Changes in Blood Circulating Cell Populations May Reflect the Anti-Angiogenic and Chemosensitizing Effects of Bortezomib and Thalidomide Treatment in Patients with Multiple Myelomatreatment in Patients with Multiple Myeloma.
Authors: Vande Broek Isabelle , Leleu Xavier , Duda Dan , Van Camp Benjamin , Vanderkerken Karin , van Riet Ivan 
Published: October 2019

Abstract
Abstract 2807
Poster Board II-783
Enumeration of circulating blood cell populations with endothelial– or progenitor-like phenotype has been proposed as surrogate biomarker for tumor response to anti-angiogenic or conventional therapies and is currently being applied in multiple clinical studies. Moreover, recent preclinical studies have suggested a role of circulating progenitor cell populations (EPCs or CPCs) in tumor re-growth after therapy. Cytotoxic agents administered at the maximal tolerated dose induce a rapid mobilization of EPC during therapy-free intervals, possibly resulting in paradoxal rebound angiogenesis (Shaked et al. Cancer Cell 2008;14,263). This EPC mobilization can be inhibited by combination therapy with anti-angiogenic agents, resulting into sustained EC suppression. Multiple myeloma (MM) is characterized by increased angiogenesis in the BM. The effect of novel agents such as Bortezomib and Thalidomide (THAL) is partially mediated by inhibition of BM angiogenesis.
In the present study, we evaluated CD31+CD45– and CD34+CD133+CD45dim circulating cell numbers in MM patients and monitored their kinetics in patients treated with MEL, Bortezomib or THAL. Cells were enumerated among blood mononuclear cells by multicolor flow cytometry according to a standardized protocol (Duda et al. Nat Protoc 2007;2,805) at baseline and at multiple time points during treatment. Baseline levels and changes over time were correlated with response and survival.
At baseline, MM patients (n=71) show significant higher CD31+CD45– and CD34+CD133+CD45dim circulating cell levels compared to healthy individuals (n=10) (7 and 2,5-fold increase, respectively, p<0,02). Moreover, both CD31+CD45– and CD34+CD133+CD45dim circulating cell numbers where higher in patients with active versus non-active disease (1,9 and 4 fold increase, p<0,05) and in patients with relapsed/refractory disease, versus at diagnosis (2,1 and 2 fold increase, p<0,05), reflecting increased angiogenesis associated with disease progression.
Treatment with Bortezomib or THAL resulted in a rapid and sustained decline in CD31+CD45– and CD34+CD133+CD45dim circulating cell numbers, whereas treatment with MEL induced an initial decrease followed by a transient, significant (up to 20-fold) increase in CD34+CD133+CD45dim circulating cell levels at the end of each cycle. This increase was even more pronounced when hematopoietic growth factors were used. Interestingly, patients treated with MEL in combination with Bortezomib or THAL showed a less pronounced CD34+CD133+CD45dim circulating cell increase than with MEL alone, suggesting that Bortezomib and THAL inhibited MEL-induced progenitor cell mobilization.
In conclusion, the findings in this study show that CD31+CD45– and CD34+CD133+CD45dim circulating cell levels are increased in MM patients and correlate with disease progression. In addition, these results suggest that CD31+CD45– and CD34+CD133+CD45dim circulating cell enumeration may represent a useful angiogenesis biomarker to assess prognosis or treatment responses in MM. Treatment with Bortezomib and THAL resulted in a sustained decrease of CD34+CD133+CD45dim circulating cell levels and inhibition of MEL-induced mobilization of these progenitor cells. These findings may reflect an additional mechanism for the anti-angiogenic and chemosensitizing effects of Bortezomib and THAL, resulting into increased anti-tumoral efficacy and clinical benefit as shown in recent randomized trials.

Disclosures:
No relevant conflicts of interest to declare.