Sulfasalazine sensitises human monocytic/macrophage cells for glucocorticoids by upregulation of glucocorticoid receptor alpha and glucocorticoid induced apoptosis.
BACKGROUND
Glucocorticoids (GCs) are commonly used in the treatment of (chronic) inflammatory diseases and cancer, but inherent or acquired resistance to these drugs limits their optimal efficacy. The availability of drugs that could modulate GC resistance is therefore of potential clinical interest.


OBJECTIVE
To explore the molecular basis of GC sensitisation of GC resistant monocytic/macrophage cells after chronic exposure to sulfasalazine.


METHODS
Human monocytic/macrophage THP1 and U937 cells represent a cell line model system characterised by inherent resistance to the GCs dexamethasone and prednisolone. Both cell lines were chronically exposed in vitro to 0.3-0.6 mM sulfasalazine (SSZ) for approximately 3 months, after which they were characterised for GC sensitivity, expression levels of GC receptor and components of the nuclear factor kappa B (NFkappaB) signalling pathway, and their ability to undergo GC induced apoptosis.


RESULTS
Chronic exposure to SSZ markedly sensitised both U937 and THP1 cells to dexamethasone (781-fold and 1389-fold, respectively) and prednisolone (562-fold and 1220-fold, respectively). Restoration of GC sensitivity in cells exposed to SSZ was provoked via GC induced apoptosis, coinciding with inhibition of NFkappaB activation. Moreover, western blot analysis revealed a markedly increased expression of glucocorticoid receptor alpha (GRalpha) in cells exposed to SSZ. Since GRalpha mRNA levels were only marginally increased, these results suggest that an altered post-transcriptional mechanism was operable which conferred a stable GRalpha protein on SSZ exposed cells.


CONCLUSIONS
These results suggest that chronic targeting of the NFkappaB signalling pathway by SSZ may be exploited as a novel strategy to stabilise GRalpha expression and thereby sensitise primary resistant cells to GCs.
Oerlemans
Ruud
R
Department of Rheumatology, Room 4A42, VU-Institute for Cancer and Immunology, VU-University Medical Center, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands.
Vink
Josefien
J
Dijkmans
Ben A C
BA
Assaraf
Yehuda G
YG
van Miltenburg
Marjolein
M
van der Heijden
Joost
J
Ifergan
Ilan
I
Lems
Willem F
WF
Scheper
Rik J
RJ
Kaspers
Gertjan J L
GJ
Cloos
Jacqueline
J
Jansen
Gerrit
G
D017209:Apoptosis / Q000187:drug effects*; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D008264:Macrophages / Q000187:drug effects*; D009000:Monocytes / Q000187:drug effects*; D016328:NF-kappa B / Q000037:antagonists & inhibitors; D011239:Prednisolone / Q000494:pharmacology; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D012460:Sulfasalazine / Q000494:pharmacology*; D020298:U937 Cells; D015854:Up-Regulation / Q000502:physiology
D005938:Glucocorticoids; D016328:NF-kappa B; D011965:Receptors, Glucocorticoid; C411470:glucocorticoid receptor alpha; D012460:Sulfasalazine; D003907:Dexamethasone; D011239:Prednisolone