PAK Kinase Inhibition Has Therapeutic Activity in Novel Preclinical Models of Adult T-Cell Leukemia/Lymphoma

Abstract

Purpose: To evaluate therapeutic activity of PAK inhibition in ATLL and to characterize the role of PAK isoforms in cell proliferation, survival, and adhesion of ATLL cells in preclinical models. Experimental Design: Frequency and prognostic impact of PAK2 amplification were evaluated in an ATLL cohort of 370 cases. Novel long-term cultures and in vivo xenograft models were developed using primary ATLL cells from North American patients. Two PAK inhibitors were used to block PAK kinase activity pharmacologically. siRNA-based gene silencing approach was used to genetically knockdown (KD) PAK1 and PAK2 in ATLL cell lines. Results: PAK1/2/4 are the three most abundantly expressed PAK family members in ATLL. PAK2 amplifications are seen in 24% of ATLLs and are associated with worse prognosis in a large patient cohort. The pan-PAK inhibitor PF-3758309 (PF) has strong in vitro and in vivo activity in a variety of ATLL preclinical models. These activities of PF are likely attributed to its ability to target several PAK isoforms simultaneously because genetic silencing of either PAK1 or PAK2 produced more modest effects. PAK2 plays a major role in CADM1-mediated stromal interaction, which is an important step in systemic dissemination of the disease. This finding is consistent with the observation that PAK2 amplification is more frequent in aggressive ATLLs and correlates with inferior outcome. Conclusions: PAK2, a gene frequently amplified in ATLL, facilitates CADM1-mediated stromal interaction and promotes survival of ATLL cells. Taken together, PAK inhibition may hold significant promise as a targeted therapy for aggressive ATLLs.

Over-representation of MEF-2 isoforms (A/C) is associated with HTLV-1-induced acute ATLL and their recruitment to 3’LTR facilitates HBZ expression from the antisense promoter via interactions with Menin and Jun D

“…In the study presented herein, we demonstrate the gene and protein level expression patterns of MEF-2 isoforms in multiple ATLL cell lines, and in a specific ATLL cohort termed North American (NA)-ATLL, which exhibit acute clinical manifestations with higher rates of aggressive subtypes compared to chronic counterparts (22). NA-ATLL patients demonstrate chemoresistance and a distinct pattern of somatic mutations (23). Most patients in this cohort showed drastically higher expression of MEF-2A; and also, of MEF-2C in a subset of patients.…”

“…Since there was elevated MEF-2A and MEF-2C expression in viral-producing and ATLL cell lines, we wanted to assess MEF-2 isoform expression patterns in patient samples to ensure clinical relevance. We characterized a specific HTLV-1-infected NA-ATLL patient cohort (22,23,36) for expression of MEF-2 isoforms and observed a significant logarithmic increase in the expression of MEF-2A in ATLL patients compared to seronegative, asymptomatic carriers and also HAM/TSP patients. We observed a similar trend with MEF-2C expression in a subset of ATLL patients, although they were not statistically significant.…”

“…Patient samples and primary cells. Samples from NA-ATLL patients, as published (22,23,56), were obtained from the Albert Einstein College of Medicine (NY, USA). In addition, samples from 11 HTLV-1-associated myelopathy/Tropical spastic paraparesis (HAM/TSP) patients (82% female) and 10 asymptomatic HTLV-1-infected individuals (60% female) were studied.…”

“…To ascertain the clinical importance of MEF-2 isoforms, we investigated their expression and relevance within patient cohorts. We obtained mRNA from PBMCs of North American ATLL (NA-ATLL) patient cohorts (23,36), along with seronegative, asymptomatic carriers (ACs) and HAM/TSP patients from the same geographic areas of and South America. We performed RT-qPCR and derived the relative fold-change in comparison to activated PBMCs as a reference.…”

Analysis of Therapeutic Targets and Prognostic Biomarkers of CXC Chemokines in Cervical Cancer Microenvironment

“…Moreover, our data indicated that the SRC family tyrosine kinases (LCK, LYN) and PAK family kinase (PAK2, PAK3) were the probable targets of the differentially expressed CXC chemokines. These kinases are involved in tumor development and progression by regulating tumor cell proliferation, migration, invasion, and apoptosis [49][50][51]. In CC, differentially expressed CXC chemokines may affect tumor development and progression by regulating these kinases.…”