Correlation of differentiation-inducing activity of retinoids on human leukemia cell lines HL-60 and NB4

The Promise of Retinoids in the Treatment of Cancer: Neither Burnt Out Nor Fading Away

Since the introduction of all-trans retinoic acid (ATRA), acute promyelocytic leukemia (APL) has become a highly curable malignancy, especially in combination with arsenic trioxide (ATO). ATRA's success has deepened our understanding of the role of the RARα pathway in normal hematopoiesis and leukemogenesis, and it has influenced a generation of cancer drug development. Retinoids have also demonstrated some efficacy in a handful of other disease entities, including as a maintenance therapy for neuroblastoma and in the treatment of cutaneous T-cell lymphomas; nevertheless, the promise of retinoids as a differentiating therapy in acute myeloid leukemia (AML) more broadly, and as a cancer preventative, have largely gone unfulfilled. Recent research into the mechanisms of ATRA resistance and the biomarkers of RARα pathway dysregulation in AML have reinvigorated efforts to successfully deploy retinoid therapy in a broader subset of myeloid malignancies. Recent studies have demonstrated that the bone marrow environment is highly protected from exogenous ATRA via local homeostasis controlled by stromal cells expressing CYP26, a key enzyme responsible for ATRA inactivation. Synthetic CYP26-resistant retinoids such as tamibarotene bypass this stromal protection and have shown superior anti-leukemic effects. Furthermore, recent super-enhancer (SE) analysis has identified a novel AML subgroup characterized by high expression of RARα through strong SE levels in the gene locus and increased sensitivity to tamibarotene. Combined with a hypomethylating agent, synthetic retinoids have shown synergistic anti-leukemic effects in non-APL AML preclinical models and are now being studied in phase II and III clinical trials.

Treatment for relapsed acute promyelocytic leukemia

The advent of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) has significantly improved the outcomes of acute promyelocytic leukemia (APL); nevertheless, a small fraction of patients still experience relapse. Due to the infrequency of APL relapse coupled with the rapid change in the therapeutic landscape, there are limited available data regarding the treatment of relapsed APL. In this situation, however, ATO-based therapy has been shown to result in high rates of hematological and molecular complete remission (CR). Autologous hematopoietic cell transplantation (HCT) is considered the postremission therapy of choice when patients achieve molecular CR, whereas recent studies have suggested that molecular CR is not prerequisite for the success of autologous HCT. Allogeneic HCT can be reserved for selected patients, i.e., those who cannot achieve CR and those who relapse after autologous HCT, because of high toxicities and the expectation of highly favorable outcomes with autologous HCT during CR. For patients who are ineligible for HCT, prolonged administration of ATRA + ATO would be a viable option. To further refine the therapy for patients with relapsed APL, it is imperative to aggregate clinical data of patients who relapse after the ATRA + ATO frontline therapy within the framework of national and international collaboration.

RARγ activation sensitizes human myeloma cells to carfilzomib treatment through the OAS-RNase L innate immune pathway

Proteasome inhibitors (PIs) such as bortezomib (Btz) and carfilzomib (Cfz) are highly efficacious for patients with multiple myeloma (MM). However, relapses are frequent, and acquired resistance to PI treatment emerges in most patients. Here, we performed a high-throughput screen of 1855 Food and Drug Administration (FDA)-approved drugs and identified all-trans retinoic acid (ATRA), which alone has no antimyeloma effect, as a potent drug that enhanced MM sensitivity to Cfz-induced cytotoxicity and resensitized Cfz-resistant MM cells to Cfz in vitro. ATRA activated retinoic acid receptor (RAR)γ and interferon-β response pathway, leading to upregulated expression of IRF1. IRF1 in turn initiated the transcription of OAS1, which synthesized 2-5A upon binding to double-stranded RNA (dsRNA) induced by Cfz and resulted in cellular RNA degradation by RNase L and cell death. Similar to ATRA, BMS961, a selective RARγ agonist, could also (re)sensitize MM cells to Cfz in vitro, and both ATRA and BMS961 significantly enhanced the therapeutic effects of Cfz in established MM in vivo. In support of these findings, analyses of large datasets of patients' gene profiling showed a strong and positive correlation between RARγ and OAS1 expression and patient's response to PI treatment. Thus, this study highlights the potential for RARγ agonists to sensitize and overcome MM resistance to Cfz treatment in patients.

