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Brain metastases (BMs) present a formidable obstacle across various primary cancer types, notably small cell lung cancer (SCLC), non-small cell lung cancer (NSCLC), melanomas, and breast cancers. In this investigation, we aim to evaluate the potential of genotype-guided targeted therapy while addressing the challenges of co-existing genomic alterations frequently encountered in BMs. This research explores the efficacy of adagrasib (MRTX849), a KRAS G12C inhibitor, and abemaciclib, a CDK 4/6 inhibitor, both individually and in combination against BMs originating from NSCLC cell lines harboring KRAS G12C and CDKN2A mutations. Utilizing a diverse array of methodologies encompassing cell viability assays, cell death assays, western blot analyses, and in vivo xenograft models, we elucidate both the therapeutic potential and underlying mechanisms. Distinct responses to adagrasib and abemaciclib monotherapies were observed across two different cell lines, underscoring the necessity for tailored treatment strategies. While adagrasib exhibited variable efficacy, abemaciclib consistently inhibited CDK 4/6 activity. Notably, the combination therapy demonstrated synergistic effects, suggesting a promising approach for enhanced therapeutic outcomes. Our findings from both in vitro assays and western blot analyses corroborate targeted pathway inhibition, although the observed pathway reactivation underscores the importance of optimizing dosing strategies. In vivo studies further support our in vitro findings, demonstrating efficacy but also raising concerns regarding toxicity with combination therapy. Pharmacokinetic / pharmacodynamic (PK/PD) analyses underscore potential advantages of combination therapy in terms of systemic exposure and brain penetration. Despite histological evidence of therapeutic effects, discrepancies between in vivo and in vitro caspase-dependent apoptosis results highlight the complexity of tumor biology and the challenges of translation. By Focusing on personalized treatment approaches and addressing therapeutic hurdles, this work establishes the foundation for clinical investigation in advancing the management of BMs and improving treatment outcomes in NSCLC patients.

Previous studies suggest that the IGF-I stimulates the elastin gene transcription through the unique responsive sequence on the elastin promoter, which is a putative retinoblastoma control element (RCE). This site interacts with (Sp)-family transcription factors whose delivery is mediated by the retinoblastoma protein (Rb). Since Rb (phosphorylated on serine 780) has been implicated in the initiation of the cell cycle, we speculated that a different phosphorylation of Rb might determine Rb involvement in elastogenesis. Obtained results demonstrated that, IGF-I-induced elastogenic signaling pathway in human dermal fibroblasts includes activation of cyclinE/cdk2 causing a site specific phosphorylation of Rb on threonine 821. This permits the sequestration of Sp1 by Rb before it could bind the elastin promoter, thereby allowing the elastin gene transcription. We also found that blocking of H-Ras in Costello syndrome fibroblasts (characterized by heightened proliferation and impaired elastogenesis), selectively down-regulated Rb phosphorylation on serine 780 and normalized impaired elastogenesis.

Previous studies suggest that the IGF-I stimulates the elastin gene transcription through the unique responsive sequence on the elastin promoter, which is a putative retinoblastoma control element (RCE). This site interacts with (Sp)-family transcription factors whose delivery is mediated by the retinoblastoma protein (Rb). Since Rb (phosphorylated on serine 780) has been implicated in the initiation of the cell cycle, we speculated that a different phosphorylation of Rb might determine Rb involvement in elastogenesis. Obtained results demonstrated that, IGF-I-induced elastogenic signaling pathway in human dermal fibroblasts includes activation of cyclinE/cdk2 causing a site specific phosphorylation of Rb on threonine 821. This permits the sequestration of Sp1 by Rb before it could bind the elastin promoter, thereby allowing the elastin gene transcription. We also found that blocking of H-Ras in Costello syndrome fibroblasts (characterized by heightened proliferation and impaired elastogenesis), selectively down-regulated Rb phosphorylation on serine 780 and normalized impaired elastogenesis.