High-dose retinol in children with acute myelogenous leukemia in remission

Retinoic acid induces the degradation of the leukemogenic protein encoded by the promyelocytic leukemia gene fused to the retinoic acid receptor alpha gene

Acute promyelocytic leukemia (APL) cells carry a mutated gene that is the result of a translocation in which the retinoic acid receptor alpha (RAR alpha) gene is fused to the promyelocytic leukemia (PML) gene, coding for a fusion protein, PML/RAR alpha. Its presence is the single event that causes APL in transgenic mice. All-trans-retinoic acid (atRA) induces the proteolytic degradation of PML/RAR alpha by ubiquitination and proteolysis. RAR alpha itself is also degraded by atRA treatment, a process representing a possible feedback mechanism to turn off RAR alpha's stimulation of transcription.

Chylomicron assembly and catabolism: role of apolipoproteins and receptors

Chylomicrons are lipoproteins synthesized exclusively by the intestine to transport dietary fat and fat-soluble vitamins. Synthesis of apoB48, a translational product of the apob gene, is required for the assembly of chylomicrons. The apob gene transcription in the intestine results in 14 and 7 kb mRNAs. These mRNAs are post-transcriptionally edited creating a stop codon. The edited mRNAs chylomicrons from the shorter apoB48 peptide remains to be elucidated. In addition, the roles of proteins involved in the assembly pathway, e.g. apobec-1, MTP and apoA-IV, needs to be studied. Cloning of enzymes involved in the intestinal biosynthesis of triglycerides will be crucial to fully appreciate the assembly of chylomicrons. There is a need for cell culture and transgenic animal models that can be used for intestinal lipoprotein assembly. The catabolism of chylomicrons is far more complex and efficient than the catabolism of VLDL. Even though the major steps involved in the catabolism of chylomicrons are now known, the determinants for apolipoprotein exchange, processing of remnants in the space of Disse, as well as the mechanism of uptake of these particles by extra-hepatic tissue needs further exploration.

Uptake of retinoids by adipose tissue

Adipose tissue was found to contain considerable amounts of retinoids and retinol-binding protein mRNA, particularly in epididymal and perinephric depots. Delivery of retinoids appears to be through the hydrolysis of retinyl esters in postprandial chylomicrons by lipoprotein lipase, with subsequent uptake of retinol by adipocytes.

Synergistic activation of simian immunodeficiency virus and human immunodeficiency virus type 1 transcription by retinoic acid and phorbol ester through an NF-kappa B-independent mechanism

The activation of human immunodeficiency virus type 1 (HIV-1) expression in latently infected cells by exogenous agents is believed to be important in the progression of AIDS. Most factors that are known to activate HIV-1 gene expression increase the binding of NF-kappa B or NF-kappa B-like transcription factors to the HIV-1 core enhancer region. In this report, we demonstrate that retinoic acid (RA) treatment of promonocytic U937 cells stimulates expression from the simian immunodeficiency virus (SIVmac) long terminal repeat (LTR). Furthermore, RA and phorbol 12-myristate 13-acetate (PMA) synergistically stimulated both SIVmac and HIV-1 LTRs to levels of expression comparable to that achieved by the viral transactivator Tat. The cis-acting elements required for a response to RA and PMA cotreatment are located between nucleotides -50 and +1 of SIVmac and between nucleotides -83 and +80 of HIV-1. Thus, the synergistic stimulation induced by RA and PMA is NF-kappa B independent. Analysis of deletion mutants of the SIVmac LTR demonstrates that RA and PMA stimulation cooperates with NF-kappa B and Sp1. An SIVmac LTR-reporter gene construct [pLTR(-50/+466)CAT] lacking NF-kappa B and Sp1 binding sites was not activated by Tat in untreated cells but was activated in cells that were cotreated with RA and PMA. Furthermore, gel retardation assays demonstrated that RA treatment causes a change in the pattern of a cellular factor(s) which binds to the -50 through +1 region of the SIVmac LTR. These data suggest that RA induces a PMA-activatable cellular factor that cooperates with NF-kappa B, Sp1, or Tat to stimulate LTR-directed transcription.

