Oral Presentation ESA-SRB-APEG-NZSE 2022

Combined IAP inhibition with rigosertib leads to synergistic anti-tumour responses in vitro in papillary and anaplastic thyroid cancer (#90)

Shananthan Balachandran 1 2 3 , Michael Mond 2 3 4 , Simon Chu 2 5 , Christopher Gilfillan 1 3 , Shan Balachandran 6
  1. Eastern Health Clinical School, Monash University, Melbourne , Victoria , Australia
  2. Hudson Institute of Medical Research, Clayton, Victoria, Australia
  3. Department of Endocrinology, Eastern Health, Box Hill, Victoria, Australia
  4. Department of Endocrinology, Monash Health, Clayton , Victoria, Australia
  5. Department of Molecular and Translational Sciences, Monash University, Clayton, Victoria, Australia
  6. Eastern Health Clinical School, Melbourne, Victoria, Australia

Background: Limited therapeutic options exist for radioiodine-refractory thyroid cancers. Overexpression of Inhibitors of Apoptosis (IAP) in thyroid cancer is associated with adverse clinicopathological features.1,2 IAP inhibition holds a promising role in combination treatment strategies for other malignancies, however is yet to be fully elucidated in thyroid cancer.3

Objective: To determine efficacious partners for combination therapy with IAP inhibition in papillary thyroid carcinoma (PTC) and anaplastic thyroid carcinoma (ATC). 

Methods: High-throughput screening (HTS) using established drug libraries was performed in the PTC cell line, TPC-1 (RET-CCDC6), following pre-treatment with the IAP inhibitor, Compound A (CmpdA; 500nM).4 Drug combination hits were defined as >80% reduction in viability compared to CmpdA alone. Validation studies of prioritised combination treatments were expanded to K1 (BRAFV600E PTC) and SW1736 (BRAFV600E ATC) cell lines. Effects on cell viability, apoptosis, cell cycle progression and cell migration capacity were studied. 

Results: HTS after CmpdA pre-treatment identified 179 hits. Rigosertib, a multikinase inhibitor, was selected for further study. Dose-response evaluation of cell viability demonstrated that CmpdA treatment alone had only modest effect, but established synergistic efficacy in combination with Rigosertib. Synergy quantification5 revealed optimal responses with 500nM Rigosertib. The combination induced apoptosis evidenced by increased caspase 3/7 activity. Rigosertib led to G2/M cell cycle arrest. There was no difference in cell cycle progression in combination with CmpdA. Scratch wound assays demonstrated that Rigosertib reduced cell migration capacity at 24 hr, whilst no difference was seen with CmpdA. 

Conclusion: IAP inhibition has synergistic potential for therapy in PTC and ATC in vitro. IAP inhibitor therapy had significant synergistic effects when used with Rigosertib. Effects are mediated primarily by enhanced apoptosis as well as G2/M phase arrest. Reduced cell migration capacity was also observed. Further study investigating optimal treatment combinations involving IAP inhibition including in vivo models is required.

  1. Hussain AR, Bu R, Ahmed M, Jehan Z, Beg S, Al-Sobhi S, et al. Role of X-Linked Inhibitor of Apoptosis as a Prognostic Marker and Therapeutic Target in Papillary Thyroid Carcinoma. J Clin Endocrinol Metab. 2015;100(7):E974-85.
  2. Tirrò E, Consoli ML, Massimino M, Manzella L, Frasca F, Sciacca L, et al. Altered expression of c-IAP1, survivin, and Smac contributes to chemotherapy resistance in thyroid cancer cells. Cancer Res. 2006;66(8):4263-72.
  3. Morrish E, Brumatti G, Silke J. Future Therapeutic Directions for Smac-Mimetics. Cells. 2020;9(2).
  4. Vince JE, Wong WW, Khan N, Feltham R, Chau D, Ahmed AU, et al. IAP antagonists target cIAP1 to induce TNFalpha-dependent apoptosis. Cell. 2007;131(4):682-93.
  5. Ianevski A, Giri AK, Aittokallio T. SynergyFinder 3.0: an interactive analysis and consensus interpretation of multi-drug synergies across multiple samples. Nucleic Acids Res. 2022;50(W1):W739-43.