Recent progresson nuclear export protein XPO1 inhibitor in the treatment of hematological malignancies

GAO Ya-ya, LI Hong, GAO Guang-xun

1. Shaanxi University of Chinese Medicine, Xianyang 712046, China

2. Department of Hematology, Xijing Hospital, Air Force Military Medical University, Xi’an 710032, Chin

Keywords:

ABSTRACT Most tumor suppressor and growth-regulating proteins are transported via the plasmic nuclear transporter exportin 1 (XPO1).Many malignancies have excessive XPO1 expression, which is associated with disease progression and resistance to therapy.A novel class of anticancer medication called selective inhibitor of nuclear export (SINE) can down-regulate the levels of a number of antigenic proteins in the cytoplasm, activate tumor suppressor and other growth regulating proteins, and promote the nuclear retention and apoptosis of tumor cells.This article discusses the function of XPO1 in drug resistance and tumor development as well as the advancement of XPO1 inhibitor research for the treatment of hematological cancers.

Transport receptor protein called nuclear export protein 1 (XPO1),also known as CRM1 (chromosome maintenance protein 1)[1],is in charge of facilitating the nucleation transport of more than 200 proteins.Targeting XPO1 is a promising therapy because it is frequently overexpressed in hematologic malignancy, which results in abnormal apoptosis regulation or abnormal cell cycle[2].Selinexor is the first selective XPO1 inhibitor, which inhibits XPO1 and promotes the activation of intranuclear storage such as tumor suppressor proteins (TSPs) and growth regulatory proteins (GRPs)and exerts anti-tumor effects; It also down regulated the mRNA levels of various oncogenes in the cytoplasm to induce selective apoptosis of tumor cells, showing obvious anti-tumor effects in different types of tumors[3, 4].KPT-185, KPT-251, KPT-276, KPT-335 (Verdinexor), and KPT-8602 (Eltanexor), which are watersoluble, reversible XPO1 inhibitors, are further SINE compounds now being studied.Second-generation oral XPO1 inhibitor Eltanexor lowers central nervous system-mediated side effects like anorexia and weight loss and may be under a higher safety profile and a larger therapeutic window than Selinexor[5].It also has a lot lower brain tissue permeability than Selinexor.This article discusses the function of XPO1 in drug resistance and tumor development as well as the advancement of XPO1 inhibitor research for the treatment of hematological cancers.

1.One physiological function of the XPO1 pathway

The primary physiological job of XPO1 is to mediate the nuclear export of many proteins and mRNAs to the cytoplasm, which is crucial for preserving cellular homeostasis[5].In the nucleus, XPO1 and RanGTP engage with nuclear pore proteins through XPO1 to traverse the nuclear pore complex’s core channel by binding to cargo proteins containing nuclear output signals to create a stable nucleated transport complex; Under the control of RanGAP and RanBP1/2, RanGTP is hydrolyzed to RanGDP after entering the cytoplasm, the nucleation transport complex is broken up, the cargo proteins are released, and XPO1 is then shuttled back to the nucleus[1, 5].XPO1 regulates cell proliferation and apoptosis through this nuclear transport mechanism, which is essential for normal cell physiological function.

2.XPO1-mediated abnormal localization of proteins is associated with tumorigenesis and drug resistance

Compared with normal cells, XPO1 over expression in tumor cells leads to subcellular localization and dysfunction of a variety of TSPs and GRPs (including the mislocalization of many drug targets), thereby inhibiting the apoptosis process of tumor cells and promoting the development of tumors[6].

Excessive nuclear output promotes the development of cancer and treatment resistance.Overexposure of XPO1 leads to cytoplasmic retention of TSPs such as p53.Mislocalization of this protein leads to its functional inactivation, leading to acquired therapeutic resistance[1].XPO1 over expression also promotes transcriptional elongation factor E2F7 output.Thereby inhibiting SphK2 in the cytoplasm and leading to tetracycline resistance[5].Similarly,enhanced nuclear output of RNA helices DDX17 and topoisomerase 2α(TOP2A) can result in resistance to definitive and doxorubicin,respectively[5].Nuclear output of prominent members of the NF-κB signaling pathway, such as NF-κB inhibitors (IκB), p65, and p50,activates the pathway and leads to vibration resistance[5, 7].Export of nucleoprotein 3 to the cytoplasm the regulation of β-captain and subsequently promotes resistance to platinum drugs[8].Nuclear output of p53 and protein phosphatase 2A (PP2A) is related to resistance to tyrosine kinase inhibitors, particularly imitative or the novel PI3K inhibitor CYH33[5, 9].

