ICG has myriad applications and poses low risk to the patient. Its historical uses have contributed to medical knowledge, and it is now undergoing investigation for quantifying tissue perfusion, providing targeted therapies, and intraoperative identification of neurovascular anatomy, ophthalmic structures, and sentinel lymph nodes. New applications of ICG may lead to reduction in postoperative wound-related complications, more effective ophthalmologic procedures, and better detection and treatment of cancer cells.

All-trans retinoic acid (ATRA) based differentiation therapy with potentially curative outcome in acute promyelocytic leukemia (APL), has limited benefit in non-APL acute myeloid leukemia (AML). Thus, identifying key mediators of ATRA-induced differentiation/apoptosis in AML cells may reveal new putative therapeutic targets. Previously, we reported (Leukemia 20: 1809, 2006) that the therapeutic efficacy of ATRA is enhanced in topoisomerase 2β (TOP2β)-deficient AML cell lines, both APL (HL-60, AP-1060) and non-APL (KG-1), in part due to decreased expression of the antioxidant enzyme, peroxiredoxin (PRDX) 2 and increased accumulation of reactive oxygen species (ROS). Based on preliminary observations that (a) ATRA leads to down-regulation of a related antioxidant protein, PRDX1 (RNA array analysis), and (b) PRDX1 mRNA expression relative to PRDX2 mRNA is significantly higher in HL-60, KG-1, and leukemic blast cells from 20 AML patients (qRT-PCR analysis), we evaluated the role of PRDX1 in sensitizing the apoptotic effects of ATRA. Specifically, we tested the hypothesis that ATRA induced growth arrest/apoptosis is associated with decreased PRDX1 levels and increased ROS, which can be modulated by TOP2β. Accordingly, downregulation of TOP2β can enhance apoptosis by increasing ROS, whereas overexpression of TOP2β can inhibit PRDX1 downregulation by ATRA and attenuate ROS-induced apoptosis. Treatment of HL-60, KG-1 and patient AML blast cells with 1 µM ATRA in the absence or presence of 0.1 µM ICRF193 (TOP2β catalytic inhibitor) led to a 3 to 4-fold decrease in PRDX1 mRNA and protein. No effect of ICRF193, which leads to degradation of TOP2β, was observed on PRDX1 levels. Interestingly, while treatment with ATRA + ICRF 193 did not enhance PRDX1 down regulation compared to ATRA alone, it did lead to significantly (p<.05) more apoptosis and greater ROS than either treatment alone. Since, expression of TOP2β correlates with that of PRDX1 in blast cells of AML patients, both of which are expressed at relatively high levels, we tested whether overexpression of TOP2β affects ATRA-induced decrease in PRDX1, ROS accumulation and apoptosis. Transfection of TOP2β in an amsacrine-resistant HL-60 cell line (AR), which lacks TOP2β, leads to overexpression of TOP2β and abrogation of ATRA-induced downregulation of PRDX1, ROS accumulation and apoptosis. In summary, the present study demonstrates that PRDX1 is an ATRA regulated protein, which plays an important role in modulating ATRA-induced differentiation/apoptosis in myeloid leukemia cells. Furthermore, down regulation of PRDX1 levels by ATRA can be manipulated by overexpression of TOP2β. Since overexpression of TOP2β is observed in patient AML blasts, the increased PRDX1 levels may partly explain the resistance of non-APL acute myeloid leukemia cells to ATRA induced differentiation and ROS-mediated apoptosis. Citation Format: Eric J. Norris, Yogin C. Patel, Michaela B. Reinhart, Ram N. Ganapathi, Mahrukh K. Ganapathi. Differentiation and apoptosis induced by all-trans retinoic acid is associated with downregulation of peroxiredoxin 1 in myeloid leukemia cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4239. doi:10.1158/1538-7445.AM2014-4239