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Lung cancer is the leading cause of cancer death worldwide. Despite significant advances in research and therapy, a dismal 5-year survival rate of only 10–20% urges the development of reliable preclinical models and effective therapeutic tools. Lung cancer is characterized by a high degree of heterogeneity in its histology, a genomic landscape, and response to therapies that has been traditionally difficult to reproduce in preclinical models. However, the advent of three-dimensional culture technologies has opened new perspectives to recapitulate in vitro individualized tumor features and to anticipate treatment efficacy. The generation of lung cancer organoids (LCOs) has encountered greater challenges as compared to organoids derived from other tumors. In the last two years, many efforts have been dedicated to optimizing LCO-based platforms, resulting in improved rates of LCO production, purity, culture timing, and long-term expansion. However, due to the complexity of lung cancer, further advances are required in order to meet clinical needs. Here, we discuss the evolution of LCO technology and the use of LCOs in basic and translational lung cancer research. Although the field of LCOs is still in its infancy, its prospective development will likely lead to new strategies for drug testing and biomarker identification, thus allowing a more personalized therapeutic approach for lung cancer patients.

705 Background: mRCC prognostic stratification is currently based on the IMDC score. However, some patients experience outcomes markedly different from those predicted by the median outcome of their risk class. Moreover, risk scores are prognostic, rather than predictive, and developing reproducible, affordable, biology-based predictive biomarkers to tailor treatment choices in individual pts remains an unmet clinical need. Methods: A retrospective cohort of 113 mRCC pts treated at the Verona University Hospital Trust between 2013 and 2021 was explored to identify additional clinical prognostic factors for OS to complement IMDC score. Outlier pts (i.e. individual pts whose clinical outcome differed significantly from the median of the IMDC group they belonged to) were further explored to find putative molecular signatures, using FISH and IHC assays. Results: At a median follow-up of 69 months (range 18-136m), novel variables impacting on OS in addition to IMDC risk group were identified: bone, central nervous system (CNS) and pancreatic mets and high neutrophil/lymphocyte ratio (N/L) with a cut-off of 3.2. We also analyzed outliers: 3 good-risk pts with lower than expected OS, 4 poor-risk pts with longer than expected OS, and two intermediate-risk pts with long treatment response. Two putative signatures were found predictive of disease behavior: a cold signature (9p loss, poor of TILs) and a hot signature (rich in CD56+, CD15+ and CD8+ infiltrating cells). The cold and hot signatures were found in good risk pts with bad OS and poor-risk pts good OS, respectively; both intermediate-risk pts had a hot signature, consistent with their disease course. Conclusions: Additional clinical and molecular factors have been identified to possibly improve IMDC prognostic performance; multivariable models including them along with standard IMDC are being developed. Molecular analysis suggests potential signatures to be applied in routine clinical practice, whose predictive performance could be validated in prospective multicentric trials. [Table: see text]

Background Mounting evidence suggests that RAF-mediated MEK activation plays a crucial role in paradox MAPK (re)activation, leading to resistance and therapeutic failure with agents hitting a single step along the MAPK cascade. Methods We examined the molecular and functional effects of single and combined BRAF (dabrafenib), pan-RAF (RAF265), MEK (trametinib) and EGFR/HER2 (lapatinib) inhibition, using Western Blot and conservative isobologram analysis to assess functional synergism, and explored genetic determinants of synergistic interactions. Immunoprecipitation based assays were used to detect the interaction between BRAF and CRAF. The Mann-Whitney U test was used for comparing quantitative variables. Results Here we demonstrated that a combination of MEK and BRAF inhibitors overcomes paradoxical MAPK activation (induced by BRAF inhibitors) in BRAF-wt/RAS-mut NSCLC and PDAC in vitro. This results in growth inhibitory synergism, both in vitro and in vivo, in the majority (65%) of the cellular models analyzed, encompassing cell lines and patient-derived cancer stem cells and organoids. However, RAS mutational status is not the sole determinant of functional synergism between RAF and MEK inhibitors, as demonstrated in KRAS isogenic tumor cell line models. Moreover, in EGFR-driven contexts, paradoxical MAPK (re)activation in response to selective BRAF inhibition was dependent on EGFR family signaling and could be offset by simultaneous EGFR/HER-2 blockade. Conclusions Overall, our data indicate that RAF inhibition-induced paradoxical MAPK activation could be exploited for therapeutic purposes by simultaneously targeting both RAF and MEK (and potentially EGFR family members) in appropriate molecular contexts. KRAS mutation per se does not effectively predict therapeutic synergism and other biomarkers need to be developed to identify patients potentially deriving benefit from combined BRAF/MEK targeting. Electronic supplementary material The online version of this article (10.1186/s13046-018-0820-5) contains supplementary material, which is available to authorized users.

