Muhammad Babur

Combining radiotherapy with AZD2171, a potent inhibitor of vascular endothelial growth factor signaling: pathophysiologic effects and therapeutic benefit

AZD2171 is a highly potent, orally active inhibitor of vascular endothelial growth factor receptor signaling. The potential for AZD2171 to enhance the antitumor effects of radiotherapy was investigated in lung (Calu-6) and colon (LoVo) human tumor xenograft models. Combined treatment resulted in a significantly enhanced growth delay compared with either modality alone. The enhancement was independent of whether chronic once daily AZD2171 treatment was given 2 h prior to each radiation fraction (2 Gy daily for 3 or 5 consecutive days), and daily thereafter, or commenced immediately following the course of radiotherapy. Histologic assessments revealed that 5 days of radiation (2 Gy) or AZD2171 (3 or 6 mg/kg/d) reduced vessel density and perfusion. Concomitant AZD2171 and radiation enhanced this effect and produced a significant increase in tumor hypoxia. Concomitant AZD2171 (6 mg/kg/d) was also found to reduce tumor growth significantly during the course of radiotherapy (5 × 2 Gy). However, the extent and duration of tumor regression observed postradiotherapy was similar to sequentially treated tumors, suggesting that preirradiated tumors were sensitized to AZD2171 treatment. An enhanced antivascular effect of administering AZD2171 postradiotherapy was observed in real-time in Calu-6 tumors grown in dorsal window chambers. Collectively, these data support the clinical development of AZD2171 in combination with radiotherapy. [Mol Cancer Ther 2007;6(2):599–606]

Endothelial heparan sulfate 6-O-sulfation levels regulate angiogenic responses of endothelial cells to fibroblast growth factor 2 and vascular endothelial growth factor.

Background: Heparan sulfate (HS) is an essential regulator of multiple angiogenic growth factors. Results: Down-regulation of 6-O-sulfation in endothelial cell HS affects FGF2- and VEGF-mediated endothelial cell functions. Conclusion: The level of 6-O-sulfation in specific HS domains regulates endothelial cell responses to angiogenic growth factors. Significance: The relationships between 6-O-sulfation and endothelial phenotypes could help to design HS sequences inhibiting angiogenic growth factors. Fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor 165 (VEGF165) are potent pro-angiogenic growth factors that play a pivotal role in tumor angiogenesis. The activity of these growth factors is regulated by heparan sulfate (HS), which is essential for the formation of FGF2/FGF receptor (FGFR) and VEGF165/VEGF receptor signaling complexes. However, the structural characteristics of HS that determine activation or inhibition of such complexes are only partially defined. Here we show that ovarian tumor endothelium displays high levels of HS sequences that harbor glucosamine 6-O-sulfates when compared with normal ovarian vasculature where these sequences are also detected in perivascular area. Reduced HS 6-O-sulfotransferase 1 (HS6ST-1) or 6-O-sulfotransferase 2 (HS6ST-2) expression in endothelial cells impacts upon the prevalence of HS 6-O-sulfate moieties in HS sequences, which consist of repeating short, highly sulfated S domains interspersed by transitional N-acetylated/N-sulfated domains. 1–40% reduction in 6-O-sulfates significantly compromises FGF2- and VEGF165-induced endothelial cell sprouting and tube formation in vitro and FGF2-dependent angiogenesis in vivo. Moreover, HS on wild-type neighboring endothelial or smooth muscle cells fails to restore endothelial cell sprouting and tube formation. The affinity of FGF2 for HS with reduced 6-O-sulfation is preserved, although FGFR1 activation is inhibited correlating with reduced receptor internalization. These data show that 6-O-sulfate moieties in endothelial HS are of major importance in regulating FGF2- and VEGF165-dependent endothelial cell functions in vitro and in vivo and highlight HS6ST-1 and HS6ST-2 as potential targets of novel antiangiogenic agents.

GDC-0941 inhibits metastatic characteristics of thyroid carcinomas by targeting both the phosphoinositide-3 kinase (PI3K) and hypoxia-inducible factor-1α (HIF-1α) pathways.

