Cancer metastasis is a multi–step process that initiates with a tumor cell obtaining the ability to migrate. A multitude of changes occur in such a cell including changes to cell adhesion molecules such as integrins. In cancer cells, integrins are known to be involved in migration, invasion and metastasis. Investigation by our group of the α6 integrin led to the discovery of a cleaved form of the integrin lacking the ligand binding domain, called α6p. While it is known that the integrin is cleaved by urokinase plasminogen activator (uPA) little is known about how this process is regulated. There is a need to better understand the players involved in regulation of α6 cleavage as inhibiting this event from occurring may contribute to prolonged or increased patient survival or ultimately a cure.The existence of the integrin–actin complex has been known for many years. In this study actin was identified as a potential regulator of α6 cleavage. Using a diverse set of tumor cell lines (DU145, PC3 and MDA–MB–231) and a number of actin modifing compounds (latrunculin A, jasplakinolide and siRNA) it is reported here that disassembling actin filaments leads to an increase in α6p production. Although the increase in cleavage product did not always correlate with an increase in uPA receptor, an increase in uPAR was observed when actin was complexed by small molecule inhibitors. Taken together the results demonstrate a potential role for actin filaments to protect α6 integrin from uPA–uPAR induced cleavage via a multi–protein complex.

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The plasminogen activator (PA) system plays an important role in cell adhesion, migration and invasion, and may require the coordinated expression of various proteins. The human urokinase-type plasminogen activator (uPA) receptor (uPAR) is a central protein component of the PA system. By binding its ligand uPA, uPAR can direct proteolysis of the extracellular matrix. Also, it is now apparent that uPAR can initiate proteolytic independent signal transduction to influence angiogenesis, inflammation, wound repair and tumour progression. To determine whether any novel proteins interacted with uPAR, a yeast two-hybrid screening analysis was undertaken using alternate uPAR domain constructs as baits. These included full-length three domain uPAR (uPAR-DIDIIDIII), two domain uPAR (uPAR-DIIDIII), and each individual uPAR domain (uPAR-DI, uPAR-DII and uPAR-DIII). A number of proteins were identified as putative candidate interactors for the alternate constructs, with two of special interest for uPAR-DIDIIDIII. These were the heat shock protein Mrj, and the extracellular matrix protein fibulin-2. The protein Mrj was shown to bind uPAR both in vitro and in vivo using GST-pull down and co-immunoprecipitation assays respectively. The GST-pull down assay identified the interaction between Mrj and uPAR dependent on the C-terminal domain of Mrj and DI of uPAR. Using in vivo co-immunoprecipitation analysis, Mrj also bound to uPAR. Preliminary data suggest the association between uPAR and Mrj may play a role in the regulation of apoptosis. In regard to the uPAR interactor of fibulin-2, a calcium dependent binding interaction with uPAR was identified using the GST-pull down assay. However due to the large molecular weight and stringent conditions needed to solubilise fibulin-2, it was not possible to co-immunoprecipitate both uPAR and fibulin-2. Together, the identification of both Mrj and fibulin-2 amongst other candidate interactors of uPAR presented here provides further insight into the intricate relationship between uPAR and other proteins which may influence a range of biological functions.

Breast cancer remains the most commonly diagnosed cancer among women over the age of 20, as recently reported by the Canadian Cancer Society. Studies have shown a strong correlation between early detection and increased survival rates thus it is important to have a means to adequately screen and detect breast cancer. Currently, tests are limited to traditional imaging methods such as ultrasound (US), magnetic resonance imaging (MRI) and standard mammography. There remains a need for a molecular imaging probe that is capable of providing further prognostic information particularly with respect to assessing tumour aggressiveness and the likelihood of a cancer to metastasize. Overexpression of the insulin receptor (IR) has been detailed in patients with breast cancer but there is currently no means of non-invasive and quantifiable detection of the receptor. The goal of the work described here was to prepare an insulin derived nuclear imaging probe via direct coupling of a prosthetic group bearing a radionuclide to the B29 lysine (B29-Lys) residue of the hormone. Benzoic acid bearing halogens were chosen as model compounds. The lead candidate N-[4-fluorobenzoyl]-(B29-Lys) insulin (4) was prepared in 60% overall yield and showed affinity for the IR similar to that of native insulin (IC50=3.6 nM). The 18F analogue (9) was successfully synthesized and showed high stability (up to 4 hours) post formulation in both saline and phosphate buffered solution (PBS). The product represents a promising new probe for assessing the role of the IR in cancer growth and metastasis. A complementary strategy for imaging markers of tumour aggressiveness was investigated through the development of a novel ultrasound probe. A pretargeting approach involving urokinase plasminogen activator receptor (uPAR), which is known to play a role in cancer metastasis, was used to develop the agent of interest. Here an in vivo reaction between tetrazine tagged microbubbles (MBs) and anti-uPAR antibodies conjugated to trans-cyclooctene (TCO) was employed. Following preparation of the antibody conjugate and tetrazine functionalized MBs, preliminary in vitro testing in a flow cell system was conducted. Results showed the ability of the uPAR expressing cells to exclusively capture the tetrazine MBs after they have been previously incubated with the TCO anti-uPAR antibody. No capture was observed when the target and/or the antibody were absent. The contrast agent developed represents the first MB targeted against uPAR and has the potential to impact current diagnostic paradigms particularly given the widespread use of ultrasound in cancer patient management. / Thesis / Master of Science (MSc)

