Karin Staflin

Activation of tumor cell integrin αvβ3 controls angiogenesis and metastatic growth in the brain

The incidence of brain metastasis is rising and poses a severe clinical problem, as we lack effective therapies and knowledge of mechanisms that control metastatic growth in the brain. Here we demonstrate a crucial role for high-affinity tumor cell integrin αvβ3 in brain metastatic growth and recruitment of blood vessels. Although αvβ3 is frequently up-regulated in primary brain tumors and metastatic lesions of brain homing cancers, we show that it is the αvβ3 activation state that is critical for brain lesion growth. Activated, but not non-activated, tumor cell αvβ3 supports efficient brain metastatic growth through continuous up-regulation of vascular endothelial growth factor (VEGF) protein under normoxic conditions. In metastatic brain lesions carrying activated αvβ3, VEGF expression is controlled at the post-transcriptional level and involves phosphorylation and inhibition of translational respressor 4E-binding protein (4E-BP1). In contrast, tumor cells with non-activated αvβ3 depend on hypoxia for VEGF induction, resulting in reduced angiogenesis, tumor cell apoptosis, and inefficient intracranial growth. Importantly, the microenvironment critically influences the effects that activated tumor cell αvβ3 exerts on tumor cell growth. Although it strongly promoted intracranial growth, the activation state of the receptor did not influence tumor growth in the mammary fat pad as a primary site. Thus, we identified a mechanism by which metastatic cells thrive in the brain microenvironment and use the high-affinity form of an adhesion receptor to grow and secure host support for proliferation. Targeting this molecular mechanism could prove valuable for the inhibition of brain metastasis.

Neural Progenitor Cell Lines Inhibit Rat Tumor Growth in Vivo

Current therapies for gliomas often fail to address their infiltrative nature. Conventional treatments leave behind small clusters of neoplastic cells, resulting in eventual tumor recurrence. In the present study, we have evaluated the antitumor activity of neural progenitor cells against gliomas when stereotactically injected into nucleus Caudatus of Fisher rats. We show that the rat neural progenitor cell lines HiB5 and ST14A, from embryonic hippocampus and striatum primordium, respectively, are able to prolong animal survival and, in 25% of the cases, completely inhibit the outgrowth of N29 glioma compared with control animals. Delayed tumor outgrowth was also seen when HiB5 cells were inoculated at the site of tumor growth 1 week after tumor inoculation or when a mixture of tumor cells and HiB5 cells were injected s.c. into Fisher rats. HiB5 cells were additionally coinoculated together with two alternative rat gliomas, N32 and N25. N32 was growth inhibited, but rats inoculated with N25 cells did not show a prolonged survival. To evaluate the possibility of the involvement of the immune system in the tumor outgrowth inhibition, we show that HiB5 cells do not evoke an immune response when injected into Fisher rats. Furthermore, the rat neural progenitor cells produce all transforming growth factor β isotypes, which could explain the observed immunosuppressive nature of these cells. Hence, some neural progenitor cells have the ability to inhibit tumor outgrowth when implanted into rats. These results indicate the usefulness of neural stem cells as therapeutically effective cells for the treatment of intracranial tumors.

Selective Formation of Covalent Protein Heterodimers with an Unnatural Amino Acid

We report a strategy for the generation of heterodimeric protein conjugates using an unnatural amino acid with orthogonal reactivity. This paper addresses the challenges of site-specificity and homogeneity with respect to the synthesis of bivalent proteins and antibody-drug conjugates. There are numerous antibody-drug conjugates in preclinical and clinical development, yet these are based either on nonspecific lysine coupling chemistry or on disulfide modification made difficult by the large number of cysteines in antibodies. Here, we describe a recombinant approach that can be used to rapidly generate a variety of constructs with defined conjugation sites. Moreover, this methodology results in homogeneous antibody conjugates whose biological, physical, and pharmacological properties can be quantitatively assessed and subsequently optimized. As proof of concept, we have generated anti-Her2 Fab-Saporin conjugates that demonstrate excellent potency in vitro.