Combined MAPK/PI3K pathway inhibition represents an attractive, albeit toxic, therapeutic strategy in oncology. Since PTEN lies at the intersection of these two pathways, we investigated whether PTEN status determines the functional response to combined pathway inhibition. PTEN (gene, mRNA, and protein) status was extensively characterized in a panel of cancer cell lines and combined MEK/mTOR inhibition displayed highly synergistic pharmacologic interactions almost exclusively in PTEN-loss models. Genetic manipulation of PTEN status confirmed a mechanistic role for PTEN in determining the functional outcome of combined pathway blockade. Proteomic analysis showed greater phosphoproteomic profile modification(s) in response to combined MEK/mTOR inhibition in PTEN-loss contexts and identified JAK1/STAT3 activation as a potential mediator of synergistic interactions. Overall, our results show that PTEN-loss is a crucial determinant of synergistic interactions between MAPK and PI3K pathway inhibitors, potentially exploitable for the selection of cancer patients at the highest chance of benefit from combined therapeutic strategies.

PTEN is the most important negative regulator of the PI3K signaling pathway. In addition to its canonical, PI3K inhibition-dependent functions, PTEN can also function as a tumor suppressor in a PI3K-independent manner. Indeed, the PTEN network regulates a broad spectrum of biological functions, modulating the flow of information from membrane-bound growth factor receptors to nuclear transcription factors, occurring in concert with other tumor suppressors and oncogenic signaling pathways. PTEN acts through its lipid and protein phosphatase activity and other non-enzymatic mechanisms. Studies conducted over the past 10 years have expanded our understanding of the biological role of PTEN, showing that in addition to its ability to regulate proliferation and cell survival, it also plays an intriguing role in regulating genomic stability, cell migration, stem cell self-renewal, and tumor microenvironment. Changes in PTEN protein levels, location, and enzymatic activity through various molecular mechanisms can generate a continuum of functional PTEN levels in inherited syndromes, sporadic cancers, and other diseases. PTEN activity can indeed, be modulated by mutations, epigenetic silencing, transcriptional repression, aberrant protein localization, and post-translational modifications. This review will discuss our current understanding of the biological role of PTEN, how PTEN expression and activity are regulated, and the consequences of PTEN dysregulation in human malignant tumors.