3.XPO1 inhibitor-Selinexor is used in the therapeutic mechanism of hematological tumors

3.1 Tumor suppressor protein pathways

3.1.1 p53,p21,and p73

p53 is TSPs that play a role in the regulation of cell cycle,apoptosis, and genomic stability through multiple mechanisms[1].P53 in hematological tumors narrows the replication and accumulation of damaged DNA and inhibits tumor cell proliferation.P73 is a homologous protein of p53 and functions similarly.P21 is the major downstream pathway of p53 activity and is implicated in DNA damage and cell cycle arrest[10].P53 in normal cells is strictly controlled, but XPO1 mediates the output of p53 nuclei in various tumors, resulting in loss of function and thus promoting tumorigenesis and progression[1].Selinexor acts highly selectively on the XPO1 target, corrects abnormal localization of proteins, and inhibits tumor cell growth by promoting nuclear aggregation and activation of p53, p21 and p73[1].

3.1.2 NF-kB

NF-κB plays a key role in the inflammatory response of cells, immune response, etc.The NF-κB pathway in tumor cells is activated, inhibiting apoptosis and promoting tumor cell proliferation.IκB-α is an inhibitory protein upstream of NFκB that binds to NF-κB and is inactivated in the cytoplasm after sequestration[11].The over expression of XPO1 in tumor cells,IκB-α in the nucleus and IκB-α and NF-κB conjugates are over-transported to the cytoplasm, promoting their degradation and inactivation by proteasomes in the cytoplasm and activating the NFκB pathway, thereby enhancing tumor cell activity[12].Selinexor can inhibit the transcriptional activity of NF-κB and prevent activation of the oncogene pathway by deregulating the atomic concentration of IκB-α, IκB-α and NF-κB subunit conjugates[12].

3.2 Glucocorticoid receptor pathways

The nucleation of glucocorticoid receptor (GR) is primarily mediated by CRT (nuclear output receptor certification), but also slowly by XPO1.GR can promote the expression of p21 and p27 genes, arrest the cell cycle, and inhibit the rapamycin target protein(mTOR) signaling pathway to exert antitumor effects[13].GR in tumor cells is overstraining out of the nucleus by XPO1.Selinexor can inhibit the nuclear output of GR, unregulated the level of intranuclear GR, enhance GR transcriptional activity, inhibit the mTOR pathway with GC, and inhibit tumor growth[13, 14].

3.3 Carcinogenic Factors

Elevated endogenic factor eIF4E (eukaryotic translation initiation factor 4E) is found in 30% of malignant tumors, which bind to the cap structure of the oncogene mRNA and are nuclear output through XPO1, which is associated with tumorigenesis and development [15].Selinexor can inhibit the nuclear output of eIF4E-dependent mRNA,thereby down regulating the translation of c-MYC, CDC25A,BRD4, Bcl-2, Mcl-1 and other related oncogene, reducing the level of antigenic proteins in the cytoplasm, and inhibiting tumorigenesis[16].

4.Application of XPO1 inhibitors in hematologic tumors

4.1 Multiple Myeloma

Selinexor induces apoptosis in multiple myeloma (MM), inhibits cell growth, and delays tumor progression[17].Selinexor in combination with other antitumor drugs shows better synergistic cytotoxic effects.Studies have found[14] that Selinexor in combination with dexamethasone can increase the expression of pro-apoptotic markers (PUMA) and narrow the expression of prosurvival markers (Bcl-2, Mcl-1).In other studies[18].Selinexor in combination with proteasome inhibitors exhibited synergistic cytotoxicity in vitro and in vivo and antitumor activity in animal models.

