Overcoming the response plateau in multiple myeloma: a novel bortezomib-based strategy for secondary induction and high-yield CD34+ stem cell mobilization

Response-Adapted Therapy for Newly Diagnosed Multiple Myeloma

PURPOSE OF REVIEW

The development of potent novel agents has improved outcomes for patients with multiple myeloma (MM). Heterogeneity of response to therapy, an expanding arsenal of treatment options, and cost are however major challenges for physicians making treatment decisions. Response-adapted therapy is hence an attractive strategy for sequencing of therapy in MM. Despite its successful application in other haematologic malignancies, response-adapted therapy is yet to become a standard of care for MM. We provide our perspective on response-adapted therapeutic strategies evaluated thus far and how they may be implemented and improved on in treatment algorithms of the future.

RECENT FINDINGS

While older studies suggested that early response based on International Myeloma Working Group response criteria could impact long-term outcomes, recent data have contradicted these findings. The advent of minimal residual disease (MRD) as a powerful prognostic factor in MM has raised the promise of MRD-adapted treatment strategies. The development of more sensitive techniques for paraprotein quantification as well as imaging modalities to detect extramedullary disease is likely to change response assessment in MM. These techniques combined with MRD assessment may provide sensitive and holistic response assessments which could be evaluated in clinical trials. Response-adapted treatment algorithms have the potential to allow an individualised treatment strategy, maximising efficacy, while minimising toxicities and cost. Standardisation of MRD methodology, incorporation of imaging into response assessment, and the optimal management of MRD positive patients are key questions to be addressed in future trials.

Stem cell mobilization in multiple myeloma: challenges, strategies, and current developments

Among hematological malignancies, multiple myeloma (MM) represents the leading indication of autologous hematopoietic stem cell transplantation (auto-HCT). Auto-HCT is predominantly performed with peripheral blood stem cells (PBSCs), and the mobilization and collection of PBSCs are essential steps for auto-HCT. Despite the improved success of conventional methods with the incorporation of novel agents for PBSC mobilization in MM, mobilization failure is still a concern. The current review comprehensively summarizes various mobilization strategies for mobilizing PBSCs in MM patients and the evolution of these strategies over time. Moreover, existing evidence substantiates that the mobilization regimen used may be an important determinant of graft content. However, limited data are available on the effects of graft characteristics in patient outcomes other than hematopoietic engraftment. In this review, we discussed the effect of graft characteristics on clinical outcomes, mobilization failure, factors predictive of poor mobilization, and potential mobilization regimens for such patients.

Intermediate-dose cyclophosphamide and bortezomib for PBSC mobilization in multiple myeloma

Although the incorporation of bortezomib into induction regimens has improved, response rates in patients with multiple myeloma (MM), the role of bortezomib in the, peripheral blood stem cell (PBSC) mobilization remains unclear. We assessed the, PBSC mobilization efficacy, safety, and disease response of intermediate-dose, cyclophosphamide and bortezomib in the PBSC mobilization. Twenty-one patients with, newly diagnosed MM were enrolled in a phase II, non-randomized study that used, bortezomib (1.3 mg/m2/day on days 1, 4, 8, and 11) and intermediate-dose, cyclophosphamide (2 g/m2/day on days 2, 3) (Bor-ID-CY). The data from 15 patients, who received intermediate-dose cyclophosphamide (ID-CY) were used as a historical, control group. The total CD34 + cell yield of Bor-ID-CY and ID-CY groups were not, significantly different (median 6.3 ×106/kg vs. 6.5 ×106/kg, p = 0.19). All three patients, with mobilization failure of two groups had t(11;14). Six patients in Bor-ID-CY group, were upgraded from a status that was less than a very good partial response (VGPR), at the time of PBSC mobilization to a VGPR or better after PBSC mobilization, (p = 0.014). Four patients in Bor-ID-CY group developed sepsis. The time to, engraftment was similar in the two groups. The addition of bortezomib to ID-CY did not, impact the stem cell yield or quality.

