Phase I Study of the Prolactin Receptor Antagonist LFA102 in Metastatic Breast and Castration-Resistant Prostate Cancer

A novel clinically relevant antagonistic interplay between prolactin and oncogenic YAP-CCN2 pathways as a differentiation therapeutic target in breast cancer

Cellular differentiation limits cellular plasticity allowing cells to attain their specialized functional characteristics and phenotypes, whereas loss of differentiation is a hallmark of cancer. Thus, characterizing mechanisms underlying differentiation is key to discover new cancer therapeutics. We report a novel functional antagonistic relationship between the prolactin (PRL)/prolactin receptor (PRLR) differentiation pathway and YAP-CCN2 oncogenic pathway in normal mammary epithelial cells and breast cancer cells that is essential for establishing/maintaining acinar morphogenesis, cell-cell junctions and the intracellular localization of apical-basal polarity protein complexes (Par, Crumb and Scrib). Importantly, using CRISPR knockout of the PRLR in MCF7, HR+ breast cancer cells, further revealed that the negative relationship between PRL/PRLR pathway and YAP-CCN2 pathway is critical in suppressing luminal-to-basal stem-like lineage plasticity. Furthermore, the clinical relevance of this interplay was evaluated using bioinformatics approaches on several human datasets, including samples from normal breast epithelium, breast cancer, and 33 other cancer types. This analysis revealed a positive correlation between PRLR and the YAP suppressor Hippo pathway and a co-expression gene network driving favourable patients' survival outcomes in breast cancer. The therapeutic potential of this interplay was also evaluated in vitro using MDA-MB-231 cells, a preclinical model of human triple-negative breast cancer, where treatment with PRL and Verteporfin, an FDA-approved pharmacological YAP-inhibitor, alone or their combination suppressed the expression of the mesenchymal marker vimentin and the stem cell marker CD44 as well as reduced their Ki67 proliferative marker expression. Collectively, our results emphasize the pro-differentiation role of PRL/PRLR pathway in mammary and breast cancer cells and highlight that promoting PRL/PRLR signaling while inhibiting the YAP-CCN2 oncogenic pathway can be exploited as a differentiation-based combination therapeutic strategy in breast cancer.

Warming-up the immune cell engagers (ICEs) era in breast cancer: state of the art and future directions

The advent of immune checkpoint inhibitors (ICIs) has deeply reshaped the therapeutic algorithm of triple-negative breast cancer (TNBC). However, there is considerable scope for better engagement of the immune system in other BC subtypes. ICIs have paved the way for investigations into emerging immunotherapeutic strategies, such as immune cell engagers (ICEs) that work by promoting efficient tumor cell killing through the redirection of immune system against cancer cells. Most ICEs are bispecific antibodies that simultaneously recognize and bind to both cancer and immune cells generating an artificial synapse. Major side effects are cytokine release syndrome, hepatotoxicity, and neurotoxicity related to inappropriate immune system activation. Here, we provide a comprehensive overview of this compounds, the available preclinical and clinical evidence supporting their investigation and development in BC also highlighting the challenges that have prevented their widespread use in oncology. Finally, major strategies are explored to broaden their use in BC.

Impact of prolactin treatment on enhancing the cellular responses of MCF7 breast cancer cells to tamoxifen treatment

Breast cancer remains one of the most challenging diseases to treat due to its heterogeneity, propensity to recur, capacity to spread to distant vital organs, and, ultimately, patient death. Estrogen receptor-positive illness comprises the most common breast cancer subtype. Preclinical progress is hampered by the scarcity of medication-naïve estrogen receptor-positive tumour models that recapitulate metastatic development and treatment resistance. It is becoming increasingly clear that loss of differentiation and increased cellular stemness and plasticity are important causes of cancer evolution, heterogeneity, recurrence, metastasis, and treatment failure. Therefore, it has been suggested that reprogramming cancer cell differentiation could offer an effective method of reversing cancer through terminal differentiation and maturation. In this context, the hormone prolactin is well recognized for its pivotal involvement in the development of the mammary glands lobuloalveolar tissue and the terminal differentiation that drives the production of the milk protein gene and lactation. Additionally, numerous studies have examined the engagement of prolactin in breast cancer as a differentiation player that resulted in the ablation of tumour growth and progression. Here, we showed that a pre-treatment of the estrogen-positive breast cancer cell line with prolactin led to a considerable improvement in the sensitivity of this cancer cell to Tamoxifen endocrine therapy. We also showed a favourable prognostic value of prolactin receptors/estrogen receptors 1 (or alpha) co-expression on breast cancer patients outcomes, and this co-expression is highly correlated with the well-differentiated breast tumour type. Our results revealed a fruitful aspect of the effects of prolactin in improving the responses of breast cancer cells to conventional endocrine therapy. Moreover, these findings further validated the ability of prolactin as a persuader of a more differentiated and less aggressive breast cancer phenotype. Hence, it suggested a potential implication of prolactin as a therapeutic candidate.

The immunotoxin targeting PRLR increases tamoxifen sensitivity and enhances the efficacy of chemotherapy in breast cancer

BACKGROUND

Though tamoxifen achieves success in treating estrogen receptor α (ERα)-positive breast cancer, the followed development of tamoxifen resistance is a common challenge in clinic. Signals downstream of prolactin receptor (PRLR) could synergize with ERα in breast cancer progression. However, the potential effect of targeting PRL-PRLR axis combined with tamoxifen has not been thoroughly investigated.

METHODS

High-throughput RNA-seq data obtained from TCGA, Metabric and GEO datasets were analyzed to explore PRLR expression in breast cancer cell and the association of PRLR expression with tamoxifen treatment. Exogenous or PRL overexpression cell models were employed to investigate the role of activated PRLR pathway in mediating tamoxifen insensitivity. Immunotoxin targeting PRLR (N8-PE24) was constructed with splicing-intein technique, and the efficacy of N8-PE24 against breast cancer was evaluated using in vitro and in vivo methods, including analysis of cells growth or apoptosis, 3D spheroids culture, and animal xenografts.

RESULTS

PRLR pathway activated by PRL could significantly decrease sensitivity of ERα-positive breast cancer cells to tamoxifen. Tamoxifen treatment upregulated transcription of PRLR and could induce significant accumulation of PRLR protein in breast cancer cells by alkalizing lysosomes. Meanwhile, tamoxifen-resistant MCF7 achieved by long-term tamoxifen pressure exhibited both upregulated transcription and protein level of PRLR. Immunotoxin N8-PE24 enhanced sensitivity of breast cancer cells to tamoxifen both in vitro and in vivo. In xenograft models, N8-PE24 significantly enhanced the efficacy of tamoxifen and paclitaxel when treating PRLR-positive triple-negative breast cancer.

CONCLUSIONS

PRL-PRLR axis potentially associates with tamoxifen insensitivity in ERα-positive breast cancer cells. N8-PE24 could inhibit cell growth of the breast cancers and promote drug sensitivity of PRLR-positive breast cancer cells to tamoxifen and paclitaxel. Our study provides a new perspective for targeting PRLR to treat breast cancer.

