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.

A Novel Family of Lysosomotropic Tetracyclic Compounds for Treating Leukemia

Acute myeloid leukemia (AML) is a heterogeneous hematological cancer characterized by poor prognosis and frequent relapses. Aside from specific mutation-related changes, in AML, the overall function of lysosomes and mitochondria is drastically altered to fulfill the elevated biomass and bioenergetic demands. On the basis of previous results, in silico drug discovery screening was used to identify a new family of lysosome-/mitochondria-targeting compounds. These novel tetracyclic hits, with a cationic amphiphilic structure, specifically eradicate leukemic cells by inducing both mitochondrial damage and apoptosis, and simultaneous lysosomal membrane leakiness. Lysosomal leakiness does not only elicit canonical lysosome-dependent cell death, but also activates the terminal differentiation of AML cells through the Ca²⁺-TFEB-MYC signaling axis. In addition to being an effective monotherapy, its combination with the chemotherapeutic arsenic trioxide (ATO) used in other types of leukemia is highly synergistic in AML cells, widening the therapeutic window of the treatment. Moreover, the compounds are effective in a wide panel of cancer cell lines and possess adequate pharmacological properties rendering them promising drug candidates for the treatment of AML and other neoplasias.

Lysosome-mediated chemoresistance in acute myeloid leukemia

Despite the outstanding advances in understanding the biology underlying the pathophysiology of acute myeloid leukemia (AML) and the promising preclinical data published lastly, AML treatment still relies on a classic chemotherapy regimen largely unchanged for the past five decades. Recently, new drugs have been approved for AML, but the real clinical benefit is still under evaluation. Nevertheless, primary refractory and relapse AML continue to represent the main clinical challenge, as the majority of AML patients will succumb to the disease despite achieving a complete remission during the induction phase. As such, treatments for chemoresistant AML represent an unmet need in this disease. Although great efforts have been made to decipher the biological basis for leukemogenesis, the mechanism by which AML cells become resistant to chemotherapy is largely unknown. The identification of the signaling pathways involved in resistance may lead to new combinatory therapies or new therapeutic approaches suitable for this subset of patients. Several mechanisms of chemoresistance have been identified, including drug transporters, key secondary messengers, and metabolic regulators. However, no therapeutic approach targeting chemoresistance has succeeded in clinical trials, especially due to broad secondary effects in healthy cells. Recent research has highlighted the importance of lysosomes in this phenomenon. Lysosomes' key role in resistance to chemotherapy includes the potential to sequester drugs, central metabolic signaling role, and gene expression regulation. These results provide further evidence to support the development of new therapeutic approaches that target lysosomes in AML.

New Therapeutic Approaches for Acute Myeloid Leukaemia

Acute myeloid leukaemia (AML) is a genetically heterogeneous haematopoietic neoplasm characterised by the accumulation of transformed immature blood progenitors in bone marrow. Since 1973, the backbone treatment has relied on the combination of cytarabine and an anthracycline, followed by allogeneic haematopoietic transplant if eligible. Therefore, the treatment decisions have largely revolved around chemotherapy drug intensity. Despite advances in our understanding of the underlying biology over the past decades, AML remains a therapeutic challenge as the overall survival is poor and treatment options are limited for relapsed/refractory AML or for unfit patients. After four decades without substantial changes, eight new noncytostatic drugs have been granted approval: vyxeos, enasidenib, gilteritinib, glasdegib, gemtuzumab ozogamicin, ivosidenib, midostaurin, and venetoclax. Despite promising preliminary results, some indications are based on early efficacy data, obtained in single-arm nonrandomised trials, highlighting the necessity for further validation in extended clinical trials. Interestingly, several druggable targets have been identified recently, associated with specific target-directed drugs. Based on the preclinical data available, great impact on clinical outcomes for patients with AML is expected, potentially increasing the therapeutic landscape for this disease.

Histamine receptor 1 is expressed in leukaemic cells and affects differentiation sensitivity

Despite the success of immunotherapy in several haematological neoplasms, the effectiveness in acute myeloid leukaemia (AML) is still controversial, partially due to the lack of knowledge regarding immune-related processes in this disease and similar neoplasias. In this study, we analysed the role and expression of histamine receptor 1 (HRH1) in haematological malignancies. Although the histamine receptor type 1 was widely expressed in healthy and malignant haematopoiesis, especially along the myeloid lineage, HRH1 lacked a relevant role in survival/proliferation and chemoresistance of AML cells, as analysed by HRH1 knockdown (KD) and pharmacological modulation. However, HRH1-mediated signalling was critical for the activation of the differentiation process induced by several agents including all-trans retinoic acid, establishing a role for HRH1 in myeloid differentiation. Pharmacological activation of Erk was able to partially restore differentiation capacity in HRH1 KD AML cells, suggesting that HRH1 signalling acts upstream MAPK-Erk pathway. As an indirect consequence of our results, treatment-related histamine release is not expected to confer a proliferative advantage in leukaemic cells.

Dual lysosomal-mitochondrial targeting by antihistamines to eradicate leukaemic cells

Background

Despite great efforts to identify druggable molecular targets for AML, there remains an unmet need for more effective therapies.

Methods

An in silico screening was performed using Connectivity Maps to identify FDA-approved drugs that may revert an early leukaemic transformation gene signature. Hit compounds were validated in AML cell lines. Cytotoxic effects were assessed both in primary AML patient samples and healthy donor blood cells. Xenotransplantation assays were undertaken to determine the effect on engraftment of hit compounds. The mechanism of action responsible for the antileukaemic effect was studied focussing on lysosomes and mitochondria.

Findings

We identified a group of antihistamines (termed ANHAs) with distinct physicochemical properties associated with their cationic-amphiphilic nature, that selectively killed leukaemic cells. ANHAs behaved as antileukaemic agents against primary AML samples ex vivo, sparing healthy cells. Moreover, ANHAs severely impaired the in vivo leukaemia regeneration capacity. ANHAs' cytotoxicity relied on simultaneous mitochondrial and lysosomal disruption and induction of autophagy and apoptosis. The pharmacological effect was exerted based on their physicochemical properties that permitted the passive targeting of both organelles, without the involvement of active molecular recognition.

Interpretation

Dual targeting of lysosomes and mitochondria constitutes a new promising therapeutic approach for leukaemia treatment, supporting the further clinical development.

Fund

This work was funded by the Fundación Mutua Madrileña (RMR), CaixaImpulse (RMR), the Spanish Ministry of Economy (RMR), the Josep Carreras International Leukaemia Foundation (RMR), l'Obra Social “La Caixa” (RMR), and Generalitat de Catalunya (IJC).