Paradoxical activation of c-Src as a drug-resistant mechanism

Caspase-3 promotes oncogene-induced malignant transformation via EndoG-dependent Src-STAT3 phosphorylation

Accumulating evidence suggests that caspase-3 plays critical roles beyond apoptosis, serving pro-survival functions in malignant transformation and tumorigenesis. However, the mechanism of non-apoptotic action of caspase-3 in oncogenic transformation remains unclear. In the present study, we show that caspase-3 is consistently activated in malignant transformation induced by exogenous expression of oncogenic cocktail (c-Myc, p53DD, Oct-4, and H-Ras) in vitro as well as in the mouse mammary tumor virus-polyomavirus middle T antigen (MMTV-PyMT) mouse model of breast cancer. Genetic ablation of caspase-3 significantly attenuated oncogene-induced transformation of mammalian cells and delayed breast cancer progression in MMTV-PyMT transgenic mice. Mechanistically, active caspase-3 triggers the translocation of endonuclease G (EndoG) from mitochondria, which migrates to the nucleus, thereby induces phosphorylation of Src-STAT3 signaling pathway to facilitate oncogenic transformation. Taken together, our data suggest that caspase-3 plays pivotal role in facilitating rather than suppressing oncogene-induced malignant transformation of mammalian cells.

FAK regulates tension transmission to the nucleus and endothelial transcriptome independent of kinase activity

The mechanical environment generated through the adhesive interaction of endothelial cells (ECs) with the matrix controls nuclear tension, preventing aberrant gene synthesis and the transition from restrictive to leaky endothelium, a hallmark of acute lung injury (ALI). However, the mechanisms controlling tension transmission to the nucleus and EC-restrictive fate remain elusive. Here, we demonstrate that, in a kinase-independent manner, focal adhesion kinase (FAK) safeguards tension transmission to the nucleus to maintain EC-restrictive fate. In FAK-depleted ECs, robust activation of the RhoA-Rho-kinase pathway increased EC tension and phosphorylation of the nuclear envelope protein, emerin, activating DNMT3a. Activated DNMT3a methylates the KLF2 promoter, impairing the synthesis of KLF2 and its target S1PR1 to induce the leaky EC transcriptome. Repleting FAK (wild type or kinase dead) or inhibiting RhoA-emerin-DNMT3a activities in damaged lung ECs restored KLF2 transcription of the restrictive EC transcriptome. Thus, FAK sensing and control of tension transmission to the nucleus govern restrictive endothelium to maintain lung homeostasis.

A proteomic approach supports the clinical relevance of TAT-Cx43266-283 in glioblastoma

Glioblastoma (GBM) is the most frequent and aggressive primary brain cancer. The Src inhibitor, TAT-Cx43266-283, exerts antitumor effects in in vitro and in vivo models of GBM. Because addressing the mechanism of action is essential to translate these results to a clinical setting, in this study we carried out an unbiased proteomic approach. Data-independent acquisition mass spectrometry proteomics allowed the identification of 190 proteins whose abundance was modified by TAT-Cx43266-283. Our results were consistent with the inhibition of Src as the mechanism of action of TAT-Cx43266-283 and unveiled antitumor effectors, such as p120 catenin. Changes in the abundance of several proteins suggested that TAT-Cx43266-283 may also impact the brain microenvironment. Importantly, the proteins whose abundance was reduced by TAT-Cx43266-283 correlated with an improved GBM patient survival in clinical datasets and none of the proteins whose abundance was increased by TAT-Cx43266-283 correlated with shorter survival, supporting its use in clinical trials.

Concurrent inhibition of ALK and SRC kinases disrupts the ALK lung tumor cell proteome

Precision oncology has revolutionized the treatment of ALK-positive lung cancer with targeted therapies. However, an unmet clinical need still to address is the treatment of refractory tumors that contain drug-induced resistant mutations in the driver oncogene or exhibit resistance through the activation of diverse mechanisms. In this study, we established mouse tumor-derived cell models representing the two most prevalent EML4-ALK variants in human lung adenocarcinomas and characterized their proteomic profiles to gain insights into the underlying resistance mechanisms. We showed that Eml4-Alk variant 3 confers a worse response to ALK inhibitors, suggesting its role in promoting resistance to targeted therapy. In addition, proteomic analysis of brigatinib-treated cells revealed the upregulation of SRC kinase, a protein frequently activated in cancer. Co-targeting of ALK and SRC showed remarkable inhibitory effects in both ALK-driven murine and ALK-patient-derived lung tumor cells. This combination induced cell death through a multifaceted mechanism characterized by profound perturbation of the (phospho)proteomic landscape and a synergistic suppressive effect on the mTOR pathway. Our study demonstrates that the simultaneous inhibition of ALK and SRC can potentially overcome resistance mechanisms and enhance clinical outcomes in ALK-positive lung cancer patients. ONE SENTENCE SUMMARY: Co-targeting ALK and SRC enhances ALK inhibitor response in lung cancer by affecting the proteomic profile, offering hope for overcoming resistance and improving clinical outcomes.

