Retinoids and interferon: a new promising combination?

Leukemia Cells and the Cytokine Network: Therapeutic Prospects

The network and balance of cytokines is of major importance in maintaining proper homeostasis of hematopoiesis. Abnormalities in this network may result in a variety of blood disorders; however, the role of this network is not clear in leukemia. The use of antineoplastic agents has improved the survival rate of some types of leukemia, and adjunctive therapy with cytokines may be helpful. Chemotherapeutic approaches are no longer the best choice because cytotoxicity may affect normal and leukemic cells, and leukemic cells may develop resistance to the chemotherapeutic agent. Induction of differentiation to a mature phenotype and the control of apoptotic-gene expression have provided other possible alternative therapies. Combined effects of cytokines and vitamin derivatives such as retinoic acid (RA) and 1, 25 dihydroxyvitamin D3 (VD3) were found more beneficial than any of these agents individually. These agents exhibit cooperative effects, potentiate each other's effects, or both. Therefore, understanding the hematopoietic actions of these agents, their interactions with their receptors, and their differentiation signaling pathways may result In the design of new therapies. However, the role of cytokines in apoptosis is controversial because in some cases they were found to increase tumor cell resistance to apoptosis-inducing agents. Recent studies in the molecular biology of gene regulation, transcription factors, and repressors have led to new possible approaches such as differentiation therapy for the treatment of leukemia. In addition, the development of drugs that act on the molecular level such as imatinib is just the beginning of a new era in molecular targeted therapy in which the drug acts specifically on the leukemic cell. There are many possible combinations of cytokines, retinoids, and VD3, and perhaps the best therapeutic combination is yet to be described. This minireview is an update on the role of cytokines and the therapeutic potential of combinations with agents such as RA, VD3, and other chemotherapeutic agents.

A phase 2 trial of all-trans-retinoic acid in combination with interferon-alpha2a in children with recurrent neuroblastoma or Wilms tumor: A Pediatric Oncology Branch, NCI and Children's Oncology Group Study

BACKGROUND

The combination of the antiproliferative and differentiation-inducing effects of retinoids together with the antiproliferative, immunostimulatory, and differentiation-potentiating effects of interferon-alpha (IFN-alpha) were the basis for the development of this combination in pediatric patients with refractory neuroblastoma or Wilms tumor.

PROCEDURE

A phase 2 trial of all-trans-retinoic acid (ATRA), administered orally at a dose of 90 mg/m(2)/day in three divided doses for 3 consecutive days per week, and IFN-alpha2a, administered subcutaneously daily at a dose of 3 x 10(6) U/m(2)/day for 5 consecutive days per week, in 4 week cycles was performed. A two-stage design was used for each disease stratum.

RESULTS

Seventeen patients (16 evaluable) with neuroblastoma, median age 9 years, and 15 patients (14 evaluable) with Wilms tumor, median age 6 years, were enrolled. Overall, the combination was well tolerated, with headache being the most common toxicity observed. There were no complete or partial responses. The median number of cycles administered was 1 (range 1-9). Four patients with neuroblastoma had stable disease for 12 or more weeks.

CONCLUSIONS

The combination of ATRA and IFN-alpha2a was inactive in children with relapsed or refractory neuroblastoma and Wilms tumor. The lack of activity with this combination in children with refractory neuroblastoma is similar to the disappointing phase 2 results of single agent 13-cis-retinoic-acid (13cRA) and does not support further development of ATRA for children with relapsed neuroblastoma.

Recurrent and metastatic clivus chordoma: systemic palliative therapy retards disease progression

We report on a male patient with progressive and metastatic clivus chordoma treated over a period of 9 years by a multidisciplinary approach. Within the first 4 years, the patient underwent surgery four times. Thereafter, he received radiotherapy and subsequent chemotherapy. Stabilization of disease was achieved repeatedly for variable periods under local radiotherapy, systemic chemotherapy, immunomodulatory and anti-angiogenic therapy with isotretinoin and interferon-alpha, followed by thalidomide. Due to the occurrence of brain and lung metastases 8 years after initial diagnosis, liposomal doxorubicin was added to thalidomide. At the last follow-up control the patient had stable disease, with no progression of the intracranial tumor and regression of pulmonary metastases. He is in a good physical, psychological and neurological condition with a Karnofsky score of 80. Our observations show that multimodal therapy including a systemic palliative approach is associated with long quiescent intervals in recurrent chordoma and with regression of its metastases. Use of substances with high efficacy on tumor tissue and low toxicity, allowing long-term administration, seems promising in similar situations.

retinoic acid, bromodeoxyuridine, and the Delta 205 mutant polyoma virus middle T antigen regulate expression levels of a common ensemble of proteins associated with early stages of inducing HL-60 leukemic cell differentiation

