Small-Molecule Protein Kinases Inhibitors and the Risk of Fungal Infections

Risk of Invasive Fungal Infections in Patients With Chronic Lymphocytic Leukemia Treated With Bruton Tyrosine Kinase Inhibitors: A Case-Control Propensity Score-Matched Analysis

Background

Prior reports have suggested a possible increase in the frequency of invasive fungal infections (IFIs) with use of a Bruton tyrosine kinase inhibitor (BTKi) for treatment of chronic lymphoid malignancies such as chronic lymphocytic leukemia (CLL), but precise estimates are lacking. We aim to characterize the prevalence of IFIs among patients with CLL, for whom a BTKi is now the first-line recommended therapy.

Methods

We queried TriNetX, a global research network database, to identify adult patients with CLL using the International Classification of Diseases, Tenth Revision code (C91.1) and laboratory results. We performed a case-control propensity score-matched analysis to determine IFIs events by BTKi use. We adjusted for age, sex, ethnicity, and clinical risk factors associated with an increased risk of IFIs.

Results

Among 5358 matched patients with CLL, we found an incidence of 4.6% of IFIs in patients on a BTKi versus 3.5% among patients not on a BTKi at 5 years. Approximately 1% of patients with CLL developed an IFI while on a BTKi within this period. Our adjusted IFI event analysis found an elevated rate of Pneumocystis jirovecii pneumonia (PJP) (0.5% vs 0.3%, P = .02) and invasive candidiasis (3.5% vs 2.7%, P = .012) with the use of a BTKi. The number needed to harm for patients taking a BTKi was 120 and 358 for invasive candidiasis and PJP, respectively.

Conclusions

We found an adjusted elevated rate of PJP and invasive candidiasis with BTKi use. The rates are, however, low with a high number needed to harm. Additional studies stratifying other IFIs with specific BTKis are required to identify at-risk patients and preventive, cost-effective interventions.

Disseminated Histoplasmosis in a Patient with Myelofibrosis on Ruxolitinib: A Case Report and Review of the Literature on Ruxolitinib-Associated Invasive Fungal Infections

Ruxolitinib, a selective inhibitor of Janus kinases, is a standard treatment for intermediate/high-risk myelofibrosis (MF) but is associated with a predisposition to opportunistic infections, especially herpes zoster. However, the incidence and characteristics of invasive fungal infections (IFIs) in these patients remain uncertain. In this report, we present the case of a 59-year-old woman with MF who developed disseminated histoplasmosis after seven months of ruxolitinib use. The patient clinically improved after ten weeks of combined amphotericin B and azole therapy, and ruxolitinib was discontinued. Later, the patient received fedratinib, a relatively JAK2-selective inhibitor, without relapse of histoplasmosis. We also reviewed the literature on published cases of proven IFIs in patients with MF who received ruxolitinib. Including ours, we identified 28 such cases, most commonly due to Cryptococcus species (46%). IFIs were most commonly disseminated (39%), followed by localized lung (21%) infections. Although uncommon, a high index of suspicion for opportunistic IFIs is needed in patients receiving JAK inhibitors. Furthermore, the paucity of data regarding the optimal management of IFIs in patients treated with JAK inhibitors underscore the need for well-designed studies to evaluate the epidemiology, pathobiology, early diagnosis, and multimodal therapy of IFIs in patients with hematological malignancies receiving targeted therapies.

Pathogenicity and virulence of Aspergillus fumigatus

Pulmonary infections caused by the mould pathogen Aspergillus fumigatus are a major cause of morbidity and mortality globally. Compromised lung defences arising from immunosuppression, chronic respiratory conditions or more recently, concomitant viral or bacterial pulmonary infections are recognised risks factors for the development of pulmonary aspergillosis. In this review, we will summarise our current knowledge of the mechanistic basis of pulmonary aspergillosis with a focus on emerging at-risk populations.

