Phase I trial of the androgen receptor modulator CR1447 in breast cancer patients

Anti-Androgenic Therapies Targeting the Luminal Androgen Receptor of a Typical Triple-Negative Breast Cancer

Triple-negative tumors are progressively delineating their existence over the extended spectrum of breast cancers, marked by intricate molecular heterogeneity, a low overall survival rate, and an unexplored therapeutic approach. Although the basal subtype transcends the group and contributes approximately 80% to triple-negative breast cancer (TNBC) cases, the exceptionally appearing mesenchymal and luminal androgen receptor (LAR) subtypes portray an unfathomable clinical course. LAR with a distinct generic profile frequently metastasizes to regional lymph nodes and bones. This subtype is minimally affected by chemotherapy and shows the lowest pathologic complete response. The androgen receptor is the only sex steroid receptor that plays a cardinal role in the progression of breast cancers and is typically overexpressed in LAR. The partial AR antagonist bicalutamide and the next-generation AR inhibitor enzalutamide are being assessed in standard protocols for the mitigation of TNBC. There arises an inevitable need to probe into the strategies that could neutralize these androgen receptors and alleviate the trajectory of concerning cancer. This paper thus focuses on reviewing literature that provides insights into the anti-androgenic elements against LAR typical TNBC that could pave the way for clinical advancements in this dynamic sphere of oncology.

Bruceine D Identified as a Drug Candidate against Breast Cancer by a Novel Drug Selection Pipeline and Cell Viability Assay

The multi-target effects of natural products allow us to fight complex diseases like cancer on multiple fronts. Unlike docking techniques, network-based approaches such as genome-scale metabolic modelling can capture multi-target effects. However, the incompleteness of natural product target information reduces the prediction accuracy of in silico gene knockout strategies. Here, we present a drug selection workflow based on context-specific genome-scale metabolic models, built from the expression data of cancer cells treated with natural products, to predict cell viability. The workflow comprises four steps: first, in silico single-drug and drug combination predictions; second, the assessment of the effects of natural products on cancer metabolism via the computation of a dissimilarity score between the treated and control models; third, the identification of natural products with similar effects to the approved drugs; and fourth, the identification of drugs with the predicted effects in pathways of interest, such as the androgen and estrogen pathway. Out of the initial 101 natural products, nine candidates were tested in a 2D cell viability assay. Bruceine D, emodin, and scutellarein showed a dose-dependent inhibition of MCF-7 and Hs 578T cell proliferation with IC₅₀ values between 0.7 to 65 μM, depending on the drug and cell line. Bruceine D, extracted from Brucea javanica seeds, showed the highest potency.

SAKK 21/12: a phase II trial of transdermal CR1447 in breast cancer patients

Objective

CR1447, a novel transdermal formulation of 4-hydroxytestosterone, has aromatase-inhibiting and androgen receptor (AR)-modulating properties (IC₅₀4.4 nM) with antitumor effects against AR-positive tumor cells in vitro. This trial investigated the efficacy and safety of CR1447 for patients with metastatic estrogen receptor-positive (A) and AR-positive triple-negative breast cancers (B).

Design and methods

(A) included patients with at most one prior endocrine therapy line without progression ≥6 months, whereas (B) included patients with ≤2 prior chemotherapy lines, all displaying advanced signs of disease. The primary endpoint was disease control at week 24 (DC24). The null hypothesis was DC24 ≤30% (A) and ≤15% (B). Thirty-seven patients were recruited (29 in (A) and 8 in (B)); accrual was stopped following an interim analysis demonstrating futility in (A) and slow accrual in (B).

Results

DC24 was attained in 5/21 (95% CI: 8.2-47.2) patients in (A) and none in (B). The median progression-free survival was 5.1 months (95% CI: 2.5-5.6) in (A) and 2.5 months (95% CI: 0.7-2.6) in (B). The median overall survival was 24.6 months (95% CI: 22.9-not applicable) in (A) and 10.8 months (95% CI: 3.3-10.9) in (B). CR1447 had a favorable safety profile without treatment-related grade 3-5 toxicities in (A). Especially no side effects linked to androgenic effects were observed.

