Pharmacological treatment with inhibitors of nuclear export enhances the antitumor activity of docetaxel in human prostate cancer

The nuclear export protein exportin-1 in solid malignant tumours: From biology to clinical trials

BACKGROUND

Exportin-1 (XPO1), a crucial protein regulating nuclear-cytoplasmic transport, is frequently overexpressed in various cancers, driving tumor progression and drug resistance. This makes XPO1 an attractive therapeutic target. Over the past few decades, the number of available nuclear export-selective inhibitors has been increasing. Only KPT-330 (selinexor) has been successfully used for treating haematological malignancies, and KPT-8602 (eltanexor) has been used for treating haematologic tumours in clinical trials. However, the use of nuclear export-selective inhibitors for the inhibition of XPO1 expression has yet to be thoroughly investigated in clinical studies and therapeutic outcomes for solid tumours.

METHODS

We collected numerous literatures to explain the efficacy of XPO1 Inhibitors in preclinical and clinical studies of a wide range of solid tumours.

RESULTS

In this review, we focus on the nuclear export function of XPO1 and results from clinical trials of its inhibitors in solid malignant tumours. We summarized the mechanism of action and therapeutic potential of XPO1 inhibitors, as well as adverse effects and response biomarkers.

CONCLUSION

XPO1 inhibition has emerged as a promising therapeutic strategy in the fight against cancer, offering a novel approach to targeting tumorigenic processes and overcoming drug resistance. SINE compounds have demonstrated efficacy in a wide range of solid tumours, and ongoing research is focused on optimizing their use, identifying response biomarkers, and developing effective combination therapies.

KEY POINTS

Exportin-1 (XPO1) plays a critical role in mediating nucleocytoplasmic transport and cell cycle. XPO1 dysfunction promotes tumourigenesis and drug resistance within solid tumours. The therapeutic potential and ongoing researches on XPO1 inhibitors in the treatment of solid tumours. Additional researches are essential to address safety concerns and identify biomarkers for predicting patient response to XPO1 inhibitors.

A synthetic lethal screen for Snail-induced enzalutamide resistance identifies JAK/STAT signaling as a therapeutic vulnerability in prostate cancer

Despite substantial improvements in the treatment landscape of prostate cancer, the evolution of hormone therapy-resistant and metastatic prostate cancer remains a major cause of cancer-related death globally. The mainstay of treatment for advanced prostate cancer is targeting of androgen receptor signaling, including androgen deprivation therapy plus second-generation androgen receptor blockade (e.g., enzalutamide, apalutamide, darolutamide), and/or androgen synthesis inhibition (abiraterone). While these agents have significantly prolonged the lives of patients with advanced prostate cancer, is nearly universal. This therapy resistance is mediated by diverse mechanisms, including both androgen receptor-dependent mechanisms, such as androgen receptor mutations, amplifications, alternative splicing, and amplification, as well as non-androgen receptor-mediated mechanisms, such as lineage plasticity toward neuroendocrine-like or epithelial-mesenchymal transition (EMT)-like lineages. Our prior work identified the EMT transcriptional regulator Snail as critical to hormonal therapy resistance and is commonly detected in human metastatic prostate cancer. In the current study, we sought to interrogate the actionable landscape of EMT-mediated hormone therapy resistant prostate cancer to identify synthetic lethality and collateral sensitivity approaches to treating this aggressive, therapy-resistant disease state. Using a combination of high-throughput drug screens and multi-parameter phenotyping by confluence imaging, ATP production, and phenotypic plasticity reporters of EMT, we identified candidate synthetic lethalities to Snail-mediated EMT in prostate cancer. These analyses identified multiple actionable targets, such as XPO1, PI3K/mTOR, aurora kinases, c-MET, polo-like kinases, and JAK/STAT as synthetic lethalities in Snail+ prostate cancer. We validated these targets in a subsequent validation screen in an LNCaP-derived model of resistance to sequential androgen deprivation and enzalutamide. This follow-up screen provided validation of inhibitors of JAK/STAT and PI3K/mTOR as therapeutic vulnerabilities for both Snail+ and enzalutamide-resistant prostate cancer.