Retinoic acid (RA), bromodeoxyuridine (BrdU), and the Delta 205 mutant polyoma middle T antigen affect the expression of a common ensemble of proteins in HL-60 human myeloblastic leukemia cells. Each of these agents is known to be able to prime HL-60 cells and accelerate subsequently induced myeloid or monocytic differentiation and G0 cell cycle arrest, suggesting that they have equal or identical cellular targets relevant to the early stages of inducing cell differentiation and G0 arrest. As a test of this possibility, a survey of protein expression changes induced by RA, BrdU, or Delta 205 transfection was performed. Retinoic acid induced numerous changes within h. Bromodeoxyuridine caused larger numbers of changes, whereas Delta 205 caused a more limited number. Among the hundreds of affected proteins detected, there were comparable numbers of up- or downregulated proteins. A small number changed between undetectable and detectable expression. The affected proteins were not restricted to a single functional class and included transcription factors, receptors, signaling molecules, cytoskeletal molecules, and effectors of various cellular processes such as deoxyribonucleic acid replication, transcription, and translation. The intersect of the sets of proteins affected by RA, BrdU, and Delta 205 was identified to determine if these agents regulated a common subset of proteins. This ensemble contained the commonly upregulated proteins AF6, ABP-280, ENC-1, ESE 1, MAP2B, NTF2, casein kinase, IRF1, SRPK2, Rb2, RhoGDI, P47phox, CD45, PKR, and SIIIp15. The commonly downregulated proteins were SHC, katanin, flotillin-2/ESA, EB 1, p43/EMAPIIprecursor, Jab1, FNK. The composition of the ensemble suggested three apparent themes for cellular processes that were affected early. The themes reflected the ultimate fate of the treated precursor cells as a mature myeloid cell, namely a cell whose hallmarks are (1) motility to migrate to a target and phagocytize it, (2) inducible oxidative metabolism to reduce the target with superoxide from a respiratory burst, and (3) biosynthetic slow down consistent with conversion from cell proliferation to quiescence. Interestingly, RA appears to induce aspects of an interferon-like response of potential significance as part of a biosynthetic slow down leading to cell cycle arrest. In conclusion, three biologically disparate ways to prime cells to differentiate were used to filter out a small ensemble of commonly regulated proteins that group as either microtubule associated, oxidative metabolism machinery, or effectors of cellular responses to interferon.

Activity of interferon-alpha and isotretinoin in patients with advanced, refractory lymphoid malignancies

BACKGROUND

Interferon-alpha (IFN-alpha) and retinoids have shown nonoverlapping toxicity and each has shown antitumor activity in patients with lymphoma. The aim of the current study was to assess the toxicity, safety, and efficacy of IFN-alpha combined with isotretinoin in patients with advanced, refractory lymphoid malignancies.

METHODS

Adults with biopsy-proven advanced lymphoid malignancy were treated. Patients with compromised bone marrow function (platelet counts as low as 30 x 10(9)/L) were eligible. Treatment was comprised of IFN-alpha at a starting daily dose of 3 mega units subcutaneously and isotretinoin orally starting at a dose of 1 mg/kg daily in 2 divided doses.

RESULTS

Forty-four patients were evaluable. Their median age was 57 years (range, 18-82 years). Eighteen patients had advanced cutaneous T-cell lymphoma, 6 patients had peripheral T-cell lymphoma, 14 patients had Hodgkin disease, and 6 patients had a variety of other lymphoid malignancies. Patients with Hodgkin disease had received a median of 6 previous therapies (range, 3-12 therapies) and patients with other lymphoid malignancies had received a median of 4 previous therapies (range, 1-9 therapies). The median duration of treatment was 4 months (range, 0.25-38 months). The overall response rate was 38.6% (complete response in 5 patients [11.3%] and partial response in 12 patients [27.3%]). The median response duration was 3 months (range, 1-95+ months). The most common toxicities were low-grade fever, flu-like symptoms, and fatigue (IFN-alpha effects); dry mouth and skin and hypertriglyceridemia (cis-retinoic acid effects); and thrombocytopenia (which generally occurred in patients with low baseline platelet counts).

CONCLUSIONS

IFN-alpha and isotretinoin combination therapy had antitumor activity and was well tolerated in heavily pretreated patients with lymphoid malignancies.

Stage IV CD30+ anaplastic large cell lymphoma: response to acitretin and interferon-alpha

Retinoids and interferon (IFN)-alpha induce differentiation, affect cell proliferation and alter various immune parameters. In combination, their effects may be additive or even synergistic in the treatment of malignancy. We present a 53-year-old woman with stage IV CD30+ anaplastic large cell lymphoma with brain, lung and skin involvement. The patient had been on methotrexate for rheumatoid arthritis. After a combination of oral acitretin 50 mg daily and IFN-alpha 3 million units subcutaneously 3 times per week, the skin lesions cleared within 2 months, lung lesions by 5 months and brain lesions by 7 months. Although we cannot exclude that methotrexate played a role in the development of this lymphoma and that its withdrawal contributed to the clearance of lesions, we propose that the patient's disease responded to the combination of acitretin and IFN-alpha.

