How beneficial is the use of NSAIDs in stem-cell transplantation?

Abstract

For a number of malignant hematologic diseases, including leukemias, lymphomas and myelomas, hematopoietic stem cell transplantation remains the only curative option. The stem cell sources for these life-saving transplants come from bone marrow, umbilical cord blood, or from the peripheral blood of patients or donors treated with mobilizing agents. Recently, the use of nonsteroidal anti-inflammatory drugs (NSAIDs) including aspirin, ibuprofen and meloxicam has been reported to enhance the ability to acquire stem cells from mobilized peripheral blood, resulting in a superior stem cell graft. The addition of NSAIDs, notably meloxicam, to current mobilization strategies is convenient, cost effective, and given the long track record of NSAID use, presumably safe. This article discusses the potential to translate these findings to clinical practice and addresses unanswered questions regarding the use of NSAIDs in stem cell transplantation.

Keywords::

• hematopoiesis
• mobilization
• NSAID
• stem cell

‘Take two aspirin and call me in the morning.' An old cliché apropos to the remarkable capacity of aspirin and aspirin-like drugs to treat any number of ailments ranging from headaches, fever, pain, inflammation, or even reducing the incidences of heart disease, stroke and cancer. Ancient Sumerians and Egyptians described the use of myrtle and willow plants that contain salicylates as part of herbal remedies. Willow was ‘rediscovered' quite some time later in Europe, and efforts by many chemists led to procedures to extract salicylic acid from willow bark or from the meadowsweet flower, Spirae ulmaria [1]. Later, efforts by Bayer chemists, notably Felix Hoffman, led to an effective method of acetylation to form acetylsalicylic acid and then the subsequent release of ‘Aspirin' by Bayer in 1899 – an abbreviation of the Latin genus, Spirae, with an ‘a' in front to recognize acetylation, and ‘in' on the end to make it easier to pronounce [1].

It took another 72 years until John Vane demonstrated that aspirin and an aspirin-like drug, indomethacin, functioned by inhibiting the synthesis of prostaglandin E₂ (PGE₂) [2]. With later discoveries identifying the cyclooxygenase enzymes COX-1 and COX-2 as targets for aspirin and similar drugs, a new era of drug development occurred resulting in a plethora of nonsteroidal anti-inflammatory drugs (NSAIDs). As of this writing, there are over 180,000 publications listed on PubMed, reporting on the myriad effects of NSAIDs in countless systems, a testament to the strong physiologic role of PGE₂ in almost every cell type in the body. Recently, we identified yet another potential use for NSAIDs in the treatment of human disease through facilitating the egress of hematopoietic stem cells (HSCs) from the bone marrow to the peripheral blood for harvesting of a hematopoietic graft for stem cell transplantation [3].

Hematopoietic stem cell transplantation is a lifesaving therapy for a number of hematologic diseases and metabolic disorders. HSCs are also a target for gene therapy applications because these cells have the capacity to self-renew. Sources of HSCs for transplant include bone marrow, umbilical cord blood and ‘mobilized' peripheral blood. Hematopoietic stem cells normally reside in the bone marrow in specialized microenvironmental stromal cell niches. These niches act to retain HSCs and a hierarchal series of multipotent and lineage restricted progenitor cells within the marrow space, supporting HSC self-renewal and preserving the pool of stem cells required to maintain lifelong blood cell production. HSCs normally traffic through the peripheral blood at very low numbers, but were found at higher levels in patients after chemotherapy. We now know that this natural trafficking can be modulated, allowing for directed mobilization of HSCs into the peripheral blood where they can be harvested by apheresis for subsequent use.

Mobilized peripheral blood stem cells have now replaced bone marrow as the predominate source of hematopoietic stem and progenitor cells (HSPCs), particularly for autologous transplantation in diseases such as multiple myeloma (MM) or non-Hodgkin's lymphoma (NHL), and are also used in allogeneic transplant in related or unrelated hosts for a number of leukemias. The utility of current mobilization regimens that use cytokines (granulocyte-colony stimulating factor; G-CSF) after chemotherapy (chemomobilization) or G-CSF alone is limited as up to 71% of patients fail to mobilize an optimal CD34⁺ cell dose (a marker for hematopoietic stem and progenitor cells) [4,5], posing a significant problem in patients requiring tandem cycles of high-dose chemotherapy. The small molecule CXCR4 antagonist AMD3100 (plerixafor), in combination with G-CSF, has been shown to increase total CD34⁺ cells mobilized compared to G-CSF alone [6,7] and is approved by the Food and Drug Administration (FDA) for use in combination with G-CSF for mobilization in patients with NHL and MM. However, in large reported trials [6,7], up to 24% of MM and NHL patients receiving plerixafor with G-CSF still failed to collect sufficient CD34⁺ cells for transplant, despite 4 days of apheresis. Further, a significant disadvantage of plerixafor is cost, adding $25,567 per patient compared to G-CSF alone in NHL patients in a recent economic analysis [8]. Novel agents are clearly needed that allow collection of sufficient numbers of HSCs for transplantation with few or no toxicities, thereby improving patient outcomes.