Uptake and storage of retinol and retinyl esters in bone marrow of children with acute myeloid leukemia treated with high-dose retinyl palmitate

Twenty-one children with AML, who achieved complete remission with cytostatics, were treated with high doses of retinoids after remission was achieved. They were given 52 mumol retinyl palmitate/m2 (50,000 International Units/m2) daily for at least 2 years thereafter. Thirteen of the children are still in complete remission with a mean observation time of 103 months. Due to the positive effects of retinoids seen in the treatment of AML, we have studied uptake of lipoprotein-associated retinyl esters in bone marrow cells and peripheral leukocytes in vivo. An oral load of 104 mumol/m2 (100,000 International Units/m2) retinyl palmitate resulted in a doubling of the concentration of total retinol in bone marrow cells and peripheral leukocytes after 5 hours. However, in the fasting state no significant difference was observed between the content of total retinol in bone marrow cells from controls and from patients receiving retinyl palmitate daily for years. Our study suggests that bone marrow cells take up retinyl esters postprandially, but do not store retinoids.

Leukemic blasts with markers of four cell lineages in Down's syndrome ("megakaryoblastic leukemia")

Among 16 patients with Down's syndrome (DS) and acute leukemia admitted to our department during a ten year period, 6 were diagnosed as acute megakaryoblastic leukemia (AMkL). The diagnosis was based on clinical and hematologic criteria, confirmed in three patients with the use of monoclonal antibodies (MoAb) specific for megakaryocytic antigens. In these three, and in a fourth patient, the leukemic blasts were positive for other myeloid, lymphoid and erythroid markers in MoAb testing. We suggest that AMkL in DS is a mixed lineage leukemia with blasts presenting a variety of cell surface antigens, indicating origin from an early progenitor cell with the capability of megakaryocytic differentiation. Of the 6 patients with AMkL, 4 treated with standard AML protocols are in complete continuing remission (CCR) with observation periods from 57+ to 148+ months.

Progress in the treatment of childhood leukaemias

The Nordic Society for Pediatric Hematology and Oncology (NOPHO) has run a population-based registry on all cases of acute leukaemias in the Nordic countries since 1981. Data on close to 2000 children with these diagnoses are presented and used as a background for a general discussion of progress in the therapy of these challenging conditions. Our material is unique in that it is population based. The results obtained are comparable to those obtained by all other major cooperative groups. Since January 1992, the treatment protocols for all types of acute leukaemias in childhood have been harmonized in the Nordic countries.

Uptake of chylomicron remnant retinyl esters in human leukocytes in vivo

Retinoids have been successfully used in the treatment of some forms of leukaemia, suggesting that such cells have an efficient uptake mechanism for circulating retinoids. Therefore, we have studied the uptake of lipoprotein-associated retinyl esters in human leukocytes in vivo. After an oral load of 100 mumol retinyl palmitate (30,000 retinol equivalents) per square meter given to healthy adults, the concentration of retinoids in circulating leukocytes was determined. A peak was measured after 5 h, which coincided with a peak of retinyl esters in plasma. To test whether low-density lipoprotein receptors are necessary for the postprandial uptake of retinoids, we studied retinoid uptake in leukocytes from two patients homozygous for familial hypercholesterolaemia. After an oral load of retinoids we found that leukocytes from these patients took up at least as much retinoid as leukocytes in normal individuals, suggesting that uptake of chylomicron remnant retinyl esters may proceed independent of the low-density lipoprotein receptor. The expression of mRNA for the low density lipoprotein receptor-related protein, which is a putative chylomicron remnant receptor, was similar in leukocytes from a patient homozygous for familial hypercholesterolaemia and normal individuals. Six hours after vitamin A administration, recovery of unesterified retinol was 71% in normal leukocytes, however, only 9% unesterified retinol was recovered in leukocytes from the two patients with familial hypercholesterolaemia. Thus, the apparent rate of retinyl ester hydrolysis was markedly reduced in leukocytes from these patients, indicating different intracellular traffic of chylomicron remnants in normal individuals and patients homozygous for familial hypercholesterolaemia.