Addition of bortezomib to high-dose cyclophosphamide therapy as a conditioning regimen for autologous peripheral blood stem cell harvest leads to an increased yield of hematopoietic stem cells

Peripheral blood stem cell harvest (PBSCH) is a crucial procedure for autologous stem cell transplantation in patients with multiple myeloma. We herein report a retrospective study to verify the usefulness of bortezomib and high-dose cyclophosphamide therapy (Bor-HDCY) as a conditioning regimen for PBSCH. Thirty-three patients were evaluated. The median age at the first apheresis was 61 (interquartile range, 53-64) years old, and 18 (54.5%) patients were male. Bor-HDCY was performed in 15 patients, and HDCY was performed in 18. In the patients who underwent Bor-HDCY, the CD34⁺ cell count at the first apheresis was significantly higher than in the others (P<0.01), and the total CD34⁺ cell count also tended to be high (P=0.0933). In terms of apheresis days, two-thirds of the patients who underwent HDCY had two-day apheresis, whereas most who underwent Bor-HDCY had one-day apheresis. According to univariate analysis, Bor-HDCY (P<0.01), VRd (Bor, lenalidomide, and dexamethasone) as induction therapy (P=0.0529), and ≥VGPR before PBSCH (P=0.0767) were factors associated with a higher CD34⁺ cell count at first apheresis. Although multivariate analysis showed that there were no independently significant factors influencing the CD34⁺ cell count at the first apheresis, the stepwise selection method revealed that only the Bor-HDCY regimen remained in the final model (P<0.005). Bor-HDCY may be a useful conditioning regimen for increasing the CD34⁺ cell yield.

Addition of plerixafor for mobilization of stem cells with bortezomib is feasible in dialysis-dependent multiple myeloma

Plerixafor and bortezomib have recently been used in autologous stem cell collection to increase the amount of stem cells collected. However, no reports have described the combined use of plerixafor and bortezomib in cases of dialysis-dependent multiple myeloma. The dialysis-dependent multiple myeloma patient in the present study had a small amount of CD34-positive cells with plerixafor and filgrastim, and also with bortezomib and cyclophosphamide. However, by adding plerixafor to bortezomib and cyclophosphamide, collected CD34-positive cells were increased six-fold compared to the previous day. These findings suggest that the combination of plerixafor and bortezomib may be effective in those patients.

A Review of Advances in Hematopoietic Stem Cell Mobilization and the Potential Role of Notch2 Blockade

Hematopoietic stem cell (HSC) transplantation can be a potential cure for hematological malignancies and some nonhematologic diseases. Hematopoietic stem and progenitor cells (HSPCs) collected from peripheral blood after mobilization are the primary source to provide HSC transplantation. In most of the cases, mobilization by the cytokine granulocyte colony-stimulating factor with chemotherapy, and in some settings, with the CXC chemokine receptor type 4 antagonist plerixafor, can achieve high yield of hematopoietic progenitor cells (HPCs). However, adequate mobilization is not always successful in a significant portion of donors. Research is going on to find new agents or strategies to increase HSC mobilization. Here, we briefly review the history of HSC transplantation, current mobilization regimens, some of the novel agents that are under investigation for clinical practice, and our recent findings from animal studies regarding Notch and ligand interaction as potential targets for HSPC mobilization.

Bortezomib enhances G-CSF-induced hematopoietic stem cell mobilization by decreasing CXCL12 levels and increasing vascular permeability

Bortezomib (BTZ) is known to enhance the mobilization of hematopoietic stem and progenitor cells (HSPCs) induced by granulocyte colony-stimulating factor (G-CSF). However, the most effective time at which to administer BTZ to produce this enhancing effect remains debatable, and the precise mechanism underlying the effect of BTZ is poorly understood. We addressed these questions in this article by performing animal experiments. First, in agreement with previous studies, BTZ administration 12 hours before blood collection was most effective for HSPC mobilization; in contrast, BTZ administration 3 days before blood collection negatively affected HSPC harvesting. Next, in terms of the mechanism of action, G-CSF, but not BTZ, downregulated the expression of very late antigen-4 on HSPCs and vascular cell adhesion molecule-1 on bone marrow (BM) stromal cells; however, intriguingly, both G-CSF and BTZ downregulated CXCL12 chemokine expression in BM. Notably, BTZ treatment also increased BM vascular permeability. These results suggest that the pro-mobilization effect of BTZ could involve the dissociation of HSPCs from BM stromal cells triggered by G-CSF, vascular hyperpermeability elicited by BTZ, and downregulation of CXCL12 concomitantly induced by G-CSF and BTZ.