Nuclear export inhibition jumbles epithelial-mesenchymal states and gives rise to migratory disorder in healthy epithelia

Dynamic nucleocytoplasmic transport of E-M factors regulates cellular E-M states; yet, it remains unknown how simultaneously trapping these factors affects epithelia at the macroscale. To explore this question, we performed nuclear export inhibition (NEI) via leptomycin B and Selinexor treatment, which biases nuclear localization of CRM1-associated E-M factors. We examined changes in collective cellular phenotypes across a range of substrate stiffnesses. Following NEI, soft substrates elevate collective migration of MCF10A cells for up to 24 hr, while stiffer substrates reduce migration at all time points. Our results suggest that NEI disrupts migration through competition between intercellular adhesions and mechanoactivation, generally causing loss of cell-cell coordination. Specifically, across substrate stiffnesses, NEI fosters an atypical E-M state wherein MCF10A cells become both more epithelial and more mesenchymal. We observe that NEI fosters a range of these concurrent phenotypes, from more epithelial shYAP MCF10A cells to more mesenchymal MDCK II cells. α-Catenin emerges as a potential link between E-M states, where it maintains normal levels of intercellular adhesion and transmits mechanoactive characteristics to collective behavior. Ultimately, to accommodate the concurrent states observed here, we propose an expanded E-M model, which may help further understand fundamental biological phenomena and inform pathological treatments.

The efficacy of selinexor (KPT-330), an XPO1 inhibitor, on non-hematologic cancers: a comprehensive review

PURPOSE

Selinexor is a novel XPO1 inhibitor which inhibits the export of tumor suppressor proteins and oncoprotein mRNAs, leading to cell-cycle arrest and apoptosis in cancer cells. While selinexor is currently FDA approved to treat multiple myeloma, compelling preclinical and early clinical studies reveal selinexor's efficacy in treating hematologic and non-hematologic malignancies, including sarcoma, gastric, bladder, prostate, breast, ovarian, skin, lung, and brain cancers. Current reviews of selinexor primarily highlight its use in hematologic malignancies; however, this review seeks to summarize the recent evidence of selinexor treatment in solid tumors.

METHODS

Pertinent literature searches in PubMed and the Karyopharm Therapeutics website for selinexor and non-hematologic malignancies preclinical and clinical trials.

RESULTS

This review provides evidence that selinexor is a promising agent used alone or in combination with other anticancer medications in non-hematologic malignancies.

CONCLUSION

Further clinical investigation of selinexor treatment for solid malignancies is warranted.

Targeting XPO1-Dependent Nuclear Export in Cancer

Nucleocytoplasmic transport of macromolecules is tightly regulated in eukaryotic cells. XPO1 is a transport factor responsible for the nuclear export of several hundred protein and RNA substrates. Elevated levels of XPO1 and recurrent mutations have been reported in multiple cancers and linked to advanced disease stage and poor survival. In recent years, several novel small-molecule inhibitors of XPO1 were developed and extensively tested in preclinical cancer models and eventually in clinical trials. In this brief review, we summarize the functions of XPO1, its role in cancer, and the latest results of clinical trials of XPO1 inhibitors.

Nuclear Export Inhibitor KPT-8602 Synergizes with PARP Inhibitors in Escalating Apoptosis in Castration Resistant Cancer Cells

Aberrant nuclear protein transport, often observed in cancer, causes mislocalization-dependent inactivation of critical cellular proteins. Earlier we showed that overexpression of exportin 1 is linked to higher grade and Gleason score in metastatic castration resistant prostate cancer (mCRPC). We also showed that a selective inhibitor of nuclear export (SINE) selinexor and second generation eltanexor (KPT-8602) could suppress mCRPC growth, reduce androgen receptor (AR), and re-sensitize to androgen deprivation therapy. Here we evaluated the combination of KPT-8602 with PARP inhibitors (PARPi) olaparib, veliparib and rucaparib in 22rv1 mCRPC cells. KPT-8602 synergized with PARPi (CI < 1) at pharmacologically relevant concentrations. KPT-8602-PARPi showed superior induction of apoptosis compared to single agent treatment and caused up-regulation of pro-apoptotic genes BAX, TP53 and CASPASE 9. Mechanistically, KPT-8602-PARPi suppressed AR, ARv7, PSA and AR targets FOXA1 and UBE2C. Western blot analysis revealed significant down-regulation of AR, ARv7, UBE2C, SAM68, FOXA1 and upregulation of cleaved PARP and cleaved CASPASE 3. KPT-8602 with or without olaparib was shown to reduce homologous recombination-regulated DNA damage response targets including BRCA1, BRCA2, CHEK1, EXO1, BLM, RAD51, LIG1, XRCC3 and RMI2. Taken together, this study revealed the therapeutic potential of a novel combination of KPT-8602 and PARP inhibitors for the treatment of mCRPC.