Human B-cell lymphoma cell lines are highly sensitive to apoptosis induced by all-trans retinoic acid and interferon-gamma

When cells were incubated in the presence of both interferon-gamma (IFN-gamma) and all-trans retinoic acid (ATRA), the concentration of IFN-gamma required to induce apoptosis of B-cell lymphoma cells was much lower than that required for myeloid or erythroid cell lines. The concentration of IFN-gamma that effectively inhibited the proliferation of BALM-3 cells was 1/40 of that required for BALM-1 cells. STAT-1 phosphorylation, IRF-1 mRNA and protein expression and RAR-beta expression were enhanced to a greater degree in BALM-3 cells treated with IFN-gamma and ATRA than in BALM-1 cells treated with IFN-gamma and ATRA, suggesting that these IFN-gamma related genes were involved in the induction of apoptosis of BALM-3 cells.

Activity of ALRT 1550, a new retinoid, with interferon-gamma on ovarian cancer cell lines

Retinoids have been shown to be effective regulators of cell proliferation and differentiation in many human cancers. The major biologic activity of the retinoids is mediated by two families of nuclear receptors: retinoic acid receptors (RARs) and retinoid X receptors (RXRs). ALRT 1550 is one of the most potent RAR selective retinoids discovered to date, with 10-100 times more activity than ATRA in competitive binding and cotransfection assays and 300 times more inhibiting activity against proliferation of cervical carcinoma cell. To evaluate the role of ALRT 1550 in ovarian cancer, the growth inhibitory activity of ALRT 1550 was determined in the ATRA-resistant ovarian cancer cell line SKOV-3 and ovarian cancer cell line 2774 after exposure to concentrations of 0.1, 1, 2.5, 5, and 10 microM for 7 days. SKOV-3 showed 51%, 53%, and 68% cell growth inhibition after treatment with ALRT 1550 at concentrations of 2.5, 5, and 10 microM, respectively, and the 2774 cell line showed 46% inhibition after treatment at 10 microM. Because interferon (IFN)-gamma was found to synergistically amplify the growth inhibition of retinoids in cultured breast cancer cells, we investigated the combination of ALRT 1550 with IFN-gamma in two ovarian cancer cell lines. ALRT 1550 (5 microM) in combination with IFN-gamma at a concentration of 500 U/ml inhibited cell growth of SKOV-3 by as much as 81% (CI = 1.88). This is a 28% greater effect than with ALRT alone. Cell line 2774 showed a 69% cell growth inhibitory effect with ALRT 1550 (5 microM) in combination with IFN-gamma at a concentration of 1000 U/ml (CI = 1.03). ALRT 1550 and IFN-gamma may act synergistically in the SKOV-3 ovarian cancer cell line and additively in the 2774 cell line. In conclusion, ALRT 1550 may be a promising drug with a high biologic modulating activity against ovarian cancer. In combination with IFN-gamma, additive and perhaps synergistic effects may be seen in some ovarian cancer cell lines. Combining these two biologic modifiers for the treatment of ovarian cancer may lower the effective dose of the retinoids, thus decreasing their side effects.

IRF-1 as a negative regulator of cell proliferation

Numerous evidence has demonstrated the involvement in growth control of interferon (IFN) regulatory factor-1 (IRF-1), which shows tumor suppressor activity. IRF-1 is a well-studied member of the IRF transcription factors that reveals functional diversity in the regulation of cellular response by activating expression of a diverse set of target genes, depending on the cell type and on the specific stimuli. IRF-1 gene rearrangements may be a crucial point in the pathogenesis of some cancer types. Furthermore, different aspects of the tumor suppressor function of IRF-1 may be explained, at least in part, by the observations that IRF-1 is a regulator of cell cycle and apoptosis and that its inactivation accelerates cell transformation. Studies on gene knockout mice contributed greatly to the clarification of these multiple IRF-1 functions. We summarize our current knowledge of the antigrowth effect of IRF-1, focusing also on a more general involvement of IRF-1 in mediating negative regulation of cell growth induced by numerous cytokines and other biologic response modifiers.

Historical perspective on the use of retinoids in cutaneous T-cell lymphoma (CTCL)

Vitamin A and its analogues influence differentiation and proliferation and may also alter immune responses. Limited clinical efficacy of these compounds given alone or as part of a combination therapy has been shown in various types of cutaneous T-cell lymphoma (CTCL), including mycosis fungoides, Sézary syndrome, and prelymphomatous disorders such as parapsoriasis en plaques. Compounds used mostly in small, nonrandomized trials are isotretinoin (13-cis-retinoic acid), etretinate, acitretin, and all-trans-retinoic acid. Clinical responses have been found despite persistent residual disease with atypical lymphocytes in various compartments. The exact mechanism of action of retinoids in CTCL is unclear and depends on the presence of retinoid receptors on the tumor cells, which is variable in different forms of CTCL. Therapies combining retinoids with psoralen-ultraviolet A or with interferons may have a synergistic effect, which deserves confirmation through randomized trials in the future.