Risk of Infections Secondary to the Use of Targeted Therapies in Hematological Malignancies

Concurrent infections in hematological malignancies (HM) are major contributors to adverse clinical outcomes, including prolonged hospitalization and reduced life expectancy. Individuals diagnosed with HM are particularly susceptible to infectious pathogens due to immunosuppression, which can either be inherent to the hematological disorder or induced by specific therapeutic strategies. Over the years, the treatment paradigm for HM has witnessed a tremendous shift, from broad-spectrum treatment approaches to more specific targeted therapies. At present, the therapeutic landscape of HM is constantly evolving due to the advent of novel targeted therapies and the enhanced utilization of these agents for treatment purposes. By initiating unique molecular pathways, these agents hinder the proliferation of malignant cells, consequently affecting innate and adaptive immunity, which increases the risk of infectious complications. Due to the complexity of novel targeted therapies and their associated risks of infection, it often becomes a daunting task for physicians to maintain updated knowledge in their clinical practice. The situation is further aggravated by the fact that most of the initial clinical trials on targeted therapies provide inadequate information to determine the associated risk of infection. In such a scenario, a cumulative body of evidence is paramount in guiding clinicians regarding the infectious complications that can arise following targeted therapies. In this review, I summarize the recent knowledge on infectious complications arising in the context of targeted therapies for HM.

Identifying Potential Molecular Targets in Fungi Based on (Dis)Similarities in Binding Site Architecture with Proteins of the Human Pharmacolome

Invasive fungal infections represent a public health problem that worsens over the years with the increasing resistance to current antimycotic agents. Therefore, there is a compelling medical need of widening the antifungal drug repertoire, following different methods such as drug repositioning, identification and validation of new molecular targets and developing new inhibitors against these targets. In this work we developed a structure-based strategy for drug repositioning and new drug design, which can be applied to infectious fungi and other pathogens. Instead of applying the commonly accepted off-target criterion to discard fungal proteins with close homologues in humans, the core of our approach consists in identifying fungal proteins with active sites that are structurally similar, but preferably not identical to binding sites of proteins from the so-called "human pharmacolome". Using structural information from thousands of human protein target-inhibitor complexes, we identified dozens of proteins in fungal species of the genera Histoplasma, Candida, Cryptococcus, Aspergillus and Fusarium, which might be exploited for drug repositioning and, more importantly, also for the design of new fungus-specific inhibitors. As a case study, we present the in vitro experiments performed with a set of selected inhibitors of the human mitogen-activated protein kinases 1/2 (MEK1/2), several of which showed a marked cytotoxic activity in different fungal species.

A fatal disseminated cryptococcal infection in a patient treated with zanubrutinib for Waldenström's macroglobulinemia

INTRODUCTION

Zanubrutinib is a second generation, irreversible small-molecule Bruton tyrosine kinase inhibitor (BTK) approved for the treatment of Waldenström's macroglobulinemia, mantle cell lymphoma, and marginal zone lymphoma. As a class, BTKs have been linked with an increased risk of respiratory infections in clinical trials.

CASE REPORT

We describe a 75-year-old patient who presented with generalized weakness, fevers, dyspnea, and dry cough four months after starting zanubrutinib therapy for Waldenström's macroglobulinemia. He was subsequently diagnosed with pneumonia. Septic work-up led to diagnosis of disseminated cryptococcal infection, complicated by fungal pneumonia and meningitis.

MANAGEMENT AND OUTCOME

Zanubrutinib was held on admission, and the patient was started on combination oral and intravenous antifungal therapy. Despite clearance of fungemia, aggressive resuscitation, and appropriate antimicrobial therapy, respiratory status deteriorated requiring intubation. His condition progressed to septic shock, multiorgan failure, and demise.

DISCUSSION/CONCLUSION

We report herein a case of fatal disseminated cryptococcosis in the setting of zanubrutinib use for Waldenström's macroglobulinemia. At the time of diagnosis, his Waldenström's macroglobulinemia was in a partial response. The mechanism by which Bruton tyrosine kinase inhibitors (BTKs) lead to invasive fungal infections in these patients remains to be explored. T- and B-cell immune defects accompanying low-grade B-cell lymphomas may contribute to the severity of these infections.

Disseminated blastomycosis in a patient with polycythemia vera on ruxolitinib

Ruxolitinib (RUX) is a kinase inhibitor used in the treatment of various medical conditions and its mechanism of action involves suppression of the immune system. While beneficial in treatment of polycythemia vera, myelofibrosis and other indications, it can also increase a patient's susceptibility to various infections, including bacterial, viral and fungal. We present a case of a patient being treated with RUX who presented with a disseminated fungal infection. This case emphasises the need for vigilance of endemic fungal infections in individuals who are on RUX therapy.