PRL-mediated STAT5B/ARRB2 pathway promotes the progression of prostate cancer through the activation of MAPK signaling

Previous study showed that higher expression of prolactin (PRL) was found in CRPC samples compared with hormone-naive prostate cancer (HNPC) and benign prostatic hyperplasia (BPH) samples. We further investigate the function of PRL in prostate cancer (PCa) and explored its downstream effects. We found heterogeneous expression of the PRLR in clinical prostate samples. The VCaP and 22Rv1 cells exhibited PRLR expression. Among the downstream proteins, STAT5B was the dominant subtype in clinical samples and cell lines. Human recombinant PRL stimulation of PCa cells with PRLR expression resulted in increased phosphorylation of STAT5B(pSTAT5B) and progression of PCa in vitro and in vivo, and STAT5B knockdown can suppress the malignant behavior of PCa. To understand the mechanism further, we performed Bioinformatic analysis, ChIP qPCR, and luciferase reporter gene assay. The results revealed that ARRB2 was the transcription target gene of STAT5B, and higher expression of ARRB2 was related to higher aggression and poorer prognosis of PCa. Additionally, Gene set enrichment analysis indicated that higher expression of ARRB2 was significantly enriched in the MAPK signaling pathway. Immunohistochemistry (IHC) demonstrated elevated pSTAT5B, ARRB2, and pERK1/2 expression levels in CRPC tissues compared to HNPC and BPH. Mechanically, ARRB2 enhanced the activation of the MAPK pathway by binding to ERK1/2, thereby promoting the phosphorylation of ERK1/2 (pERK1/2). In conclusion, our study demonstrated that PRL stimulation can promote the progression of PCa through STAT5B/ARRB2 pathway and activation of MAPK signaling, which can be suppressed by intervention targeting STAT5B. Blockade of the STAT5B can be a potential therapeutic target for PCa.

Prolactin receptor signaling induces acquisition of chemoresistance and reduces clonogenicity in acute myeloid leukemia

BACKGROUND

Development of precision medicine requires the identification of easily detectable and druggable biomarkers. Despite recent targeted drug approvals, prognosis of acute myeloid leukemia (AML) patients needs to be greatly improved, as relapse and refractory disease are still difficult to manage. Thus, new therapeutic approaches are needed. Based on in silico-generated preliminary data and the literature, the role of the prolactin (PRL)-mediated signaling was interrogated in AML.

METHODS

Protein expression and cell viability were determined by flow cytometry. Repopulation capacity was studied in murine xenotransplantation assays. Gene expression was measured by qPCR and luciferase-reporters. SA-β-Gal staining was used as a senescence marker.

RESULTS

The prolactin receptor (PRLR) was upregulated in AML cells, as compared to their healthy counterpart. The genetic and molecular inhibition of this receptor reduced the colony-forming potential. Disruption of the PRLR signaling, either using a mutant PRL or a dominant-negative isoform of PRLR, reduced the leukemia burden in vivo, in xenotransplantation assays. The expression levels of PRLR directly correlated with resistance to cytarabine. Indeed, acquired cytarabine resistance was accompanied with the induction of PRLR surface expression. The signaling associated to PRLR in AML was mainly mediated by Stat5, in contrast to the residual function of Stat3. In concordance, Stat5 mRNA was significantly overexpressed at mRNA levels in relapse AML samples. A senescence-like phenotype, measured by SA-β-gal staining, was induced upon enforced expression of PRLR in AML cells, partially dependent on ATR. Similar to the previously described chemoresistance-induced senescence in AML, no cell cycle arrest was observed. Additionally, the therapeutic potential of PRLR in AML was genetically validated.

CONCLUSIONS

These results support the role of PRLR as a therapeutic target for AML and the further development of drug discovery programs searching for specific PRLR inhibitors.

The Potential Prognostic and Therapeutic Implications of Prolactin Receptor and Growth Hormone-releasing Hormone Receptor Expression in Uterine Leiomyosarcomas

The management of uterine leiomyosarcomas (uLMS) remains challenging. The rate of recurrence and metastasis is high, with 5-yr survival reaching only 40% to 50% in patients with tumor confined to the uterus (FIGO stage I or II). Prolactin receptor (PRLR) and growth hormone-releasing hormone receptor (GHRHR) have been implicated in the carcinogenesis of malignant tumors of the breast, endometrium, ovary, liver, and prostate. GHRHR antagonists inhibit in vitro growth of many human tumors and the expression of PRLR is associated with resistance to chemotherapy. The immunohistochemical expression of PRLR and GHRH in 24 primary and 2 recurrent uLMS was evaluated. Representative sections were stained with PRLR and GHRHR antibodies and immunoreactivity was calculated using H -score. The results were correlated with clinicopathologic data using Kaplan-Meier survival and multivariable Cox proportion hazard regression analyses. All tumors were positive for both markers with predominantly moderate to strong expression of PRLR (89%) and GHRHR (82%). Patients with tumors showing moderate to strong expression of PRLR were significantly less likely to achieve disease-free survival ( P =0.004) and significantly more likely to have a poor overall survival ( P =0.049). No significant difference in mean PRLR expression was found between tumors with higher mitotic counts (>20/10 hpf) and lower mitotic counts (20 or less/10 hpf). Furthermore, in 2 patients where the primary and recurrent tumors were tested, there was stronger expression of PRLR in the recurrence compared with the primary. This correlation was not found with GHRHR. Both PRLR and GHRHR may play a role in carcinogenesis in uLMS, as they do in other malignant neoplasms. To our knowledge, this study is the first evaluating the expression of these receptors in uLMS. Moderate or high expression of PRLR may serve as a prognostic marker associated with recurrences and increased mortality in uLMS patients.

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.

Serum prolactin level as a predictive factor for abiraterone response in patients with metastatic castration-resistant prostate cancer

BACKGROUND

To investigate the prognostic value and potential therapeutic target of the baseline serum hormones in patients with metastatic castration-resistant prostate cancer (mCRPC) treated with abiraterone.

METHODS

This retrospective study was performed in patients with mCRPC receiving abiraterone acetate (AA) from July 2016 to September 2020. Patients who had serum hormone tests within 2 weeks before AA treatment were included. Univariate analysis and Cox regression were performed to evaluate the correlation of sex hormones with progression-free survival (PFS) and overall survival (OS). Prolactin (PRL) expression in the clinical specimens was evaluated by immunohistochemistry. Bone metastases were quantified by automated Bone Scan Index (aBSI).

RESULTS

The study included 61 patients with a median follow-up of 19.0 months. Patients with lower baseline PRL levels (median) responded better to AA than those with higher baseline PRL levels as indicated by prostate-specific antigen (PSA) reduction (PSA90, 66.7% vs. 25.8%, p = 0.001), PFS (19.6 vs. 7.9 months), and OS (52.8 vs. 19.2 months). Cox regression adjusted for clinical factors also confirmed that baseline PRL level was an independent predictive factor for PFS (hazard ratio = 1.096, p = 0.007). Prostatic PRL expression increased as the disease progressed. PRL expression was also detected in biopsy samples from bone metastasis but not in normal bone tissue, and the serum PRL levels were positively correlated with aBSIs (r = 0.28, p = 0.037).

CONCLUSIONS

Serum PRL levels are predictive of response to AA in patients with mCRPC. Serum PRL levels are positively correlated with the volume of metastatic bone disease.

Prolactin receptor signaling: A novel target for cancer treatment - Exploring anti-PRLR signaling strategies

Prolactin (PRL) is a peptide hormone mainly secreted from the anterior pituitary gland. PRL is reported to play a role in pregnancy, mammary gland development, immune modulation, reproduction, and differentiation of islet cells. PRL binds to its receptor PRLR, which belongs to a superfamily of the class I cytokine receptor that has no intrinsic kinase activity. In canonical signaling, PRL binding to PRLR induces downstream signaling including JAK-STAT, AKT and MAPK pathways. This leads to increased cell proliferation, stemness, migration, apoptosis inhibition, and resistance to chemotherapy. PRL-signaling is upregulated in numerous hormone-dependent cancers including breast, prostate, ovarian, and endometrial cancer. However, more recently, the pathway has been reported to play a tumor-promoting role in other cancer types such as colon, pancreas, and hepatocellular cancers. Hence, the signaling pathway is an attractive target for drug development with blockade of the receptor being a potential therapeutic approach. Different strategies have been developed to target this receptor including modification of PRL peptides (Del1-9-G129R-hPRL, G129R-Prl), growth hormone receptor/prolactin receptor bispecific antibody antagonist, neutralizing antibody LFA102, an antibody-drug conjugate (ABBV-176) of the humanized antibody h16f (PR-1594804) and pyrrolobenzodiazepine dimer, a bispecific antibody targeting both PRLR and CD3, an in vivo half-life extended fusion protein containing PRLR antagonist PrlRA and albumin binding domain. There have also been attempts to discover and develop small molecular inhibitors targeting PRLR. Recently, using structure-based virtual screening, we identified a few antipsychotic drugs including penfluridol as a molecule that inhibits PRL-signaling to inhibit PDAC tumor progression. In this review, we will summarize the recent advances in the biology of this receptor in cancer and give an account of PRLR antagonist development for the treatment of cancer.

