Giredestrant reverses progesterone hypersensitivity driven by estrogen receptor mutations in breast cancer.

ESR1 (estrogen receptor 1) hotspot mutations are major contributors to therapeutic resistance in estrogen receptor-positive (ER+) breast cancer. Such mutations confer estrogen independence to ERα, providing a selective advantage in the presence of estrogen-depleting aromatase inhibitors. In addition, ESR1 mutations reduce the potency of tamoxifen and fulvestrant, therapies that bind ERα directly. These limitations, together with additional liabilities, inspired the development of the next generation of ERα-targeted therapeutics, of which giredestrant is a high-potential candidate. Here, we generated Esr1 mutant-expressing mammary gland models and leveraged patient-derived xenografts (PDXs) to investigate the biological properties of the ESR1 mutations and their sensitivity to giredestrant in vivo. In the mouse mammary gland, Esr1 mutations promote hypersensitivity to progesterone, triggering pregnancy-like tissue remodeling and profoundly elevated proliferation. These effects were driven by an altered progesterone transcriptional response and underpinned by gained sites of ERα-PR (progesterone receptor) cobinding at the promoter regions of pro-proliferation genes. PDX experiments showed that the mutant ERα-PR proliferative program is also relevant in human cancer cells. Giredestrant suppressed the mutant ERα-PR proliferation in the mammary gland more so than the standard-of-care agents, tamoxifen and fulvestrant. Giredestrant was also efficacious against the progesterone-stimulated growth of ESR1 mutant PDX models. In addition, giredestrant demonstrated activity against a molecularly characterized ESR1 mutant tumor from a patient enrolled in a phase 1 clinical trial. Together, these data suggest that mutant ERα can collaborate with PR to drive protumorigenic proliferation but remain sensitive to inhibition by giredestrant.

Therapeutic resistance and susceptibility is shaped by cooperative multi-compartment tumor adaptation.

Emerging research suggests that multiple tumor compartments can influence treatment responsiveness and relapse, yet the search for therapeutic resistance mechanisms remains largely focused on acquired genomic alterations in cancer cells. Here we show how treatment-induced changes occur in multiple tumor compartments during tumor relapse and can reduce benefit of follow-on therapies. By using serial biopsies, next-generation sequencing, and single-cell transcriptomics, we tracked the evolution of multiple cellular compartments within individual lesions during first-line treatment response, relapse, and second-line therapeutic interventions in an autochthonous model of melanoma. We discovered that although treatment-relapsed tumors remained genetically stable, they converged on a shared resistance phenotype characterized by dramatic changes in tumor cell differentiation state, immune infiltration, and extracellular matrix (ECM) composition. Similar alterations in tumor cell differentiation were also observed in more than half of our treatment-relapsed patient tumors. Tumor cell-state changes were coincident with ECM remodeling and increased tumor stiffness, which alone was sufficient to alter tumor cell fate and reduce treatment responses in melanoma cell lines in vitro. Despite the absence of acquired mutations in the targeted pathway, resistant tumors showed significantly decreased responsiveness to second-line therapy intervention within the same pathway. The ability to preclinically model relapse and refractory settings-while capturing dynamics within and crosstalk between all relevant tumor compartments-provides a unique opportunity to better design and sequence appropriate clinical interventions.

Kras mutant genetically engineered mouse models of human cancers are genomically heterogeneous.

KRAS mutant tumors are largely recalcitrant to targeted therapies. Genetically engineered mouse models (GEMMs) of Kras mutant cancer recapitulate critical aspects of this disease and are widely used for preclinical validation of targets and therapies. Through comprehensive profiling of exomes and matched transcriptomes of >200 KrasG12D-initiated GEMM tumors from one lung and two pancreatic cancer models, we discover that significant intratumoral and intertumoral genomic heterogeneity evolves during tumorigenesis. Known oncogenes and tumor suppressor genes, beyond those engineered, are mutated, amplified, and deleted. Unlike human tumors, the GEMM genomic landscapes are dominated by copy number alterations, while protein-altering mutations are rare. However, interspecies comparative analyses of the genomic landscapes demonstrate fidelity between genes altered in KRAS mutant human and murine tumors. Genes that are spontaneously altered during murine tumorigenesis are also among the most prevalent found in human indications. Using targeted therapies, we also demonstrate that this inherent tumor heterogeneity can be exploited preclinically to discover cancer-specific and genotype-specific therapeutic vulnerabilities. Focusing on Kras allelic imbalance, a feature shared by all three models, we discover that MAPK pathway inhibition impinges uniquely on this event, indicating distinct susceptibility and fitness advantage of Kras-mutant cells. These data reveal previously unknown genomic diversity among KrasG12D-initiated GEMM tumors, places them in context of human patients, and demonstrates how to exploit this inherent tumor heterogeneity to discover therapeutic vulnerabilities.

