Selective impact of ALK and MELK inhibition on ERα stability and cell proliferation in cell lines representing distinct molecular phenotypes of breast cancer.

Breast cancer (BC) is a leading cause of global cancer-related mortality in women, necessitating accurate tumor classification for timely intervention. Molecular and histological factors, including PAM50 classification, estrogen receptor α (ERα), breast cancer type 1 susceptibility protein (BRCA1), progesterone receptor (PR), and HER2 expression, contribute to intricate BC subtyping. In this work, through a combination of bioinformatic and wet lab screenings, followed by classical signal transduction and cell proliferation methods, and employing multiple BC cell lines, we identified enhanced sensitivity of ERα-positive BC cell lines to ALK and MELK inhibitors, inducing ERα degradation and diminishing proliferation in specific BC subtypes. MELK inhibition attenuated ERα transcriptional activity, impeding E2-induced gene expression, and hampering proliferation in MCF-7 cells. Synergies between MELK inhibition with 4OH-tamoxifen (Tam) and ALK inhibition with HER2 inhibitors revealed potential therapeutic avenues for ERα-positive/PR-positive/HER2-negative and ERα-positive/PR-negative/HER2-positive tumors, respectively. Our findings propose MELK as a promising target for ERα-positive/PR-positive/HER2-negative BC and highlight ALK as a potential focus for ERα-positive/PR-negative/HER2-positive BC. The synergistic anti-proliferative effects of MELK with Tam and ALK with HER2 inhibitors underscore kinase inhibitors' potential for selective treatment in diverse BC subtypes, paving the way for personalized and effective therapeutic strategies in BC management.

The antiviral drug telaprevir induces cell death by reducing FOXA1 expression in estrogen receptor α (ERα)-positive breast cancer cells.

Previously, we found that telaprevir (Tel), the inhibitor of hepatitis C virus NS3/4A serine protease, reduces estrogen receptor α (ERα) content at the transcriptional level without binding to the receptor, prevents ERα transcriptional activity, and inhibits basal and 17ß-estradiol (E2)-dependent cell proliferation in different breast cancer (BC) cell lines. Here, we further characterize the Tel action mechanisms on ERα levels and function, identify a possible molecular target of Tel in BC cells, and evaluate Tel as an antiproliferative agent for BC treatment. Tel-dependent reduction in ERα levels and function depends on a Tel-dependent decrease in FOXA1 levels and activity. The effect of Tel is transduced by the IGF1-R/AKT/FOXA1 pathway, with the antiviral compound interacting with IGF1-R. Tel prevents the proliferation of several BC cell lines, while it does not affect the proliferation of normal nontransformed cell lines, and its antiproliferative effect is correlated with the ratio of FOXA1/IGF1-R expression. In conclusion, Tel interferes with the IGF1-R/AKT/FOXA1 pathway and induces cell death in ERα-expressing BC cells. Thus, we propose that this antiviral could be repurposed for the treatment of ERα-expressing BC.

Clinically relevant CHK1 inhibitors abrogate wild-type and Y537S mutant ERα expression and proliferation in luminal primary and metastatic breast cancer cells.

BACKGROUND: Challenges exist in the clinical treatment of luminal estrogen receptor α (ERα)-positive breast cancers (BCs) both to prevent resistance to endocrine therapy (ET) and to treat ET-resistant metastatic BCs (MBC). Therefore, we evaluated if kinases could be new targets for the treatment of luminal primary and MBCs. METHODS: ~ 170 kinase inhibitors were applied to MCF-7 cells either with adaptative or genetic resistance to ET drugs and both ERα levels and cell proliferation were measured. Robust-Z-score calculation identified AZD7762 (CHK1/CHK2 inhibitor) as a positive hit. Subsequently, Kaplan-Meier analyses of CHK1 and CHK2 impact on ERα-positive BC patients relapse-free-survival (RFS), bioinformatic evaluations of CHK1 and CHK2 expression and activation status as a function of ERα activation status as well as drug sensitivity studies in ERα-positive BC cell lines, validation of the impact of the ATR:CHK1 and ATM:CHK2 pathways on the control of ERα stability and BC cell proliferation via inhibitor- and siRNA-based approaches, identification of the molecular mechanism required for inhibitor-dependent ERα degradation in BC and the impact of CHK1 and CHK2 inhibition on the 17ß-estradiol (E2):ERα signaling, synergy proliferation studies between ET-drugs and clinically relevant CHK1 inhibitors in different luminal BC cell lines, were performed. RESULTS: A reduced CHK1 expression correlates with a longer RFS in women with ERα-positive BCs. Interestingly, women carrying luminal A BC display an extended RFS when expressing low CHK1 levels. Accordingly, CHK1 and ERα activations are correlated in ERα-positive BC cell lines, and the ATR:CHK1 pathway controls ERα stability and cell proliferation in luminal A BC cells. Mechanistically, the generation of DNA replication stress rather than DNA damage induced by ATR:CHK1 pathway inhibition is a prerequisite for ERα degradation. Furthermore, CHK1 inhibition interferes with E2:ERα signaling to cell proliferation, and drugs approved for clinical treatment of primary and MBC (4OH-tamoxifen and the CDK4/CDK6 inhibitors abemaciclib and palbociclib) exert synergic effects with the CHK1 inhibitors in clinical trials for the treatment of solid tumors (AZD7762, MK8776, prexasertib) in preventing the proliferation of cells modeling primary and MBC. CONCLUSIONS: CHK1 could be considered as an appealing novel pharmacological target for the treatment of luminal primary and MBCs.

A Tale of Ice and Fire: The Dual Role for 17ß-Estradiol in Balancing DNA Damage and Genome Integrity.

17ß-estradiol (E2) regulates human physiology both in females and in males. At the same time, E2 acts as a genotoxic substance as it could induce DNA damages, causing the initiation of cellular transformation. Indeed, increased E2 plasma levels are a risk factor for the development of several types of cancers including breast cancer. This paradoxical identity of E2 undermines the foundations of the physiological definition of "hormone" as E2 works both as a homeostatic regulator of body functions and as a genotoxic compound. Here, (i) the molecular circuitries underlying this double face of E2 are reviewed, and (ii) a possible framework to reconcile the intrinsic discrepancies of the E2 function is reported. Indeed, E2 is a regulator of the DNA damage response, which this hormone exploits to calibrate its genotoxicity with its physiological effects. Accordingly, the genes required to maintain genome integrity belong to the E2-controlled cellular signaling network and are essential for the appearance of the E2-induced cellular effects. This concept requires an "upgrade" to the vision of E2 as a "genotoxic hormone", which balances physiological and detrimental pathways to guarantee human body homeostasis. Deregulation of this equilibrium between cellular pathways would determine the E2 pathological effects.