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.

Current understandings and clinical translation of nanomedicines for breast cancer therapy

Breast cancer is one of the most frequently diagnosed cancers that is threatening women's life. Current clinical treatment regimens for breast cancer often involve neoadjuvant and adjuvant systemic therapies, which somewhat are associated with unfavorable features. Also, the heterogeneous nature of breast cancers requires precision medicine that cannot be fulfilled by a single type of systemically administered drug. Taking advantage of the nanocarriers, nanomedicines emerge as promising therapeutic agents for breast cancer that could resolve the defects of drugs and achieve precise drug delivery to almost all sites of primary and metastatic breast tumors (e.g. tumor vasculature, tumor stroma components, breast cancer cells, and some immune cells). Seven nanomedicines as represented by Doxil® have been approved for breast cancer clinical treatment so far. More nanomedicines including both non-targeting and active targeting nanomedicines are being evaluated in the clinical trials. However, we have to realize that the translation of nanomedicines, particularly the active targeting nanomedicines is not as successful as people have expected. This review provides a comprehensive landscape of the nanomedicines for breast cancer treatment, from laboratory investigations to clinical applications. We also highlight the key advances in the understanding of the biological fate and the targeting strategies of breast cancer nanomedicine and the implications to clinical translation.

Prolactin is Expressed in Uterine Leiomyomas and Promotes Signaling and Fibrosis in Myometrial Cells

Uterine leiomyomas are benign, estrogen-sensitive, fibrotic smooth muscle cell tumors occurring in the uterine myometrium. Leiomyomas are a considerable health burden, with a lifetime prevalence of 80% and limited treatment options. Estrogen and progesterone have positive effects on leiomyoma growth, but little is known about the roles of other hormones. One hormone of interest is prolactin, as it has been described to be present and functional in leiomyomas. The current study investigates prolactin production within leiomyomas and its effects on myometrial cells. RNA isolation and quantitative-PCR of human leiomyoma samples relative to matched adjacent myometrium confirms significant expression of prolactin and dopamine receptor D2, a known regulator of prolactin production and release in the pituitary, with no difference in prolactin receptor expression. Immunohistochemistry confirms increased prolactin in leiomyomas compared to adjacent myometrium and uteri from women without leiomyomas. These results suggest that leiomyomas contain cells that produce prolactin, which may then promote signaling in leiomyoma cells to regulate leiomyoma development/growth. Accordingly, we find that prolactin robustly activates STAT5 and MAPK signaling in rat and human myometrial cell lines. Furthermore, prolactin stimulates expression of myofibroblast markers in rat myometrial cells. Our findings suggest that local prolactin production in leiomyomas may stimulate trans-differentiation of myometrial cells to myofibroblasts, which in turn contributes to the fibrotic nature of leiomyomas.

Prolactin and endocrine therapy resistance in breast cancer: The next potential hope for breast cancer treatment

Breast cancer, a hormone‐dependent tumour, generally includes four molecular subtypes (luminal A, luminal B, HER2 enriched and triple‐negative) based on oestrogen receptor, progesterone receptor and human epidermal growth factor receptor‐2. Multiple hormones in the body regulate the development of breast cancer. Endocrine therapy is one of the primary treatments for hormone‐receptor‐positive breast cancer, but endocrine resistance is the primary clinical cause of treatment failure. Prolactin (PRL) is a protein hormone secreted by the pituitary gland, mainly promoting mammary gland growth, stimulating and maintaining lactation. Previous studies suggest that high PRL levels can increase the risk of invasive breast cancer in women. The expression levels of PRL and PRLR in breast cancer cells and breast cancer tissues are elevated in most ER⁺ and ER⁻ tumours. PRL activates downstream signalling pathways and affects endocrine therapy resistance by combining with prolactin receptor (PRLR). In this review, we illustrated and summarized the correlations between endocrine therapy resistance in breast cancer and PRL, as well as the pathophysiological mechanisms and clinical practices. The study on PRL and its receptor would help explore reversing endocrine therapy‐resistance for breast cancer.

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

Most breast cancer deaths are caused by estrogen receptor-α–positive (ER+) disease. Preclinical progress is hampered by a shortage of therapy-naïve ER+ tumor models that recapitulate metastatic progression and clinically relevant therapy resistance. Human prolactin (hPRL) is a risk factor for primary and metastatic ER+ breast cancer. Because mouse prolactin fails to activate hPRL receptors, we developed a prolactin-humanized Nod-SCID-IL2Rγ (NSG) mouse (NSG-Pro) with physiological hPRL levels. Here, we show that NSG-Pro mice facilitate establishment of therapy-naïve, estrogen-dependent PDX tumors that progress to lethal metastatic disease. Preclinical trials provide first-in-mouse efficacy of pharmacological hPRL suppression on residual ER+ human breast cancer metastases and document divergent biology and drug responsiveness of tumors grown in NSG-Pro versus NSG mice. Oncogenomic analyses of PDX lines in NSG-Pro mice revealed clinically relevant therapy-resistance mechanisms and unexpected, potently actionable vulnerabilities such as DNA-repair aberrations. The NSG-Pro mouse unlocks previously inaccessible precision medicine approaches for ER+ breast cancers.

The implications of ABCC3 in cancer drug resistance: can we use it as a therapeutic target?

Drug resistance is one of the main causes of chemotherapy failure. Although several factors are involved in cancer drug resistant, the exporter pumps overexpression that mediates the drugs flow to outside the cells and reduces both the drugs intracellular concentration and effectiveness, has been one of the most important challenges. Overexpression of ABCC3, a member of the ABCC subfamily, has been strongly associated to the resistance to multiple drugs. ABCC3 has been found highly expressed in different types of cancers and is associated with poor prognosis and resistance to treatments. In this review, we summarize the molecular mechanisms involved in cancer drug resistance and discuss the current knowledge about the structure, function and role of ABCC3 in drug resistance, as well as, the expression status of ABCC3 in different types of cancer. We also provide evidences that place ABCC3 as a potential therapeutic target for improving the cancer treatment by focusing on the need of developing more effective cancer therapies to target ABCC3 in translational researches.

Prolactin and Estrogen Levels in Postmenopausal Women Receiving Aripiprazole Augmentation Treatment for Depression

BACKGROUND

Antipsychotic drugs are well established to alter serum prolactin levels, often resulting in adverse effects including amenorrhea, galactorrhea, osteoporosis, and loss of libido. There is growing preclinical evidence that prolactin-elevating drugs can instigate the progression of precancerous lesions to breast cancer and that genes activated by prolactin are associated with the development and proliferation of breast cancer. Current guides advise a cautious approach (weighing risks and benefits) to the administration of prolactin-elevating antipsychotic drugs in women with a previously detected breast cancer. Aripiprazole is known to be a prolactin-sparing antipsychotic; however, data regarding its effects on prolactin and estrogens in postmenopausal women are lacking.

