Chronic lymphocytic leukaemia (CLL) is a chronic malignancy characterised by the progressive and uncontrolled multiplication and accumulation of morphologically mature but non-functional lymphocytes B. It is the most common type of leukaemia in adults in Slovenia. CLL is a morphologically, immunologically and genetically extremely heterogeneous disease, which is reflected both in its course and in its response to treatment. The prostaglandin receptor EP4 represents a potential target for the treatment of B-cell malignancies. Previous studies have shown that activation of prostaglandin receptor EP4 on lymphocytes B inhibits the NF-ĸB signalling pathway, leading to apoptosis of malignant B cells.
In this master thesis we evaluated the synergistic effects of the target drugs venetoclax, ibrutinib, acalabrutinib, idelalisib and duvelisib with the EP4 receptor agonist, PgE1-OH, on CLL cell lines MEC-1, MEC-1-VER and HG-3. As resistance to the target drug venetoclax is increasingly emerging in the treatment of CLL, we have used a clinically relevant in vitro model of venetoclax-resistant MEC-1-VER CLL cells. First, we evaluated the cytotoxic effects of the EP4 receptor agonists and target drugs on the cell lines using the PrestoBlue metabolic activity assay and determined the EC50 values. Time- and concentration-dependent cytotoxicity was detected for all of the tested compounds. Comparing the EC50 values on MEC-1 and MEC-1-VER lines, we concluded that PgE1-OH has comparable activity also when the resistance to venetoclax was established. The results suggest that the cytotoxic activity of the EP4 receptor agonist PgE1-OH was not affected by venetoclax resistance, suggesting that it has the potential to overcome resistance to the target drugs. We found that all tested combinations of PgE1-OH with the target drugs, at least at several concentrations tested, acted synergistically. On the MEC-1 cell line, the combinations of PgE1-OH with the PI3K signalling pathway inhibitors idelalisib and duvelisib had the strongest synergistic effect. These results were confirmed on the MEC-1-VER cell line. Using Ramos Blue reporter cell line, we have shown that PgE1-OH inhibited TNF-α-mediated activation of the NF-κB signalling pathway.
In conclusion, EP4 receptor agonist PgE1-OH exhibited synergistic effects with target drugs in vitro also on venetoclax resistant CLL cells MEC-1-VER, which could represent potential options for the treatment of CLL.
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