By using human melanoma and glioblastoma cell lines and their derivative BCL-X_L overexpressing clones, we investigated the role of BCL-X_L in aggressive features of these two tumor histotypes. We found that in both models, BCL-X_L overexpression increased in vitro cell migration and invasion and facilitated tumor cells to form de novo vasculogenic structures. Furthermore, BCL-X_L overexpressing cells exhibited higher tumors sphere formation capacity and expressed higher levels of some stem cell markers, supporting the concept that BCL-X_L plays essential roles in the maintenance of cancer stem cell phenotype. BCL-X_L expression reduction by siRNA, the exposure to a BCL-X_L-specific inhibitor and the use of a panel of human melanoma cell lines corroborated the evidence that BCL-X_L regulates tumor progression-associated properties. Finally, the vascular markers and the vasculogenic mimicry were up-regulated in the BCL-X_L overexpressing xenografts derived from both tumor histotypes. In conclusion, our work brings further support to the understanding of the malignant actions of BCL-X_L and, in particular, to the concept that BCL-X_L promotes stemness and contributes to the aggressiveness of both melanoma and glioblastoma.

The multifaceted role of lysine acetylation in cancer: prognostic biomarker and therapeutic target

Protein acetylation is one of the most important posttranslational modifications catalyzed by acetyltransferases and deacetylases, through the addition and removal of acetyl groups to lysine residues. Lysine acetylation can affect protein-nucleic acid or protein-protein interactions and protein localization, transport, stability, and activity. It regulates the function of a large variety of proteins, including histones, oncoproteins, tumor suppressors, and transcription factors, thus representing a crucial regulator of several biological processes with particular prominent roles in transcription and metabolism. Thus, it is unsurprising that alteration of protein acetylation is involved in human disease, including metabolic disorders and cancers. In this context, different hematological and solid tumors are characterized by deregulation of the protein acetylation pattern as a result of genetic or epigenetic changes. The imbalance between acetylation and deacetylation of histone or nonhistone proteins is also involved in the modulation of the self-renewal and differentiation ability of stem cells, including cancer stem cells. Here, we summarize a combination ofin vitroandin vivostudies, undertaken on a set of acetyltransferases, and discuss the physiological and pathological roles of this class of enzymes. We also review the available data on the involvement of acetyltransferases in the regulation of stem cell renewal and differentiation in both normal and cancer cell population.

Essential oils (EOs) have been recently emerging for their promising biological activities in preventing tumorigenesis or progression of different tumor histotypes, including melanoma. In this study, we investigated the antitumor activity of a panel of EOs in different tumor models. The ability of Melaleuca alternifolia (tea tree oil) and its main component, terpinen-4-ol, to sensitize the target therapy currently used for melanoma treatment was also assessed. Our results demonstrated that EOs differently affect the viability of human cancer cells and led us to select six EOs effective in melanoma and lung cancer cells, without toxic effects in human fibroblasts. When combined with dabrafenib and/or trametinib, Melaleuca alternifolia synergistically reduced the viability of melanoma cells by activating apoptosis. Through machine learning classification modeling, α-terpineol, tepinolene, and terpinen-4-ol, three components of Melaleuca alternifolia, were identified as the most likely relevant components responsible for the EO’s antitumor effect. Among them, terpinen-4-ol was recognized as the Melaleuca alternifolia component responsible for its antitumor and proapoptotic activity. Overall, our study holds promise for further analysis of EOs as new anticancer agents and supports the rationale for their use to improve target therapy response in melanoma.

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related death worldwide. Pemetrexed, a multi-target folate antagonist, has demonstrated efficacy in NSCLC histological subtypes characterized by low thymidylate synthase (TS) expression. Among many other potential targets, histone deacetylase inhibitors (HDACi) modulate TS expression, potentially sensitizing to the cytotoxic action of anti-cancer drugs that target the folate pathway, such as pemetrexed. Since high levels of TS have been linked to clinical resistance to pemetrexed in NSCLC, herein we investigated the molecular and functional effects of combined pemetrexed and ITF2357, a pan-HDACi currently in clinical trials as an anti-cancer agent. In NSCLC cell lines, HDAC inhibition by ITF2357 induced histone and tubulin acetylation and downregulated TS expression at the mRNA and protein level. In combination experiments in vitro ITF2357 and pemetrexed demonstrated sequence-dependent synergistic growth-inhibitory effects, with the sequence pemetrexed followed by ITF2357 inducing a strikingly synergistic reduction in cell viability and induction of both apoptosis and autophagy in all cell line models tested, encompassing both adenocarcinoma and squamous cell carcinoma. Conversely, simultaneous administration of both drugs achieved frankly antagonistic effects, while the sequence of ITF2357 followed by pemetrexed had additive to slightly synergistic growth-inhibitory effects only in certain cell lines. Similarly, highly synergistic growth inhibition was also observed in patient-derived lung cancer stem cells (LCSC) exposed to pemetrexed followed by ITF2357. In terms of molecular mechanisms of interaction, the synergistic growth-inhibitory effects observed were only partially related to TS modulation by ITF2357, as genetic silencing of TS expression potentiated growth inhibition by either pemetrexed or ITF2357 and, to a lesser extent, by their sequential combination. Genetic and pharmacological approaches provided an interesting link between the autophagic and apoptotic pathways, and showed that sequential pemetrexed/ITF2357 causes a toxic form of autophagy with consequent activation of a caspase-dependent apoptotic program. In vivo experiments in NSCLC xenografts confirmed that sequential pemetrexed/ITF2357 is feasible and results in increased inhibition of tumor growth and increased mice survival. Overall, these data provide a strong rationale for the clinical development of sequential schedules employing pemetrexed followed by HDACi in NSCLC.