A Phase 1 Study of IRX195183, a RARα-Selective CYP26 Resistant Retinoid, in Patients With Relapsed or Refractory AML

Subsets of non-acute promyelocytic leukemia (APL) acute myelogenous leukemia (AML) exhibit aberrant retinoid signaling and demonstrate sensitivity to retinoids in vitro. We present the results of a phase 1 dose-escalation study that evaluated the safety, pharmacodynamics, and efficacy of IRX195183, a novel retinoic acid receptor α agonist, in patients with relapsed or refractory myelodysplastic syndrome (MDS) or AML. In this single center, single arm study, eleven patients with relapsed or refractory MDS/AML were enrolled and treated. Oral IRX195183 was administered at two dose levels: 50 mg daily or 75 mg daily for a total of two 28-day cycles. Patients with stable disease or better were allowed to continue on the drug for four additional 28-day cycles. Common adverse events included hypertriglyceridemia, fatigue, dyspnea, and edema. Three patients at the first dose level developed asymptomatic Grade 3 hypertriglyceridemia. The maximally tolerated dose was not reached. Four of the eleven patients had (36%) stable disease or better. One had a morphological complete remission with incomplete hematologic recovery while on the study drug. Two patients had evidence of in vivo leukemic blast maturation, as reflected by increased CD38 expression. In a pharmacodynamics study, plasma samples from four patients treated at the lowest dose level demonstrated the capacity to differentiate leukemic cells from the NB4 cell line in vitro. These results suggest that IRX195183 is safe, achieves biologically meaningful plasma concentrations and may be efficacious in a subset of patients with MDS/AML. Clinical Trial Registration: clinicaltrials.gov, identifier NCT02749708.

Impact of CD56 Continuously Recognizable as Prognostic Value of Acute Promyelocytic Leukemia: Results of Multivariate Analyses in the Japan Adult Leukemia Study Group (JALSG)-APL204 Study and a Review of the Literature

BACKGROUND

After long-term analysis of the JALSG-APL204 study we recently reported that maintenance therapy with tamibarotene was more effective than all-trans retinoic acid (ATRA) by reducing relapse in APL patients. Here, the clinical significance of other important prognostic factors was evaluated with multivariate analyses.

PATIENTS AND METHODS

Newly diagnosed acute promyelocytic leukemia (APL) patients were registered with the study. Induction was composed of ATRA and chemotherapy. Patients who achieved molecular remission after consolidation were randomly assigned to maintenance with tamibarotene or ATRA.

RESULTS

Of the 344 eligible patients, 319 (93%) achieved complete remission (CR). After completing consolidation, 269 patients underwent maintenance random assignment-135 to ATRA, and 134 to tamibarotene. By multivariate analysis, overexpression of CD56 in blast was an independent unfavorable prognostic factor for relapse-free survival (RFS) (p = 0.006) together with more than 10.0 × 10⁹/L WBC counts (p = 0.001) and the ATRA arm in maintenance (p = 0.028). Of all phenotypes, CD56 was related most clearly to an unfavorable prognosis. The CR rate, mortality rate during induction and overall survival of CD56⁺ APL were not significantly different compared with CD56^- APL. CD56 is continuously an independent unfavorable prognostic factor for RFS in APL patients treated with ATRA and chemotherapy followed by ATRA or tamibarotene maintenance therapy.

Strategies to generate functionally normal neutrophils to reduce infection and infection-related mortality in cancer chemotherapy

Neutrophils form an essential part of innate immunity against infection. Cancer chemotherapy-induced neutropenia (CCIN) is a condition in which the number of neutrophils in a patient's bloodstream is decreased, leading to increased susceptibility to infection. Granulocyte colony-stimulating factor (GCSF) has been the only approved treatment for CCIN over two decades. To date, CCIN-related infection and mortality remain a significant concern, as neutrophils generated in response to administered GCSF are functionally immature and cannot effectively fight infection. This review summarizes the molecular regulatory mechanisms of neutrophil granulocytic differentiation and innate immunity development, dissects the biology of GCSF in myeloid expansion, highlights the shortcomings of GCSF in CCIN treatment, updates the recent advance of a selective retinoid agonist that promotes neutrophil granulocytic differentiation, and evaluates the benefits of developing GCSF biosimilars to increase access to GCSF biologics versus seeking a new mode to fundamentally advance GCSF therapy for treatment of CCIN.

Tamibarotene maintenance improved relapse-free survival of acute promyelocytic leukemia: a final result of prospective, randomized, JALSG-APL204 study

Between April 2004 and December 2010, we conducted a prospective randomized controlled study comparing tamibarotene with all-trans retinoic acid (ATRA) in the maintenance therapy of newly diagnosed acute promyelocytic leukemia (APL), and here report the final results of this study with a median follow-up of 7.3 years. Of 344 eligible patients who had received ATRA and chemotherapy, 319 (93%) achieved complete remission (CR). After completion of three courses of consolidation chemotherapy, 269 patients in molecular remission underwent maintenance randomization, 135 to ATRA (45 mg/m² daily), and 134 to tamibarotene (6 mg/m² daily) for 14 days every 3 months for 2 years. The primary endpoint was relapse-free survival (RFS). The 7-year RFS was 84% in the ATRA arm and 93% in the tamibarotene arm (p = 0.027, HR = 0.44, 95% CI, 0.21 to 0.93). The difference was prominent in high-risk patients with initial leukocytes ≥ 10.0 × 10⁹/L (62% vs. 89%; p = 0.034). Tamibarotene was significantly superior to ATRA by decreasing relapse in high-risk patients. Overall survival after randomization did not differ (96% vs. 97%; p = 0.520). Secondary hematopoietic disorders developed in nine patients, secondary malignancies in 11, and grade 3 or more late cardiac comorbidities in three. These late complications did not differ between the two arms.