Combined Anti-Cancer Effects of Platycodin D and Sorafenib on Androgen-Independent and PTEN-Deficient Prostate Cancer

Castration-resistant (androgen-independent) and PTEN-deficient prostate cancer is a challenge in clinical practice. Sorafenib has been recommended for the treatment of this type of cancer, but is associated with several adverse effects. Platycodin D (PD) is a triterpene saponin with demonstrated anti-cancer effects and a good safety profile. Previous studies have indicated that PC3 cells (PTEN -/-, AR -/-) are sensitive to PD, suggesting that it may also be a useful treatment for castration-resistance prostate cancer. We herein investigated the effects of combining PD with sorafenib to treat PTEN-deficient prostate cancer cells. Our data show that PD promotes sorafenib-induced apoptosis and cell cycle arrest in PC3 cells. Of interest, PD only promoted the anti-cancer effects of sorafenib in Akt-positive and PTEN-negative prostate cancer cells. Mechanistic studies revealed that PD promoted p-Akt ubiquitination by increasing the p-Akt level. PD also increased the protein and mRNA expression of FOXO3a, the downstream target of Akt. Meanwhile, PD promoted the activity of FOXO3a and increased the protein expression of Fasl, Bim and TRAIL. Interestingly, when FOXO3a expression was inhibited, the antitumor effects of both PD and sorafenib were individually inhibited, and the more potent effects of the combination treatment were inhibited. Thus, the combination of PD and sorafenib may exert potent anti-cancer effects specifically via FOXO3a. The use of Akt inhibitors or FOXO3a agonists, such as PD, may represent a promising approach for the treatment of androgen-independent and PTEN-deficient prostate cancer.

Selinexor versus doxorubicin in dedifferentiated liposarcoma PDXs: evidence of greater activity and apoptotic response dependent on p53 nuclear accumulation and survivin down-regulation

BACKGROUND

Dedifferentiated liposarcoma (DDLPS), a tumor that lacks effective treatment strategies and is associated with poor outcomes, expresses amplified MDM2 in the presence of wild-type p53. MDM2 ubiquitination of p53 facilitates its XPO1-mediated nuclear export, thus limiting p53 tumor suppressor functions. Consequently, nuclear export is a rational target in DDLPS. We directly compared the antitumor activity of the first-in class XPO1 inhibitor selinexor and doxorubicin, the standard front-line therapy in sarcomas, in DDLPS patient-derived xenografts (PDXs) and primary cell lines.

METHODS

Drug activity was assessed in three PDXs (and two corresponding cell lines) established from the dedifferentiated component of primary untreated retroperitoneal DDLPS with myogenic (N = 2) and rhabdomyoblastic (N = 1) differentiation from patients who underwent surgery. These models were marked by amplification of MDM2, CDK4 and HMGA2 genes.

RESULTS

Selinexor was moderately active in the three PDXs but achieved greater tumor response compared to doxorubicin (maximum tumor volume inhibition: 46-80 % vs. 37-60 %). The PDX harboring rhabdomyoblastic dedifferentiation showed the highest sensitivity to both agents. PDX response to selinexor and doxorubicin was not associated with the extent of MDM2 and CDK4 gene amplification. Interestingly, the most chemosensitive PDX model showed the lowest extent of HMGA2 amplification. Selinexor was also more efficient than doxorubicinin in inducing an apoptotic response in PDXs and cell lines. Consistently, an increased nuclear accumulation of p53 was seen in all selinexor-treated models. In addition, a time-dependent decrease of survivin expression, with an almost complete abrogation of the cytoplasmic anti-apoptotic pool of this protein, was observed as a consequence of the decreased acetylation/activation of STAT3 and the increased ubiquitination of nuclear survivin.

CONCLUSIONS

Selinexor showed a moderate antitumor activity in three DDLPS PDXs, which was, however, consistently higher than doxorubicin across all different models regardless the extent of MDM2 amplification and the histological differentiation. The depletion of survivin protein seems to significantly contribute to the induction of apoptosis through which selinexor exerts its antitumor activity.

