Liposomal All-trans Retinoic Acid Research Articles

Delivery of all-trans-retinoic-acid (ATRA) in liposomes modulated MDSCs and T-cell activities in the tumor microenvironment.

e15644 Background: All-Trans-Retinoid-Acid (ATRA) is a naturally occurring vitamin A metabolite that participates in many biological processes. Beside its highly potent effect of promoting terminal differentiation of acute promyelocytic leukemia blasts into mature granulocytes, there have been many other studies suggesting its activity on the myeloid derived suppressor cells (MDSCs) and tumor specific CD8+ T cells in animal models as well as using clinical samples. But the use of ATRA as an immune-oncological agent in solid tumor therapy has been limited by the very poor solubility of the compound, its fast metabolism, and very limited exposure achieved after oral administration. Methods: We prepared a new dosage form by encapsulating ATRA inside PEGylated liposomes. The liposomes were shown to accumulate inside solid tumor tissues and deliver more ATRA with longer duration. Results: The effect and dose response of the liposomal ATRA on CT26 murine tumor growth were examined, as well as specific molecular signatures concerning tumor infiltrating myeloid cells. Notably, there was significant higher expression of CD86 and lower expression of PD-L1. These myeloid cells had very low inhibitory effect on ex vivo activated T cells, while on the other hand could promote specific antigen presentation to amplify CD8+ T cells. Furthermore, the liposomal ATRA was also shown to synergize with anti-PD-1 treatment to result in more CD8 T cell distribution in the tumor tissues. Conclusions: These data may suggest an exciting opportunity for targeting MDSCs using liposomal ATRA for combination with T cell based therapeutics in cancer immunotherapy.

Single-Agent Liposomal All-Trans-Retinoic Acid as Initial Therapy for Acute Promyelocytic Leukemia: 13-Year Follow-Up Data

Clinical significance of all-trans retinoic acid (ATRA) in the initial therapy of acute promyelocytic leukemia (APL) is well established.[1],[2] Non-chemotherapeutic strategies have been sought to treat APL in order to avoid the adverse effects of chemotherapy.[3–6] Here, we report the 13 year follow up of a study of single agent liposomal-encapsulated ATRA in the frontline therapy of patients with APL[7]; the data were last updated in 2006.[8] Better pharmacokinetic data with liposomal ATRA [9] as compared with oral ATRA led to this study. The baseline characteristics of the 34 patients enrolled as well as the treatment protocol have been described previously. The complete remission (CR) rates were 79% (27/34) overall, and 92% (24/26) and 38% (3/8) among the low risk (with initial WBC counts <10,000) and in high risk (WBC ≥ 10,000) patients respectively (Table 1). Similar results were observed with respect to molecular response. The median time to hematological and molecular CR was 35 days (range, 24 – 64 days), and 123 days (range, 62 – 133 days), respectively. 27 patients achieved CR and one was lost to follow up. Among the 26 remaining patients, 24 had a molecular CR by qualitative PCR at 3 months. Eighteen patients maintained molecular remission after a median of 142.7 months (range, 18 – 172 months) after CR despite never having received any other antileukemic therapy. After a median follow up of 154.8 months (1.6–181.9 months), eleven patients have died. 5 of 11 deaths (45%) were early and 3 (30%) were due to cerebral hemorrhage. There were 8 relapses (6 alive, 2 dead), and a total of 17 events. The 13-year event-free survival (EFS), disease free survival (DFS) and overall survival (OS) were 46%, 69% and 65% respectively (Figure 1). The EFS and DFS were similar between low and high risk groups, while OS (not shown) was significantly longer in the low risk group (p=0.01). Since the study is limited by the small number of patients with disproportionate distribution among the low and high risk categories, the survival analyses among the risk categories may not be conclusive. Although, 8 patients who relapsed had low risk and none with high risk category relapsed, no definitive conclusions can be made due to the small number of patients. The eight relapses occurred after a median DFS of 11.9 months (range, 5–29 months) and six of the patients who relapsed were in molecular CR prior to relapse. Two relapsed patients underwent stem cell transplantation following salvage therapy with ATO, ATRA, ATO+ATRA, or ATO+ATRA+gemtuzumab ozogamicin, and both remain in remission at 11 and 12 years. Sixteen of the 18 patients who remain in molecular remission had low risk disease. None of the patients had any long term toxicities, in particular secondary myelodysplastic syndrome or AML, second malignancies or cardiotoxicity. These long term data suggest that liposomal ATRA is safe and has significant efficacy in patients with APL, even as monotherapy. We propose that liposomal ATRA is a potential lifesaving alternative to oral ATRA in situations where oral administration is difficult. Prospective studies (with larger cohorts of patients) combining liposomal ATRA with ATO in the frontline setting are warranted. Figure 1 Table -1 Distribution of patients among low and high risk categories

