Pharmacological studies of novel antitumoral compounds

Over the years biomedical research was focused on the development of new anticancer agents able to selectively target cancer cells at low concentration efficacy. Based on the idea that oncogenes and tumour suppressor genes are a critical force in the malignant transformation of cells, research efforts have focused on developing drugs that directly target these genes. In the first study we focused on B-cell acute lymphoblastic leukaemia (B-ALL), that is one of the most common paediatric malignant disorders characterized by an accumulation of B-cell blasts reminiscent of normal stages of differentiation and by infiltration of various extramedullary sites. Excessive cell proliferation induced by aberrant entry into the cell cycle is considered an hallmark of cancer. Recent findings have revealed that CDK4/6 and its regulatory subunit cyclin D1 are potentially oncogenes and are overexpressed in a diverse set of human cancers, including B-cell acute lymphoblastic leukemia (B-ALL). Moreover, CDK6 is essential for MLL-rearranged leukemias. These findings suggest that CDK4/6 may be effective targets for therapeutic intervention. To test this possibility, we have inhibited CDK4 and CDK6 in four cell lines of B-ALL, characterized by different genetic rearrangements, using Ribociclib, an orally bioavailable, small molecule inhibitor of both CDK4 and CDK6. At low concentration, Ribociclib potently inhibit CDK4/6 without induction of apoptosis; therefore, standard treatment for newly diagnosed childhood B-ALL patients includes glucocorticoids (GC) treatment, but the molecular basis of GC sensitivity and resistance remains largely unknown; for this reason we have tested if Ribociclib in combination with Dexamethasone, a glucocorticoid that is currently used as antitumour agent in the treatment of leukemia, may lead to synergistic killing of leukemia cells. B-ALL patients that respond poorly to glucocorticoid therapy when diagnosed are usually predicted to undergo relapse. Therefore, understanding the biological mechanisms underlying this poor responsiveness is crucial for the development of more effective therapies.

Una delle caratteristiche peculiari dei tumori è la deregolazione del ciclo cellulare che porta ad una iperproliferazione con conseguente aumento della tumorigenesi e progressione della malattia. In una cellula tumorale il complesso ciclina D1 CDK4/CDK6 è frequentemente deregolato: la ciclina D1 è overespressa e può essere considerata un potenziale oncogene in molti tumori, la CDK4 e la CDK6 sono anch'esse overespresse; inoltre, la CDK6 è target diretto delle MLL fusion protein in quelle leucemie con riarrangiamento di MLL. Lo scopo dello studio è stato quello di valutare gli effetti dell'inibizione farmacologica della CDK4/CDK6 mediante l'ultilizzo del Ribociclib, un dual inhibitor specifico in fase avanzata di trial in tumori quali breast cancer, mieloma multiplo ecc. Poco si sa nelle leucemie e per questo abbiamo condotto il nostro studio nelle leucemie linfoblastiche acute di tipo B pediatriche (B-ALL). Questo farmaco inibisce potentemente la CDK4/CDK6 senza induzione di apoptosi e abbiamo voluto investigare se questo effetto potesse aumentare l'efficacia di farmaci normalmente utilizzati in terapia, come il desametasone. I pazienti B-ALL che rispondono scarsamente alla terapia con desametasone spesso subiscono una ricaduta. Pertanto, la comprensione dei meccanismi biologici alla base di questa resitenza è fondamentale per lo sviluppo di terapie più efficaci.