We investigated whether FNIII14, a 22-mer peptide derived from fibronectin (FN) that potently impairs interaction of FN with b1-integrin, could overcome cell adhesion-mediated drug resistance (CAM-DR) induced by very late antigen (VLA)-4-to-FN interaction in acute myelogenous leukemia (AML). Two AML cell lines, U937 cells and HL-60 cells, and fresh leukemic cells from six AML patients with high a4-integrin expression exhibited CAM-DR to cytosine arabinoside (Ara C) through VLA-4-to-FN interaction, while fresh leukemic cells from two AML patients with low a4-integrin expression did not display CAM-DR to Ara C. FNIII14 impaired VLA-4-to-FN interaction and restored sensitivity to Ara C in the CAM-DR leukemic cells. In these CAM-DR leukemic cells, upregulation of Bcl-2, which was induced through the focal adhesion kinase/Akt signal pathway upon VLA-4-to-FN interaction, was inhibited by FNIII14 treatment. In a mouse model of minimal residual disease (MRD) in bone marrow, 100% survival was achieved by combining FNIII14 with Ara C, whereas Ara C alone prolonged survival only slightly. The myelosuppression induced by Ara C was not augmented by the combination of FNIII14 in mouse experiments. Thus, the combination of anticancer drugs and FNIII14 holds promise to eradicate MRD in bone marrow after chemotherapy.
The acquisition of drug resistance mediated by the interaction of tumor cells with the extracellular matrix (ECM), commonly referred to as cell adhesion-mediated drug resistance (CAM-DR), has been observed not only in hematopoietic tumor cells but also in solid tumor cells. We have previously demonstrated that a 22-mer peptide derived from fibronectin, FNIII14, can inhibit cell adhesion through the inactivation of β1 integrin; when coadministered with cytarabine, FNIII14 completely eradicates acute myelogenous leukemia by suppressing CAM-DR. In this study, we show that our FNIII14 peptide also enhances chemotherapy efficacy in solid tumors. Coadministration of FNIII14 synergistically enhances the cytotoxicity of doxorubicin and aclarubicin in mammary tumor and melanoma cells, respectively. The solid tumor cell chemosensitization induced by FNIII14 is dependent upon the upregulation and activation of the pro-apoptotic protein, Bim. Furthermore, the metastasis of tumor cells derived from ventrally transplanted mammary tumor grafts is suppressed by the coadministration of FNIII14 and doxorubicin. These results suggest that the coadministration of our FNIII14 peptide with chemotherapy could achieve efficient solid tumor eradication by increasing chemosensitivity and decreasing metastasis. The major causes of tumor recurrence are the existence of chemotherapy-resistant primary tumor cells and the establishment of secondary metastatic lesions. As such, coadministering FNIII14 with anti-cancer drugs could provide a promising new approach to improve the prognosis of patients with solid tumors.
Spontaneously Diabetic Torii (SDT) rats are a well-known animal model of non-obese type 2 diabetes mellitus. Although this animal model has been studied extensively over the last decade, the incidence rates of Leydig cell hyperplasia and tumors in this model have not been reported. In this study, pathophysiological analyses of the testes were performed on male SDT rats, to understand the effect of insulin treatment on the development of Leydig cell hyperplasia and tumors and the expression of integrins and extracellular matrix proteins. Testicular Leydig cell hyperplasia and tumors were observed in SDT rats at 64 weeks of age but were rarely identified in Sprague-Dawley (SD) rats of the same age. Insulin treatment decreased plasma glucose and HbA1c levels, and interestingly, decreased the number of hyperplastic Leydig cell foci and Leydig cell tumors in treated animals. A similar reduction in the expression of Ki67 in these Leydig cell foci was also observed. In addition, insulin treatment decreased the expression of integrin α5, integrin β1, integrin αvβ3, fibronectin, and vitronectin in hyperplastic Leydig cell foci. These results suggest that insulin might decrease the incidence of Leydig cell hyperplasia by reducing Leydig cell proliferation and the expression of integrins and extracellular matrix proteins through the reduction of serum glucose concentrations in these animals.
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