DeBouganin Diabody Fusion Protein Overcomes Drug Resistance to ADCs Comprised of Anti-Microtubule Agents.

Antibody drug conjugates (ADC), comprised of highly potent small molecule payloads chemically conjugated to a full-length antibody, represent a growing class of therapeutic agents. The targeting of cytotoxic payloads via the specificity and selectivity of the antibody has led to substantial clinical benefits. However, ADC potency can be altered by mechanisms of resistance such as overexpression of efflux pumps or anti-apoptotic proteins. DeBouganin is a de-immunized variant of bouganin, a ribosome-inactivating protein (RIP) that blocks protein synthesis, thereby leading to apoptosis. When conjugated to trastuzumab (T-deB), deBouganin was more potent than ado-trastuzumab-emtansine (T-DM1) and unaffected by resistance mechanisms to which DM1 is susceptible. To further highlight the differentiating mechanism of action of deBouganin, HCC1419 and BT-474 tumor cells that survived T-DM1 or trastuzumab-MMAE (T-MMAE) treatment were treated with an anti-HER2 C6.5 diabody-deBouganin fusion protein or T-deB. C6.5 diabody-deBouganin and T-deB were potent against HCC1419 and BT-474 cells that were resistant to T-DM1 or T-MMAE killing. The resistant phenotype involved MDR pumps, Bcl-2 family members, and the presence of additional unknown pathways. Overall, the data suggest that deBouganin is effective against tumor cell resistance mechanisms selected in response to ADCs composed of anti-microtubule payloads.

Development of a GMP Phase III purification process for VB4-845, an immunotoxin expressed in E. coli using high cell density fermentation.

VB4-845 is a recombinant immunotoxin comprised of an anti-epithelial cell adhesion molecule (EpCAM) scFv fused to a truncated form of the bacterial toxin, Pseudomonas exotoxin A. VB4-845, purified from TB fed-batch fermentation, showed clinical efficacy when administered locally to treat non-muscle invasive bladder cancer (NMIBC) and squamous cell carcinomas of the head and neck (SCCHN). Here, we describe the implementation of an Escherichia coli high cell density (HCD) cultivation and purification process for VB4-845. HCD cultivation was a prerequisite for achieving higher yields necessary for Phase III clinical trials and commercialization. Using this process, the VB4-845 titer in the supernatant was increased by 30-fold over the original TB fed-batch cultivation. To obtain clinical grade material, a process involving a five-step column purification procedure was implemented and led to an overall recovery of ∼ 40%. VB4-845 purity of >97% was achieved after the first three columns following the removal of low-molecular weight product-related impurities and aggregates. Endotoxins were effectively separated from VB4-845 on the Q-columns and by washing the Ni-column with a detergent buffer while host cell proteins were removed using ceramic hydroxyapatite. Comparability studies demonstrated that the purified product from the Phase III process was identical to the Phase II reference standard produced using TB fed-batch fermentation.

Fluorescence-guided tumor detection with a novel anti-EpCAM targeted antibody fragment: Preclinical validation.

Tumor-specific fluorescent imaging agents are moving towards the clinic, supporting surgeons with real-time intraoperative feedback about tumor locations. The epithelial cell adhesion molecule (EpCAM) is considered as one of the most promising tumor-specific proteins due its high overexpression on epithelial-derived cancers. This study describes the development and evaluation of EpCAM-F800, a novel fluorescent anti-EpCAM antibody fragment, for intraoperative tumor imaging. Fab production, conjugation to the fluorophore IRDye 800CW, and binding capacities were determined and validated using HPLC, spectrophotometry and cell-based assays. In vivo, dose escalation-, blocking-, pharmacokinetic- and biodistribution studies (using both fluorescence and radioactivity) were performed, next to imaging of clinically relevant orthotopic xenografts for breast and colorectal cancer. EpCAM-F800 targets EpCAM with high specificity in vitro, which was validated using in vivo blocking experiments with a 10x higher dose of unlabeled Fab. The optimal dose range for fluorescence tumor detection in mice was 1-5 nmol (52-260 µg), which corresponds to a human equivalent dose of 0.2-0.8 mg/kg. Biodistribution showed high accumulation of EpCAM-F800 in tumors and metabolizing organs. Breast and colorectal tumors could clearly be visualized within 8 h post-injection and up to 96 h, while the agent already showed homogenous tumor distribution within 4 h. The blood half-life was 4.5 h. This study describes the development and evaluation of a novel EpCAM-targeting agent and the feasibility to visualize breast and colorectal tumors by fluorescence imaging during resections. EpCAM-F800 will be translated for clinical use, considering its abundance in a broad range of tumor types.

Trastuzumab-deBouganin Conjugate Overcomes Multiple Mechanisms of T-DM1 Drug Resistance.

The development of antibody drug conjugates has provided enhanced potency to tumor-targeting antibodies by the addition of highly potent payloads. In the case of trastuzumab-DM1 (T-DM1), approved for the treatment of metastatic breast cancer, the addition of mertansine (DM1) to trastuzumab substantially increased progression-free survival. Despite these improvements, most patients eventually relapse due to complex mechanisms of resistance often associated with small molecule chemotherapeutics. Therefore, identifying payloads with different mechanisms of action (MOA) is critical for increasing the efficacy of targeted therapeutics and ultimately improving patient outcomes. To evaluate payloads with different MOA, deBouganin, a deimmunized plant toxin that inhibits protein synthesis, was conjugated to trastuzumab and compared with T-DM1 both in vitro and in vivo. The trastuzumab-deBouganin conjugate (T-deB) demonstrated greater potency in vitro against most cells lines with high levels of Her2 expression. In addition, T-deB, unlike T-DM1, was unaffected by inhibitors of multidrug resistance, Bcl-2-mediated resistance, or Her2-Her3 dimerization. Contrary to T-DM1 that showed only minimal cytotoxicity, T-deB was highly potent in vitro against tumor cells with cancer stem cell properties. Overall, the results demonstrate the potency and efficacy of deBouganin and emphasize the importance of using payloads with different MOAs. The data suggest that deBouganin could be a highly effective against tumor cell phenotypes not being addressed by current antibody drug conjugate formats and thereby provide prolonged clinical benefit.

Fusogenics: a recombinant immunotoxin-based screening platform to select internalizing tumor-specific antibody fragments.

Antibody-based therapeutics play a vital role in the treatment of certain cancers; however, despite commercial success, various strategies are being pursued to increase their potency and hence improve patient outcomes. The use of antibodies to deliver a cytotoxic payload offers a promising alternative for more efficacious therapies. Immunotoxins are composed of an internalizing antibody fragment linked to a bacterial or plant toxin. Once internalized, the payload, such as Pseudomonas exotoxin A (PE), blocks protein synthesis and induces apoptosis. Typically, immunotoxins are developed by first isolating a tumor-specific antibody, which is then either chemically linked to a toxin or reengineered as a fusion protein. Here, the authors describe the development of Fusogenics, an immunotoxin-based screening method that selects internalizing tumor-specific antibodies using a functional assay. Selected immune library clones were characterized and shown to be selective against normal tissues and specific to tumor tissues. In summary, the Fusogenics immunotoxin platform represents a unique, single-step selection approach combining specificity and functionality to isolate novel internalizing tumor-specific antibody fragments with potential for direct clinical application in the treatment of cancer.