The safety of JAK-1 inhibitors

As efficacy and safety data emerge, differences between JAK inhibitor subclasses are appearing. JAK1 selective drugs, upadacitinib and filgotinib, have broadly come with the same overarching safety recommendations as other immunosuppressive drugs for RA: caution is needed regarding infection risk; monitoring for laboratory abnormalities, including lipids and muscle enzymes, is indicated. A distinguishing feature of JAK inhibitors is a risk for zoster reactivation. Numerically, overall rates of serious infection are similar among JAK inhibitor classes. There are currently no signals for diverticular perforation. VTE incidence rates were similar across comparator groups for the JAK1 selective agents. These observations are not yet conclusive evidence for different safety profiles between JAK1 selective agents and other JAK inhibitors. Differences in study population, design, and concomitant steroid use are examples of potential confounders. It is too early to draw conclusions on long-term outcomes such as malignancy and cardiovascular risk. Post-marketing pharmacovigilance studies will be essential.

Risk of infection associated with targeted therapies for solid organ and hematological malignancies

Higher risks of infection are associated with some targeted drugs used to treat solid organ and hematological malignancies, and an individual patient’s risk of infection is strongly influenced by underlying diseases and concomitant or prior treatments. This review focuses on risk levels and specific suggestions for management, analyzing groups of agents associated with a significant effect on the risk of infection. Due to limited clinical experience and ongoing advances in these therapies, recommendations may be revised in the near future. Bruton tyrosine kinase (BTK) inhibitors are associated with a higher rate of infections, including invasive fungal infection, especially in the first months of treatment and in patients with advanced, pretreated disease. Phosphatidylinositol 3-kinase (PI3K) inhibitors are associated with an increased risk of Pneumocystis pneumonia and cytomegalovirus (CMV) reactivation. Venetoclax is associated with cytopenias, respiratory infections, and fever and neutropenia. Janus kinase (JAK) inhibitors may predispose patients to opportunistic and fungal infections; need for prophylaxis should be assessed on an individual basis. Mammalian target of rapamycin (mTOR) inhibitors have been linked to a higher risk of general and opportunistic infections. Breakpoint cluster region-Abelson (BCR-ABL) inhibitors are associated with neutropenia, especially over the first months of treatment. Anti-CD20 agents may cause defects in the adaptative immune response, hypogammaglobulinemia, neutropenia, and hepatitis B reactivation. Alemtuzumab is associated with profound and long-lasting immunosuppression; screening is recommended for latent infections and prevention strategies against CMV, herpesvirus, and Pneumocystis infections. Checkpoint inhibitors (CIs) may cause immune-related adverse events for which prolonged treatment with corticosteroids is needed: prophylaxis against Pneumocystis is recommended.

Targeting Crucial Host Factors of SARS-CoV-2

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread worldwide since its first incidence in Wuhan, China, in December 2019. Although the case fatality rate of COVID-19 appears to be lower than that of SARS and Middle East respiratory syndrome (MERS), the higher transmissibility of SARS-CoV-2 has caused the total fatality to surpass other viral diseases, reaching more than 1 million globally as of October 6, 2020. The rate at which the disease is spreading calls for a therapy that is useful for treating a large population. Multiple intersecting viral and host factor targets involved in the life cycle of the virus are being explored. Because of the frequent mutations, many coronaviruses gain zoonotic potential, which is dependent on the presence of cell receptors and proteases, and therefore the targeting of the viral proteins has some drawbacks, as strain-specific drug resistance can occur. Moreover, the limited number of proteins in a virus makes the number of available targets small. Although SARS-CoV and SARS-CoV-2 share common mechanisms of entry and replication, there are substantial differences in viral proteins such as the spike (S) protein. In contrast, targeting cellular factors may result in a broader range of therapies, reducing the chances of developing drug resistance. In this Review, we discuss the role of primary host factors such as the cell receptor angiotensin-converting enzyme 2 (ACE2), cellular proteases of S protein priming, post-translational modifiers, kinases, inflammatory cells, and their pharmacological intervention in the infection of SARS-CoV-2 and related viruses.

