Strategy for the treatment of acute myelogenous leukemia based on folate receptor β–targeted liposomal doxorubicin combined with receptor induction using all-trans retinoic acid

Abstract

Up-regulation of folate receptor (FR) type-␤ in acute myelogenous leukemia (AML) by all-trans retinoic acid (ATRA) and its restricted normal tissue distribution makes it a potential target for therapeutic intervention. The FR-␤ in peripheral blood granulocytes was unable to bind folate and appeared to have a variant GPI membrane anchor, evident from its insensitivity to phosphatidylinositol-specific phospholipase C but not nitrous acid. Granulocyte FR-␤ lacked mutations, and neither deglycosylation nor detergent solubilization restored folate binding. The posttranslational modification causing its nonfunctionality was evi- IntroductionAcute myelogenous leukemia (AML) is the most common type of acute leukemia in adults. Standard chemotherapy results in a 70% complete remission rate in AML patients. 1 Treatment with drugs such as anthracyclines, however, is associated with severe side effects such as myelosuppression and dose-limiting cardiotoxicity and a high incidence of relapse. 2 Relapsed disease is frequently refractory to chemotherapy and exhibits multidrug resistance (MDR). 3 A potential means of treating AML is by targeted drug delivery through liposomes. Liposomal delivery of drugs has been shown to extend their systemic circulation time, reduce dose-limiting toxicity, and overcome MDR. [4][5][6][7] Liposomal anthracyclines have reached clinical use for the treatment of Kaposi sarcoma 5 and are in clinical trial for solid tumors and leukemias. [8][9][10][11][12][13][14] Liposomal delivery has also been shown to increase anthracycline cytotoxicity in tumor cells exhibiting MDR. 6,7,[15][16][17] The efficacy of liposomal drugs can potentially be further enhanced by selective targeting to tumor cells through a cell surface molecule that is differentially expressed on tumor cells. 18,19 The folate receptor (FR) is a promising target because of its narrow tissue specificity, its overexpression in malignant tissues, and its ability to bind and internalize folic acid conjugates. Of the 3 human folate receptor isoforms, 20-22 2 (FR-␣ and FR-␤) are attached to the cell surface through a glycosyl-phosphatidylinositol (GPI) membrane anchor, 20,23 whereas the third (FR-␥) is constitutively secreted. 24 The expression of FR-␣ in normal tissues is restricted to certain epithelial cells, where it is inaccessible by the circulation. 25,26 FR-␣ is found to be amplified in many epitheliallineage human tumors, including approximately 90% of ovarian carcinomas. [26][27][28][29] A wide variety of experimental therapies, 30 including drug-loaded liposomes, 31-34 have successfully targeted FR-␣ selectively in gynecologic and other tumors. The expression of FR-␤ in normal tissues is restricted to placenta and hematopoietic cells, where it is expressed in the myelomonocytic lineage and is particularly elevated during neutrophil maturation or during monocyte or macrophage activation. 29,35,36 FR-␤ is also known to be expressed in chronic myelogenous leukemia (CML) and in AML. 22,37,38 FR-␤ from membrane preparations from CML and ...

Synthesis and evaluation of a novel ligand for folate-mediated targeting liposomes

“…Liposomes were prepared by thin film hydration followed by polycarbonate membrane extrusion, as described previously (Haran et al, 1993;Pan et al, 2002). DOX was remoteloaded into the liposomes by a transmembrane pH gradient.…”

Resistance to antifolates

“…In contrast, FR-b expression is much more restricted. It appears to be present in some normal cells of myeloid lineage but is highly expressed in myeloid but not lymphoid leukemias (Shen et al, 1994;Reddy et al, 1999;Ross et al, 1999b;Pan et al, 2002). FR-b may have little function in normal myeloid progenitor cells, since receptors on these cells do not appear to bind or transport folate, possibly due to a defect in the GPI membrane anchor (Reddy et al, 1999;Pan et al, 2002).…”

Induction of folate receptor type β in a bone marrow engraftment model of acute myelogenous leukemia

“…2 We have previously reported that the expression of FRb is limited to the myelomonocytic lineage and that its expression is increased during neutrophil maturation and during the activation of macrophage; 3,4 however, among normal hematopoietic cells, only the receptor expressed in activated macrophage is functional in having the ability to bind folate. 4,5 FRb is also expressed in a functional form in approximately 70% of acute myelogenous leukemia (AML) in which it is frequently coexpressed with CD34. 6 These observations suggest that FRb is a potential target for drug delivery to AML cells, but prospects of its clinical utility are limited by the variable and the frequently low expression of the receptor in the leukemic cells of AML patients.…”

“…6 Our previous in vitro studies in both AML cell lines and primary AML cells have demonstrated that all-trans retinoic acid (ATRA) acts directly on the FRb gene to selectively upregulate its expression 6,7 and that this effect is potentiated by innocuous histone deacetylase (HDAC) inhibitors, including valproic acid (VPA). 8 The receptor induction sensitized AML cells to FRtargeted drugs including folate-coated liposomal doxorubicin 5 and the antifolate, dideazatetrahydrofolate. 8 Treatment with ATRA also increased the survival of mice that were injected KG1 AML cells in their peritoneal cavity upon treatment with FR-targeted liposomal doxorubicin.…”

“…8 Treatment with ATRA also increased the survival of mice that were injected KG1 AML cells in their peritoneal cavity upon treatment with FR-targeted liposomal doxorubicin. 5 Combination treatment with innocuous agents that upregulate FRb in AML cells is, therefore, an attractive means of addressing a major limitation of experimental FR-targeted therapies in AML.…”