NSG-Pro mouse model for uncovering resistance mechanisms and unique vulnerabilities in human luminal breast cancers

Leveraging preclinical models of metastatic breast cancer

Women that present to the clinic with established breast cancer metastases have limited treatment options. Yet, the majority of preclinical studies are actually not directed at developing treatment regimens for established metastatic disease. In this review we will discuss the current state of preclinical macro-metastatic breast cancer models, including, but not limited to syngeneic GEMM, PDX and xenografts. Challenges within these models which are often overlooked include fluorophore-immunogenic neoantigens, differences in experimental vs spontaneous metastasis and tumor heterogeneity. Furthermore, due to cell plasticity in the tumor immune microenvironment (TIME) of the metastatic landscape, the treatment efficacy of newly approved immune checkpoint blockade (ICB) may differ in metastatic sites as compared to primary localized tumors.

Dual role of pregnancy in breast cancer risk

Reproductive history is one of the strongest risk factors for breast cancer in women. Pregnancy can promote short-term breast cancer risk, but also reduce a woman's lifetime risk of breast cancer. Changes in hormone levels before and after pregnancy are one of the key factors in breast cancer risk. This article summarizes the changes in hormone levels before and after pregnancy, and the roles of hormones in mammary gland development and breast cancer progression. Other factors, such as changes in breast morphology and mammary gland differentiation, changes in the proportion of mammary stem cells (MaSCs), changes in the immune and inflammatory environment, and changes in lactation before and after pregnancy, also play key roles in the occurrence and development of breast cancer. This review discusses the dual effects and the potential mechanisms of pregnancy on breast cancer risk from the above aspects, which is helpful to understand the complexity of female breast cancer occurrence.

The Power and Promise of Patient-Derived Xenografts of Human Breast Cancer

In 2016, a group of researchers engaged in the development of patient-derived xenografts (PDXs) of human breast cancer provided a comprehensive review of the state of the field. In that review, they summarized the clinical problem that PDXs might address, the technical approaches to their generation (including a discussion of host animals and transplant conditions tested), and presented transplantation success (take) rates across groups and across transplantation conditions. At the time, there were just over 500 unique PDX models created by these investigators representing all three clinically defined subtypes (ER+, HER2+, and TNBC). Today, many of these PDX resources have at least doubled in size, and several more PDX development groups now exist, such that there may be well upward of 1000 PDX models of human breast cancer in existence worldwide. They also presented a series of open questions for the field. Many of these questions have been addressed. However, several remain open, or only partially addressed. Herein, we revisit these questions, and recount the progress that has been made in a number of areas with respect to generation, characterization, and use of PDXs in translational research, and re-present questions that remain open. These open questions, and others, are now being addressed not only by individual investigators, but also large, well-funded consortia including the PDXNet program of the National Cancer Institute in the United States, and the EuroPDX Consortium, an organization of PDX developers across Europe. Finally, we discuss the new opportunities in PDX-based research.

Stat5 induces androgen receptor (AR) gene transcription in prostate cancer and offers a druggable pathway to target AR signaling

Androgen receptor (AR) drives prostate cancer (PC) growth and progression, and targeting AR signaling is the mainstay of pharmacological therapies for PC. Resistance develops relatively fast as a result of refueled AR activity. A major gap in the field is the lack of understanding of targetable mechanisms that induce persistent AR expression in castrate-resistant PC (CRPC). This study uncovers an unexpected function of active Stat5 signaling, a known promoter of PC growth and clinical progression, as a potent inducer of AR gene transcription. Stat5 suppression inhibited AR gene transcription in preclinical PC models and reduced the levels of wild-type, mutated, and truncated AR proteins. Pharmacological Stat5 inhibition by a specific small-molecule Stat5 inhibitor down-regulated Stat5-inducible genes as well as AR and AR-regulated genes and suppressed PC growth. This work introduces the concept of Stat5 as an inducer of AR gene transcription in PC. Pharmacological Stat5 inhibitors may represent a new strategy for suppressing AR and CRPC growth.

Frequent upregulation of HER2 protein in hormone-receptor-positive HER2-negative breast cancer after short-term neoadjuvant endocrine therapy

BACKGROUND

Endocrine resistant metastatic disease develops in ~ 20-25% of hormone-receptor-positive (HR+) breast cancer (BC) patients despite endocrine therapy (ET) use. Upregulation of HER family receptor tyrosine kinases (RTKs) represent escape mechanisms in response to ET in some HR+ tumors. Short-term neoadjuvant ET (NET) offers the opportunity to identify early endocrine escape mechanisms initiated in individual tumors.

