Salvage Therapy with Gilteritinib Plus Venetoclax for FLT3-ITD-Positive AML: A Case Report and Literature Review

Introduction

Acute myeloid leukemia (AML) is a malignancy of the hematopoietic system, which is characterized by clonal evolution and genetic heterogeneity. In AML there are numerous recurrent genetic mutations to determine prognosis. Among which FMS-like tyrosine kinase 3 (FLT3) remains as one of the most frequently mutated genes^[1]. There are two distinct types of activating mutations that have been identified in AML samples. One is internal tandem duplications in the juxtamembrane domain (ITD) and the other is point mutations in the tyrosine kinase domain (TKD)^[2]. It has been established that FLT3-ITD mutation with a normal karyotype is associated with poor prognosis^[3]. Identification of FLT3-ITD mutation is important not only for risk stratification of patients with AML based on the genetic status of FLT3 but also for development of a molecular targeting drug.

Gilteritinib is a potent and selective FLT3 inhibitor, which actively inhibits FLT3-ITD, FLT3-TKD, tyrosine kinase AXL and weak activity inhibits c-Kit^[4,5], and has single-agent clinical efficacy in R/R AML with FLT3 mutations^[6,7]. But the role of gilteritinib in combination of chemotherapy or targeted agents remains unclear. It is possible that the combination of gilteritinib and targeted agents provides longer survival and higher remission rates in patients with FLT3 mutations compared with salvage therapy. Here, we reported a case of refractory AML with FLT3-ITD mutation in which the combination regimen of gilteritinib and venetoclax was performed and CR was observed at 4 months after the initiation of salvage treatment.

Case presentation

A 62-years old male was admitted to the Hematology of the Second Affiliated Hospital of Air Force Military Medical University on January 3, 2021, because of fever. The physical examination showed edema of both lower limbs, but it did not indicate hepatosplenomegaly or lymphadenopathy. The patient had a history of "subarachnoid hemorrhage" and a history of "after endoscopic operation of left renal upper pole clear cell carcinoma". Results of the laboratory examination indicated leucocytosis, and thrombocytopenia. The following findings were observed: white blood cell count, 46.7 × 10⁹/L; hemoglobin level, 131 g/L; platelet count, 86 × 10⁹/L; neutrophil count, 3.77 × 10⁹/L; lymphocyte count, 6 × 10⁹/L; monocyte count, 36.9 × 10⁹/L. Lactate dehydrogenase was 458 IU/L and C-reactive protein level was 88.2 mg/L. The morphological examination of bone marrow (BM) aspirate showed 89.5% myeloblast cells of large size. The immunophenotypic analysis performed on a FACScalibur flow cytometer using standard protocol revealed that blast cells were CD25+, CD117+, CD11c+, cMPO+, CD200+, CD38+, CD33+, CD34+/−, CD2+/−, CD64+/−. The patient was classified as M1 under the FAB classification. Elevated Wilms tumor gene (WT1) expression was detected by quantitative real-time PCR. Chromosomal G-banding of BM cells revealed 46, XY, [20]. The next generation sequencing (NGS) was used to screen for the presence of 34 recurrently mutated genes in myeloid cancers, and the result showed that NRAS Q61R (5.46%) and FLT3-ITD (152.17%) mutations were detected.

Because of the absence of gilteritinib, we used conventional chemotherapy after the consent of the patient's family. First, hydroxyurea was used to reduce leukocytes, then according to the successful treatment of elderly patients with AML^[8-10], the following chemotherapy regimen were administered (Fig. 1): decitabine combined with CAG regimen; venetoclax combined with azacytidine regimen; the standard “3+7” regimen. After the above three courses of induction chemotherapy, but CR was not achieved, and the monitoring of bone marrow and peripheral blood myeloblast cells were > 90%. During the whole treatment period, the patient was complicated with grade IV hematological adverse events and recurrent appeared oral mucositis, after the treatment of anti-infection, stimulating bone marrow hematopoiesis with granulocyte colony-stimulating factor (G-CSF) and Interleukin-11 (IL-11), and gargling with IL-11, the patient successfully overcame the bone marrow suppression period. We have repeatedly recommended the patient for allogeneic hematopoietic stem cell transplantation (allo-HSCT), but the patient’ family refused, and also the patient did not have a suitable relative donor.