CONTEXT Phosphoinositide 3-kinase (PI3K) regulates the transcription factor hypoxia-inducible factor-1 (HIF-1) in thyroid carcinoma cells. Both pathways are associated with aggressive phenotype in thyroid carcinomas. OBJECTIVE Our objective was to assess the effects of the clinical PI3K inhibitor GDC-0941 and genetic inhibition of PI3K and HIF on metastatic behavior of thyroid carcinoma cells in vitro and in vivo. DESIGN Vascular endothelial growth factor ELISA, HIF activity assays, proliferation studies, and scratch-wound migration and cell spreading assays were performed under various O(2) tensions [normoxia, hypoxia (1 and 0.1% O(2)), and anoxia] with or without GDC-0941 in a panel of four thyroid carcinoma cell lines (BcPAP, WRO, FTC133, and 8505c). Genetic inhibition was achieved by overexpressing phosphatase and tensin homolog (PTEN) into PTEN-null cells and by using a dominant-negative variant of HIF-1α (dnHIF). In vivo, human enhanced green fluorescence protein-expressing follicular thyroid carcinomas (FTC) were treated with GDC-0941 (orally). Spontaneous lung metastasis was confirmed by viewing enhanced green fluorescence protein-positive colonies cultured from lung tissue. RESULTS GDC-0941 inhibited hypoxia/anoxia-induced HIF-1α and HIF-2α expression and HIF activity in thyroid carcinoma cells. Basal (three of four cell lines) and/or hypoxia-induced (four of four) secreted vascular endothelial growth factor was inhibited by GDC-0941, whereas selective HIF targeting predominantly affected hypoxia/anoxia-mediated secretion (P < 0.05-0.0001). Antiproliferative effects of GDC-0941 were more pronounced in PTEN mutant compared with PTEN-restored cells (P < 0.05). Hypoxia increased migration in papillary cells and cell spreading/migration in FTC cells (P < 0.01). GDC-0941 reduced spreading and migration in all O(2) conditions, whereas dnHIF had an impact only on hypoxia-induced migration (P < 0.001). In vivo, GDC-0941 reduced expression of HIF-1α, phospho-AKT, GLUT-1, and lactate dehydrogenase A in FTC xenografts. DnHIF expression and GDC-0941 reduced FTC tumor growth and metastatic lung colonization (P < 0.05). CONCLUSIONS PI3K plays a prominent role in the metastatic behavior of thyroid carcinoma cells irrespective of O(2) tension and appears upstream of HIF activation. GDC-0941 significantly inhibited the metastatic phenotype, supporting the clinical development of PI3K inhibition in thyroid carcinomas.

Hypoxia-inducible factor in thyroid carcinoma.

Intratumoural hypoxia (low oxygen tension) is associated with aggressive disease and poor prognosis. Hypoxia-inducible factor-1 is a transcription factor activated by hypoxia that regulates the expression of genes that promote tumour cell survival, progression, metastasis, and resistance to chemo/radiotherapy. In addition to hypoxia, HIF-1 can be activated by growth factor-signalling pathways such as the mitogen-activated protein kinases- (MAPK-) and phosphatidylinositol-3-OH kinases- (PI3K-) signalling cascades. Mutations in these pathways are common in thyroid carcinoma and lead to enhanced HIF-1 expression and activity. Here, we summarise current data that highlights the potential role of both hypoxia and MAPK/PI3K-induced HIF-1 signalling in thyroid carcinoma progression, metastatic characteristics, and the potential role of HIF-1 in thyroid carcinoma response to radiotherapy. Direct or indirect targeting of HIF-1 using an MAPK or PI3K inhibitor in combination with radiotherapy may be a new potential therapeutic target to improve the therapeutic response of thyroid carcinoma to radiotherapy and reduce metastatic burden.

[18F]-FLT Positron Emission Tomography can be used to image the response of sensitive tumors to PI3-Kinase inhibition with the novel agent GDC-0941.

