Genetic Silencing of AKT Induces Melanoma Cell Death via mTOR Suppression

Aberrant activation of the PI3K-AKT pathway is common in many cancers, including melanoma, and AKT1, 2 and 3 (AKT1-3) are bona fide oncoprotein kinases with well-validated downstream effectors. However, efforts to pharmacologically inhibit AKT have proven to be largely ineffective. In this study, we observed paradoxical effects following either pharmacologic or genetic inhibition of AKT1-3 in melanoma cells. Although pharmacological inhibition was without effect, genetic silencing of all three AKT paralogs significantly induced melanoma cell death through effects on mTOR. This phenotype was rescued by exogenous AKT1 expression in a kinase-dependent manner. Pharmacological inhibition of PI3K and mTOR with a novel dual inhibitor effectively suppressed melanoma cell proliferation in vitro and inhibited tumor growth in vivo. Furthermore, this single-agent-targeted therapy was well-tolerated in vivo and was effective against MAPK inhibitor-resistant patient-derived melanoma xenografts. These results suggest that inhibition of PI3K and mTOR with this novel dual inhibitor may represent a promising therapeutic strategy in this disease in both the first-line and MAPK inhibitor-resistant setting.

Abstract 2853: TP-6379, an investigational TGFBR1 inhibitor, shows improvement in survival and enhances activity of standard of care in preclinical ovarian cancer models

Ovarian cancer is still associated with poor prognosis and remains amongst the leading causes of cancer related deaths in females. High recurrence rates, resistance to chemotherapy, and meager outcome highlight the need for improved therapies that stem from understanding the complex and multifactorial etiology of ovarian malignancies. Transforming growth factor-β (TGF-β) signaling can regulate both oncogenesis and metastasis in ovarian cancer (Kumri et al. 2021). This, in part, is done by affecting apoptosis and survival mechanisms, epithelial to mesenchymal transition, immune cell recruitment and response. Inhibition of the TGF-β signaling pathway is a potential pharmaceutical approach for treating ovarian malignancies.TP-6379 is a potent and orally available investigational TGF-β receptor 1 (TGFBR1) inhibitor and is currently in preclinical development at Sumitomo Pharma Oncology, Inc. (SMP Oncology). We hypothesized that TP-6379 may inhibit the TGF-β signaling pathway and show activity in preclinical ovarian cancer models. TP-6379 was observed to inhibit TGFBR1 potently in a biochemical kinase assay. Dose dependent increase in compound concentration was observed in ES-2 tumor burdened animals treated with TP-6379. Preclinical data showed TP-6379 (150 mg/kg, BID) treatment significantly improved overall survival compared to vehicle treatment in an ES-2 mouse xenograft model of clear cell carcinoma. We hypothesize this result was, in part, due to alleviation of ovarian cancer induced cachexia, as animals treated with TP-6379 showed retention of muscle mass in their hind limbs compared to the vehicle treated animals. To investigate a combination effect with the standard of care in ovarian cancer, a SK-OV-3 ovarian cancer adenocarcinoma cell line was treated in vitro with TP-6379 and paclitaxel. Class III β-tubulin (TUBB3), a potential resistance mechanism to paclitaxel, showed induced expression in response to TGF-β, paclitaxel or both, after 24 hr treatment, and this effect was observed to be inhibited by TP-6379 treatment. In a SK-OV-3 xenograft model, TP-6379 (150 mg/kg, BID) treatment showed the trend of tumor growth inhibition (TGI) as a monotherapy and showed enhanced TGI in combination with paclitaxel (7.5 mg/kg, QW) when compared to vehicle treatment. Combination treatment in this xenograft model showed significant reduction of TUBB3 mRNA compared to paclitaxel treatment alone. In conclusion, our preliminary preclinical studies have shown promising activity for TP-6379 in ovarian malignancies as monotherapy and/or in combination with standard of care. TP-6379 may be a viable therapeutic option by targeting the TGF-β pathway in ovarian cancer.

Citation Format: Tetyana V. Forostyan, David A. Kircher, Richard E. Heinz, Curtis Allred, Sal Sommakia, Yuta Matsumura, Adam Siddiqui, Jason M. Foulks, Steven L. Warner. TP-6379, an investigational TGFBR1 inhibitor, shows improvement in survival and enhances activity of standard of care in preclinical ovarian cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2853.

The role of PI3'-lipid signalling in melanoma initiation, progression and maintenance