Targeting LGR5+ cells with an antibody-drug conjugate for the treatment of colon cancer.

Cancer stem cells (CSCs) are hypothesized to actively maintain tumors similarly to how their normal counterparts replenish differentiated cell types within tissues, making them an attractive therapeutic target for the treatment of cancer. Because most CSC markers also label normal tissue stem cells, it is unclear how to selectively target them without compromising normal tissue homeostasis. We evaluated a strategy that targets the cell surface leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5), a well-characterized tissue stem cell and CSC marker, with an antibody conjugated to distinct cytotoxic drugs. One antibody-drug conjugate (ADC) demonstrated potent tumor efficacy and safety in vivo. Furthermore, the ADC decreased tumor size and proliferation, translating to improved survival in a genetically engineered model of intestinal tumorigenesis. These data demonstrate that ADCs can be leveraged to exploit differences between normal and cancer stem cells to successfully target gastrointestinal cancers.

Castration-resistant Lgr5(+) cells are long-lived stem cells required for prostatic regeneration.

The adult prostate possesses a significant regenerative capacity that is of great interest for understanding adult stem cell biology. We demonstrate that leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5) is expressed in a rare population of prostate epithelial progenitor cells, and a castration-resistant Lgr5(+) population exists in regressed prostate tissue. Genetic lineage tracing revealed that Lgr5(+) cells and their progeny are primarily luminal. Lgr5(+) castration-resistant cells are long lived and upon regeneration, both luminal Lgr5(+) cells and basal Lgr5(+) cells expand. Moreover, single Lgr5(+) cells can generate multilineage prostatic structures in renal transplantation assays. Additionally, Lgr5(+) cell depletion revealed that the regenerative potential of the castrated adult prostate depends on Lgr5(+) cells. Together, these data reveal insights into the cellular hierarchy of castration-resistant Lgr5+ cells, indicate a requirement for Lgr5(+) cells during prostatic regeneration, and identify an Lgr5(+) adult stem cell population in the prostate.

Antitumor efficacy of a bispecific antibody that targets HER2 and activates T cells.

Clinical results from the latest strategies for T-cell activation in cancer have fired interest in combination immunotherapies that can fully engage T-cell immunity. In this study, we describe a trastuzumab-based bispecific antibody, HER2-TDB, which targets HER2 and conditionally activates T cells. HER2-TDB specifically killed HER2-expressing cancer cells at low picomolar concentrations. Because of its unique mechanism of action, which is independent of HER2 signaling or chemotherapeutic sensitivity, HER2-TDB eliminated cells refractory to currently approved HER2 therapies. HER2-TDB exhibited potent antitumor activity in four preclinical model systems, including MMTV-huHER2 and huCD3 transgenic mice. PD-L1 expression in tumors limited HER2-TDB activity, but this resistance could be reversed by anti-PD-L1 treatment. Thus, combining HER2-TDB with anti-PD-L1 yielded a combination immunotherapy that enhanced tumor growth inhibition, increasing the rates and durability of therapeutic response.

Androgen deprivation causes epithelial-mesenchymal transition in the prostate: implications for androgen-deprivation therapy.

Androgen deprivation is currently a standard-of-care, first-line therapy for prostate cancer in the United States. Although this regimen effectively regresses androgen-dependent disease, relapse often occurs in an androgen-independent manner and is associated with poor prognosis. Such castration-resistant prostate cancer represents a major clinical challenge, and the mechanisms underlying castration resistance are not fully understood. Epithelial-mesenchymal transition (EMT) is a key developmental process and has also been implicated in cancer metastasis and therapeutic resistance in recent years. However, the factors contributing to EMT in human cancers remain unclear. Here, we show that both normal mouse prostate tissue and human LuCaP35 prostate tumor explants display an EMT as well as increased stem cell-like features following androgen deprivation. Importantly, we observed similar changes in mesenchymal features in prostate tumors from patients treated with androgen-deprivation therapy. In addition, we have delineated a feedback loop involving the androgen receptor and the Zeb1 transcription factor that seems to mediate this transition. In summary, we show for the first time that androgen deprivation induces EMT in both normal prostate and prostate cancer, revealing a potentially important consequence of a standard-of-care treatment for prostate cancer. This finding could have significant implications for second-line treatment strategies in this clinical setting.

Pegylated kunitz domain inhibitor suppresses hepsin-mediated invasive tumor growth and metastasis.

