Abstract 1737: Nanotherapeutic targeting of drug resistant multiple myeloma cells through VLA4-contact facilitated drug-delivery of camptothecin prodrug
Authors: Fontana Francesca , Scott Michael J. , Allen John S. , Cui Grace , Yang Xiaoxia , O'Neal Julie , Fletcher Steven , Yanaba Noriko , Schmieder Anne H. , Rettig Michael P. , Ritchey Julie , Fiala Mark A. , Vij Ravi , Lanza Gregory M. 
Published: September 2020

Multiple Myeloma (MM) is a recurring-relapsing plasma cell malignancy, which invariably develops drug resistance. Acquired resistance often involves mutation of drug targets or activation of compensatory pathways, making new targets in high demand. Physical contact of MM cells (MMC) with the bone microenvironment further protects MMC, via cell adhesion mediated-drug resistance (CAM-DR). Integrin α4β1 (Very Late Antigen 4; VLA4), mediates adhesion of MMC both to fibronectin in the matrix and to stromal cells expressing VCAM1, providing survival signals and protection from cell death upon drug treatment.Aiming to treat resistant cells, we proposed to utilize nanotechnology to safely deliver a drug whose target would not be lost in refractory MMC and to exploit, rather than bypassing, CAM-DR by introducing selective pressure for VLA4 overexpression then targeting it with drug-carrying nanoparticles (VLA4-NP). In particular, we hypothesized that, in combination treatments, VLA4-NP carrying a camptothecin prodrug (CPT-PD) would target drug-resistant MMC, reducing tumor burden and prolonging survival. Camptothecin (CPT) is a potent but poorly bioavailable topoisomerase 1 (TOP1) inhibitor. In vitro, CPT reduced proliferation and induced apoptosis in a panel of MM cell lines, including sub-lines resistant to other agents. RNAseq showed that MM cells from patients with relapsing or refractory MM had high levels of TOP1 expression. We modified CPT into an inactive lipase-sensitive prodrug (CPT-PD) that stabilizes the compound in micellar nanoparticles until enzymatically liberated in the MM cytosol (VLA4-CPT-PD-NP, 20 nm). In vitro and in vivo fluorescence tracking experiments showed that VLA4-NP binding increased in drug-resistant MM cells with minimal off-target delivery. In vitro, VLA4-CPT-PD-NP reduced MM cell proliferation and enhanced the effects of free drugs (melphalan, dexamethasone, lenalidomide). When MMC were co-cultured with primary bone marrow stroma from MM donors, MMC adhering to stroma survived free drug treatment, while VLA4-CPT-PD-NP had strong toxic effects on the myeloma cells and spared the stroma. In the KaLwRij/5TGM1 mouse model, melphalan resistant MMC are adherent to the bone. In these mice, uptake of fluorescently labeled VLA4-NP by MMC increased after melphalan treatment, while co-treatment with VLA4-CPT-PD-NP and free melphalan reduced tumor burden at multiple skeletal sites (p&lt;0.01) and the M-protein levels by SPEP (p&lt;0.01) relative to melphalan alone. Further, treatment with VLA4-CPT-PD and melphalan prolonged survival even after drug withdrawal (p&lt;0.001), without added toxicity to the kidneys, liver or gut. This work provides proof of principle that CAM-DR can be exploited to safely deliver chemortherapeutics to resistant cells and effectively enhance treatment in myeloma.

Citation Format: Francesca Fontana, Michael J. Scott, John S. Allen, Grace Cui, Xiaoxia Yang, Julie O'Neal, Steven Fletcher, Noriko Yanaba, Anne H. Schmieder, Michael P. Rettig, Julie Ritchey, Mark A. Fiala, Ravi Vij, Gregory M. Lanza. Nanotherapeutic targeting of drug resistant multiple myeloma cells through VLA4-contact facilitated drug-delivery of camptothecin prodrug [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 1737.