Phase I trial of ATRA-IV and depakote in patients with advanced solid tumor malignancies

Retinoic acid derivatives have shown their greatest benefit in acute promyelocytic leukemia, but have also demonstrated pre-clinical anti-cancer effects in some solid tumors. Histone deacetylase inhibitors, by up-regulating gene expression, are able to limit cancer cell proliferation and induce apoptosis. The combination of all-trans retinoic acid (ATRA) and the histone deacetylase inhibitor valproic acid has been previously studied in hematologic malignancies. We conducted a phase I two-step dose escalation trial of the liposomal ATRA analog ATRA-IV and divalproex sodium (Depakote

Incidence, Clinical Features and Outcome of Patients with Differentiation Syndrome in Acute Promyelocytic Leukemia Treated with All-Trans Retinoic Acid (ATRA) Alone Versus ATRA Plus Idarubicin Versus ATRA Plus Arsenic Trioxide.

Abstract 1044Poster Board I-66 Background:Differentiation Syndrome (DS) in patients (pts) with acute promyelocytic leukemia (APL) remains a source of significant morbidity and mortality. DS is reported in 2-27% of pts with newly diagnosed APL treated with all-trans retinoic acid (ATRA) alone or in combination with idarubicin (IDA). More recently, arsenic trioxide (ATO) has been used in combination with ATRA as frontline therapy to improve rates of complete remission (CR) and overall survival (OS). It has been postulated that with the use of ATO, the risk of DS may decrease. AimTo describe the incidence, characteristics and outcome of differentiation syndrome with various modalities of ATRA-based therapy used for APL. Methods:We reviewed the records of 167 pts with newly diagnosed APL treated at our institution from 1992-2009 with three regimens: ATRA + IDA (Group 1), liposomal ATRA (Group 2) and ATRA plus ATO (Group 3). Patients in Group 1 (n=52; 1992-1997) received induction with ATRA 45mg/m2 orally daily in two divided doses until CR and IDA 12mg/m2 IV daily for 4 days. Group 2 (n=34; 1997-2000) received liposomal ATRA at 90mg/m2 IV every other day until CR. Patients in Group3 (n=82; 2002-2009) received 45mg/m2 ATRA orally daily in two divided doses, 9mg/m2 gemtuzumab ozogamicin if the WBC count exceeded 30 ×109/L in the first 4 weeks of therapy, ATO 0.15mg/kg/day IV starting on day 10 in 47 patients and on day 1 in 35 patients, and methylprednisolone (50 mg daily for 5 days) to prevent DS. A diagnosis of DS was made by the presence of: dyspnea, unexplained fever, weight gain, peripheral edema, unexplained hypotension, acute renal failure or congestive heart failure, and particularly by a chest radiograph demonstrating interstitial pulmonary infiltrates, or pleuropericardial effusion [Sanz MA, Blood. 2009;113(9):1875-91].Patients with ≥4 features were classified as having severe DS and those with ≤3 mild DS. No single sign or symptom was considered sufficient for diagnosis of DS. Patients with a final diagnosis of pneumonia, sepsis, diffuse alveolar hemorrhage and decompensated heart failure were not considered to have DS. Patients who developed DS ≤7 days of starting therapy with ATRA were classified as “early DS” and others as having “late DS”. Results:Forty one patients (24%) were diagnosed with DS: 14 (27%) in Group 1, 12 (35%) in Group 2, and 15 (18%) in Group 3. Baseline characteristics of patients with DS in each group are shown in Table. Dyspnea, weight gain and pulmonary infiltrates were the most common features of DS in all groups. The median number of days to develop DS after starting ATRA was 3 (1-15) in Group 1, 5 (2-18) in Group 2 and 10 (1-18) in Group 3. ATRA was held in 8 pts (57%) in Group 1, 9 pts (75%) in Group 2, and 8 pts (53%) in Group 3. Intravenous corticosteroids were used for treatment of all patients with DS. CR was achieved in 7 (50%) pts in group 1, 10 (83%) in Group 2 and 14 (93%) in Group 3. The number of patients who died during induction therapy was 6, 2 and 1 in Groups 1, 2 and 3 respectively. There were no deaths directly attributable to DS in any groups. Three-year survival was 65% for pts with DS and 83% for those without DS (p-value: 0.07). Conclusion:The incidence of DS is higher when ATRA alone is used as frontline therapy for APL. With ATRA + ATO (and prophylaxis with corticosteroids) there is a trend for decreased frequency and more delayed occurrence of DS. The severity of DS appears lower for patients not receiving chemotherapy with ATRA. With adequate management, a diagnosis of DS during induction therapy for APL does not influence outcomes independent of therapy.CharacteristicsGroup 1Group 2Group 3TotalDS14/52 (27%)12/34 (35%)15/82 (18%)41/167 (24%)Median age, yrs (range)42 (22-67)37 (10-77)45 (18-74)43 (10-77)Sex (M/F)8/67/58/723/18ECOG*0-16 (43)6 (50)13 (87)25 (61)2-38 (57)6 (50)2 (13)16 (39)WBC (K/μL)< 107 (50)8 (67)9 (60)24 (59)≥ 107 (50)4 (33)6 (40)17 (41)Platelets (K/μL)< 406 (43)9 (75)9 (60)24 (59)≥ 408 (57)3 (25)6 (40)17 (41)SeverityMild7 (50)7 (58)6 (40)20 (49)Severe7 (50)5 (42)9 (60)21 (51)Time course*Early12 (86)8 (67)6 (40)26 (63)Late2 (14)4 (33)9 (60)15 (37)Median time to develop DS*, days3 (1-15)5 (2-18)10 (2-18)4 (1-18)ATRA held8 (57)9 (75)8 (53)25 (61)Dialysis*3 (21)0 (0)1 (7)4 (10)Ventilation*6 (43)1 (8)2 (13)9 (22)*p-value <0.05; otherwise all NS Disclosures:Ravandi:Cephalon: Consultancy, Honoraria.