Conclusions

Despite this trial being negative, the 24% DC24 rate in a second-line setting, and the prolonged partial response experienced by a patient, indicate activity. Further evaluation of CR1447 in endocrine-sensitive patients or combination trials appears warranted.

Is it time to consider the Androgen receptor as a therapeutic target in breast cancer?

Breast cancer (BC) is a heterogeneous disease and the most prevalent malignant tumor in women worldwide. The majority of BC cases are positive for estrogen receptor (ER) and progesterone receptor (PgR), both known to be involved in cancer pathogenesis, progression, and invasion. In line with this, hormonal deprivation therapy appears to be a useful tool and an effective treatment for these BC subtypes. Unfortunately, prognosis among patients with hormone-negative tumors or therapy-refractory and metastatic patients remains poor. Novel biomarkers are urgently needed in order to predict the course of the disease, make better therapy decisions and improve the overall survival of patients. In this respect, the androgen receptor (AR), a member of the hormonal nuclear receptor superfamily and ER and PgR, emerges as an interesting feature widely expressed in human BCs. Despite the advances, the precise tumorigenic mechanism of AR and the role of its endogenous ligands are yet not well-understood. In this review, we aim to elaborate on the prognostic impact of AR expression and current AR-targeting approaches based on previous studies investigating AR's role in different BC subtypes.

Androgen receptor expression in breast cancer: Implications on prognosis and treatment, a brief review

Approximately 70%-85% of breast cancers express androgen receptors (ARs). The role of AR in breast cancer pathogenesis is currently in exploration. Both androgens and anti-androgens have demonstrated variable inhibitory and stimulatory effects in AR-positive breast cancer depending on estrogen receptor and HER2 co-expression. Androgen signaling pathways interact with other critical cellular pathways, such as the PI3K/AKT/mTOR, Ras/Raf/MAPK/ERK, Wnt/β-catenin, and estrogen signaling pathways. Therapeutic exploitation of AR has been the crux of management of prostate cancer for decades. In recent years there has been increasing interest in AR as a novel therapeutic target in breast cancer. There have been many early phase clinical trials evaluating the safety and efficacy of various AR-targeted agents in breast cancer. Some of these studies have shown promising clinical benefits. Studies of biomarkers to identify the patients likely to benefit from AR-targeted therapies are currently in progress. Besides, AR expression may be an important prognostic and predictive marker for breast cancer, which needs to be defined better in future studies.

ARe we there yet? Understanding androgen receptor signaling in breast cancer

The role of androgen receptor (AR) activation and expression is well understood in prostate cancer. In breast cancer, expression and activation of AR is increasingly recognized for its role in cancer development and its importance in promoting cell growth in the presence or absence of estrogen. As both prostate and breast cancers often share a reliance on nuclear hormone signaling, there is increasing appreciation of the overlap between activated cellular pathways in these cancers in response to androgen signaling. Targeting of the androgen receptor as a monotherapy or in combination with other conventional therapies has proven to be an effective clinical strategy for the treatment of patients with prostate cancer, and these therapeutic strategies are increasingly being investigated in breast cancer. This overlap suggests that targeting androgens and AR signaling in other cancer types may also be effective. This manuscript will review the role of AR in various cellular processes that promote tumorigenesis and metastasis, first in prostate cancer and then in breast cancer, as well as discuss ongoing efforts to target AR for the more effective treatment and prevention of cancer, especially breast cancer.

Role of human 3α-hydroxysteroid dehydrogenase isoforms (AKR1C1-AKR1C3) in the extrahepatic metabolism of the steroidal aromatase inactivator Formestane

