Cassandra L Hodgkinson

Activity of the Monocarboxylate Transporter 1 Inhibitor AZD3965 in Small Cell Lung Cancer

Purpose: The monocarboxylate transporter 1 (MCT1) inhibitor, AZD3965, is undergoing phase I evaluation in the United Kingdom. AZD3965 is proposed, via lactate transport modulation, to kill tumor cells reliant on glycolysis. We investigated the therapeutic potential of AZD3965 in small cell lung cancer (SCLC) seeking rationale for clinical testing in this disease and putative predictive biomarkers for trial use. Experimental Design: AZD3965 sensitivity was determined for seven SCLC cell lines, in normoxia and hypoxia, and for a tumor xenograft model. Proof of mechanism was sought via changes in intracellular/tumor lactate. Expression of MCT1 and related transporter MCT4 was assessed by Western blot analysis. Drug resistance was investigated via MCT4 siRNAi and overexpression. The expression and clinical significance of MCT1 and MCT4 were explored in a tissue microarray (TMA) from 78 patients with SCLC. Results: AZD3965 sensitivity varied in vitro and was highest in hypoxia. Resistance in hypoxia was associated with increased MCT4 expression. In vivo, AZD3965 reduced tumor growth and increased intratumor lactate. In the TMA, high MCT1 expression was associated with worse prognosis (P = 0.014). MCT1 and hypoxia marker CA IX expression in the absence of MCT4 was observed in 21% of SCLC tumors. Conclusions: This study provides a rationale to test AZD3965 in patients with SCLC. Our results suggest that patients with tumors expressing MCT1 and lacking in MCT4 are most likely to respond. Clin Cancer Res; 20(4); 926–37. ©2013 AACR.

Inhibition of FGFR2 and FGFR1 increases cisplatin sensitivity in ovarian cancer

Fibroblast Growth Factors (FGFs) have been implicated in malignant transformation, tumour mitogenesis, angiogenesis and chemoresistance. The aim of this study was to determine which FGFs and FGFRs play functional roles in epithelial ovarian cancer. Restriction enzyme analysis of mRNA revealed that transformation was associated with a switch in FGFR2 and FGFR3, from the IIIc to the IIIb isoform. There was widespread expression of FGFs, including FGF7, in all tissues but, FGF3 and FGF19 were expressed by malignant cell lines and cancer tissue but were not present in normal tissue. Using FGFR-specific shRNAi we demonstrated that reductions in FGFR2 inhibited proliferation of ovarian cancer cell lines in vitro (>50%, p < 0.006), and reduced cisplatin IC50 (>60%, p < 0.0001). Cell cycle analysis revealed increased cisplatin sensitivity was associated with increased G2/M arrest and increased apoptosis. FGFR2 shRNAi reduced growth rates of ovarian tumour xenografts by 20% (p<0.006) and when combined with cisplatin caused a 40% reduction in proliferation rates (p<0.007). In contrast, RNAi-induced reductions in FGFR1 increased SKOV3 cell numbers, with associated changes in cell cycle but had no effect on ES2 cells. However, the cisplatin IC50 was reduced (>50%, p < 0.0001) by FGFR1 shRNAi in both cell lines and there was increased apoptosis (46-50%) compared with control cells (35%) (p < 0.004). Together our data suggest that combining FGFR2 inhibitors with platinum-containing cytotoxic agents for the treatment of epithelial ovarian cancer may yield increased anti-tumour activity. However, data on the inhibition of FGFR1 suggest that broad spectrum FGFR inhibitors may have unexpected effects on proliferation.

Preclinical evaluation of M30 and M65 ELISAs as biomarkers of drug induced tumor cell death and antitumor activity

M30 and M65 are ELISAs that detect different circulating forms of cytokeratin 18. Using the aurora kinase inhibitor AZD1152 and the SW620 human colon cancer xenograft, experiments were conducted to qualify preclinically both assays as serologic biomarkers of cell death. Using two different apoptotic markers, the kinetics of cell death induced by AZD1152 was first characterized in vitro in three different cell lines and shown to peak 5 to 7 days after drug addition. Treatment of non-tumor-bearing rats with AZD1152 (25 mg/kg) produced no alterations in circulating baseline values of M30 and M65 antigens. In treated, tumor-bearing animals, M30 detected a 2- to 3-fold (P < 0.05) increase in plasma antigen levels by day 5 compared with controls. This correlated to a 3-fold increase in the number of apoptotic cells detected on day 5 in SW620 xenografts using immunohistochemistry. By contrast, M65 did not detect a drug-induced increase in circulating antigen levels at day 5. However, M65 plasma levels correlated to changes in tumor growth in control animals (r2 = 0.93; P < 0.01) and also followed the magnitude of the temporal effect of AZD1152 on tumor growth. An intermediate but active dose of AZD1152 (12.5 mg/kg) produced a less significant increase in M30 plasma levels at day 5. It was also confirmed that the plasma profiles of M30 and M65 mirrored closely those measured in whole tumor lysates. We conclude that M30 is a pharmacodynamic biomarker of AZD1152-induced apoptosis in the SW620 xenograft model, whereas M65 is a biomarker of therapeutic response. [Mol Cancer Ther 2008;7(3):455–63]

