Biology subjects

Katzenellenbogen, J. A.

Publications and source records attributed to Katzenellenbogen, J. A..

4 recordsLinked to original sources

bioRxiv2024

Inhibition of FOXM1 synergizes with BCL2 inhibitor Venetoclax in killing non-t(11;14) multiple myeloma cells via repressing MYC pathway

Despite significant improvements in the prognosis of Multiple Myeloma (MM), relapsed/refractory MM remains a major challenge. BCL2 inhibitor Venetoclax induced complete or very good partial responses in 6% of non-t(11;14) MM cases, compared to 27% in t(11;14) cases, when used as monotherapy in relapsed/refractory MM. Though Venetoclax was proposed to treat t(11;14) cases, the resistance became a concern. Furthermore, non-t(11;14) cases account for 80-85% of MM cases, which underscores the value of Venetoclax in non-t(11;14) MM. Here, we report a recently-invented small molecule inhibitor of FOXM1 NB73 synergizing with Venetoclax in killing MM cells. FOXM1, a critical forkhead box transcription factor in high-risk and relapsed/refractory MM, represents a promising therapeutic target of MM. We examined the mechanisms underlying the synergies of Venetoclax and NB73 using multi-omics and molecular and cellular biology tools in non-t(11;14) myeloma cell lines with high FOXM1 expression. NB73 induces immediate loss of FOXM1, decreases BCL2 expression, and increases Puma expression in myeloma cells. Venetoclax enhances NB73-induced FOXM1 ubiquitination and degradation. The NB73-Venetoclax combination abrogates the binding of FOXM1 to the promoters of genes in the MYC pathway, such as PLK1, MYC, CDC20, and CCNA2, leading to the repression of the transcription of these MYC pathway genes. The PLK1-specific inhibitor GSK461364 synergies with NB73 in suppressing myeloma cell growth. Therefore, NB73 synergizes with Venetoclax in killing myeloma cells. Conclusively, the NB73-Venetoclax combination abolishes FOXM1-mediated transcriptional activation of the MYC pathway, resulting in intensive apoptosis of myeloma cells without t(11;14) but with high FOXM1 expression. Statement of significanceThis study implicates that targeting FOXM1 will alleviate resistance to BCL2 inhibitor Venetoclax in non-t(11;14) myeloma cells expressing high FOXM1.

cancer biology↗

bioRxiv2024

Asymmetric Allostery in Estrogen Receptor-α Homodimers Drives Responses to the Ensemble of Estrogens in the Hormonal Milieu

The estrogen receptor- (ER) is thought to function only as a homodimer, but responds to a variety of environmental, metazoan, and therapeutic estrogens at sub-saturating doses, supporting binding mixtures of ligands as well as dimers that are only partially occupied. Here, we present a series of flexible ER ligands that bind to receptor dimers with individual ligand poses favoring distinct receptor conformations --receptor conformational heterodimers--mimicking the binding of two different ligands. Molecular dynamics simulations showed that the pairs of different ligand poses changed the correlated motion across the dimer interface to generate asymmetric communication between the dimer interface, the ligands, and the surface binding sites for epigenetic regulatory proteins. By examining binding of the same ligand in crystal structures of ER in the agonist versus antagonist conformers, we also showed that these allosteric signals are bidirectional. The receptor conformer can drive different ligand binding modes to support agonist versus antagonist activity profiles, a revision of ligand binding theory that has focused on unidirectional signaling from ligand to the coregulator binding site. We also observed differences in the allosteric signals between ligand and coregulator binding sites in the monomeric versus dimeric receptor, and when bound by two different ligands, states that are physiologically relevant. Thus, ER conformational heterodimers integrate two different ligand-regulated activity profiles, representing new modes for ligand-dependent regulation of ER activity. SignificanceThe estrogen receptor- (ER) regulates transcription in response to a hormonal milieu that includes low levels of estradiol, a variety of environmental estrogens, as well as ER antagonists such as breast cancer anti-hormonal therapies. While ER has been studied as a homodimer, the variety of ligand and receptor concentrations in different tissues means that the receptor can be occupied with two different ligands, with only one ligand in the dimer, or as a monomer. Here, we use X-ray crystallography and molecular dynamics simulations to reveal a new mode for ligand regulation of ER activity whereby sequence-identical homodimers can act as functional or conformational heterodimers having unique signaling characteristics, with ligand-selective allostery operating across the dimer interface integrating two different signaling outcomes.