The phosphoinositide 3-kinase (PI3K) pathway is deregulated in a range of cancers, and several targeted inhibitors are entering the clinic. This study aimed to investigate whether the positron emission tomography tracer 3′-deoxy-3′-[18F]fluorothymidine ([18F]-FLT) is suitable to mark the effect of the novel PI3K inhibitor GDC-0941, which has entered phase II clinical trial. CBA nude mice bearing U87 glioma and HCT116 colorectal xenografts were imaged at baseline with [18F]-FLT and at acute (18 hours) and chronic (186 hours) time points after twice-daily administration of GDC-0941 (50 mg/kg) or vehicle. Tumor uptake normalized to blood pool was calculated, and tissue was analyzed at sacrifice for PI3K pathway inhibition and thymidine kinase (TK1) expression. Uptake of [18F]-FLT was also assessed in tumors inducibly overexpressing a dominant-negative form of the PI3K p85 subunit p85α, as well as HCT116 liver metastases after GDC-0941 therapy. GDC-0941 treatment induced tumor stasis in U87 xenografts, whereas inhibition of HCT116 tumors was more variable. Tumor uptake of [18F]-FLT was significantly reduced following GDC-0941 dosing in responsive tumors at the acute time point and correlated with pharmacodynamic markers of PI3K signaling inhibition and significant reduction in TK1 expression in U87, but not HCT116, tumors. Reduction of PI3K signaling via expression of Δp85α significantly reduced tumor growth and [18F]-FLT uptake, as did treatment of HCT116 liver metastases with GDC-0941. These results indicate that [18F]-FLT is a strong candidate for the noninvasive measurement of GDC-0941 action. Mol Cancer Ther; 12(5); 819–28. ©2013 AACR.

Detection of apoptosis by PET/CT with the diethyl ester of [18F]ML-10 and fluorescence imaging with a dansyl analogue

The diethyl ester of [(18)F]ML-10 is a small molecule apoptotic PET probe for cancer studies. Here we report a novel multi-step synthesis of the diethyl ester of ML-10 in excellent yields via fluorination using Xtal-Fluor-E. In addition, a one-pot radiosynthesis of the diethyl ester of [(18)F]ML-10 from nucleophilic [(18)F]fluoride was completed in 23% radiochemical yield (decay corrected). The radiochemical purity of the product was ≥99%. The diethyl ester of [(18)F]ML-10 was used in vivo to detect apoptosis in the testes of mice. In parallel studies, the dansyl-ML-10 diethyl ester was prepared and used to detect apoptotic cells in an in vitro cell based assay.

Vasoactivity of Rucaparib, a PARP-1 Inhibitor, is a Complex Process that Involves Myosin Light Chain Kinase, P2 Receptors, and PARP Itself

Therapeutic inhibition of poly(ADP-ribose) polymerase (PARP), as monotherapy or to supplement the potencies of other agents, is a promising strategy in cancer treatment. We previously reported that the first PARP inhibitor to enter clinical trial, rucaparib (AG014699), induced vasodilation in vivo in xenografts, potentiating response to temozolomide. We now report that rucaparib inhibits the activity of the muscle contraction mediator myosin light chain kinase (MLCK) 10-fold more potently than its commercially available inhibitor ML-9. Moreover, rucaparib produces additive relaxation above the maximal degree achievable with ML-9, suggesting that MLCK inhibition is not solely responsible for dilation. Inhibition of nitric oxide synthesis using L-NMMA also failed to impact rucaparib’s activity. Rucaparib contains the nicotinamide pharmacophore, suggesting it may inhibit other NAD+-dependent processes. NAD+ exerts P2 purinergic receptor-dependent inhibition of smooth muscle contraction. Indiscriminate blockade of the P2 purinergic receptors with suramin abrogated rucaparib-induced vasodilation in rat arterial tissue without affecting ML-9-evoked dilation, although the specific receptor subtypes responsible have not been unequivocally identified. Furthermore, dorsal window chamber and real time tumor vessel perfusion analyses in PARP-1-/- mice indicate a potential role for PARP in dilation of tumor-recruited vessels. Finally, rucaparib provoked relaxation in 70% of patient-derived tumor-associated vessels. These data provide tantalising evidence of the complexity of the mechanism underlying rucaparib-mediated vasodilation.

