Leukemia
Hematological Malignacy

Author: Gianpiero Pescarmona
Date: 12/08/2007

Description

Leukemia or leukaemia (Greek leukos λευκός, "white"; aima αίμα, "blood") is a cancer of the blood or bone marrow and is characterized by an abnormal proliferation (production by multiplication) of blood cells, usually white blood cells (leukocytes)
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E' stata identificata una lesione oncogenica che accompagna la trasformazione da leucemia mielogena cronica (CML) a leucemia linfoblastica acuta (ALL). L'anomalia cromosomica che definisce la CML è chiamata cromosoma Filadelfia, ed è il risultato di una traslocazione genica descritta la prima volta nel 1960 da ricercatori di questa città. Nel 1973 è stato scoperto che questa anomalia deriva da uno scambio di materiale genetico fra i bracci lunghi dei cromosomi 9 e 22. Circa il cinque percento dei casi pediatrici ed il 40 percento di quelli adulti di ALL presentano il cromosoma Filadelfia. Se la CML non viene trattata, evolve in una forma di leucemia blastica di impronta mieloide o linfoide, anche se la frequenza della conversione è stata ridotta dall'avvento di farmaci che inibiscono la tirosin-chinasi prodotta dal cromosoma Filadelfia. Sfortunatamente, i farmaci che sono efficaci nella fase cronica della CML potrebbero non produrre risposte prolungate nell'ALL. L'identificazione del coinvolgimento della delezione denominata Ikaros nell'ALL suggerisce che mirare a queste cascate potrebbe essere un approccio valido per il miglioramento della risposta nel trattamento di queste leucemie. Si tratta comunque di di mutazioni che comportano la perdita della funzionalità, forse meno trattabili farmaceuticamente di quelle che determinano un'attivazione costitutiva. (Nature online 2008, pubblicato il 14/4)

Comments
2012-06-30T08:23:41 - Luca Lo Sardo

Interaction between p38α MAPK and retinoids used to treat Acute Myeloid Leukemia

The retinoids, used in medicine in the regulation of epithelial cell growth, are compounds related chemically to Vitamin A. They have important functions throughout the body including roles in vision and regulation of cell proliferation and differentiation. There are three generations of retinoids:

° First generation retinoids ( retinol, retinal etc)
° Second generation retinoids (etretinate and acitretin)
° Third generation retinoids ( tazarotene, bexarotene and adapalene )

The basic structure of the hydrophobic retinoid molecule consists of a cyclic end group, a polyene side chain and a polar end group.

Figure Retinoids

All trans retinoic acid in acute promyelocytic leukemia, 2001
All trans retinoic acid (ATRA)can induce complete remission in patients with APL, that is the acute promyelocytic leukemia. It's important that this therapy is used in combination with anthracycline-based chemotherapy in order to be effective. Has been clearly shown that the combination of ATRA and chemotherapy gives better survival in newly diagnosed APL than chemotherapy alone because of fewer relapses; more than 90% of patients with newly diagnosed APL can achieve the complete remission and about 75% can be cured by this combination.

A coordinated phosphorylation cascade initiated by p38MAPK/MSK1 directs RARα to target promoters, 2008
The RARα (nuclear retinoic acid receptor alpha) controls the expression of specific genes through binding at response elements and interactions with coregulators. The transcription of RARα target genes is controlled by phosphorylation cascades that start with the activation of the p38MAPK/MSK1 pathway by Acid retinoic. MSK1 phosphorylates RARα in the ligand-binding domain, allowing the binding of TFIIH and thereby phosphorylation of the N-terminal domain by cdk7/cyclin H. So the phosphorylation cascade started by MSK1 controls the RARα target gene activation. Cancer cells characterized by a deregulated p38MAPK/MSK1 pathway, do not respond to RA, outlining the essential contribution of the RA-triggered phosphorylation cascade in RA signalling.

Figure Phosphorylation cascade induced by RA, 2008

The suppression of P38αMAPK enhances the therapeutic activity of retinoids in AML, 2012
P38MAPK interacts with RARα and the suppression of this interaction enhances the therapeutic activity of retinoids in acute myeloid leukemia cells. In fact all-trans retinoic acid (ATRA)is used in the treatment of acute promyelocytic leukemia (APL) and in other types of acute myelogenous leukemia (AML) and inhibition of the genic expression of this protein kinase, p38α, favors the anti-proliferative activity of ATRA and synthetic retinoids. P38α inhibits transactivation of the nuclear retinoic acid receptor, RARα, and the derived protein expressed in the majority of APL cases. Inhibition is the consequence of ligand-independent binding of p38α, which results in stabilization of RARα and PML-RARα via blockade of their constitutive degradation by the proteasome. The inhibitory effect requires a catalytically active p38α and direct physical interaction with RARα and PML-RARα.

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