Combinatorial screen of targeted agents with the PI3K inhibitors inavolisib, alpelisib, duvelisib, and copanlisib in multi-cell type tumor spheroids

Dysregulation of the phosphatidylinositol 3-kinase (PI3K) pathway is a key contributor to cancer, making PI3K inhibitors a promising approach for targeted therapy. The selectivity of these inhibitors varies among different PI3K isoforms: alpelisib and inavolisib are selective for the α-isoform, duvelisib targets the δ- and γ-isoforms, and copanlisib is a pan-PI3K inhibitor active against all isoforms.

This study evaluated the activity of these four PI3K inhibitors in combination with other targeted agents using multicellular tumor spheroids composed of 60% malignant cells, 25% endothelial cells, and 15% mesenchymal stem cells. A total of 29 tumor spheroid models were examined, including 26 patient-derived cancer cell lines from the NCI Patient-Derived Models Repository and three established cell lines from the NCI-60 human tumor cell line panel.

Additive and synergistic effects were observed when alpelisib, inavolisib, or copanlisib were combined with inhibitors of the RAS/MEK/ERK pathway, such as selumetinib (MEK inhibitor), ravoxertinib (ERK 1/2 inhibitor), or tovorafenib (RAF inhibitor, DAY101). Moreover, combining these three PI3K inhibitors with KRAS mutation-specific inhibitors—MTRX1133 for KRAS G12D or sotorasib for KRAS G12C—yielded selective activity in cell lines harboring the corresponding mutation.

Finally, vertical inhibition of the PI3K/AKT/mTOR pathway was achieved by combining a PI3K inhibitor with either the mTORC1/2 inhibitor sapanisertib or an AKT inhibitor, such as ipatasertib or afuresertib, which further enhanced the anti-cancer effects. These findings underscore the potential of combinatorial targeted therapy to improve treatment efficacy across multiple cancer types.