Retinoic acid syndrome: a review

The retinoic acid syndrome (RAS) is an unpredictable but frequent complication which may develop after administration of all-trans retinoic acid (ATRA) most commonly in patients with acute promyelocytic leukaemia (APL). In this review, we describe the incidence, predictive factors, clinical course, outcome and treatment of RAS in patients with APL treated with ATRA. The incidence of RAS in patients receiving ATRA is about 14-16%, with an associated mortality of about 2%. Initial high white blood cell (WBC) count, rapidly increasing WBC count and/or the presence of the CD 13 expression on leukaemic cells may help in identifying patients likely to develop RAS. Concurrent chemotherapy will probably decrease the risk of developing RAS but often exacerbates bleeding, leading to leucocytosis, thrombocytopenia, disseminated intravascular coagulation and fibrinolysis. Prophylactic steroids are not recommended but prompt administration of steroids at the first sign of unexplained dyspnea, fever, weight gain or pulmonary infiltrate, is critical. Liposomal ATRA is being investigated to induce haematological cure in APL without chemotherapy and to reduce the incidence of RAS but further validation of its usefulness is necessary.

Single-agent liposomal all-trans retinoic acid can cure some patients with untreated acute promyelocytic leukemia: an update of The University of Texas M. D. Anderson Cancer Center Series