Molecular analysis of circulating tumor cells identifies distinct copy-number profiles in patients with chemosensitive and chemorefractory small-cell lung cancer

In most patients with small-cell lung cancer (SCLC)—a metastatic, aggressive disease—the condition is initially chemosensitive but then relapses with acquired chemoresistance. In a minority of patients, however, relapse occurs within 3 months of initial treatment; in these cases, disease is defined as chemorefractory. The molecular mechanisms that differentiate chemosensitive from chemorefractory disease are currently unknown. To identify genetic features that distinguish chemosensitive from chemorefractory disease, we examined copy-number aberrations (CNAs) in circulating tumor cells (CTCs) from pretreatment SCLC blood samples. After analysis of 88 CTCs isolated from 13 patients (training set), we generated a CNA-based classifier that we validated in 18 additional patients (testing set, 112 CTC samples) and in six SCLC patient-derived CTC explant tumors. The classifier correctly assigned 83.3% of the cases as chemorefractory or chemosensitive. Furthermore, a significant difference was observed in progression-free survival (PFS) (Kaplan–Meier P value = 0.0166) between patients designated as chemorefractory or chemosensitive by using the baseline CNA classifier. Notably, CTC CNA profiles obtained at relapse from five patients with initially chemosensitive disease did not switch to a chemorefractory CNA profile, which suggests that the genetic basis for initial chemoresistance differs from that underlying acquired chemoresistance.

Hypoxic human cancer cells are sensitized to BH-3 mimetic–induced apoptosis via downregulation of the Bcl-2 protein Mcl-1

Solid tumors contain hypoxic regions in which cancer cells are often resistant to chemotherapy-induced apoptotic cell death. Therapeutic strategies that specifically target hypoxic cells and promote apoptosis are particularly appealing, as few normal tissues experience hypoxia. We have found that the compound ABT-737, a Bcl-2 homology domain 3 (BH-3) mimetic, promotes apoptotic cell death in human colorectal carcinoma and small cell lung cancer cell lines exposed to hypoxia. This hypoxic induction of apoptosis was mediated through downregulation of myeloid cell leukemia sequence 1 (Mcl-1), a Bcl-2 family protein that serves as a biomarker for ABT-737 resistance. Downregulation of Mcl-1 in hypoxia was independent of hypoxia-inducible factor 1 (HIF-1) activity and was consistent with decreased global protein translation. In addition, ABT-737 induced apoptosis deep within tumor spheroids, consistent with an optimal hypoxic oxygen tension being necessary to promote ABT-737–induced cell death. Tumor xenografts in ABT-737–treated mice also displayed significantly more apoptotic cells within hypoxic regions relative to normoxic regions. Synergies between ABT-737 and other cytotoxic drugs were maintained in hypoxia, suggesting that this drug may be useful in combination with chemotherapeutic agents. Taken together, these findings suggest that Mcl-1–sparing BH-3 mimetics may induce apoptosis in hypoxic tumor cells that are resistant to other chemotherapeutic agents and may have a role in combinatorial chemotherapeutic regimens for treatment of solid tumors.

Noninvasive tumor hypoxia measurement using magnetic resonance imaging in murine U87 glioma xenografts and in patients with glioblastoma.

There is a clinical need for noninvasive, nonionizing imaging biomarkers of tumor hypoxia and oxygenation. We evaluated the relationship of T1‐weighted oxygen‐enhanced magnetic resonance imaging (OE‐MRI) measurements to histopathology measurements of tumor hypoxia in a murine glioma xenograft and demonstrated technique translation in human glioblastoma multiforme.

Non-invasive tumor hypoxia measurement using magnetic resonance imaging in mouse and human glioblastoma

There is a clinical need for noninvasive, nonionizing imaging biomarkers of tumor hypoxia and oxygenation. We evaluated the relationship of T1‐weighted oxygen‐enhanced magnetic resonance imaging (OE‐MRI) measurements to histopathology measurements of tumor hypoxia in a murine glioma xenograft and demonstrated technique translation in human glioblastoma multiforme.

