Targeting the DNA damage response kinase Chk1 in TP53-mutated aggressive thyroid cancers: in vitro studies

Aims Differentiated thyroid cancers (TC) are generally sensitive to first line treatments and tyrosine kinase inhibitors (TKIs). Though, part of them and Poorly Differentiated and Anaplastic TC are particularly aggressive and refractory also to TKI treatments such as Lenvatinib (LENV). A significant correlation between resistance to TKIs and inactivating TP53 mutations was proven in aggressive TC by our group, consistently with other tumors. To find a novel treatment for these TC, we investigated the DNA damage response (DDR) pathway where p53 is crucial. Indeed, the pharmacological inhibition of DDR kinases in p53-deficient tumors is a promising strategy currently studied and clinically tested in several cancers. Methods Western blot, immunofluorescence and cell viability analyses to characterize the DDR in response to Doxorubicin (DOXO), a double-strand DNA breaks inducing agent, in a panel of TC cell lines with known TP53 alterations, and to evaluate Prexasertib (PX) effect, a selective Chk1 kinase inhibitor. Results p53-deficient and LENV-resistant TC cells (FRO, SW1736, B-CPAP, HTC/C3) showed the presence of genomic instability and variable DDR kinase protein levels as opposed to the p53-proficient and LENV-sensitive ones (TPC-1, IHH-4). Notably Chk1 was activated in response to DOXO only in p53- deficient TC cells, hence PX was chosen. In p53-deficient PX-sensitive TC cells, <10 nM PX induced DNA damages and an IC50 antiproliferative effect. Moreover, combined treatments with the lowest PX and DOXO doses (4nM and IC25 each) showed higher viability reduction with respect to single treatments, especially in all p53-deficient TC cells, some of which underwent apoptosis. PX and DOXO treatments did not affect healthy thyrocytes viability. PX effects on cell proliferation are potentiated by LENV only in p53-proficient TC cells. Conclusions Our data show, for the first time in TC, that Prexasertib may be a novel treatment option for p53- deficient aggressive TC.