High dose melphalan followed by autologous stem cell transplantation remains standard of care for eligible patients with multiple myeloma, but disease response and toxicity, including severe mucositis, varies among patients. Our randomized trial investigated duration of cryotherapy (2 and 6 hours) for reduction of mucositis prevalence and severity and explored factors associated with variability in pharmacokinetics and outcomes from melphalan therapy. The results demonstrate 2-hour is at least as effective as 6-hour cryotherapy in decreasing severe mucositis. From a population pharmacokinetic model, we identified fat free mass, hematocrit, and creatinine clearance were significant covariates, as had been reported previously. Furthermore, we observed the rs4240803 SLC7A5 polymorphism was significantly associated with pharmacokinetic variability, and pharmacokinetics was associated with both mucositis and neutropenia. However, melphalan exposure was not associated with progression-free or overall survival in our dataset. These findings contribute to ongoing efforts to personalize melphalan dosing in transplant patients.

Multiple myeloma (MM) is a hematologic malignancy characterized by clonal proliferation of plasma cells and overproduction of monoclonal immunoglobins. Treatment with melphalan is currently standard of care for younger and fit patients when followed by hematopoietic stem cell transplantation (HSCT), and in transplant ineligible patients when used in combination regimens. It has been previously shown that changes in the p53 pathway are associated with melphalan efficacy, but the regulatory role of the p14ARF-MDM2-p53 axis has yet to be fully explored. Recently, a non-coding RNA, ANRIL (antisense non-coding RNA in the INK4-ARF locus) has been shown to negatively regulate the transcription of the entire INK4-ARF locus and simultaneously modulate the p53 and pRb pathways. Moreover, some single nucleotide polymorphisms (SNPs) in ANRIL have previously been associated with susceptibility to several malignancies. Here we investigated select ANRIL SNPs in DNA from patient-derived peripheral blood mononuclear cells obtained from 108 MM patients treated with high-dose melphalan followed by HSCT. Our results show that the rs2151280 (CàT) SNP in ANRIL was associated with worse progression-free survival (TC/CC vs TT: HR = 0.53, 95%CI, [0.26, 1.07], P = 0.07; adjusted HR = 0.39, 95%CI, [0.18, 0.84], P = 0.016), and the TT variant had higher ANRIL expression and lower p15, p14ARF, and p16 expression compared to the TC/CC variants. Our results indicate that ANRIL may be involved in melphalan-mediated apoptosis via down-regulating p14ARF and subsequent p53, and that the rs2151280 polymorphism may be a potential prognostic biomarker for relapse in melphalan-treated MM patients.

Background/Aim: SLC7A5 is recognized as the major mediator of melphalan uptake into multiple myeloma (MM) cells; however, its contribution to the inter-patient variability of melphalan efficacy and toxicity is yet to be well elucidated. This study aimed to investigate the impact of a single nucleotide polymorphism (SNP) rs4240803 in SLC7A5 on the gene expression, ex vivo sensitivity to melphalan, and clinical outcomes in MM patients who were undergoing autologous stem cell transplantation with high-dose melphalan. Materials and Methods: Peripheral blood mononuclear cells (PBMC) were collected from 108 MM patients prior to melphalan therapy. Clinical data were also collected from these patients following melphalan therapy. Results: rs4240803 was associated with elevated expression of SLC7A5 mRNA, higher ex vivo sensitivity to melphalan in PBMCs, and positive 90-day response in these patients (p=0.047, 0.10, 0.049, respectively). Conclusion: rs4240803 impacted the expression of SLC7A5, thus contributing to the clinical response of MM patients to melphalan therapy.

High‐dose melphalan (HDM) is part of the conditioning regimen in patients with multiple myeloma (MM) receiving autologous stem cell transplantation (ASCT). However, individual sensitivity to melphalan varies, and many patients experience severe toxicities. Prolonged severe neutropenia is one of the most severe toxicities and contributes to potentially life‐threatening infections and failure of ASCT. Granulocyte‐colony stimulating factor (G‐CSF) is given to stimulate neutrophil proliferation after melphalan administration. The aim of this study was to develop a population pharmacokinetic/pharmacodynamic (PK/PD) model capable of predicting neutrophil kinetics in individual patients with MM undergoing ASCT with high‐dose melphalan and G‐CSF administration. The extended PK/PD model incorporated several covariates, including G‐CSF regimen, stem cell dose, hematocrit, sex, creatinine clearance, p53 fold change, and race. The resulting model explained portions of interindividual variability in melphalan exposure, therapeutic effect, and feedback regulation of G‐CSF on neutrophils, thus enabling simulation of various doses and prediction of neutropenia duration.

Autologous stem cell transplant (ASCT) with high‐dose melphalan (HDM) is the standard treatment for fit multiple myeloma (MM) patients. It is generally believed that some DNA repair proteins impact the activity to repair melphalan‐induced DNA damage, thus potentially contributing to the patient's clinical response. However, knowledge of these proteins is limited. In the current study, we investigated the roles of XRCC1, a protein involved in base excision repair and single‐strand break repair, in melphalan response in MM cells. Small interfering RNA knockdown of XRCC1 significantly increased the accumulation of melphalan‐induced DNA damage in MM cells and sensitized them to melphalan treatment, indicating that genetic variation in XRCC1 may impact response to melphalan treatment. We then evaluated the association between an XRCC1 variant with reduced activity, rs25487 (R399Q), and clinical outcomes of 108 MM patients with melphalan therapy. Our results showed that XRCC1 rs25487 was associated with prolonged progression‐free survival (PFS) in MM patients. The adjusted hazard ratio for PFS between patients carrying rs25487 AA/AG and GG was 0.42 (95% confidence interval: 0.25, 0.84, P = .014). Taken together, these results indicate that XRCC1 is involved in the repair of melphalan‐induced DNA damage and XRCC1 rs25487 variant with impaired DNA repair function influences the clinical responses of HDM in MM patients.