Abstract 1358: p21 activated kinase 4 (pak4) as a novel therapeutic target for non-hodgkin's lymphoma
Authors: Azmi Asfar S. , Aboukameel Amro , Muqbil Irfana , Li Yiwei , Senapedis William , Baloglu Erkan , Landesman Yosef , Kauffman Michael , Shacham Sharon , Al-Katib Ayad , Mohammad Ramzi M. 
Published: July 2017

Objective: The p21-activated kinase 4 (PAK4) is a key downstream effector of the Rho GTPase family and is over-expressed in many different cancer types. PAK4 protein, by virtue of its ability to engage multiple ligands, regulates a repertoire of signaling pathways. A survey of non-Hodgkin’s lymphoma (NHL) cell lines shows that there is increase in PAK4 mRNA and/or protein expression when compared to normal peripheral lymphocytes (PBL). Considering PAK4 RNA interference suppresses lymphoma cell proliferation, these findings point to a novel role for PAK4 in promoting NHL cell growth. To this end we examined the impact of the newly developed PAK4 allosteric modulators (PAMs) on NHL proliferation both in vitro and in vivo.

Methods: WSU-FSCCL (representing follicular small cell cleaved lymphoma) and WSU-DLCL2 (diffused large B-cell lymphoma) were exposed to increasing concentrations of different PAM analogs (KPT-7523, KPT-7189, KPT-9037, KPT-9274, or KPT-7010 [inactive]) or the Pan-PAK inhibitor, PF-3758309, in the presence or absence of CHOP (used at IC25) for 72 hrs. Following combination treatment viability was evaluated using Trypan Blue, apoptosis was analyzed using 7AAD, tetrachrome staining, Annexin V FITC and cell cycle arrest was accessed by flow cytometry. Protein and mRNA expression changes were evaluated using immunoblotting and RT-PCR. The toxicity and efficacy of PAMs were evaluated in sub-cutaneous and disseminated xenograft models of NHL.

Results: As single agents, PAMs show anti-proliferative activity in vitro against NHL cell lines (IC50s for: WSU-FSCCL = 50 nM and WSU-DLCL2 = 250 nM) while sparing normal PBL (IC50s in μM range). There was a statistically significant dose-dependent difference in apoptosis induction in NHL cell lines treated with PAMs when compared to vehicle control. PAMs reduced total p-PAK4 and downstream signaling proteins involved in proliferation and apoptosis. In R-CHOP combination studies we observed enhanced viability suppression, increased apoptosis, and concurrent down-regulation of PAK4 signaling pathway proteins when compared to any single agent alone. The clinical compound, KPT-9274, is well tolerated and showed remarkable anti-tumor activity in WSU-DLCL2 sub-cutaneous xenograft in mice (p &lt; 0.01 at 140 mg/kg/bid for 4 weeks with no loss in body weight). Residual tumors analysis showed suppression of PAK4 signaling pathways. Single agent and R-CHOP combination efficacy is currently being evaluated in subcutaneous and systemic WSU-FSCCL and in primary patient derived xenografts in mice.

Conclusions: This is the first study demonstrating a role for PAK4 in diffused large B-cell and follicular small cell cleaved NHL. Our data shows that inhibition of PAK4 could become a viable therapy for NHL either alone or in combination with R-CHOP. Our data is directly applicable to the current Phase 1 trial of KPT-9274 in patients with advanced solid malignancies or NHL.

Citation Format: Asfar S. Azmi, Amro Aboukameel, Irfana Muqbil, Yiwei Li, William Senapedis, Erkan Baloglu, Yosef Landesman, Michael Kauffman, Sharon Shacham, Ayad Al-Katib, Ramzi M. Mohammad. p21 activated kinase 4 (pak4) as a novel therapeutic target for non-hodgkin's lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1358. doi:10.1158/1538-7445.AM2017-1358