In vitro studies on the role of recombinant human soluble thrombomodulin in the context of retinoic acid mediated APL differentiation syndrome

Recombinant human soluble thrombomodulin (rTM) is a newly developed anti-coagulant approved for treatment of disseminated intravascular coagulation (DIC) in Japan. rTM exerts anti-inflammatory and cytoprotective functions via its lectin-like and epidermal growth factor-like domains, respectively. In this study, we retrospectively reviewed the treatment of 21 consecutive patients with coagulopathy, complicated by acute promyelocytic leukemia (APL), with all-trans retinoic acid (ATRA) with or without combination with rTM. Surprisingly, none of the 14 rTM-treated patients developed retinoic acid (RA)-related differentiation syndrome (DS). The co-culture of vascular endothelial cell-derived EA.hy926 and APL-derived NB4 cells in the presence of RA increased production of tumor necrosis factor alpha (TNF-α) in culture media, in parallel with activation of p38 mitogen-activated protein kinase and increased levels of intracellular adhesion molecule 1 (ICAM1) in EA.hy926 cells. This was also associated with increased levels of the phosphorylated forms of VE-cadherin and enhanced vascular permeability of EA.hy926 monolayers. Importantly, addition of rTM to this co-culture system inhibited the RA-induced phosphorylation of p38 and VE-cadherin and decreased ICAM1 and vascular permeability in EA.hy926 cells, without a decrease inthe levels of TNF-α. Taken together, use of rTM may be a promising treatment strategy to prevent DS in APL patients who receive ATRA.

Reprogramming acute myeloid leukemia into sensitivity for retinoic-acid-driven differentiation

The success of all-trans retinoic acid (ATRA) therapy for acute promyelocytic leukemia (APL) provides a rationale for using retinoic acid (RA)-based therapy for other subtypes of acute myeloid leukemia (AML). Recently, several studies showed that ATRA may drive leukemic cells efficiently into differentiation and/or apoptosis in a subset of AML patients with an NPM1 mutation, a FLT3-ITD, an IDH1 mutation, and patients overexpressing EVI-1. Because not all patients within these molecular subgroups respond to ATRA and clinical trials that tested ATRA response in non-APL AML patients have had disappointing results, the identification of additional biomarkers may help to identify patients who strongly respond to ATRA-based therapy. Searching for response biomarkers might also reveal novel RA-based combination therapies with an efficient differentiation/apoptosis-inducing effect in non-APL AML patients. Preliminary studies suggest that the epigenetic or transcriptional state of leukemia cells determines their susceptibility to ATRA. We hypothesize that reprogramming by inhibitors of epigenetic-modifying enzymes or by modulation of microRNA expression might sensitize non-APL AML cells for RA-based therapy. AML relapse is caused by a subpopulation of leukemia cells, named leukemic stem cells (LSCs), which are in a different epigenetic state than the total bulk of the AML. The survival of LSCs after therapy is the main cause of the poor prognosis of AML patients, and novel differentiation therapies should drive these LSCs into maturity. In this review, we summarize the current knowledge on the epigenetic aspects of susceptibility to RA-induced differentiation in APL and non-APL AML.

Down-regulation of histone deacetylase 4, -5 and -6 as a mechanism of synergistic enhancement of apoptosis in human lung cancer cells treated with the combination of a synthetic retinoid, Am80 and green tea catechin

(-)-Epigallocatechin gallate (EGCG), a green tea catechin, acts as a synergist with various anticancer drugs, including retinoids. Am80 is a synthetic retinoid with a different structure from all-trans-retinoic acid: Am80 is now clinically utilized as a new drug for relapsed and intractable acute promyelocytic leukemia patients. Our experiments showed that the combination of EGCG and Am80 synergistically induced both apoptosis in human lung cancer cell line PC-9 and up-regulated expressions of growth arrest and DNA damage-inducible gene 153 (GADD153), death receptor 5, and p21^waf1 genes in the cells. To understand the mechanisms of synergistic anticancer activity of the combination, we gave special attention to the lysine acetylation of proteins. Proteomic analysis using nanoLC-ESI-MS/MS revealed that PC-9 cells treated with the combination contained 331 acetylated proteins, while nontreated cells contained 553 acetylated proteins, and 59 acetylated proteins were found in both groups. Among them, the combination increased acetylated-p53 and acetylated-α-tubulin through reduction of histone deacetylase (HDAC) activity in cytosol fraction, although the levels of acetylation in histones H3 or H4 did not change, and the combination reduced protein levels of HDAC4, -5 and -6 by 20% to 80%. Moreover, we found that a specific inhibitor of HDAC4 and -5 strongly induced p21^waf1 gene expression, and that of HDAC6 induced both GADD153 and p21^waf1 gene expression, which resulted in apoptosis. All results demonstrate that EGCG in combination with Am80 changes levels of acetylation in nonhistone proteins via down-regulation of HDAC4, -5 and -6 and stimulates apoptotic induction.

