Abstract 5315: Anti-tumor activity of KRASG12C inhibitors is enhanced when combined with Cdc42 effector p21-activated kinase 4 targeting agents
Authors: Khan Husain Yar , Bannoura Sahar , Mamdani Hirva , Aboukameel Amro , Mzannar Yousef , Li Yiwei , Al-Hallak Mohammad Najeeb , Azar Ibrahim , Kim Steve , Beydoun Rafic , Mohammad Ramzi , Landesman Yosef , Zhang Yue , Baloglu Erkan , Senapedis William , Sukari Ammar , Nagasaka Misako , Shields Anthony , Azmi Asfar S. 
Published: June 2022

Background: KRASG12C inhibitors sotorasib and adagrasib have shown impressive results in clinical studies. These inhibitors efficiently block KRAS downstream effectors such as RAF, MEK, and ERK/p-ERK. However, factors such as feedback reactivation or bypass of KRAS dependence are emerging, resulting in the need for rational combination approaches. KRASG12C inhibitors have limited impact on the parallel oncogenic signaling driven by PI3K/AKT, its regulator molecules such as the Rho GTPases, and their effectors. This signaling pathway can collectively promote p-ERK re-activation thereby blunting the efficacy of KRASG12C targeted drugs. The p21-activated kinase (PAK) family are crucial effectors of the Rho family of GTPases and act as regulatory switches that control important cellular processes including motility, proliferation, and survival. PAK4 is the main effector of Rho GTPase, cell division control protein 42 homolog (Cdc42), and has an established role in mutant RAS-dependent tumor metastasis. In this study, we rationally targeted two parallel signaling pathways by combining KRASG12C inhibitors with the PAK4 inhibitor KPT-9274 in KRASG12C mutant PDAC and NSCLC in vitro and in vivo models.

Methods: We evaluated the cytotoxicity and molecular profile of KRASG12C inhibitors in combination with PAK4 inhibitor KPT-9274 as well as positive control PF-3758309 in KRASG12C mutant 2D and 3D cellular/spheroid models. The anti-tumor activity of the combinations was evaluated in KRASG12C mutant cell line-derived xenograft. Tumor volumes were assessed throughout the treatment period using an ultrasound scanner.

Results: PAK4 inhibitor KPT-9274 synergized with both sotorasib and adagrasib yielding suppressed growth of KRASG12C mutant PDAC and NSCLC cells in 2D and 3D cultures, but not in KRASwt, KRASG12V, and KRASG12D cell lines (NCI RASless MEFs). In addition, the combination reduced the clonogenic potential of KRASG12C mutant cancer cells. PAK4-KRASG12C inhibitor combinations resulted in enhanced and prolonged inhibition of KRAS downstream effector pathways. In xenograft studies, oral administration of KPT-9274 at sub-optimal dose (100 mg/kg QD x 5 x 3 weeks) and sotorasib at one-fourth of MTD (25 mg/kg QD x 5 x 3 weeks) demonstrated remarkable inhibition of KRASG12C mutant MiaPaCa-2 tumor burden (p&lt;0.001 single agents vs combination treatment). Residual tumor analysis showed a reduction in proliferation index (ki67), activation of pro-apoptotic caspases, and inhibition of mutant RAS effector signaling. Studies in additional KRASG12C xenograft and tumor explant models are ongoing.

Conclusion: This is the first study showing that KRASG12C inhibitors can synergize with PAK4 inhibitors. This combination can simultaneously target direct KRAS downstream effectors and the parallel PI3K/AKT oncogenic signaling warranting further clinical investigations.

Citation Format: Husain Yar Khan, Sahar Bannoura, Hirva Mamdani, Amro Aboukameel, Yousef Mzannar, Yiwei Li, Mohammad Najeeb Al-Hallak, Ibrahim Azar, Steve Kim, Rafic Beydoun, Ramzi Mohammad, Yosef Landesman, Yue Zhang, Erkan Baloglu, William Senapedis, Ammar Sukari, Misako Nagasaka, Anthony Shields, Asfar S. Azmi. Anti-tumor activity of KRASG12C inhibitors is enhanced when combined with Cdc42 effector p21-activated kinase 4 targeting agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5315.