Dabrafenib and its use in the treatment of metastatic melanoma

Histone deacetylases in the regulation of cell death and survival mechanisms in resistant BRAF-mutant cancers

Small-molecule BRAF inhibitors (e.g., vemurafenib and dabrafenib) and MEK (MAPK/ERK) kinases inhibitors (e.g., trametinib) have distinctly improved the survival of patients suffering from BRAF-mutant cancers such as melanomas. However, the emergence of resistance to BRAF and MEK inhibitor-based melanoma therapy, as well as the reduced sensitivity of other BRAF-mutant cancers such as CRC, poses a considerable clinical problem. For instance, the reactivation of MAPK/ERK signaling hampering cell death induction mechanisms was responsible for BRAF inhibitor resistance, which can be correlated with distinct post-translational and epigenetic processes. Histone deacetylases (HDACs) are prominent epigenetic drug targets and some HDAC inhibitors have already been clinically approved for the therapy of various blood cancers. In addition, several HDACs were identified, which also play a crucial role in the drug resistance of BRAF-mutant cancers. Consequently, inhibition of HDACs was described as a promising approach to overcome resistance. This review summarizes the influence of HDACs (Zn2+-dependent HDACs and NAD+-dependent sirtuins) on BRAF-mutant cancers and BRAF inhibitor resistance based on upregulated survival mechanisms and the prevention of tumor cell death. Moreover, it outlines reasonable HDAC-based strategies to circumvent BRAF-associated resistance mechanisms based on downregulated cell death mechanisms.

Analysis of Clinical Success and Molecular Mechanisms of Action of Novel Anti-glioblastoma Drugs: A Review

BACKGROUND

Gliomas and glioblastomas (GBM) are common primary malignant brain tumors, which are highly malignant and have a poor prognosis. The presence of cancer stem cells with unrestricted proliferative capacity and ability to generate glial neoplastic cells, the diffuse nature of GBM, and other specific factors of GBM contribute to poor results of drug therapy in patients with GBM. Despite the worldwide efforts to improve the treatment, many novel anti-GBM drugs are active just in vitro, in silico, and in preclinical trials, and they sometimes demonstrate poor or no activity in clinical trials. In this paper, we have casually selected and analyzed the most promising evidence-based results related to glioblastoma treatment at FDA and Clinical Trials.gov databases. It was observed that the most prospective trend in the development of anti-GBM drugs is combination therapy vs. monotherapy. Our analysis of clinical trials has allowed us to predict that the most promising combination therapy that has shown the best results in patient's surveillance should include drugs that block different growth-promoting signals in glioblastoma cells and that are activated by the V600E BRAF mutation. One drug should inhibit signals from the BRAF protein, whereas the second drug in combination should inhibit signals from the MEK protein.

METHODS

The content of this review is based on information obtained from PubMed, ClinicalTrials.- gov, and the U.S. Food and Drug Administration (https://www.fda.gov/). In ClinicalTrials.gov, we retrieved studies published from January 1, 2015. In the data search, "Glioblastoma" was used as the keyword. A study was deleted if it studied remedies for concomitant tumor diseases, as well as if it did not include descriptions of treatment methods and/or if GBM was not mentioned. The analysis of the effectiveness of treatment was carried out according to the increasing overall survival in GBM patients, compared to the gold standard for this cancer.

RESULTS

GBM patients treated with novel immunotherapy agents and drugs acting on epigenetic factors and receptor tyrosine kinase inhibitors have shown encouraging potential for future development in clinic. However, combinations of drugs have led to more significant improvements in the results and an increase in life expectancy of patients. For example, the combination of nivolumab and ipilimumab showed a 72% increase in life expectancy compared to using nivolumab alone (9.8 vs. 16.85).

CONCLUSION

Combining anti-GBM drugs appears to be a key direction for increasing treatment effectiveness and overall survival. Radiotherapy of GBM can increase the effect of combination drug therapy.