METHODS

This was a single arm, interventional phase II clinical trial evaluating 4 weeks (± 1 week) of NET in patients with early-stage HR+/HER2-negative (HER2-) BC. The primary objective was to assess NET-induced changes in HER1-4 proteins by immunohistochemistry (IHC) score. Protein upregulation was defined as an increase of ≥ 1 in IHC score following NET.

RESULTS

Thirty-seven patients with cT1-T3, cN0, HR+/HER2- BC were enrolled. In 35 patients with evaluable tumor HER protein after NET, HER2 was upregulated in 48.6% (17/35; p = 0.025), with HER2-positive status (IHC 3+ or FISH-amplified) detected in three patients at surgery, who were recommended adjuvant trastuzumab-based therapy. Downregulation of HER3 and/or HER4 protein was detected in 54.2% of tumors, whereas HER1 protein remained low and unchanged in all cases. While no significant volumetric reduction was detected radiographically after short-term NET, significant reduction in tumor proliferation rates were observed. No significant associations were identified between any clinicopathologic covariates and changes in HER1-4 protein expression on multivariable analysis.

CONCLUSION

Short-term NET frequently and preferentially upregulates HER2 over other HER family RTKs in early-stage HR+/HER2- BC and may be a promising strategy to identify tumors that utilize HER2 as an early endocrine escape pathway.

CLINICAL TRIAL REGISTRY

Trial registration number: NCT03219476.

Frequent Upregulation Of HER2 Protein In Hormone Receptor-Positive HER2-Negative Breast Cancer After Short-Term Neoadjuvant Endocrine Therapy

Background. Endocrine resistant metastatic disease develops in ~20-25% of hormone-receptor positive (HR+) breast cancer (BC) patients despite endocrine therapy (ET) use. Upregulation of HER family receptor tyrosine kinases (RTKs) represent escape mechanisms in response to ET in some HR+ tumors. Short-term neoadjuvant ET (NET) offers the opportunity to identify early endocrine escape mechanisms initiated in individual tumors. Methods. This was a single arm, interventional phase II clinical trial evaluating 4 weeks (+/-1 week) of NET in patients with early-stage HR+/HER2-negative (HER2-) BC. The primary objective was to assess NET-induced changes in HER1-4 proteins by immunohistochemistry (IHC) score. Protein upregulation was defined as an increase of ≥1 in IHC score following NET. Results. Thirty-seven patients with cT1-T3, cN0, HR+/HER2- BC were enrolled. In 35 patients with evaluable tumor HER protein after NET, HER2 was upregulated in 48.6% (17/35; p=0.025), with HER2-positive status (IHC 3+ or FISH-amplified) detected in three patients at surgery, who were recommended adjuvant trastuzumab-based therapy. Downregulation of HER3 and/or HER4 protein was detected in 54.2% of tumors, whereas HER1 protein remained low and unchanged in all cases. While no significant volumetric reduction was detected radiographically after short-term NET, significant reduction in tumor proliferation rates were observed. No significant associations were identified between any clinicopathologic covariates and changes in HER1-4 protein expression on multivariable analysis. Conclusion . Short-term NET frequently and preferentially upregulates HER2 over other HER-family RTKs in early-stage HR+/HER2- BC and may be a promising strategy to identify tumors that utilize HER2 as an early endocrine escape pathway. Trial registration number: NCT03219476 Date of registration for prospectively registered trials: July 17, 2017.

Preparation of Superactive Prolactin Receptor Antagonists

Most breast cancer deaths are caused by malignant estrogen receptor-positive breast tumors that later recur as metastatic disease. Prolactin (PRL) has been documented as a factor promoting breast cancer development and metastasis. We therefore developed superactive prolactin receptor (PRLR) antagonists aimed at blocking PRL action. We purified 12 novel mutants to homogeneity as monomers, and the most potent antagonist was over 95-fold more active than the previously reported weak antagonist, the mutant Del 1-9 human PRL G129R. This enhanced antagonistic activity resulted mostly from prolonged interaction with the extracellular domain (ECD) of PRLR. All mutants were properly refolded, as indicated by interaction with human PRLR-ECD and by circular dichroism analysis. We then prepared monopegylated variants of the most active mutants to extend their biological half-life in vivo.

