Neurotoxicity Associated with Treatment of Acute Lymphoblastic Leukemia Chemotherapy and Immunotherapy

Immunotherapy is a milestone in the treatment of poor-prognosis pediatric acute lymphoblastic leukemia (ALL) and is expected to improve treatment outcomes and reduce doses of conventional chemotherapy without compromising the effectiveness of the therapy. However, both chemotherapy and immunotherapy cause side effects, including neurological ones. Acute neurological complications occur in 3.6–11% of children treated for ALL. The most neurotoxical chemotherapeutics are L-asparaginase (L-ASP), methotrexate (MTX), vincristine (VCR), and nelarabine (Ara-G). Neurotoxicity associated with methotrexate (MTX-NT) occurs in 3–7% of children treated for ALL and is characterized by seizures, stroke-like symptoms, speech disturbances, and encephalopathy. Recent studies indicate that specific polymorphisms in genes related to neurogenesis may have a predisposition to MTX toxicity. One of the most common complications associated with CAR T-cell therapy is immune effector cell-associated neurotoxicity syndrome (ICANS). Mechanisms of neurotoxicity in CAR T-cell therapy are still unknown and may be due to disruption of the blood–brain barrier and the effects of elevated cytokine levels on the central nervous system (CNS). In this review, we present an analysis of the current knowledge on the mechanisms of neurotoxicity of standard chemotherapy and the targeted therapy in children with ALL.

Characterization of Disulfide Bond Rebridged Fab-Drug Conjugates Prepared Using a Dual Maleimide Pyrrolobenzodiazepine Cytotoxic Payload

We describe the characterization of antigen binding fragments (Fab)-drug conjugates prepared using a dual maleimide pyrrolobenzodiazepine dimer cytotoxic payload (SG3710). Pyrrolobenzodiazepine dimers, which are DNA cross-linkers, are a class of payloads used in antibody-drug conjugates (ADCs). SG3710 was designed to rebridge two adjacent cysteines, such as those that form the canonical interchain disulfide bond between the light and heavy chain in Fab fragments. The rebridging generated homogenous Fab conjugates, with a drug-to-Fab ratio of one, as demonstrated by the preparation of rebridged Fabs derived from the anti-HER2 trastuzumab antibody and from a negative control antibody both prepared using recombinant expression and papain digestion. The resulting anti-HER2 trastuzumab Fab-rebridged conjugate retained antigen binding, was stable in rat serum, and demonstrated potent and antigen-dependent cancer cell-killing ability. Disulfide rebridging with SG3710 is a generic approach to prepare Fab-pyrrolobenzodiazepine dimer conjugates, which does not require the Fabs to be engineered for conjugation. Thus, SG3710 offers a flexible and straightforward platform for the controlled assembly of pyrrolobenzodiazepine dimer conjugates from any Fab for oncology applications.

Chk1 Inhibition Restores Inotuzumab Ozogamicin Citotoxicity in CD22-Positive Cells Expressing Mutant p53

Inotuzumab ozogamicin (IO) is an anti-CD22 calicheamicin immunoconjugate that has been recently approved for the treatment of relapsed or refractory B-Acute Lymphoblastic Leukemia (r/r B-ALL). We employed both immortalized and primary cells derived from CD22-positive lymphoproliferative disorders to investigate the signaling pathways contributing to IO sensitivity or resistance. We found that the drug reduced the proliferation rate of CD22-positive cell lines expressing wild-type p53, but was remarkably less effective on cells exhibiting mutant p53. In addition, CD22-positive cells surviving IO were mostly blocked in the G2/M phase of the cell cycle because of Chk1 activation that, in the presence of a wild-type p53 background, led to p21 induction. When we combined IO with the Chk1 inhibitor UCN-01, we successfully abrogated IO-induced G2/M arrest regardless of the underlying p53 status, indicating that the DNA damage response triggered by IO is also modulated by p53-independent mechanisms. To establish a predictive value for p53 in determining IO responsiveness, we expressed mutant p53 in cell lines displaying the wild-type gene and observed an increase in IO IC₅₀ values. Likewise, overexpression of an inducible wild-type p53 in cells natively presenting a mutant protein decreased their IC₅₀ for IO. These results were also confirmed in primary CD22-positive cells derived from B-ALL patients at diagnosis and from patients with r/r B-ALL. Furthermore, co-treatment with IO and UCN-01 significantly increased cell death in primary cells expressing mutant p53. In summary, our findings suggest that p53 status may represent a biomarker predictive of IO efficacy in patients diagnosed with CD22-positive malignancies.