All-trans retinoic acid and hematopoietic growth factors regulating the growth and differentiation of blast progenitors in acute promyelocytic leukemia

Although acute leukemia is generally thought to be characterized by maturation arrest, it has been shown that differentiation occurs in blast cells of acute myelogenous leukemia (AML) in vitro as well as in vivo, and that morphologically abnormal mature polymorphonuclear neutrophils (PMNs) often seen in patients with AML are possibly derived from spontaneously differentiating leukemic cells. Acute promyelocytic leukemia (APL) is an unique example in which these features of AML are evident in an almost complete form; administration of all-trans retinoic acid (ATRA) induces differentiation of neoplastic cells into mature neutrophils and successfully induce complete remission in most patients. However, PMNs appearing during ATRA treatment are morphologically abnormal, as indicated not only by the presence of Auer rods but also by neutrophil secondary-granule deficiency that is commonly seen in AML. Moreover, ATRA has heterogeneous effects on the growth of blast progenitors in APL in different patients, being inhibitory, stimulatory or ineffective, which might account in part for the leukemia relapse in patients treated with ATRA alone. Hematopoietic growth factors regulate the growth of blast progenitors in APL. Among them, granulocyte colony-stimulating factor (G-CSF) is unique in that it preferentially stimulates clonal growth, but not self-renewal, in many APL cases, and synergistically enhances the differentiation-inducing effect of ATRA when used in combination. Many other compounds also exert such synergistic effects with ATRA, for which a variety of mechanisms have been suggested. It is crucial to precisely elucidate the functions of these molecules governing the growth/differentiation balance of AML blast progenitors and the mechanisms underlying their deregulated differentiation program in order to achieve effective differentiation therapy for patients with AML, not restricted to APL.

Granulocyte colony-stimulating factor-induced dephosphorylation of a 45 kD cytosolic protein in HL-60 cells differentiating into neutrophils

Granulocyte colony-stimulating factor (G-CSF)-induced alteration of phosphoprotein during differentiation of HL-60 cells was studied. From the two-dimensional gel electrophoresis analysis of phosphoproteins, a 45 kD phosphoprotein in the cytosolic fraction of DMSO-pretreated HL-60 cells was rapidly dephosphorylated by the addition of G-CSF. This 45 kD phosphoprotein migrated into four or five spots between 4.5 and 5.5 pI. The dephosphorylation of 45 kD protein was observed within at least 10 min and reached a maximum at 60 min. Phosphoamino acid analysis showed that only serine residue of 45 kD phosphoprotein was phosphorylated, suggesting that G-CSF induced an activation of serine phosphatase. Furthermore, Staurosporine and calphostin C inhibited the phosphorylation of 45 kD protein, suggesting that protein kinase C or its downstream kinase(s) is involved in the phosphorylation of 45 kD protein. These results indicate that G-CSF causes dephosphorylation of a 45 kD cytosolic phosphoprotein which may play a role in signal transduction of G-CSF.

Granulocyte colony-stimulating factor promotes functional maturation of O-2 generating system during differentiation of HL-60 cells to neutrophil-like cells

The effects of granulocyte colony-stimulating factor (G-CSF) on development of O-2 generating system during differentiation of HL-60 cells to neutrophil-like cells have been studied. G-CSF enhanced O-2 generating ability of HL-60 cells whose differentiation had been initiated by dimethylsulfoxide (DMSO) or retinoic acid (RA). The O-2 generations by the differentiated HL-60 cells in response to opsonized zymosan (OZ), formyl-Met-Leu-Phe (fMLP), and IgG-coated zymosan were increased two- to fourfold as a result of incubation of the cells undergoing the differentiation with G-CSF. The potentiation by G-CSF occurred in a dose-dependent manner with the maximum effect at about 10 ng/ml G-CSF. The effect of G-CSF could not be fully explained by up-regulation of the receptor expression on the HL-60 cells, because the number of C3bi receptors was not altered by G-CSF, whereas the expression of fMLP receptor was enhanced by G-CSF. On the other hand, the O2 generation of the differentiated cells activated by phorbol 12-myristate 13-acetate was not affected by the G-CSF treatment, suggesting that the biochemical events in the cells after PKC activation might not be enhanced by G-CSF. Assuming that the signaling pathways linking OZ or fMLP receptor might be enhanced by G-CSF, alteration in the cellular sn-1, 2-diacylglycerols (DAG) level upon stimulation with OZ or fMLP was compared between the G-CSF-treated and nontreated cells. Whereas DAG level was not increased by the stimulation in the cells treated with DMSO alone, a significant increase in DAG level upon the stimulation was observed in the cells treated with G-CSF and DMSO. These results suggest that G-CSF would enhance the organization of a receptor-linked DAG generating system in the differentiating cells, leading the cells to generate more O2.