Bortezomib and cyclophosphamide based chemo-mobilization in multiple myeloma

Hematopoietic stem and progenitor cell (HSPC) mobilization regimens in multiple myeloma typically use filgrastim (GCSF) alone or combination of GCSF with plerixafor or high-dose cyclophosphamide. Murine model and human studies have shown HSPC mobilization potential of bortezomib. A total of 37 patients underwent mobilization using bortezomib 1.3 mg/m² on day 1, 4, 8 and 11, cyclophosphamide 1 g/m² on day 8 and 9, and GCSF 10 μg/kg from day 10 (B-Cy-GCSF). This regimen was compared with our earlier cohort of patients where cyclophosphamide was given at dose of 1 g/m² on day 1 and day 2 followed by GCSF 10 μg/kg from day 4 (Cy-GCSF). In B-Cy-GCSF group, median CD34 cells collected were 9.21 × 10⁶/kg (range 4.95-17.1) while in the Cy-GCSF cohort, the median CD34 cell yield was 8.2 × 10⁶/kg (0.4-24.2). Target CD34 cells yield of 5 × 10⁶/kg was achieved with single apheresis in 58.6% of patients after B-Cy-GCSF mobilization as compared to 44.3% in Cy-GCSF group (p = 0.07). Three patients failed mobilization after Cy-GCSF, while no patients failed mobilization in bortezomib group. Addition of bortezomib to Cy-GCSF mobilization showed a trend towards increased CD34 collection and reduced need for apheresis sessions.

Bortezomib-based strategy with autologous stem cell transplantation for newly diagnosed multiple myeloma: a phase II study by the Japan Study Group for Cell Therapy and Transplantation (JSCT-MM12)

BACKGROUND

The Japan Study Group for Cell Therapy and Transplantation (JSCT) organized a phase II study to evaluate the efficacy and safety of a treatment protocol (JSCT-MM12) for multiple myeloma (MM) patients who were previously untreated and transplantation-eligible. Since bortezomib-based therapy is known to be effective for MM, the protocol is intensified more than the previous protocol (JSCT-MM10) and comprised the subsequent treatments: bortezomib + cyclophosphamide + dexamethasone (VCD) induction; bortezomib + high-dose-melphalan (B-HDM) conditioning with autologous stem cell transplantation (ASCT); bortezomib + thalidomide + dexamethasone (VTD) consolidation; and lenalidomide (LEN) maintenance.

METHODS

Sixty-four symptomatic patients aged between 20 and 65 years were enrolled for treatment and received three cycles of VCD, followed by cyclophosphamide administration for autologous stem cell harvest and B-HDM/ASCT, and subsequently two cycles of VTD, after that LEN for 1 year.

RESULTS

Complete response (CR)/stringent CR (sCR) rates for induction, ASCT, consolidation, and maintenance therapies were 20, 39, 52, and 56%, respectively. The grade 3/4 toxicities (≥ 10%) with VCD treatment included neutropenia (27%), anemia (19%), and thrombocytopenia (11%). There was no treatment-related mortality. After median follow-up of 41 months, estimated 3-year progression-free survival (PFS) and overall survival (OS) rates were 64% and 88%, respectively. The high-risk group revealed lower CR/sCR, PFS, and OS than the standard-risk group.

CONCLUSIONS

The study revealed that the treatment protocol consisting of VCD induction, B-HDM/ASCT followed by VTD consolidation, and LEN maintenance could produce highly beneficial responses and favorable tolerability in newly diagnosed MM. However, future study is required for improving treatment in the high-risk group.

Peripheral blood stem cell mobilization; a look ahead

THE PURPOSE OF REVIEW

Mobilized peripheral blood is the predominant source of stem and progenitor cells for hematologic transplantation. Successful transplant requires sufficient stem cells of high enough quality to recapitulate lifelong hematopoiesis, but in some patients and normal donors, reaching critical threshold stem cell numbers are difficult to achieve. Novel strategies, particularly those offering rapid mobilization and reduced costs, remains an area of interest.This review summarizes critical scientific underpinnings in understanding the process of stem cell mobilization, with a focus on new or improved strategies for their efficient collection and engraftment.

RECENT FINDINGS

Studies are described that provide new insights into the complexity of stem cell mobilization. Agents that target new pathways such HSC egress, identify strategies to collect more potent competing HSC and new methods to optimize stem cell collection and engraftment are being evaluated.

SUMMARY

Agents and more effective strategies that directly address the current shortcomings of hematopoietic stem cell mobilization and transplantation and offer the potential to facilitate collection and expand use of mobilized stem cells have been identified.

