Tumors exhibit several physical and physiological barriers that limit the distribution of molecules as small as oxygen; tumor barriers are compressed vessels due to solid stress, immature vasculature with geometric resistances, high interstitial fluid pressure, and the dense extracellular matrix. Tumors are also thrombotic in nature; pancreatic, colon, gastric, lung, ovarian cancers, melanoma, glioblastoma, lymphomas, etc. are associated with a high rate of thrombosis. Solid tumors obstruct venous return which cause static blood flow, endothelial cell injury, and coagulation activation. We hypothesize that coagulation/thrombosis act as a drug transport barrier inside the tumors and the use of anticoagulants or anti-thrombotics overcome this barrier. We posit that perfusion and penetration of drugs trap in thrombotic tumor vessels, whereas the small intra-thrombotic spacing within the vessel wall and interstitial space of tumor retards the movement of particles. In this work, we show that heparin or heparin-based anticoagulants prevent clot formation in tumors, enhances blood perfusion and nanoparticle distribution, and potentiates both chemo- and nano-therapeutic efficiency in tumor treatment.
We compared the vessel perfusion and their thrombi fractions in tumors of P-selectin-/- vs wild-type (WT) mice. B16f10 melanoma cells were grown subcutaneously in P-selectin-/- and WT mice and Cy7 labeled dextran (Dex-Cy7; as a marker of perfused vessels) and Cy5.5 labeled fibrinoigen (Fib-Cy5.5; a marker of blood clots) were injected simultaneously through the tail vein. B16f10 tumors in WT mice grew with high level of thrombus, as Fib-Cy5.5 concentrated inside their vessels. However, B16f10 tumors, when grown in P-selectin-/- mice, had lower accumulation of Fib-Cy5.5 and higher fractions of perfused vessels; Dex-Cy7 concentrated and overlapped with tumor vessels. Studies with several subcutaneously developed tumors—squamous (SCC7), melanoma, pancreatic (AsPC-1), glioblastoma (U87)—and an orthotopically developed pancreatic (AsPC-1-Luc) cancer suggest that tumor vessel thrombosis fractions were inversely associated with perfused vessel fractions. SCC7 was the only tumor with high Dex-Cy7 perfusion and low abundance of Fib-Cy5.5. Intravenous administration of chitosan-based nanoparticles (CNPs) showed high perfusion and distribution in SCC7 tumors. Interestingly, thermal-heating to SCC7 tumors disrupted blood vessels, activated coagulation cascades, and produced enormous thrombus in their vessels, which blocked the intratumoral distribution of CNPs.
Here we address that the use of anticoagulant, preferably with low molecular weight heparin (LMWH) or its orally available LMWH-based conjugate (LHe-tetraD) as an adjuvant, leads to easier passage of chemotherapy or nanoparticles into the deep recesses of a tumor. Subcutaneous LMWH or oral LHe-tetraD pretreatment for 7 days improved the CNPs accumulation and distribution in B16f10 tumors. Doppler ultrasound analysis revealed that LHe-tetraD treatment increased B16f10 tumor blood flow and perfusion. Orthotopic B16f10 melanoma (n = 5) and AsPC-1-Luc pancreatic tumors (n = 8~10) were treated with placebo, LHe-tetraD once daily, 3 cycles of oxaliplatin/gemcitabine once per three days, and combination after 14 days of tumor inoculation. LHe-tetraD alone did not regress tumor growth; however, LHe-tetraD/oxaliplatin/gemcitabine combination markedly reduced tumor volume than oxaliplatin/gemcitabine treated group. In another set of experiment, B16f10 tumors were treated with 4 cycles of doxorubicin loaded CNPs (CNP-Dox; 3 mg/kg per three days) with or without LHe-tetraD. Co-treatment with LHe-tetraD also enhanced the tumor-inhibition efficacy of CNP-Dox than CNP-Dox only.
Our results demonstrate that anticoagulant prevents the generation of tumor thrombus and represents a new way to improve the penetration and drug efficacy into solid tumors.
Citation Format: Taslim A. Al-Hilal, Jeong Uk Choi, In-San Kim, Youngro Byun, Fakhrul Ahsan. De-clotting tumor to improve the perfusion, distribution and efficacy of chemotherapy and nanotherapeutics. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr B24.