ABSTRACTS – ORAL PRESENTATIONS - AMCA, spol. s r.o.

egulate expression of different genes. PPAR isoforms (PPAR alpha, beta/delta, gamma)
function through very specific mechanisms. PPAR alpha is predominantly expressed in
liver, heart muscle and brown adipose tissues. It controls fatty acid oxidation and lipid
metabolism by regulation of target genes, like ApoA1, the major apolipoprotein in highdensity
lipoprotein. PPAR alpha agonist turns on ApoA1 expression. PPAR alpha also
controls the expression of lipoprotein lipase, which hydrolyzes triglycerides. PPAR delta
is the second member of this family. It is ubiquitously expressed and has crucial role
in fatty acid oxidation. PPAR gamma is expressed mainly in white and brown adipose
tissues where it functions as central regulator of adipogenesis but it also has important
roles in glucose control and insulin sensitivity by regulation expression of target genes.
In addition, PPAR gamma has been described in many different types of normal and
cancer cells. All PPAR are activated by specific ligands and then they form complex with
RXR alpha. Co-repressors are released and co-activators are recruited to this complex.
Finally, they modify expression of different target genes. The ligand-binding domain for
these receptors is exceptionally large. There are various ligands for the same receptor
that would have different responses with different side effect profiles. Thiazolidinediones
(e.g. rosiglitazone, pioglitazone) are selective PPAR gamma ligands, but their effects in
cancer monotherapy is not very convincing.
Oxaliplatin is the newest platinum derivative used in standard chemotherapy acting
primarily through DNA damage. However, serious side-effects and resistance to
treatment are the main disadvantages of oxaliplatin. Therefore, the new combined
chemotherapeutic strategies are considered with the aim to suppress these unfavorable
effects of platinum-based drugs.
Our study was focused on the combination of oxaliplatin with PPAR gamma ligand
(rosiglitazone; RGZ) in human colon cancer cell lines. The results confirmed that
oxaliplatin and RGZ alone inhibit proliferation of human colon adenocarcinoma cell line
HT-29 in dose - dependent manner. RGZ caused localization of PPAR gamma receptor
into the nucleus after 0.5 - 1 hour treatment. Expression of PPAR gamma was decreased
and localization was translocated perinuclearly after 5 – 48 hour RGZ treatment. Using
PPAR gamma siRNA we confirmed that the decline of PPAR gamma expression is caused
by protein degradation after longer time of RGZ application. This verified that RGZ
decreased either protein expression or nuclear localization in longer time interval. RGZ
alone slightly increased BrdU (5-bromo-2-deoxyuridine) incorporation into the nucleus
after 24 hours. Combination of RGZ with oxaliplatin promoted antiproliferative effects
and cell cycle arrest in the G2/M phase. At the same time we observed enhanced
apoptosis and increased expression of cell cycle related and DNA damage proteins. We
suggest that increased percentage of active BrdU cells induced by RGZ may support the
effects of oxaliplatin.
Because resistance to oxaliplatin is major problem in colorectal cancer treatment we
established cell line derived from HT-29 that acquired resistance to 10mM oxaliplatin
(HT-29 res). We confirmed that in those cells RGZ or oxaliplatin alone did not affect cell
cycle progression. Interestingly, combination of RGZ and oxaliplatin arrested these cells
in G2/M phase, similarly to sensitive cells treated only by oxaliplatin. In addition, single
cell sorting of HT-29 res showed that combination of RGZ with oxaliplatin suppress their
colony formation ability.
124 Analytical Cytometry VII