PARP Inhibition Enhances Radiotherapy of SMAD4-Deficient Human Head and Neck Squamous Cell Carcinomas in Experimental Models

Clin Cancer Res. 2020 Jun 15;26(12):3058-3070. doi: 10.1158/1078-0432.CCR-19-0514. Epub 2020 Mar 5.

Abstract

Purpose: SMAD4 loss causes genomic instability and the initiation/progression of head and neck squamous cell carcinoma (HNSCC). Here, we study whether SMAD4 loss sensitizes HNSCCs to olaparib (PARP inhibitor) in combination with radiotherapy (RT).

Experimental design: We analyzed HNSCC The Cancer Genome Atlas data for SMAD4 expression in association with FANC/BRCA family gene expression. Human HNSCC cell lines were screened for sensitivity to olaparib. Isogenic HNSCC cell lines were generated to restore or reduce SMAD4 expression and treated with olaparib, radiation, or the combination. HNSCC pretreatment specimens from a phase I trial investigating olaparib were analyzed.

Results: SMAD4 levels correlated with levels of FANC/BRCA genes in HNSCC. HNSCC cell lines with SMAD4 homozygous deletion were sensitive to olaparib. In vivo, olaparib or RT monotherapy reduced tumor volumes in SMAD4-mutant but not SMAD4-positive tumors. Olaparib with RT dual therapy sustained tumor volume reduction in SMAD4-deficient (mutant or knockdown) xenografts, which exhibited increased DNA damage and cell death compared with vehicle-treated tumors. In vitro, olaparib alone or in combination with radiation caused lower clonogenic survival, more DNA damage-associated cell death, and less proliferation in SMAD4-deficient cells than in SMAD4-positive (endogenous SMAD4 or transduced SMAD4) cells. Applicable to clinic, 5 out of 6 SMAD4-negative HNSCCs and 4 out of 8 SMAD4-positive HNSCCs responded to a standard treatment plus olaparib in a phase I clinical trial, and SMAD4 protein levels inversely correlated with DNA damage.

Conclusions: SMAD4 levels are causal in determining sensitivity to PARP inhibition in combination with RT in HNSCCs.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Antineoplastic Combined Chemotherapy Protocols / pharmacology*
  • Apoptosis
  • Cell Proliferation
  • Cetuximab / administration & dosage
  • Disease Models, Animal*
  • Female
  • Head and Neck Neoplasms / drug therapy
  • Head and Neck Neoplasms / metabolism
  • Head and Neck Neoplasms / pathology
  • Head and Neck Neoplasms / radiotherapy*
  • Humans
  • Mice
  • Mice, Nude
  • Phthalazines / administration & dosage
  • Piperazines / administration & dosage
  • Poly(ADP-ribose) Polymerase Inhibitors / pharmacology*
  • Prognosis
  • Smad4 Protein / deficiency*
  • Squamous Cell Carcinoma of Head and Neck / drug therapy
  • Squamous Cell Carcinoma of Head and Neck / metabolism
  • Squamous Cell Carcinoma of Head and Neck / pathology
  • Squamous Cell Carcinoma of Head and Neck / radiotherapy*
  • Tumor Cells, Cultured
  • Xenograft Model Antitumor Assays

Substances

  • Phthalazines
  • Piperazines
  • Poly(ADP-ribose) Polymerase Inhibitors
  • SMAD4 protein, human
  • Smad4 Protein
  • Cetuximab
  • olaparib