Retinyl esters in chylomicron remnants inhibit growth of myeloid and lymphoid leukaemic cells

We have studied the effects of retinyl esters in chylomicron remnants on cell growth and differentiation of myeloid and lymphoid leukaemic cells. Ten mumol l-1 retinyl ester in chylomicron remnants effectively reduced proliferation of the myeloid leukaemic cell lines HL60, U937 and KG-1, and induced differentiation of 68% and 53% of the HL60 and U937 cells, respectively, in 5 days. While no effect on cell growth of the lymphoid cell lines Daudi, Raji and SOS was observed, 10 mumol 1-1 retinyl esters in chylomicron remnants reduced the growth of the B lymphoid cell line Reh by more than 50%. Primary cell cultures from six patients with acute leukaemia (four non-lymphocytic and two lymphocytic) were incubated with chylomicron remnant retinyl esters and proliferation was measured by means of thymidine incorporation. Among the myeloid leukaemic cells, the monomyelocytic, the two promyelocytic and the monoblastic leukaemic cells were growth inhibited. Chylomicron remnants had no effect on the growth of the c-ALL primary culture, but reduced proliferation of the T-ALL primary culture by approximately 20% after 48 h. These data suggest that high doses of retinol may be used in the treatment of some forms of acute leukaemia.

New synergistic combinations of differentiation inducing agents in the treatment of acute myeloid leukaemia

Differentiation inducing agents in double and triple combinations can induce differentiation in primary culture of more than 80% of blast cells from some AML patients. In the present study, the interactions between these differentiating agents have been analysed using Berenbaum's general algebraic solution and three new, potentially clinically useful synergistic combinations: have been identified all trans retinoic acid (RA) + hexamethylene bisacetamide (HMBA), cytosine arabinoside (Ara-C) + HMBA and RA + Ara-C + HMBA. A measure of the effectiveness of these combinations was that the doses of Ara-C and HMBA required to induce 50% differentiation were decreased about 10-fold and 5-fold, respectively, in combination with 1 microM RA. The new synergistic combinations are important not only to limit toxicity but also because multiple drug combinations may better overcome the inherent molecular heterogeneity of the differentiation defect in AML patients. They warrant clinical trial in AML patients who are either unsuitable for or are unresponsive to conventional cytotoxic chemotherapy.

Recombinant human interleukin-6 enhances the antiproliferation and differentiation inducing effects of retinoic acid in HL-60 human myeloid leukaemic cells

1. The effect of recombinant human interleukin-6 on the antiproliferation and differentiation inducing actions of all-trans retinoic acid in HL-60 human myeloid leukaemia cells was studied in short-term liquid suspension culture. 2. Interleukin-6 alone showed no significant effect on HL-60 human myeloid leukaemia cells. 3. The addition of interleukin-6 to all-trans retinoic acid-treated cultures of HL-60 human myeloid leukaemia cells significantly enhanced the desired antiproliferation effect of all-trans retinoic acid. 4. The combination of interleukin-6 with all-trans retinoic acid reduced the doses of all-trans retinoic acid required to induce the same differentiation of HL-60 cells as single agent by between 1.7- and 4.8-fold; that is, the efficacy of all-trans retinoic acid in inducing the differentiation of human myeloid leukaemia HL-60 cells was increased up to 4.8 times by its combination with interleukin-6. 5. The combination of all-trans retinoic acid and interleukin-6 could provide an effective alternative therapy for elderly myeloid leukaemia patients.

Synergistic interactions between differentiation-inducing agents in inhibiting the proliferation of HL-60 human myeloid leukaemia cells in clonogenic micro assays