The present study aimed to investigate single-agent liposomal all-trans retinoic acid (Lipo-ATRA) in untreated acute promyelocytic leukemia (APL). Induction therapy consisted of Lipo-ATRA 90 mg/m2 i.v. every other day. Patients in complete remission (CR) continued to receive Lipo-ATRA 90 mg/m2 i.v. three times a week for 9 months. Idarubicin was added only if a polymerase chain reaction test for promyelocytic leukemia-retinoic acid receptor alpha (sensitivity level, 10−4), performed every 3 months from CR, was positive. The results were compared with those of a historical control group treated with oral ATRA and idarubicin. Lipo-ATRA induced CR in 79% of patients; CR rates were 92% and 38% in patients with white blood cell (WBC) counts <10 × 109/L and >10 × 109/L, respectively. Ten of the 26 responders to Lipo-ATRA remain in first CR at a median of 6.4 years, despite never receiving idarubicin; all 10 had initial WBC counts <10 × 109/L. The 5-year survival rate was 76% for patients treated with Lipo-ATRA. Comparisons with oral ATRA+idarubicin as given at M. D. Anderson are confounded because of their historical nature and the absence of ATRA from post-remission therapy in the former group. Nonetheless, a multivariate Cox model identified higher WBC counts and older age, but not treatment (historical vs. Lipo-ATRA), as being predictive of shorter relapse-free and overall survival. Lipo-ATRA can cure patients presenting with WBC counts <10 × 109/L (low risk) without additional therapy, contrary to conventional ATRA, which, when given alone, probably cures no patients. The observation that patients can be cured of APL without the use of chemotherapy should encourage further study of ‘targeted’ therapy in APL and in other leukemias.

Regulation of a highly specific retinoic acid-4-hydroxylase (CYP26A1) enzyme and all-trans-retinoic acid metabolism in human intestinal, liver, endothelial, and acute promyelocytic leukemia cells

The recently identified retinoic acid (RA)-metabolizing cytochrome P450RAI-1 (CYP26A1) has been implicated in accelerated metabolism and rapid clearance of all-trans-retinoic acid (ATRA) during prolonged oral administration in patients with acute promyelocytic leukemia (APL), leading to a progressive decline in plasma drug levels. We studied induction and regulation of CYP26A1 expression and ATRA metabolism in human intestinal (Caco-2), liver (HepG2), endothelial (HUVEC), and APL (NB4) cell lines. ATRA rapidly induced upregulation of CYP26A1 mRNA expression in a dose-dependent manner. Other retinoids (retinol, 9-cis-RA, and 13-cis-RA) also induced significant CYP26A1 expression in HepG2 and NB4 cells. CYP26A1 mRNA expression in HepG2 cells returned to baseline in 48 h upon removal of ATRA from the culture medium, suggesting that the expression is reversible and requires the presence of ATRA. In endothelial cells, however, a higher concentration of ATRA (10 μM) was required to induce expression of CYP26A1. A specific RA receptor-α antagonist totally inhibited ATRA-induced expression of CYP26A1, indicating that RA receptor-α plays a major role in CYP26A1 expression in HepG2 cells. Liposomal incorporation of ATRA has been shown to alter its metabolism. Therefore, we also tested CYP26A1 expression after administration of free ATRA and liposomal ATRA (L-ATRA). L-ATRA induced lower CYP26A1 expression and metabolic activity in HepG2 and NB4 cells when compared with free ATRA. Pretreatment of cells with free ATRA resulted in higher metabolic activity as indicated by conversion of radiolabeled [3H]-ATRA into its metabolites (4-oxo-RA and 4-hydroxy-RA), which was associated with lower nuclear localization of [3H]-ATRA when compared with pretreatment with L-ATRA. Our data suggest that upregulation of CYP26A1 expression in intestinal, endothelial, liver, and APL cells and metabolism of ATRA may play a role in rapid clearance of ATRA after continuous oral administration. Therapeutic strategies such as liposomal encapsulation and intermittent administration of ATRA may circumvent accelerated ATRA metabolism and improve the treatment of APL.

Management of APL

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 more than 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 to ATRA, 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 (ATO) will be the treatment of choice under careful electrocardiogram monitoring. Am80, liposomal ATRA or gemtuzumab ozogamicin may be used at this stage or later. Whether ATO may be used for newly diagnosed APL should wait for the results of on-going randomized trials, and probably for the long-range outcome including possible secondary malignancy due to ATO. Allogeneic stem cell transplantation will be the treatment of choice after patients of age B/50 years have relapsed, provided that they have HLA-identical family donors or DNAidentical unrelated donors.

Single Knock-In PML-RARα Expressing Murine APL Tumors Provide a Unique Model for Studying In Vivo Sensitivity and Resistance to ATRA and Arsenic Trioxide.