Notch2 blockade enhances hematopoietic stem cell mobilization and homing

Despite use of newer approaches, some patients being considered for autologous hematopoietic cell transplantation (HCT) may only mobilize limited numbers of hematopoietic progenitor cells (HPCs) into blood, precluding use of the procedure, or being placed at increased risk of complications due to slow hematopoietic reconstitution. Developing more efficacious HPC mobilization regimens and strategies may enhance the mobilization process and improve patient outcome. Although Notch signaling is not essential for homeostasis of adult hematopoietic stem cells (HSCs), Notch-ligand adhesive interaction maintains HSC quiescence and niche retention. Using Notch receptor blocking antibodies, we report that Notch2 blockade, but not Notch1 blockade, sensitizes hematopoietic stem cells and progenitors (HSPCs) to mobilization stimuli and leads to enhanced egress from marrow to the periphery. Notch2 blockade leads to transient myeloid progenitor expansion without affecting HSC homeostasis and self-renewal. We show that transient Notch2 blockade or Notch2-loss in mice lacking Notch2 receptor lead to decreased CXCR4 expression by HSC but increased cell cycling with CXCR4 transcription being directly regulated by the Notch transcriptional protein RBPJ. In addition, we found that Notch2-blocked or Notch2-deficient marrow HSPCs show an increased homing to the marrow, while mobilized Notch2-blocked, but not Notch2-deficient stem cells and progenitors, displayed a competitive repopulating advantage and enhanced hematopoietic reconstitution. These findings suggest that blocking Notch2 combined with the current clinical regimen may further enhance HPC mobilization and improve engraftment during HCT.

Mobilization of human immature hematopoietic progenitors through combinatory use of bortezomib and immunomodulatory drugs

Combination use of the proteasome inhibitor bortezomib and the immunomodulatory drugs lenalidomide or thalidomide has provided superior outcomes in multiple myeloma over their single use; however, these combinations can produce significant toxicities. Unexpectedly, we found a small but significant increase in the population of immature granulocytes and erythrocytes/megakaryocytes in peripheral blood in 16 of 22 patients (73%) treated with dexamethasone in combination with bortezomib and immunomodulatory drugs (triplet), but not in any of 25 patients treated with either bortezomib or immunomodulatory drugs with dexamethasone (doublet). These immature cells gradually increased to a peak level (mean 2.6% per white blood cells) with triplet therapy, and disappeared immediately after therapy cessation. The numbers of circulating CD34⁺ cells and colony-forming cells derived from peripheral blood mononuclear cells increased after triplet therapy compared with those in patients treated by either bortezomib or immunomodulatory drugs plus dexamethasone. Furthermore, triplet regimen downregulated the expression of CXCR4, a chemokine receptor essential for bone marrow retention, on CD34⁺ cells, suggesting an unexpected effect on normal hematopoietic stem/progenitor cells through the reduced interaction with the bone marrow microenvironment. Our observations suggest that combination use should be carefully evaluated to exert synergistic anti-myeloma effects while avoiding unexpected adverse events.

A randomized phase II study of stem cell mobilization with cyclophosphamide+G-CSF or G-CSF alone after lenalidomide-based induction in multiple myeloma

The most common means of mobilizing autologous stem cells is G-CSF alone or combined with cyclophosphamide (CY) to obtain sufficient CD34⁺ cells for one to two transplants. There are few prospective, randomized studies investigating mobilization regimens in multiple myeloma (MM), especially after lenalidomide-based induction. We designed this prospective, randomized study to compare low-dose CY 2 g/m²+G-CSF (arm A) and G-CSF alone (arm B) after lenalidomide-based up-front induction in MM. Of the 80 initially randomized patients, 69 patients were evaluable, 34 and 35 patients in arms A and B, respectively. The primary end point was the proportion of patients achieving a yield of ⩾3 × 10⁶/kg CD34⁺ cells with 1−2 aphereses, which was achieved in 94% and 77% in arms A and B, respectively (P=0.084). The median number of aphereses needed to reach the yield of ⩾3 × 10⁶/kg was lower in arm A than in arm B (1 vs 2, P=0.035). Two patients needed plerixafor in arm A and five patients in arm B (P=0.428). Although CY-based mobilization was more effective, G-CSF alone was successful in a great majority of patients to reach the defined collection target after three cycles of lenalidomide-based induction.

The Analysis of the Relationship between Multiple Myeloma Cells and Their Microenvironment

The bone marrow microenvironment plays a key role in the stimulation of growth and survival of multiple myeloma (MM) cells. We investigated whether membrane microfragments (MFBs) exert a stimulatory effect on mesenchymal stem cell (MSC) gene expression or differentiation. MSCs from patients with multiple myeloma (MMBM-MSCs) proliferated at a slower rate than MSCs from healthy volunteers (BM-MSCs), and fewer MMBM-MSCs adhered to the substrate as compared to BM-MSCs. Phenotypic analysis revealed that MMBM-MSCs and BM-MSCs differed significantly in terms of their CD166 and CXCR4 expressions. In conclusion, our comparative analysis of mesenchymal cells from MM patients and healthy volunteers revealed differences in the genetic and phenotypic profiles of these two populations, their potential for osteodifferentiation, and expression of surface antigens. Moreover, we showed that membrane MFBs may alter the genetic profile of MSCs, leading to disorders of their osteodifferentiation, and interact with the WNT pathway via presentation of the DKK-1 protein.