Clinical studies have demonstrated that the use of XPO1 inhibitors in MM patients has also shown good efficacy.The STORM trial[19]evaluated the efficacy of Selinexor in combination with low-dose dexamethasone in 123 patients with relapsed/refractory multiple myeloma (RRMM) who had received multiple lines of therapy and were resistant to five different therapies, including conventional chemotherapy, glucocorticoids, at least one proteasome inhibitor,at least one immunomodulatory drug, and anti-CD38 monoclonal antibody therapy, The results showed that the ORR reached 26.2%,and the median progression-free survival (PFS) and overall survival(OS) were 3.7 months and 8.6 months, respectively.Among them, 2 patients had a strict complete response (CR) and 30 patients achieved partial response (PR) or above.The BOSTON study[20, 21] explored the efficacy and safety of 42 patients with MM who had previously received 1～3 lines of therapy.The results showed that the median PFS (13.9 versus 9.5 months) in the SVd (Selinexor + bortezomib+ dexamethasone) group (n=195) was significantly longer (13.9 months vs 9.5 months) than in the Vd (bortezomib + dexamethasone)group, and the incidence of peripheral neuropathy above grade 2 was lower than that in the Vd group (21 versus 34%).Subgroup analysis showed that older patients, patients with renal insufficiency, and patients at high genetic risk[22] could benefit from SVd therapy.The STOMPI/II phase[23-25] trial explored the efficacy and safety of Sd(Selinexor + dexamethasone) combined with different mechanisms in patients with RRMM, and the results showed that the ORR of Sd combined with pomalidomide (SPd) in 48 patients was 50%, and the median PFS was 12.2 months; the ORR of Sd combined with carfilzomib (SKd) in 24 patients was 78%.The median PFS was 23.7 months; the ORR of 34 patients treated with Sd combined with daratumab (SDd) were 69%, and the median PFS was 12.5 months.In addition, studies have begun to evaluate the efficacy of Selinexor in patients with MM who have progressed rapidly after autologous hematopoietic stem cell transplantation pretreatment[26] and CAR-T[27] treatments.Selinexor provides new options for the treatment of MM patients.

4.2 Non-Hodgkin Lymphoma

In animal models of non-Hodgkin lymphoma, Selinexor in combination with dexamethasone or enrollment reduces caspase-3 and XPO1 expression[28].In addition, Selinexor has been proven to overcome vibration resistance in mantle cell lymphoma[7].XPO1 inhibitors combined with bcl-2 inhibitors have also been proven to exhibit synergistic antitumor activity in mouse xenograft models of diffuse large B cells[29].

Phase I clinical trials of Selinexor iontotherapy for relapse and refractory diffuse large B-cell lymphoma (RRDLBCL) showed ORR of 32 percent (CR10 percent, PR22 percent) and five patients with double-hit lymphoma (CR20 percent, PR40 percent)[30].A phase II clinical study (SADAL)[31] evaluated Selinexor iontotherapy in patients with RRDLBCL who had previously received 2nd line therapy with an ORR of 29%, of which CR was 13%, and a disease control rate of 37%; Of the 39 patients who received CR or PR, 38%had a duration of response (DOR) of more than 6 months, and 15%had a DOR of more than 12 months.This study shows that Selinexor has a significant efficacy in patients with RRDLBCL who have come to least 2 or more multidrug combination regimens and are not candidates for autologous hematopoietic stem cell transplantation.

Another phase I clinical study[32] evaluating Selinexor in combination with R-CHOP for first-line treatment of non-Hodgkin’s lymphoma (NHL) enrolled a total of 12 newly diagnosed NHL patients, including 10 with DLBCL.The results showed that the ORR was 100% and the CR was 90%, and the efficacy was significant.Therefore, the new oral, non-cytotoxic drug Selinexor is supposed to be a novel treatment option for such RRDLBCL patients.The TOUCH study[33] evaluated the efficacy and safety of Selinexor in combination with cimetidine and oxalacetate (GemOx)regimens in R/R PTCL/NKTL.As of June 10 2022, a total of 39 patients were included in the study, with an ORR of 48.6% and CR of 22.9% in 35 patients with beneficial efficacy, and good disease response was achieved in all subtypes.In general, the treatment plan of TOUCH study will have a few guiding significance in clinical practice at home and abroad.