METHODS

We examined serum hormone levels in n = 66 women who participated in a randomized, double-blind, placebo-controlled, multicenter trial of aripiprazole (high and low doses) added to an antidepressant in adults older than 60 years. Aripiprazole or placebo tablets were administered for 12 weeks as an augmentation strategy in venlafaxine-treated women. The primary outcomes were the difference in prolactin and estrogen levels.

RESULTS

There was no significant effect of aripiprazole treatment on prolactin or estrogen levels, including in models that divided groups into low and high doses: prolactin (P = 0.075), estrone (P = 0.67), and estradiol (P = 0.96).

CONCLUSIONS

Aripiprazole addition to an antidepressant did not alter serum estrogens or prolactin. These findings may be relevant in the treatment of some postmenopausal women with depression.

Connections between prolactin and ovarian cancer

Ovarian cancer (OC) is characterized by a high morbidity and mortality, highlighting a great need for a better understanding of biological mechanisms that affect OC progression and improving its early detection methods. This study investigates effects of prolactin (PRL) on ovarian cancer cells, analyzes PRL receptors (PRLR) in tissue micro arrays and relates PRLR expression to survival of ovarian cancer. A database, composed of transcript profiles from OC, was searched for PRLR expression and results were put in relation to survival. Expression of PRLR in OC tissue sections and OC cell lines SKOV3, OV2008 and OVSAHO was assessed using immunohistochemistry, western blots and quantitative real-time PCR. The biological function of PRLR was evaluated by proliferation, colony formation and wound healing assays. Levels of PRLR mRNA are related to survival; in epithelial OC a high PRLR mRNA expression is related to a shorter survival. Analysis of a tissue micro array consisting of 84 OC showed that 72% were positive for PRLR immuno-staining. PRLR staining tended to be higher in OC of high grade tumors compared to lower grades. PRLR mRNA and protein can further be detected in OC cell lines. Moreover, in vitro treatment with PRL significantly activated the JAK/STAT pathway. PRLR expression is associated with OC survivals. PRL and its receptor may play an onco-modulatory role and promote tumor aggressiveness in OC. Alternatively, increased PRLR levels may form a base for the development of PRLR antagonist or PRLR antagonist-drug conjugate to increase selective uptake of anti-cancer drugs.

ABBV-176, a PRLR antibody drug conjugate with a potent DNA-damaging PBD cytotoxin and enhanced activity with PARP inhibition

BACKGROUND

Prolactin receptor (PRLR) is an attractive antibody therapeutic target with expression across a broad population of breast cancers. Antibody efficacy, however, may be limited to subtypes with either PRLR overexpression and/or those where estradiol no longer functions as a mitogen and are, therefore, reliant on PRLR signaling for growth. In contrast a potent PRLR antibody-drug conjugate (ADC) may provide improved therapeutic outcomes extending beyond either PRLR overexpressing or estradiol-insensitive breast cancer populations.

METHODS

We derived a novel ADC targeting PRLR, ABBV-176, that delivers a pyrrolobenzodiazepine (PBD) dimer cytotoxin, an emerging class of warheads with enhanced potency and broader anticancer activity than the clinically validated auristatin or maytansine derivatives. This agent was tested in vitro and in vivo cell lines and patient derived xenograft models.

RESULTS

In both in vitro and in vivo assays, ABBV-176 exhibits potent cytotoxicity against multiple cell line and patient-derived xenograft breast tumor models, including triple negative and low PRLR expressing models insensitive to monomethyl auristatin (MMAE) based PRLR ADCs. ABBV-176, which cross links DNA and causes DNA breaks by virtue of its PBD warhead, also demonstrates enhanced anti-tumor activity in several breast cancer models when combined with a poly-ADP ribose polymerase (PARP) inhibitor, a potentiator of DNA damage.

CONCLUSIONS

Collectively the efficacy and safety profile of ABBV-176 suggest it may be an effective therapy across a broad range of breast cancers and other cancer types where PRLR is expressed with the potential to combine with other therapeutics including PARP inhibitors.

Emerging Immunotherapies against Novel Molecular Targets in Breast Cancer

Immunotherapy is a highly emerging form of breast cancer therapy that enables clinicians to target cancers with specific receptor expression profiles. Two popular immunotherapeutic approaches involve chimeric antigen receptor-T cells (CAR-T) and bispecific antibodies (BsAb). Briefly mentioned in this review as well is the mRNA vaccine technology recently popularized by the COVID-19 vaccine. These forms of immunotherapy can highly select for the tumor target of interest to generate specific tumor lysis. Along with improvements in CAR-T, bispecific antibody engineering, and therapeutic administration, much research has been done on novel molecular targets that can especially be useful for triple-negative breast cancer (TNBC) immunotherapy. Combining emerging immunotherapeutics with tumor marker discovery sets the stage for highly targeted immunotherapy to be the future of cancer treatments. This review highlights the principles of CAR-T and BsAb therapy, improvements in CAR and BsAb engineering, and recently identified human breast cancer markers in the context of in vitro or in vivo CAR-T or BsAb treatment.

Regulation of extracellular and intracellular prolactin on cell proliferation and survival rate through GHR/JAK2/STAT3 pathway in NSCLC

Styrene increases serum prolactin (PRL) concentration. Hyperprolactinemia is associated with poor prognosis in lung cancer patients, but the mechanism of PRL action is unclear. The aims of this study were to (i) investigate the mechanism of PRL-action receptor in NSCLC cells (ii) measure whether PRL was secreted by NSCLC cells and its stimulatory mechanism in vitro and in vivo. We found that cell proliferation was increased after treatment of a pharmacological dose of PRL in A549 cells, which through up regulation of growth hormone receptor (GHR) and downstream of JAK2/STAT3/VEGF pathway. All NSCLC cells in the present study secreted PRL and expressed GHR, but not PRLR. Inhibition of GHR protein level led to decrease the PRL-induced cell proliferation. PRL was detected in NSCLC cells culture medium. Knockdown of intracellular PRL downregulated JAK2/STAT3 protein activities and GHR and VEGF protein levels. Furthermore, knockdown of intracellular PRL reduced the cell proliferation and the ability of colony-forming. In lung cancer tissues, PRL, GHR and VEGF levels were higher in the tumor tissues than in normal tissues and the protein expressions of these three proteins are positively correlated, respectively. High expression levels of both PRL and GHR cause a poor survival rate in lung cancer patients. Taken together, our results suggested that extracellular and intracellular PRL were involved in cell proliferation through GHR. Combination of in vitro and in vivo results, GHR and PRL are important targets for suppressing NSCLC cell proliferation, which might improve the survival rate in NSCLC patients.

Prolactin receptor-driven combined luminal and epithelial differentiation in breast cancer restricts plasticity, stemness, tumorigenesis and metastasis

Dedifferentiation increased cellular plasticity and stemness are established derivers of tumor heterogeneity, metastasis and therapeutic failure resulting in incurable cancers. Therefore, it is essential to decipher pro/forward-differentiation mechanisms in cancer that may serve as therapeutic targets. We found that interfering with expression of the receptor for the lactogenic hormone prolactin (PRLR) in breast cancer cells representative of the luminal and epithelial breast cancer subtypes (hormone receptor positive (HR+) and HER2-enriched (HER2-E) resulted in loss of their differentiation state, enriched for stem-like cell subpopulations, and increased their tumorigenic capacity in a subtype-specific manner. Loss of PRLR expression in HR+ breast cancer cells caused their dedifferentiation generating a mesenchymal-basal-like phenotype enriched in CD44+ breast cancer stem-like cells (BCSCs) showing high tumorigenic and metastatic capacities and resistance to anti-hormonal therapy. Whereas loss of PRLR expression in HER2-E breast cancer cells resulted in loss of their luminal differentiation yet enriched for epithelial ALDH+ BCSC population showing elevated HER2-driven tumorigenic, multi-organ metastatic spread, and resistance to anti-HER2 therapy. Collectively, this study defines PRLR as a driver of precise luminal and epithelial differentiation limiting cellular plasticity, stemness, and tumorigenesis and emphasizing the function of pro/forward-differentiation pathways as a foundation for the discovery of anti-cancer therapeutic targets.