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is a non-redundant lipid phosphatase that restrains and fine tunes the phosphatidylinositol-3-kinase (PI3K) signaling pathway. PTEN is involved in inherited syndromes, which predispose to different types of cancers and is among the most frequently inactivated tumor suppressor genes in sporadic cancers. Indeed, loss of PTEN function occurs in a wide spectrum of human cancers through a variety of mechanisms, including mutations, deletions, transcriptional silencing, or protein instability. PTEN prevents tumorigenesis through multiple mechanisms and regulates a plethora of cellular processes, including survival, proliferation, energy metabolism and cellular architecture. Moreover, recent studies have demonstrated that PTEN is able to exit, exist, and function outside the cell, allowing for inhibition of the PI3K pathway in neighboring cells in a paracrine fashion. Most recently, studies have shown that PTEN is also critical for stem cell maintenance and that PTEN loss can lead to the emergence and proliferation of cancer stem cell (CSC) clones. Depending on the cellular and tissue context of origin, PTEN deletion may result in increased self-renewal capacity or normal stem cell exhaustion and PTEN-deficient stem and progenitor cells have been reported in prostate, lung, intestinal, and pancreatic tissues before tumor formation; moreover, reversible or irreversible PTEN loss is frequently observed in CSC from a variety of solid and hematologic malignancies, where it may contribute to the functional phenotype of CSC. In this review, we will focus on the role of PTEN expression and function and downstream pathway activation in cancer stem cell biology and regulation of the tumorigenic potential; the emerging role of PTEN in mediating the crosstalk between the PI3K and MAPK pathways will also be discussed, together with prospects for the therapeutic targeting of tumors lacking PTEN expression.

Non-small-cell lung cancer (NSCLC) subtypes are driven by specific genetic aberrations. For reasons such as this, there is a call for treatment personalization. The ability to instigate NSCLC fragmentation poses new methodological problems, and new 'driver' molecular aberrations are being discovered at an unprecedented pace.This article describes the clinical development of epidermal growth factor-tyrosine kinase inhibitors (EGFR-TKIs) and crizotinib for EGFR-mutant and anaplastic lymphoma kinase (ALK)-rearranged NSCLC. Further, the authors briefly describe the emerging molecular targets in NSCLC, in terms of both rationale for therapeutic targeting and strategies, for clinical development.Target identification and validation in NSCLC still requires considerable effort, as not all of the molecular alterations are clear 'drivers' nor can they be efficiently targeted with available drugs. However, 50% of the NSCLC cases are without clear-defined molecular aberrations. Clinical trial methodology will need to develop novel paradigms for targeted drug development, aiming at the validation of an ideal 'biology-to-trial' approach. Despite significant challenges, a truly 'personalized' approach to NSCLC therapy appears to be within our reach.

The mitogen-activated protein kinase (MAPK) and PI3K pathways are regulated by extensive crosstalk, occurring at different levels. In tumors, transactivation of the alternate pathway is a frequent "escape" mechanism, suggesting that combined inhibition of both pathways may achieve synergistic antitumor activity. Here we show that, in the M14 melanoma model, simultaneous inhibition of both MEK and mammalian target of rapamycin (mTOR) achieves synergistic effects at suboptimal concentrations, but becomes frankly antagonistic in the presence of relatively high concentrations of MEK inhibitors. This observation led to the identification of a novel crosstalk mechanism, by which either pharmacologic or genetic inhibition of constitutive MEK signaling restores phosphatase and tensin homolog (PTEN) expression, both in vitro and in vivo, and inhibits downstream signaling through AKT and mTOR, thus bypassing the need for double pathway blockade. This appears to be a general regulatory mechanism and is mediated by multiple mechanisms, such as MAPK-dependent c-Jun and miR-25 regulation. Finally, PTEN upregulation appears to be a major effector of MEK inhibitors' antitumor activity, as cancer cells in which PTEN is inactivated are consistently more resistant to the growth inhibitory and anti-angiogenic effects of MEK blockade.

Mammalian target of rapamycin (mTOR) is a key protein kinase controlling signal transduction from various growth factors and upstream proteins to the level of mRNA translation and ribosome biogenesis, with pivotal regulatory effects on cell cycle progression, cellular proliferation and growth, autophagy and angiogenesis. The mTOR pathway, and its upstream regulators in the PI3K/PTEN/AKT cascade, are altered in a variety of experimental and human malignancies.This has led to the prediction that mTOR inhibitors may be used as anticancer agents. With the recent approval of two mTOR-targeted drugs (temsirolimus and everolimus) for the treatment of renal cell carcinoma and mantle cell lymphoma, this paradigm has been effectively translated into the clinical setting. In this review, we discuss mTOR biology and regulation, the mode of action of mTOR inhibitors as anti-cancer agents, and current clinical evidence supporting the use of rapamycin-like mTOR inhibitors in cancer treatment.