4.3 Acute myeloid leukemia

Selinexor has a killing effect on leukemia stem/progenitor cells and is mildly toxic to normal hematopoietic stem cells[34].The combination of Selinexor and the FLT3 inhibitor serotonin has been found to show synergistic antidiuretic effects in human FLT3-mutated xenograft models[35, 36], and other preclinical studies[37,38] have also reported synergistic effects of Selinexor and type II inhibitors (imbibition, ethosuximide, and mitoxantrone) or Bcl-2 inhibitors.

A Selinexor iontotherapy study[39] enrolled 95 patients with relapsed and refractory acute misogynous leukemia (AML), with an ORR of 14% in 81 evaluate patients and a 50% reduction in blasts in bone marrow in 31%.Median PFS (5.1 versus 1.3 months) and OS (9.7 versus 2.7 months) were much improved compared with non-responders.Combination therapy clinical trials have focused on older patients with limited treatment options, with a phase Ib clinical trial[40] enrolling patients with treatment-na?Ve AML with poor prognosis (n=21, median age 65 years), and achieving CR in 53%of patients treated with Selinexor plus daunorubicin and cytarabine.In a phase 1 study of 25 AML patients aged ＞ 60 years[41], the ORR of patients treated with selenium in combination with digitalin were 40 percent.Another Phase 1b study[42] enrolled 20 patients with treatment-na?Ve or relapsed refractory AML with an ORR of 70%, a CR of 50%, a 1-year OS of 69%, and a PFS of 68% after treatment with Selinexor combined with high-dose cytarabine and mitoxantrone.Other studies are evaluating the efficacy of Selinexor in combination with clonidine, cytarabine and Filgrastim in AML resulted in 18 out of 40 patients achieving CR, median DOR of 9.1 months, median PFS and OS of 6.1 months and 7.8 months,respectively.It can be seen that Selinexor have a good effect in combination with AML traditional treatment regimen.

4.4 Chronic lymphocytic leukemia

In chronic lymphocytic leukemia (CLL), most XPO1 mutations(79-100%) are associated with IGHV-free states, and in addition to the regulatory mechanisms of TSPs (TP53, IκB, and FOXOa),Selinexor is able to block the BCR downstream signaling pathway and inhibit the CXCL12-mediated survival signaling pathway in vitro [43].In addition, Selinexor can inhibit the proliferation of IGHV-unmutated slow geomorphology and overcome brutified resistance caused by BTK C481S mutation, and has shown good antitumor efficacy in Eμ-TCL1-tumor-bearing mouse models, either alone or in combination with vibration[44].

In a phase I study of patients with relapsed refractory CLL who had previously received ibrutinib, patients with a combination of selinexor and ibrutinib had an ORR of 43 percent, a CR of 6 percent, a PR of 31 percent, and a median PFS of 8.9 months, with two patients with BTK mutations benefiting significantly from treatment[45].Another study [46] evaluating the efficacy and safety of Selinexor in combination with ibrutinib in patients with CLL(n=16) and NHL (n=18) showed that 47% of all enrolled patients achieved stable disease (SD) with an ORR of 32%.The median PFS for patients with CLL and NHL was 8.9 months and 2.7 months,respectively.The 2-year OS of CLL and NHL patients was 73.7%and 27.8%, respectively.The combination regimen of Selinexor and ibrutinib has shown good efficacy in patients with high-risk CLL and NHL with multi-line therapy, and the patients are well tolerated.

4.5 Myelofibrosis

A study of myelofibrosis (MF)[47] was designed to evaluate the efficacy of Selinexor in adult patients with MF (n=12) who were ineffective or intolerant to JAK inhibitor therapy, with the primary endpoint of the effect of Selinexor on spleen volume (SVR).The assessable patients enrolled, 9 received Selinexor for 24 weeks,with 5 patients having a reduced SVR 25% and 3 patients having a reduced SVR 35%.The 2-year OS is 91.7%.In summary, Selinexor showed good iontotherapy activity, vulnerability, and maintained spleen response in patients with refractory MF treated with JAK inhibitors.