Interactions of FK506 and Rapamycin With FK506 Binding Protein 12 in Opportunistic Human Fungal Pathogens

Over the past few decades advances in modern medicine have resulted in a global increase in the prevalence of fungal infections. Particularly people undergoing organ transplants or cancer treatments with a compromised immune system are at an elevated risk for lethal fungal infections such as invasive candidiasis, aspergillosis, cryptococcosis, etc. The emergence of drug resistance in fungal pathogens poses a serious threat to mankind and it is critical to identify new targets for the development of antifungals. Calcineurin and TOR proteins are conserved across eukaryotes including pathogenic fungi. Two small molecules FK506 and rapamycin bind to FKBP12 immunophilin and the resulting complexes (FK506-FKBP12 and rapamycin-FKBP12) target calcineurin and TOR, respectively in both humans and fungi. However, due to their immunosuppressive nature these drugs in the current form cannot be used as an antifungal. To overcome this, it is important to identify key differences between human and fungal FKBP12, calcineurin, and TOR proteins which will facilitate the development of new small molecules with higher affinity toward fungal components. The current review highlights FK506/rapamycin-FKBP12 interactions with calcineurin/TOR kinase in human and fungi, and development of non-immunosuppressive analogs of FK506, rapamycin, and novel small molecules in inhibition of fungal calcineurin and TOR kinase.

Properties of FDA-approved small molecule protein kinase inhibitors: A 2020 update

Because genetic alterations including mutations, overexpression, translocations, and dysregulation of protein kinases are involved in the pathogenesis of many illnesses, this enzyme family is currently the subject of many drug discovery programs in the pharmaceutical industry. The US FDA approved four small molecule protein kinase antagonists in 2019; these include entrectinib, erdafitinib, pexidartinib, and fedratinib. Entrectinib binds to TRKA/B/C and ROS1 and is prescribed for the treatment of solid tumors with NTRK fusion proteins and for ROS1-postive non-small cell lung cancers. Erdafitinib inhibits fibroblast growth factor receptors 1-4 and is used in the treatment of urothelial bladder cancers. Pexidartinib is a CSF1R antagonist that is prescribed for the treatment of tenosynovial giant cell tumors. Fedratinib blocks JAK2 and is used in the treatment of myelofibrosis. Overall, the US FDA has approved 52 small molecule protein kinase inhibitors, nearly all of which are orally effective with the exceptions of temsirolimus (which is given intravenously) and netarsudil (an eye drop). Of the 52 approved drugs, eleven inhibit protein-serine/threonine protein kinases, two are directed against dual specificity protein kinases, eleven target non-receptor protein-tyrosine kinases, and 28 block receptor protein-tyrosine kinases. The data indicate that 46 of these drugs are used in the treatment of neoplastic diseases (eight against non-solid tumors such as leukemias and 41 against solid tumors including breast and lung cancers; some drugs are used against both tumor types). Eight drugs are employed in the treatment of non-malignancies: fedratinib, myelofibrosis; ruxolitinib, myelofibrosis and polycythemia vera; fostamatinib, chronic immune thrombocytopenia; baricitinib, rheumatoid arthritis; sirolimus, renal graft vs. host disease; nintedanib, idiopathic pulmonary fibrosis; netarsudil, glaucoma; and tofacitinib, rheumatoid arthritis, Crohn disease, and ulcerative colitis. Moreover, sirolimus and ibrutinib are used for the treatment of both neoplastic and non-neoplastic diseases. Entrectinib and larotrectinib are tissue-agnostic anti-cancer small molecule protein kinase inhibitors. These drugs are prescribed for the treatment of any solid cancer harboring NTRK1/2/3 fusion proteins regardless of the organ, tissue, anatomical location, or histology type. Of the 52 approved drugs, seventeen are used in the treatment of more than one disease. Imatinib, for example, is approved for the treatment of eight disparate disorders. The most common drug targets of the approved pharmaceuticals include BCR-Abl, B-Raf, vascular endothelial growth factor receptors (VEGFR), epidermal growth factor receptors (EGFR), and ALK. Most of the approved small molecule protein kinase antagonists (49) bind to the protein kinase domain and six of them bind covalently. In contrast, everolimus, temsirolimus, and sirolimus are larger molecules (MW ≈ 1000) that bind to FK506 binding protein-12 (FKBP-12) to generate a complex that inhibits the mammalian target of rapamycin (mTOR) protein kinase complex. This review presents the physicochemical properties of all of the FDA-approved small molecule protein kinase inhibitors. Twenty-two of the 52 drugs have molecular weights greater than 500, exceeding a Lipinski rule of five criterion. Excluding the macrolides (everolimus, sirolimus, temsirolimus), the average molecular weight of the approved drugs is 480 with a range of 306 (ruxolitinib) to 615 (trametinib). More than half of the antagonists (29) have lipophilic efficiency values of less than five while the recommended optima range from 5 to 10. One of the troublesome problems with both targeted and cytotoxic drugs in the treatment of malignant diseases is the near universal development of resistance to every therapeutic modality.