BME Doctoral Dissertation Defense: Deep Hathi

Jan 10
12:00 PM
Holden Auditorium, FLTC, WUSM

Title: Preclinical Imaging of Multiple Myeloma Therapy Response

Abstract:

Multiple myeloma (MM) is a debilitating hematologic malignancy of terminally
differentiated plasma cells in the bone marrow (BM). Advances in therapeutic regimens and the
use of autologous stem cell transplantation have significantly improved survival rates and quality
of life in patients. However, the disease remains incurable, with shorter, successive remission
cycles following relapse. To reduce systemic, off-target toxicity and improve quality of life, there
is a need for improved stratification of responding patients. Identification of specific,
noninvasive, imaging biomarkers that correlate to therapeutic efficacy is an attractive strategy
for stratifying responding patients, since the use of positron emission tomography (PET),
computed tomography (CT), and magnetic resonance imaging (MRI) is clinically established.
Here, we have developed a strategy for imaging MM disease pathogenesis and response to
clinically relevant therapeutics by studying the bidirectional interactions between the BM
microenvironment and myeloma cells at the cellular, environmental, and anatomical levels.
Specifically, we have validated imaging markers that identify BM and myeloma-specific
behaviors through three specific aims:

The first aim validated the use of the phenylalanine analog 18F-FDOPA for monitoring
the uptake and efficacy of the DNA alkylating agent melphalan, which is used extensively in
elderly, non-transplant eligible patients and in relapsed, refractory disease. 18F-FDOPA uptake
was significantly reduced in melphalan-treated mice with orthotopic myeloma tumors, and was
concordant with the established 18F-FDG-PET imaging. Immunohistochemistry was used to
validate 18F-FDOPA uptake results. Importantly, expression of LAT1, which is known to mediate
18F-FDOPA and melphalan uptake, was visibly increased, although this may be a result of
increased tumor vascularity. Our results suggest that 18F-FDOPA-PET can provide
complementary imaging to 18F-FDG-PET for monitoring response to melphalan therapy and
overall LAT1 expression in MM.

The second aim assessed the specificity and sensitivity of the peptidomimetic near
infrared fluorophore LLP2A-Cy5 for imaging the expression of the activated conformation of the
VLA-4 integrin on the surface of myeloma cells. LLP2A-Cy5 imaging was also used to study
response to treatment with the proteasome inhibitor bortezomib, which forms the backbone of
several front-line MM therapy strategies. Uptake of LLP2A-Cy5 was significantly reduced in
bortezomib-treated mice bearing intramedullary tumors, indicating a reduction in the expression
of activated VLA-4. These observations are concordant with the known downregulation of
adhesion-mediated drug resistance and VLA-4 by bortezomib. Our results indicate the viability
of using LLP2A-Cy5 near-infrared imaging for sensitive, longitudinal assessment of VLA-4
expression for monitoring bortezomib treatment response.

Finally, the third aim validated the use of preclinical, multi-parametric MRI for studying
changes in the BM in a diffuse infiltrative intramedullary tumor model. Longitudinal imaging of
the BM in the femur and tibia demonstrated significant regional differences in T1-weighted
contrast uptake and parametric T2 that correlated to changes in viable tumor burden following
treatment with bortezomib. Hematoxylin and eosin staining (H&E) was used to validate the MRI
observations. H&E showed complete diffuse infiltration of the BM in untreated animals, while
bortezomib therapy caused the concentration of tumor burden near the epiphyseal plate of the
distal femur and proximal tibia. These observations, in combination with MRI results, establish
the use of preclinical MRI for studying effects of disease progression and therapy response on
the BM in a longitudinal, noninvasive manner.

In summary, these studies established a combination of qualitative observations and
quantitative results in PET, optical, and MRI based strategies. Thus, this project has integrated
a structured, multi-modal approach for assessing changes in tumor burden and monitoring
therapy response at varying granular levels within the myeloma/BM interaction spectrum. Future
studies would adapt this approach into different cell lines and tumor models.