Figure  1.  Clinical course.

DAC-CAG decitabine 25 mg/day on days 1-5, arorubicin 10 mg/day on days 3-6, cytarabine 10 mg/m² 1/12 h on days 3-9, G-CSF 5 ug/kg/day when necessary. AZA Venetoclax azacytidine 75 mg/m²/day on days 1-7, venetoclax 100 mg day 1, 200 mg day 2, 400 mg on days 3-28. IA idarubicin 12 mg/m²/day on days 1-3, cytarabine 100 mg/m²/day on days 1-7. Gilteritinib Venetoclax gilteritinib 120 mg/day on days 1-28, venetoclax 100 mg/day on days 1-28. Gilteritinib Venetoclax Low-dose HA gilteritinib 120 mg/day on days 1-28, venetoclax 100 mg/day on days 1-28, homoharringtonine 1 mg/day on days 1-14, cytarabine 10 mg/m² 1/12 h on days 1-14.

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At this time, gilteritinib was finally available, so the fourth course of induction chemotherapy was treated with FLT3 inhibitor gilteritinib combined with venetoclax regimen (Fig.1), while CYP3A4 inhibitor voriconazole was given for aspergillus infection. After this course of induction chemotherapy, monitoring bone marrow showed that the proportion of myeloblast cells accounted for 26.0%. It suggested that the proportion of bone marrow myeloblast cells decreased significantly, although CR was not achieved. Taking advantage of the victory, again the patient received the former gilteritinib combined with venetoclax regimen. After this course of treatment, monitoring bone marrow showed that the proportion of myeloblast cells accounted for 2.5%, suggesting that CR was achieved finally. During the whole treatment process, only grade IV hematological adverse events were observed, and non hematological adverse events such as elevated transaminase and QT prolongation were not observed. However, during the consolidation treatment with gilteritinib combined with venetoclax, the primary disease continued to progress till to recurrence, meanwhile FLT3-ITD mutation burden has decreased to 2.74% and NRAS Q61R mutation burden has increased to 41.75% monitored by NGS. Unfortunately, the patient died because of severe infection and multiple organ failure on August 31, 2021.

Discussion

FLT3 gene is located on chromosome 13q12 and contains 24 exons, that can encode a receptor tyrosine kinase^[11,12]. It is normally expressed by hematopoietic stem cells or progenitor cells and plays an important role in the early stage of both myeloid and lymphoid lineage development^[13] . Mutations of FLT3 can destroy the proliferation, differentiation and apoptosis of normal blood cells, lead to the occurrence of leukemia. It is related to the progress of the leukemia. Mutations of FLT3 usually occur in the form of ITD or TKD^[14]. Both FLT3-ITD and FLT3-TKD mutations constitutively activate FLT3 kinase activity, resulting in proliferation and survival of AML^[13] . AML patients with FLT3-ITD mutations often have a particularly poor prognosis, compared with patients without FLT3-ITD mutations. Patients with FLT3-ITD mutations have been specifically associated with higher leukemic burden, increased risk of recurrence and shorter overall survival (OS), which suggests a poor prognosis of leukemia^[3,15]. Current studies have shown that^[16,17], FLT3-ITD^high confers a poorer prognosis, and has a worse impact on the management of patients with AML. Thus, the NCCN and ELN guidelines stratify patients with FLT3-ITD^high mutations into poor/adverse risk group^[18,19].