Exploring a novel thiazole derivatives hybrid with fluorinated-indenoquinoxaline as dual inhibitors targeting VEGFR2/AKT and apoptosis inducers against hepatocellular carcinoma with docking simulation

Hepatocellular carcinoma (HCC) ranks as the third most prevalent reason for cancer-related death on a global scale. Tyrosine kinase inhibitors (TKIs) continue to be the primary treatment option for advanced hepatocellular carcinoma. A series of fluoro-11H-indeno[1,2-b]quinoxaline derivatives as an HCC drug targeting the VEGFR2/AKT axis was designed and synthesized. The novel compounds were investigated against HepG-2 and HuH-7 liver tumor cell lines. Compound 5 was the most active derivative against HepG-2 and HuH-7 cell lines with IC50 = 0.75 ± 0.04 and 3.43 ± 0.16 μM, respectively, in contrast to Sorafenib which shows IC50 values of 5.23 ± 0.31 and 4.58 ± 0.21 μM, respectively. IC50 values on normal liver cells (THLE-2) show that all tests are more selective than Sorafenib, prompting further research. The most promising cytotoxic compound has virtually equal VEGFR2 inhibition efficacy to Sorafenib. The total VEGFR2 and p-VEGFR2 inhibitory effects were subsequently evaluated, showing 38.32 % and 77.64 % attenuation, respectively. Compound 5 also reduced total and phosphorylated AKT concentrations in HepG-2 cells by 55.29 % and 78.01 %, respectively. Furthermore, Compound 5 upregulated BAX and caspase-3 and downregulated Bcl-2 to promote apoptosis. Hybrid 5 stops HepG-2's cell cycle at the S phase 48.02 % higher than untreated. Docking experiments assessed AKT and VEGFR2 binding patterns.

The development of drug resistance in metastatic tumours under chemotherapy: An evolutionary perspective

We present a mathematical model of the evolutionary dynamics of a metastatic tumour under chemotherapy, comprising non-local partial differential equations for the phenotype-structured cell populations in the primary tumour and its metastasis. These equations are coupled with a physiologically-based pharmacokinetic model of drug administration and distribution, implementing a realistic delivery schedule. The model is carefully calibrated from the literature, focusing on BRAF-mutated melanoma treated with Dabrafenib as a case study. By means of long-time asymptotic and global sensitivity analyses, as well as numerical simulations, we explore the impact of cell migration from the primary to the metastatic site, physiological aspects of the tumour tissues and drug dose on the development of chemoresistance and treatment efficacy. Our findings provide a possible explanation for empirical evidence indicating that chemotherapy may foster metastatic spread and that metastases may be less impacted by the chemotherapeutic agent.

Exploring markers of immunoresponsiveness in papillary thyroid carcinoma and future treatment strategies

BACKGROUND

The study summarizes the potential use of immunotherapy for BRAF-mutated papillary thyroid cancer (PTC) by analyzing the immune profile of City of Hope PTC patient samples and comparing them to the thyroid dataset available in the TCGA database.

MATERIALS AND METHODS

PTC cases with available formalin-fixed paraffin-embedded archived tumor tissue were identified. RNA was extracted from the tumor tissue and analyzed by NanoString to evaluate their immune gene expression profile. Immunohistochemistry was used to determine the expression of immune suppressive genes and lymphocytic infiltration into the tumor tissue. Thyroid cancer cell lines (MDA-T32, MDA-T68, MDA-T85, and MDA-T120) were used to determine the correlation between the BRAF inhibition and CD274 expression.

RESULTS

The study found that PTC cases with BRAF mutations had higher expression of immune checkpoint markers CD274 and CTLA4, as well as higher tumor-infiltrating lymphocytes, particularly CD4+T cells. Additionally, the study identified immunosuppressive markers expressed by tumor cells like CD73, CD276, and CD200 that could be targeted for immunotherapy. Further experiments using PTC cell lines lead to the conclusion that CD274 expression correlates with BRAF activity and that inhibitors of BRAF could potentially be used in combination with immunotherapy to treat PTC.

CONCLUSIONS

These findings suggest that PTC cases with BRAF mutations or high expression may be correlated with an immune hot signature and could benefit from immunotherapeutic strategies.

Durable response to BRAF inhibitor monotherapy in recurrent metastatic low grade serous ovarian cancer

Low grade serous ovarian cancers (LGSOC) in an advanced setting have limited systemic treatment options. In this paper we report a case of metastatic LGSOC harboring a BRAF mutation, treated with dabrafenib. We discuss the clinical, pathologic and molecular characteristics as well as surgical considerations and ongoing investigations in LGSOC.