Phosphatidylinositol-3'-kinases (PI3Ks) are a family of lipid kinases that phosphorylate the 3' hydroxyl (OH) of the inositol ring of phosphatidylinositides (PI). Through their downstream effectors, PI3K generated lipids (PI3K-lipids hereafter) such as PI(3,4,5)P3 and PI(3,4)P2 regulate myriad biochemical and biological processes in both normal and cancer cells including responses to growth hormones and cytokines; the cell division cycle; cell death; cellular growth; angiogenesis; membrane dynamics; and autophagy and many aspects of cellular metabolism. Engagement of receptor tyrosine kinase by their cognate ligands leads to activation of members of the Class I family of PI3'-kinases (PI3Kα, β, δ & γ) leading to accumulation of PI3K-lipids. Importantly, PI3K-lipid accumulation is antagonized by the hydrolytic action of a number of PI3K-lipid phosphatases, most notably the melanoma suppressor PTEN (lipid phosphatase and tensin homologue). Downstream of PI3K-lipid production, the protein kinases AKT1-3 are believed to be key effectors of PI3'-kinase signalling in cells. Indeed, in preclinical models, activation of the PI3K→AKT signalling axis cooperates with alterations such as expression of the BRAFV600E oncoprotein kinase to promote melanoma progression and metastasis. In this review, we describe the different classes of PI3K-lipid effectors, and how they may promote melanomagenesis, influence the tumour microenvironment, melanoma maintenance and progression to metastatic disease. We also provide an update on both FDA-approved or experimental inhibitors of the PI3K→AKT pathway that are currently being evaluated for the treatment of melanoma either in preclinical models or in clinical trials.

Abstract 2736: AKT1E17K activates focal adhesion kinase and promotes melanoma brain metastasis

Hyper-activation of the PI3K/AKT signaling pathway occurs in most metastatic melanomas and increased PI3K/AKT pathway activity correlates with disease progression. The serine/threonine kinase, AKT, represents a major signaling hub within the pathway and consists of three highly conserved paralogs that have both distinct and overlapping functions. Activating mutations of AKT1 and AKT3 occur in human melanoma but their role in melanoma formation and metastasis remains unclear. Using an established melanoma mouse model, we evaluated the ability of constitutively active E17K, E40K, or Q79K mutants of each AKT paralog to promote tumor progression and metastasis in the context of BRAFV600E expression and loss of Cdkn2a and Pten. Expression of AKT1E17K promoted highly aggressive melanomas that metastasized to the lungs and brain. This metastatic phenotype was not significantly observed in the case of other mutant AKT-positive tumors, suggesting that the AKT paralogs have distinct, non-overlapping roles in the development of melanoma metastases. AKT1E17K-positive tumors showed AKT1E17K-dependent up-regulation of multiple focal adhesion (FA) factors, which are key components of focal adhesions and established stimulators of cell motility, as well as phosphorylation of focal adhesion kinase (FAK). Ectopic expression of AKT1E17K in non-metastatic melanoma cells increased cell invasion, a phenotype abrogated by pharmacological inhibition of AKT or FAK. These findings strongly suggest that one mechanism by which AKT1 promotes melanoma metastasis is through regulation and activation of proteins involved in focal adhesions. This has important implications for the development of therapeutic strategies aimed at preventing or treating disseminated disease.

Citation Format: David A. Kircher, Kirby A. Trombetti, Mark R. Silvis, Gennie L. Parkman, Grant M. Fischer, Stephanie N. Angel, Christopher M. Stehn, Sean C. Strain, Allie H. Grossmann, Keith L. Duffy, Martin McMahon, Michael A. Davies, Michelle C. Mendoza, Matthew W. VanBrocklin, Sheri L. Holmen. AKT1E17K activates focal adhesion kinase and promotes melanoma brain metastasis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2736.

AKT1E17K Activates Focal Adhesion Kinase and Promotes Melanoma Brain Metastasis

Alterations in the PI3K/AKT pathway occur in up to 70% of melanomas and are associated with disease progression. The three AKT paralogs are highly conserved but data suggest they have distinct functions. Activating mutations of AKT1 and AKT3 occur in human melanoma but their role in melanoma formation and metastasis remains unclear. Using an established melanoma mouse model, we evaluated E17K, E40K, and Q79K mutations in AKT1, AKT2, and AKT3 and show that mice harboring tumors expressing AKT1E17K had the highest incidence of brain metastasis and lowest mean survival. Tumors expressing AKT1E17K displayed elevated levels of focal adhesion factors and enhanced phosphorylation of focal adhesion kinase (FAK). AKT1E17K expression in melanoma cells increased invasion and this was reduced by pharmacologic inhibition of either AKT or FAK. These data suggest that the different AKT paralogs have distinct roles in melanoma brain metastasis and that AKT and FAK may be promising therapeutic targets. IMPLICATIONS: This study suggests that AKT1E17K promotes melanoma brain metastasis through activation of FAK and provides a rationale for the therapeutic targeting of AKT and/or FAK to reduce melanoma metastasis.

