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Small cell lung carcinoma (SCLC) is a highly malignant cancer with early metastatic dissemination and poor clinical outcomes. Mutations in the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway, including the frequently occurring rapamycin-insensitive protein (RICTOR) amplification, have been described in these tumours. Moreover, the associated mTOR hyperactivity could be exploited for personalised treatment. Our aim was to study mTOR activity, RICTOR amplification, and their role during SCLC progression. In situ mTOR activity and Rictor expression were characterised by immunohistochemistry in 50 primary and 50 brain metastatic tumours, and 14 paired SCLC patient samples. RICTOR copy number changes were analysed by fluorescence in situ hybridisation of the paired SCLC patient samples and in vivo experiments. Additionally, in vitro sensitivity to cisplatin and mTOR inhibitors was evaluated in SCLC cell lines harbouring RICTOR amplification and other mTOR pathway mutations. High Rictor expression and mTOR complex 2 (mTORC2) hyperactivity were significantly associated with brain metastases and worse overall survival. An increase in RICTOR copy number was observed in paired samples during progression. The importance of these alterations was confirmed both by the sensitising effect of vistusertib in vitro and the RICTOR copy number/expression changes in xenografts. Our study highlights the role of mTORC2 in SCLC progression. Early detection of RICTOR amplification in primary tumours and targeting mTORC2 in these cases may represent a promising novel strategy to develop personalised therapy for metastasis prevention.

Simple Summary: Despite recent advances in targeted therapy and immunotherapy, the treatment of lung cancer remains challenging due to its high metastatic potential, which adversely affects both the prognosis and the quality of life of these patients. Rictor, the scaffold protein of the mTORC2 complex, plays an important role in regulating essential cellular functions and promoting metastases through epithelial–mesenchymal transition. Amplification of the RICTOR gene and subsequent overexpression of the Rictor protein can activate mTORC2 and promote cell survival and migration. Recent studies suggest that RICTOR amplification and Rictor overexpression may serve as markers of mTORC2 activation. Potentially, they can also provide druggable targets for advanced therapy. Although these drugs are still in a preclinical phase, selective mTORC2 inhibitors are a promising approach to inhibit tumor cell migration and metastasis formation. This review highlights the importance of Rictor and mTORC2 as predictive markers and promising therapeutic targets in the treatment of lung cancer. Lung carcinoma is one of the most common cancer types for both men and women. Despite recent breakthroughs in targeted therapy and immunotherapy, it is characterized by a high metastatic rate, which can significantly affect quality of life and prognosis. Rictor (encoded by the RICTOR gene) is known as a scaffold protein for the multiprotein complex mTORC2. Among its diverse roles in regulating essential cellular functions, mTORC2 also facilitates epithelial–mesenchymal transition and metastasis formation. Amplification of the RICTOR gene and subsequent overexpression of the Rictor protein can result in the activation of mTORC2, which promotes cell survival and migration. Based on recent studies, RICTOR amplification or Rictor overexpression can serve as a marker for mTORC2 activation, which in turn provides a promising druggable target. Although selective inhibitors of Rictor and the Rictor-mTOR association are only in a preclinical phase, they seem to be potent novel approaches to reduce tumor cell migration and metastasis formation. Here, we summarize recent advances that support an important role for Rictor and mTORC2 as potential therapeutic targets in the treatment of lung cancer. This is a traditional (narrative) review based on Pubmed and Google Scholar searches for the following keywords: Rictor, RICTOR amplification, mTORC2, Rictor complexes, lung cancer, metastasis, progression, mTOR inhibitors. [ABSTRACT FROM AUTHOR]

