Acute sensitization of colon cancer cells to inflammatory cytokines by prophase arrest

Simultaneous silencing Aurora-A and UHRF1 inhibits colorectal cancer cell growth through regulating expression of DNMT1 and STAT1

Aurora-A has attracted a great deal of interest as a potential therapeutic target for patients with CRC. However, the outcomes of inhibitors targeting Aurora-A are not as favorable as expected, and the basis behind the ineffectiveness remains unknown. Here, we found that signal transducer and activator of transcription 1 (STAT1) was highly expressed in colorectal cancer (CRC) xenograft mouse models that were resistant to alisertib, an Aurora-A inhibitor. Unexpectedly, we found that alisertib disrupted Aurora-A binding with ubiquitin-like with plant homeodomain and ring finger domain 1 (UHRF1), leading to UHRF1 mediated ubiquitination and degradation of DNA methyltransferase 1 (DNMT1), which in turn resulted in demethylation of CpG islands of STAT1 promoter and STAT1 overexpression. Simultaneous silencing Aurora-A and UHRF1 prevented STAT1 overexpression and effectively inhibited CRC growth. Hence, concomitant targeting Aurora-A and UHRF1 can be a promising therapeutic strategy for CRC.

Efficient Activation of Apoptotic Signaling during Mitotic Arrest with AK301

Mitotic inhibitors are widely utilized chemotherapeutic agents that take advantage of mitotic defects in cancer cells. We have identified a novel class of piperazine-based mitotic inhibitors, of which AK301 is the most potent derivative identified to date (EC₅₀ < 200 nM). Colon cancer cells arrested in mitosis with AK301 readily underwent a p53-dependent apoptosis following compound withdrawal and arrest release. This apoptotic response was significantly higher for AK301 than for other mitotic inhibitors tested (colchicine, vincristine, and BI 2536). AK301-treated cells exhibited a robust mitosis-associated DNA damage response, including ATM activation, γH2AX phosphorylation and p53 stabilization. The association between mitotic signaling and the DNA damage response was supported by the finding that Aurora B inhibition reduced the level of γH2AX staining. Confocal imaging of AK301-treated cells revealed multiple γ-tubulin microtubule organizing centers attached to microtubules, but with limited centrosome migration, raising the possibility that aberrant microtubule pulling may underlie DNA breakage. AK301 selectively targeted APC-mutant colonocytes and promoted TNF-induced apoptosis in p53-mutant colon cancer cells. Our findings indicate that AK301 induces a mitotic arrest state with a highly active DNA damage response. Together with a reversible arrest state, AK301 is a potent promoter of a mitosis-to-apoptosis transition that can target cancer cells with mitotic defects.

Aurora kinase A in gastrointestinal cancers: time to target

Gastrointestinal (GI) cancers are a major cause of cancer-related deaths. During the last two decades, several studies have shown amplification and overexpression of Aurora kinase A (AURKA) in several GI malignancies. These studies demonstrated that AURKA not only plays a role in regulating cell cycle and mitosis, but also regulates a number of key oncogenic signaling pathways. Although AURKA inhibitors have moved to phase III clinical trials in lymphomas, there has been slower progress in GI cancers and solid tumors. Ongoing clinical trials testing AURKA inhibitors as a single agent or in combination with conventional chemotherapies are expected to provide important clinical information for targeting AURKA in GI cancers. It is, therefore, imperative to consider investigations of molecular determinants of response and resistance to this class of inhibitors. This will improve evaluation of the efficacy of these drugs and establish biomarker based strategies for enrollment into clinical trials, which hold the future direction for personalized cancer therapy. In this review, we will discuss the available data on AURKA in GI cancers. We will also summarize the major AURKA inhibitors that have been developed and tested in pre-clinical and clinical settings.

