Acute lymphoblastic leukemia (ALL) is a malignancy of white blood cells and it is the most common form of cancer in children and can affect patients of all ages. ALL can be classified into B and T cell lineage diseases (or mixed phenotype), with B- ALL having several clinically relevant subtypes with overall survival rate of over 90%. In contrast, no such strong predictive biomarkers exist for T-ALL and despite the increase in survival rates, up to 80-90% among pediatric patients, the prognosis of relapsed T-ALL remains dismal.
Better understanding of the biology of T-ALL, including abnormal activity of transcriptional regulators and derailed cellular signaling, creates a foundation for exploration and discovery of clinically applicable biomarkers and novel targeted treatments.
In order to start uncovering new features and therapies, we investigated gene expression patterns in a large data set of hematological malignancies and observed a high and T-ALL specific expression of tyrosine kinase LCK. In silico analysis, that combined gene expression data with information of drug targets, uncovered a strong inhibition of LCK by tyrosine kinase inhibitor dasatinib. This was confirmed in ex vivo drug assay of primary patient samples where six out of 22 T-ALL samples were sensitive to dasatinib monotherapy at low nanomolar doses that had no effect on healthy lymphocytes.
Monotherapies often lead to drug resistance and relapse. Hence, we tested whether combination of dasatinib with other drugs generates synergy. First, we developed T-ALL specific Lck:mMyc zebrafish leukemia model and optimized ex vivo screening method for zebrafish leukemia cells. We identified synergy between dasatinib and an AKT inhibitor MK-2206 and this was validated in human T-ALL cell lines. Synergy was found also when dasatinib was combined with different inhibitors of the PI3K/AKT/mTOR pathway, such as mTOR inhibitor temsirolimus and PI3K inhibitor IPI-549.
In mouse experiments with xenografted T-ALL cells lines, animals receiving dasatinib and temsirolimus had significantly longer survival and lower disease burden in comparison to single drug and vehicle treated animals. Furthermore, two patient-derived xenografts and two primary samples showed synergistic response in the leukemic blast cells. In mechanistic studies, we confirmed that LCK kinase is the prime target of dasatinib, and necessary for T-ALL pathogenesis in a subset of patients.
We also discovered a transcription factor called SIX6 to be highly expressed in T-ALL and found that high mRNA level of SIX6 was associated with inferior event free survival in three independent pediatric T-ALL cohorts. SIX6 was upregulated by the oncogenic TAL1 transcription factor and associated with the TAL1-related T-ALL subgroup.
In conclusion, a novel prognostic biomarker associated with inferior survival was discovered for T-ALL. We also identified a novel synergistic drug combination for T-ALL, elucidated the main determinants of the drug sensitivity and proved preclinical efficacy of this combination. These studies allow for better stratification of patients and serve as a starting point for clinical investigation in relapsed T-ALL.
The doctoral dissertation of M.Sc. Saara Laukkanen in the field of paediatrics titled Novel targeted therapies and prognostic markers for T cell acute lymphoblastic leukemia will be publicly examined at the Faculty of Medicine and Health Technology of Tampere University at 12 o'clock on Friday 4 June, 2021. The venue is Arvo building audotorium F115, address: Arvo Ylpön katu 34. Professor Riitta Lahesmaa from the University of Turku will be the opponent while Docent Olli Lohi will act as the custos.
Only a limited amount of persons are allowed to participate in the event. The buildings of the University are closed because of the corona virus pandemics and entering the public defence of the thesis is possible only by registering at saara.laukkanen [at] tuni.fi
The study administration of the Faculty will send the PFD version of the dissertation on request. Please send a mail to met.doc.tau [at] tuni.fi
The event can be followed via remote connection.
The dissertation is available online at
http://urn.fi/URN:ISBN:978-952-03-1965-6