KSR1 Knockout Mouse Model Demonstrates MAPK Pathway's Key Role in Cisplatin- and Noise-induced Hearing Loss

Hearing loss is a major disability in everyday life and therapeutic interventions to protect hearing would benefit a large portion of the world population. Here we found that mice devoid of the protein kinase suppressor of RAS 1 (KSR1) in their tissues (germline KO mice) exhibit resistance to both cisplatin- and noise-induced permanent hearing loss compared with their wild-type KSR1 littermates. KSR1 is a scaffold protein that brings in proximity the mitogen-activated protein kinase (MAPK) proteins BRAF, MEK1/2 and ERK1/2 and assists in their activation through a phosphorylation cascade induced by both cisplatin and noise insults in the cochlear cells. KSR1, BRAF, MEK1/2, and ERK1/2 are all ubiquitously expressed in the cochlea. Deleting the KSR1 protein tempered down the MAPK phosphorylation cascade in the cochlear cells following both cisplatin and noise insults and conferred hearing protection of up to 30 dB SPL in three tested frequencies in male and female mice. Treatment with dabrafenib, an FDA-approved oral BRAF inhibitor, protected male and female KSR1 wild-type mice from both cisplatin- and noise-induced hearing loss. Dabrafenib treatment did not enhance the protection of KO KSR1 mice, providing evidence dabrafenib works primarily through the MAPK pathway. Thus, either elimination of the KSR1 gene expression or drug inhibition of the MAPK cellular pathway in mice resulted in profound protection from both cisplatin- and noise-induced hearing loss. Inhibition of the MAPK pathway, a cellular pathway that responds to damage in the cochlear cells, can prove a valuable strategy to protect and treat hearing loss.

Modeling combination therapies in patient cohorts and cell cultures using correlated drug action

Characterizing the effect of combination therapies is vital for treating diseases like cancer. We introduce correlated drug action (CDA), a baseline model for the study of drug combinations in both cell cultures and patient populations, which assumes that the efficacy of drugs in a combination may be correlated. We apply temporal CDA (tCDA) to clinical trial data, and demonstrate the utility of this approach in identifying possible synergistic combinations and others that can be explained in terms of monotherapies. Using MCF7 cell line data, we assess combinations with dose CDA (dCDA), a model that generalizes other proposed models (e.g., Bliss response-additivity, the dose equivalence principle), and introduce Excess over CDA (EOCDA), a new metric for identifying possible synergistic combinations in cell culture.

Cutaneous adverse reactions resulting from targeted cancer therapies: histopathologic and clinical findings

Targeted cancer treatments-designed to interfere with specific molecular signals responsible for tumor survival and progression-have shown benefit over conventional chemotherapies but may lead to diverse cutaneous adverse effects. This review highlights clinically significant dermatologic toxicities and their associated histopathologic findings, resulting from various targeted cancer drugs. Case reports and series, clinical trials, reviews, and meta-analyses are included for analysis and summarized herein. Cutaneous side effects resulting from targeted cancer therapies were reported with incidences as high as 90% for certain medications, and reactions are often predictable based on mechanism(s) of action of a given drug. Common and important reaction patterns included: acneiform eruptions, neutrophilic dermatoses, hand-foot skin reaction, secondary cutaneous malignancies, and alopecia. Clinical and histopathologic recognition of these toxicities remains impactful for patient care.

The Cytoprotective Role of Autophagy in Response to BRAF-Targeted Therapies

BRAF-targeted therapies are widely used for the treatment of melanoma patients with BRAF V600 mutations. Vemurafenib, dabrafenib as well as encorafenib have demonstrated substantial therapeutic activity; however, as is the case with other chemotherapeutic agents, the frequent development of resistance limits their efficacy. Autophagy is one tumor survival mechanism that could contribute to BRAF inhibitor resistance, and multiple studies support an association between vemurafenib-induced and dabrafenib-induced autophagy and tumor cell survival. Clinical trials have also demonstrated a potential benefit from the inclusion of autophagy inhibition as an adjuvant therapy. This review of the scientific literature relating to the role of autophagy that is induced in response to BRAF-inhibitors supports the premise that autophagy targeting or modulation could be an effective adjuvant therapy.

