The cyclin dependent kinase inhibitor P21 CDKN1A has been shown to be upregulated during differentiation and after DNA damage in somatic cells. We examined the expression of P21 CDKN1A and of γ-H2AX during the differentiation of germ cells in normal mouse testis. P21 CDKN1A was normally expressed in in a variable mode in different cell types (spermatogonia, spermatocytes, spermatids, Sertoli cell) located since the basal till the lumen of the seminiferous tubules. Moreover, in agreement with γ-H2AX expression, P21 maybe involved in different cell cycle checkpoints in spermatocytes such as a pre-replication, XY body inactivation, a mid-pachytene and a metaphase I checkpoints. Finally, in comparison to control, the p21 deficient mouse testis show elevated numbers of apoptosis of elongated spermatids within stages VIII-IX but any difference in the number of spermatogonia mitosis.These results suggest that P21 also may take part in the regulation of the differentiation of the male germ cells and may have a role in spermatogonia not related with a mitotic checkpoint.

Alterations in gene expressions are often due to epigenetic modifications that can lead to significant influence on cancer development, growth, and progression. The main epigenetic modifications observed in human are methylation and acetylation. In this regard, the HDAC inhibitors (HDACi) such as SAHA (Vorinostat), which can exert epigenetic alterations through impacting the acetylation status of histones, are in clinical trials as a new class of drugs with promising effects on the cancer growth and metastatic process. The small molecule RG7388 is a newly developed inhibitor that is specific for an oncogene-derived protein called MDM2, which is in clinical trials for the treatment of various types of cancers. One of the common characteristics for these two drugs is their ability to induce p21 expression through distinct mechanisms in MCF-7 and LNCaP cells. This difference was expected trigger cell cycle arrest and cell death through intra-cellular mechanisms that are not identical. Hence, the molecular mechanism whereby SAHA can induce cell cycle arrest and trigger necrosis, apoptosis or necroptosis is still evolving. Similarly, the ability of RG7388 for producing anticancer effect is undergoing thorough investigation, since it can produce p53 dependent and p53 independent effects. In this study we performed experiments to measure the cell cycle arrest effects of SAHA and RG7388 on using MCF-7 and LNCaP cells. The cytotoxicity, cell cycle arrest and apoptosis/necroptosis effects of the treatments were assessed by using Trypan Blue Dye Exclusion (TBDE) method, MTT assay, Fluorescence assay with DEVD-amc fluorogenic substrate and Immunoblotting methods. Our results from MCF-7 and LNCaP cells confirmed that SAHA and RG7388 treatments were able to induce cell death via combination of cell cycle arrest and cytotoxic mechanisms. We are speculating that our findings could lead to the development of newer treatments for breast and prostate cancers using this type of combinations.

Pancreatic ductal adenocarcinoma (PDA) remains the most lethal malignancy due to lack of an effective treatment. P21-activated kinases (PAKs) play key roles in PDA growth, and the PAK inhibitor PF-3758309 synergistically reduced PDA growth with gemcitabine. The aim of this study was to determine the effect of PF-3758309 with multiple chemotherapeutic reagents on a panel of patient-derived PDA cell lines. Cells were treated with PF-3758309 plus or minus gemcitabine, 5-fluorouracil (5-FU) or abraxane, and cell proliferation was determined. Protein expression profiles were measured by Western blot. PDA cells were subcutaneously injected into the flanks of SCID mice which were then treated with PF-3758309, gemcitabine, PF-3758309 plus gemcitabine, or gemcitabine plus abraxane. Tumour growth was measured by volume and weight. PF-3758309 enhanced the inhibitory effects of 5-FU, gemcitabine and abraxane on a panel of patient-derived PDA cells, inhibited HIF-1 protein expression and reduced the protein levels of palladin and -SMA in these cells. The combination of PF-3758309 with gemcitabine maximally inhibited PDA growth in vivo, which was comparable to the combination of gemcitabine with abraxane. PF-3758309 enhanced the suppressive effects of multiple chemotherapeutic reagents on the growth of a panel of patient-derived PDA cell lines. The combination of PF-3758309 with gemcitabine provides a potential treatment option with less toxicity than gemcitabine plus abraxane.

High-grade gliomas are the most common and aggressive adult primary brain tumors with a median survival of only 12-15 months. Current standard therapy consists of maximal safe surgical resection followed by DNA-damaging agents, such as irradiation and chemotherapy that can delay but not prevent inevitable recurrence. Some have interpreted glioma recurrence as evidence of glioma stem cells which persist in a relatively quiescent state after irradiation and chemotherapy, before the ultimate cell cycle re-entry and glioma recurrence. Conversely, latent cancer cells with a therapy-induced senescent phenotype have been shown to escape senescence, giving rise to more aggressive stem-like tumor cells than those present in the original tumor. Therefore, approaches are needed to either eliminate or keep these glioma-initiating cells in a senescent state for a longer time to prolong survival. In our current study, we demonstrate that the radiation-induced cell cycle inhibitor P21 can provide a powerful route to induce cell death in short-term explants of PDXs derived from three molecularly diverse human gliomas. Additionally, cells not killed by P21 overexpression were maintained in a stable senescent state for longer than control cells. Collectively, these data suggest that P21 activation may provide an attractive therapeutic target to improve therapeutic outcomes.

Pleural mesothelioma (PM) comprises three main subtypes: epithelioid, biphasic and sarcomatoid, which have a different impact on prognosis and treatment definition. However, PM subtyping can be complex given the inter- and intra-tumour morphological heterogeneity. We aim to use immunohistochemistry (IHC) to evaluate five markers (Mesothelin, Claudin-15, Complement Factor B, Plasminogen Activator Inhibitor 1, and p21-activated Kinase 4), whose encoding genes have been previously reported as deregulated among PM subtypes. Immunohistochemical expressions were determined in a case series of 73 PMs, and cut-offs for the epithelioid and non-epithelioid subtypes were selected. Further validation was performed on an independent cohort (30 PMs). For biphasic PM, the percentage of the epithelioid component was assessed, and IHC evaluation was also performed on the individual components separately. Mesothelin and Claudin-15 showed a good sensitivity (79% and 84%) and specificity (84% and 73%) for the epithelioid subtype. CFB and PAK4 had an inferior performance, with higher sensitivity (89% and 84%), but lower specificity (64% and 36%). In the biphasic group, all markers showed a different expression when comparing epithelioid with sarcomatoid areas. Mesothelin, Claudin-15 and CFB can be useful in subtype discrimination. PAI1 and PAK4 can improve component distinction in biphasic PM.