Current first- and second-line treatment options in acute promyelocytic leukemia

Outcome of acute promyelocytic leukemia (APL) has remarkably improved during the last 30 years, especially after the identification of PML-RARA oncogene as a key in the pathogenesis of APL and all-trans retinoic acid as therapeutic agent. Arsenic trioxide has been recently demonstrated to be the most effective single antileukemic agent and it has also showed synergistic action when combined with all-trans retinoic acid, decreasing relapse rate especially in low/intermediate-risk settings. Therapeutic advances led to complete remission rates of more than 90%, modifying disease history. In relapse setting, arsenic trioxide-based regimens showed efficacy for the achievement of second molecular complete remission. The most challenging issue in APL management remains the significant early deaths rate, nowadays the principal reason for treatment failure.

Design, synthesis, and biological characterization of tamibarotene analogs as anticancer agents

In our efforts of developing novel compounds as potential anticancer agents, a series of tamibarotene analogs containing Zn(2+) -binding moieties were designed and developed. Biological characterization identified compound 7b as the most potent one with improved antiproliferative activities against multiple cancer cell lines, compared to parent compound tamibarotene. Further characterization also demonstrated that compound 7b exhibited moderate activities as a histone deacetylase inhibitor with IC50 of 1.8 ± 0.1 μm, thus suggesting that this could contribute to the improved antiproliferative activities of 7b. Pharmacokinetic studies revealed that compound 7b could release tamibarotene after administration and prolong the circulation time of tamibarotene, and this may also potentially contribute to the improved antiproliferative activities. Collectively, the results demonstrated that compound 7b could serve as a new lead for further development of more potent analogs as potential anticancer agents.

The Effect of a Retinoic Acid Derivative on Cell-Growth Inhibition in a Pulmonary Carcinoma Cell Line

Pulmonary carcinoma is a major cause of cancer-related death worldwide. Because the prognosis remains poor, the development of novel therapeutic approaches is highly desirable. In this study, we investigated the effect of Tamibarotene (Am80), a retinoic acid derivative, on the growth of human lung adenocarcinoma cell line A549. Our ultimate goal in this study is to provide pulmonary carcinoma therapy with a new approach. First, we treated A549 cells with Am80 to clarify the effect of cell-growth inhibition. Am80 significantly reduced the viability of A549 cells in a dose- and time-dependent manner. The IC50 value, which was determined using CellTiter-Glo Luminescent Cell Viability assay, of Am80 and all-trans retinoic acid (ATRA) against A549 cells at 6 d was 49.1±8.1 µM and 92.3±8.0 µM, respectively. Furthermore, Am80 reduced the anchorage-independent cell-growth ability of A549 cells. However, it was not an apoptosis-mediated mechanism. These results suggest that Am80 can be used as an effective, novel cell-growth inhibitor in lung adenocarcinoma.

Refractory acute promyelocytic leukemia successfully treated with combination therapy of arsenic trioxide and tamibarotene: A case report

A 40-year-old male developed refractory acute promyelocytic leukemia (APL) after various treatments including all-trans retinoic acid, tamibarotene, arsenic trioxide (As₂O₃), conventional chemotherapy, and autologous peripheral blood stem cell transplantation. We attempted to use both tamibarotene and As₂O₃ as a combination therapy, and he achieved molecular complete remission. Grade 2 prolongation of the QTc interval on the electrocardiogram was observed during the therapy. The combination therapy of As₂O₃ and tamibarotene may be effective and tolerable for treating refractory APL cases who have no treatment options, even when they have previously been treated with tamibarotene and As₂O₃as a single agent.

Tamibarotene in patients with acute promyelocytic leukaemia relapsing after treatment with all-trans retinoic acid and arsenic trioxide

Treatment of acute promyelocytic leukaemia (APL) with arsenic trioxide (ATO) and all-trans retinoic acid (ATRA) is highly effective first-line therapy, although approximately 5-10% of patients relapse. Tamibarotene is a synthetic retinoid with activity in APL patients who relapse after chemotherapy and ATRA, but has not been studied in relapse after treatment with ATO and ATRA. We report on a phase II study of tamibarotene in adult patients with relapsed or refractory APL after treatment with ATRA and ATO (n = 14). Participants were treated with tamibarotene (6 mg/m(2) /d) during induction and for up to six cycles of consolidation. The overall response rate was 64% (n = 9), the rate of complete cytogenetic response was 43% (n = 6) and the rate of complete molecular response was 21% (n = 3). Relapse was frequent with 7 of 9 responders relapsing after a median of 4·6 months (range 1·6-26·8 months). The median event-free survival (EFS) was 3·5 months [95% confidence interval (CI) 0-8·6 months] and the median overall survival (OS) was 9·5 months (95% CI 5·9-13·1 months). These results demonstrate that tamibarotene has activity in relapsed APL after treatment with ATO and ATRA and further studies using tamibarotene as initial therapy and in combination with ATO are warranted.