Although approximately 70% of patients with acute promyelocytic leukemia (APL) are cured after treatment with all-trans retinoic acid (ATRA) and anthracycline based chemotherapy, those who relapse cannot be cured even with chemotherapy or arsenic trioxide salvage therapy. In order to study the molecular mechanisms of resistance to ATRA, liposomal ATRA, and arsenic trioxide, we have utilized a murine model of APL generated by “knocking in” the PML/RARα gene into the murine cathepsin G locus (Westervelt et al. Blood. 102(5):1857). Of the 76 single knock-in (SKI) mice followed for a median time of 368 days, 30 (39%) suffered from rapid-onset leukocytosis, anemia, thrombocytopenia, and hepato-splenomegaly. Spleens from these leukemic animals were removed and the tumors cells (> 90% CD34+/Gr-1+ APL cells) were frozen in aliquots and banked for future passive transfer into genetically compatible recipients. The SKI mice exhibited the expected median time to death of 222 days. Attempts to expand these tumors in vitro failed, thus precluding the use of in vitro methods to generate ATRA and arsenic resistant SKI APL tumor cells. An alternate in vitro model of identifying de novo resistant SKI APL tumors to the drugs was established by incubating individual SKI APL tumors with ATRA, liposomal ATRA, and arsenic in vitro for only 3 days and using ELISA to measure upregulation of MMP-9 (gelatinase B), a surrogate marker for neutrophil differentiation. ATRA, liposomal ATRA, and arsenic induced 6.2 ± 4.4, 5.7 ± 3.5, 1.7 ± 1.0 fold increase in accumulated levels of MMP-9, respectively. These data suggest that ATRA and liposomal ATRA are more potent inducers of terminal differentiation than arsenic in these APL tumors. More importantly, the SKI APL tumors were also assessed for in vivo resistance to these agents by injecting 1 x 106 banked APL tumor cells into the peritoneal cavity of wild-type genetically compatible mice. The mice were then treated i.p. with either arsenic trioxide (0.4 mg q.d.), liposomal ATRA (0.4 mg q.d.), or diluent control. Doses were administered daily starting on day +5 until death. Tumors in the recipient mice were tracked by PCR for the transgene and FACS. The tumors proliferated in the peritoneal cavity (days 1–14) followed by migration to the bone marrow and spleen (days 14–28). By the eighth week post-injection, all mice suffered from leukocytosis and eventually died. Of the 22 banked tumors studied, only two tumors showed de novo resistance to ATRA both in vitro and in vivo. We will present data on preliminary RNA profiling and DNA sequencing of the PML-RARα transgenes in these APL tumors and attempt to correlate these results and the results of in vitro induction of MMP-9. The SKI APL tumors will provide us with unique reagents to study the biology of resistance to ATRA and arsenic trioxide.

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.

Liposomal-all-trans-retinoic Acid in Treatment of Acute Promyelocytic Leukemia

Acute promyelocytic leukemia (APL) characterized by the translocation t(15;17) is uniquely sensitive to the differentiation-inducing effects of all-trans-retinoic acid (ATRA). All-trans-retinoic acid therapy induces complete clinical remissions (CRs) in most of patients with APL. However, chronic daily oral administration of ATRA results in accelerated metabolism of ATRA, leading to a progressive decline in plasma drug concentrations. These lower drug levels are associated with relapses and resistance to oral ATRA in patients with APL; thus the use of ATRA as a single agent is precluded. Liposomal ATRA (Lipo-ATRA) was designed to maintain high and stable plasma concentrations and to further improve the outcome of the APL disease by overcoming the development of ATRA resistance. Liposomal ATRA was shown to circumvent accelerated drug metabolism in the liver of rats in an animal model. In a phase I clinical study, intravenous (i.v.) administration of lipo-ATRA was shown to produce a significantly better pharmacokinetic profile than oral ATRA (non-liposomal) and to maintain higher and sustained plasma drug concentrations, with a similar side effects. More importantly, lipo-ATRA as a single agent induces PCR-negative molecular remissions in a high proportion of newly diagnosed patients with APL and maintain remissions up to 15–17 months or longer. In this review, we discuss the pharmacological features of lipo-ATRA and the molecular remissions induced by lipo-ATRA in newly diagnosed patients with APL or patients previously treated with ATRA or chemotherapy, and the possible impact of lipo-ATRA on the outcome of APL.