Background. Complex feedback loops and crosstalk between the MEK/ERK and PI3K/mTOR pathways, thus molecular predictors of sensitivity/resistance and synergistic/antagonistic interactions are urgently needed for the effective clinical development of combination strategies. Here we hypothesize that PTEN status critically modulates the growth inhibitory activity of single and combined MEK and PI3K/mTOR inhibition. Methods. Molecular and functional effects of single and combined MEK (trametinib, T) and mTOR (everolimus, E) blockade were assessed in a panel of 29 cancer cell lines with different molecular ‘drivers’. Pharmacologic interactions were analyzed by conservative isobologram analysis. PTEN role was mechanistically assessed by either silencing PTEN expression by shRNA or overexpressing a functional PTEN protein by stable transfection. Specific proteins and their phosphorylation states were analyzed using Kinexus Antibody Microarrays. Results. In the cell line panel analyzed, the presence of a wt-PTEN was the only significant predictor of sensitivity to T (p=0.001), while BRAF mutations were significantly related to E resistance (p=0.015). PTEN silencing slightly increased resistance to T in the wt-PTEN melanoma cell line M14; conversely, wt-PTEN overexpression in the PTEN-del WM115 cell line, dramatically increased sensitivity to T. E-induced growth inhibition was not significantly affected. Combined MEK and mTOR inhibition resulted in a striking growth inhibitory synergism in cells lacking PTEN expression (CI: 0.4-0.0005), but not in those with an intact PTEN (CI: 1.2-107; p=0.001). However, PTEN silencing restored growth inhibitory synergism of combined T and E in M14 cells (CI:0.36); similarly, the slope of the CI/fraction affected curve was dramatically altered in PTEN-overexpressing WM115 cells, as compared to their control-transfected counterpart, again indicating that PTEN expression/function causally influences functional response to combined MEK and mTOR inhibition. Similar results in terms of synergistic/antagonistic pharmacologic interactions were obtained when either double PI3K/mTOR kinase inhibitors (PF-5212384) or AKT allosteric inhibitors (MK-2206) were used to block the PI3K/mTOR pathway in combination with T. Proteomic analysis indicated that a greater modification of protein expression/phosphorylation profiles in response to MEK or combined MEK/mTOR inhibition occurs in cells lacking a functional PTEN, as compared to the wt-PTEN-expressing ones; preliminary analysis suggests that AKT phosphorylation and NF-κB activation maybe be crucial mediators of synergistic growth-inhibitory interactions occurring with combined treatment. Conclusions. PTEN loss may constitute a suitable genetic/molecular marker of synergistic activity interactions between MEK/ERK and PI3K/mTOR pathway inhibitors. Citation Format: Ludovica Ciuffreda, Italia Falcone, Silvia Matteoni, Andrea Sacconi, Federico Malusa, Teresa De Luca, Ursula Cesta Incani, Anais Del Curatolo, Marina Konopleva, Michael Andreeff, Adriana Eramo, Ruggero De Maria, Donatella Del Bufalo, Francesco Cognetti, Michele Milella. PTEN loss as a putative biomarker of synergistic growth inhibitory activity of combined MEK/ERK and PI3K/mTOR pathway blockade. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2618. doi:10.1158/1538-7445.AM2014-2618