Data from another trial[48] showed that combination therapy consisting of selinexor and resolution induced a rapid splenic response at week 12 in patients with treatment-na?ve MF, with a reduction in SVR of at least 35% and a median SVR reduction of 45% in 75% of evaluate patients after combination therapy at week 12; In 92% of valuable patients, SVR was reduced by ≥35% after at least 24 weeks of combination therapy, and the median SVR reduction was 49%.No dose-limiting toxicity was observed in the treatment group throughout the treatment period.

4.6 Myelodysplastic Syndrome

A study[49] explored the role of Selinexor in combination with azacitidine on Myelodysplastic Syndromes (MDS) cell lines (SKM-1 and MUTZ-1).The results showed that Selinexor in combination with azacitidine sympathetically inhibited MDS cell proliferation and blocked the cell cycle at the G2/M phase.In addition, it promotes apoptosis in MDS cells and increases the accumulation of p53 in the nucleus, so that p53 is activated and functions as a tumor suppressor protein.It can be observed that the combination of Selinexor and azacitidine may be a promising treatment in the field of MDS.

The main treatments for high-risk MDS include allogeneic hematopoietic stem cell transplantation and depreciating drugs(HMAs), and patients who fail HMA therapy currently lack effective treatment regimens and are under a survival time of only 5-6 months.In a study of Selinexor in the treatment of HMA-refractory high-risk MDS or AML[50], ORR was 26% of 23 evaluate patients,and SD was achieved in 52% of patients.The median duration of response was 6.3 months and median OS was 8.7 months.Subgroup analysis showed that patients who achieved complete bone marrow remission (mCR) or SD had a more significant improvement in survival reported to those in the inactive group, with OS at 9.6 and 7.9 months, respectively.The results confirm that Selinexor is useful in the treatment of HMA-refractory MDS and AML.

Another study is placed on the exploration of the second-generation SINE compound Eltanexor in the field of MDS.Compared to Selinexor, Eltanexor is better tolerated due to its lower bloodbrain barrier penetration and in wider treatment window.A phase I/II clinical study[51] to evaluate single-agent Eltanexor in patients with high-risk MDS enrolled 20 patients with mCR and 5 of the 15 evaluate patients achieving mCR and 5 achieving SD, with a total disease control rate of 80%.Four of the valuable patients achieved hematologic improvement with a median OS of 10.58 months.Survival analysis showed that the median OS (11.86 months) of 7 patients with mCR was significantly better than that of patients without mCR (8.67 months).The data of this study show that singleagent XPO1 inhibitors show superior efficacy in patients with high-risk HMA-resistant MDS, and other related studies of XPO1 inhibitors alone or in combination in MDS patients are ongoing.

5.Common adverse events and management of Selinexor in clinical applications

Nausea and vomiting are the most common numismatology adverse effects of Selinexor, and grade 1 to 2 does not require adjustment,Grade 3 withdrawals are used, and 5-HT3 receptor antagonists and clozapine can be used for supportive care[24].Fatigue and fatigue are also common adverse effects of Selinexor, and a stimulant such as oral methylphenidate may be regarded as correct fatigue[52].Megesterol acetate may be taken orally in patients with anorexia and severe weight loss [53].Hyponatremia is among the adverse effects in the treatment of Selinexor.The vast majority of these clinical symptoms are mild, requiring no dose adjustment in patients with grade 1 to 2 hyponatremia, and patients with grade 3 hyponatremia require withdrawal until improvement in grade 1 or baseline [19].Thrombocytopenia and anemia are major hematologic adverse effects of Selinexor and can be treated with dose adjustment and thrombopoietins [21].Grade 1 to 2 neutropenia does not require adjustment.Grade 3 without fever can be adjusted, and grade 4 or febrile neutropenia should be withheld and a whitening agent such as G-CSF should be withheld [53].

In conclusion, XPO1 plays a major role in the nuclear export of various proteins and mRNA.In tumor cells, XPO1 is overexpressed and mediated by increasing nuclear output.As a new targeted drug,XPO1 inhibitor has shown good anti-tumor activity in a variety of hematological malignancies, and has broad development prospects,which will bring new treatment options and survival benefits to patients with hematologic malignancy.

Authors’ contribution

Gao Yaya’s topic selection, article conception and thesis writing;Li Hong gave the revised opinion; Gao Guangxun Guides topic selection and article writing, and provides project fund support.

All authors declare that there is not any conflict of interest.