biophysics↗

bioRxiv2020

Dual-Mechanism Estrogen Receptor Inhibitors Reveal an Ensemble of Binding Modes for Robust Breast Cancer Antagonism

Efforts to improve estrogen receptor-a (ER)-targeted therapies in breast cancer have relied upon a single mechanism, with ligands having a single side chain on the ligand core that extends outward to determine antagonism of breast cancer growth. Here, we describe inhibitors with two ER-targeting moieties, one of which uses an alternate structural mechanism to generate full antagonism, freeing the side chain to independently determine other critical properties of the ligands. By combining two molecular targeting approaches into a single ER ligand, we have generated antiestrogens that function through new mechanisms and structural paradigms to achieve antagonism. These dual-mechanism ER inhibitors (DMERIs) cause alternate, non-canonical structural perturbations of the receptor ligand-binding domain (LBD) to drive antagonism of proliferation in ER-positive breast cancer cells and in allele-specific resistance models. Solution structural and coregulator peptide binding analyses with DMERIs highlight marked differences from current standard-of-care, single-mechanism antiestrogens. These findings uncover an enhanced flexibility of the ER LBD through which it can access non-consensus conformational modes in response to DMERI binding, broadly and effectively suppressing ER activity. Significance StatementTo address the unmet clinical need for effectively suppressing estrogen receptor (ER) activity with both de novo resistance and in advanced ER-positive breast cancers that are resistant to standard-of-care antiestrogens, we have developed dual-mechanism ER inhibitors (DMERIs) that employ two distinct ER targeting moieties. These DMERI elicited non-canonical structural perturbations of the receptor ligand-binding domain and stabilized multiple antagonist sub-states within the dimer to generate highly efficacious antagonism of proliferation in ER-positive breast cancer cells and in allele-specific resistance models. This work reveals new conformational modes by which the activity of ER can be effectively suppressed to block breast cancer proliferation.

cancer biology↗

bioRxiv2018

The SERM/SERD Bazedoxifene Disrupts ESR1 Helix 12 to Overcome Acquired Hormone Resistance in Breast Cancer Cells

Acquired resistance to endocrine therapy remains a significant clinical burden for breast cancer patients. Somatic mutations in the ESR1 (estrogen receptor alpha (ER) gene ligand-binding domain (LBD) represent a recognized mechanism of acquired resistance. Antiestrogens with improved efficacy versus tamoxifen might overcome the resistant phenotype in ER+ breast cancers. Bazedoxifene (BZA) is a potent antiestrogen that is clinically approved for use in hormone replacement therapies. We find BZA possesses improved inhibitory potency against the Y537S and D538G ER mutants compared to tamoxifen and has additional inhibitory activity in combination with the CDK4/6 inhibitor palbociclib. In addition, comprehensive biophysical and structural biology studies show that BZAs selective estrogen receptor degrading (SERD) properties that override the stabilizing effects of the Y537S and D538G ER mutations.\n\nSignificanceBazedoxifene (BZA) is a potent orally available antiestrogen that is clinically approved for use in hormone replacement therapy (DUAVEE). We explore the efficacy of BZA to inhibit activating somatic mutants of ER that can arise in metastatic breast cancers after prolonged exposure to aromatase inhibitors or tamoxifen therapy. Breast cancer cell line, biophysical, and structural data show that BZA disrupts helix 12 of the ER ligand binding domain to achieve improved potency against Y537S and D538G somatic mutants compared to 4-hydroxytamoxifen.

cancer biology↗