RICTOR gene, which encodes the scaffold protein of mTORC2, can be amplified in various tumor types, including squamous cell carcinoma (SCC) of the lung. RICTOR amplification can lead to hyperactivation of mTORC2 and may serve as a targetable genetic alteration, including in lung SCC patients with no PD-L1 expression who are not expected to benefit from immune checkpoint inhibitor therapy. This study aimed to compare RICTOR amplification detected by fluorescence in situ hybridization (FISH) with Rictor and PD-L1 protein expression detected by immunohistochemistry (IHC) in SCC of the lung. The study was complemented by analysis of the publicly available Lung Squamous Cell Carcinoma (TCGA, Firehose legacy) dataset. RICTOR amplification was observed in 20% of our cases and 16% of the lung SCC cases of the TCGA dataset. Rictor and PD-L1 expression was seen in 74% and 44% of the cases, respectively. Rictor IHC showed two staining patterns: membrane staining (16% of the cases) and cytoplasmic staining (58% of the cases). Rictor membrane staining predicted RICTOR amplification as detected by FISH with high specificity (95%) and sensitivity (70%). We did not find any correlation between RICTOR amplification and PD-L1 expression; RICTOR amplification was detected in 18% and 26% of PD-L1 positive and negative cases, respectively. The TCGA dataset analysis showed similar results; RICTOR copy number correlated with Rictor mRNA and protein expression but showed no association with PD-L1 mRNA and protein expression. In conclusion, the correlation between RICTOR amplification and Rictor membrane staining suggests that the latter can potentially be used as a surrogate marker to identify lung SCC cases with RICTOR amplification. Since a significant proportion of PD-L1 negative SCC cases harbor RICTOR amplification, analyzing PD-L1 negative tumors by RICTOR FISH or Rictor IHC can help select patients who may benefit from mTORC2 inhibitor therapy.

The increasing knowledge of molecular alterations in malignancies, including mutations and regulatory failures in the mTOR (mechanistic target of rapamycin) signaling pathway, highlights the importance of mTOR hyperactivity as a validated target in common and rare malignancies. This review summarises recent findings on the characterization and prognostic role of mTOR kinase complexes (mTORC1 and mTORC2) activity regarding differences in their function, structure, regulatory mechanisms, and inhibitor sensitivity. We have recently identified new tumor types with RICTOR (rapamycin-insensitive companion of mTOR) amplification and associated mTORC2 hyperactivity as useful potential targets for developing targeted therapies in lung cancer and other newly described malignancies. The activity of mTOR complexes is recommended to be assessed and considered in cancers before mTOR inhibitor therapy, as current first-generation mTOR inhibitors (rapamycin and analogs) can be ineffective in the presence of mTORC2 hyperactivity. We have introduced and proposed a marker panel to determine tissue characteristics of mTOR activity in biopsy specimens, patient materials, and cell lines. Ongoing phase trials of new inhibitors and combination therapies are promising in advanced-stage patients selected by genetic alterations, molecular markers, and/or protein expression changes in the mTOR signaling pathway. Hopefully, the summarized results, our findings, and the suggested characterization of mTOR activity will support therapeutic decisions.

Small cell lung carcinoma (SCLC) is a highly malignant cancer with early metastatic dissemination and poor clinical outcomes. Mutations in the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway, including the frequently occurring rapamycin-insensitive protein (RICTOR) amplification, have been described in these tumours. Moreover, the associated mTOR hyperactivity could be exploited for personalised treatment. Our aim was to study mTOR activity, RICTOR amplification, and their role during SCLC progression. In situ mTOR activity and Rictor expression were characterised by immunohistochemistry in 50 primary and 50 brain metastatic tumours, and 14 paired SCLC patient samples. RICTOR copy number changes were analysed by fluorescence in situ hybridisation of the paired SCLC patient samples and in vivo experiments. Additionally, in vitro sensitivity to cisplatin and mTOR inhibitors was evaluated in SCLC cell lines harbouring RICTOR amplification and other mTOR pathway mutations. High Rictor expression and mTOR complex 2 (mTORC2) hyperactivity were significantly associated with brain metastases and worse overall survival. An increase in RICTOR copy number was observed in paired samples during progression. The importance of these alterations was confirmed both by the sensitising effect of vistusertib in vitro and the RICTOR copy number/expression changes in xenografts. Our study highlights the role of mTORC2 in SCLC progression. Early detection of RICTOR amplification in primary tumours and targeting mTORC2 in these cases may represent a promising novel strategy to develop personalised therapy for metastasis prevention. • High Rictor expression and mTORC2 activity were linked to brain metastases in SCLC. • Increased RICTOR copy number was observed in paired SCLC samples during progression. • Vistusertib sensitised the effect of cisplatin in SCLC cell lines in vitro. • RICTOR copy number was increased continuously in long-term xenografts. [ABSTRACT FROM AUTHOR]

