Phase I/II trial of the CXCR4 inhibitor plerixafor in combination with bortezomib as a chemosensitization strategy in relapsed/refractory multiple myeloma.

We tested the hypothesis that using CXCR4 inhibition to target the interaction between the tumor cells and the microenvironment leads to sensitization of the tumor cells to apoptosis. Eligibility criteria included multiple myeloma (MM) patients with 1-5 prior lines of therapy. The purposes of the phase I study were to evaluate the safety and maximal-tolerated dose (MTD) of the combination. The treatment-related adverse events and response rate of the combination were assessed in the phase II study. A total of 58 patients were enrolled in the study. The median age of the patients was 63 years (range, 43-85), and 78% of them received prior bortezomib. In the phase I study, the MTD was plerixafor 0.32 mg/kg, and bortezomib 1.3 mg/m2 . The overall response rate for the phase II study was 48.5%, and the clinical benefit rate 60.6%. The median disease-free survival was 12.6 months. The CyTOF analysis demonstrated significant mobilization of plasma cells, CD34+ stem cells, and immune T cells in response to plerixafor. This is an unprecedented study that examines therapeutic targeting of the bone marrow microenvironment and its interaction with the tumor clone to overcome resistance to therapy. Our results indicate that this novel combination is safe and that the objective response rate is high even in patients with relapsed/refractory MM. ClinicalTrials.gov, NCT00903968.

CXCL12 and CXCR7 are relevant targets to reverse cell adhesion-mediated drug resistance in multiple myeloma.

Cell adhesion-mediated drug resistance (CAM-DR) by the bone marrow (BM) is fundamental to multiple myeloma (MM) propagation and survival. Targeting BM protection to increase the efficacy of current anti-myeloma treatment has not been extensively pursued. To extend the understanding of CAM-DR, we hypothesized that the cytotoxic effects of novel anti-myeloma agents may be abrogated by the presence of BM stroma cells (BMSCs) and restored by addition of the CXCL12 antagonist NOX-A12 or the CXCR4 inhibitor plerixafor. Following this hypothesis, we evaluated different anti-myeloma agents alone, with BMSCs and when combined with plerixafor or NOX-A12. We verified CXCR4, CD49d (also termed ITGA4) and CD44 as essential mediators of BM adhesion on MM cells. Additionally, we show that CXCR7, the second receptor of stromal-derived-factor-1 (CXCL12), is highly expressed in active MM. Co-culture proved that co-treatment with plerixafor or NOX-A12, the latter inhibiting CXCR4 and CXCR7, functionally interfered with MM chemotaxis to the BM. This led to the resensitization of MM cells to the anti-myeloma agents vorinostat and pomalidomide and both proteasome inhibitors bortezomib and carfilzomib. Within a multicentre phase I/II study, NOX-A12 was tested in combination with bortezomib-dexamethasone, underlining the feasibility of NOX-A12 as an active add-on agent to antagonize myeloma CAM-DR.

The myeloid-binding peptide adenoviral vector enables multi-organ vascular endothelial gene targeting.

Vascular endothelial cells (ECs) are ideal gene therapy targets as they provide widespread tissue access and are the first contact surfaces following intravenous vector administration. Human recombinant adenovirus serotype 5 (Ad5) is the most frequently used gene transfer system because of its appreciable transgene payload capacity and lack of somatic mutation risk. However, standard Ad5 vectors predominantly transduce liver but not the vasculature following intravenous administration. We recently developed an Ad5 vector with a myeloid cell-binding peptide (MBP) incorporated into the knob-deleted, T4 fibritin chimeric fiber (Ad.MBP). This vector was shown to transduce pulmonary ECs presumably via a vector handoff mechanism. Here we tested the body-wide tropism of the Ad.MBP vector, its myeloid cell necessity, and vector-EC expression dose response. Using comprehensive multi-organ co-immunofluorescence analysis, we discovered that Ad.MBP produced widespread EC transduction in the lung, heart, kidney, skeletal muscle, pancreas, small bowel, and brain. Surprisingly, Ad.MBP retained hepatocyte tropism albeit at a reduced frequency compared with the standard Ad5. While binding specifically to myeloid cells ex vivo, multi-organ Ad.MBP expression was not dependent on circulating monocytes or macrophages. Ad.MBP dose de-escalation maintained full lung-targeting capacity but drastically reduced transgene expression in other organs. Swapping the EC-specific ROBO4 for the CMV promoter/enhancer abrogated hepatocyte expression but also reduced gene expression in other organs. Collectively, our multilevel targeting strategy could enable therapeutic biological production in previously inaccessible organs that pertain to the most debilitating or lethal human diseases.