Progesterone receptor isoform-dependent cross-talk between prolactin and fatty acid synthase in breast cancer

Progesterone receptor (PR) isoforms can drive unique phenotypes in luminal breast cancer (BC). Here, we hypothesized that PR-B and PR-A isoforms differentially modify the cross-talk between prolactin and fatty acid synthase (FASN) in BC. We profiled the responsiveness of the FASN gene promoter to prolactin in T47D_co BC cells constitutively expressing PR-A and PR-B, in the PR-null variant T47D-Y cell line, and in PR-null T47D-Y cells engineered to stably re-express PR-A (T47D-YA) or PR-B (T47D-YB). The capacity of prolactin to up-regulate FASN gene promoter activity in T47D_co cells was lost in T47D-Y and TD47-YA cells. Constitutively up-regulated FASN gene expression in T47-YB cells and its further stimulation by prolactin were both suppressed by the prolactin receptor antagonist hPRL-G129R. The ability of the FASN inhibitor C75 to decrease prolactin secretion was more conspicuous in T47-YB cells. In T47D-Y cells, which secreted notably less prolactin and downregulated prolactin receptor expression relative to T47D_co cells, FASN blockade resulted in an augmented secretion of prolactin and up-regulation of prolactin receptor expression. Our data reveal unforeseen PR-B isoform-specific regulatory actions in the cross-talk between prolactin and FASN signaling in BC. These findings might provide new PR-B/FASN-centered predictive and therapeutic modalities in luminal intrinsic BC subtypes.

Prolactin: A hormone with diverse functions from mammary gland development to cancer metastasis

Prolactin has a rich mechanistic set of actions and signaling in order to elicit developmental effects in mammals. Historically, prolactin has been appreciated as an endocrine peptide hormone that is responsible for final, functional mammary gland development and lactation. Multiple signaling pathways impacted upon by the microenvironment contribute to cell function and differentiation. Endocrine, autocrine and paracrine signaling are now apparent in not only mammary development, but also in cancer, and involve multiple cell types including those of the immune system. Multiple ligands agonists are capable of binding to the prolactin receptor, potentially expanding receptor function. Prolactin has an important role not only in tumorigenesis of the breast, but also in a number of hormonally responsive cancers such as prostate, ovarian and endometrial cancer, as well as pancreatic and lung cancer. Although pituitary and extra-pituitary sources of prolactin such as the epithelium are important, stromal sourced prolactin is now also being recognized as an important factor in tumor progression, all of which potentially signal to multiple cell types in the tumor microenvironment. While prolactin has important roles in milk production including calcium and bone homeostasis, in the disease state it can also affect bone homeostasis. Prolactin also impacts metastatic cancer of the breast to modulate the bone microenvironment and promote bone damage. Prolactin has a fascinating contribution in both physiologic and pathologic settings of mammals.

The role of the prolactin receptor pathway in the pathogenesis of glioblastoma: what do we know so far?

Introduction: Prolactin (PRL) and its receptor (PRLR) have been associated with the development of hormone-dependent tumors and have been detected in glioblastoma (GBM) biopsies. GBM is the most common and aggressive primary brain tumor in adults and the prognosis for patients is dismal; hence researchers are exploring the PRLR pathway as a therapeutic target in this disease. Areas covered: This paper explores the effects of PRLR activation on the biology of GBM, the correlation between PRL and PRLR expression and GBM progression and survival in male and female patients. Finally, we discuss how a better understanding of the PRLR pathway may allow the development of novel treatments for GBM. Expert opinion: We propose PRL and PRLR as potential prognosis biomarkers and therapeutic targets in GBM. Local administration of PRLR inhibitors using gene therapy may offer a beneficial strategy for targeting GBM cells disseminated in the non-neoplastic brain; however, efficacy and safety require careful and extensive evaluation. The data depicted herein underline the need to (i) improve our understanding of sexual dimorphism in GBM, and (ii) develop accurate preclinical models that take into consideration different hormonal contexts, specific genetic alterations, and tumor grades.

Post-diagnostic antipsychotic use and cancer mortality: a population based cohort study

BACKGROUND

Many antipsychotics elevate prolactin, a hormone implicated in breast cancer aetiology however no studies have investigated antipsychotic use in patients with breast cancer. This study investigated if antipsychotic use is associated with an increased risk of cancer-specific mortality among breast cancer patients.

METHODS

A cohort of 23,695 women newly diagnosed with a primary breast cancer between 1st January 1998 and 31st December 2012 was identified from the UK Clinical Practice Research Datalink linked to English cancer-registries and followed for until 30th September 2015. Time-dependent Cox proportional hazards models were used to calculate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) of breast cancer-specific mortality comparing use of antipsychotics with non-use, overall, and by prolactin elevating activitiy. Analyses were repeated restricting to patients with a history of severe mental illness to control for potential confounding by indication.

RESULTS

In total 848 patients were prescribed an antipsychotic and of which 162 died due to their breast cancer. Compared with non-use, antipsychotic use was associated with an increased risk of breast-cancer specific mortality (HR 2.25, 95%CI 1.90-2.67), but this did not follow a dose response relation. Restricting the cohort to patients with severe mental illness attenuated the association between antipsychotic use and breast cancer-specific mortality (HR 1.11, 95%CI 0.58-2.14).

CONCLUSIONS

In this population-based cohort of breast cancer patients, while the use of antipsychotics was associated with increased breast cancer-specific mortality, there was a lack of a dose response, and importantly null associations were observed in patients with severe mental illness, suggesting the observed association is likely a result of confounding by indication. This study provides an exemplar of confounding by indication, highlighting the importance of consideration of this important bias in studies of drug effects in cancer patients.

Novel Analgesics with Peripheral Targets

A limited number of peripheral targets generate pain. Inflammatory mediators can sensitize these. The review addresses targets acting exclusively or predominantly on sensory neurons, mediators involved in inflammation targeting sensory neurons, and mediators involved in a more general inflammatory process, of which an analgesic effect secondary to an anti-inflammatory effect can be expected. Different approaches to address these systems are discussed, including scavenging proinflammatory mediators, applying anti-inflammatory mediators, and inhibiting proinflammatory or facilitating anti-inflammatory receptors. New approaches are contrasted to established ones; the current stage of progress is mentioned, in particular considering whether there is data from a molecular and cellular level, from animals, or from human trials, including an early stage after a market release. An overview of publication activity is presented, considering a IuPhar/BPS-curated list of targets with restriction to pain-related publications, which was also used to identify topics.

