טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentBeyar Katz Ofrat
SubjectAnalysis of the Reactive Host in Response to Bortezomib
Therapy on the Outgrowth of Multiple Myeloma
DepartmentDepartment of Medicine
Supervisors Professor Yuval Shaked
Professor Israel Vlodavsky
Full Thesis textFull thesis text - English Version


Abstract

Multiple myeloma (MM) is a chronic progressive malignancy of plasma cells and is

known to be the second most common hematological malignancy. Treatment

frequently involves combination of several agents and autologous transplant if a

patient is eligible for bone marrow transplantation. Although treatment with the

novel proteasome inhibitor, bortezomib, significantly improves patients’ survival,

some patients fail to respond due to the development of de novo resistance. We

have previously shown that cytotoxic drugs can induce pro-tumorigenic host mediated effects which contribute to tumor re-growth and metastasis, and thus limit

the anti-tumor efficacy. There are several mechanisms to explain this regrowth of

tumors, one of which is the presence of enriched population of cancer stem cells

(CSCs), also called tumor initiating cells (TICs). This unique subpopulation of tumor

cells within the tumor microenvironment, has been shown to support tumor regrowth and spread once treatment is ceased. At the center of this thesis, with

respect to MM, the impact of therapy on MM cell aggressiveness has not been

investigated using targeted, cytostatic agents such as bortezomib, and whether such

effects are related to MM TIC enrichment and proliferation.

Here we show that plasma from bortezomib-treated mice significantly increases

migration, viability and proliferation of MM cells in vitro, compared to plasma from

vehicle treated mice. In vivo, bortezomib induces the mobilization of pro-angiogenic

bone marrow cells known to support MM growth. Furthermore, mice treated with

bortezomib and subsequently were used as recipients for an injection of MM cells

succumb to MM aggressive disease earlier than mice treated with the vehicle

control. We show that bortezomib promotes pro-inflammatory macrophages which

account for MM cell aggressiveness. This effect is partially mediated by interleukin-

16. Accordingly, co-inoculation of MM cells with pro-inflammatory macrophages

from bortezomib-treated mice accelerates MM disease progression, and blocking

these macrophage-induced pro-tumorigenic effects resulted in enhanced survival.

To uncover the mechanisms by which macrophages contribute to MM

aggressiveness, we focused on TICs. We found that bortezomib-treated

macrophages enhanced TIC enrichment. This effect was mediated via the secretion

of interleukin-1β (IL-1β) from macrophages obtained from mice treated with

bortezomib. Furthermore, CD47 expression is upregulated on clonogenic myeloma

cells in response to IL-1β and this has been shown by others to induce phagocytic

protection, illustrating the role of immune cells in MM aggressiveness.

We next studied the clinical implications of our mouse findings. We found that in

10/16 MM patients, plasma obtained three days after bortezomib therapy resulted

in increased MM cell viability when compared to plasma at baseline. In addition,

patients who displayed increased percentage of TICs, M1 macrophages and CD47

expression on TICs in the bone marrow after bortezomib therapy had poor prognosis

and reduced survival compared to those who displayed decreased levels of these

parameters.

Taken together, our results suggest that in addition to the known effective antitumor

activity of bortezomib, host-driven pro-tumorigenic effects generated in

response to cytostatic treatment can promote MM aggressiveness, in part via

enrichment of TICs, and contribute to the overall limited efficacy.