Beating the Clock in T-cell Acute Lymphoblastic Leukemia

Palbociclib in combination with chemotherapy in pediatric and young adult patients with relapsed/refractory acute lymphoblastic leukemia and lymphoma: A Children's Oncology Group study (AINV18P1)

BACKGROUND

Cyclin D has been shown to play an essential role in acute lymphoblastic leukemia (ALL) initiation and progression, providing rationale for targeting the CDK4/6-cyclin D complex that regulates cell cycle progression.

PROCEDURE

The Children's Oncology Group AINV18P1 phase 1 trial evaluated the CDK4/6 inhibitor, palbociclib, in combination with standard four-drug re-induction chemotherapy in children and young adults with relapsed/refractory B- and T-cell lymphoblastic leukemia (ALL) and lymphoma. Palbociclib (50 mg/m2 /dose) was administered orally once daily for 21 consecutive days, first as a single agent (Days 1-3) and subsequently combined with re-induction chemotherapy. This two-part study was designed to determine the maximum tolerated dose (MTD) or recommended phase 2 dose (RP2D), followed by an expansion pharmacokinetic cohort.

RESULTS

Twelve heavily pretreated patients enrolled, all of whom were evaluable for toxicity. One dose-limiting hematologic toxicity (DLT) occurred at the starting dose of 50 mg/m2 /dose orally for 21 days. No additional DLTs were observed in the dose determination or pharmacokinetic expansion cohorts, and overall rates of grade 3/4 nonhematologic toxicities were comparable to those observed with the chemotherapy platform alone. Five complete responses were observed, two among four patients with T-ALL and three among seven patients with B-ALL. Pharmacokinetic studies showed similar profiles with both liquid and capsule formulations of palbociclib.

CONCLUSIONS

Palbociclib in combination with re-induction chemotherapy was well tolerated with a RP2D of 50 mg/m2 /day for 21 days. Complete responses were observed among heavily pretreated patients.

New biomarkers and therapeutic strategies in acute lymphoblastic leukemias: Recent advances

Acute lymphoblastic leukemia (ALL) represents a heterogeneous group of hematologic malignancies, and it is normally characterized by an aberrant proliferation of immature lymphoid cells. Moreover, dysregulation of multiple signaling pathways that normally regulate cellular transcription, growth, translation, and proliferation is frequently encountered in this malignancy. ALL is the most frequent tumor in childhood, and adult ALL patients still correlate with poor survival. This review focuses on modern therapies in ALL that move beyond standard chemotherapy, with a particular emphasis on immunotherapeutic approaches as new treatment strategies. Bi-specific T-cell Engagers (BiTE) antibodies, the chimeric antigen receptor (CAR)-T cells, or CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats [CRISPR]-associated nuclease 9) represent other new innovative approaches for this disease. Target and tailored therapy could make the difference in previously untreatable cases, i.e., precision and personalized medicine. Clinical trials will help to select the most efficient novel therapies in ALL management and to integrate them with existing treatments to achieve durable cures.

Chimeric antigen receptor T cells (CAR-T) for the treatment of T-cell malignancies

At present, the only curative therapy for patients with T-cell malignancies is allogeneic stem cell transplant, which has associated risks and toxicities. Novel agents have been tried in relapsed T-cell acute lymphoblastic leukemia (T-ALL), but only one, with 20%-30% complete remission rates, has been approved by the US Food and Drug Administration. T-ALL is a heterogeneous disease, but it has universal overexpression of CD7 as well as several other T-cell markers, such as CD2 and CD5. T cells engineered to express a chimeric antigen receptor (CAR) are a promising cancer immunotherapy. Such targeted therapies have shown great potential for inducing both remissions and even long-term relapse-free survival in patients with B-cell leukemia and lymphoma. UCART7 for CD7⁺ T-cell malignancies is in development for treatment of relapsed T-ALL in children and adults. It may also have potential in other CD7⁺ hematologic malignancies that lack both effective therapies and targeted therapies. The challenges encountered and progress made in developing a novel fratricide-resistant "off-the-shelf" CAR-T (or UCART7) that targets CD7⁺ T-cell malignancies are discussed here.

Strategies to Overcome Resistance Mechanisms in T-Cell Acute Lymphoblastic Leukemia

Chemoresistance is a major cause of recurrence and death from T-cell acute lymphoblastic leukemia (T-ALL), both in adult and pediatric patients. In the majority of cases, drug-resistant disease is treated by selecting a combination of other drugs, without understanding the molecular mechanisms by which malignant cells escape chemotherapeutic treatments, even though a more detailed genomic characterization and the identification of actionable disease targets may enable informed decision of new agents to improve patient outcomes. In this work, we describe pathways of resistance to common chemotherapeutic agents including glucocorticoids and review the resistance mechanisms to targeted therapy such as IL7R, PI3K-AKT-mTOR, NOTCH1, BRD4/MYC, Cyclin D3: CDK4/CDK6, BCL2 inhibitors, and selective inhibitors of nuclear export (SINE). Finally, to overcome the limitations of the current trial-and-error method, we summarize the experiences of anti-cancer drug sensitivity resistance profiling (DSRP) approaches as a rapid and relevant strategy to infer drug activity and provide functional information to assist clinical decision one patient at a time.

Targeting mTOR in Acute Lymphoblastic Leukemia

Acute Lymphoblastic Leukemia (ALL) is an aggressive hematologic disorder and constitutes approximately 25% of cancer diagnoses among children and teenagers. Pediatric patients have a favourable prognosis, with 5-years overall survival rates near 90%, while adult ALL still correlates with poorer survival. However, during the past few decades, the therapeutic outcome of adult ALL was significantly ameliorated, mainly due to intensive pediatric-based protocols of chemotherapy. Mammalian (or mechanistic) target of rapamycin (mTOR) is a conserved serine/threonine kinase belonging to the phosphatidylinositol 3-kinase (PI3K)-related kinase family (PIKK) and resides in two distinct signalling complexes named mTORC1, involved in mRNA translation and protein synthesis and mTORC2 that controls cell survival and migration. Moreover, both complexes are remarkably involved in metabolism regulation. Growing evidence reports that mTOR dysregulation is related to metastatic potential, cell proliferation and angiogenesis and given that PI3K/Akt/mTOR network activation is often associated with poor prognosis and chemoresistance in ALL, there is a constant need to discover novel inhibitors for ALL treatment. Here, the current knowledge of mTOR signalling and the development of anti-mTOR compounds are documented, reporting the most relevant results from both preclinical and clinical studies in ALL that have contributed significantly into their efficacy or failure.