Prostaglandin E₂ and other eicosanoids are potent regulators of hematopoietic trafficking and the hematopoietic niche [9,10]. Recently, we have shown in a mouse model that the addition of NSAIDs to G-CSF increases mobilization of HSCs, resulting in a 2.6-fold enhancement in long-term repopulating HSCs and a 4-day faster recovery of neutrophils and platelets in lethally irradiated mice transplanted with a G-CSF plus meloxicam mobilized graft [3]. NSAIDs of varying COX-1 and COX-2 selectivity were assessed in animal models, with the dual COX inhibitors indomethacin, aspirin, ibuprofen and meloxicam demonstrating stem cell egress to the periphery. Originally approved by the FDA in 2000, meloxicam requires only once-a-day dosing and is capable of inhibiting both COX-1 and COX-2, with a six-fold selectivity for COX-2. Meloxicam has a long track record of safety and a favorable side-effect profile compared to other dual COX inhibitors. Trials in healthy volunteers showed that meloxicam did not prolong bleeding time or affect platelet aggregation [11]. With regard to the potential gastrointestinal side effects of NSAIDs, meloxicam is very well tolerated [12]. Adverse events with NSAIDs almost always occur in the context of prolonged use at high doses, and at least one large-scale cohort study that followed 13,000 patients on meloxicam for 3 months found only a 0.8% rate of GI adverse events [13]. We believe this pharmacologic profile for meloxicam makes it ideally suitable for clinical investigation to enhance hematopoietic mobilization and was the focus of nonhuman primate studies and healthy volunteer studies.

When baboons were mobilized with a standard regimen of G-CSF, or the combination of G-CSF plus meloxicam, in all cases meloxicam significantly increased the number of circulating CD34⁺ cells and also increased colony-forming units (CFUs), a functional measurement of hematopoietic progenitors, when compared to G-CSF alone. Similarly, in healthy human volunteers, short-term meloxicam treatment resulted in significant increases in CD34⁺ cells, CFU and SCID-repopulating cells in xenograft mice, a surrogate in vivo assay for human HSC, demonstrating stem cell mobilization efficacy in man. These preclinical results demonstrate that NSAIDs enhance HSC mobilization in mice, baboons and man, resulting in a superior hematopoietic graft in animal models and warrant further clinical study.

Expert opinion

Hematopoietic transplantation is the only curative option for a number of diseases and novel methods that enhance the harvesting of stem cells for transplantation and/or facilitate successful engraftment should be explored. Preclinical results demonstrate that administration of the NSAID meloxicam, along with current mobilization agents, notably G-CSF and plerixafor, results in enhanced recovery of stem and progenitor cells in mice, baboon and healthy volunteers.

However, there remain several unanswered questions before NSAID administration can be routinely applied to hematopoietic mobilization. First, mobilized grafts are widely used in the setting of autologous transplants. As such, mobilization is occurring in patients with underlying disease, many of which have received one or more rounds of chemotherapeutic drugs and/or other agents. The inflammatory environment within the bone marrow niche, particularly with respect to PGE₂ levels, is almost assuredly different than those explored in the healthy volunteer study. While the standard 15 mg once-daily dosing of meloxicam demonstrated efficacy in healthy individuals, dose escalation may be necessary in the autologous mobilized patient. Similarly, many patients with inflammatory syndromes, such as osteoarthritis and rheumatoid arthritis, are using NSAIDs chronically. To our knowledge, the long-term effects of NSAID use on the hematopoietic compartment have not been reported clinically. However, in terms of hematopoietic mobilization, animal studies demonstrated that mobilization response to NSAIDs subsided after 8 days of administration and returned to baseline stem and progenitor levels in the blood, likely indicative of compensatory mechanisms. Further analysis of the hematopoietic effects of NSAIDs and on the mechanisms of compensation within the niche are warranted.

Prostaglandin E₂ signaling has been demonstrated by us and others to facilitate HSC engraftment in the transplant setting [9,14], partly by enhancing HSC expression of the chemoattractive receptor CXCR4 [9], which guides HSCs from the blood back to the bone marrow microenvironment. In animal models exploring NSAIDs in mobilization, it was found that while circulating levels of HSC were increased with NSAIDs, their expression of CXCR4 was significantly reduced, which attenuated the enhanced engraftment potential. To overcome this barrier, NSAID administration could be staggered by 48 h relative to G-CSF administration. This strategy allowed for enhanced mobilization to occur, with restoration of PGE₂ signaling and subsequent increase in CXCR4 expression, resulting in a superior hematopoietic graft compared to G-CSF alone. Evaluation of staggered dosing, CD34⁺ cell CXCR4 levels, and ultimate hematopoietic engraftment will need to be evaluated in clinical studies as the kinetics of restored PGE₂ signaling after meloxicam withdrawal may be different in patient groups. Alternatively, ex vivo treatment of hematopoietic grafts with PGE₂ is currently being explored in Phase II trials to enhance cord blood transplantation. Should this strategy prove to be successful, it may be able to be coupled with NSAID-enhanced mobilization to eliminate the need for staggered dosing to restore PGE₂ signaling/CXCR4 expression, by directly stimulating mobilized cells to enhance homing and engraftment.

Finally, numerous groups are exploring a wide array of cellular therapies outside of the hematopoietic transplantation realm, including transplantation of CD34⁺ cells after myocardial infarction or other ischemic events [15]. The entire repertoire of stem and progenitor cells potentially mobilized with NSAIDs has yet to be thoroughly studied, though it is intriguing to speculate that perhaps yet another mechanism of cardioprotection by aspirin is the egress from the bone marrow of progenitor cells capable of vascular repair. Analysis of the full content and regenerative potential of NSAID mobilized grafts may identify new potential therapeutic uses, particularly in the harvesting of regenerative cells by mobilization regimens.

Declaration of interest

J Hoggatt is funded by NIH grant HL119559. LM Pelus is funded by NIH Grant HL096305. Both authors have filed patent applications on NSAID mobilization.