Abstract 1419: Adipocytes protect leukemia cells from L-asparaginase treatment

Abstract

Abstract Obesity increases cancer incidence and mortality. This is also true for acute lymphoblastic leukemia (ALL). L-Asparaginase (ASNase), an important front-line drug in leukemia treatment, acts through the hydrolysis of asparagine (ASN) and glutamine (GLN) into aspartic acid and glutamic acid. As lymphoblastic leukemia cells are highly dependent on these two non-essential amino acids, ASNase leads to decreased protein synthesis, cell cycle arrest, and apoptosis. We have previously shown that obesity impairs ASNase treatment in C57BL/J mice transplanted with syngeneic leukemia cells. The present study was designed to elucidate how obesity protects ALL cells from this drug. The effects of adipocytes on ALL ASNase resistance were examined in vitro using co-cultures with 3T3-L1 adipocytes and ALL cells, separated by TransWells. Differentiated 3T3-L1 adipocytes significantly protected ALL cells from a 3-day treatment with ASNase, compared to undifferentiated 3T3-L1 fibroblasts or no feeder layer (viable cells after ASNase treatment: 3.1 ± 1.2 fold greater than no feeder layer, 2.1 ± 0.6 greater than fibroblast feeder layer, p<0.05, n=6). Since ASNase acts through the hydrolysis of both ASN and GLN, we next determined whether the protection afforded by adipocytes was through the secretion of one or both of these amino acids. Seven human leukemia cell lines (RCH-ACV, SEM, BV-173, Nalm 6, K562, SD-1, and RS4;11) were tested for their ability to proliferate in media lacking either of these two amino acids. Compared to complete media, six had significantly decreased proliferation in media lacking GLN (n=4, p<.05), while only one (RS4;11) showed dependence on ASN. The GLN-dependent SD-1's and ASN-dependent RS4;11's were plated in TransWells over undifferentiated 3T3-L1 fibroblasts, 3T3-L1 adipocytes, and no feeder layer in media lacking both amino acids. Differentiated 3T3-L1 adipocytes significantly protected both cell lines from amino acid starvation (RS4;11: 3.6 ± 0.4 fold greater than no feeder, 2.0 ± 0.3 fold great than fibroblasts, p<.05, n=3; SD-1: 4.2 ± 2.4 fold greater than feeder, 4.0 ± 1.0 fold greater than fibroblasts, p<.05, n=3). Furthermore, we determined that adipocytes secrete both amino acids over a 72 hour period (media concentration of ASN after 24, 48, and 72 hours: 34 uM, 166 uM, 369 uM; GLN: 0, 42, 85 uM, respectively). Most importantly GLN and ASN depleted media decreased mTOR signaling (measured by p70s6k phosphorylation), conditioning of this media by adipocytes for 48 hours reversed this effect. The current data demonstrate that adipocytes directly protect leukemia cells from ASNase treatment. We have demonstrated that adipocytes increase leukemia survival in media starved of ASN and/or GLN, secrete ASN and GLN, and enhance mTOR signaling in amino acid starved leukemia cells. Thus, obesity may impair the effects of ASNase on leukemia cells through adipose tissue secretion of both ASN and GLN. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1419.