Biophysical Characterization of the Leukemic Bone Marrow Vasculature Reveals Benefits of Neoadjuvant Low-Dose Radiation Therapy

Abstract

Purpose: Although vascular alterations in solid tumor malignancies are known to decrease therapeutic delivery, the effects of leukemia-induced bone marrow vasculature (BMV) alterations on therapeutic delivery are not well known. Additionally, functional quantitative measurements of the leukemic BMV during chemotherapy and radiation therapy are limited, largely due to a lack of high-resolution imaging techniques available preclinically. This study develops a murine model using compartmental modeling for quantitative multiphoton microscopy (QMPM) to characterize the malignant BMV before and during treatment. Methods and Materials: Using QMPM, live time-lapsed images of dextran leakage from the local BMV to the surrounding bone marrow of mice bearing acute lymphoblastic leukemia (ALL) were taken and fit to a 2-compartment model to measure the transfer rate (K trans), fractional extracellular extravascular space (n ec), and vascular permeability parameters, as well as functional single-vessel characteristics. In response to leukemia-induced BMV alterations, the effects of 2 to 4 Gy low-dose

Longitudinal preclinical imaging characterization of drug delivery potential after radiotherapy in the healthy and leukemic bone marrow vascular microenvironment

“…Similar observations of improved tissue drug perfusion after radiotherapy have been made in solid tumor models (30,31), suggesting that the leukemic BMV and solid tumor vasculature may have similar responses to radiotherapy. Our results suggest that increased WIS tissue may be found shortly after a variety of TBI doses, and directly demonstrate the role of the BMV in previous observations of improved cellular chemotherapy uptake after neo-adjuvant radiotherapy (12).…”

“…Mice were injected with 1×10 6 green fluorescent protein (GFP) + BCR-ABL (p190Kd) expressing B-cell ALL cells (17) or 1×10 6 GFP + Cbfb-MYH11/Mpl + AML cells (18). The percentage of leukemia in peripheral blood (PB) and in bone samples was measured by flow cytometry as described previously (12). Complete details of the mice and leukemia injections can be found in Appendix 1:A…”

“…For identification of extravascular, vascular, and whole tissue regions of interest (ROI), we calculated a series of automatic thresholds from fluorescent blood pool agents and time-lapsed 4 kDa dextran images using Otsu’s method (22) in Fiji/ImageJ. Time-lapsed dextran accumulation in the vascular and extravascular tissue ROIs were analyzed using a custom Matlab® (R2018a 9.41.0.81364, MathWorks Natick, MA) script to obtain K trans , the fractional extracellular extravascular space (ν ec ), and the backflux rate (K ep ) using a 2-compartment model (23) as described prevously (12). The additional parameters of dextran accumulation that we quantified included WIS tissue , wash-in slope for the whole tissue ROI (WIS whole ), peak height for the extravascular tissue ROI (PH tissue ), peak height for the whole tissue ROI (PH whole ), and peak height for the vascular tissue ROI (PH blood ).…”

“…Fluorescent dextran conjugates of a variety of molecular weights are commonly used for multiphoton microscopy as a contrast agent. d leakage of dextran with molecular weights up to 150 kDa have been observed in the bone marrow (1,12) due to the presence of highly permeable sinusoidal vessels (13). In comparison to 150 kDa sized dextran, 4kDa sized dextran easily permeates the BMV and is similar in molecular weight to typical chemotherapies used in the treatment of leukemia such as daunorubicin (563.98 Da) or cytarabine (243.22 Da) (14).…”

“…A recent study using multiphoton microscopy found that low dose (2-4 Gy) radiotherapy increases single-vessel blood flow in mice bearing acute lymphoblastic leukemia (ALL) (12). Increases in perfusion coincided with increased cellular uptake of chemotherapy, as well as improved survival outcome for mice treated with chemotherapy after neo-adjuvant low-dose radiotherapy.…”