All-trans-retinoic acid, hexamethylene bisacetamide and 5-azacytidine are inducers of granulocytic differentiation of HL-60 human myeloid leukaemic cells, which eventually leads to inhibition of cell proliferation. The effect of graded concentrations of all-trans-retinoic acid (RA) (1 nM-1 microM), hexamethylene bisacetamide (HMBA) (0.5-4 mM) and/or 5-azacytidine (5azaC) (1 nM-1 mM), alone and in combination with each other on colony formation and growth of HL-60 cells was studied in agar capillary clonogenic micro assays in order to identify new potential therapeutic regimens for elderly patients with acute myeloid leukaemia. ED90 concentrations, inducing 90% inhibition of colony formation for RA, HMBA and 5azaC, were 128 nM, 2.7 mM and 40 microM, respectively. The drug interactions between these differentiating agents were analysed by Berenbaum's general algebraic solution. The combinations: RA + HMBA, 5azaC + HMBA and RA + 5azaC were significantly synergistic in inhibiting HL-60 colony formation. Their interaction indices were 0.62, 0.83, and 0.97, respectively, at a specific effect level of 15%. The addition of 1 mM HMBA to 100 nM 5azaC- and 1 nM RA-treated cultures significantly increased the colony-formation inhibition from only 2.6% and 7.0% to 46.4%, and 43.1%, respectively. Also, HMBA showed marked synergism with RA and 5azaC in inhibiting colony growth. The interaction indices (I) of HMBA + RA and HMBA + 5azaC were 0.013 and 0.009, respectively, at the same specific level of 15%. Moreover, the triple combination of RA + HMBA + 5azaC showed synergism in inhibiting both the colony formation (I = 0.7) and colony growth (I = 0.4) at the same specific level of 15%. Since RA, HMBA and 5azaC were effective when administered alone in phase I clinical trials of myeloid leukaemic patients, their synergistic combinations could provide shorter and less toxic courses of treatment in elderly myeloid leukaemic patients. I is less than 1, = 1 or greater than 1 in synergistic, additive or antagonistic interactions, respectively.

Retinoic acid in mono- or combined differentiation therapy of myelodysplasia and acute promyelocytic leukemia

Myelodysplastic preleukemic syndromes (MDPS) and acute promyelocytic leukemia (APL) share a surprising in vivo sensitivity to the hormonally acting 13 cis or all trans retinoic acids (transRA). Here we show that transRA as a monotherapeutic agent induced a stable remission in APL at the third relapse. In MDPS, treatment with prednisone and 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25D3) 13 cis RA induced a long-lasting hematological remission. Initially both patients had an impaired BM microenvironment which regenerated on retinoid therapy as judged by reappearance of the Hematon fraction in the BM aspirates. Our preclinical experiments using long-term liquid BM cultures (LTBMC) indicated that several individual patterns of growth and differentiation responses can be induced by combinations of transRA, 1 alpha,25D3 and hemopoietic growth factors (HGFs). The biological responses may vary from complete clonal extinction to a significant growth stimulation of the leukemic blast cell populations. These results further support the importance of preclinical studies in selecting "good" responders for, and excluding "poor" responders from protocols using differentiation therapy.

Effect of 5-aza-2'-deoxycytidine and retinoic acid on differentiation and c-myc expression in HL-60 myeloid leukemic cells

The antineoplastic effects of 5-aza-2'-deoxycytidine (5-AZA-CdR) and retinoic acid on human HL-60 myeloid leukemic cells were investigated. 5-AZA-CdR or retinoic acid reduced the clonogenicity and induced the differentiation of HL-60 leukemic cells. The effects produced by 5-AZA-CdR and retinoic acid in combination on clonogenicity and differentiation of HL-60 leukemic cells were additive. These agents in combination also produced an additive decrease in the mRNA expression of the c-myc. These data indicate that 5-AZA-CdR and retinoic acid in combination produce an additive antineoplastic effect against HL-60 human myeloid leukemic cells.

Triple combination of retinoic acid plus actinomycin D plus dimethylformamide induces differentiation of human acute myeloid leukaemic blasts in primary culture