Regulation of retinoidal actions by diazepinylbenzoic acids. Retinoid synergists which activate the RXR-RAR heterodimers

In human HL-60 promyelocytic leukemia cells, diazepinylbenzoic acid derivatives can exhibit either antagonistic or synergistic effects on the differentiation-inducing activities of natural or synthetic retinoids, the activity depending largely on the nature of the substituents on the diazepine ring. Thus, a benzolog of the retinoid antagonist LE135 (6), 4-(13H-10,11,12,13-tetrahydro-10, 10,13,13,15-pentamethyldinaphtho[2,3-b][1,2-e]diazepin-7-yl) benzoic acid (LE540, 17), exhibits a 1 order of magnitude higher antagonistic potential than the parental LE135 (6). In contrast, 4-[5H-2,3-(2,5-dimethyl-2,5-hexano)-5-methyldibenzo[b,e] [1,4]diazepin-11-yl]-benzoic acid (HX600, 7), a structural isomer of the antagonistic LE135 (6), enhanced HL-60 cell differentiation induced by RAR agonists, such as Am80 (2). This synergistic effect was further increased for a thiazepine, HX630 (29), and an azepine derivative, HX640 (30); both synergized with Am80 (2) more potently than HX600 (7). Notably, the negative and positive effects of the azepine derivatives on retinoidal actions can be related to their RAR-antagonistic and RXR-agonistic properties, respectively, in the context of the RAR-RXR heterodimer.

The effects of 13-cis retinoic acid and interferon-alpha in chronic myelogenous leukemia cells in vivo in patients

The effects of the administration of a 3-day course of 13-cis retinoic acid in combination with interferon a [RA/IFN] on the leukemia cells was measured in vivo in 43 patients with chronic myelogenous leukemia. The administration of RA/IFN was associated with a significant fall in the white blood cell count of patients with chronic-phase disease and with a fall in the percentage S-phase cells in CML patients regardless of the stage of their leukemia. In two thirds of the patients studied the administration of RA/IFN was also associated with an increase in marrow apoptosis. The cytokine combination also suppressed bcl-2 and myc expression in a minority of patients and such expression appears to be associated with response to a treatment regimen which includes RA/IFN. These studies are the first to directly assess the effects of the combination of RA/IFN on chronic myelogenous leukemia cells in vivo in patients. These effects, if seen in other malignant diseases, could account for the therapeutic benefit which has been associated with the administration of this combination of biological agents to patients with malignant disease.

Intralesional administration of biological response modifiers in the treatment of localized cancer of the prostate: a feasibility study

OBJECTIVES

The primary aims of this pilot study were to establish the feasibility of intraprostatic administration of biological response modifiers (BRMs) and to investigate the toxicity and side effects of recombinant interferon (IFN)-alpha-2b injected into prostate glands harboring cancer. A secondary goal was to perform a preliminary assessment of the antitumor effect of this treatment.

METHODS

Nine patients with histologically documented carcinoma of the prostate participated in the study. IFN was administered weekly for 5 weeks, under transrectal ultrasound visualization, with a modified gun that permitted the controlled injection of small volumes initially into the area of the tumor and later into the whole gland. Total doses of IFN ranged between 15 and 100 MU.

RESULTS

The procedure resulted in minor local discomfort, comparable to a prostatic biopsy. Side effects from the drug were those anticipated from most BRMs (chills, fever, malaise, headache, fatigue), and in every case they were minor and self-limiting to several hours. Local adverse events were limited to gross hematuria (2 patients [22%]) and hematospermia (1 patient [11%]) and resolved spontaneously within 2 weeks. Antitumor activity, a secondary goal of the study, was noted in 3 (33%) patients with limited follow-up (mean 22.5 months).

CONCLUSIONS

The results of this pilot study indicate that the intraprostatic administration of IFN-alpha-2b can be readily accomplished by the method described here and is associated with minor, self-limited toxicity. With the regimen and doses used, IFN demonstrated modest antineoplastic activity. Modifications of the schedule, routes, and amounts administered may result in enhanced therapeutic value.

Retinoic acid induced growth arrest of human breast carcinoma cells requires protein kinase C alpha expression and activity

Retinoic acid inhibits proliferation of hormone-dependent, but not hormone-independent breast cancer cells. Retinoic acid-induced changes in cellular proliferation and differentiation are associated with disturbances in growth factor signaling and frequently with changes in protein kinase C expression. PKC delta, epsilon, and zeta are expressed in both hormone-dependent (T-47D) and hormone-independent (MDA-MB-231) cell lines. Retinoic acid arrested T-47D proliferation, induced PKC alpha expression and concomitantly repressed PKC zeta expression. The changes in PKC alpha and PKC zeta reflect retinoic acid-induced changes in mRNA. In contrast, retinoic acid had no effect on growth, or PKC expression in MDA-MB-231 cells. Growth arrest and the induction of PKC alpha, but not the reduction in PKC zeta, resulted from selective activation of RAR alpha. In total, these results support an important role for PKC alpha in mediating the anti-proliferative action of retinoids on human breast carcinoma cells.