Identification of proteins involved in neural progenitor cell targeting of gliomas

BackgroundGlioblastoma are highly aggressive tumors with an average survival time of 12 months with currently available treatment. We have previously shown that specific embryonic neural progenitor cells (NPC) have the potential to target glioma growth in the CNS of rats. The neural progenitor cell treatment can cure approximately 40% of the animals with malignant gliomas with no trace of a tumor burden 6 months after finishing the experiment. Furthermore, the NPCs have been shown to respond to signals from the tumor environment resulting in specific migration towards the tumor. Based on these results we wanted to investigate what factors could influence the growth and progression of gliomas in our rodent model.MethodsUsing microarrays we screened for candidate genes involved in the functional mechanism of tumor inhibition by comparing glioma cell lines to neural progenitor cells with or without anti-tumor activity. The expression of candidate genes was confirmed at RNA level by quantitative RT-PCR and at the protein level by Western blots and immunocytochemistry. Moreover, we have developed in vitro assays to mimic the antitumor effect seen in vivo.ResultsWe identified several targets involved in glioma growth and migration, specifically CXCL1, CD81, TPT1, Gas6 and AXL proteins. We further showed that follistatin secretion from the NPC has the potential to decrease tumor proliferation. In vitro co-cultures of NPC and tumor cells resulted in the inhibition of tumor growth. The addition of antibodies against proteins selected by gene and protein expression analysis either increased or decreased the proliferation rate of the glioma cell lines in vitro.ConclusionThese results suggest that these identified factors might be useful starting points for performing future experiments directed towards a potential therapy against malignant gliomas.

Activated tumor cell integrin αvβ3 cooperates with platelets to promote extravasation and metastasis from the blood stream

Metastasis is the main cause of death in cancer patients, and understanding mechanisms that control tumor cell dissemination may lead to improved therapy. Tumor cell adhesion receptors contribute to cancer spreading. We noted earlier that tumor cells can expressing the adhesion receptor integrin αvβ3 in distinct states of activation, and found that cells which metastasize from the blood stream express it in a constitutively high affinity form. Here, we analyzed steps of the metastatic cascade in vivo and asked, when and how the affinity state of integrin αvβ3 confers a critical advantage to cancer spreading. Following tumor cells by real time PCR, non-invasive bioluminescence imaging, intravital microscopy and histology allowed us to identify tumor cell extravasation from the blood stream as a rate-limiting step supported by high affinity αvβ3. Successful transendothelial migration depended on cooperation between tumor cells and platelets involving the high affinity tumor cell integrin and release of platelet granules. Thus, this study identifies the high affinity conformer of integrin αvβ3 and its interaction with platelets as critical for early steps during hematogenous metastasis and target for prevention of metastatic disease.

Instructive cross-talk between neural progenitor cells and gliomas

Gliomas are the most common primary brain tumors and offer a poor prognosis in patients because of their infiltrative and treatment‐resistant nature. The median survival time after diagnosis is approximately 11–12 months. There is a strong need for novel treatment modalities in targeting gliomas, and recent advances use neural progenitor cells as delivery systems for different therapeutic strategies. In this study, we show that rat embryonic neural progenitor cell (NPC) lines, transplanted at a distant site from a 3‐day‐preestablished glioma in the striatum, were able to migrate toward and colocalize with tumor isles without general spread into the brain parenchyma. Upon encounter with tumor, neural progenitor cells changed phenotype and became vimentin positive. These results demonstrate that transplanted neural progenitor cells respond to queues from a tumor and home to and exert an antitumor effect on the preestablished glioma, significantly decreasing the tumor volume with approximately 67% compared with control tumors after 1–2 weeks. Moreover, these early effects could be translated into increased survival times of animals treated with neural progenitor cell grafts 3 days after intrastriatal tumor inoculation. In contrast, there was no activation or migration of endogenous subventricular zone (SVZ) neuroblasts in response to an intrastriatal syngeneic tumor. In conclusion, NPC possess the ability to influence tumor growth as well as respond to queues from the tumor or tumor microenvironment, demonstrating a cross‐talk between the cells.

Absence of striatal newborn neurons with mature phenotype following defined striatal and cortical excitotoxic brain injuries

Experimental stroke and excitotoxic brain lesion to the striatum increase the proliferation of cells residing within the ventricular wall and cause subsequent migration of newborn neuroblasts into the lesioned brain parenchyma. In this study, we clarify the different events of neurogenesis following striatal or cortical excitotoxic brain lesions in adult rats. Newborn cells were labeled by intraperitoneal injection of bromo-deoxy-uridine (BrdU), or by green fluorescent protein (GFP)-expressing lentiviral vectors injected into the subventricular zone (SVZ). We show that only neural progenitors born the first 5 days in the SVZ reside and expand within this neurogenic niche over time, and that these early labeled cells are more prone to migrate towards the striatum as neuroblasts. However, these neuroblasts could not mature into NeuN+ neurons in the striatum. Furthermore, we found that cortical lesions, close or distant from the SVZ, could not upregulate SVZ cell proliferation nor promote neurogenesis. Our study demonstrates that both the time window for labeling proliferating cells and the site of lesion are crucial when assessing neurogenesis following brain injury.