Blocking Phosphoinositide 3-Kinase Activity in Colorectal Cancer Cells Reduces Proliferation but Does Not Increase Apoptosis Alone or in Combination with Cytotoxic Drugs

In response to growth factors, class IA phosphoinositide 3-kinases (PI3K) phosphorylate phosphatidylinositol-4,5-bisphosphate, converting it to phosphatidylinositol-3,4,5-trisphosphate to activate protein kinase B/Akt. This is widely reported to promote tumorigenesis via increased cell survival, proliferation, migration, and invasion, and many tumor types, including colorectal cancer, exhibit increased PI3K signaling. To investigate the effect of inhibiting PI3K and as an alternative to the use of small molecular inhibitors of PI3K with varying degrees of selectivity, HT29 and HCT116 colorectal cancer cells bearing mutant PIK3CA were generated that could be induced with doxycycline to express synchronously a dominant negative subunit of PI3K, Δp85α. On induction, decreased levels of phosphorylated protein kinase B were detected, confirming PI3K signaling impairment. Induction of Δp85α in vitro reduced cell number via accumulation in G0-G1 phase of the cell cycle in the absence of increased apoptosis. These effects were recapitulated in vivo. HT29 cells expressing Δp85α and grown as tumor xenografts had a significantly slower growth rate on administration of doxycycline with reduced Ki67 staining without increased levels of apoptotic tissue biomarkers. Furthermore, in vitro Δp85α expression did not sensitize HT29 cells to oxaliplatin- or etoposide-induced apoptosis, irrespective of drug treatment schedule. Further analysis comparing isogenic HCT116 cells with and without mutation in PIK3CA showed no effect of the mutation in either proliferative or apoptotic response to PI3K inhibition. These data show in colorectal cancer cells that PI3K inhibition does not provoke apoptosis per se nor enhance oxaliplatin- or etoposide-induced cell death. (Mol Cancer Res 2009;7(6):955–65)

Specific demonstration of drug-induced tumour cell apoptosis in human xenografts models using a plasma biomarker

Pharmacodynamic (PD) assays should be used before advancing new drugs to clinical trials. Most PD assays measure the response to drugs in tissue, a procedure which requires tissue biopsies. The M30-Apoptosense ELISA is a PD biomarker assay for the quantitative determination of caspase-cleaved cytokeratin 18 (CK18) released from apoptotic carcinoma cells into blood. We here demonstrate that whereas the M30-Apoptosense ELISA assay detects human caspase-cleaved CK18, the mouse and rat CK18 caspase cleavage products are detected with low affinity. The M30-Apoptosense ELISA therefore facilitates the determination of drug-induced apoptosis in human tumour xenografts in rodents using plasma samples, largely independently from host toxicity. Increases of caspase-cleaved CK18 were observed in plasma from different carcinoma xenograft models in response to anticancer drugs. The appearance caspase-cleaved CK18 in plasma was found to reflect formation of the caspase-cleaved epitope in FaDu head-neck carcinomas and in cultured cells. The M30-Apoptosense assay allows determination of tumour response in blood from xenograft models and from patients, providing a powerful tool for translational studies of anticancer drugs.

A caspase-3 ?death-switch? in colorectal cancer cells for induced and synchronous tumor apoptosis in vitro and in vivo facilitates the development of minimally invasive cell death biomarkers

Novel anticancer drugs targeting key apoptosis regulators have been developed and are undergoing clinical trials. Pharmacodynamic biomarkers to define the optimum dose of drug that provokes tumor apoptosis are in demand; acquisition of longitudinal tumor biopsies is a significant challenge and minimally invasive biomarkers are required. Considering this, we have developed and validated a preclinical ‘death-switch’ model for the discovery of secreted biomarkers of tumour apoptosis using in vitro proteomics and in vivo evaluation of the novel imaging probe [18F]ML-10 for non-invasive detection of apoptosis using positron emission tomography (PET). The ‘death-switch’ is a constitutively active mutant caspase-3 that is robustly induced by doxycycline to drive synchronous apoptosis in human colorectal cancer cells in vitro or grown as tumor xenografts. Death-switch induction caused caspase-dependent apoptosis between 3 and 24 hours in vitro and regression of ‘death-switched’ xenografts occurred within 24 h correlating with the percentage of apoptotic cells in tumor and levels of an established cell death biomarker (cleaved cytokeratin-18) in the blood. We sought to define secreted biomarkers of tumor apoptosis from cultured cells using Discovery Isobaric Tag proteomics, which may provide candidates to validate in blood. Early after caspase-3 activation, levels of normally secreted proteins were decreased (e.g. Gelsolin and Midkine) and proteins including CD44 and High Mobility Group protein B1 (HMGB1) that were released into cell culture media in vitro were also identified in the bloodstream of mice bearing death-switched tumors. We also exemplify the utility of the death-switch model for the validation of apoptotic imaging probes using [18F]ML-10, a PET tracer currently in clinical trials. Results showed increased tracer uptake of [18F]ML-10 in tumours undergoing apoptosis, compared with matched tumour controls imaged in the same animal. Overall, the death-switch model represents a robust and versatile tool for the discovery and validation of apoptosis biomarkers.