Systems approach to rational combination therapy: PARP inhibitors

Poly (ADP-ribose) polymerase inhibitors (PARPi) have demonstrated activity across a broad spectrum of molecular backgrounds and tumor types, with the greatest activity observed in patients with aberrations in the homologous recombination DNA damage repair pathway. Despite remarkable responses in a subset of patients, the response is usually modest and transient due to the almost inevitable emergence of resistance. Tumors develop resistance through rapid adaptation to the effects of PARPi as well as by generation or selection of genomic aberration. Although adaptive responses results in drug resistance, it also induces therapeutic vulnerabilities that could be exploited with rational combination therapies. To fulfill this role, we established the combinatorial adaptive response therapy (CART) platform by performing reverse-phase protein arrays to characterize adaptive responses, and develop rational combination therapies. Our series of studies strongly support the efficacy of this strategy, wherein targeting the emerging adaptive responses to PARPi with MEK/ERK inhibitors, WEE1/ATR inhibition (inhibitors of S-phase and G2 DNA damage checkpoint), and PI3K/AKT/mTOR inhibition, and showed promising anti-tumor activity in various preclinical models. Importantly, this approach has been proven highly efficient, and several combinational therapies developed from the CART platform are being evaluated in ongoing clinical trials (NCT03801369, NCT03586661, NCT03162627, NCT03544125, NCT02659241, NCT02208375, NCT02316834, and NCT03637491).