RICTOR gene, which encodes the scaffold protein of mTORC2, can be amplified in various tumor types, including squamous cell carcinoma (SCC) of the lung. RICTOR amplification can lead to hyperactivation of mTORC2 and may serve as a targetable genetic alteration, including in lung SCC patients with no PD-L1 expression who are not expected to benefit from immune checkpoint inhibitor therapy. This study aimed to compare RICTOR amplification detected by fluorescence in situ hybridization (FISH) with Rictor and PD-L1 protein expression detected by immunohistochemistry (IHC) in SCC of the lung. The study was complemented by analysis of the publicly available Lung Squamous Cell Carcinoma (TCGA, Firehose legacy) dataset. RICTOR amplification was observed in 20% of our cases and 16% of the lung SCC cases of the TCGA dataset. Rictor and PD-L1 expression was seen in 74% and 44% of the cases, respectively. Rictor IHC showed two staining patterns: membrane staining (16% of the cases) and cytoplasmic staining (58% of the cases). Rictor membrane staining predicted RICTOR amplification as detected by FISH with high specificity (95%) and sensitivity (70%). We did not find any correlation between RICTOR amplification and PD-L1 expression; RICTOR amplification was detected in 18% and 26% of PD-L1 positive and negative cases, respectively. The TCGA dataset analysis showed similar results; RICTOR copy number correlated with Rictor mRNA and protein expression but showed no association with PD-L1 mRNA and protein expression. In conclusion, the correlation between RICTOR amplification and Rictor membrane staining suggests that the latter can potentially be used as a surrogate marker to identify lung SCC cases with RICTOR amplification. Since a significant proportion of PD-L1 negative SCC cases harbor RICTOR amplification, analyzing PD-L1 negative tumors by RICTOR FISH or Rictor IHC can help select patients who may benefit from mTORC2 inhibitor therapy., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Krencz, Sztankovics, Sebestyén, Pápay, Dankó, Moldvai, Lutz and Khoor.)

The increasing knowledge of molecular alterations in malignancies, including mutations and regulatory failures in the mTOR (mechanistic target of rapamycin) signaling pathway, highlights the importance of mTOR hyperactivity as a validated target in common and rare malignancies. This review summarises recent findings on the characterization and prognostic role of mTOR kinase complexes (mTORC1 and mTORC2) activity regarding differences in their function, structure, regulatory mechanisms, and inhibitor sensitivity. We have recently identified new tumor types with RICTOR (rapamycin-insensitive companion of mTOR) amplification and associated mTORC2 hyperactivity as useful potential targets for developing targeted therapies in lung cancer and other newly described malignancies. The activity of mTOR complexes is recommended to be assessed and considered in cancers before mTOR inhibitor therapy, as current first-generation mTOR inhibitors (rapamycin and analogs) can be ineffective in the presence of mTORC2 hyperactivity. We have introduced and proposed a marker panel to determine tissue characteristics of mTOR activity in biopsy specimens, patient materials, and cell lines. Ongoing phase trials of new inhibitors and combination therapies are promising in advanced-stage patients selected by genetic alterations, molecular markers, and/or protein expression changes in the mTOR signaling pathway. Hopefully, the summarized results, our findings, and the suggested characterization of mTOR activity will support therapeutic decisions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Sztankovics, Moldvai, Petővári, Dankó, Szalai, Miyaura, Varga, Nagy, Papp, Pápay, Krencz and Sebestyén.)