A first-in-human, phase 1, dose-escalation study of ABBV-176, an antibody-drug conjugate targeting the prolactin receptor, in patients with advanced solid tumors

ABBV-176 is an antibody-drug conjugate composed of the humanized antibody h16f (PR-1594804) conjugated to a highly potent, cytotoxic cross-linking pyrrolobenzodiazepine dimer (PBD; SGD-1882) targeting the prolactin receptor (PRLR), which is overexpressed in several solid tumor types. This phase 1, dose-escalation study (NCT03145909) evaluated the safety, pharmacokinetics, and preliminary activity of ABBV-176 in patients with advanced solid tumors likely to exhibit elevated levels of PRLR. Patients received ABBV-176 once every 3 weeks. Dose escalation was by an exposure-adjusted, continual reassessment method. Dose-limiting toxicities (DLTs) were assessed from the first day of dosing until the next dose of ABBV-176 to determine the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D). Nineteen patients received ABBV-176 at doses from 2.7-109.35 μg/kg. Patients enrolled had colorectal cancer (n = 11), breast cancer (n = 6), or adrenocortical carcinoma (n = 2). DLTs occurred in 4 patients and included thrombocytopenia (n = 2; both at 99.9-μg/kg dose level), neutropenia (n = 2; 78.3-μg/kg and 99.9-μg/kg dose levels), and pancytopenia (n = 1; 109.35-μg/kg dose level). The most common treatment-emergent adverse events related to ABBV-176 were thrombocytopenia, neutropenia, increased aspartate aminotransferase, nausea, fatigue, and pleural effusions. Effusions and edema were common, and timing of onset suggested possible cumulative ABBV-176 toxicity. Tumor expression of PRLR varied among patients enrolled and analyzed. No patient had an objective response. MTD was not formally determined, as identification of a tolerable dose was confounded by late-onset toxicities. ABBV-176 was associated with significant toxicity in this phase 1, dose-escalation study. Although cytopenias were often dose limiting, effusions and edema were also common and had late onset that suggested cumulative toxicity. No responses were observed, although data were available from a small number of patients with variable tumor PRLR expression. This study was terminated after the dosing of 19 patients.

A novel bispecific antibody targeting CD3 and prolactin receptor (PRLR) against PRLR-expression breast cancer

BACKGROUND

Prolactin receptor (PRLR) is highly expressed in a subset of human breast cancer and prostate cancer, which makes it a potential target for cancer treatment. In clinical trials, the blockade of PRLR was shown to be safe but with poor efficacy. It is therefore urgent to develop new therapies against PRLR target. Bispecific antibodies (BsAbs) could guide immune cells toward tumor cells, and produced remarkable effects in some cancers.

METHODS

In this study, a bispecific antibody targeting both tumor antigen PRLR and T cell surface CD3 antigen (PRLR-DbsAb) was constructed by split intein mediated protein transsplicing (BAPTS) system for the first time. Its binding activity was determined by Biacore and Flow cytometry, and target-dependent T cell mediated cytotoxicity was detected using LDH release assay. ELISA was utilized to study the secretion of cytokines by immune cells. Subcutaneous tumor mouse models were used to analyze the in vivo anti-tumor effects of PRLR-DbsAb.

RESULTS

PRLR-DbsAb in vitro could recruit and activate T cells to promote the release of Th1 cytokines IFN- γ and TNF- α, which could kill PRLR expressed breast cancer cells. In xenograft models with breast cancer cell line T47D, NOD/SCID mice intraperitoneally injected with PRLR-DbsAb exhibited significant inhibition of tumor growth and a longer survival compared to mice treated with PRLR monoclonal antibody (PRLR mAb).

CONCLUSIONS

Both in vitro and in vivo experiments showed PRLR-DbsAb had a potential therapy of cancer treatment potential therapy for cancer. Immunotherapy may be a promising treatment against the tumor target of PRLR.

Prolactin hormone exerts anti-tumorigenic effects in HER-2 overexpressing breast cancer cells through regulation of stemness

BACKGROUND

Breast cancers characterized by HER2 overexpression, belong to HER-2 enriched or luminal B subtypes, are frequently associated with higher incidence of tumor recurrence and therapeutic failure. These aggressive features have been attributed to the presence of cancer stem-like cell subpopulations known to have high tumor initiation, self -renewal capacities and high metastatic potential. Depleting these stem-like cells in these tumors therefore might help in improving therapeutic response and patient outcome.

METHODS

Here we used human breast cancer cells representative of HER2- enriched and luminal B subtypes as well as purified ALDH-positive stem-like cell subpopulation for in vitro cell viability, proliferation, tumorshpere formation analyses and gene expression studies. In addition, we used a pre-clinical xenograft HER2 mouse model (NOD/SCID mice) for in vivo tumorigenesis assessment. Furthermore, patient survival outcomes were evaluated using in silico bioinformatics analyses of publicly available datasets.

RESULTS

Our results indicate that prolactin (PRL) exerts anti-tumorigenic effects in HER-2 positive breast cancer cells. Importantly, PRL caused a significant reduction in ALDH^hi stem-like subpopulation, as well as their viability and tumorsphere formation capacity. Molecularly we found PRL to suppress gene expression of markers involved in stemness, tumor initiation, drug resistance and poor patient outcome found to be enriched in the ALDH^hi stem-like subpopulation. Furthermore, we show PRL to impede tumor growth of HER-2 xenografts and to suppress expression of Ki67 proliferative marker. Finally, we found PRL pathway gene signature to correlate with favorable patient outcomes in HER-2 and luminal B breast cancer patients.

CONCLUSION

Together these results emphasize an anti-tumorigenic role with a potential therapeutic value for PRL in HER-2 and luminal B breast cancer subtypes targeting the cancer stem-like cells.

Prolactin Receptor Isoforms as the Basis of Tissue-Specific Action of Prolactin in the Norm and Pathology

The review describes functional and structural features of different isoforms of prolactin receptor, mechanisms of signaling pathway activation, and molecular messengers involved in the transmission and termination of signal from the prolactin receptor isoforms. Changes in the ratio between prolactin receptor isoforms, key mediators of prolactin signal transduction and termination in various organs and tissues, are analyzed. Special attention is given to the role of molecular mediators and the ratio between the isoforms in normal physiological functions and pathologies. Approaches for therapeutic correction of prolactin signaling impairments are discussed.

Seasonal expressions of prolactin, prolactin receptor and STAT5 in the scented glands of the male muskrats (Ondatra zibethicus)

Prolactin (PRL) production in mammals has been demonstrated in extrapituitary gland, which can activate autocrine/ paracrine signaling pathways to regulate physiological activity. In the current study, we characterized the gene expression profiles of PRL, prolactin receptor (PRLR) and signal transducers and activators of transcription 5 (STAT5) in the scented glandular tissues of the muskrats, to further elucidate the relationship between PRL and the scented glandular functions of the muskrats. The weight and volume of the scented glands in the breeding season were significantly higher than those of the non-breeding season. Immunohistochemical data showed that PRL, PRLR and STAT5/phospho-STAT5 (pSTAT5) were found in the glandular and epithelial cells of the scented glands in both seasons. Furthermore, we found that PRL, PRLR and STAT5 had higher immunoreactivities in the scented glands during the breeding season when compared to those of the non-breeding season. In parallel, the gene expressions of PRL, PRLR and STAT5 were significantly higher in the scented glands during the breeding season than those of the non-breeding season. The concentrations of PRL in scented glandular tissues and sera were measured by enzymelinked immunosorbent assay (ELISA), and their levels were both notably higher in the breeding season than those of the nonbreeding season. These findings suggested that the scented glands of the muskrats were capable of extrapituitary synthesis of PRL, which might attribute PRL a specific function to an endocrine or autocrine/paracrine mediator.

Monoclonal Antibody Against Prolactin Receptor: A Randomized Placebo-Controlled Study Evaluating Safety, Tolerability, and Pharmacokinetics of Repeated Subcutaneous Administrations in Postmenopausal Women

BAY 1158061 is a potent monoclonal prolactin (PRL) receptor antibody, blocking PRL receptor (PRLR)-mediated signaling in a noncompetitive manner, which was tested in a randomized, placebo-controlled multiple dose study in postmenopausal women. The objective was to investigate safety, tolerability, pharmacokinetic characteristics, and effects of BAY 1158061 on serum PRL level. The study consisted of 4 parallel groups receiving up to 3 subcutaneous (sc) administrations of BAY 1158061 or placebo in 2 different dosing regimens. Twenty-nine healthy postmenopausal women were randomized and treated with BAY 1158061 or placebo: 30 mg at 14-day interval (7 participants), 60 mg at 28-day interval (8 participants), 90 mg at 14-day interval (7 participants), and placebo (7 participants). To keep the blinding, all randomized participants received sc injections biweekly (14-day interval) on 3 occasions in the lower abdomen. The PRLR antibody showed a favorable safety and tolerability profile in postmenopausal women with no distinct differences in occurrence of adverse events in BAY 1158061 or placebo-treated participants. BAY 1158061 displayed low immunogenicity with low titers of antidrug antibodies and absence of neutralizing antidrug antibodies. Pharmacokinetics were characterized by slow absorption after sc administration with median peak plasma concentrations 7 to 11 days after first dose and about 2-fold accumulation after repeated dosing every 2 weeks. The apparent mean elimination half-life was 9 to 16 days. The PRL concentration-time profiles over 24 hours showed no differences between verum- and placebo-treated participants. Based on the data obtained, BAY 1158061 is considered a good candidate for further development in endometriosis or other PRL-mediated disease conditions.