Action mechanism of retinoid-synergistic dibenzodiazepines

4-[5H-2,3-(2,5-Dimethyl-2,5-hexano)-5-methyldibenzo[b,e][1,4 ]diazepin-11-yl]benzoic acid (HX600), as well as its oxa- (HX620) and thia- (HX630) analogs, enhanced the activity of retinoic acid and a receptor alpha (RAR alpha)-selective agonist Am80 in HL-60 cell differentiation assays. HX600 synergizes with Am80 by binding to, and transactivating through, the RXR subunit of the RXR-RAR heterodimer. HX600 exhibited RXR pan-agonist activity in transient transfections with a DR1-based reporter gene and synergized with RA-bound RAR alpha and RAR beta in inducing transcription from a DR5-based reporter. In addition, all three compounds at high concentrations acted as RAR pan-antagonists in stably transfected RAR "reporter cells." These efficient synergists bind only weakly with RXRs in vitro, suggesting that they are RXR-RAR heterodimer-selective activators. These HX retinoids exhibited dual functionality, since they affected signalling through both retinoid receptor families (RARs and RXRs).

Clinical relevance of all-trans retinoic acid pharmacokinetics and its modulation in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is uniquely sensitive to treatment with all-trans retinoic acid (ATRA) which exerts its action via a well-documented cytodifferentiating mechanism. The combination of this retinoid with anthracyclines gives high percentages of complete remission and is now considered the optimal induction treatment for APL patients. Continuous treatment with ATRA, however, induces accelerated drug catabolism, with progressive decline in plasma drug concentrations potentially to below the levels required to maintain differentiation of leukemic cells. This process, which occurs rapidly and consistently has led to the hypothesis that the development of acquired clinical resistance to ATRA in APL has a pharmacologic basis. The rapid autoinduction of the hypercatabolic state precludes maintenance with continuous ATRA oral dosing, and is a limitation of better use of the drug both in APL and in other disorders in which it could be beneficial. Here we briefly review the pharmacologic alterations of ATRA metabolism induced by continuous oral administration, the clinical implications of this phenomenon, and the strategies currently under investigation to prevent or overcome the induced catabolism of this retinoid.

All-trans retinoic acid combined with interferon-alpha effectively inhibits granulocyte-macrophage colony formation in chronic myeloid leukemia

We investigated the effect of all-trans retinoic acid (ATRA) alone and in combination with interferon-alpha (IFN-alpha) on the granulocyte-macrophage (GM) colony formation of peripheral blood progenitors isolated from patients with chronic myeloid leukemia (CML) (n = 12) or other myeloproliferative disorders (n = 10) as well as from healthy controls (n = 7). The ATRA or IFN-alpha alone inhibited slightly, but not significantly, the GM colony growth in CML. Granulocyte-macrophage colony formation decreased significantly (P<0.05) when ATRA and IFN-alpha were combined (114 +/- 96 versus 74 +/- 53 colonies/10(4) mononuclear cells). The combination did not have any inhibitory effect on the other MPDs. In healthy controls, ATRA or IFN-alpha alone or their combination stimulated GM colony growth, the increase being from 22 +/- 9 to 39 +/- 16 colonies for ATRA (P<0.05), up to 47 +/- 12 colonies for IFN-alpha (P<0.05) and up to 50 +/- 19 colonies for the combination (P<0.05). In conclusion, ATRA combined with IFN-alpha inhibits GM colony growth in CML. This combination may be worth testing clinically as a treatment of CML.

Tretinoin. A review of its pharmacodynamic and pharmacokinetic properties and use in the management of acute promyelocytic leukaemia

Tretinoin (all-trans retinoic acid), a vitamin A derivative, induces cellular differentiation in several haematological precursor cell lines and cells from patients with acute promyelocytic leukaemia. Drug treatment with tretinoin is associated with morphological and functional maturation of leukaemic promyelocytes and a progressive reduction in the occurrence of the characteristic t(15;17) chromosomal translocation. Recent therapeutic trials indicate that tretinoin induces remission in 64 to 100% of patients with acute promyelocytic leukaemia. In newly diagnosed patients, remission induction treatment with tretinoin followed by intensive chemotherapy resulted in a significant reduction in relapse rate and prolongation of event-free and overall survival compared with chemotherapy alone in 1 comparative trial. Tretinoin alone does not totally eradicate the leukaemic clone and consolidation chemotherapy is recommended as follow-up. The use of reverse transcription polymerase chain reaction (RT-PCR) provides a sensitive and specific technique to assist in prediction and monitoring of a patient's response to treatment and to help detect the presence of residual or recurrent disease. The use of tretinoin is potentially limited by the rapid and almost universal development of drug resistance and occurrence of the often severe retinoic acid syndrome. Useful strategies have been described to manage these effects but current and future efforts must be directed at elucidating the mechanisms involved and determining the optimum therapeutic management. In summary, results to date indicate that the combination of tretinoin and intensive chemotherapy is more effective than chemotherapy alone and appears to improve the prognosis of newly diagnosed patients with acute promyelocytic leukaemia. Further information on the relative efficacy of various induction and post-remission strategies in subsets of patients will help determine optimum use of this promising agent in the management of acute promyelocytic leukaemia.