The transmembrane serine protease hepsin is one of the most highly upregulated genes in prostate cancer. Here, we investigated its tumor-promoting activity by use of a mouse orthotopic prostate cancer model. First, we compared the tumor growth of low hepsin-expressing LnCaP-17 cells with hepsin-overexpressing LnCaP-34 cells. After implantation of cells into the left anterior prostate lobe, LnCaP-34 tumors not only grew faster based on increased serum prostate-specific antigen levels but also metastasized to local lymph nodes and, most remarkably, invaded the contralateral side of the prostate at a rate of 100% compared with only 18% for LnCaP-17 tumors. The increased tumor growth was not due to nonspecific gene expression changes and was not predicted from the unaltered in vitro growth and invasion of LnCaP-34 cells. A likely explanation is that the in vivo effects of hepsin were mediated by specific hepsin substrates present in the tumor stroma. In a second study, mice bearing LnCaP-34 tumors were treated with a PEGylated form of Kunitz domain-1, a potent hepsin active site inhibitor derived from hepatocyte growth factor activator inhibitor-1 (K(i)(app) 0.30 +/- 0.02 nmol/L). Treatment of established tumors with PEGylated Kunitz domain-1 decreased contralateral prostate invasion (46% weight reduction) and lymph node metastasis (50% inhibition). Moreover, serum prostate-specific antigen level remained reduced during the entire treatment period, reaching a maximal reduction of 76% after 5 weeks of dosing. The findings show that hepsin promotes invasive prostate tumor growth and metastasis and suggest that active site-directed hepsin inhibition could be effective in prostate cancer therapy.

Prostate-specific Klf6 inactivation impairs anterior prostate branching morphogenesis through increased activation of the Shh pathway.

Krüppel-like factor 6 (Klf6) belongs to a family of zinc finger transcription factors known to play a role in development and tumor suppression. Although Klf6 is highly mutated in prostate cancer, its function in prostate development is unknown. We have generated a prostate-specific Klf6-deficient mouse model and report here a novel role for Klf6 in the regulation of prostate branching morphogenesis. Importantly, our study reveals a novel relationship between Klf6 and the Shh pathway. Klf6-deficiency leads to elevated levels of hedgehog pathway components (Shh, Ptc, and Gli) and loss of their localized expression, which in turn causes impaired lateral branching.

Generation of a prostate from a single adult stem cell.

The existence of prostate stem cells (PSCs) was first postulated from the observation that normal prostate regeneration can occur after repeated cycles of androgen deprivation and replacement in rodents. Given the critical role of PSCs in maintaining prostate tissue integrity and their potential involvement in prostate tumorigenesis, it is important to define specific markers for normal PSCs. Several cell-surface markers have been reported to identify candidate PSCs, including stem cell antigen-1 (Sca-1, also known as Ly6a), CD133 (Prom1) and CD44 (refs 3-10). However, many non-PSCs in the mouse prostate also express these markers and thus identification of a more defined PSC population remains elusive. Here we identify CD117 (c-kit, stem cell factor receptor) as a new marker of a rare adult mouse PSC population, and demonstrate that a single stem cell defined by the phenotype Lin(-)Sca-1(+)CD133(+)CD44(+)CD117(+) can generate a prostate after transplantation in vivo. CD117 expression is predominantly localized to the region of the mouse prostate proximal to the urethra and is upregulated after castration-induced prostate involution-two characteristics consistent with that of a PSC marker. CD117(+) PSCs can generate functional, secretion-producing prostates when transplanted in vivo. Moreover, CD117(+) PSCs have long-term self-renewal capacity, as evidenced by serial isolation and transplantation in vivo. Our data establish that single cells in the adult mouse prostate with multipotent, self-renewal capacity are defined by a Lin(-)Sca-1(+)CD133(+)CD44(+)CD117(+) phenotype.

Regulation of epithelial branching morphogenesis and cancer cell growth of the prostate by Wnt signaling.

Although Wnt signaling has been shown to be important for embryonic morphogenesis and cancer pathogenesis of several tissues, its role in prostatic development and tumorigenesis is not well understood. Here we show that Wnt signaling regulated prostatic epithelial branching morphogenesis and luminal epithelial cell differentiation in developing rat prostate organ cultures. Specifically, Wnt signaling regulated the proliferation of prostate epithelial progenitor cells. Assessment of the expression levels of a Wnt pathway transcriptional target gene, Axin2, showed that the Wnt pathway was activated in the developing prostate, but was down-regulated in the adult. Castration resulted in an upregulation of Axin2 whereas androgen replacement resulted in a down regulation of Axin2. Such dynamic changes of Wnt activity was also confirmed in a BAT-gal transgenic mouse line in which beta-galactosidase reporter is expressed under the control of beta-catenin/T cell factor responsive elements. Furthermore, we evaluated the role of Wnt signaling in prostate tumorigenesis. Axin2 expression was found upregulated in the majority of human prostate cancer cell lines examined. Moreover, addition of a Wnt pathway inhibitor, Dickkopf 1 (DKK1), into the culture medium significantly inhibited prostate cancer cell growth and migration. These findings suggest that Wnt signaling regulates prostatic epithelial ductal branching morphogenesis by influencing cell proliferation, and highlights a role for Wnt pathway activation in prostatic cancer progression.