The clinical use of the steroidal aromatase inhibitor Formestane (4-hydroxandrostenedione, 4-OHA) in the treatment of advanced ER+ breast cancer has been discontinued, and therefore, interest in this remarkable drug has vanished. As a C-19 sterol, 4-OHA can undergo extensive intracellular metabolism depending on the expression of specific enzymes in the corresponding cells. We used the metabolites 4β-hydroxyandrosterone, 4β-hydroxyepiandrosterone and its 17β-reduced derivative as standards for the proof of catalytic activity present in the cell culture medium and expressed by the isolated enzymes. All of the aldo-keto reductases AKR1C1, AKR1C2, AKR1C3 and AKR1C4 catalysed the reduction of the 3-keto-group and the Δ^4,5 double bond of 4-OHA at the same time. Molecular docking experiments using microscale thermophoresis and the examination of the kinetic behaviour of the isolated enzymes with the substrate 4-OHA proved that AKR1C3 had the highest affinity for the substrate, whereas AKR1C1 was the most efficient enzyme. Both enzymes (AKR1C1and AKR1C3) are highly expressed in adipose tissue and lungs, exhibiting 3β-HSD activity. The possibility that 4-OHA generates biologically active derivatives such as the androgen 4-hydroxytestosterone or some 17β-hydroxy derivatives of the 5α-reduced metabolites may reawaken interest in Formestane, provided that a suitable method of administration can be developed, avoiding oral or intramuscular depot-injection administration.

Consideration of breast cancer subtype in targeting the androgen receptor

The androgen receptor (AR) is a drug target in breast cancer, and AR-targeted therapies have induced tumor responses in breast cancer patients. In this review, we summarized the role of AR in breast cancer based on preclinical and clinical data. Response to AR-targeted therapies in unselected breast cancer populations is relatively low. Preclinical and clinical data show that AR antagonists might have a role in estrogen receptor (ER)-negative/AR-positive tumors. The prognostic value of AR for patients remains uncertain due to the use of various antibodies and cut-off values for immunohistochemical assessment. To get more insight into the role of AR in breast cancer, we additionally performed a retrospective pooled analysis to determine the prognostic value of the AR using mRNA profiles of 7270 primary breast tumors. Our analysis shows that a higher AR mRNA level is associated with improved disease outcome in patients with ER-positive/human epidermal growth factor receptor 2 (HER2)-negative tumors, but with worse disease outcome in HER2-positive subgroups. In conclusion, next to AR expression, incorporation of additional tumor characteristics will potentially make AR targeting a more valuable therapeutic strategy in breast cancer.

The Divergent Function of Androgen Receptor in Breast Cancer; Analysis of Steroid Mediators and Tumor Intracrinology

Androgen receptor (AR) is the most widely expressed steroid receptor protein in normal breast tissue and is detectable in approximately 90% of primary breast cancers and 75% of metastatic lesions. However, the role of AR in breast cancer development and progression is mired in controversy with evidence suggesting it can either inhibit or promote breast tumorigenesis. Studies have shown it to antagonize estrogen receptor alpha (ERα) DNA binding, thereby preventing pro-proliferative gene transcription; whilst others have demonstrated AR to take on the mantle of a pseudo ERα particularly in the setting of triple negative breast cancer. Evidence for a potentiating role of AR in the development of endocrine resistant breast cancer has also been mounting with reports associating high AR expression with poor response to endocrine treatment. The resurgence of interest into the function of AR in breast cancer has resulted in various emergent clinical trials evaluating anti-AR therapy and selective androgen receptor modulators in the treatment of advanced breast cancer. Trials have reported varied response rates dependent upon subtype with overall clinical benefit rates of ~19-29% for anti-androgen monotherapy, suggesting that with enhanced patient stratification AR could prove efficacious as a breast cancer therapy. Androgens and AR have been reported to facilitate tumor stemness in some cancers; a process which may be mediated through genomic or non-genomic actions of the AR, with the latter mechanism being relatively unexplored in breast cancer. Steroidogenic ligands of the AR are produced in females by the gonads and as sex-steroid precursors secreted from the adrenal glands. These androgens provide an abundant reservoir from which all estrogens are subsequently synthesized and their levels are undiminished in the event of standard hormonal therapeutic intervention in breast cancer. Steroid levels are known to be altered by lifestyle factors such as diet and exercise; understanding their potential role in dictating the function of AR in breast cancer development could therefore have wide-ranging effects in prevention and treatment of this disease. This review will outline the endogenous biochemical drivers of both genomic and non-genomic AR activation and how these may be modulated by current hormonal therapies.