Acute promyelocytic leukemia: where did we start, where are we now, and the future

Historically, acute promyelocytic leukemia (APL) was considered to be one of the most fatal forms of acute leukemia with poor outcomes before the introduction of the vitamin A derivative all-trans retinoic acid (ATRA). With considerable advances in therapy, including the introduction of ATRA initially as a single agent and then in combination with anthracyclines, and more recently by development of arsenic trioxide (ATO)-containing regimens, APL is now characterized by complete remission rates of 90% and cure rates of ∼80%, even higher among low-risk patients. Furthermore, with ATRA-ATO combinations, chemotherapy may safely be omitted in low-risk patients. The disease is now considered to be the most curable subtype of acute myeloid leukemia (AML) in adults. Nevertheless, APL remains associated with a significant incidence of early death related to the characteristic bleeding diathesis. Early death, rather than resistant disease so common in all other subtypes of AML, has emerged as the major cause of treatment failure.

Tamibarotene As Maintenance Therapy for Acute Promyelocytic Leukemia: Results From a Randomized Controlled Trial

Purpose

The introduction of all-trans-retinoic acid (ATRA) has significantly improved outcomes for acute promyelocytic leukemia (APL), although a subset of patients still suffer relapse. The purpose of this study was to evaluate the role of maintenance therapy with the synthetic retinoid tamibarotene in APL.

Patients and Methods

Patients with newly diagnosed APL in molecular remission at the end of consolidation therapy were randomly assigned to receive ATRA or tamibarotene, both orally, for 14 days every 3 months for up to 2 years.

Results

A total of 347 patients were enrolled. Of the 344 eligible patients, 319 (93%) achieved complete remission. After completing three courses of consolidation therapy, 269 patients underwent maintenance random assignment. The relapse-free survival (RFS) rate at 4 years was 84% for the ATRA arm and 91% for the tamibarotene arm (hazard ratio [HR], 0.54; 95% CI, 0.26 to 1.13). When the analysis was restricted to 52 high-risk patients with an initial WBC count ≥ 10.0 × 109/L, the intergroup difference was statistically significant, with 4-year RFS rates of 58% for the ATRA arm and 87% for the tamibarotene arm (HR, 0.26; 95% CI, 0.07 to 0.95). For patients with non–high-risk disease, the HR was 0.82 (95% CI, 0.32 to 2.01). The test for interaction between treatment effects and these subgroups resulted in P = .075. Both treatments were generally well tolerated.

Conclusion

In this trial, no difference was detected between ATRA and tamibarotene for maintenance therapy. In an exploratory analysis, there was a suggestion of improved efficacy of tamibarotene in high-risk patients, but this requires further study.

Retinoid agonist Am80-enhanced neutrophil bactericidal activity arising from granulopoiesis in vitro and in a neutropenic mouse model

Despite advances in the therapeutic use of recombinant granulocyte colony-stimulating factor (G-CSF) to promote granulopoiesis of human hematopoietic stem cells (HSCs), neutropenia remains one of the most serious complications of cancer chemotherapy. We discovered that retinoid agonist Am80 (tamibarotene) is more potent than G-CSF in coordinating neutrophil differentiation and immunity development. Am80-induced neutrophils (AINs) either in vitro or in neutropenic mouse model displayed strong bactericidal activities, similar to those of human peripheral blood neutrophils (PBNs) or mouse peripheral blood neutrophils (MPBNs) but markedly greater than did G-CSF–induced neutrophils (GINs). In contrast to GINs but similar to PBNs, the enhanced bacterial killing by AINs accompanied both better granule maturation and greater coexpression of CD66 antigen with the integrin β2 subunit CD18. Consistently, anti-CD18 antibody neutralized Am80-induced bactericidal activities of AINs. These studies demonstrate that Am80 is more effective than G-CSF in promoting neutrophil differentiation and bactericidal activities, probably through coordinating the functional interaction of CD66 with CD18 to enhance the development of neutrophil immunity during granulopoiesis. Our findings herein suggest a molecular rationale for developing new therapy against neutropenia using Am80 as a cost-effective treatment option.

Am80 inhibits stromal cell-derived factor-1-induced chemotaxis in T-cell acute lymphoblastic leukemia cells

C-X-C motif chemokine receptor 4 (CXCR4) and stromal cell-derived factor-1 (SDF-1) play a potent role in metastasis and infiltration of many types of tumors, including T-cell acute lymphoblastic leukemia (T-ALL), into the central nervous system or lymph nodes. Although higher levels of CXCR4 expression have been shown to correlate with shorter survival of patients, effective drugs affecting cell surface CXCR4 expression are still unknown. In the present study, we examined the effects of a synthetic retinoid Am80 on CXCR4 expression of cultured T-ALL cells, such as Jurkat. Am80 inhibited surface CXCR4 expression and SDF-1-induced chemotaxis by the acceleration of CXCR4 internalization via activation of conventional PKC. Am80 may be an effective drug to inhibit the extramedullary infiltration of T-ALL cells.

