Investigating PAK inhibition in combination with PD-1 blockade to enhance cytotoxic CD8+ T cell-mediated killing and suppress invasion of ovarian cancer cells.

[BACKGROUND] P-21 activated kinase (PAK) overexpression, phosphorylation, and gene amplification have been reported to increase cellular invasion in ovarian cancer (ovcan), worsening patient prognoses. One notable method of ovcan survival is through the PD-(L)1 checkpoint pathway, and PD-L1 expression in ovcan is correlated with poor patient outcomes. However, PD-1 and PD-L1 targeted clinical trials in ovcan have shown modest results. This work has examined the possibility of using PAKi and PD-1 blockade as a combination therapy.

[METHODS] PAK and PD-L1 expression in ovarian cells was determined. A novel 3D spheroid assay was used to assess ovcan invasion. Ovcan cell viability, downstream pathway signalling, and surface PD-L1 expression were evaluated after treatment with PAK inhibitors and co-culture with cytotoxic CD8 T cells. Ovcan cell and CD8 T cell co-cultures were treated with a combination of PAK inhibition and PD-1 checkpoint blockade and ovcan cell viability was assessed.

[RESULTS] Ovcan cells showed significant sensitivity to PAKi. CD8 T cell killing of ovcan cells improved following pre-treatment with PAK inhibitors, and this was further augmented with PD-1 blockade.

[DISCUSSION] The work presented here demonstrates the efficacy of PAK inhibition and PD-1 checkpoint blockade as a combination therapy for high-grade serous ovarian cancer.