29 tumor xenografts at room temperature showed a slow decrease in total Akt with a half-life of 180 minutes and a rapid decrease in p-Akt with a half-life of 20 minutes. Conclusions: Caution should be used when using phosphoprotein levels in human tumor specimens to measure intrinsic signaling activity or drug effects because of the potential for rapid dephosphorylation. Rapid processing of biopsies is essential and postoperative surgical samples may be of limited value because of the time to fixation.

The phosphatidylinositol-3-kinase inhibitor PX-866 overcomes resistance to the epidermal growth factor receptor inhibitor gefitinib in A-549 human non–small cell lung cancer xenografts

Epidermal growth factor receptor (EGFR) inhibitors such as gefitinib show antitumor activity in a subset of non–small cell lung cancer (NSCLC) patients having mutated EGFR. Recent work shows that phosphatidylinositol-3-kinase (PI3-K) is coupled to the EGFR only in NSCLC cell lines expressing ErbB-3 and that EGFR inhibitors do not inhibit PI3-K signaling in these cells. The central role PI3-K plays in cell survival suggests that a PI3-K inhibitor offers a strategy to increase the antitumor activity of EGFR inhibitors in resistant NSCL tumors that do not express ErbB-3. We show that PX-866, a PI3-K inhibitor with selectivity for p110α, potentiates the antitumor activity of gefitinib against even large A-549 NSCL xenografts giving complete tumor growth control in the early stages of treatment. A-549 xenograft phospho-Akt was inhibited by PX-866 but not by gefitinib. A major toxicity of PX-866 administration was hyperglycemia with decreased glucose tolerance, which was reversed upon cessation of treatment. The decreased glucose tolerance caused by PX-866 was insensitive to the AMP-activated protein kinase inhibitor metformin but reversed by insulin and by the peroxisome proliferator-activated receptor-γ activator pioglitazone. Prolonged PX-866 administration also caused increased neutrophil counts. Thus, PX-866, by inhibiting PI3-K signaling, may have clinical use in increasing the response to EGFR inhibitors such as gefitinib in patients with NSCLC and possibly in other cancers who do not respond to EGFR inhibition.

Redox Signaling and the Control of Cell Growth and Death

Publisher Summary Cells maintain an intracellular environment that is reducing in the face of a highly oxidizing extracellular environment. Regulated alterations in the intracellular redox state (redox signaling) can modulate events such as DNA synthesis, enzyme activation, selective gene expression, and regulation of the cell cycle. The primary consequence of intracellular redox signaling is a change in the oxidation state of cysteine residues of key proteins. This form of posttranslational modification of protein is difficult to follow because it lacks a convenient marker and is readily reversed when the cell contents are exposed to extracellular oxidizing conditions. For this reason, knowledge of the role that redox signaling may play in cell function has lagged behind that of protein modification produced. This chapter discusses the components of the cellular machinery used for the redox regulation of protein activity and its consequences for cell growth and death. Discussed here are the cellular redox systems—glutathione/glutathione reductase, thioredoxin reductase/thioredoxin, protein disulfide isomerase, glutaredoxin, ref-I, and metallothionein. NADPH reduces oxidized glutathione (GSSG) and thioredoxin [Trx (ox)] through glutathione reductase and thioredoxin reductase, respectively, giving reduced glutathione (GSH) and reduced thioredoxin Trx (red). GSH reduces oxidized glutaredoxin [Grx (ox)], and Trx reduces oxidized Ref-1.Trx and Grx provide reducing equivalents to ribonucleotide reductase (RR) for deoxyribonucleotide synthesis. The chapter details the redox targets—ribonucleotide reductase, receptor proteins, and the transcription factors: OxyR, NF-KB/Rel, AP-1—and protein folding and degradation. Mentioned are the cellular responses to redox changes—cell proliferation and activities of thioredoxin related to cell proliferation, oxidant signaling and apoptosis, oxidative stress, and hypoxia. Compelling evidence from in vitro studies shows that alterations in the redox state of proteins involving key cysteine residues lead to conformational changes. Recent studies have identified several redox systems in cells that appear to respond to external stimuli.

Thioredoxin redox control of cell growth and death and the effects of inhibitors.