Efficient transduction of neurons using Ross River glycoprotein-pseudotyped lentiviral vectors.

Lentiviral vectors are promising tools for CNS gene transfer since they efficiently transduce the cells of the nervous system in vivo. In this study, we have investigated the transduction efficiency of lentiviral vectors pseudotyped with Ross River virus glycoprotein (RRV-G) (RRV-G-pseudotyped lentiviral vectors (RRV-LV)). The RRV is an alphavirus with an extremely broad host range, including the cells of the central nervous system. Previous studies have shown that lentiviral vectors can be efficiently pseudotyped with this envelope protein and have demonstrated promising features of such vectors, including the possibility to establish stable producer cell lines. After injection of RRV-LV expressing green fluorescent protein into different structures in the rat brain we found efficient transduction of both neurons and glial cells. By using two cell-type-specific promoters, neuron-specific enolase and human glial fibrillary acidic protein, we demonstrated cell-specific transgene expression in the desired cell type. Ross River virus glycoprotein-pseudotyped lentiviral vectors also transduced human neural progenitor cells in vitro, showing that receptors for the RRV-G are present on human neural cells.

Targeting activated integrin αvβ3 with patient-derived antibodies impacts late-stage multiorgan metastasis

Advanced metastatic disease is difficult to manage and specific therapeutic targets are rare. We showed earlier that metastatic breast cancer cells use the activated conformer of adhesion receptor integrin αvβ3 for dissemination. We now investigated if targeting this form of the receptor can impact advanced metastatic disease, and we analyzed the mechanisms involved. Treatment of advanced multi-organ metastasis in SCID mice with patient-derived scFv antibodies specific for activated integrin αvβ3 caused stagnation and regression of metastatic growth. The antibodies specifically localized to tumor lesions in vivo and inhibited αvβ3 ligand binding at nanomolar levels in vitro. At the cellular level, the scFs associated rapidly with high affinity αvβ3 and dissociated extremely slowly. Thus, the scFvs occupy the receptor on metastatic tumor cells for prolonged periods of time, allowing for inhibition of established cell interaction with natural αvβ3 ligands. Potential apoptosis inducing effects of the antibodies through interaction with caspase-3 were studied as potential additional mechanism of treatment response. However, in contrast to a previous concept, neither the RGD-containing ligand mimetic scFvs nor RGD peptides bound or activated caspase-3 at the cellular or molecular level. This indicates that the treatment effects seen in the animal model are primarily due to antibody interference with αvβ3 ligation. Inhibition of advanced metastatic disease by treatment with cancer patient derived single chain antibodies against the activated conformer of integrin αvβ3 identifies this form of the receptor as a suitable target for therapy.

Abstract 5090: The role of p32 in brain metastasis

Brain metastases are among the most feared complication in cancer. To develop effective and targeted therapies for treatment of brain metastases, we need a better understanding of the mechanisms that control cancer cell growth within the brain microenvironment. We previously found evidence that brain metastatic cells have increased rates of oxidative phosphorylation and redox potential compared to tumor cells from extracranial lesions. Here we sought to identify mechanisms involved, and to identify potential targets for the inhibition of metastatic growth in the brain. Many of the genes involved in transformation such as Myc, AKT, and p53 have extensive effects on the metabolism, suggesting that tumors might be susceptible to antimetabolic drugs. One of the proteins that has been shown to be upregulated in many solid tumors is the protein p32. P32 is a multi-compartmental and multi-functional protein which has a regulatory function in oxidative phosphorylation, in addition to being involved in the regulation of apoptosis and autophagy. We found p32 expressed in human cancer cells capable of seeding brain metastases in immune deficient mice, and we hypothesized that p32 contributes to cell survival and proliferation within the brain microenvironment. We knocked down p32 in brain homing variants of the MDA-MB-231 and MDA-MB-435 metastasis cell models. Following luciferase tagged tumor cells by non-invasive bioluminescence imaging revealed that stable p32 knockdown greatly reduced metastatic activity in both MDA-MB-231 brain specific variant and the MDA-MB 435 cell line. Furthermore, our genomic profiling of p32 knock-down and control cells identified candidate genes in the respiration chain involved in p32-dependent tumor cell survival and growth that may impact progression to brain metastasis. Thus, the expression and functionality of p32 in tumor cells capable of colonizing the brain appears associated with changes in crucial pathways that enable the tumor cells to proliferate and survive within the brain microenvironment. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5090.