Inecalcitol, an analog of 1,25D3, displays enhanced antitumor activity through the induction of apoptosis in a squamous cell carcinoma model system

Cell Cycle. 2013 Mar 1;12(5):743-52. doi: 10.4161/cc.23846. Epub 2013 Feb 6.


Epidemiological data suggest an important role of vitamin D signaling in cancer development and progression, and experimental studies demonstrate that the active vitamin D metabolite 1α, 25-dihydroxyvitamin D₃ (1,25D₃) has broad spectrum antitumor activity. Hypercalcemia has often been suggested to limit the clinical application of these data. The 14-epi-analog of 1,25D₃, inecalcitol [19-nor-14-epi-23-yne-1,25-(OH)₂D₃; TX522], was developed to have superagonistic antitumor activities but low hypercalcemia potential. We examined the antitumor activity of inecalcitol and the underlying mechanisms in a murine squamous cell carcinoma (SCC) model system. In vitro, compared with 1,25D₃, inecalcitol showed enhanced vitamin D receptor (VDR)-mediated transcriptional activity. Inecalcitol suppressed SCC cell proliferation in a dose-dependent manner with an IC50 value 30 times lower than that of 1,25D₃. Both inecalcitol and 1,25D₃ induced a comparable level of G0/G₁ cell cycle arrest in SCC cells. The level of apoptosis induced by inecalcitol was markedly higher than that of 1,25D₃. Apoptosis was mediated through the activation of the caspase 8/10- caspase 3 pathway. Further, inecalcitol markedly inhibited the mRNA and protein expression of c-IAP1 and XIAP compared with 1,25D₃. In vivo, inecalcitol inhibits SCC tumor growth in a dose-dependent fashion. Notably, inecalcitol induced a significantly higher level of apoptosis in the SCC xenograft model. While in vitro inecalcitol demonstrates apparent enhanced VDR binding and antiproliferative effects compared to 1,25D₃, in vivo these advantages disappear; at doses of inecalcitol that have equivalent antitumor effects, similar hypercalcemia is seen. This may be explained by the pharmacokinetics of 1,25D₃ vs. inecalcitol and attributed to the much shorter serum half-life of inecalcitol.We show that inecalcitol has potent antitumor activity in the SCC model system, and this is associated with a strong induction of apoptosis. These findings support the further development of inecalcitol in cancer treatment.

Keywords: 1,25D3; SCC; TX522; apoptosis; inecalcitol.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Alkynes / pharmacology*
  • Alkynes / therapeutic use
  • Animals
  • Antineoplastic Agents / pharmacology
  • Antineoplastic Agents / therapeutic use
  • Apoptosis / drug effects*
  • Carcinoma, Squamous Cell / drug therapy
  • Carcinoma, Squamous Cell / enzymology
  • Carcinoma, Squamous Cell / genetics
  • Carcinoma, Squamous Cell / pathology*
  • Caspases / metabolism
  • Cell Cycle Checkpoints / drug effects
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cholecalciferol / pharmacology*
  • Cholecalciferol / therapeutic use
  • Disease Models, Animal
  • Drug Screening Assays, Antitumor
  • Enzyme Activation / drug effects
  • Inhibitor of Apoptosis Proteins / metabolism
  • Mice
  • Transcription, Genetic / drug effects
  • Vitamin D / analogs & derivatives*
  • Vitamin D / pharmacology
  • X-Linked Inhibitor of Apoptosis Protein / metabolism


  • Alkynes
  • Antineoplastic Agents
  • Inhibitor of Apoptosis Proteins
  • X-Linked Inhibitor of Apoptosis Protein
  • dihydroxy-vitamin D3
  • inecalcitol
  • Vitamin D
  • Cholecalciferol
  • Caspases