Investigation of evolutionary dynamics for drug resistance in 3D spheroid model system using cellular barcoding technology

Complex evolutionary dynamics governing the drug resistance is one of the major challenges in cancer treatment. Understanding these mechanisms requires a sequencing technology with higher resolution to delineate whether pre-existing or de novo drug mechanisms are behind the drug resistance. Combining this technology with clinically very relevant model system, namely 3D spheroids, better mimicking tumorigenesis and drug resistance have so far been lacking. Thus, we sought to establish dabrafenib and irinotecan resistant derivatives of barcoded 3D spheroids with the ultimate aim to quantify the selection-induced clonal dynamics and identify the genomic determinants in this model system. We found that dabrafenib and irinotecan induced drug resistance in 3D-HT-29 and 3D-HCT-116 spheroids are mediated by pre-existing and de novo resistant barcodes, indicating the presence of polyclonal drug resistance in this system. Moreover, whole-exome sequencing analysis found chromosomal gains and mutations associated with dabrafenib and irinotecan resistance in 3D-HT-29 and 3D-HCT-116 spheroids. Last, we show that dabrafenib and irinotecan resistance are also mediated by multiple drug resistance by detection of upregulation of the drug efflux pumps, ABCB1 and ABCG2, in our spheroid model system. Overall, we present the quantification of drug resistance and evolutionary dynamics in spheroids for the first time using cellular barcoding technology and the underlying genomic determinants of the drug resistance in our model system.

Exploring the Molecular Landscape of Myelofibrosis, with a Focus on Ras and Mitogen-Activated Protein (MAP) Kinase Signaling

Myelofibrosis (MF) is a clonal myeloproliferative neoplasm (MPN) characterized clinically by cytopenias, fatigue, and splenomegaly stemming from extramedullary hematopoiesis. MF commonly arises from mutations in JAK2, MPL, and CALR, which manifests as hyperactive Jak/Stat signaling. Triple-negative MF is diagnosed in the absence of JAK2, MPL, and CALR but when clinical, morphologic criteria are met and other mutation(s) is/are present, including ASXL1, EZH2, and SRSF2. While the clinical and classic molecular features of MF are well-established, emerging evidence indicates that additional mutations, specifically within the Ras/MAP Kinase signaling pathway, are present and may play important role in disease pathogenesis and treatment response. KRAS and NRAS mutations alone are reportedly present in up to 15 and 14% of patients with MF (respectively), and other mutations predicted to activate Ras signaling, such as CBL, NF1, BRAF, and PTPN11, collectively exist in as much as 21% of patients. Investigations into the prevalence of RAS and related pathway mutations in MF and the mechanisms by which they contribute to its pathogenesis are critical in better understanding this condition and ultimately in the identification of novel therapeutic targets.

BRAF Mutations in Melanoma: Biological Aspects, Therapeutic Implications, and Circulating Biomarkers

Melanoma is an aggressive form of skin cancer resulting from the malignant transformation of melanocytes. Recent therapeutic approaches, including targeted therapy and immunotherapy, have improved the prognosis and outcome of melanoma patients. BRAF is one of the most frequently mutated oncogenes recognised in melanoma. The most frequent oncogenic BRAF mutations consist of a single point mutation at codon 600 (mostly V600E) that leads to constitutive activation of the BRAF/MEK/ERK (MAPK) signalling pathway. Therefore, mutated BRAF has become a useful target for molecular therapy and the use of BRAF kinase inhibitors has shown promising results. However, several resistance mechanisms invariably develop leading to therapeutic failure. The aim of this manuscript is to review the role of BRAF mutational status in the pathogenesis of melanoma and its impact on differentiation and inflammation. Moreover, this review focuses on the mechanisms responsible for resistance to targeted therapies in BRAF-mutated melanoma and provides an overview of circulating biomarkers including circulating tumour cells, circulating tumour DNA, and non-coding RNAs.

Fc Epsilon RI-Neuroimmune Interplay in Pruritus Triggered by Particulate Matter in Atopic Dermatitis Patients

Atopic dermatitis (AD) is the most common chronic relapsing neuroinflammatory skin disease that is characterized by a complex and multifactorial pathophysiology. It reflects a profound interplay between genetic and environmental factors, and a recently disclosed neuroimmune dysregulation that drives skin barrier disruption, pruritus, and microbial imbalance. In terms of the key external environmental players that impact AD, air quality and itch severity linkage have been thoroughly researched. The impact of ambient air pollutants including particulate matter (PM) and AD pruritic exacerbation has been recorded despite reductions in air pollution levels in in developed countries. The developing countries have, on the contrary, experienced significant urbanization and industrialization with limited environmental protection standards in the past decades. This unprecedented construction, petrochemical industry utilization, and increment in population counts has been paired with consistent exposure to outdoor PM. This may present a key cause of AD pruritic exacerbation supported by the fact that AD prevalence has intensified globally in the past 50 years, indicating that environmental exposure may act as a trigger that could flare up itch in vulnerable persons. At the molecular level, the impact of PM on severe pruritus in AD could be interpreted by the toxic effects on the complex neuroimmune pathways that govern this disease. AD has been recently viewed as a manifestation of the disruption of both the immune and neurological systems. In light of these facts, this current review aims to introduce the basic concepts of itch sensory circuits in the neuroimmune system. In addition, it describes the impact of PM on the potential neuroimmune pathways in AD pathogenesis with a special focus on the Fc Epsilon RI pathway. Finally, the review proposes potential treatment lines that could be targeted to alleviate pruritus based on immune mediators involved in the Fc Epsilon signaling map.