Preclinical evidence shows that hitting a single point along the RAF/MEK/ERK cascade disrupts intra-pathway negative feedback loop, may cause paradoxical pathway activation and may lead to functional resistance. Thus, the “vertical” combination of agents simultaneously inhibiting RAF and MEK has been proposed as a strategy to synergistically inhibit tumor growth and delay resistance. Experimental procedures: Molecular and functional effects of single and combined MEK (using trametinib, T), BRAF (using dabrafenib, D), and RAF (using the pan-RAF inhibitor, RAF265, R) inhibition were dissected by WB analysis and conservative isobologram analysis to assess functional synergism, using a fixed dose-ratio experimental design. Summary data: We examined the in vitro molecular and functional consequences of D and T, alone or in combination, in a panel of different human BRAFV600E melanoma cell lines; both drugs inhibited cell growth and inactivated the MAPK pathway, but little or no synergistic growth inhibition was observed with their combination (CI: 0.7 - 1.3x106). Conversely, combined D+T suppressed malignant growth with highly synergistic effects in KRAS-mutant lung (2/5 cell lines tested) and pancreatic (4/6 cell lines tested) cancer models (CI: 0.1 - 0.7), in which selective BRAF inhibition induced hyperphosphorylation of MEK, ERK, and p90RSK (paradox effect). At concentrations inhibiting both BRAF and CRAF, R did not induce paradox MAPK activation and did not result in growth inhibitory synergism when combined with T. To define the role of RAS gene status in determining sensitivity/resistance to single and combined RAF and MEK blockade, we analyzed two isogenic tumor cell line models: H1299 expressing individual codon 12 KRAS mutants and isogenic HCT116 clones differing for the presence of a homo or heterozygous G13D KRAS mutation. Conversely, in lung cancer models driven by either EGFR mutations (HCC827, H1650) or HER-2 overexpression (Calu-3), selective BRAF inhibition also induced a paradox MAPK activation, which could be blocked using a reversible EGFR/HER-2 inhibitor (Lapatinib); in this context, combination (D+T) resulted in a non-synergic growth inhibitory effects. Conclusions: Overall, our data indicate that, in appropriate cellular contexts, vertical RAF/MEK inhibition-based combination strategies exert highly synergistic antitumor effects across different cancer models. Citation Format: Anais Del Curatolo, Ursula Cesta Incani, Ludovica Ciuffreda, Italia Falcone, Senji Shirasawa, Massimo Broggini, Isabella Sperduti, Adriana Eramo, Ruggero De Maria, Francesco Cognetti, Michele Milella. A vertical combination strategy hitting multiple steps along the MAPK cascade: Molecular mechanisms of action and putative genetic determinants of synergism. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 803. doi:10.1158/1538-7445.AM2014-803

e13512 Background: PTEN is a lipid phosphatase couteracting the activity of the PI3K pathway. PTEN mutations and deficiencies are prevalent in many types of human cancers and are associated with poor prognosis and therapeutic resistance. MAPK is another key cellular network that works independently from, in parallel to, and/or through interconnections with PI3K to promote cancer development. Here we investigated whether a strategy combining MEK and mTOR inhibition may be effective in preclinical models of human cancer and the role of PTEN loss in determining sensivity/resistance to single and combined pathway inhibition. Methods: We employed in vitro assays (cell proliferation assays, cell cycle and apoptosis analysis, WB, and ELISA assays) to determine functional and molecular drug effects. Pharmacologic interactions between MEK and mTOR inhibitors were analyzed by conservative isobologram analysis using a fixed dose-ratio experimental design. Results: In cell lines with wt-PTEN (including melanoma, breast, lung, and colon cancer), combined MEK and mTOR blockade achieves synergistic effects at suboptimal drug concentrations but becomes frankly antagonistic in the presence of complete inhibition of MEK-to-ERK signaling (combination index - CI: 1.2->1000). This, in turn, led to the identification of a novel crosstalk mechanism by which MEK blockade restores PTEN expression and cross-inhibits the PI3K/AKT/mTOR pathway, thus bypassing the need for double pathway blockade. Conversely, in cancer cell lines with PTEN loss, combined MEK and mTOR blockade resulted in strongly synergistic effects (CI: 0.0005-0.4), due to cooperative induction of apoptosis. A similar synergistic growth inhibition was also observed in a patient-derived lung cancer stem cell line, which displayed low to undetectable PTEN protein levels. Conclusions: Our results suggest that combined MEK and mTOR inhibition exerts strongly synergistic effects in cancer models with PTEN loss. This notion may be helpful in selecting appropriate cellular (and possibly clinical) contexts for the design rational therapeutic strategies based on concomitant inhibition of the RAF/MEK/ERK and PI3K/AKT/mTOR pathways.

