A novel cytostatic form of autophagy in sensitization of non-small cell lung cancer cells to radiation by vitamin D and the vitamin D analog, EB 1089

Abstract

The standard of care for unresectable lung cancer is chemoradiation. However, therapeutic options are limited and patients are rarely cured. We have previously shown that vitamin D and vitamin D analogs such as EB 1089 can enhance the response to radiation in breast cancer through the promotion of a cytotoxic form of autophagy. In A549 and H460 non-small cell lung cancer (NSCLC) cells, 1,25-D3 (the hormonally active form of vitamin D) and EB 1089 prolonged the growth arrest induced by radiation alone and suppressed proliferative recovery, which translated to a significant reduction in clonogenic survival. In H838 or H358 NSCLC cells, which lack VDR/vitamin D receptor or functional TP53, respectively, 1,25-D3 failed to modify the extent of radiation-induced growth arrest or suppress proliferative recovery post-irradiation. Sensitization to radiation in H1299 NSCLC cells was evident only when TP53 was induced in otherwise tp53-null H1299 NSCLC cells. Sensitization was not associated with increased DNA damage, decreased DNA repair or an increase in apoptosis, necrosis, or senescence. Instead sensitization appeared to be a consequence of the conversion of the cytoprotective autophagy induced by radiation alone to a novel cytostatic form of autophagy by the combination of 1,25-D3 or EB 1089 with radiation. While both pharmacological and genetic suppression of autophagy or inhibition of AMPK phosphorylation sensitized the NSCLC cells to radiation alone, inhibition of the cytostatic autophagy induced by the combination treatment reversed sensitization. Evidence for selectivity was provided by lack of radiosensitization in normal human bronchial cells and cardiomyocytes. Taken together, these studies have identified a unique cytostatic function of autophagy that appears to be mediated by VDR, TP53, and possibly AMPK in the promotion of an enhanced response to radiation by 1,25-D3 and EB 1089 in NSCLC.

The Role of Vitamin D in the Immune System as a Pro-survival Molecule

“…216 In this perspective, a fundamental role should be exerted by mitochondria. 217,218 As previously reported, cytosolic calcium may inhibit autophagy, while a calcium increase promotes apoptosis. 18,219 As a modulating factor, calcium signaling has a major role in autophagy through the activity of the Ca 2þ /calmodulin-dependent kinase kinase beta, which activates AMP-activated protein kinase (AMPK), a mechanistic target of rapamycin-dependent autophagy, this latter being also a result of the promoting role of vitamin D. 217 The regulation of autophagy by VDR, together with further components such as AMPK and TP53, has been reported also in cancer models.…”

Ivermectin Induces Cytostatic Autophagy by Blocking the PAK1/Akt Axis in Breast Cancer

“…As a backup strategy to inhibit tumor growth, cytostatic autophagy may overcome these barriers by inhibiting the growth of cancer cells regardless of their sensitivity to apoptosis (39,40). In support of this, very recently, it has been reported that the combination of radiotherapy with vitamin D inhibits cell proliferation through inducing cytostatic autophagy in non-small cell lung cancer cells (41). Our results revealed that autophagy induced by ivermectin has the capacity to inhibit breast cancer cell growth in a cytostatic way, suggesting that the use of ivermectin as an anticancer agent may reduce the self-renewal capacity and proliferation recovery in breast cancer cells.…”

Radiosensitization by PARP Inhibition in DNA Repair Proficient and Deficient Tumor Cells: Proliferative Recovery in Senescent Cells

“…We and others have reported that a primary response of tumor cells to radiation is autophagy [44–47]. Figures 2A presents images of irradiated cells stained with acridine orange, which is indicative of autophagy while Figures 2B provides quantification of the extent of autophagy over a range of radiation doses.…”