Anti-adult T-cell leukemia effects of a novel synthetic retinoid, Am80 (Tamibarotene)

Clinical trials for treatment of adult T-cell leukemia (ATL) caused by human T-cell leukemia virus type I (HTLV-I) using all-trans-retinoic acid (ATRA) have shown satisfactory therapeutic responses, although efficacies were limited. Recently, many synthetic retinoids have been developed and among them, a novel synthetic retinoid, Am80 (Tamibarotene) is an RARalpha- and RARbeta-specific retinoid expected to overcome ATRA resistance. The present study examined the inhibitory effects of Am80 on HTLV-I-infected T-cell lines and ATL cells. Am80 had negligible growth inhibition of peripheral blood mononuclear cells but marked growth inhibition of both HTLV-I-infected T-cell lines and ATL cells. Am80 arrested cells in the G1 phase of the cell cycle and induced apoptosis in HTLV-I-infected T-cell lines. It inhibited also the phosphorylation of IkappaBalpha and NF-kappaB-DNA binding, in conjunction with reduction of expression of proteins involved in the G1/S cell cycle transition and apoptosis. Am80 also inhibited the expression of JunD, resulting in suppression of AP-1-DNA binding. Furthermore, severe combined immunodeficient mice with tumors induced by subcutaneous inoculation of HTLV-I-infected T cells, responded to Am80 treatment with partial regression of tumors and no side-effects. These findings demonstrate that Am80 is a potential inhibitor of NF-kappaB and AP-1, and is a potentially useful therapeutic agent against ATL.

PML-RARalpha inhibitors (ATRA, tamibaroten, arsenic troxide) for acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is characterized by generation of the PML-RARalpha fusion gene. PML-RARalpha can homodimerize with another PML-RARalpha, and the hybrid binds the histone-deacetylase recruiting co-repressor complex with higher affinity than the wild-type RARalpha. However, the co-repressor complex is releasable by pharmacological doses of all-trans retinoic acid (ATRA). More than 90% of patients with APL achieve a complete remission (CR) with differentiation therapy consisting of ATRA combined with chemotherapy. A new synthetic retinoid, tamibaroten, showed therapeutic effectiveness in patients with ATRA-resistant APL with increased expression of cellular retinoic acid binding protein (CRABP), and about 60% of patients with relapsed APL achieved a CR. Arsenic trioxide triggers the rapid degradation of PML-RARalpha through the targeting of the PML moieties of the fusion protein and showed a high CR rate in relapsed APL. The combination of ATRA, chemotherapy, and/or new agents improved the long-term survival in patients with APL.

Treatment of acute promyelocytic leukemia: strategy toward further increase of cure rate

Acute promyelocytic leukemia (APL) has become a curable disease by all-trans retinoic acid (ATRA)-based induction therapy followed by two or three courses of consolidation chemotherapy. Currently around 90% of newly diagnosed patients with APL achieve complete remission (CR) and over 70% of patients are curable. To further increase the CR and cure rates, detection and diagnosis of this disease at its early stage is very important, hopefully before the appearance of APL-associated coagulopathy. In induction therapy, concomitant chemotherapy is indispensable, except for patients with low initial leukocyte counts. Prophylactic use of intrathecal methotrexate and cytarabine should be done, particularly for patients with hyperleukocytosis. If patients relapse hematologically or even molecularly, arsenic trioxide will be the treatment of choice under careful electrocardiogram monitoring. Am80, liposomal ATRA, gemtuzumab ozogamicin or ATRA in combination with cytotoxic drugs may be used at this stage or later. Allogeneic SCT will be the treatment of choice after patients of age <50 years have relapsed, provided that they have HLA-identical family donors or DNA-identical unrelated donors.

Role of P-glycoprotein in all-trans retinoic acid (ATRA) resistance in acute promyelocytic leukaemia cells: analysis of intracellular concentration of ATRA

We analysed the relationship between all-trans retinoic acid (ATRA) resistance and P-glycoprotein (P-gp)-associated multidrug resistance (MDR) in acute promyelocytic leukaemia (APL). There was no difference in the intracellular ATRA accumulation between NB4 cells and an MDR1 cDNA-transduced NB4 subline and between ATRA-resistant NB4 cells (NB4/RA) and an MDR1 cDNA-transduced NB4/RA subline. PSC833, a MDR modifier, did not increase the intracellular accumulation of ATRA or affect the expression of CD11b, the nitroblue tetrazolium (NBT) reduction activity, the proportion of apoptotic cells or the morphology of these four ATRA-treated cell lines. Similar results were obtained in the analysis of APL cells from five patients relapsed after ATRA-induced complete remission.

