Abstract 5150: MIF-2 in bladder cancer: potential therapeutic target
Authors: Rajendran Ganeshkumar , Woolbright Benjamin L. , Abbott Erika , Martin Austin , Dennis Katie , Taylor John Arthur 
Published: September 2020

Abstract
Macrophage migration inhibitory factor (MIF1) is a pro-tumorigenic cytokine overexpressed in multiple cancers. Our previous data in a carcinogen (BBN) induced murine bladder cancer (BCa) model indicates genetic depletion of MIF1 induces stage arrest. Pharmacological inhibition of MIF1 with the inhibitor CPSI-1306 reduces tumor stage and bladder weights. These data indicate MIF1 is a therapeutic target in BCa. However, a second protein with significant homology to MIF1 was recently identified and termed MIF2. Both MIF1 and MIF2 bind and activate their receptor CD74 yielding significant functional homology and thus, targeting both proteins may be more efficacious. We hypothesize MIF2 recapitulates the pro-tumorigenic effects of MIF1 in BCa in a CD74 dependent manner. We assessed MIF1 and MIF2 by ELISA in serum from human patients with BCa and MIF1/2 expression were evaluated in TCGA. WT mice (C57Bl/6 background), MIF-/-, and CD74-/- mice were treated with 0.05% BBN for 16 weeks to induce BCa, and then switched to water. Tumors were allowed to develop until 20 weeks post initiation of BBN, a time frame consistent with muscle invasive tumor development. Some animals were given either vehicle, or a dual MIF1/MIF2 inhibitor 4-IPP (80mg/kg i.p. daily) for 4 weeks after cessation of BBN. We assessed bladder weights as a surrogate for tumor weight, tumor stage and immunohistochemistry for proliferation, angiogenesis and inflammation. In vitro cell proliferation was measured using the hexosaminidase assay and tautomerase activity was measured using two separate enzymatic assays for MIF tautomerase activity. MIF1 and MIF2 mRNA levels were elevated in TCGA. Analysis of serum from BCa patients indicated increased MIF1 and MIF2 in BCa patients, although this didn't reach statistical significance. 4-IPP treated C57Bl/6 animals had reductions in bladder weight, although tumor staging was similar between groups. 4-IPP treatment had no effect on bladder weights or tumor stage in CD74-/- mice supporting a role for CD74 mediated MIF signaling. To more fully assess the role of MIF2 directly, MIF1-/- mice were treated with 4-IPP to solely block MIF2
4-IPP treatment lead to major reductions in tumor stage, tumor incidence and bladder weight indicating inhibition of MIF2 may be more effective when MIF1 is chronically absent. Inflammation and proliferation trended lower, but did not reach statistical significance. MIF1 depletion did not affect MIF2 mRNA levels in bladder, heart or liver. In vitro treatment with 4-IPP substantially reduced proliferation of two high grade BCa cell lines (HTB-5, HTB-9) at concentrations consistent with doses found to inhibit recombinant MIF activity. These data indicate MIF1/2 enhance BCa tumorigenesis through activation of CD74. Combined MIF1/MIF2 may improve therapeutic targeting of MIF, especially during chronic MIF1 inhibition.
Citation Format: Ganeshkumar Rajendran, Benjamin L. Woolbright, Erika Abbott, Austin Martin, Katie Dennis, John Arthur Taylor. MIF-2 in bladder cancer: potential therapeutic target [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5150.