This patient was a refractory one who could not yet achieved CR after three efficacy standard courses of induction chemotherapy. For decades, the effective treatment of R/R AML has been a severe challenge for hematologists, the 1-year OS for adult patients with R/R AML is less than 10%^[20-22]. Allo-HSCT is still the only means to cure R/R AML, but most R/R AML do not have the conditions for allo-HSCT. With the continuous development of molecular diagnosis technology, targeted therapy brings light to patients who are not suitable for allo-HSCT. In view of the high incidence of FLT3 mutation in AML, many tyrosine kinase inhibitors (TKIs) are investigated, that can destroy the carcinogenic signal initiated by FLT3 and improve the prognosis of FLT3 positive AML patients. Compared with the first-generation FLT3 inhibitors, the second-generation FLT3 inhibitors, including gilteritinib, quizartinib and crenolanib, have greater specificity and higher potency^[23].

Gilteritinib is class I inhibitor that target both the active and inactive conformational states of the FLT3 kinase domain^[24], which can prolong OS duration of R/R AML with FLT3 mutation and a favorable safety profile^[7]. The latest research data from the ADMIRAL study^[6], which is an open-label, multicenter, randomized phase III study, aims to study the effectiveness of FLT3 inhibitor gilteritinib by comparing gilteritinib with salvage chemotherapy in R/R AML with FLT3 mutation, shows that the CRc (composite CR) rate reached 54.3% and the CR / CRh (complete remission with partial hematologic recovery) rate is 34% for those patients treated with gilteritinib single, which are better than those patients treated with salvage chemotherapy. The median DOR (duration of remission) of CR / CRh in gilteritinib group is 11.0 months, and the median time to the first compound CR was 1.8 months, which are also better than that in salvage chemotherapy group. In patients with R/R AML with FLT3 mutations, the median OS of patients treated with gilteritinib single is 9.3 months, which is significantly better than that of salvage chemotherapy group (5.6 months). When the median follow-up time was 17.8 months (about 1.5 years), the risk of death in patients treated with gilteritinib single decreased by 36%, and when the median follow-up time was 29.2 months (about 2.5 years), the risk of death in patients treated with gilteritinib single decreased by 32%, which is still significantly better than those receiving salvage chemotherapy. Based on these data, gilteritinib has been approved by US FDA for R/R AML patients with FLT3 mutation in November 2018 and also treatment strategies have been changed ^[25].

Venetoclax is an oral highly selective Bcl-2 inhibitor and an analog of a member of the bcl-2 protein family. It directly binds to Bcl-2 protein, replaces Bim and other proteins that assist apoptosis, triggers the change of mitochondrial outer membrane permeability and the activation of cysteine protease, promotes the activation of internal apoptosis pathway, and leads to leukemic cell death^[26]. Venetoclax can selectively kill leukemic cells and increase the sensitivity of leukemic cells to chemotherapeutic drugs ^[27]. However, the study shows that^[28], the curative effect in R/R AML patients with FLT3 mutation treated with venetoclax single and / or combined with chemotherapeutic drugs is limited, there are only 21% of patients received treatment response, the median survival time of all patients is 3.0 months (range 0.5-8.0), and the estimated 6-month survival rate is 24%. DiNardo and his colleagues^[29] have reported that FLT3-ITD is the driver of the primary resistance to venetoclax, because it can enhance the expression of anti-apoptotic BCL-2 relatives like BCL-XL and MCL-1, leading to resistance and clonal evolution. Thus, simultaneous targeting of BCL-2 and FLT3 may be an effective approach to overcome resistance to venetoclax therapy in AML patients. A multicenter, open-label, phase 1b trial (NCT03625505) had been conducted to assess safety and efficacy of venetoclax in combination with gilteritinib for R/R AML. Patients in the dose expansion cohort received venetoclax 400mg and gilteritinib 120mg daily in 28 day cycle. This trail showed that mCRc was achieved 74.5% (38/51) and the median OS was 10 months among all FLT3⁺ patients. In addition, this trail also showed that FLT3 mutaion clearance was seen in a majority of patients and associated with longer OS time. At present, there are few relevant clinical reports.

