Abstract
We investigated the therapeutic potential of targeting integrin/FAK-dependent signaling, an adhesion receptor-mediated pathway that has been increasingly linked to non-small cell lung cancer (NSCLC) malignancy. Our analysis of the TCGA cohort showed that a subset of pro-tumorigenic integrins, including α1β1, α2β1, α3β1, α5β1, and α6β4, were frequently amplified or upregulated at the genomic or mRNA level in KRAS or EGFR mutation/overexpression-enriched adenocarcinomas. These alterations appeared complementary, correlated with poor patient survival (p < 0.0072), and were collaborative with KRAS mutation-coupled αv integrins (p < 0.00159). Since integrin/FAK-dependent signaling is tightly coupled with normal human physiology, we sought to use a synthetic lethal-type targeting comprising of VS-6063, a chemical inhibitor of integrin-mediated FAK activity, and A549 cells, which carry a KRAS mutation and EGFR overexpression. Our screening analysis revealed that JQ1 and IBET-762, inhibitors of epigenetic reader BRD4, and LBH589, a pan inhibitor of histone deacetylases (HDACs), exhibited synergy with VS-6063 in mitigating tumor cell viability. This epigenetic link was corroborated by strong effects of additional inhibitors and RNAi-mediated knockdown of FAK and BRD4 or its downstream effector, c-Myc. Low doses of JQ1 (≤0.5 μM) markedly escalated efficacy of VS-6063 across a panel of 10 NSCLC cell lines. This catalyst-like effect is in line with the oncogenic landscape in the TCGA cohort since c-Myc falls downstream of the KRAS and EGFR oncogenes. Mechanistically, co-inhibiting the integrin-FAK and BRD4/c-Myc axes synergistically induced apoptotic cell death and DNA damage response, and impaired stemness-associated tumorsphere formation. These effects were accompanied by a marked inhibition of Akt- and p130Cas/Src-dependent signaling, but not Erk1/2 activity. Meanwhile, JQ1 alone or in combination with VS-6063 attenuated cell-cell adhesion and extracellular matrix (ECM)-dependent cell spreading, which is reminiscent of phenotype induced by malfunctional E-cadherin or integrins. Paradoxically, this phenotypic impact coincided with downregulation of epithelial-mesenchymal transition (EMT)-inducting transcription factor ZEB1 or Snail. Finally, we showed that the effect of the VS-6063/JQ1 combination was nearly equivalent to that of VS-6063 plus Carboplatin or Osimertinib. Overall, our study indicates that the integrin/FAK and BRD4/c-Myc axes cooperatively drive NSCLC virulence, and a co-targeting may provide a line of therapy capable of overcoming EGFR/KRAS-driven malignancy.
Highlights
Lung cancer, non-small cell lung cancer (NSCLC), is one of leading causes of cancer-related deaths worldwide, despite recent progress in targeted therapies and early diagnosis for the disease (Kleczko and Heasley, 2018; Cao and Chen, 2019; Hinz et al, 2019; Li W.Y. et al, 2019)
The lung adenocarcinomas exhibiting integrin upregulation were highly enriched in mutation and mRNA upregulation of KRAS or EGFR, and were linked to poor clinical prognosis compared to those carrying alterations in single oncogene (Supplementary Figure S1B)
We describe a close crosstalk between the integrin/FAKdependent pathway and the BRD4-associated epigenetic network in human NSCLC in the context of KRAS mutations
Summary
Non-small cell lung cancer (NSCLC), is one of leading causes of cancer-related deaths worldwide, despite recent progress in targeted therapies and early diagnosis for the disease (Kleczko and Heasley, 2018; Cao and Chen, 2019; Hinz et al, 2019; Li W.Y. et al, 2019). More than 30% of NSCLC patients, carry active KRAS mutations and are confronted with limited therapeutic options with a poor clinical outlook (Brugger et al, 2011; Vestergaard et al, 2018). While the chemical inhibitor-based targeting of this mutational KRAS is under clinical trial investigation (Yuan et al, 2018), there remains a lack of an effective therapeutic strategy for treating NSCLC tumors carrying non G/C substitutions of KRAS or with co-activation of other oncogenes or tumor suppressors (Yuan et al, 2018; Skoulidis and Heymach, 2019). More targeted therapies are still urgently needed to enhance NSCLC treatment
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