| Abstract |
Metastasis and drug resistance present as major problems to patients
during cancer chemotherapy. The research outlined in this thesis aims to
further our knowledge about the molecular mechanisms involved in these
processes and the relationship between drug resistance and cancer invasion
and/or metastasis. One explanation for the link between resistance and
metastasis is that resistance facilitates tumour progression and invasion
into both surrounding and distal tissues. Investigations were conducted on
a clonal sub-population of poorly differentiated human lung squamous
carcinoma cells (DLKP). These were pulsed with mitoxantrone and the
resulting cell populations extensively characterised. Two sub-lines
emerged: SQ-Mitox-BCRP and SQ-Mitox-MDR cell lines. These two cell lines
typically exhibited resistance to the selecting agent (ranging approx. 210
to 320-fold). This occurred as an early event during the pulsing process.
The two sublines differed in their morphology and pattern of gene
expression. In addition, BCRP was significantly increased in one
population (SQ-Mitox-BCRP) while P-gp was significantly increased in the
other population (SQ-Mitox-MDR). A crucial step in human lung cancer
progression appears to be the acquisition of invasiveness. The population
of cells arising from the 4th drug pulse remained noninvasive but had
acquired a high level of drug resistance. However, after two additional
drug pulses, all cell lines acquired invasiveness. The invasive, drug
resistant BCRP and MDR cell line variants were characterised in depth and
microarray analysis was used to find functionally significant changes in
the transition from the preinvasive to the invasive phenotype. Functional
and cellular signaling analyses were performed on the cell lines using
pharmacological inhibitors, function-blocking antibodies, and gene
silencing by RNA interference. The DLKP cell line appears to contain at
least three morphologically distinct sub-populations of cells with
different levels of invasiveness. Microarray analysis generated gene lists
that were specific to an invasive phenotype, identifying possible genetic
markers for invasion. Proteins (including the cell adhesion molecules,
N-cadherin and ALCAM and the axon guidance molecule SLIT2) were also
identified as possible and alternative markers capable of distinguishing
between the different cell line clones.
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