Repolarization of tumor infiltrating macrophages and increased survival in mouse primary CNS lymphomas after XPO1 and BTK inhibition

BACKGROUND

Patients diagnosed with primary central nervous system lymphoma (PCNSL) often face dismal outcomes due to the limited availability of therapeutic options. PCNSL cells frequently have deregulated B-cell receptor (BCR) signaling, but clinical responses to its inhibition using ibrutinib have been brief. In this regard, blocking nuclear export by using selinexor, which covalently binds to XPO1, can also inhibit BCR signaling. Selinexor crosses the blood-brain barrier and was recently shown to have clinical activity in a patient with refractory diffuse large B-cell lymphoma in the CNS. We studied selinexor alone or in combination with ibrutinib in pre-clinical mouse models of PCNSL.

METHODS

Orthotopic xenograft models were established by injecting lymphoma cells into the brain parenchyma of athymic mice. Tumor growth was monitored by bioluminescence. Malignant cells and macrophages were studied by immunohistochemistry and flow cytometry.

RESULTS

Selinexor blocked tumor growth and prolonged survival in a bioluminescent mouse model, while its combination with ibrutinib further increased survival. CNS lymphoma in mice was infiltrated by tumor-promoting M2-like macrophages expressing PD-1 and SIRPα. Interestingly, treatment with selinexor and ibrutinib favored an anti-tumoral immune response by shifting polarization toward inflammatory M1-like and diminishing PD-1 and SIRPα expression in the remaining tumor-promoting M2-like macrophages.

CONCLUSIONS

These data highlight the pathogenic role of the innate immune microenvironment in PCNSL and provide pre-clinical evidence for the development of selinexor and ibrutinib as a new promising therapeutic option with cytotoxic and immunomodulatory potential.

Dual CXCR4 and E-Selectin Inhibitor, GMI-1359, Shows Anti-Bone Metastatic Effects and Synergizes with Docetaxel in Prostate Cancer Cell Intraosseous Growth

Metastatic castration resistant prostate cancer (mCRPC) relapses due to acquired resistance to docetaxel-based chemotherapy and remains a major threat to patient survival. In this report, we tested the effectiveness of a dual CXCR4/E-selectin antagonist, GM-I1359, in vitro and in vivo, as a single agent or in combination with docetaxel (DTX). This agent was compared to the single CXCR4 antagonist, CTCE-9908, and E-selectin antagonist, GMI-1271. Here we demonstrate that CXCR4 antagonism reduced growth and enhanced DTX treatment in PCa cell lines as well as restored DTX effectiveness in DTX-resistant cell models. The efficacy of dual antagonist was higher respect to those observed for single CXCR4 antagonism. GM1359 impacted bone marrow colonization and growth in intraventricular and intratibial cell injection models. The anti-proliferative effects of GMI-1359 and DTX correlated with decreased size, osteolysis and serum levels of both mTRAP and type I collagen fragment (CTX) in intra-osseous tumours suggesting that the dual CXCR4/E-selectin antagonist was a docetaxel-sensitizing agent for bone metastatic growth. Single agent CXCR4 (CTCE-9908) and E-selectin (GMI-1271) antagonists resulted in lower sensitizing effects compared to GMI-1359. These data provide a biologic rationale for the use of a dual E-selectin/CXCR4 inhibitor as an adjuvant to taxane-based chemotherapy in men with mCRPC to prevent and reduce bone metastases.

Impregnation of Curcumin into a Biodegradable (Poly-lactic-co-glycolic acid, PLGA) Support, to Transfer Its Well Known In Vitro Effect to an In Vivo Prostate Cancer Model

Prostate cancer (PCa) is one of the most common cancers in older men and is associated with high mortality. Despite advances in screening for early detection of PCa, a large proportion of patients continue to be diagnosed with metastatic disease, with ~20% of men showing a high tumor grade and stage. Medicinal plant extracts have a great potential to prevent/treat PCa, as well as to reduce its incidence/prevalence and improve survival rates. One of the most promising extracts is curcumin, which is a major, nontoxic, bioactive compound of Curcuma longa. Curcumin has strong antitumor activity in vitro. However, its potential beneficial in vivo affects are limited by its low intestinal absorption and rapid metabolism. In this study, curcumin was impregnated into a biodegradable poly(lactic-co-glycolic) acid (PLGA) support and characterized by FTIR and DSC, and its release by UV spectrophotometry. PLGA-curcumin was tested in different subcutaneous PCa xenograft models (PC3, 22rv1, and DU145 PCa cell-lines), and its effects evaluated by tumor progression an immuno-histochemical analysis (Trichromic, Ki67 and TUNEL stainings), were compared with those of a commercial curcumin preparation. Our results indicate that curcumin-impregnated PLGA is significantly more active (~2-fold increase) with respect to oral curcumin, which supports its use for subcutaneous administration.