Irradiation Decreases the Neuroendocrine Biomarker Pro-Opiomelanocortin in Small Cell Lung Cancer Cells In Vitro and In Vivo

Background Small cell lung cancer (SCLC) is an extremely aggressive disease, commonly displaying therapy-resistant relapse. We have previously identified neuroendocrine and epithelial phenotypes in SCLC tumours and the neuroendocrine marker, pro-opiomelanocortin (POMC), correlated with worse overall survival in patients. However, the effect of treatment on these phenotypes is not understood. The current study aimed to determine the effect of repeated irradiation treatment on SCLC cell phenotype, focussing on the neuroendocrine marker, POMC. Results Human SCLC cells (DMS 79) were established as subcutaneous xenograft tumours in CBA nude mice and then exposed to repeated 2Gy irradiation. In untreated animals, POMC in the blood closely mirrored tumour growth; an ideal characteristic for a circulating biomarker. Following repeated localised irradiation in vivo, circulating POMC decreased (p< 0.01), in parallel with a decrease in tumour size, but remained low even when the tumours re-established. The excised tumours displayed reduced and distinctly heterogeneous expression of POMC compared to untreated tumours. There was no difference in the epithelial marker, cytokeratin. However, there were significantly more N-cadherin positive cells in the irradiated tumours. To investigate the tumour response to irradiation, DMS79 cells were repeatedly irradiated in vitro and the surviving cells selected. POMC expression was reduced, while mesenchymal markers N-cadherin, β1-integrin, fibroblast-specific protein 1, β-catenin and Zeb1 expression were amplified in the more irradiation-primed cells. There were no consistent changes in epithelial marker expression. Cell morphology changed dramatically with repeatedly irradiated cells displaying a more elongated shape, suggesting a switch to a more mesenchymal phenotype. Conclusions In summary, POMC biomarker expression and secretion were reduced in SCLC tumours which regrew after irradiation and in repeatedly irradiation (irradiation-primed) cells. Therefore, POMC was no longer predictive of tumour burden. This highlights the importance of fully evaluating biomarkers during and after therapy to assess clinical utility. Furthermore, the gain in mesenchymal characteristics in irradiated cells could be indicative of a more invasive phenotype.

Data-driven mapping of hypoxia-related tumor heterogeneity using DCE-MRI and OE-MRI

Previous work has shown that combining dynamic contrast‐enhanced (DCE)‐MRI and oxygen‐enhanced (OE)‐MRI binary enhancement maps can identify tumor hypoxia. The current work proposes a novel, data‐driven method for mapping tissue oxygenation and perfusion heterogeneity, based on clustering DCE/OE‐MRI data.

Dissemination via the lymphatic or angiogenic route impacts the pathology, microenvironment and hypoxia-related drug response of lung metastases

Complications associated with the development of lung metastases have a detrimental effect on the overall survival rate of many cancer patients. Preclinical models that mimic the clinical aspects of lung metastases are an important tool in developing new therapy options for these patients. The commonly used intravenous models only recapitulate dissemination of cancer cells to the lungs via the haematological route. Here we compared spontaneous and intravenous lung metastases of the highly metastatic KHT mouse fibrosarcoma cells after injecting KHT cells into the subcutaneous layer of the skin or directly into the tail vein. In contrast to the intravenous model, metastases spontaneously arising from the subcutaneous tumours disseminated most consistent with the lymph nodes/lymphatics route and were more hypoxic than the metastases observed following tail-vein administration and haematological spread. To ascertain whether this impacted on drug response, we tested the effectiveness of the hypoxia-sensitive cytotoxin AQ4N (Banoxantrone) in both models. AQ4N was more effective as an anti-metastatic drug in mice with subcutaneous KHT tumours, significantly reducing the metastatic score. Complementing the KHT studies, pathology studies in additional models of spontaneous lung metastases showed haematological (HCT116 intrasplenic implant) or mixed haematological/lymphatic (B16 intradermal implant) spread. These data suggest that preclinical models can demonstrate differing, clinically relevant dissemination patterns, and that careful selection of preclinical models is required when evaluating new strategies for targeting metastatic disease.