Phenotype Switching and the Melanoma Microenvironment; Impact on Immunotherapy and Drug Resistance

Melanoma, a highly heterogeneous tumor, is comprised of a functionally diverse spectrum of cell phenotypes and subpopulations, including stromal cells in the tumor microenvironment (TME). Melanoma has been shown to dynamically shift between different transcriptional states or phenotypes. This is referred to as phenotype switching in melanoma, and it involves switching between quiescent and proliferative cell cycle states, and dramatic shifts in invasiveness, as well as changes in signaling pathways in the melanoma cells, and immune cell composition in the TME. Melanoma cell plasticity is associated with altered gene expression in immune cells and cancer-associated fibroblasts, as well as changes in extracellular matrix, which drive the metastatic cascade and therapeutic resistance. Therefore, resistance to therapy in melanoma is not only dependent on genetic evolution, but it has also been suggested to be driven by gene expression changes and adaptive phenotypic cell plasticity. This review discusses recent findings in melanoma phenotype switching, immunotherapy resistance, and the balancing of the homeostatic TME between the different melanoma cell subpopulations. We also discuss future perspectives of the biology of neural crest-like state(s) in melanoma.

RAS: Circuitry and therapeutic targeting

Cancer has affected the lives of millions worldwide and is truly regarded as a devastating disease process. Despite advanced understanding of the genomic underpinning of cancer development and progression, therapeutic challenges are still persistent. Among all the human cancers, around 33% are attributed to mutations in RAS oncogene, a crucial component of the signaling pathways. With time, our understanding of RAS circuitry has improved and now the fact that it activates several downstream effectors, depending on the type and grades of cancer has been established. The circuitry is controlled via post-transcriptional mechanisms and frequent distortions in these mechanisms lead to important metabolic as well as immunological states that favor cancer cells' growth, survival, plasticity and metastasis. Therefore, understanding RAS circuitry can help researchers/clinicians to develop novel and potent therapeutics that, in turn, can save the lives of patients suffering from RAS-mutant cancers. There are many challenges presented by resistance and the potential strategies with a particular focus on novel combinations for overcoming these, that could move beyond transitory responses in the direction of treatment. Here in this review, we will look at how understanding the circuitry of RAS can be put to use in making strategies for developing therapeutics against RAS- driven malignancies.

Synthetic Vulnerabilities in the KRAS Pathway

Mutations in Kristen Rat Sarcoma viral oncogene (KRAS) are among the most frequent gain-of-function genetic alterations in human cancer. Most KRAS-driven cancers depend on its sustained expression and signaling. Despite spectacular recent success in the development of inhibitors targeting specific KRAS alleles, the discovery and utilization of effective directed therapies for KRAS-mutant cancers remains a major unmet need. One potential approach is the identification of KRAS-specific synthetic lethal vulnerabilities. For example, while KRAS-driven oncogenesis requires the activation of a number of signaling pathways, it also triggers stress response pathways in cancer cells that could potentially be targeted for therapeutic benefit. This review will discuss how the latest advances in functional genomics and the development of more refined models have demonstrated the existence of molecular pathways that can be exploited to uncover synthetic lethal interactions with a promising future as potential clinical treatments in KRAS-mutant cancers.

Impressive and durable clinical responses obtained with dabrafenib and trametinib in low-grade serous ovarian cancer harbouring a BRAF V600E mutation

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LGSOC is characterized scarce therapeutic options in the advanced setting.

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BRAF mutations are frequent on these types of tumours.

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Dabrafenib/trametinib yield impressive responses in patients with BRAF mutations.