Thioredoxin is a redox protein found over-expressed in some human tumors. Thioredoxin is secreted by tumor cells and stimulates cancer cell growth. Redox activity is essential for growth stimulation by thioredoxin. Cells transfected with thioredoxin cDNA show increased tumor growth and decreased apoptosis in vivo and decreased sensitivity to apoptosis induced by a variety of agents both in vitro and in vivo. Cells transfected with a redox-inactive mutant thioredoxin show inhibited tumor growth in vivo. Thus, thioredoxin offers an attractive target for anticancer drug development. A class of disulfide inhibitors of thioredoxin has been identified. These disulfides inhibit cancer cell growth in culture and have antitumor activity against some human tumor xenografts in animals.

A Phase I Pharmacokinetic and Pharmacodynamic Study of PX-12, a Novel Inhibitor of Thioredoxin-1, in Patients with Advanced Solid Tumors

Purpose: Thioredoxin-1 (Trx-1) is a cellular redox protein that promotes tumor growth, inhibits apoptosis, and up-regulates hypoxia-inducible factor-1α and vascular endothelial growth factor. Objectives of this study were to determine safety, tolerability, pharmacodynamics, and pharmacokinetics of PX-12, a small-molecule inhibitor of Trx-1. Experimental Design: Thirty-eight patients with advanced solid tumors received PX-12 at doses of 9 to 300 mg/m2, as a 1- or 3-h i.v. infusion on days 1 to 5, repeated every 3 weeks. Results: At the 300 mg/m2 dose level, one patient experienced a reversible episode of pneumonitis during the first cycle, and a second patient developed pneumonitis after the second cycle. Doses up to 226 mg/m2 were well tolerated, and grade 3/4 events were uncommon (<3% of patients). The limiting factor on this dosing schedule was pungent odor caused by expired drug metabolite, 2-butanethiol. The best response was stable disease in seven patients (126-332 days). Whereas PX-12 was not detectable following the infusion, the Cmax of its inactive metabolite, 2-mercaptoimidazole, increased linearly with dose. PX-12 treatment lowered plasma Trx-1 concentrations in a dose-dependent manner. Conclusions: PX-12, the first Trx-1 inhibitor to enter clinical trials, was tolerated up to a dose of 226 mg/m2 by a 3-h infusion. Based on pharmacodynamic and pharmacokinetic data, a trial of prolonged infusion schedule of PX-12 has been initiated.

In vivo molecular pharmacology and antitumor activity of the targeted Akt inhibitor PX-316.

Akt, a serine/threonine kinase that promotes cell survival, is activated by binding of its pleckstrin homology (PH) domain to membrane phosphatidylinositol (PtdIns)-3-phosphates formed by PtdIns-3-kinase. D-3-Deoxy-phosphatidyl-myo-inositols that cannot be phosphorylated on the 3-position of the myo-inositol group are inhibitors of the Akt PH domain. The most active compound is D-3-deoxy-phosphatidyl-myo-inositol 1-[(R)-2-methoxy-3-octadecyloxypropyl hydrogen phosphate] (PX-316). PX-316 administered intraperitoneally to mice at 150 mg/kg inhibits Akt activation in HT-29 human tumor xenografts up to 78% at 10 h with recovery to 34% at 48 h. Phosphorylation of GSK-3beta, a downstream target of Akt, is also inhibited. There is no decrease in PtdIns(3,4,5)-trisphosphate levels by PX-316, showing it is not an inhibitor of PtdIns-3-K in vivo. Gene expression profiling of HT-29 tumor xenografts shows many similarities between the effects of PX-316 and the PtdIns-3-K inhibitor wortmannin, with downregulation of several ribosomal-related genes, while PX-316 uniquely increases the expression of a group of mitochondrial-related genes. PX-316 has antitumor activity against early human MCF-7 breast cancer and HT-29 colon cancer xenografts in mice. PX-316 formulated in 20% hydroxypropyl-beta-cyclodextrin for intravenous administration is well tolerated in mice and rats with no hemolysis and no hematological toxicity. Thus, PX-316 is the lead compound of a new class of potential agents that inhibit Akt survival signaling.