The Small GTPase ARF6 Activates PI3K in Melanoma to Induce a Prometastatic State

Melanoma has an unusual capacity to spread in early-stage disease, prompting aggressive clinical intervention in very thin primary tumors. Despite these proactive efforts, patients with low-risk, low-stage disease can still develop metastasis, indicating the presence of permissive cues for distant spread. Here, we show that constitutive activation of the small GTPase ARF6 (ARF6^Q67L) is sufficient to accelerate metastasis in mice with BRAF^V600E/Cdkn2a^NULL melanoma at a similar incidence and severity to Pten loss, a major driver of PI3K activation and melanoma metastasis. ARF6^Q67L promoted spontaneous metastasis from significantly smaller primary tumors than PTEN^NULL, implying an enhanced ability of ARF6-GTP to drive distant spread. ARF6 activation increased lung colonization from circulating melanoma cells, suggesting that the prometastatic function of ARF6 extends to late steps in metastasis. Unexpectedly, ARF6^Q67L tumors showed upregulation of Pik3r1 expression, which encodes the p85 regulatory subunit of PI3K. Tumor cells expressing ARF6^Q67L displayed increased PI3K protein levels and activity, enhanced PI3K distribution to cellular protrusions, and increased AKT activation in invadopodia. ARF6 is necessary and sufficient for activation of both PI3K and AKT, and PI3K and AKT are necessary for ARF6-mediated invasion. We provide evidence for aberrant ARF6 activation in human melanoma samples, which is associated with reduced survival. Our work reveals a previously unknown ARF6-PI3K-AKT proinvasive pathway, it demonstrates a critical role for ARF6 in multiple steps of the metastatic cascade, and it illuminates how melanoma cells can acquire an early metastatic phenotype in patients. SIGNIFICANCE: These findings reveal a prometastatic role for ARF6 independent of tumor growth, which may help explain how melanoma spreads distantly from thin, early-stage primary tumors.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/11/2892/F1.large.jpg.

Molecular Profiling Reveals Unique Immune and Metabolic Features of Melanoma Brain Metastases

There is a critical need to improve our understanding of the pathogenesis of melanoma brain metastases (MBM). Thus, we performed RNA sequencing on 88 resected MBMs and 42 patient-matched extracranial metastases; tumors with sufficient tissue also underwent whole-exome sequencing, T-cell receptor sequencing, and IHC. MBMs demonstrated heterogeneity of immune infiltrates that correlated with prior radiation and post-craniotomy survival. Comparison with patient-matched extracranial metastases identified significant immunosuppression and enrichment of oxidative phosphorylation (OXPHOS) in MBMs. Gene-expression analysis of intracranial and subcutaneous xenografts, and a spontaneous MBM model, confirmed increased OXPHOS gene expression in MBMs, which was also detected by direct metabolite profiling and [U-13C]-glucose tracing in vivo. IACS-010759, an OXPHOS inhibitor currently in early-phase clinical trials, improved survival of mice bearing MAPK inhibitor-resistant intracranial melanoma xenografts and inhibited MBM formation in the spontaneous MBM model. The results provide new insights into the pathogenesis and therapeutic resistance of MBMs. SIGNIFICANCE: Improving our understanding of the pathogenesis of MBMs will facilitate the rational development and prioritization of new therapeutic strategies. This study reports the most comprehensive molecular profiling of patient-matched MBMs and extracranial metastases to date. The data provide new insights into MBM biology and therapeutic resistance.See related commentary by Egelston and Margolin, p. 581.This article is highlighted in the In This Issue feature, p. 565.

Melanoma Brain Metastasis: Mechanisms, Models, and Medicine

The development of brain metastases in patients with advanced stage melanoma is common, but the molecular mechanisms responsible for their development are poorly understood. Melanoma brain metastases cause significant morbidity and mortality and confer a poor prognosis; traditional therapies including whole brain radiation, stereotactic radiotherapy, or chemotherapy yield only modest increases in overall survival (OS) for these patients. While recently approved therapies have significantly improved OS in melanoma patients, only a small number of studies have investigated their efficacy in patients with brain metastases. Preliminary data suggest that some responses have been observed in intracranial lesions, which has sparked new clinical trials designed to evaluate the efficacy in melanoma patients with brain metastases. Simultaneously, recent advances in our understanding of the mechanisms of melanoma cell dissemination to the brain have revealed novel and potentially therapeutic targets. In this review, we provide an overview of newly discovered mechanisms of melanoma spread to the brain, discuss preclinical models that are being used to further our understanding of this deadly disease and provide an update of the current clinical trials for melanoma patients with brain metastases.

Melanoma metastases caught in the AKT

Dysregulated protein kinase B alpha (PKB/AKT1) signaling has been increasingly implicated in melanoma metastasis to distant organs, especially the brain. In a recent study, we expressed activated AKT1 in a non-metastatic melanoma model in vivo and discovered that AKT1 activation decreased tumor latency and elicited lung and brain metastases in this context.

AKT1 Activation Promotes Development of Melanoma Metastases

Metastases are the major cause of melanoma-related mortality. Previous studies implicating aberrant AKT signaling in human melanoma metastases led us to evaluate the effect of activated AKT1 expression in non-metastatic BRAF(V600E)/Cdkn2a(Null) mouse melanomas in vivo. Expression of activated AKT1 resulted in highly metastatic melanomas with lung and brain metastases in 67% and 17% of our mice, respectively. Silencing of PTEN in BRAF(V600E)/Cdkn2a(Null) melanomas cooperated with activated AKT1, resulting in decreased tumor latency and the development of lung and brain metastases in nearly 80% of tumor-bearing mice. These data demonstrate that AKT1 activation is sufficient to elicit lung and brain metastases in this context and reveal that activation of AKT1 is distinct from PTEN silencing in metastatic melanoma progression. These findings advance our knowledge of the mechanisms driving melanoma metastasis and may provide valuable insights for clinical management of this disease.