All Trans-Retinoic Acid Selectively Down-Regulates Matrix Metalloproteinase-9 (MMP-9) and Up-Regulates Tissue Inhibitor of Metalloproteinase-1 (TIMP-1) in Human Bronchoalveolar Lavage Cells

The balance between proteinases and antiproteinases plays an important role in tissue destruction and remodelling. In chronic obstructive pulmonary disease (COPD) and emphysema, an imbalance between matrix metalloproteinases (MMPs) and inhibitors of tissue metalloproteinase (TIMPs) has been reported. Alveolar macrophages are considered to be the main source of MMPs. We therefore have analyzed the effects of free and liposomal all trans-retinoic acid (ATRA) on the expression of MMP-9 and TIMP-1 in bronchoalveolar lavage (BAL) cells from patients with COPD and patients with other lung diseases. BAL cells were incubated 1-3 day with either liposomal or free ATRA. Supernatants were tested for MMP-9 and TIMP-1 protein in specific ELISA systems; mRNA analysis was performed by semi-quantitative RT-PCR and by quantitative LightCycler PCR. We demonstrate that either liposomal or free ATRA selectively down-regulates MMP-9 and up-regulates TIMP-1. At the protein level, MMP-9 is decreased 3-fold and TIMP-1 is increased 3.5-fold compared to the base line with empty liposomes or untreated cells. The ratio of MMP-9 and its inhibitor TIMP-1, which may be crucial to the overall proteolytic potential decreased by factor 8. That this countercurrent effect of ATRA is not due to an altered protein stability but to transcriptional regulation could be demonstrated by RT-PCR. Quantitative LightCycler analysis revealed a 2.5-fold decrease of MMP-9 mRNA and a 4.5 fold increase of TIMP- 1 mRNA. These data suggest that ATRA treatment via its impact on the proteinase/antiproteinase ratio may become a new therapeutic strategy for patients with inflammatory destructive lung diseases.

Treatment of newly diagnosed and relapsed acute promyelocytic leukemia with intravenous liposomal all-transretinoic acid

AbstractA novel intravenous liposomal formulation of all-transretinoic acid (ATRA) was evaluated in 69 patients with acute promyelocytic leukemia (APL): 32 new diagnoses, 35 relapses, and 2 oral ATRA failures. Liposomal ATRA (90 mg/m2) was administered every other day until complete remission (CR) or a maximum of 56 days. Treatment following CR was liposomal ATRA with or without chemotherapy. In an intent-to-treat (ITT) analysis of all patients, CR rates were 62%, 70%, and 20% in newly diagnosed, group 1 first relapses (ATRA naive or off oral ATRA more than or equal to 1 year), or group 2 relapses (second or subsequent relapse or first relapses off oral ATRA less than 1 year), respectively. In 56 evaluable patients (receiving 4 or more doses), CR rates for the same groups were 87% (20 of 23), 78% (14 of 18), and 23% (3 of 13). Remission failure in newly diagnosed patients was not from resistant disease. Several patients in CR became polymerase chain reaction (PCR) negative for promyelocytic leukemia/retinoic acid receptor-alpha (PML/RARα) after liposomal ATRA alone. Toxicity was generally mild, most commonly headaches (67.5%). Eighteen patients (26%) had ATRA syndrome develop during induction. One-year survival of ITT patients was 62%, 56%, and 20% for newly diagnosed, group 1, and group 2, respectively. The medium duration of CR has not yet been reached and was 18 and 5.5 months in the same groups. These results demonstrate that liposomal ATRA is effective in inducing CR in newly diagnosed or group 1 APL patients. It provides a reliable dosage of ATRA for patients with APL unable to swallow or absorb medications and can induce molecular remissions without chemotherapy.