Overexpression of Tumor Vascular Endothelial Growth Factor A May Portend an Increased Likelihood of Progression in a Phase II Trial of Bevacizumab and Erlotinib in Resistant Ovarian Cancer

Purpose: This phase II trial evaluated bevacizumab plus erlotinib in platinum-resistant ovarian cancer; exploratory biomarker analyses, including that of tumor vascular endothelial growth factor A (VEGF-A), were also done. Experimental Design: Forty heavily pretreated patients received erlotinib (150 mg/d orally) and bevacizumab (10 mg/kg i.v.) every 2 weeks until disease progression. Primary end points were objective response rate and response duration; secondary end points included progression-free survival (PFS), toxicity, and correlations between angiogenic protein levels, toxicity, and efficacy. Results: Grade 3 toxicities included skin rash (n = 6), diarrhea (n = 5), fatigue (n = 4), and hypertension (n = 3). Grade 4 toxicities were myocardial infarction (n = 1) and nasal septal perforation (n = 1). Only one grade 3 fistula and one grade 2 bowel perforation were observed. Nine (23.1%) of 39 evaluable patients had a response (median duration, 36.1+ weeks; one complete response), and 10 (25.6%) patients achieved stable disease, for a disease control rate of 49%. Median PFS was 4 months, and 6-month PFS was 30.8%. Biomarker analyses identified an association between tumor cell VEGF-A expression and progression (P = 0.03); for every 100-unit increase in the VEGF-A score, there was a 3.7-fold increase in the odds of progression (95% confidence interval, 1.1-16.6). Conclusions: Bevacizumab plus erlotinib in heavily pretreated ovarian cancer patients was clinically active and well tolerated. Erlotinib did not seem to contribute to efficacy. Our study raises the intriguing possibility that high levels of tumor cell VEGF-A, capable of both autocrine and paracrine interactions, are associated with resistance to bevacizumab, emphasizing the complexity of the tumor microenvironment. Clin Cancer Res; 16(21); 5320–8. ©2010 AACR.

Identification of thioredoxin-interacting protein 1 as a hypoxia-inducible factor 1α-induced gene in pancreatic cancer

Objective: To investigate the expression of thioredoxin-interacting protein (TXNIP) during hypoxia and its dependency on hypoxia-inducible factor 1&agr; (HIF-1&agr;) in pancreatic cancer cell lines. Methods: MiaPaCa-2 pancreatic cancer cells were transiently transfected with siRNA to HIF-1&agr; and TXNIP protein measured after growth in normoxia or hypoxia. In addition, HIF-1&agr; dependency was assessed by transiently transfecting MiaPaCa-2 pancreatic cancer cells with HIF-1&agr; with a mutated oxygen degradation domain resulting in stable HIF-1&agr; expression in normoxic conditions. Panc-1 pancreatic cancer cells with low endogenous TXNIP expression were stably transfected with TXNIP, and cell survival and response to platinum cancer agents were tested. Quantitative immunohistochemistry was utilized to measure the expression of TXNIP and thioredoxin 1 in human pancreatic cancer tissues. Results: Thioredoxin-interacting protein was induced during hypoxia in pancreatic cancer cells in a HIF-1&agr;-dependent manner. Overexpression of TXNIP in the Panc-1 cells resulted in a higher basal apoptosis and increased sensitivity to cisplatin and oxaliplatin. A negative correlation was observed between TXNIP and thioredoxin 1 expression in human pancreatic cancer tissues. Conclusions: Thioredoxin-interacting protein, a putative tumor suppressor gene, is induced in response to hypoxia in a HIF-1&agr;-dependent manner in pancreatic cancer cells, resulting in increased apoptosis and increased sensitivity to platinum anticancer therapy. Increased TXNIP may be a mechanism to counterbalance the prosurvival effects of HIF-1&agr;.

Detection of in vivo enzyme activity with CatalyCEST MRI.

CatalyCEST MRI compares the detection of an enzyme‐responsive chemical exchange saturation transfer (CEST) agent with the detection of an unresponsive “control” CEST agent that accounts for other conditions that influence CEST. The purpose of this study was to investigate the feasibility of in vivo catalyCEST MRI.