Abstract 5327: In vivo fluorescence imaging of solid tumor-bisphosphonate interaction

Abstract Bisphosphonates are used for the osteoporosis and in palliative cancer related bone pain management. A role in the cancer cell proliferation and metastases prevention has been proposed. Here, we determined the possibility of utilizing NIR dye conjugated bisphosphonate drug as a potential theragnostic agent. Alendronate was conjugated to water soluble, near-infrared tricarbocyanine, cyclic enamine-functionalized dye, and the imaging probe was used for the purpose. Near-infrared (NIR) fluorescence imaging of both LNCaP cells in cell culture and grown orthotopically in nude mice indicate NIR-bisphosphonate binding. Both in vivo and ex vivo NIRF image analysis of 4 nmol of NIR conjugate delivery show substantial tumor residence time and routine biodistribution to areas of high metabolic bone activity. We present here early evidence of NIR-bisphosphonate analog as a potential diagnostic tool. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5327. doi:10.1158/1538-7445.AM2011-5327</jats:p

Noninvasive Assessment of Tumor VEGF Receptors in Response to Treatment with Pazopanib: A Molecular Imaging Study1

Vascular endothelial growth factor (VEGF) and its receptors (VEGFRs) drive angiogenesis, and several VEGFR inhibitors are already approved for use as single agents or in combination with chemotherapy. Although there is a clear benefit with these drugs in a variety of tumors, the clinical response varies markedly among individuals. Therefore, there is a need for an efficient method to identify patients who are likely to respond to antiangiogenic therapy and to monitor its effects over time. We have recently developed a molecular imaging tracer for imaging VEGFRs known as scVEGF/99mTc; an engineered single-chain (sc) form of VEGF radiolabeled with technetium Tc 99m (99mTc). After intravenous injection, scVEGF/99mTc preferentially binds to and is internalized by VEGFRs expressed within tumor vasculature, providing information on prevalence of functionally active receptors. We now report that VEGFR imaging readily detects the effects of pazopanib, a small-molecule tyrosine kinase inhibitor under clinical development, which selectively targets VEGFR, PDGFR, and c-Kit in mice with HT29 tumor xenografts. Immunohistochemical analysis confirmed that the changes in VEGFR imaging reflect a dramatic pazopanib-induced decrease in the number of VEGFR-2+/CD31+ endothelial cells (ECs) within the tumor vasculature followed by a relative increase in the number of ECs at the tumor edges. We suggest that VEGFR imaging can be used for the identification of patients that are responding to VEGFR-targeted therapies and for guidance in rational design, dosing, and schedules for combination regimens of antiangiogenic treatment

Chemosensitivity of rat medullary raphe neurones in primary tissue culture

The medullary raphe, within the ventromedial medulla (VMM), contains putative central respiratory chemoreceptors. To study the mechanisms of chemosensitivity in the raphe, rat VMM neurones were maintained in primary dissociated tissue culture, and studied using perforated patch-clamp recordings. Baseline electrophysiological properties were similar to raphe neurones in brain slices and in vivo.Neurones were exposed to changes in CO2 from 5% to 3 or 9% while maintaining a constant [NaHCO3]. Fifty-one per cent of neurones (n = 210) did not change their firing rate by more than 20% in response to hypercapnic acidosis. However, 22% of neurones responded to 9% CO2 with an increase in firing rate (‘stimulated’), and 27% of neurones responded with a decrease in firing rate (‘inhibited’).Chemosensitivity has often been considered an all-or-none property. Instead, a method was developed to quantify the degree of chemosensitivity. Stimulated neurones had a mean increase in firing rate to 298 ± 215% of control when pH decreased from 7.40 to 7.19. Inhibited neurones had a mean increase in firing rate to 232 ± 265% of control when pH increased from 7.38 to 7.57.Neurones were also exposed to isocapnic acidosis. All CO2-stimulated neurones tested (n = 15) were also stimulated by isocapnic acidosis, and all CO2-inhibited neurones tested (n = 19) were inhibited by isocapnic acidosis. Neurones with no response to hypercapnic acidosis also had no response to isocapnic acidosis (n = 12). Thus, the effects of CO2 on these neurones were mediated in part via changes in pH.In stimulated neurones, acidosis induced a small increase in the after-hyperpolarization level of 1.38 ± 1.15 mV per −0.2 pH units, which was dependent on the level of tonic depolarizing current injection. In voltage clamp mode at a holding potential near resting potential, there were small and inconsistent changes in whole-cell conductance and holding current in both stimulated and inhibited neurones. These results suggest that pH modulates a conductance in stimulated neurones that is activated during repetitive firing, with a reversal potential close to resting potential.The two subtypes of chemosensitive VMM neurones could be distinguished by characteristics other than their response to acidosis. Stimulated neurones had a large multipolar soma, whereas inhibited neurones had a small fusiform soma. Stimulated neurones were more likely than inhibited neurones to fire with the highly regular pattern typical of serotonergic raphe neurones in vivo.Within the medullary raphe, chemosensitivity is a specialization of two distinct neuronal phenotypes. The response of these neurones to physiologically relevant changes in pH is of the magnitude that suggests that this chemosensitivity plays a functional role. Elucidating their mechanisms in vitro may help to define the cellular mechanisms of central chemoreception in vivo

Chaperone-Targeting Cytotoxin and Endoplasmic Reticulum Stress-Inducing Drug Synergize to Kill Cancer Cells12

Diverse physiological and therapeutic insults that increase the amount of unfolded or misfolded proteins in the endoplasmic reticulum (ER) induce the unfolded protein response, an evolutionarily conserved protective mechanism that manages ER stress. Glucose-regulated protein 78/immunoglobulin heavy-chain binding protein (GRP78/BiP) is an ER-resident protein that plays a central role in the ER stress response and is the only known substrate of the proteolytic A subunit (SubA) of a novel bacterial AB5 toxin. Here, we report that an engineered fusion protein, epidermal growth factor (EGF)-SubA, combining EGF and SubA, is highly toxic to growing and confluent epidermal growth factor receptor-expressing cancer cells, and its cytotoxicity is mediated by a remarkably rapid cleavage of GRP78/BiP. Systemic delivery of EGF-SubA results in a significant inhibition of human breast and prostate tumor xenografts in mouse models. Furthermore, EGF-SubA dramatically increases the sensitivity of cancer cells to the ER stress-inducing drug thapsigargin, and vice versa, demonstrating the first example of mechanism-based synergism in the action of a cytotoxin and an ER-targeting drug