The frequent dysregulation of
SRC family kinases (SFK) in multiple
cancers prompted various inhibitors to be actively tested in preclinical and clinical trials. Disappointingly,
dasatinib and
saracatinib failed to demonstrate monotherapeutic efficacy in patients with
head and neck squamous cell carcinomas (
HNSCC). Deeper functional and mechanistic knowledge of the actions of these drugs is therefore needed to improve clinical outcome and to develop more efficient combinational strategies. Even though the SFK inhibitors
dasatinib and
saracatinib robustly blocked cell migration and invasion in
HNSCC cell lines, this study unveils undesirable stem cell-promoting functions that could explain the lack of clinical efficacy in
HNSCC patients. These deleterious effects were targeted by the
mithramycin analog
EC-8042 that efficiently eliminated cancer stem cells (CSC)-enriched tumorsphere cultures as well as
tumor bulk cells and demonstrated potent antitumor activity in vivo. Furthermore, combination treatment of
dasatinib with
EC-8042 provided favorable complementary anti-proliferative, anti-invasive, and anti-CSC functions without any noticeable adverse interactions of both agents. These findings strongly support combinational strategies with
EC-8042 for clinical testing in
HNSCC patients. These data may have implications on ongoing
dasatinib-based trials.