Novel piperazine-based compounds inhibit microtubule dynamics and sensitize colon cancer cells to tumor necrosis factor-induced apoptosis

We recently identified a series of mitotically acting piperazine-based compounds that potently increase the sensitivity of colon cancer cells to apoptotic ligands. Here we describe a structure-activity relationship study on this compound class and identify a highly active derivative ((4-(3-chlorophenyl)piperazin-1-yl)(2-ethoxyphenyl)methanone), referred to as AK301, the activity of which is governed by the positioning of functional groups on the phenyl and benzoyl rings. AK301 induced mitotic arrest in HT29 human colon cancer cells with an ED50 of ≈115 nm. Although AK301 inhibited growth of normal lung fibroblast cells, mitotic arrest was more pronounced in the colon cancer cells (50% versus 10%). Cells arrested by AK301 showed the formation of multiple microtubule organizing centers with Aurora kinase A and γ-tubulin. Employing in vitro and in vivo assays, tubulin polymerization was found to be slowed (but not abolished) by AK301. In silico molecular docking suggests that AK301 binds to the colchicine-binding domain on β-tubulin, but in a novel orientation. Cells arrested by AK301 expressed elevated levels of TNFR1 on their surface and more readily activated caspases-8, -9, and -3 in the presence of TNF. Relative to other microtubule destabilizers, AK301 was the most active TNF-sensitizing agent and also stimulated Fas- and TRAIL-induced apoptosis. In summary, we report a new class of mitosis-targeting agents that effectively sensitizes cancer cells to apoptotic ligands. These compounds should help illuminate the role of microtubules in regulating apoptotic ligand sensitivity and may ultimately be useful for developing agents that augment the anti-cancer activities of the immune response.

Identification of novel compounds that enhance colon cancer cell sensitivity to inflammatory apoptotic ligands

Immune and inflammatory death ligands expressed within neoplastic tissue could potentially target apoptosis to transformed cells. To develop approaches that accentuate the anti-cancer potential of the inflammatory response, the Chembridge DIVERSet (TM) library was screened for compounds that accentuated apoptosis in a strictly TNF-dependent manner. We identified a number of novel compounds with this activity, the most active of these, AK3 and AK10, sensitized colon cancer cells to TNF at 0.5 μM and 2 μM, respectively, without inducing apoptosis on their own. The activity of these compounds was structure-dependent and general, as they accentuated cell death by TNF or Fas ligation in multiple colon cancer cell lines. Both AK3 and AK10 arrested cells in mitosis, with live cell imaging indicating that mitotically arrested cells were the source of apoptotic bodies. AK3 accentuated caspase-8 and caspase-9 activation with little effect on NFκB target gene activation. Enhanced caspase activation corresponded to an increased expression of TNFR1 on the cell surface. To determine the general interplay between mitotic arrest and TNF sensitivity, Aurora kinase (MLN8054 and MLN8237) and PLK1 (BI2536) inhibitors were tested for their ability to sensitize cells to TNF. PLK1 inhibition was particularly effective and influenced TNFR1 surface presentation and caspase cleavage like AK3, even though it arrested mitosis at an earlier stage. We propose that AK3 and AK10 represent a new class of mitotic inhibitor and that selected mitotic inhibitors may be useful for treating colon cancers or earlier lesions that have a high level of inflammatory cell infiltrate.

Hyperbaric oxygen preconditioning protects skin from UV-A damage

Hyperbaric oxygen therapy (HBOT) is used for a number of applications, including the treatment of diabetic foot ulcers and CO poisoning. However, we and others have shown that HBOT can mobilize cellular antioxidant defenses, suggesting that it may also be useful under circumstances in which tissue protection from oxidative damage is desired. To test the protective properties of hyperbaric oxygen (HBO) on a tissue level, we evaluated the ability of a preconditioning treatment regimen to protect cutaneous tissue from UV-A-induced oxidative damage. Three groups of hairless SKH1-E mice were exposed to UV-A 3 days per week for 22 weeks, with two of these groups receiving an HBO pretreatment either two or four times per week. UV-A exposure increased apoptosis and proliferation of the skin tissue, indicating elevated levels of epithelial damage and repair. Pretreatment with HBO significantly reduced UV-A-induced apoptosis and proliferation. A morphometric analysis of microscopic tissue folds also showed a significant increase in skin creasing following UV-A exposure, which was prevented by HBO pretreatment. Likewise, skin elasticity was found to be greatest in the group treated with HBO four times per week. The effects of HBO were also apparent systemically as reductions in caspase-3 activity and expression were observed in the liver. Our findings support a protective function of HBO pretreatment from a direct oxidative challenge of UV-A to skin tissue. Similar protection of other tissues may likewise be achievable.