Investigation of antiangiogenic tyrosine kinase inhibitors in primary and metastatic tumor models

Background: A frequent and poor prognostic event in the progression of malignant tumors is the appearance of lung metastases. Patients with lung metastasis often receive antiangiogenic (AA) agents in combination with chemotherapy. However, the efficacy of these combinations falls far short of what would be predicted from preclinical animal studies, resulting in an overall survival benefit of only a few months. AA agents that are applied in the clinic are designed to inhibit the mechanism of endothelial sprouting, however, in highly vascularized organs (e.g. lung), alternative vascularization mechanisms are of greater importance. Since these organs are also the most common sites of metastasis of solid tumors, we hypothesize that primary and metastatic tumors may use distinct mechanisms to form their vascular network, and thus respond differently to AA therapy.

Objectives: Our aim was to compare the efficacy (i.e. inhibition of tumor growth and angiogenesis) of an AA agent, sunitinib malate in in vivo models of primary and secondary breast and renal cell carcinomas.

Materials and methods: The following cell lines were selected for our studies: 4T1 mouse mammary carcinoma, MDA-MB-231 human mammary carcinoma, RENCA mouse renal cell carcinoma. Cells were inoculated orthotopically in the case of primary tumor models, while injected into the tail vein to mimic migration and tumor formation of lung metastases. Mice were treated with 80 mg/kg sunitinib malate suspended in 1.5% carboxymethyl cellulose (CMC) or with 1.5% CMC in the control group for 2x5 days. The proportion of microvessels and proliferating cells, as well as the size of apoptotic and hypoxic areas were examined by immunofluorescence labeling on frozen tissue samples. The tissue distribution of sunitinib was investigated using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI).

Results: Treatment with sunitinib malate significantly reduced tumor size and weight in all primary models and in the RENCA metastasis model, but had no effect on tumor growth in metastasis models of breast carcinomas. Moreover, the area of the vascular network in the sunitinib treated tumors was significantly decreased compared to controls. Additionally, we found that sunitinib malate treatment increased the proportion of hypoxic and necrotic areas only in tumors of the primary models. Evaluation of the MSI data revealed that the mean sunitinib signal was higher in metastatic tumors than in the corresponding primary models, and this difference was significant in breast carcinomas. Furthermore, we found that in all primary models, a significantly higher sunitinib signal was detected in the viable tumor compartments compared to the non-viable areas. A similar trend was observed in the metastasis models, but no significant difference was found.

Funding: Mrs. Berta Kamprad"s Cancer Foundation (FBKS-2020-22-(291), National Research, Development and Innovation Office (2021-1.2.4-TÉT-2021-00030).