All-trans retinoic acid (ATRA) differentiates acute promyelocytic leukemia cells independently of P-glycoprotein (P-gp) related multidrug resistance

Here the relationship between all-trans retinoic acid (ATRA)-resistance and P-glycoprotein (P-gp)-associated multidrug resistance (MDR) is discussed in acute promyelocytic leukemia (APL). First, the remission rates of ATRA therapy are similar in relapsed/refractory APL to the preceding chemotherapy given and in newly diagnosed APL. Second, MDR1 cDNA-transduced NB4 (NB4/MDR) cells accumulate less Rhodamine-123 (Rh123) than NB4 cells, but there is no difference in the intracellular ATRA concentration between them. PSC833 or MS209. MDR modifiers, increases the intracellular accumulation of Rh123 in NB4/MDR and APL cells expressing P-gp, but not of ATRA. Third, the expression of CD11b, the NBT reduction activity, the proportion of apoptotic cells and the morphology are not different between NB4/MDR and NB4 cells, and between APL cells expressing P-gp and not. APL cells express little P-gp, and mainly express CD33 but no CD34. Despite previous reports that ATRA-resistant APL cells express more P-gp than ATRA-sensitive ones, P-gp and ATRA-resistance seems to exist independently.

Involvement of insulin-like growth factor binding protein-3 in the retinoic acid receptor-alpha-mediated inhibition of hepatocellular carcinoma cell proliferation

We examined the relationship between the expression of retinoic acid receptor-alpha (RAR-alpha) and upregulation of insulin-like growth factor binding protein-3 (IGFBP-3) in the retinoid-induced inhibition of hepatocellular carcinoma (HCC) cell proliferation. HCC cell lines showed a marked expression of RAR-alpha, whereas the expression levels of RAR-beta and RAR-gamma were relatively lower. An RAR-alpha agonist significantly inhibited the HCC cell proliferation both in vitro and in vivo. The RAR-alpha expression closely related to the upregulation of IGFBP-3 as compared with RAR-beta or RAR-alpha expressions. RAR-alpha agonist would be beneficial to inhibit the growth of HCC.

Relapsed acute promyelocytic leukemia previously treated with all-trans retinoic acid: clinical experience with a new synthetic retinoid, Am-80

All-trans retinoic acid (ATRA), a potent differentiating drug for acute promyelocytic leukemia (APL), induces a high incidence of complete remission (CR) in patients with APL and is now established as a first-line therapy. However, ATRA resistance has become a clinical problem. Patients who relapsed after ATRA-induced CR have had difficulty in obtaining a second CR with ATRA therapy. Although several mechanisms have been postulated, treatment strategies to overcome resistance have not been established. We used a new synthetic retinoid, Am-80, as reinduction therapy for APL relapse after from ATRA-induced CR. Am-80 was several times more potent than ATRA in inducing differentiation in vitro. At a 6 mg/m2 dose, there were 24 evaluable patients; 14 (58%) achieved CR between days 20 and 58 (median, 37 days). Clinical response correlated with the in vitro response to Am-80. Adverse effects included retinoic acid syndrome (n = 1), hyperleukocytosis (n = 1), xerosis (n = 9), cheilitis (n = 8), hypertriglyceridemia (n = 16), and hypercholesterolemia (n = 15). Am-80 is active in APL after relapse from ATRA-induced CR. Further clinical trials are needed to establish strategies to overcome ATRA resistance.

Induction of Differentiation in Acute Promyelocytic Leukemia Cells by 9-cis Retinoic Acid α-Tocopherol Ester (9-cisTretinoin Tocoferil)

Acute promyelocytic leukemia (APL) has a specific genetic rearrangement between the retinoic acid receptor (RAR)-α gene and the pml nuclear protein gene. All-trans retinoic acid (ATRA) induces granulocytic differentiation of APL-derived cells and is used to treat APL patients. However, ATRA interacts with normal cells with RAR throughout the entire body, and when used at high doses or over a long duration, it induces several adverse effects. The development of drugs that selectively act on APL cells may contribute to increasing the therapeutic efficacy of APL treatment as well as elucidating the mechanisms of response to ATRA. In this study, 9-cis retinoic acid α-tocopherol ester (9CTT) inhibited the proliferation of APL-derived NB4 and HT93 cells and induced differentiation markers, such as granulocytic maturation, nitroblue tetrazolium reduction, and CD11b expression, in these cells. The effects of 9CTT on non-APL cells, including HL-60 and U937 cells, were much weaker than those on APL cells, and tretinoin tocoferil (TT), which is an α-tocopherol ester of ATRA, did not induce the differentiation of APL cells as effectively as 9CTT. The differentiation-inducing effects of 9CTT were inhibited by RAR antagonists. 9CTT and TT similarly induced the transactivating activity of RARs, but were not effective on RXRs. 9CTT downregulated the expression of PML/RAR-α protein more effectively than TT, which suggests that it may be involved in the selectivity of 9CTT against APL cells. Interestingly, 9CTT enhanced the differentiation of APL cells induced by ATRA, 9-cis retinoic acid, and synthetic retinobenzoic acids. Combined with 1α,25-dihydroxyvitamin D3 (VD3), 9CTT also more than additively induced the differentiation of APL cells. Thus, 9CTT, alone or in combination with other retinoids or VD3, may be useful for the treatment of APL.

