(72f) Myosin 1B Regulates the Extravasation of Brain-Targeting Cells and Shifts Metastatic Organ Targeting in Larval Zebrafish
AIChE Annual Meeting
2019
2019 AIChE Annual Meeting
Food, Pharmaceutical & Bioengineering Division
Engineering in Cancer Biology and Therapy II: Mechanisms of Disease
Monday, November 11, 2019 - 9:30am to 9:48am
font-family:" times new roman>Cancer metastasis is the process whereby
cells from a primary tumor establish lesions in other organs of the body, and
difficulties in treating metastasis lead to the majority of cancer-related
deaths1. About 15-25% of patients presenting with brain metastases have
primary breast cancers, and these patients have median survivals ranging from
only ~4-10 months after the metastatic lesions are discovered2,3.
Delineating the mechanisms of breast cancer metastasis to the brain is
therefore critical in developing more effective therapies. To study potential
drivers of brain metastasis, brain- and bone marrow-targeting clones of metastatic
human MDA-MB-231 breast adenocarcinoma cells (231BR and 231BO, respectively)
and 4T1 murine mammary cancer cells (4T1Br4 and 4T1BM2, respectively) were
profiled using whole-lysate, label-free mass spectrometry. Screening of
proteins that were significantly upregulated in brain-targeting vs. bone
marrow-targeting cells for both cell line models indicated that myosin 1B was
upregulated in brain-targeting cells (Fig. 1B). Therefore, we explored
myosin 1B as a putative driver of brain metastasis.
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font-family:" times new roman>We have recently
demonstrated that breast cancer cells that home to specific murine organs
(brain and bone) ultimately colonized analogous tissues (brain and
hematopoietic tissue) in larval zebrafish, thereby recapitulating organotropic
tissue targeting in a larval zebrafish xenograft model4. The zebrafish is
amenable to imaging at single-cell resolution in multiple organs5 in
addition to possessing vascular vessels on the scale of human capillaries, a
brain with structural and cellular similarity to the mammalian brain, and
hematopoietic tissue in the caudal vein plexus (CVP) analogous to mammalian
bone marrow. Therefore, the early stages of metastasis can be examined at
single-cell resolution using this model. Brain- and bone marrow-targeting cells
arrested in the brain at equal rates, regardless of myosin 1B expression
levels, suggesting that tropic organ selectivity emerged after cell arrest. We
therefore focused on the effects of myosin 1B on cell extravasation in the
brain. Silencing of myosin 1B in brain-targeting 231BR cells prior to injection
to the zebrafish circulation
" times new roman>decreased extravasation in the brain without changing
extravasation in the CVP (Fig. 1A,C). This led to a decrease in
the percentage of larvae with cells that had successfully extravasated in the
brain, significantly shifting the distribution of extravasated cells in the
larvae by decreasing brain targeting (Fig. 1D). Current work is focused
on elucidating mechanisms by which myosin 1B expression facilitates specific
extravasation in the brain and testing the effects of myosin 1B knockdown on
brain metastasis in murine models.
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font-family:" times new roman>References:
1. Paul, C.D. et al.
Cancer cell motility: lessons from migration in confined spaces. Nat Rev
Cancer 17: 131-140 (2017)
2. Eichler, A.F. et
al. The biology of brain metastases – translation to new therapies. Nat Rev
Clin Oncol 8: 344-356 (2011)
3. Berghoff, A.S. et
al., Descriptive statistical analysis of a real life cohort of 2419 patients
with brain metastasis of solid cancers. ESMO Open 1: e000024 (2016)
Tissue architectural cues drive organ targeting of tumor cells in zebrafish. In
revision; BioRxiv version available at font-family:" times new roman>https://doi.org/10.1101/233361
5. Paul, C.D. et al.
Human macrophages survive and adopt activated genotrypes in living zebrafish. Nature
Scientific Reports 9: 1759 (2019)
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font-family:" times new roman>Fig. 1. Redirection of metastatic brain targeting
following silencing of myosin 1B.
font-family:" times new roman> (A) Distribution of brain-targeting 231BR
breast cancer cells in the zebrafish brain and CVP at 5 days post-injection
(dpi) following silencing of myosin 1B. Left inset illustrates robust
extravasation of control cells. Following knockdown of myosin 1B, cells in the
brain frequently remained intravascular (right inset). (B) Baseline myosin 1B
protein levels in MDA-MB-231 and 4T1 organotropic cell line clones. For each
cell line, levels were normalized to the brain-targeting cells. P-values are
indicated. (C) Percentage of extravasated 231BR cells in the brain and CVP
following silencing of myosin 1B, normalized to the extravasation rate of
control cells in each tissue. *, p<0.05 by Sidak’s multiple comparisons test
following two-way ANOVA. (D) Percentage of larvae injected with control or
myosin 1B knockdown cells with cells extravasated only in the brain, only in
the CVP, or in both tissues, or with no cells extravasated, at 5 dpi. ***,
p=0.0001 by chi-square test.
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