Search

Barbara Muz,1 Rachel Nicole Ghazarian,1,2 Monica Ou,1,3 Micah John Luderer,1 Hubert Daniel Kusdono,1,2 Abdel Kareem Azab1 1Department of Radiation Oncology, Cancer Biology Division, Washington University in St Louis School of Medicine, 2Department of Pharmaceutical and Administrative Sciences, St Louis College of Pharmacy, 3Department of Biology, St Louis University, StLouis, MO, USA Abstract: Despite the significant therapeutic advances achieved with proteasome inhibitors (PIs) such as bortezomib and carfilzomib in prolonging the survival of patients with multiple myeloma, the development of drug resistance, peripheral neuropathy, and pharmacokinetic limitations continue to pose major challenges when using these compounds. Ixazomib is a second-generation PI with improved activity over other PIs. Unlike bortezomib and carfilzomib, which are administered by injection, ixazomib is the first oral PI approved by US Food and Drug Administration. This review discusses the biochemical properties, mechanisms of action, preclinical efficacy, and clinical trial results leading to the US Food and Drug Administration approval of ixazomib. Keywords: proteasome inhibitor, oral administration, biological mechanism, clinical trials

Multiple myeloma (MM) is a hematological malignancy that remains incurable because most patients will eventually relapse or become refractory to the treatments. Although the treatments have improved, the major problem in MM is the resistance to therapy. Novel agents are currently in development for the treatment of relapsed/refractory MM, including immunomodulatory drugs, proteasome inhibitors, monoclonal antibodies, cell signaling targeted therapies, and strategies targeting the tumor microenvironment. We have previously reviewed in detail the contemporary immunomodulatory drugs, proteasome inhibitors, and monoclonal antibodies therapies for MM. Therefore, in this review, we focused on the role of molecular targeted therapies in the treatment of relapsed/refractory multiple myeloma, including cell signaling targeted therapies (HDAC, PI3K/AKT/mTOR, p38 MAPK, Hsp90, Wnt, Notch, Hedgehog, and cell cycle) and strategies targeting the tumor microenvironment (hypoxia, angiogenesis, integrins, CD44, CXCR4, and selectins). Although these novel agents have improved the therapeutic outcomes for MM patients, further development of new therapeutic agents is warranted.

Imaging sentinel lymph nodes (SLN) could provide us with critical information about the progression of a cancerous disease. Real-time high-resolution intraoperative photoacoustic imaging (PAI) in conjunction with a near infrared (NIR) probe may offer the opportunities for the immediate imaging for direct identification and resection of SLN or collecting tissue samples. In this work a commercially amenable synthetic methodology is revealed for developing luminescent carbon nanoparticles with rapid clearance properties. A one-pot "green" technique is pursued, which involved rapid surface passivation of carbon nanoparticles with organic macromolecules (e.g. polysorbate, polyethyleneglycol) in a solvent free condition. Interestingly, the naked carbon nanoparticles are derived for the first time, from commercial food grade honey. Surface coated particles are markedly smaller (~7 nm) than the previously explored particles (gold, SWNT, copper) for SLN imaging. Results indicate an exceptionally rapid signal enhancement (~2 min) of the SLN. Owing to their strong optical absorption in the near infrared region, tiny size and rapid lymphatic transport, this platform offers great potential for faster resection of SLN and may lower complications caused by axillary investigation for mismarking with dyes or low-resolution imaging techniques.

INTRODUCTION: Flow cytometry has been used extensively to detect MM cells in the bone marrow (BM), micro-residual disease and circulating myeloma cells. Accumulating literature defines MM cells as CD138+/CD38+ for the primary gating of plasma cells; however, several studies demonstrated the presence of clonogenic CD138-negative MM cells, and that hypoxia can decrease the expression of CD138 in MM cells. We propose a novel set of biomarkers to detect MM cells regardless of their CD138 expression or hypoxic status. METHODS and RESULTS: We have tested the effect of hypoxia on the expression of the MM markers, CD138 and CD38, and found that hypoxia decreased the expression of CD138, therefore it cannot be used as a universal marker for MM cells. Hypoxia did not alter the expression of CD38 in MM cells; however, CD38 is a general leukocyte marker and cannot be used alone to identify MM cells, since it is expressed on multiple other leukocytes including T-cells, B-cells, monocytes, NK cells, and dendritic cells. Therefore, we negatively selected these cells by flow cytometry using the specific markers for each of these populations including CD3, CD19, CD14, CD16, and CD123; respectively. Therefore, we detected MM cells as CD38+/CD3-/CD19-/CD14-/CD16-/CD123-. We used CD38 antibody conjugated with APC and FITC-conjugated antibodies for all the other markers, thus MM cells were defined as APC+/FITC- population. To compare traditional method (CD138-based) with our strategy to detect hypoxic and normoxic MM cells, MM cell lines were stained with a cocktail of CD38-APC, FITC-antibodies, and CD138-V450, and analyzed by flow cytometry. The use of CD138+ as a universal marker for MM cells detected 85-100% of the normoxic cells, and only 60-75% of the hypoxic MM cells. While APC+/FITC- strategy detected close to a 100% of the MM cells independent of the cells’ normoxic/hypoxic status or expression of CD138. The ability of the new strategy to detect hypoxic and normoxic MM cells in the peripheral blood was tested by staining hypoxic and normoxic MM cells with cell-tracker Calcein-Red-Orange (as a positive control), spiked 104 MM cells into 106 mononuclear cells from a healthy donor (1% MM in total), and the percentile of Calcein-Red-Orange+ (as a positive control), APC+/FITC-, and CD138+ populations, were analyzed by flow cytometry. Calcein-Red-Orange staining showed exact 1% of MM cells detected in total mononuclear cells for both hypoxic and normoxic MM cells; detection with CD138+ showed 0.95% for normoxic and 0.45% for hypoxic cells; and detection of MM cells using the APC+/FITC- strategy showed 1.05% for normoxic and 1.1% for hypoxic MM cells. Hence, the new strategy detects MM cells selectively and independently of their CD138 expression or hypoxic status. We have used the APC+/FITC- strategy to detect MM cells in BM CD138-negative fractions of 20 MM patients. The APC+/FITC- strategy was able to detect a range of 1.6-44% myeloma cells in the CD138-negative population of BM mononuclear cells isolated from MM patients. Moreover, we have assessed the clonality of this population using APC+/FITC- in the CD138-negative fractions of MM patients. We found that the clonality of the APC+/FITC- population was similar to the clonality of the original disease (CD138+ cells) in 70% of the cases. The other 30% of the cases showed very low involvement of myeloma population in the BM and showed Kappa/Lambda ratio within normal range. Analyzing the prevalence of circulating MM cells in the peripheral blood from 12 MM patients showed that all patients had a higher number of circulating MM cells as detected by APC+/FITC- strategy compared to CD138+, and the fold change ranged from 1.5 to 86 times. CONCLUSION: We found that CD138 cannot be used as a universal marker to detect MM cells. Moreover, we developed a novel strategy to detect MM cells independent of their CD138 expression or hypoxic status; and we used CD38+/CD3-/CD19-/CD14-/CD16-/CD123- population as an alternative set of biomarkers to detect MM cells. This strategy was able to detect a clonal MM cell population in the CD138-negative fraction of BM mononuclear cells isolated from MM patients, as well as in the peripheral blood. Currently, we are exploring the ability of this strategy to predict relapse in MM patients whose BM was defined a CD138-negative. More investigation to characterize this population and the role in tumor recurrence and drug resistance in MM is warranted. Disclosures No relevant conflicts of interest to declare.