Digitoxin and its synthetic analog MonoD have potent antiproliferative effects on lung cancer cells and potentiate the effects of hydroxyurea and paclitaxel

Abstract

Despite significant advances in the understanding of lung cancer biology, the prognosis of cancer patients remains poor. Part of the failure of anticancer therapy is due to intratumoral heterogeneity in these patients that limits the efficacy of single agents. Therefore, there is an urgent need for new anticancer drugs or drug combination regimens that possess increased activity against all cellular subtypes found within the tumor. In this study, we evaluated the in vitro antiproliferative activity of the cardiac glycosides (CGs) digitoxin and its synthetic analog MonoD on H460 lung cancer cells grown under different culture conditions. The CGs were tested alone in H460 cells under routine culture as well as in cells growing under short (24–72 h) and prolonged serum starvation (7 days) in order to evaluate the activity of drugs on cancer cells under varied degrees of proliferation. Our results showed that both CGs, and MonoD in particular, have potent antiproliferative activity at clinically relevant concentrations against cells in all the tested culture conditions. In contrast, paclitaxel, hydroxyurea and colchicine were only active in cells growing in routine culture conditions, and relatively inactive in serum-starved conditions. Importantly, both CGs were able to potentiate the effect of clinically relevant concentrations of hydroxyurea or paclitaxel in serum-starved conditions. When paclitaxel was used in combination with CGs, the highest antiproliferative effect was obtained when paclitaxel was administered first, followed by either digitoxin or MonoD. Our results indicate that CGs have potential clinical applications in translational oncology especially in combination with other drugs, and warrants further investigation of CGs in more advanced preclinical models of lung cancer.

Chemoresistance of Lung and Breast Cancer Cells Growing Under Prolonged Periods of Serum Starvation

“…We previously demonstrated that therapeutic levels of Digitoxin (20–50 nM) were able to decrease the viability of cells growing under RCCs, PPSS as well as floating LTs (Yakisich et al, ,). In LTs, Digitoxin (DIG) reduced the expression of Sox2 (Yakisich et al, ).…”

“…). The latter seems paradoxical since DIG inhibited the viability of H460 cells more potently in cells growing under RCCs compared to cells growing under PPSS (IC 50 = 19.4 ± 1.7 and 88.66 ± 8.12 nM, respectively at 48 h) (Yakisich et al, ). This apparent paradox may be the result of altered basal activity of signaling networks present in cells growing under RCCs and PPSS that may mediate the effect of DIG on protein pathways in a concentration‐ and time‐dependent manner.…”

Anti‐Tumor Effects of Cardiac Glycosides on Human Lung Cancer Cells and Lung Tumorspheres

“…We recently designed a novel set of cardenolide analogs that recapitulate the therapeutic benefits of Digitoxin signaling in cancer while overcoming Digitoxin‐associated toxicity, and our preliminary study demonstrated potent anti‐tumorigenic effects against several forms of cancer (Iyer et al, ). We have further characterized the action of cardiac glycosides in exerting tumoristatic effects in multiple models of lung cancer including routine culture, long‐term serum starvation as well as lung tumorspheres (Yakisich et al, ,). This led us to investigate other naturally occurring forms of cardiac glycosides that may similarly exert strong anti‐tumor effects against lung cancer.…”

Nigericin decreases the viability of multidrug-resistant cancer cells and lung tumorspheres and potentiates the effects of cardiac glycosides

“…19 We have recently shown that Digitoxin (DIG), a cardiac glycoside that inhibits the Na + /K + -ATPase, and its synthetic analog MonoD (MD) were able to decrease the viability of H460 cells growing under RCCs, as well as under PPSS. 13 More importantly, both NIG 20 and DIG or MD, 13 at low (nM) concentrations, have effects on key signaling pathways (see section "Discussion") that may be exploited to enhance drug sensitivity when used in combination with other drugs. The aim of this study was to test the anticancer activity of NIG alone or in combination with DIG or MD in human H460 lung cancer cells displaying varying degrees of proliferation and stemness.…”

“…12 Compared to cells growing under RCCs, cells growing in PPSS proliferate slower and are strongly resistant to conventional anticancer drugs such as Paclitaxel (PX), Hydroxyurea (HU), Colchicine (CX), Obatoclax (OBT), Wortmannin (WT), and LY294002 (LY). 13 The multidrug-resistant phenotype of cells growing under PPSS is likely the result of extensive rewiring of signaling pathways involved in the regulation of multidrug resistance and survival proteins such as MDR1, ABCG2, and Bcl-2. 14 Therefore, distinct in vitro culture conditions may in part mimic the intratumoral heterogeneity found in vivo in tumors with the additional advantage that specific cancer cells subpopulations (phenotypes) can be identified as target of the drug tested.…”