Background: One of the key events in the progression of cancer metastasis is the migration of tumor cells through the vascular endothelium. Tumors induce abnormal endothelial permeability to promote cancer cell invasion. Recently, inhibition of tumor‐induced vascular permeability has been shown to attenuate metastasis in vivo (Tichet M et al. Nat Commun. 2015;6:6993). Low molecular weight heparins (LMWHs) inhibit metastasis in vivo (Klerk et al. J Clin Oncol. 2005;23(10):2130-5) but may cause bleeding complications when used at effective doses. Consequently, LMWHs are unlikely to be used for prevention of metastatic progression unless bleeding side-effects can be diminished. To address this issue, we have recently demonstrated that a LMWH/statin combination (tinzaparin and simvastatin) attenuates abnormal vascular permeability and reduces epithelial cell transmigration at concentrations unlikely to cause bleeding side-effects in vivo. (Kevane et al. Res Pract Thromb Haemost. 2017;1(1)). Here, we aim to interrogate the anti-metastatic effect of the LMWH/statin combination (tinzaparin and simvastatin) in an orthotopic surgical resection model of triple negative breast cancer implementing a LMWH/stain dose that does not increase bleeding risk.

Methods: NOD/SCID mice were surgically implanted with 5x105 MDA-MB-231-LUC2 triple negative breast cancer cells in the right inguinal mammary fat pad. Tumors were allowed to grow until they reached 250mm3. Subsequently, primary tumors were surgically resected. 5 days post-resection, mice were randomized into 4 groups (group 1: 0.5% methylcellulose (vehicle), group 2: 150IU/kg TNZ, group 3: 3mg/kg SVS and group 4: TNZ (150IU/kg) and SVS (3mg/kg)) and treated daily for 4 weeks. Post-resection metastatic progression was monitored by weekly bioluminescence imaging (BLI) [IVIS Spectrum]. Animals that displayed metastatic progression or significant regrowth of primary tumour were euthanized. At time of death, apical lymph nodes and lungs were removed and fixed in 10% formalin for quantification of metastatic burden

Results: Prior to study commencement it was determined that a combination of 150IU/kg TNZ and 3mg/kg SVS did not significantly increase bleeding time in a cohort of tumour naïve animals. Following primary tumor resection, BLI assessment of metastatic progression revealed that 150IU/kg TNZ, 3mg/kg SVS and combination therapy of 150IU/kg TNZ and 3mg/kg SVS significantly (P= 0.0373, P=0.0086 and P=0.0409 respectively N=11) increased the time to metastasis compared to the vehicle treated animals.

Conclusion: For the first time we demonstrate that tinzaparin and simvastatin may be combined to significantly delay time to metastasis while diminishing the associated bleeding risk of LMWHs in a clinically relevant mouse model of aggressive triple negative breast cancer.

Citation Format: Ian S. Miller, Liam P. Shiels, Grace Buckley, Kate Connor, Annette T. Byrne, Fionnuala Ní Ainle. Interrogating the in vivo anti-metastatic action of tinzaparin and simvastatin in an orthotopic surgical resection mouse model of triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2012.