Selective High Affinity Ligands (SHALs) are small molecules that can be designed to bind selectively and with high affinity to any protein target by linking together several ligands that recognize and bind to different sites on the protein’s surface. SH7139, our first SHAL therapeutic for treating advanced non-Hodgkin’s lymphoma, has shown remarkable efficacy in B-cell lymphoma xenograft models by providing permanent cures for up to two-thirds of the animals at a human equivalent dose as low as 0.4 μg/kg. Functioning similar to an antibody-drug conjugate and a pro-drug, SH7139 targets and binds to a unique structural epitope within the antigen-binding pocket of HLA-DR10. HLA-DRs containing this epitope are expressed in approximately 85% of B-cell lymphomas. Upon binding to its HLA-DR target, SH7139 is carried into the cytoplasm where it is concentrated and subsequently metabolized, releasing toxic metabolites (derived from each of the linked ligands) that inhibit a series of cellular activities required for tumor cell function. In preparation for an IND application submission and advancing SH7139 into clinical trials, acute dose range finding (i.v. bolus) and multiple dose (i.v. bolus on days 1, 8, and 15) toxicology and safety studies have been conducted with SH7139 in rats and beagle dogs. In the rat studies, doses up to 30 mg/kg (NOAEL = 30 mg/kg, 11,854 fold higher than the efficacy dose), were well tolerated with no findings associated with the drug. Beagle dogs were found to be the most sensitive species (NOAEL = 0.3mg/kg, 395 fold higher than the efficacy dose), with doses at 1 and 10mg/kg producing a reversible allergic-type reaction. A maximum tolerated dose (MTD) was reached in rats (100 mg/kg). No attempt was made to identify the MDT in dogs. In vitro assays conducted to evaluate potential cardiac safety showed SH7139 had no effect on potassium (hERG) and calcium (hCaV1.2) ion channel function up to the highest concentration tested (25 μM). A detectable effect above background was only observed with the sodium channel hNaV1.5 at 25 μM, a plasma concentration that would only be achieved in patients administered a dose ~2,000 fold higher than the efficacy dose. SH7139 was found to be negative in inducing gene mutation in five tester strains of Salmonella and E. coli (AMES assay). In a CHO-K1 micronucleus assay, no genotoxicity was observed in the presence of S9 over the entire concentration range tested. In the absence of S9, a positive response (3.3 fold) just above the triggering threshold (3 fold) of the assay was observed at the highest SH7139 concentration (500 μM). Based on these results and others derived from mouse xenograft efficacy studies, a maximum recommended Phase I trial starting dose has been tentatively set at 0.5 μg/kg with a safety factor of 324. This research was supported by the National Cancer Institute Phase II SBIR Award R44CA159843.

Citation Format: Rod Balhorn, Monique Cosman Balhorn. Pre-clinical toxicology and safety of SH7139: The first of a new class of targeted therapeutics for non-Hodgkin's lymphoma and other cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4079. doi:10.1158/1538-7445.AM2017-4079