The insulin-like growth factor (IGF) pathway consists of two ligands (IGF-I and IGF-II), two receptors (IGF-IR and IGF-IIR) and six IGF binding proteins (IGFBP-I through -6). There is considerable evidence from both laboratory and population studies that IGF physiology is relevant to neoplastic growth. For example, it has been shown that IGF-I and/or IGF-II act as mitogens and anti-apoptotic agents for both normal and malignant cells by binding to the IGF-IR and activating downstream signalling pathways. Consistent with this data, IGF-IR inhibition by a variety of strategies inhibits cancer cell proliferation and/or induces apoptosis both in vitro and in animal models of neoplasia. Furthermore, epidemiological studies have demonstrated a positive correlation between serum IGF-I levels and risk of subsequent cancer. Classically, the IGFBPs were considered to be growth inhibitors, as they had a well-defined role in sequestering the mitogens IGF-I and IGF-II, therefore preventing binding and subsequent activation of mitogenic and anti-apoptotic pathways downstream of the IGF-IR. However, increasing evidence indicates that under certain conditions, IGFBPs can act as growth stimulators, and both IGF-dependent and -independent mechanisms have been proposed. / Although the roles of the IGFs, IGF-IR and IGFBPs in cancer have been studied extensively, this thesis describes several new links between IGF physiology and neoplasia. In the first section, we demonstrate that IGF-I can attenuate growth inhibition and apoptosis induced by a class of drugs called COX-2 inhibitors in BxPC-3 pancreatic cancer cells. This effect could be attributed to opposite influences of IGF-IR signalling and COX-2 inhibitors on activation of Akt, with IGF-IR signalling increasing activity and COX-2 inhibitors decreasing activity. In the second section, we demonstrate that in 184htert cells, an immortal but untransformed breast epithelial cell line, COX-2 inhibitors can induce IGFBP-3 expression. We go on to show that IGFBP-3 can inhibit growth of this cell line in an IGF-dependent manner, and speculate that this action of COX-2 inhibitors may be relevant to data linking use of this class of drugs to decreased breast cancer risk. In the third section, we demonstrate that the expression of IGFBP-2 in U251 glioma cells is inhibited by the induction of the tumor suppressor PTEN. Furthermore, IGFBP-2 does not effect the growth of this cell line, indicating that published associations between tumor IGFBP-2 expression and grade of glioma may be a result of IGFBP-2 acting as a marker for loss of function of PTEN. In the fourth and final section, we demonstrate that in MDA-MB-231 breast cancer cells, over-expression of IGFBP-2 can enhance growth, indicating that the effect of IGFBP-2 on growth of neoplastic cells is tissue specific. Furthermore, antisense strategies targeting IGFBP-2 mRNA (antisense oligonucleotides and siRNA) can inhibit growth of IGFBP-2-expressing breast cancer cells both in vitro and in vivo. / Taken together, these results extend the existing body of evidence demonstrating that IGF physiology contributes to neoplastic growth, and suggest that strategies to inhibit IGF-IR signalling and/or IGFBP-2 expression may have therapeutic value for some types of cancers.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.111826 |
| Date | January 2006 |
| Creators | Levitt, Randy J. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Experimental Medicine.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002330143, proquestno: AAINR25194, Theses scanned by UMI/ProQuest. |
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