Modulation of all-trans retinoid acid pharmacokinetics in acute promyelocytic leukaemia by prolonged interferon-alpha therapy

Continuous treatment with all-trans retinoid acid (ATRA) induces accelerated drug catabolism which is considered responsible for acquired resistance to ATRA. We studied the effect of interferon-alpha 2a (IFN) on ATRA pharmacokinetics in two patients with acute promyelocytic leukaemia (APL) in complete remission maintained by alternating 15 d of IFN and 15 d of ATRA. Day 15 ATRA levels obtained during IFN+ATRA treatment were significantly higher than those observed in patients maintained on ATRA alone. In one patient IFN was discontinued and day 15 ATRA levels decreased to those observed in patients scheduled for maintenance with ATRA alone. In our two patients IFN substantially reduced the induction of ATRA catabolism, indicating a potential role for IFN in modulating ATRA pharmacokinetics.

Interferon-gamma in multiple myeloma

Biological heterogeneity is a characteristic of multiple myeloma. A dysregulated cytokine network underlies the various phases of the disease. Numerous cytokines, either promoting or inhibiting plasma cell growth, are involved in tumor control. Interferon-gamma (IFN-gamma) showed the most powerful inhibiting activity on myeloma cell proliferation. This effect was demonstrated on IL-6 dependent myeloma cell lines, but not on IL-6 independent ones. It was also evident on fresh explanted bone marrow myeloma cells. The antiproliferative effect of IFN-gamma seems mainly due to the inhibition of IL-6, the central myeloma growth factor. IL-6 inhibition may occur at various levels: a downregulation of IL-6 receptor has been reported, and also a block of the IL-6 signal transduction pathway via interaction with cytoplasmic proteins such as p91 has been suggested. Our findings showed that IFN-gamma strongly inhibited myeloma cell proliferation to the same extent as dexamethasone (DEX), whereas interferon-alpha (IFN-alpha) inhibited Ig secretion. The combined use of interferons (IFNs) showed inhibitory activities both on proliferation and Ig synthesis that paralleled the effects of DEX. In some cases, IFN-gamma was also shown to augment monoclonal immunoglobulin secretion suggesting a possible differentiating activity on plasma cells. The in vitro data encouraged pilot studies to evaluate the in vivo antitumor effects of IFN-gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

Differentiation induction of human leukemia cells (HL60) by a combination of 1,25-dihydroxyvitamin D3 and retinoic acid (all trans or 9-cis)

1,25(OH)2D3 and two stereoisomers of retinoic acid, all trans and 9-cis retinoic acid, are regulators of cell proliferation and differentiation. The aim of this study was to evaluate the effects of a combination of 1,25(OH)2D3 and retinoic acid (all trans or 9-cis) on proliferation and cell differentiation of the human promyelocytic leukemia cell line HL60, and to test the reversibility of the induced differentiation. Cell proliferation was inhibited as expected by 1,25(OH)2D3 and all trans retinoic acid alone (IC50 of cell survival was 4 x 10(-7) M, 9 x 10(-6) M and 9 x 10(-7) M for 1,25(OH)2D3, all trans and 9-cis retinoic acid, respectively). Combination of 1,25(OH)2D3 and either form of retinoic acid resulted in a partially additive decrease in cell proliferation. 1,25(OH)2D3 induced a monocytic differentiation (100% CD14+ cells with 10(-7) M 1,25(OH)2D3), while retinoic acid led to a predominantly granulocytic differentiation (36 and 42% CD67+ cells with 10(-6) M all trans and 9-cis retinoic acid, respectively). Additive effects on differentiation were observed upon combination of subtherapeutical doses of the drugs, achieving a mainly monocytic population, demonstrating the dominant role of 1,25(OH)2D3 in determining the direction of differentiation. The effects on proliferation and differentiation of the solitary drugs were reversible, while the proliferation arrest and differentiation induced by the combination persisted and even progressed after withdrawal of the drugs. We conclude that 1,25(OH)2D3 and retinoic acid (all trans or 9-cis) exert additive effects on inhibition of proliferation and induction of cell differentiation of HL60 cells, leading to a persistent differentiation, even after drug withdrawal.