Low-grade serous ovarian cancer (LGSOC) is now considered a different entity from high-grade serous ovarian cancer. The chemoresistance inherent to this type of ovarian cancer narrows the therapeutic options, especially in the recurrent setting. It is thought that the mitogen-activated protein kinase (MAPK) pathway plays a significant role in the pathogenesis of these tumours, and about 2 to 20% of LGSOC harbour a BRAF mutation. Here we present a case report of two patients with a BRAF V600E mutation that achieved sustained clinical responses with combination treatment with dabrafenib (BRAF inhibitor) and trametinib (MEK inhibitor).

Mitochondrial Metabolism in Melanoma

Melanoma and its associated alterations in cellular pathways have been growing areas of interest in research, especially as specific biological pathways are being elucidated. Some of these alterations include changes in the mitochondrial metabolism in melanoma. Many mitochondrial metabolic changes lead to differences in the survivability of cancer cells and confer resistance to targeted therapies. While extensive work has gone into characterizing mechanisms of resistance, the role of mitochondrial adaptation as a mode of resistance is not completely understood. In this review, we wish to explore mitochondrial metabolism in melanoma and how it impacts modes of resistance. There are several genes that play a major role in melanoma mitochondrial metabolism which require a full understanding to optimally target melanoma. These include BRAF, CRAF, SOX2, MCL1, TRAP1, RHOA, SRF, SIRT3, PTEN, and AKT1. We will be discussing the role of these genes in melanoma in greater detail. An enhanced understanding of mitochondrial metabolism and these modes of resistance may result in novel combinatorial and sequential therapies that may lead to greater therapeutic benefit.

The importance of Ras in drug resistance in cancer

In this review, we analyse the impact of oncogenic Ras mutations in mediating cancer drug resistance and the progress made in the abrogation of this resistance, through pharmacological targeting. At a physiological level, Ras is implicated in many cellular proliferation and survival pathways. However, mutations within this small GTPase can be responsible for the initiation of cancer, therapeutic resistance and failure, and ultimately disease relapse. Often termed "undruggable," Ras is notoriously difficult to target directly, due to its structure and intrinsic activity. Thus, Ras-mediated drug resistance remains a considerable pharmacological problem. However, with advances in both analytical techniques and novel drug classes, the therapeutic landscape against Ras is changing. Allele-specific, direct Ras-targeting agents have reached clinical trials for the first time, indicating there may, at last, be hope of targeting such an elusive but significant protein for better more effective cancer therapy.

Population Pharmacokinetics/Pharmacodynamics of Dabrafenib Plus Trametinib in Patients with BRAF-Mutated Metastatic Melanoma

Patients treated with dabrafenib/trametinib (DAB/TRA) exhibit a large interindividual variability in clinical outcomes. The aims of this study were to characterize the pharmacokinetics of DAB, hydroxy-dabrafenib (OHD), and TRA in BRAF-mutated patients and to investigate the exposure–response relationship for toxicity and efficacy in metastatic melanoma (MM) patients. Univariate Fisher and Wilcoxon models including drug systemic exposure (area under the plasma concentration curve, AUC) were used to identify prognostic factors for the onset of dose-limiting toxicities (DLT), and Cox models for overall (OS) and progression-free survival (PFS). Seventy-three BRAF-mutated patients were included in pharmacokinetic (n = 424, NONMEM) and 52 in pharmacokinetic/pharmacodynamic analyses. Age and sex were identified as determinants of DAB and OHD clearances (p < 0.01). MM patients experiencing DLT were overexposed to DAB compared to patients without DLT (AUC: 9624 vs. 7485 ng∙h/mL, respectively, p < 0.01). Eastern Cooperative Oncology Group Performance Status (ECOG PS) ≥ 2 and plasma ratio AUC_OHD/AUC_DAB ≥ 1 were independently associated with shorter OS (HR: 6.58 (1.29–33.56); p = 0.023 and 10.61 (2.34–48.15), p = 0.022, respectively). A number of metastatic sites ≥3 and cerebral metastases were associated with shorter PFS (HR = 3.25 (1.11–9.50); p = 0.032 and HR = 1.23 (1.35–10.39), p = 0.011; respectively). TRA plasma exposure was neither associated with toxicity nor efficacy. Our results suggest that early drug monitoring could be helpful to prevent the onset of DLT in MM patients, especially in fragile patients such as the elderly. Regarding efficacy, the clinical benefit to monitor plasma ratio AUC_OHD/AUC_DAB deserves more investigation in a larger cohort of MM patients.