We studied the effects of rapamycin on cultures of erythroid progenitors derived from the peripheral blood of 10 beta-thalassaemia patients differing widely with respect to their potential to produce foetal haemoglobin (HbF). For this, we employed the two-phase liquid culture procedure for growing erythroid progenitors, high performance liquid chromatography for analysis of HbF production and reverse transcription polymerase chain reaction for quantification of the accumulation of globin mRNAs. The results demonstrated that rapamycin induced an increase of HbF in cultures from all the beta-thalassaemia patients studied and an increase of their overall Hb content/cell. The inducing effect of rapamycin was restricted to gamma-globin mRNA accumulation, being only minor for beta-globin and none for alpha-globin mRNAs. The ability of rapamycin to preferentially increase gamma-globin mRNA content and production of HbF in erythroid precursor cells from beta-thalassaemia patients is of great importance as this agent (also known as sirolimus or rapamune) is already in clinical use as an anti-rejection agent following kidney transplantation. These data suggest that rapamycin warrants further evaluation as a potential therapeutic drug in beta-thalassaemia and sickle cell anaemia.

Summary.The human leukaemic K562 cell line can be induced in vitro to undergo erythroid differentiation by a variety of chemical compounds, including haemin, butyric acid, 5-azacytidine and cytosine arabinoside. Differentiation of K562 cells is associated with an increased expression of embryo-fetal globin genes, such as the z, e and g globin genes. Therefore the K562 cell line has been proposed as a useful in vitro model system to determine the therapeutic potential of new differentiating compounds as well as to study the molecular mechanism(s) regulating changes in the expression of embryonic and fetal human globin genes. Inducers of erythroid differentiation which stimulate gglobin synthesis could be considered for possible use in the experimental therapy of those haematological diseases associated with a failure in the expression of adult b-globin genes. In this paper we demonstrated that the G þ C selective DNA-binding drugs chromomycin and mithramycin were powerful inducers of erythroid differentiation of K562 cells. Erythroid differentiation was associated with an increase in the accumulation of (a) Hb Gower 1 and Hb Portland and (b) g-globin mRNA.

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Peptide nucleic acids (PNAs) are DNA-mimicking molecules in which the sugar-phosphate backbone is replaced by a pseudopeptide backbone composed of N-(2-aminoethyl)glycine units. We determined whether double-stranded molecules based on PNAs and PNA-DNA-PNA (PDP) chimeras could be capable of stable interactions with nuclear proteins belonging to the Sp1 transcription factor family and, therefore, could act as decoy reagents able to inhibit molecular interactions between Sp1 and DNA. Since the structure of PNA/PNA hybrids is very different from that of the DNA/DNA double helix, they could theoretically alter the molecular structure of the double-stranded PNA-DNA-PNA chimeras, perturbing interactions with specific transcription factors. We found that PNA-based hybrids do not inhibit Sp1/DNA interactions. In contrast, hybrid molecules based on PNA-DNA-PNA chimeras are very effective decoy molecules, encouraging further experiments focused on the possible use of these molecules for the development of potential agents for a decoy approach in gene therapy. In this respect, the finding that PDPbased decoy molecules are more resistant than DNA/ DNA hybrids to enzymatic degradation appears to be of great interest. Furthermore, their resistance can even be improved after complexation with cationic liposomes to which PDP/PDP chimeras are able to bind by virtue of their internal DNA structure.In vitro transfection of cis elements that decoy against nuclear factors leads to alteration of gene expression and was recently proposed in molecular medicine as a novel tool for the possible therapy of several disorders (1-12). One of the most effective decoy approaches so far described involves nuclear proteins belonging to the NF-B 1 superfamily (7-9, 13-20).Decoy molecules against NF-B inhibit the expression of NF-B regulated genes (MHC complex genes, IL2 receptor ␣, Igk, IL6, ␦ opioid receptor, preprogalanin, adhesion molecule-1) (20). More recently, dumbell DNA decoy elements against NF-B were demonstrated to be active in inhibiting ex vivo transcription driven by the long terminal repeat (LTR) of human immunodeficiency type-1 virus (HIV-1) (19). In addition to proteins belonging to the NF-B superfamily, decoy molecules for other target transcription factors, such as HNF-1, RFX1, nuclear factor YB, E2F, cAMP-response element, and Sp1, were found to be effective (1-6, 10 -12, 21).As to the molecular targets for the decoy approach, proteins belonging to the Sp1 family are of great interest since these transcription factors are involved in the regulation of the expression of several genes relevant to human pathologies, including those encoding vascular endothelial growth factor, plasminogen-activator inhibitor type-1 (PAI-1), COL1A2, urokinase-type plasminogen activator (uPA), and uPA receptor (3,(21)(22)(23)(24)(25). Sp1 binding sites are also present in the HIV-1 LTR (26). Thus, the development of experimental approaches based on Sp1 decoys to modulate the transcription of Sp1-dependent genes appears to be of great interest (3).Rec...

Summary. Human leukaemic K562 cells can be induced in vitro to erythroid differentiation by a variety of chemical compounds, including haemin, butyric acid, 5-azacytidine, cytosine arabinoside, mithramycin and chromomycin, cisplatin and cisplatin analogues. Differentiation of K562 cells is associated with an increase of expression of embryofetal globin genes, such as the z-, 1-and g-globin genes. The K562 cell line has been proposed as a very useful in vitro model system to determine the therapeutic potential of new differentiating compounds as well as to study the molecular mechanism(s) regulating changes in the expression of embryonic and fetal human globin genes. Inducers of erythroid differentiation stimulating g-globin synthesis could be considered for possible use in the therapy of haematological diseases associated with a failure in the expression of normal b-globin genes. We have analysed the effects of tallimustine and distamycin on cell growth and differentiation of K562 cells. The results demonstrated that tallimustine is a potent inducer, while distamycin is a weak inducer, of K562 cell erythroid differentiation. Erythroid differentiation was associated with an increase of accumulation of g-globin mRNA and of production of both haemoglobin (Hb) Gower 1 and Hb Portland. In addition, tallimustine-mediated erythroid induction occurred in the presence of activation of the apoptotic pathway. The reasons for proposing tallimustine as an inducer of g-globin gene expression are strongly sustained by the finding that this compound stimulates fetal haemoglobin production in human erythroid precursor cells from normal subjects.