Lack of comparability between binding of monoclonal antibodies to melanoma cells in vitro and localization in vivo

In Silico Investigation of the Clinical Translatability of Competitive Clearance Glucose-Responsive Insulins

The glucose-responsive insulin (GRI) MK-2640 from Merck was a pioneer in its class to enter the clinical stage, having demonstrated promising responsiveness in in vitro and preclinical studies via a novel competitive clearance mechanism (CCM). The smaller pharmacokinetic response in humans motivates the development of new predictive, computational tools that can improve the design of therapeutics such as GRIs. Herein, we develop and use a new computational model, IM3PACT, based on the intersection of human and animal model glucoregulatory systems, to investigate the clinical translatability of CCM GRIs based on existing preclinical and clinical data of MK-2640 and regular human insulin (RHI). Simulated multi-glycemic clamps not only validated the earlier hypothesis of insufficient glucose-responsive clearance capacity in humans but also uncovered an equally important mismatch between the in vivo competitiveness profile and the physiological glycemic range, which was not observed in animals. Removing the inter-species gap increases the glucose-dependent GRI clearance from 13.0% to beyond 20% for humans and up to 33.3% when both factors were corrected. The intrinsic clearance rate, potency, and distribution volume did not apparently compromise the translation. The analysis also confirms a responsive pharmacokinetics local to the liver. By scanning a large design space for CCM GRIs, we found that the mannose receptor physiology in humans remains limiting even for the most optimally designed candidate. Overall, we show that this computational approach is able to extract quantitative and mechanistic information of value from a posteriori analysis of preclinical and clinical data to assist future therapeutic discovery and development.

Single tumor imaging with multiple antibodies targeting different antigens

Antibodies are important drugs for treating cancer and there is strong rationale for using multiple antibodies to improve outcomes. We labeled two breast cancer binding antibodies, anti-ErbB2 and anti-EpCAM, with infrared fluorescence dyes of different wavelengths and determined their in vivo distribution in a breast cancer xenograft model using a near-infrared (NIR) fluorescence imaging system. Our data show that these two antibodies can be readily assessed simultaneously in mouse xenograft model. This will help guide design of dosing strategies for multiple antibodies and identify potential interaction that could affect pharmacokinetics and possible side effects.

Selective delivery of adriamycin to a solid tumor using a polymeric micelle carrier system

The anticancer drug, adriamycin (ADR), was incorporated by physical entrapment into polymeric micelles for selective delivery to a murine solid tumor colon adenocarcinoma 26 (C 26). In vivo antitumor activity of ADR was greatly enhanced by this incorporation into polymeric micelles. Using one polymeric micelle delivery system, the tumor completely disappeared at two doses, while free ADR exhibited a fair inhibition effect on tumor growth only at the maximum tolerated dose. Biodistribution analysis revealed that the physically entrapped micellar ADR accumulated at tumor sites in a highly selective manner. These results indicate that these polymeric micelles are a promising system for delivering hydrophobic anticancer drugs selectively to solid tumor sites using a passive targeting mechanism.

Clinical radioimmunotherapy

Radioimmunotherapy (RIT) is a promising new therapy for the treatment of a variety of malignancies. General principles of RIT are discussed, including important considerations in the selection of monoclonal antibodies (MAb) and radionuclides for RIT. Results of clinical trials using RIT for the treatment of lymphoma, leukemia, and solid tumors are summarized. The results from many of these trials are promising, especially for the treatment of lymphohematopoietic malignancies, in which a variety of MAb, radionuclides, and study designs have resulted in high response rates with a number of durable responses. Encouraging results have also been obtained using RIT to treat some solid tumors, primarily in patients with relatively low tumor burdens. RIT is generally well tolerated, with the primary toxicity being transient reversible myelosuppression in most nonmyeloablative studies. Nonhematologic toxicity, especially at nonmyeloablative doses, has been minimal in most studies. Approaches for increasing the therapeutic index of RIT are reviewed, which may further potentiate the efficacy and decrease the toxicity of RIT.