e13572 Background: BRAF-selective kinase inhibitors have potent antitumor effects in mutant BRAF(V600E) tumors; however, in BRAF-wt cells, they paradoxically activate MEK/ERK. In addition, MEK blockade may induce compensatory signaling through both upstream pathway elements (RAF) and parallel pathways (PI3K/AKT/mTOR). Methods: We set out to define molecular and functional effects of single and combined BRAF (GSK2118436A, BRAF-I) and MEK (GSK1120212B, MEK-I) inhibition, using WB analysis to dissect signaling and a fixed dose-ratio experimental design to assess functional synergism by conservative isobologram analysis. Results: In A549 lung adenocarcinoma (KRAS G12S), BRAF-I (10 μM) induces hyperphosphorylation of CRAF, MEK, ERK, and p90RSK, while MEK-I (10 nM), alone or in combination with BRAF-I, potently offsets MAPK activation. Combined BRAF-I and MEK-I suppress malignant growth and survival at 72 h with highly synergistic effects in the A549 (lung, KRAS G12S), H1299 (lung, NRAS), HCT116 (colon, KRAS G13D), and MIAPACA (pancreatic, KRAS G12V) models, with combination indexes (CI), ranging from 1.37 to 0.12. Conversely, in other lung cancer models (H460, Calu-1, Calu-3) the combination of BRAF-I and MEK-I produced modestly additive to highly antagonistic antitumor effects. In BRAF-mutant melanoma and colon carcinoma models (M14 and HT29), there was no paradoxical activation of the MEK/ERK module in response to BRAF-I and both BRAF-I and MEK-I had pronounced growth inhibitory effects as single agents, but were frankly antagonistic in combination. Similarly, the pan-RAF inhibitor RAF265 did not cause MAPK activation and did not result in synergistic growth inhibition when combined with the MEK-I in the A549 and MIAPACA cell lines. Conclusions: Overall, our data indicate that combined inhibition of multiple signaling elements along the RAF/MEK/ERK pathway results in strongly synergistic growth inhibition, particularly in tumors with RAS mutations. Additional studies to better define genetic determinants of sensitivity/resistance and molecular mechanisms of therapeutic synergism of combined BRAF-I and MEK-I are currently ongoing.

The RAS/RAF/MEK/ ERK and the PI3K/AKT/mTOR pathways govern fundamental physiological processes, such as cell proliferation, differentiation, metabolism, cytoskeleton reorganization and cell death and survival. Constitutive activation of these signal transduction pathways is a required hallmark of cancer and dysregulation, on either genetic or epigenetic grounds, of these pathways has been implicated in the initiation, progression and metastastic spread of lung cances. Targeting components of the MAPK and PI3K cascades is thus an attractive strategy in the development of novel therapeutic approaches to treat lung cancer, although the use of single pathway inhibitors has met with limited clinical success so far. Indeed, the presence of intra- and inter-pathway compensatory loops that re-activate the very same cascade, either upstream or downstream the point of pharmacological blockade, or activate the alternate pathway following the blockade of one signaling cascade has been demonstrated, potentially driving preclinical (and possibly clinical) resistance. Therefore, the blockade of both pathways with combinations of signaling inhibitors might result in a more efficient anti-tumor effect, and thus potentially overcome and/or delay clinical resistance, as compared with single agent. The current review aims at summarizing the current status of preclinical and clinical research with regard to pathway crosstalks between the MAPK and PI3K cascades in NSCLC and the rationale for combined therapeutic pathway targeting.