Glioblastoma multiforme (GBM) is a grade IV astrocytoma and the most common form of malignant brain tumor in adults. GBM remains one of the most fatal and least successfully treated solid tumors: current therapies provide a median survival of 12–15 months after diagnosis, due to the high recurrence rate. Glioma Stem Cells (GSCs) are believed to be the real driving force of tumor initiation, progression and relapse. Therefore, better therapeutic strategies GSCs-targeted are needed. Resveratrol is a polyphenolic phytoalexin found in fruits and vegetables displaying pleiotropic health benefits. Many studies have highlighted its chemo-preventive and chemotherapeutic activities in a wide range of solid tumors. In this work, we analyzed the effects of Resveratrol exposure on cell viability, proliferation and motility in seven GSC lines isolated from GBM patients. For the first time in our knowledge, we investigated Resveratrol impact on Wnt signaling pathway in GSCs, evaluating the expression of seven Wnt signaling pathway-related genes and the protein levels of c-Myc and β-catenin. Finally, we analyzed Twist1 and Snail1 protein levels, two pivotal activators of epithelial-mesenchymal transition (EMT) program.Results showed that although response to Resveratrol exposure was highly heterogeneous among GSC lines, generally it was able to inhibit cell proliferation, increase cell mortality, and strongly decrease cell motility, modulating the Wnt signaling pathway and the EMT activators. Treatment with Resveratrol may represent a new interesting therapeutic approach, in order to affect GSCs proliferation and motility, even if further investigations are needed to deeply understand the GSCs heterogeneous response.

Purpose: Evasion from chemotherapy-induced apoptosis due to p53 loss strongly contributes to drug resistance. Identification of specific targets for the treatment of drug-resistant p53-null tumors would therefore increase the effectiveness of cancer therapy.Experimental Design: By using a kinase-directed short hairpin RNA library and HCT116p53KO drugresistant colon carcinoma cells, glycogen synthase kinase 3 beta (GSK3B) was identified as a target whose silencing bypasses drug resistance due to loss of p53. p53-null colon cancer cell lines with different sets of mutations were used to validate the role of GSK3B in sustaining resistance and to characterize cell death mechanisms triggered by chemotherapy when GSK3B is silenced. In vivo xenograft studies were conducted to confirm resensitization of drug-resistant cells to chemotherapy upon GSK3 inhibition. Colon cancer samples from a cohort of 50 chemotherapy-treated stage II patients were analyzed for active GSK3B expression.Results: Downregulation of GSK3B in various drug-resistant p53-null colon cancer cell lines abolished cell viability and colony growth after drug addition without affecting cell proliferation or cell cycle in untreated cells. Cell death of 5-fluorouracil (5FU)-treated p53-null GSK3B-silenced colon carcinoma cells occurred via PARP1-dependent and AIF-mediated but RIP1-independent necroptosis. In vivo studies showed that drug-resistant xenograft tumor mass was significantly reduced only when 5FU was given after GSK3B inhibition. Tissue microarray analysis of colon carcinoma samples from 5FU-treated patients revealed that GSK3B is significantly more activated in drug-resistant versus responsive patients.Conclusions: Targeting GSK3B, in combination with chemotherapy, may represent a novel strategy for the treatment of chemotherapy-resistant tumors.

Combined MEK and CDK4/6 inhibition (MEKi + CDK4i) has shown promising clinical outcomes in patients with -mutant melanoma. Here, we interrogated longitudinal biopsies from a patient who initially responded to MEKi + CDK4i therapy but subsequently developed resistance. Whole-exome sequencing and functional validation identified an acquired mutation as conferring drug resistance. We demonstrate that preexisted in a rare subpopulation that was missed by both clinical and research testing, but was revealed upon multiregion sampling due to being nonuniformly distributed. This resistant population rapidly expanded after the initiation of MEKi + CDK4i therapy and persisted in all successive samples even after immune checkpoint therapy and distant metastasis. Functional studies identified activated S6K1 as both a key marker and specific therapeutic vulnerability downstream of -induced resistance. These results demonstrate that difficult-to-detect preexisting resistance mutations may exist more often than previously appreciated and also posit S6K1 as a common downstream therapeutic nexus for the MAPK, CDK4/6, and PI3K pathways. We report the first characterization of clinical acquired resistance to MEKi + CDK4i, identifying a rare preexisting subpopulation that expands upon therapy and exhibits drug resistance. We suggest that single-region pretreatment biopsy is insufficient to detect rare, spatially segregated drug-resistant subclones. Inhibition of S6K1 is able to resensitize PIK3CA-expressing NRAS-mutant melanoma cells to MEKi + CDK4i. .

TGF-β pathway is generally associated with the processes of metastasis, angiogenesis and EMT in cancer. Very little is known, however, about the role of TGF-β in cancer drug resistance. In this work, we show a specific activation of the TGF-β pathway in consequence of chemotherapeutic treatment in in vivo and in vitro models of colorectal carcinoma. 5-Fluorouracil (5FU) was able to stimulate the activation of SMAD3 and the transcription of specific genes such as ACVRL1, FN1 and TGFB1. On the other hand, the specific inhibition of TGF-βRI was able to repress the 5FU-induced genes transcription and to restore the sensitivity of chemoresistant cells to the toxic action of the drug, by decreasing the expression of BCL2L1 and ID1 genes. The role of the TGF-β molecule in the chemoresistant colon carcinoma cells' response to 5FU was further demonstrated by conditioned medium (CM) experiments: CM from 5FU-treated chemoresistant cells was able to protect chemosensitive cells against the toxic action of 5FU. In conclusion, these findings showed the pivotal role of TGF-β pathway in colon cancer mechanisms of drug resistance suggesting new possible approaches in diagnosis and treatment of colon cancer patients.

miRNAs are central players in cancer biology and they play a pivotal role in mediating the network communication between tumor cells and their microenvironment. In melanoma, miRNAs can impair or facilitate a wide array of processes, and here we will focus on: the epithelial to mesenchymal transition (EMT), the immune milieu, and metabolism. Multiple miRNAs can affect the EMT process, even at a distance, for example through exosome-mediated mechanisms. miRNAs also strongly act on some components of the immune system, regulating the activity of key elements such as antigen presenting cells, and can facilitate an immune evasive/suppressive phenotype. miRNAs are also involved in the regulation of metabolic processes, specifically in response to hypoxic stimuli where they can mediate the metabolic switch from an oxidative to a glycolytic metabolism. Overall, this review discusses and summarizes recent findings on miRNA regulation in the melanoma tumor microenvironment, analyzing their potential diagnostic and therapeutic applications.