This patient in our research is an elderly patient with FLT3-ITD^high mutation, and the primary disease is difficult to treat. After comprehensive evaluation and the consent of the patient's family, gilteritinib was given at 80 mg daily and venetoclax was given at 100 mg daily. After two courses of above treatment, the clinical efficacy was evaluated as CR, and the FLT3-ITD mutation burden detected by NGS decreased to 2.74%, suggesting that the molecular response of gilteritinib was good. However, the patient's primary disease progresses rapidly and the disease relapses, and the NRAS Q61R mutation burden significantly increased monitored by NGS. Subsequently, the patient's state of physical condition deteriorated rapidly, and again given gilteritinib combined with venetoclax was ineffective. At the same time, the patient developed multiple organ failure due to disease progression, and finally died. The OS time was 7.8 months. Comparison with clinical trial (NCT03625505), the patient in our research had a shorter OS time (7.8 VS 10 months). It also seemed that FLT3 mutaion clearance did not prolong survival time. Through literature review, we found that the acquisition of various somatic mutations may confer resistance to gilteritinib. McMahon et al. have reported that^[30], RAS mutations develop in FLT3-mutant cells during gilteritinib therapy, indicating that the most common mechanism of resistance to gilteritinib is the acquisition of activating RAS/MAPK pathway mutations. These results are consistent with our findings that NRAS Q61R mutation burden has increased obviously after two courses of gilteritinib combined with venetoclax. Despite high initial response rates, gilteritinib is limited by the development of resistance leading to leukemia relapse, typically within weeks to months. McMahon et al^[30] have also reported that the combination of FLT3 and MEK inhibitors may overcome RAS/MAPK pathway-mediated resistance to gilteritinib.

In our cases, gilteritinib was given in combination with venetoclax, and the most common side effect was myelosuppression. In addition, the important side effects such as hepatotoxicity and QT prolongation were not observed.

In conclusion, this case highlighted that gilteritinib could be effective in R/R AML patients with FLT3 mutation in addition to traditional chemotherapy. During administration of gilteritinib, grade IV hematological adverse events were observed, but it was controlled. Although response rate to gilteritinib is high, clonal evolution in AML after gilteritinib should be eradicated to prolong response and survival time.

Abbreviations

AML, acute myeloid leukemia; allo-HSCT, allogeneic hematopoietic stem cell transplantation; BCL2, B-cell lymphoma 2; BCL-XL, B-cell lymphoma XL; CAG, arorubicin combined with cytarabine and G-CSF; CR, complete remission; CRc, composite complete remission; CRh, complete remission with partial hematologic recovery; CYP3A4, cytochrome P450 3A4; DAC, decitabine; DOR, duration of remission; ELN, European LeukmiaNet; FDA, the US Food and Drug Administration; FLT3, FMS-like tyrosine kinase 3; FLT3-ITD, FLT3 mutation in the internal tandem duplication; FLT3-TKD, FLT3 mutation in the tyrosine kinase domain; G-CSF, Granulocyte colony stimulating factor; HA, homoharringtonine and cytarabine; IL-11, interleukin-11; MCL-1, myeloid cell leukemia-1; NCCN, National Comprehensive Cancer Network; NGS, next generation sequencing; OS, overall survival; PCR, polymerase chain reaction; R/R, relapsed or refractory; SC, salvage chemotherapy; WT1, Wilms tumor gene.

Funding

This work was supported by the Key Research and Development Projects in Shaanxi Province (2019SF-080).

Conflicts of interest

All authors declared that there are no conflicts of interest.

Authors’ contributions

DL wrote the manuscript, analyzed all data, prepared all tables and figures, and conducted the most of the experimental work. DL and LL performed the initial analyses, and reviewed and revised the manuscript. WWQ critically reviewed the manuscript. All authors approved the final manuscript and agreed to be accountable for all aspects of the work.