Differentiation induction therapy provides an alternative for treatment of acute myeloid leukaemia (AML) patients who are either unsuitable for or unresponsive to conventional cytotoxic chemotherapy. The effect of a triple combination of retinoic acid (RA) + actinomycin D (Act-D) + dimethylformamide (DMF) on differentiation of blasts from 24 AML patients was studied. Non-adherent mononuclear cells were seeded at a concentration of 5 x 10(5) cells/ml in 24-well tissue-culture plates containing RPMI 1640 culture medium with 20% fetal calf serum, 10% autologous serum and 10% 5637-conditioned medium and incubated with 10(-6) M retinoic acid, 5 nM actinomycin D and/or 100 mM dimethylformamide alone and in combination with each other for 6 days at 37 degrees C in a humidified incubator and an atmosphere containing 5% CO2. The triple combination of 10(-6) M retinoic acid + 5 nM actinomycin D + 100 mM dimethylformamide induced 90% of the blasts from 22 of the 24 AML patients to differentiate. The combination of N-methylformamide (a compound similar to dimethylformamide) with cyclophosphamide significantly increased the in vivo activity with no concomitant increase in its reversible hepatotoxicity. Since several polar compounds related to dimethyl-formamide, e.g. hexamethylene bisacetamide and N-methylformamide, are currently undergoing phase II clinical trials, it may be feasible to combine one of these with retinoic acid and/or actinomycin D in the treatment of AML patients.

Triple combination of retinoic acid + low concentration of cytosine arabinoside + hexamethylene bisacetamide induces differentiation of human AML blasts in primary culture

Differentiation induction therapy provides an alternative therapeutic approach for patients with acute myeloid leukemia (AML) who are either unsuitable for or unresponsive to conventional cytotoxic chemotherapy. The effect of a triple combination of retinoic acid (RA) + low concentration of cytosine arabinoside (Ara-C) + hexamethylene bisacetamide (HMBA) on differentiation of blasts from 24 AML patients was studied. Non-adherent mononuclear cells were seeded at a concentration of 5 x 10(5) cells per ml in 24-well tissue culture plates containing RPMI 1640 culture medium with 20 per cent fetal calf serum and 10 per cent 5637-conditioned medium and incubated with 10(-6) M retinoic acid, 10(-6) M cytosine arabinoside and/or 2 mM hexamethylene bisacetamide for six days at 37 degrees C in a humidified incubator under 5 per cent CO2. Morphological, cytochemical and functional differentiation into mature cells were induced in blasts from 22 out of the 24 AML patients following exposure to the triple combination of 10(-6) M RA + 10(-6)M Ara-C + 2 mM HMBA in primary culture. These effective results justify a clinical trial of such triple combination for AML patients who are either unsuitable for or unresponsive to conventional cytotoxic chemotherapy.

Acute myelogenous leukaemia in children

Acute myelogenous leukaemia in childhood is considerably more resistant to chemotherapy than the acute lymphocytic leukaemias. Recently, more aggressive therapy has improved the outlook for children with this difficult form of leukaemia. Long-term disease-free survival of children achieving remission has been reported to be more than 40% in some studies. This paper reviews both the present concept of leukaemogenesis as well as some of the more recent therapeutic studies on childhood AML.

Uptake of retinyl ester in HL-60 cells via the low-density-lipoprotein-receptor pathway

Newly absorbed retinol is transported in association with chylomicrons and their remnants. In addition, after intake of high doses of retinol, significant amounts are also found in low-density lipoprotein (LDL). As both chylomicron remnants and LDL may be taken up by cells via the LDL receptor, and retinoids inhibit proliferation of some leukaemic cells, we have studied the uptake of retinol in leukaemic cells via the LDL-receptor pathway. HL-60 cells contain saturable binding sites for LDL. The binding of LDL to its receptor has a dissociation constant of about 3.2 x 10(-9) M, and the number of receptors per cell was calculated to be about 2700. Uptake of 125I-LDL by HL-60 cells was increased 2-fold by preincubating the cells with mevinolin. The presence of specific receptors for LDL on HL-60 cells was further confirmed by the finding that exogenous LDL cholesterol was able to up-regulate the ACAT (acyl-CoA: cholesterol acyltransferase) activity of HL-60 cells. We then tested the uptake of retinyl ester in leukaemic cells via the LDL-receptor pathway. HL-60 cells were incubated with LDL or chylomicron remnants labelled with [3H]retinyl palmitate. Uptake of retinyl ester associated with both LDL and chylomicron remnants was observed. Furthermore, the presence of excess LDL decreased the uptake by 75-100%, supporting the hypothesis that the uptake of retinyl ester occurred via the LDL receptor in HL-60 cells.