Retinoic acid inhibits the growth of human myeloma cells in vitro

Retinoic acid has been shown to induce growth inhibition in a variety of cell types including human myeloma cell lines. Bone marrow plasma cells from 31 multiple myeloma (MM) patients were cultured to investigate the activity of 13-cis-retinoic acid (cRA), all-trans-retinoic acid (tRA), interferon-alpha (IFN-alpha), interferon-gamma (IFN-gamma), and dexamethasone (DEX), alone or in combination, on in vitro proliferation and immunoglobulin (Ig) secretion. Both cRA and tRA inhibited proliferation: the labelling index (LI) of treated cultures/controls, was 0.47 +/- 0.05 (mean +/- standard error mean, M +/- SEM) P < 0.0001, and 0.67 +/- 0.04 (M +/- SEM), P < 0.0001, respectively. The inhibitory effect of cRA was significantly superior to tRA (P = 0.0129) and IFN-alpha, similar to IFN-gamma and DEX. The combinations of cRA + IFN alpha, tRA + IFN-gamma, tRA + DEX did not show any synergistic effect on myeloma proliferation. In contrast, the combination cRA + DEX (0.29 +/- 0.04, M +/- SEM) markedly increased the effect of both cRA and DEX used as single agents. Ig synthesis was not significantly affected by CRA, tRA, IFN-gamma and the combination tRA + IFN-gamma. As expected, only IFN-alpha (P = 0.002) and DEX (P < 0.001) inhibited Ig production. The combinations cRA + IFN-alpha, cRA + DEX and tRA + DEX decreased Ig secretion to the same extent as IFN-alpha and DEX alone respectively. In conclusion, our data indicate that tRA and especially cRA strongly inhibited plasma cell proliferation but had no effect on Ig synthesis. The combination of cRA + DEX showed the highest degree of inhibitory activity of all cytokines, alone or in combination.

Effect of retinoic acid and interferon alpha on granulocyte-macrophage colony forming cells in chronic myeloid leukemia: increased inhibition by all-trans- and 13-cis-retinoic acids in advanced stage disease

Granulocyte-macrophage colony forming units (CFU-GM) from patients with advanced stage chronic myelogenous leukemia (CML), i.e. in blastic crisis (BC) or accelerated phase (AP), were inhibited by all-trans-retinoic acid (tRA) approximately 1000-fold more potently than those from chronic phase (CP) CML patients (median IC50 = 10(-9) M tRA for six CML-AP/BC cases vs > 10(-6) M tRA for seven CML-CP cases). A similar activity pattern was observed for the stereoisomer 13-cis-RA (cRA). There was no apparent correlation of CFU-GM retinoid sensitivity with cloning efficiency or other colony characteristics. Interferon alpha-2a (INF alpha) alone strongly inhibited CFU-GM growth in all four CML-AP/BC cases (IC50 < or = 250 IU/ml) and three out of seven CML-CP cases (IC50 < or = 500 IU/ml), but there was little or no interactive effect between various concentrations of tRA and INF alpha (50 IU/ml) on CFU-GM from either CML-AP/BC or CML-CP cases. These results suggest that CML-AP/BC CFU-GM have some intrinsic molecular alteration(s) which markedly enhances their responsiveness to tRA and cRA, which may be clinically exploitable.

Acute promyelocytic leukemia

Perhaps the most important advance in this field is not the specific actions of all-trans-retinoic acid in acute promyelocytic leukemia, but rather the conclusive documentation of differentiation as a practical and consistently effective method of treating human cancer. As a drug, all-trans-retinoic acid has certain undesirable pharmacologic properties that might be overcome by the use of alternative retinoids, such as 9-cis-retinoic acid, that are equally active against acute promyelocytic leukemia cells in vitro. In addition to retinoids that selectively activate RARs or RXRs, other ligands of the steroid-thyroid receptor superfamily, such as vitamin D3, glucocorticoids, and sex steroids also have cytodifferentiating actions in model systems. Numerous other agents can effect differentiation of neoplastic cells in such systems, including sodium butyrate, hexamethylene bisacetamide and its analogues, colony-stimulating factors, and interferons. Each of these compounds apparently acts through different pathways, and their activity may be greatly amplified when they are used in combination. Just as the practical usefulness of all-trans-retinoic acid in combination with conventional treatments continues to evolve, the use of differentiation agents in combination represents a novel and promising approach for oncologic therapy in the next decade. Although acute promyelocytic leukemia remains an "orphan" disease, its importance as a model for human neoplasia should not be minimized. The specific molecular lesion of acute promyelocytic leukemia is not shared by other cancers, but the physiologic actions of retinoids, their documented cytodifferentiating activity against a variety of human cancer cells in vitro, and their usefulness in cancer chemoprevention are clearly not mediated by identifiable mutations of retinoid receptors. The insights into transformation and leukemogenesis gained in acute promyelocytic leukemia may be a harbinger of further clinical applications and offer a glimpse into the next generation of cancer therapy.

Retinoids for the future: oncology

A major incentive for the development of the synthetic retinoids has been their potential for the treatment and prevention of cancer. Early studies demonstrated that treatment with isotretinoin or etretinate alone could result in the regression of some existing skin cancers. However, even at high doses the response rates were poor. Greater efficacy has been observed with retinoids used in the prevention of cancer of the skin and oral cavity in high-risk patients. The potential for retinoids as chemopreventive agents is being further explored as selected retinoids are being targeted to specific malignancies, such as fenretinide for breast cancer chemoprevention. The effectiveness of tretinoin as a treatment for promyelocytic leukemia has raised enthusiasm for retinoids as cancer therapeutic agents. Furthermore, evidence of synergy between the retinoids and a variety of cytokines as enhances of differentiation chart a bright future for retinoids in oncology.