Induction of Differentiation in Acute Promyelocytic Leukemia Cells by 9-cis Retinoic Acid α-Tocopherol Ester (9-cisTretinoin Tocoferil)

Acute promyelocytic leukemia (APL) has a specific genetic rearrangement between the retinoic acid receptor (RAR)-α gene and the pml nuclear protein gene. All-trans retinoic acid (ATRA) induces granulocytic differentiation of APL-derived cells and is used to treat APL patients. However, ATRA interacts with normal cells with RAR throughout the entire body, and when used at high doses or over a long duration, it induces several adverse effects. The development of drugs that selectively act on APL cells may contribute to increasing the therapeutic efficacy of APL treatment as well as elucidating the mechanisms of response to ATRA. In this study, 9-cis retinoic acid α-tocopherol ester (9CTT) inhibited the proliferation of APL-derived NB4 and HT93 cells and induced differentiation markers, such as granulocytic maturation, nitroblue tetrazolium reduction, and CD11b expression, in these cells. The effects of 9CTT on non-APL cells, including HL-60 and U937 cells, were much weaker than those on APL cells, and tretinoin tocoferil (TT), which is an α-tocopherol ester of ATRA, did not induce the differentiation of APL cells as effectively as 9CTT. The differentiation-inducing effects of 9CTT were inhibited by RAR antagonists. 9CTT and TT similarly induced the transactivating activity of RARs, but were not effective on RXRs. 9CTT downregulated the expression of PML/RAR-α protein more effectively than TT, which suggests that it may be involved in the selectivity of 9CTT against APL cells. Interestingly, 9CTT enhanced the differentiation of APL cells induced by ATRA, 9-cis retinoic acid, and synthetic retinobenzoic acids. Combined with 1α,25-dihydroxyvitamin D3 (VD3), 9CTT also more than additively induced the differentiation of APL cells. Thus, 9CTT, alone or in combination with other retinoids or VD3, may be useful for the treatment of APL.

Treatment With a New Synthetic Retinoid, Am80, of Acute Promyelocytic Leukemia Relapsed From Complete Remission Induced by All-trans Retinoic Acid

Differentiation therapy with all-trans retinoic acid (ATRA) has marked a major advance and become the first choice drug in the treatment of acute promyelocytic leukemia (APL). However, patients who relapse from ATRA-induced complete remission (CR) have difficulty in obtaining a second CR with a second course of ATRA therapy alone. We tested the efficacy of a new synthetic retinoid, Am80, in APL that had relapsed from CR induced by ATRA in a prospective multicenter study. Am80 is approximately 10 times more potent than ATRA as an in vitro differentiation inducer, is more stable to light, heat, and oxidation than ATRA, has a low affinity for cellular retinoic acid binding protein, and does not bind to retinoic acid receptor-γ. Patients received Am80, 6 mg/m2, orally alone daily until CR. Of 24 evaluable patients, 14 (58%) achieved CR. The interval from the last ATRA therapy was not different between CR and failure cases. The clinical response was well correlated with the in vitro response to Am80 in patients examined. Adverse events included 1 retinoic acid syndrome, 1 hyperleukocytosis, 9 xerosis, 8 cheilitis, 16 hypertriglyceridemia, and 15 hypercholesterolemia, but generally milder than those of ATRA, which all patients had received previously. Am80 is effective in APL relapsed from ATRA-induced CR and deserves further trials, especially in combination with chemotherapy.

Treatment With a New Synthetic Retinoid, Am80, of Acute Promyelocytic Leukemia Relapsed From Complete Remission Induced by All-trans Retinoic Acid

Differentiation therapy with all-trans retinoic acid (ATRA) has marked a major advance and become the first choice drug in the treatment of acute promyelocytic leukemia (APL). However, patients who relapse from ATRA-induced complete remission (CR) have difficulty in obtaining a second CR with a second course of ATRA therapy alone. We tested the efficacy of a new synthetic retinoid, Am80, in APL that had relapsed from CR induced by ATRA in a prospective multicenter study. Am80 is approximately 10 times more potent than ATRA as an in vitro differentiation inducer, is more stable to light, heat, and oxidation than ATRA, has a low affinity for cellular retinoic acid binding protein, and does not bind to retinoic acid receptor-γ. Patients received Am80, 6 mg/m2, orally alone daily until CR. Of 24 evaluable patients, 14 (58%) achieved CR. The interval from the last ATRA therapy was not different between CR and failure cases. The clinical response was well correlated with the in vitro response to Am80 in patients examined. Adverse events included 1 retinoic acid syndrome, 1 hyperleukocytosis, 9 xerosis, 8 cheilitis, 16 hypertriglyceridemia, and 15 hypercholesterolemia, but generally milder than those of ATRA, which all patients had received previously. Am80 is effective in APL relapsed from ATRA-induced CR and deserves further trials, especially in combination with chemotherapy.