Background: Cisplatin is an efficient antitumor agent used as salvage treatment for DLBCL patients
that have relapsed or become refractory to their first-line treatment (rrDLBCL). However,
approximately 70% of rrDLBCL patients will again experience relapse of their disease after salvage
treatment caused by various factors, such as resistance towards the drugs, including cisplatin. This
leaves the patients with few therapeutical options and poor prognosis. Cisplatin resistance has been
linked with overexpression of components of the DNA damage response (DDR), thus, inhibiting
DDR during cisplatin exposure could plausibly improve cisplatin efficacy and response. 17AAG is a
potent Hsp90 inhibitor that through binding to the Hsp90 complex leads to degradation of its clients
including components of the DDR and have therefore been considered as an add-on drug to cisplatin
treatment.

Hypothesis: We hypothesize that 17AAG can sensitize DLBCL cells to cisplatin, whereby cisplatin
resistance can be overcome.

Methods: Two DLBCL cell lines, RIVA and SU-DHL-5, were investigated after treatment with
cisplatin and 17AAG as single drugs and in combination, along with vehicle controls for effect on
DNA damage, cell cycle distribution and apoptosis activity with flow cytometry. Additionally, cell
viability was determined with cell counting assay and differential DDR protein expressions were
investigated with quantitative proteomic analysis in the treated DLBCL cells through time.

Results: Synergistic effects of combining 17AAG with cisplatin was observed in RIVA characterized
by increased DNA damage, disturbed cell cycle distribution, increased apoptosis and decreased cell
viability. However, synergistic effect in SU-DHL-5 was not observed, suggesting a cell line specific
combinatory effects in resistant DLBCL cells, such as RIVA. Furthermore, tendencies of decreasing
effect on expression of the DDR proteins MSH2 and MSH6 was observed for both cell lines after
treatment with 17AAG, implying that the synergistic effects of cisplatin and 17AAG could at least
partly be based on 17AAG’s inhibitory effect on DDR proteins.

Conclusion: This thesis has discovered that 17AAG sensitizes cisplatin resistant DLBCL cells to
cisplatin. Thus, constituting a potential treatment strategy to overcome cisplatin resistance.