Selective and Potent PROTAC Degraders of c-Src Kinase

Using dasatinib linked to E3 ligase ligands, we identified a potent and selective dual Csk/c-Src PROTAC degrader. We then replaced dasatinib, the c-Src-directed ligand, with a conformation-selective analogue that stabilizes the αC-helix-out conformation of c-Src. Using the αC-helix-out ligand, we identified a PROTAC that is potent and selective for c-Src. We demonstrated a high degree of catalysis with our c-Src PROTACs. Using our c-Src PROTACs, we identified pharmacological advantages of c-Src degradation compared to inhibition with respect to cancer cell proliferation.

Role of c-Src in Carcinogenesis and Drug Resistance

The aberrant transformation of normal cells into cancer cells, known as carcinogenesis, is a complex process involving numerous genetic and molecular alterations in response to innate and environmental stimuli. The Src family kinases (SFK) are key components of signaling pathways implicated in carcinogenesis, with c-Src and its oncogenic counterpart v-Src often playing a significant role. The discovery of c-Src represents a compelling narrative highlighting groundbreaking discoveries and valuable insights into the molecular mechanisms underlying carcinogenesis. Upon oncogenic activation, c-Src activates multiple downstream signaling pathways, including the PI3K-AKT pathway, the Ras-MAPK pathway, the JAK-STAT3 pathway, and the FAK/Paxillin pathway, which are important for cell proliferation, survival, migration, invasion, metastasis, and drug resistance. In this review, we delve into the discovery of c-Src and v-Src, the structure of c-Src, and the molecular mechanisms that activate c-Src. We also focus on the various signaling pathways that c-Src employs to promote oncogenesis and resistance to chemotherapy drugs as well as molecularly targeted agents.

A TGF-β-responsive enhancer regulates SRC expression and epithelial-mesenchymal transition-associated cell migration

The non-receptor tyrosine kinase SRC is overexpressed and/or hyperactivated in various human cancers, and facilitates cancer progression by promoting invasion and metastasis. However, the mechanisms underlying SRC upregulation are poorly understood. In this study, we demonstrate that transforming growth factor-β (TGF-β) induces SRC expression at the transcriptional level by activating an intragenic the SRC enhancer. In the human breast epithelial cell line MCF10A, TGF-β1 stimulation upregulated one of the SRC promotors, the 1A promoter, resulting in increased SRC mRNA and protein levels. Chromatin immunoprecipitation (ChIP)-sequencing analysis revealed that the SMAD complex is recruited to three enhancer regions ∼15 kb upstream and downstream of the SRC promoter, and one of them is capable of activating the SRC promoter in response to TGF-β. JUN, a member of the activator protein (AP)-1 family, localises to the enhancer and regulates TGF-β-induced SRC expression. Furthermore, TGF-β-induced SRC upregulation plays a crucial role in epithelial-mesenchymal transition (EMT)-associated cell migration by activating the SRC-focal adhesion kinase (FAK) circuit. Overall, these results suggest that TGF-β-induced SRC upregulation promotes cancer cell invasion and metastasis in a subset of human malignancies.

An In Vitro Analysis of TKI-Based Sequence Therapy in Renal Cell Carcinoma Cell Lines

The tyrosine kinase inhibitor (TKI) cabozantinib might impede the growth of the sunitinib-resistant cell lines by targeting MET and AXL overexpression in metastatic renal cell carcinoma (mRCC). We studied the role of MET and AXL in the response to cabozantinib, particularly following long-term administration with sunitinib. Two sunitinib-resistant cell lines, 786-O/S and Caki-2/S, and the matching 786-O/WT and Caki-2/WT cells were exposed to cabozantinib. The drug response was cell-line-specific. The 786-O/S cells were less growth-inhibited by cabozantinib than 786-O/WT cells (p-value = 0.02). In 786-O/S cells, the high level of phosphorylation of MET and AXL was not affected by cabozantinib. Despite cabozantinib hampering the high constitutive phosphorylation of MET, the Caki-2 cells showed low sensitivity to cabozantinib, and this was independent of sunitinib pretreatment. In both sunitinib-resistant cell lines, cabozantinib increased Src-FAK activation and impeded mTOR expression. The modulation of ERK and AKT was cell-line-specific, mirroring the heterogeneity among the patients. Overall, the MET- and AXL-driven status did not affect cell responsiveness to cabozantinib in the second-line treatment. The activation of Src-FAK might counteract cabozantinib activity and contribute to tumor survival and may be considered an early indicator of therapy response.