Treatment of Newly-Diagnosed Acute Promyelocytic Leukemia with Liposomal All-Trans Retinoic Acid

It has been postulated that recurrence of disease in some patients with newly-diagnosed APL induced into CR, and subsequently maintained, with single agent oral ATRA results from the decline in ATRA levels that occurs with repeated dosing. Administration of liposomal ATRA (lipoATRA) circumvents, for perhaps several months, the decrease in ATRA levels and produces CRs in patients with relapsed APL. These findings led us to administer lipoATRA “monotherapy” to patients with newly-diagnosed APL. Patients received lipoATRA (90 mg/m2) for induction and continued to receive the drug, by itself, for 9 months unless 2 PCR tests done within 2–4 weeks of each other at a sensitivity level of 10 (-4) were positive at 3 or 6 months from CR date, in which case idarubicin was added to lipoATRA. If the PCR test was negative 9 months from CR date, treatment stopped. 34 patients were enrolled, of whom 79% entered CR. The PCR test at time of CR was positive in 23/24 patients, but was negative in 24/26 (92%) 3 months later. Of most interest 11 of the 26 evaluable responding patients have remained PCR negative (tested Q 3 months) with a median follow-up of 18 months (range up to 34 months). It is generally believed that this type of result would be unlikely with oral ATRA monotherapy. Recurrence of morphologic APL has occurred in 4 patients, at 5,6,12, and 12 months, with a median follow-up time of 18 months in the patients remaining alive in CR. Comparison of this lipoATRA +/- idarubicin trial with oral ATRA + idarubicin induction and idarubicin + POMP maintenance, our previous trial, indicates similar survival, CR, and DFS in CR rates, with a suggestion that lipoATRA may produce lower CR rates and hence shorter survival in patients with high-risk disease (wbc count > 10,000/μl. Nonetheless, the rates and duration of PCR negativity produced by lipoATRA monotherapy suggest that lipoATRA is a superior anti-APL agent man oral ATRA.

Differences in the lipoprotein distribution of free and liposome-associated all-trans-retinoic acid in human, dog, and rat plasma are due to variations in lipoprotein lipid and protein content.

The objective of the proposed study was to determine the distribution in plasma lipoprotein of free all-trans retinoic acid (ATRA) and liposomal ATRA (Atragen; composed of dimyristoyl phosphatidylcholine and soybean oil) following incubation in human, rat, and dog plasma. When ATRA and Atragen at concentrations of 1, 5, 10, and 25 micrograms/ml were incubated in human and rat plasma for 5, 60, and 180 min, the majority of the tretinoin was recovered in the lipoprotein-deficient plasma fraction. However, when ATRA and Afragen were incubated in dog plasma, the majority of the tretinoin (> 40%) was recovered in the high-density lipoprotein (HDL) fraction. No differences in the plasma distribution between ATRA and Atragen were found. These data suggest that a significant percentage of tretinoin associates with plasma lipoproteins (primarily the HDL fraction) upon incubation in human, dog, and rat plasma. Differences between the lipoprotein lipid and protein profiles in human plasma and in dog and rat plasma influenced the plasma distribution of ATRA and Atragen. Differences in lipoprotein distribution between ATRA and Atragen were not observed, suggesting that the drug's distribution in plasma in not influenced by its incorporation into these liposomes.

Liposome encapsulation circumvents the hepatic clearance mechanisms of all- trans-retinoic acid

All- trans-retinoic acid (ATRA) has been proven active against a range of malignancies in isolated tissue culture systems and in human clinical trials, but the duration of its effects has been transient. Recent evidence indicates that the basis for the limited duration of ATRA's activity, at least in one form of leukemia, is a pharmacological adaptation that results in reduced serum concentration after prolonged treatment. This finding suggests that an i.v. formulation of ATRA may significantly improve the potency and duration of ATRA's activity in leukemia and, potentially, other malignancies as well. Liposomal ATRA (L-ATRA) was developed to provide a formulation of this retinoic acid isomer that can be administered intravenously to provide potential pharmacological advantages over the oral formulation. When L-ATRA was administered to rats over a prolonged period, the blood levels of the drug did not change over time. In vitro studies of isolated liver microsomes revealed that catabolism of the drug was not altered in rats that were repeatedly administered the L-ATRA formulation. Whereas microsomes isolated from animals that were orally administered free ATRA the same number of times with the same doses showed a significant increase in metabolism of the drug. These results suggest that an i.v. formulation of ATRA such as L-ATRA could be extremely useful in inducing long-term remissions in patients with APL.