Breast Cancer and Prolactin - New Mechanisms and Models

The pathogenesis of breast cancer is driven by multiple hormones and growth factors. One of these, prolactin (PRL), contributes to both mammary differentiation and oncogenesis, and yet the basis for these disparate effects has remained unclear. The focus of this review is to examine and place into context 2 recent studies that have provided insight into the roles of PRL receptors and PRL in tumorigenesis and tumor progression. One study provides novel evidence for opposing actions of PRL in the breast being mediated in part by differential PRL receptor (PRLr) isoform utilization. Briefly, homomeric complexes of the long isoform of the PRLr (PRLrL-PRLrL) promotes mammary differentiation, while heteromeric complexes of the intermediate and long PRLr (PRLrI-PRLrL) isoforms trigger mammary oncogenesis. Another study describes an immunodeficient, prolactin-humanized mouse model, NSG-Pro, that facilitates growth of PRL receptor-expressing patient-derived breast cancer xenografts. Evidence obtained with this model supports the interactions of physiological levels of PRL with estrogen and ERBB2 gene networks, the modulatory effects of PRL on drug responsiveness, and the pro-metastatic effects of PRL on breast cancer. This recent progress provides novel concepts, mechanisms and experimental models expected to renew interest in harnessing/exploiting PRLr signaling for therapeutic effects in breast cancer.

In vitro breast cancer models for studying mechanisms of resistance to endocrine therapy

The development of endocrine resistance is a common reason for the failure of endocrine therapies in hormone receptor-positive breast cancer. This review provides an overview of the different types of in vitro models that have been developed as tools for studying endocrine resistance. In vitro models include cell lines that have been rendered endocrine-resistant by ex vivo treatment; cell lines with de novo resistance mechanisms, including genetic alterations; three-dimensional (3D) spheroid, co-culture, and mammosphere techniques; and patient-derived organoid models. In each case, the key discoveries, different analysis strategies that are suitable, and strengths and weaknesses are discussed. Certain recently developed methodologies that can be used to further characterize the biological changes involved in endocrine resistance are then emphasized, along with a commentary on the types of research outcomes that using these techniques can support. Finally, a discussion anticipates how these recent developments will shape future trends in the field. We hope this overview will serve as a useful resource for investigators that are interested in understanding and testing hypotheses related to mechanisms of endocrine therapy resistance.

Prolactin: The Third Hormone in Breast Cancer

Prolactin coordinates with the ovarian steroids to orchestrate mammary development and lactation, culminating in nourishment and an increasingly appreciated array of other benefits for neonates. Its central activities in mammary epithelial growth and differentiation suggest that it plays a role(s) in breast cancer, but it has been challenging to identify its contributions, essential for incorporation into prevention and treatment approaches. Large prospective epidemiologic studies have linked higher prolactin exposure to increased risk, particularly for ER+ breast cancer in postmenopausal women. However, it has been more difficult to determine its actions and clinical consequences in established tumors. Here we review experimental data implicating multiple mechanisms by which prolactin may increase the risk of breast cancer. We then consider the evidence for role(s) of prolactin and its downstream signaling cascades in disease progression and treatment responses, and discuss how new approaches are beginning to illuminate the biology behind the seemingly conflicting epidemiologic and experimental studies of prolactin actions across diverse breast cancers.

Terminal differentiation and anti-tumorigenic effects of prolactin in breast cancer

Breast cancer is a major disease affecting women worldwide. A woman has 1 in 8 lifetime risk of developing breast cancer, and morbidity and mortality due to this disease are expected to continue to rise globally. Breast cancer remains a challenging disease due to its heterogeneity, propensity for recurrence and metastasis to distant vital organs including bones, lungs, liver and brain ultimately leading to patient death. Despite the development of various therapeutic strategies to treat breast cancer, still there are no effective treatments once metastasis has occurred. Loss of differentiation and increased cellular plasticity and stemness are being recognized molecularly and clinically as major derivers of heterogeneity, tumor evolution, relapse, metastasis, and therapeutic failure. In solid tumors, breast cancer is one of the leading cancer types in which tumor differentiation state has long been known to influence cancer behavior. Reprograming and/or restoring differentiation of cancer cells has been proposed to provide a viable approach to reverse the cancer through differentiation and terminal maturation. The hormone prolactin (PRL) is known to play a critical role in mammary gland lobuloalveolar development/remodeling and the terminal differentiation of the mammary epithelial cells promoting milk proteins gene expression and lactation. Here, we will highlight recent discoveries supporting an anti-tumorigenic role for PRL in breast cancer as a "pro/forward-differentiation" pathway restricting plasticity, stemness and tumorigenesis.