Cytomegalovirus US28 regulates cellular EphA2 to maintain viral latency

Cytomegalovirus (CMV) reactivation from latency following immune dysregulation remains a serious risk for patients, often causing substantial morbidity and mortality. Here, we demonstrate the CMV-encoded G protein-coupled receptor, US28, in coordination with cellular Ephrin receptor A2, attenuates mitogen-activated protein kinase signaling, thereby limiting viral replication in latently infected primary monocytes. Furthermore, treatment of latently infected primary monocytes with dasatinib, a Food and Drug Association-approved kinase inhibitor used to treat a subset of leukemias, results in CMV reactivation. These ex vivo data correlate with our retrospective analyses of the Explorys electronic health record database, where we find dasatinib treatment is associated with a significant risk of CMV-associated disease (odds ratio 1.58, P = 0.0004). Collectively, our findings elucidate a signaling pathway that plays a central role in the balance between CMV latency and reactivation and identifies a common therapeutic cancer treatment that elevates the risk of CMV-associated disease.

Src: coordinating metabolism in cancer

Metabolism must be tightly regulated to fulfil the dynamic requirements of cancer cells during proliferation, migration, stemness and differentiation. Src is a node of several signals involved in many of these biological processes, and it is also an important regulator of cell metabolism. Glucose uptake, glycolysis, the pentose-phosphate pathway and oxidative phosphorylation are among the metabolic pathways that can be regulated by Src. Therefore, this oncoprotein is in an excellent position to coordinate and finely tune cell metabolism to fuel the different cancer cell activities. Here, we provide an up-to-date summary of recent progress made in determining the role of Src in glucose metabolism as well as the link of this role with cancer cell metabolic plasticity and tumour progression. We also discuss the opportunities and challenges facing this field.

Overcoming Paradoxical Kinase Priming by a Novel MNK1 Inhibitor

Targeting the kinases MNK1 and MNK2 has emerged as a valuable strategy in oncology. However, most of the advanced inhibitors are acting in an adenosine triphosphate (ATP)-competitive mode, precluding the evaluation of different binding modes in preclinical settings. Using rational design, we identified and validated the 4,6-diaryl-pyrazolo[3,4-b]pyridin-3-amine scaffold as the core for MNK inhibitors. Signaling pathway analysis confirmed a direct effect of the hit compound EB1 on MNKs, and in line with the reported function of these kinases, EB1 only affects the growth of tumor but not normal cells. Molecular modeling revealed the binding of EB1 to the inactive conformation of MNK1 and the interaction with the specific DFD motif. This novel mode of action appears to be superior to the ATP-competitive inhibitors, which render the protein in a pseudo-active state. Overcoming this paradoxical activation of MNKs by EB1 represents therefore a promising starting point for the development of a novel generation of MNK inhibitors.

A Conformation Selective Mode of Inhibiting SRC Improves Drug Efficacy and Tolerability

Despite the approval of several multikinase inhibitors that target SRC and the overwhelming evidence of the role of SRC in the progression and resistance mechanisms of many solid malignancies, inhibition of its kinase activity has thus far failed to improve patient outcomes. Here we report the small molecule eCF506 locks SRC in its native inactive conformation, thereby inhibiting both enzymatic and scaffolding functions that prevent phosphorylation and complex formation with its partner FAK. This mechanism of action resulted in highly potent and selective pathway inhibition in culture and in vivo. Treatment with eCF506 resulted in increased antitumor efficacy and tolerability in syngeneic murine cancer models, demonstrating significant therapeutic advantages over existing SRC/ABL inhibitors. Therefore, this mode of inhibiting SRC could lead to improved treatment of SRC-associated disorders. SIGNIFICANCE: Small molecule-mediated inhibition of SRC impairing both catalytic and scaffolding functions confers increased anticancer properties and tolerability compared with other SRC/ABL inhibitors.