ImmunoPET Imaging of Endogenous and Transfected Prolactin Receptor Tumor Xenografts

Antibodies labeled with positron-emitting isotopes have been used for tumor detection, predicting which patients may respond to tumor antigen-directed therapy, and assessing pharmacodynamic effects of drug interventions. Prolactin receptor (PRLR) is overexpressed in breast and prostate cancers and is a new target for cancer therapy. We evaluated REGN2878, an anti-PRLR monoclonal antibody, as an immunoPET reagent. REGN2878 was labeled with Zr-89 after conjugation with desferrioxamine B or labeled with I-131/I-124. In vitro determination of the half-maximal inhibitory concentration (IC50) of parental REGN2878, DFO-REGN2878, and iodinated REGN2878 was performed by examining the effect of the increasing amounts of these on uptake of trace-labeled I-131 REGN2878. REGN1932, a non-PRLR binding antibody, was used as a control. Imaging and biodistribution studies were performed in mice bearing tumor xenografts with various expression levels of PRLR, including MCF-7, transfected MCF-7/PRLR, PC3, and transfected PC3/PRLR and T4D7v11 cell lines. The specificity of uptake in tumors was evaluated by comparing Zr-89 REGN2878 and REGN1932, and in vivo competition compared Zr-89 REGN2878 uptake in tumor xenografts with and without prior injection of 2 mg of nonradioactive REGN2878. The competition binding assay of DFO-REGN2878 at ratios of 3.53-5.77 DFO per antibody showed IC50 values of 0.4917 and 0.7136 nM, respectively, compared to 0.3455 nM for parental REGN2878 and 0.3343 nM for I-124 REGN2878. Imaging and biodistribution studies showed excellent targeting of Zr-89 REGN2878 in PRLR-positive xenografts at delayed times of 189 h (presented as mean ± 1 SD, percent injected activity per mL (%IA/mL) 74.6 ± 33.8%IA/mL). In contrast, MCF-7/PRLR tumor xenografts showed a low uptake (7.0 ± 2.3%IA/mL) of control Zr-89 REGN1932 and a very low uptake and rapid clearance of I-124 REGN2878 (1.4 ± 0.6%IA/mL). Zr-89 REGN2878 has excellent antigen-specific targeting in various PRLR tumor xenograft models. We estimated, using image-based kinetic modeling, that PRLR antigen has a very rapid in vivo turnover half-life of ∼14 min from the cell membrane. Despite relatively modest estimated tumor PRLR expression numbers, PRLR-expressing cells have shown final retention of the Zr-89 REGN2878 antibody, with an uptake that appeared to be related to PRLR expression. This reagent has the potential to be used in clinical trials targeting PRLR.

Truncating Prolactin Receptor Mutations Promote Tumor Growth in Murine Estrogen Receptor-Alpha Mammary Carcinomas

Estrogen receptor alpha-positive (ERα+) luminal tumors are the most frequent subtype of breast cancer. Stat1(-/-) mice develop mammary tumors that closely recapitulate the biological characteristics of this cancer subtype. To identify transforming events that contribute to tumorigenesis, we performed whole genome sequencing of Stat1(-/-) primary mammary tumors and matched normal tissues. This investigation identified somatic truncating mutations affecting the prolactin receptor (PRLR) in all tumor and no normal samples. Targeted sequencing confirmed the presence of these mutations in precancerous lesions, indicating that this is an early event in tumorigenesis. Functional evaluation of these heterozygous mutations in Stat1(-/-) mouse embryonic fibroblasts showed that co-expression of truncated and wild-type PRLR led to aberrant STAT3 and STAT5 activation downstream of the receptor, cellular transformation in vitro, and tumor formation in vivo. In conclusion, truncating mutations of PRLR promote tumor growth in a model of human ERα+ breast cancer and warrant further investigation.

A pilot study of cabergoline for the treatment of metastatic breast cancer

PURPOSE

The prolactin (PRL) receptor is over-expressed in breast cancer, and pre-clinical data indicate that it contributes to breast oncogenesis. Cabergoline is a potent dopamine receptor agonist of D2 receptors and has a direct inhibitory effect on pituitary PRL secretion.

METHODS

A phase II study of cabergoline in patients with metastatic breast cancer was conducted. The primary end point of the study was to determine the clinical benefit rate (CBR) at 2 months. Eligible patients had tumors of any receptor status with no limit of prior lines of therapy. Measurable and unmeasurable diseases were allowed. Cabergoline 1 mg orally, twice weekly (1 cycle = 4 weeks) was given until disease progression or unacceptable toxicity. PRL receptor immunohistochemical staining was performed on available baseline tumor tissue; serial serum PRL levels were assessed.

RESULTS

Twenty women were enrolled; 18 were evaluable for CBR. Tumor receptor status was distributed as follows: HR-any/HER2+ 2(10%), HR+/HER2- 18 (90%). The CBR was 33% (6/18), median progression free survival was 1.8 months, and median overall survival was 10.4 months. Two patients experienced disease control for over 12 months. Most common treatment-related adverse events were nausea (30%), fatigue (25%), and elevation in alkaline phosphatase (15%). Nine patients had baseline tissue for analysis; there was no association between baseline tumor PRL receptor expression and clinical benefit (p = 0.24). Change in serum PRL level and response were not correlated after 2 months of treatment (p = 0.64).

CONCLUSION

Cabergoline was well tolerated, and while the ORR was low, a small subset of patients experienced extended disease control.

Insight into the Endocrine System and the Immune System: A Review of the Inflammatory Role of Prolactin in Rheumatoid Arthritis and Psoriatic Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease that affects females three times more frequently than males. A potential role for hormones, such as prolactin (PRL), may in part explain this phenomenon. The risk of developing RA is increased in women who are lactating after the first pregnancy, which might be related to breastfeeding and the release of PRL. Other studies found a protective effect of PRL on RA development. Some studies have reported that hyperprolactinemia is more common in RA and serum PRL levels are correlated with several disease parameters, although others could not confirm these findings. Overall the plasma PRL levels are on average not elevated in RA. Previously, a small number of open-label clinical trials using bromocriptine, which indirectly decreases PRL levels, were performed in RA patients and showed clinical benefit, although others found the opposite effect. Locally produced PRL at the site of inflammation may have a crucial role in RA as well, as it has been shown that PRL can be produced by synovial macrophages. Locally produced PRL has both pro-inflammatory and anti-inflammatory effects in arthritis. Psoriatic arthritis (PsA) is also an autoinflammatory disease, in which the prolactin receptor is also expressed in macrophages. The aim of this review is to provide an overview of the potential role of PRL signaling in inflammatory joint diseases (RA and PsA) and its potential as a therapeutic target.

