Comparison of Pyrrolobenzodiazepine Dimer Bis-imine versus Mono-imine: DNA Interstrand Cross-linking, Cytotoxicity, Antibody-Drug Conjugate Efficacy and Toxicity.

Antibody-drug conjugates (ADC) delivering pyrrolobenzodiazepine (PBD) DNA cross-linkers are currently being evaluated in clinical trials, with encouraging results in Hodgkin and non-Hodgkin lymphomas. The first example of an ADC delivering a PBD DNA cross-linker (loncastuximab tesirine) has been recently approved by the FDA for the treatment of relapsed and refractory diffuse large B-cell lymphoma. There has also been considerable interest in mono-alkylating PBD analogs. We conducted a head-to-head comparison of a conventional PBD bis-imine and a novel PBD mono-imine. Key Mitsunobu chemistry allowed clean and convenient access to the mono-imine class. Extensive DNA-binding studies revealed that the mono-imine mediated a type of DNA interaction that is described as "pseudo cross-linking," as well as alkylation. The PBD mono-imine ADC demonstrated robust antitumor activity in mice bearing human tumor xenografts at doses 3-fold higher than those that were efficacious for the PBD bis-imine ADC. A single-dose toxicology study in rats demonstrated that the MTD of the PBD mono-alkylator ADC was approximately 3-fold higher than that of the ADC bearing a bis-imine payload, suggesting a comparable therapeutic index for this molecule. However, although both ADCs caused myelosuppression, renal toxicity was observed only for the bis-imine, indicating possible differences in toxicologic profiles that could influence tolerability and therapeutic index. These data show that mono-amine PBDs have physicochemical and pharmacotoxicologic properties distinct from their cross-linking analogs and support their potential utility as a novel class of ADC payload.

Preclinical and phase I studies of KA2237, a selective and potent inhibitor of PI3K ß/δ in relapsed refractory B cell lymphoma.

PI3-kinase p110δ is mainly expressed in lymphocytes and is an attractive therapeutic target in B cell lymphomas. Targeting p110ß may further suppress tumor growth and overcome escape mechanisms. KA2237 is an oral, potent, dual p110ß/p110δ inhibitor. In preclinical studies, KA2237 inhibited p110ß- and p110δ-dependent AKT activation and suppressed proliferation of diverse hematological and epithelial tumors. Twenty-one patients received KA2237 in a first-in-human phase I study (NCT02679196; diffuse large B cell, n = 8; follicular, n = 5; mantle cell, n = 3; chronic lymphocytic leukemia/small lymphocytic lymphoma, n = 3; marginal zone, n = 1; Waldenstrom's, n = 1). Median age 69; median prior therapies 3. Eighty-six percent of patients experienced treatment-related adverse events (TRAEs). Forty-three percent of patients experienced grade ≥3 TRAEs, with rash (n = 3), pneumonia (n = 3), transaminitis (n = 2), and pneumonitis (n = 2) being most common. Thirty-three percent discontinued treatment due to adverse events. KA2237 induced objective responses in indolent and aggressive lymphoma (overall response rate 37%; complete response n = 4, partial response n = 3).

Preclinical Development and First-in-Human Study of KA2507, a Selective and Potent Inhibitor of Histone Deacetylase 6, for Patients with Refractory Solid Tumors.

PURPOSE: Inhibition of histone deacetylase 6 (HDAC6) is predicted to deliver both direct antitumor activity and modulation of the antitumor immune response. This study describes the development of a novel HDAC6 inhibitor. PATIENTS AND METHODS: KA2507 was characterized in HDAC biochemical and cellular target engagement assays and in preclinical efficacy models of melanoma and colorectal cancer. In a phase I study, KA2507 was administered orally using a 3+3 dose-escalation design (NCT03008018). RESULTS: KA2507 is a potent and selective inhibitor of HDAC6 (biochemical IC50 = 2.5 nmol/L). Preclinical models demonstrated antitumor efficacy in syngeneic tumor-bearing mice, with translational studies highlighting modulation of the antitumor immune response. Twenty patients were treated in a phase I study. KA2507 was well tolerated; dose-limiting toxicity was not observed up to the maximum dose administered. Pharmacokinetic profiling supported twice-daily oral dosing. Pharmacodynamic analysis demonstrated selective HDAC6 target engagement in peripheral blood cells, free from off-target class I HDAC activity. Stable disease was the best clinical response (7 patients). Three of these patients (adenoid cystic carcinoma, n = 2; rectal adenocarcinoma, n = 1) had prolonged disease stabilization that lasted for 16.4, 12.6, and 9.0 months, respectively. CONCLUSIONS: KA2507 is a potent and selective inhibitor of HDAC6 showing antitumor efficacy and immune modulatory effects in preclinical models. In a phase I study, KA2507 showed selective target engagement, no significant toxicities, and prolonged disease stabilization in a subset of patients. Further clinical studies of KA2507 are warranted, as a single agent or, preferably, combined with other immuno-oncology drugs.

Fibrodysplasia induced in dog skin by a matrix metalloproteinase (MMP) inhibitor--a mechanistic analysis.

Matrix metalloproteinase (MMP) inhibitors, candidate therapeutic agents for a number of diseases, are known to be associated with acute fibrosis-type adverse effects in a number of species, including humans. The broad-spectrum MMP inhibitor, AZM551248, has previously been shown to cause these effects in the dog. Changes were characterized by the abnormal and extensive proliferation of fibroblasts and the deposition of collagen particularly in the subcutaneous connective tissues (subcutis) and were termed fibrodysplasia (FD). We performed a time-course study in dogs using AZM551248 and sampled skin, subcutis, and plasma before and during the development of FD. Detailed histopathological analysis and global gene expression profiling were performed on the subcutaneous tissues. The gene expression analysis of the subcutis indicated that extracellular matrix (ECM) remodeling was initiated asymptomatically at or before the earliest time point, day 4, and this was associated with dysregulation of expression of a number of MMPs and proteolytic enzymes. At later time points, the FD became progressively more extensive and severe, and this was associated with gene expression changes characteristic of tissue fibrosis, for example those associated with procollagen synthesis and processing. We postulate that AZM551248 inhibition of MMP action within the subcutis modulates the activity of several transcription factors and this in turn upregulates expression of specific proteases which initiate ECM remodeling. Persistent MMP inhibition results in the progression of ECM remodeling, culminating in collagen deposition and overt fibrosis. Our data indicate that inhibition of MMPs 1, 2, 3, and 9 is a key early event in AZM551248-induced FD in dog subcutis.