Despite recent advances in early detection, in 2017 prostate cancer is estimated to claim over 26,000 lives in the United States alone. Prostate cancer related morbidity and mortality is a result of secondary skeletal metastasis. Therefore, better understanding of the underlying molecular mechanisms of prostate tumor cell migration and subsequent metastasis is vital for improved clinical outcomes. Interestingly, integrin α6, a laminin receptor, is highly expressed in a number of aggressive tumor types including prostate and is associated with increased metastasis and reduced patient survival. Preliminary studies by our group found that α6 integrin undergoes a post-translational modification mediated by the serine protease, uPA and its receptor, uPAR, leading to the cleavage of α6 integrin and production of the tumor specific structural variant integrin α6p. Cleavage of this laminin receptor and production of α6p variant gives rise to an aggressive phenotype, markedly increasing tumor cell migration and invasion. Thus, the work conducted here sought to identify the function and efficacy of these prominent proteins in various aspects of tumor cell migration as well as the factors regulating α6 integrin cleavage. Interestingly, utilization of a co-culture system of prostate tumor cells and macrophages found that a direct and indirect interaction between the two cell populations influenced α6 integrin cleavage. Specifically, prostate tumor cell interactions with macrophages, a known immune cell population that is highly observed in a number of primary tumors, resulted in increased protein levels of uPAR on the surface of prostate tumor cells that led to a significant production of α6p and subsequently increased invasion. Additionally, key downstream effectors of integrin signaling, including FAK, ILK, and actin, were found to regulate production of the tumor specific variant integrin α6p. Depletion of FAK, ILK, or actin, resulted in a significant increase in uPAR protein expression and subsequent α6 integrin cleavage, a regulatory event previously not known of these integrin signaling effector molecules. In addition, silencing of another prominently expressed laminin receptor, integrin α3β1, led to a significant increase in the cohesive collective phenotype exhibited by aggressive prostate tumor cells that was found to be facilitated by α6 integrin cleavage. Depletion of integrin α3β1 resulted in increased surface uPAR expression and increased lateral association with α6 integrin, which resulted in a striking increase in α6p production, a novel finding showing the regulation of one laminin receptor is dependent on the expression of another. Furthermore, the expression of α6 integrin as well as uPAR, was found to be highly expressed in aggressive pancreatic tumor cells. This expression pattern was found to significantly increase in response to the development of drug resistance and increased invasive potential. This finding showed a never before seen efficacy of integrin and uPAR expression in dictating acquired drug resistance in pancreatic tumor cells and demonstrates their potential use as prognostic biomarkers for acquired chemotherapy resistance. Taken together, the work conducted here illustrates the utility in further understanding the role of integrins and their regulation in mediating tumor cell migration and subsequent metastasis in the progression of aggressive epithelial cancers.

We defined how blood-derived vitronectin (VTN) rapidly and potently activates leukemia inhibitory factor (LIF) and pro-inflammatory interleukin 6 (IL-6) in vitro and after vascular injury in the brain. Treatment with VTN (but not fibrinogen, fibronectin, laminin-111 or collagen-I) substantially increased LIF and IL-6 within 4 h in C6-astroglioma cells, while VTN-/- mouse plasma was less effective than that from wild-type mice. LIF and IL-6 were induced by intracerebral injection of recombinant human (rh)VTN in mice, but induction seen upon intracerebral hemorrhage was less in VTN-/- mice than in wild-type littermates. In vitro, VTNeffects were inhibited by RGD, αvβ3 and αvβ5 integrin-blocking peptides and antibodies. VTN activated focal adhesion kinase (FAK; also known as PTK2), whereas pharmacological- or siRNA-mediated inhibition of FAK, but not PYK2, reduced the expression of LIF and IL-6 in C6 and endothelial cells and after traumatic cell injury.Dominant-negative FAK (Y397F) reduced the amount of injury-induced LIF and IL-6. Pharmacological inhibition or knockdown of uPAR (also known as PLAUR), which binds VTN, also reduced cytokine expression, possibly through a common target of uPAR and integrins. We propose that VTN leakage into tissues promotes inflammation. Integrin-FAKsignaling is therefore a novel IL-6 and LIF regulation mechanism relevant to the inflammation and stem cell fields.

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Indiana University-Purdue University Indianapolis (IUPUI) / Protein-protein interactions play a crucial role in a wide range of biological processes. Research on the design and synthesis of small molecules to modulate these proteinprotein interactions can lead to new targets and drugs to modulate their function. In Chapter one, we discuss the design and synthesis of small molecules to probe a proteinprotein interaction in a voltage-gated Ca2+ channel. Virtual screening identified a compound (BTT-3) that contained a 3,4-dihydro-3,4’-pyrazole core. This compound had modest biological activity when tested in a fluorescence polarization (FP) assay. The synthetic route to BTT-3 consisted of six steps. In addition, analogs of BTT-3 were made for a structure-activity study to establish the importance of a carboxylate moiety. We also synthesized a biotinylated benzophenone photo-affinity probe and linked it to BTT-3 to identify additional protein targets of the compound. In Chapter two, small-molecule antagonists targeting uPA-uPAR protein-protein interaction are presented. A total of 500 commercially-available compounds were previously identified by virtual screening and tested by a FP assay. Three classes of compounds were found with biological activity. The first class of compounds contains pyrrolidone core structures represented by IPR- 1110, the second class has a novel pyrrolo[3,4-c]pyrazole ring system, represented by xv IPR-1283 and the last series had compounds with a 1,2-disubstituted 1,2- dihydropyrrolo[3,4-b]indol-3(4H)-one core structure, represented by IPR-540. Each of these three compounds were synthesized and assessed by FP and ELISA assays. A binding mode of IPR-1110 with uPA was subsequently proposed. Based on this binding mode, another 61 IPR-1110 derivatives were synthesized by us to illustrate the SAR activity. Analogs of the other two series were also synthesized.