TUBB3 Reverses Resistance to Docetaxel and Cabazitaxel in Prostate Cancer

Recent studies have reported that TUBB3 overexpression is involved in docetaxel (DTX) resistance in prostate cancer (PCa). The aim of this study was to clarify the role of TUBB3 in DTX and cabazitaxel (CBZ) resistance, and cross-resistance between DTX and CBZ in PCa. We analyzed the effect of TUBB3 knockdown on DTX and CBZ resistance and examined the interaction between TUBB3 and PTEN. We also investigated the role of phosphoinositide 3-kinases (PI3K) inhibitor (LY294002) in DTX and CBZ resistance. TUBB3 expression was upregulated in DTX-resistant and CBZ-resistant cells. TUBB3 knockdown re-sensitized DTX-resistant cells to DTX and CBZ-resistant cells to CBZ. Additionally, TUBB3 knockdown re-sensitized DTX-resistant cell lines to CBZ, indicating that TUBB3 mediates cross-resistance between DTX and CBZ. Knockdown of TUBB3 enhanced PTEN expression, and PTEN knockout enhanced TUBB3 expression. LY294002 suppressed TUBB3 expression in DTX-resistant and CBZ-resistant cell lines. LY294002 re-sensitized DTX-resistant cell lines to DTX and CBZ-resistant cell lines to CBZ. These results suggest that TUBB3 is involved in DTX resistance and CBZ resistance. A combination of LY294002/DTX and that of LY294002/CBZ could be potential strategies for PCa treatment.

Controlling the Gatekeeper: Therapeutic Targeting of Nuclear Transport

Nuclear transport receptors of the karyopherin superfamily of proteins transport macromolecules from one compartment to the other and are critical for both cell physiology and pathophysiology. The nuclear transport machinery is tightly regulated and essential to a number of key cellular processes since the spatiotemporally expression of many proteins and the nuclear transporters themselves is crucial for cellular activities. Dysregulation of the nuclear transport machinery results in localization shifts of specific cargo proteins and associates with the pathogenesis of disease states such as cancer, inflammation, viral illness and neurodegenerative diseases. Therefore, inhibition of the nuclear transport system has future potential for therapeutic intervention and could contribute to the elucidation of disease mechanisms. In this review, we recapitulate clue findings in the pathophysiological significance of nuclear transport processes and describe the development of nuclear transport inhibitors. Finally, clinical implications and results of the first clinical trials are discussed for the most promising nuclear transport inhibitors.

RNA sequencing reveals upregulation of a transcriptomic program associated with stemness in metastatic prostate cancer cells selected for taxane resistance

Patients with metastatic castration-resistant prostate cancer (mCRPC) develop resistance to conventional therapies including docetaxel (DTX). Identifying molecular pathways underlying DTX resistance is critical for developing novel combinatorial therapies to prevent or reverse this resistance. To identify transcriptomic signatures associated with acquisition of chemoresistance we profiled gene expression in DTX-sensitive and -resistant mCRPC cells using RNA sequencing (RNA-seq). PC3 and DU145 cells were selected for DTX resistance and this phenotype was validated by immunoblotting using DTX resistance markers (e.g. clusterin, ABCB1/P-gp, and LEDGF/p75). Overlapping genes differentially regulated in the DTX-sensitive and -resistant cells were ranked by Gene Set Enrichment Analysis (GSEA) and validated to correlate transcript with protein expression. GSEA revealed that genes associated with cancer stem cells (CSC) (e.g., NES, TSPAN8, DPPP, DNAJC12, and MYC) were highly ranked and comprised 70% of the top 25 genes differentially upregulated in the DTX-resistant cells. Established markers of epithelial-to-mesenchymal transition (EMT) and CSCs were used to evaluate the stemness of adherent DTX-resistant cells (2D cultures) and tumorspheres (3D cultures). Increased formation and frequency of cells expressing CSC markers were detected in DTX-resistant cells. DU145-DR cells showed a 2-fold increase in tumorsphere formation and increased DTX resistance compared to DU145-DR 2D cultures. These results demonstrate the induction of a transcriptomic program associated with stemness in mCRPC cells selected for DTX resistance, and strengthen the emerging body of evidence implicating CSCs in this process. In addition, they provide additional candidate genes and molecular pathways for potential therapeutic targeting to overcome DTX resistance.