Rheumatoid arthritis and psoriatic arthritis synovial fluids stimulate prolactin production by macrophages

Prolactin (PRL) is a neuroendocrine hormone that can promote inflammation. We examined the synovial tissue and fluid levels of PRL in patients with inflammatory arthritis, PRL expression in differentiated Mϕs from patients with arthritis and from healthy donors, and the effects of different stimuli on PRL production by Mϕs. PRL levels were measured in paired synovial fluid (SF) and peripheral blood of patients with rheumatoid arthritis (RA, n = 19), psoriatic arthritis (PsA, n = 11), and gout (n = 11). Synovial-tissue PRL mRNA expression was measured by quantitative PCR in patients with RA (n = 25), PsA (n = 11), and gout (n = 12) and in Mϕs differentiated in SF of patients with RA, PsA, other subtypes of spondyloarthritis (SpA), and gout. Synovial-tissue PRL mRNA expression correlated significantly with clinical disease parameters in patients with RA and PsA, including erythrocyte sedimentation rate (ESR, r = 0.424; P = 0.049) and disease activity score evaluated in 28 joints (DAS28, r = 0.729; P = 0.017). Synovial-tissue PRL expression was similar in RA, PsA, and gout. PRL mRNA expression was detected in monocyte-derived Mϕs from patients with RA and was significantly higher (P ≤ 0.01) in Mϕs differentiated in pooled SF from patients with RA and PsA compared with SpA or gout. PRL production by Mϕ differentiation in the SF from patients with RA was not further regulated by stimulation with CD40L, IgG, LPS, or TNF. PRL is produced locally in the synovium of patients with inflammatory arthritis. The production of PRL by Mϕs was increased by unknown components of RA and PsA SF, where it could contribute to disease progression.

Preclinical Activity of the Novel Anti-Prolactin Receptor (PRLR) Antibody-Drug Conjugate REGN2878-DM1 in PRLR-Positive Breast Cancers

The Prolactin Receptor (PRLR) is a type 1 cytokine receptor that is expressed in a subset of breast cancers and may contribute to its pathogenesis. It is relatively overexpressed in approximately 25% of human breast tumors while expressed at low levels in some normal human tissues including the mammary gland. We developed an anti-PRLR antibody-drug conjugate (ADC), to target PRLR-positive breast cancer. REGN2878-DM1 is comprised of a fully human high-affinity function-blocking anti-PRLR IgG1 antibody (REGN2878) conjugated via a noncleavable SMCC linker to the cytotoxic maytansine derivative DM1. Both unconjugated REGN2878 and conjugated REGN2878-DM1 block PRL-mediated activation in vitro and are rapidly internalized into lysosomes. REGN2878-DM1 induces potent cell-cycle arrest and cytotoxicity in PRLR-expressing tumor cell lines. In vivo, REGN2878-DM1 demonstrated significant antigen-specific antitumor activity against breast cancer xenograft models. In addition, REGN2878-DM1 showed additive activity when combined with the antiestrogen agent fulvestrant. These results illustrate promising antitumor activity against PRLR-positive breast cancer xenografts and support the evaluation of anti-PRLR ADCs as potential therapeutic agents in breast cancer. Mol Cancer Ther; 16(7); 1299-311. ©2017 AACR.

Prolactin/androgen-inducible carboxypeptidase-D increases with nitrotyrosine and Ki67 for breast cancer progression in vivo, and upregulates progression markers VEGF-C and Runx2 in vitro

PURPOSE

Carboxypeptidase-D (CPD) cleaves C-terminal arginine (Arg) to produce nitric oxide (NO). Upregulation of CPD and NO by 17β-estradiol, prolactin (PRL), and androgen increases survival of human breast cancer (BCa) cells in vitro. To demonstrate similar events in vivo, CPD, nitrotyrosine (NT, hallmark of NO action), androgen receptor (AR), prolactin receptor (PRLR), and phospho-Stat5a (for activated PRLR) levels were evaluated in benign and malignant human breast tissues, and correlated with cell proliferation (Ki67) and BCa progression (Cullin-3) biomarkers.

METHODS

Paraffin-embedded breast tissues were analyzed by immunohistochemistry (IHC). BCa progression markers in human MCF-7 and T47D BCa cell lines treated with NO donor SIN-1 or PRL, ±CPD inhibitors were analyzed by RT-qPCR and immunoblotting.

RESULTS

IHC showed progressive increases in CPD, NT, Ki67, and Cullin-3 from low levels in benign tissues to high levels in ductal carcinoma in situ, low-grade, high-grade, and triple-negative BCa. CPD and NT staining were closely associated, implicating CPD in NO production. Phospho-Stat5a increased significantly from benign to high-grade BCa and was mostly nuclear. AR and PRLR were abundant in benign breast and BCa, including triple-negative tumors. SIN-1 and PRL increased VEGF-C and Runx2, but not Cullin-3, in BCa cell lines. PRL induction of VEGF-C and Runx2 was inhibited partly by CPD inhibitors, implicating NO, produced by PRL-regulated CPD, in BCa progression.

CONCLUSIONS

The CPD-Arg-NO pathway contributes to BCa progression in vitro and in vivo. PRL/androgen activation of the pathway support combined AR and PRLR blockade as an additional therapy for BCa.

Prolactin receptor in breast cancer: marker for metastatic risk

Prolactin and prolactin receptor signaling and function are complex in nature and intricate in function. Basic, pre-clinical and translational research has opened up our eyes to the understanding that prolactin and prolactin receptor signaling function differently within different cellular contexts and microenvironmental conditions. Its multiple roles in normal physiology are subverted in cancer initiation and progression, and gradually we are teasing out the intricacies of function and therapeutic value. Recently, we observed that prolactin has a role in accelerating the time to bone metastasis in breast cancer patients and identified the mechanism by which prolactin stimulated breast cancer cell-mediated lytic osteoclast formation. The possibility that the prolactin receptor is a marker for metastasis, and specifically bone metastasis, is one that may have to be put into the context of the different variants of prolactin, different prolactin receptor isoforms and intricate signaling pathways that are regulated by the microenvironment. The more complete the picture, the better one can test biomarker identity and design clinical trials to test therapeutic intervention. This review will cover the recent advances and highlight the complexity of prolactin receptor biology.

Prolactin Pro-Differentiation Pathway in Triple Negative Breast Cancer: Impact on Prognosis and Potential Therapy

Triple negative breast cancer (TNBC) is a heterogeneous disease associated with poor clinical outcome and lack of targeted therapy. Here we show that prolactin (PRL) and its signaling pathway serve as a sub-classifier and predictor of pro-differentiation therapy in TNBC. Using immunohistochemistry and various gene expression in silica analyses we observed that prolactin receptor (PRLR) protein and mRNA levels are down regulated in TNBC cases. In addition, examining correlation of PRLR gene expression with metagenes of TNBC subtypes (580 cases), we found that PRLR gene expression sub-classifies TNBC patients into a new subgroup (TNBC-PRLR) characterized by epithelial-luminal differentiation. Importantly, gene expression of PRL signaling pathway components individually (PRL, PRLR, Jak2 and Stat5a), or as a gene signature is able to predict TNBC patients with significantly better survival outcomes. As PRL hormone is a druggable target we determined the biological role of PRL in TNBC biology. Significantly, restoration/activation of PRL pathway in TNBC cells representative of mesenchymal or TNBC-PRLR subgroups led to induction of epithelial phenotype and suppression of tumorigenesis. Altogether, these results offer potential new modalities for TNBC stratification and development of personalized therapy based on PRL pathway activation.

Targeting Prolactin Receptor (PRLR) Signaling in PRLR-Positive Breast and Prostate Cancer

In this issue of The Oncologist, Agarwal et al. report negative results from a phase I trial of LFA102. Although “negative” in terms of antitumor activity, the study provides useful pharmacokinetic and pharmacodynamic information. Future trials evaluating PRLR blockers alone and in combination with other agents may still be warranted in patients with breast and prostate cancer.