Expression profiling of the mouse prostate after castration and hormone replacement: implication of H-cadherin in prostate tumorigenesis.

Mice have been used extensively for studying normal prostate development and for generation of transgenic or knock-out prostate cancer animal models. To understand systematically and thoroughly the androgen responsive program in the mouse prostate, we carried out microarray analysis to profile gene expression changes during prostate involution and re-growth triggered by castration and subsequent hormone replacement. Genes with significant changes in these two processes were identified and gene ontology analyses revealed that they were mainly involved in response mechanisms, cell adhesion, metabolism, protein metabolism, and cell-cycle progression. The changes observed during prostate involution were largely reversed during re-growth. Sixty-four genes, including Nkx3.1 and probasin, and 65 other genes, including insulin-like growth factor binding protein 3 and H-cadherin (H-Cad), were further identified respectively as androgen-responsive genes and genes inversely correlated with androgen, based on their down- or up-regulation following castration and up- or down-regulation following androgen replacement. Potential androgen-responsive elements were found in the 5' upstream promoter region of 47 of those 65 genes, suggesting a potential suppression mechanism by androgen receptor. Of these, the role of H-Cad in tumorigenesis was further evaluated. Reduction of H-Cad transcript level was found in the majority of human prostate cancer cell lines and prostatic adenocarcinoma samples examined. Furthermore, induced H-Cad expression in DU145 cells, and knock-down of H-Cad expression in BPH1 cells inhibited and facilitated tumorigenicity, respectively. Taken together, our study provides a molecular understanding of the mouse prostate involution and re-growth processes and identifies a set of genes that are inversely correlated with androgen and may be potentially suppressive for tumorigenesis.

Isolation and culture of hair cell progenitors from postnatal rat cochleae.

Cochlear hair cells are a terminally differentiated cell population that is crucial for hearing. Although recent work suggests that there are hair cell progenitors in postnatal mammalian cochleae, isolation and culture of pure hair cell progenitors from a well-defined cochlear area have not been reported. Here we present an experimental method that allows isolation and culture of hair cell progenitors from postnatal rat cochleae. These progenitor cells are isolated from the lesser epithelial ridge (LER, or outer spiral sulcus cell) area of pre-plated neonatal rat cochlear segments. They express the same markers as LER cells in vivo, including ZO1, Islet1, Hes1, and Hes5. When these cells are induced to express Hath1, they show the potential to differentiate into hair cell-like cells. Interestingly, these cells can be lifted from monolayer cultures and maintained in aggregate cultures in which spheres can be formed. Hair cell progenitors in the spheres display their proliferating capability and express only epithelial markers. Furthermore, when these spheres are mixed with dissociated mesenchymal cells prepared from postnatal rat utricular whole mounts, and replated onto a collagen substratum, the epithelial progenitor cells are able to differentiate into cells expressing markers of hair cells and supporting cells in epithelial islands, which mirrors the inner ear sensory epithelium in vivo. Successful isolation and culture of hair cell progenitors from the mammalian cochlea will facilitate studies on gene expression profiling and mechanism of differentiation/regeneration of hair cells, which are crucial for repairing hearing loss.

Inhibition of epithelial ductal branching in the prostate by sonic hedgehog is indirectly mediated by stromal cells.

Sonic hedgehog (Shh), a vertebrate homologue of the Drosophila segment-polarity gene hedgehog, has been reported to play an important role during normal development of various tissues. Abnormal activities of Shh signaling pathway have been implicated in tumorigenesis such as basal cell carcinomas and medulloblastomas. Here we show that Shh signaling negatively regulates prostatic epithelial ductal morphogenesis. In organotypic cultures of developing rat prostates, Shh inhibited cell proliferation and promoted differentiation of luminal epithelial cells. The expression pattern of Shh and its receptors suggests a paracrine mechanism of action. The Shh receptors Ptc1 (Patched1) and Ptc2 were found to be expressed in prostatic stromal cells adjacent to the epithelium, where Shh itself was produced. This paracrine model was confirmed by co-culturing the developing prostate in the presence of stromal cells transfected with a vector expressing a constitutively active form of Smoothened, the real effector of the Shh signaling pathway. Furthermore, expression of activin A and TGF-beta1 that were shown previously to inhibit prostatic epithelial branching was up-regulated following Shh treatment in the organotypic cultures. Taken together, these results suggest that Shh negatively regulates prostatic ductal branching indirectly by acting on the surrounding stromal cells, at least partly via up-regulating expression of activin A and TGF-beta1.