Direct in vivo measurement of targeted binding in a human tumor xenograft

Binding is crucial to the function of most biologically active molecules, but difficult to quantify directly in living tissue. To this end, fluorescence recovery after photobleaching was used to detect the immobilization of fluorescently labeled ligand caused by binding to receptors in vivo. Measurements of mAb affinity to target antigen within human tumor xenografts revealed a saturable binding isotherm, from which an in vivo carcinoembryonic antigen density of 0.56 nmol/g (5.0 x 10(5)/cell) and an association constant of Ka < or = 4 x 10(7) M(-1) were estimated. The present method can be adapted for in vivo studies of cell signaling, targeted drugs, gene therapy, and other processes involving receptor-ligand binding.

Epitope masking of rat esophageal carcinoma tumor-associated antigen by certain coexisting glycolipid and phospholipid molecules: a potential mechanism for tumor cell escape from the host immune responses

A monoclonal antibody (mAb-5G) produced against a tumorigenic rat esophageal cell line, B2T, was shown to react specifically with a unique glycolipid antigen expressed on the cell surface of tumorigenic and certain non-tumorigenic, immortalized rat esophageal cell lines [Cancer Immunol Immunother 36: 94 (1993)]. In enzyme-linked immunosorbent assay experiments, mAb-5G reacted with crude lipid extracts prepared from B2T cells cultured in vitro, but showed very little reactivity with crude lipid extracts prepared from the same cell line passaged once in vivo, unless the antigen was separated from other lipid components by column or thin-layer chromatography (TLC). When a secondary tissue-culture cell line was established from the above B2T tumor tissues and serially subcultured in vitro, the percentage of positively stained cells was increased significantly in immunofluorescence assay. It was also demonstrated that the amount of extractable antigen was increased as the cells were subcultured in vitro up to passage 15, and stabilized thereafter. These results indicate the presence of certain lipid components in crude lipid extracts from B2T cells grown in vivo that are capable of interfering with antigen-antibody binding. On TLC plates, these interfering lipids were identified as phosphatidylcholine, phosphatidylserine, sphingomyelin and gangliosides. The interfering lipids did not bind the antibody, rather they appeared to interfere with antigen accessibility. These lipid substances may modify tumor cell surface antigen(s), thus protecting the tumor cells from host immune destruction.

Localization and therapy of human cervical tumor xenografts with radiolabeled monoclonal antibody 1H10

Murine IgG3 monoclonal antibody (Mab) 1H10, which recognizes a tumor-associated antigen expressed on the surface of more than 40% of human cervical carcinoma tissues, was used for in vivo localization and therapy of cervical tumor xenografts. A human cervical carcinoma cell line, CaSki, was used as our experimental tumor system. Mab 1H10 antigen expression on the surface of CaSki cells was found to be cell-cycle independent. The ability of Mab 1H10 F(ab')2 to bind to CaSki tumor xenografts was verified by direct immunohistochemical staining of thin tumor sections with a Mab 1H10-peroxidase conjugate. Radioimmunoscintigraphy of nude mice bearing CaSki tumors after iv administration of [131I]1H10 F(ab')2 showed clear tumor images 48 hr after Mab injection. Radiolabeled Mab 1H10 F(ab')2 was found to specifically localize in solid CaSki tumors 96 hr after antibody injection. Radioactivity in tumor tissue was 4 times higher than that in kidney tissue and over 6 times higher than that in liver tissue. Mab 1H10 F(ab')2 binding to xenografted CaSki tumors was 17 times greater than a control IgG3 F(ab')2 after 96 hr. Therapy of athymic mice bearing established CaSki tumors with three iv injections of 100 microCi [131I]1H10 F(ab')2 resulted in extensive tumor necrosis and significant suppression (p < 0.05) of tumor growth compared to that in control mice. These results indicate that Mab 1H10 F(ab')2 may be clinically useful for detection or treatment of cervical cancer.