VLS-101 blocks tumor growth and prolongs survival in a systemic model of RS. RS cells were IV injected, left to engraft and mice were randomly assigned to treatment with vehicle, VLS-101 2.5 mg/kg, or VLS-101 5.0 mg/kg every 4 days for a total of 6 doses. At the end of drug administration, mice were evaluated for disease spreading to target organs by tracing RS cells by flow cytometry. (A-B) Data from RS1316 (A) and RS1050 (B) are shown. Data are reported as scattered plot with mean values. Statistical analyses were performed using a multiple Student t test. (C) Results were confirmed also by IHC staining using an anti-CD20 antibody to mark RS cells. Slides were developed with DAB (3,3'‑diaminobenzidine) and counter-stained with hematoxylin and eosin. Images were acquired with an AXIO Laboratory.A1 microscope (Zeiss), equipped with a Canon EOS600D reflex camera; original magnification ×20. (D-E) In another set of experiments, injected mice were assessed for survival after 1 cycle of treatment (Tx) with vehicle or VLS-101. Kaplan-Meier curves of RS1316 (D) and RS1050 (E) are reported and statistical analyses for survival were made using log-rank Mantel-Cox test. Bra, brain; Eng, engraftment; Kid, kidney; Liv, liver; Spl, spleen; W&W, watch and wait. *P < .05; **P < .01.