New insights in the mobilization of hematopoietic stem cells in lymphoma and multiple myeloma patients

Following chemotherapy and/or the administration of growth factors, such as granulocyte-colony stimulated factor (G-CSF), hematopoietic stem cells (HSC) mobilize from bone marrow to peripheral blood. This review aims to systematically present the structure of the HSC "niche" and elucidate the mechanisms of their mobilization. However, this field is constantly evolving and new pathways and molecules have been shown to contribute to the mobilization process. Understanding the importance and the possible primary pathophysiologic role of each pathway is rather difficult, since they share various overlapping components. The primary initiating event for the mobilization of HSC is chemotherapy-induced endogenous G-CSF production or exogenous G-CSF administration. G-CSF induces proliferation and expansion of the myelomonocytic series, which leads to proteolytic enzyme activation. These enzymes result in disruption of various receptor-ligand bonds, which leads to the disanchorage of HSC from the bone marrow stroma. In everyday clinical practice, CXC chemokine receptor-4 (CXCR4) antagonists are now being used as mobilization agents in order to improve HSC collection. Furthermore, based on the proposed mechanisms of HSC mobilization, novel mobilizing agents have been developed and are currently evaluated in preclinical and clinical studies.

Efficacy of Subcutaneous Bortezomib in the Management of Patients with Multiple Myeloma or Relapsed Mantle Cell Lymphoma

The identification of the ubiquitin–proteasome system as a new therapeutic target has been one of the most recent successes in cancer treatment. The development and clinical approval of the first-in-class proteasome inhibitor, bortezomib has revolutionized the treatment of multiple myeloma (MM) and mantle cell lymphoma (MCL). In MM, bortezomib is now integrated in induction, conditioning, consolidation, maintenance, and salvage treatment protocols. Bortezomib-based regimens provide high remission rates and confer significant survival advantage compared to conventional chemotherapy in both the bone marrow transplant and non-transplant setting. In MCL, overall response rates in patients who have received at least one prior therapy range from 30 to 45%, even in chemotherapy resistant patients. Clinical trials to further improve the sequencing of bortezomib-containing combination therapies are ongoing. Until recently, intravenous injection was the standard route of bortezomib administration. However, severe adverse side effects, peripheral neuropathy in particular, were observed in up to 16% of MM patients and up to 54% of MCL patients treated with intravenous bortezomib, with grade 3 and 4 in 11 and 12% of patients, respectively. Moreover, complete remission rates, if at all, are low and duration of response is short both in MM and MCL. These limitations may be overcome by changing the method of bortezomib administration as well as by rationally combining bortezomib with other therapeutic agents. Indeed, recent data demonstrate that subcutaneous bortezomib administration is non-inferior to intravenous administration, with an improved systemic safety profile, good local tolerance, and a more convenient route of administration. Based on these data, subcutaneous bortezomib injection was approved as a supplemental new drug application for all approved indications in MM and MCL after at least one prior therapy. More than 30 clinical trials in MM and MCL are currently ongoing to evaluate the efficacy and safety profile of subcutaneous bortezomib also in induction, maintenance, and salvage therapy.

Advances in stem cell mobilization

Use of granulocyte colony stimulating factor (G-CSF)-mobilized peripheral blood hematopoietic progenitor cells (HPCs) has largely replaced bone marrow (BM) as a source of stem cells for both autologous and allogeneic cell transplantation. With G-CSF alone, up to 35% of patients are unable to mobilize sufficient numbers of CD34 cells/kg to ensure successful and consistent multi-lineage engraftment and sustained hematopoietic recovery. To this end, research is ongoing to identify new agents or combinations which will lead to the most effective and efficient stem cell mobilization strategies, especially in those patients who are at risk for mobilization failure. We describe both established agents and novel strategies at various stages of development. The latter include but are not limited to drugs that target the SDF-1/CXCR4 axis, S1P agonists, VCAM/VLA-4 inhibitors, parathyroid hormone, proteosome inhibitors, Groβ, and agents that stabilize HIF. While none of the novel agents have yet gained an established role in HPC mobilization in clinical practice, many early studies exploring these new pathways show promising results and warrant further investigation.