A novel anti-tumor/anti-tumor-associated fibroblast/anti-mPEG tri-specific antibody to maximize the efficacy of mPEGylated nanomedicines against fibroblast-rich solid tumor.

The therapeutic efficacy of methoxypolyethylene glycol (mPEG)-coated nanomedicines in solid tumor treatment is hindered by tumor-associated fibroblasts (TAFs), which promote tumor progression and form physical barriers. We developed an anti-HER2/anti-FAP/anti-mPEG tri-specific antibody (TsAb) for one-step conversion of mPEG-coated liposomal doxorubicin (Lipo-Dox) to immunoliposomes, which simultaneously target HER2+ breast cancer cells and FAP+ TAFs. The non-covalent modification did not adversely alter the physical characteristics and stability of Lipo-Dox. The TsAb-Lipo-Dox exhibited specific targeting and enhanced cytotoxicity against mono- and co-cultured HER2+ breast cancer cells and FAP+ TAFs, compared to bi-specific antibody (BsAb) modified or unmodified Lipo-Dox. An in vivo model of human breast tumor containing TAFs also revealed the improved tumor accumulation and therapeutic efficacy of TsAb-modified mPEGylated liposomes without signs of toxicity. Our data indicate that arming clinical mPEGylated nanomedicines with the TsAb is a feasible and applicable approach for overcoming the difficulties caused by TAFs in solid tumor treatment.

Selective activation of pro-anti-IL-1ß antibody enhances specificity for autoinflammatory disorder therapy.

Canakinumab is a fully human monoclonal antibody that specifically neutralizes human interleukin (IL)-1ß and has been approved by the US Food and Drug Administration for treating different types of autoinflammatory disorders such as cryopyrin-associated periodic syndrome, tumor necrosis factor receptor-associated periodic syndrome and systemic juvenile idiopathic arthritis. However, long-term systemic neutralization of IL-1ß by Canakinumab may cause severe adverse events such as serious upper respiratory tract infections and inflammation, thereby decreasing the quality of life of patients. Here, we used an IgG1 hinge as an Ab lock to cover the IL-1ß-binding site of Canakinumab by linking with matrix metalloprotease 9 (MMP-9) substrate to generate pro-Canakinumab that can be specifically activated in the inflamed regions in autoinflammatory diseases to enhance the selectivity and safety of treatment. The Ab lock significantly inhibited the IL-1ß-binding by 68-fold compared with Canakinumab, and MMP-9 completely restored the IL-1ß neutralizing ability of pro-Canakinumab within 60 min and blocked IL-1ß-downstream signaling and IL-1ß-regulated genes (i.e., IL-6). It is expected that MMP-9 cleavable and efficient Ab lock will be able to significantly enhance the selective reaction of Canakinumab at the disease site and reduce the on-target toxicities of Canakinumab during systemic circulation, thereby showing potential for development to improve the safety and quality of life of patients with autoinflammatory disorders in the future.

Enhancement of tumor tropism of mPEGylated nanoparticles by anti-mPEG bispecific antibody for ovarian cancer therapy.

Ovarian cancer is highly metastatic, with a high frequency of relapse, and is the most fatal gynecologic malignancy in women worldwide. It is important to elevate the drug susceptibility and cytotoxicity of ovarian cancer cells, thereby eliminating resident cancer cells for more effective therapeutic efficacy. Here, we developed a bispecific antibody (BsAb; mPEG × HER2) that can easily provide HER2+ tumor tropism to mPEGylated liposomal doxorubicin (PLD) and further increase the drug accumulation in cancer cells via receptor-mediated endocytosis, and improve the cytotoxicity and therapeutic efficacy of HER2+ ovarian tumors. The mPEG × HER2 can simultaneously bind to mPEG molecules on the surface of PLD and HER2 antigen on the surface of ovarian cancer cells. Simply mixing the mPEG × HER2 with PLD was able to confer HER2 specificity of PLD to HER2+ ovarian cancer cells and efficiently trigger endocytosis and enhance cytotoxicity by 5.4-fold as compared to non-targeted PLD. mPEG × HER2-modified PLD was able to significantly increase the targeting and accumulation of HER2+ ovarian tumor by 220% as compared with non-targeted PLD. It could also significantly improve the anti-tumor activity of PLD (P < 0.05) with minimal obvious toxicity in a tumor-bearing mouse model. We believe that the mPEG × HER2 can significantly improve the therapeutic efficacy, potentially reduce the relapse freqency and thereby achieve good prognosis in ovarian cancer patients.

Double attack strategy for leukemia using a pre-targeting bispecific antibody (CD20 Ab-mPEG scFv) and actively attracting PEGylated liposomal doxorubicin to enhance anti-tumor activity.

BACKGROUND: Tumor-targeted nanoparticles hold great promise as new tools for therapy of liquid cancers. Furthermore, the therapeutic efficacy of nanoparticles can be improved by enhancing the cancer cellular internalization. METHODS: In this study, we developed a humanized bispecific antibody (BsAbs: CD20 Ab-mPEG scFv) which retains the clinical anti-CD20 whole antibody (Ofatumumab) and is fused with an anti-mPEG single chain antibody (scFv) that can target the systemic liquid tumor cells. This combination achieves the therapeutic function and simultaneously "grabs" Lipo-Dox® (PEGylated liposomal doxorubicin, PLD) to enhance the cellular internalization and anticancer activity of PLD. RESULTS: We successfully constructed the CD20 Ab-mPEG scFv and proved that CD20 Ab-mPEG scFv can target CD20-expressing Raji cells and simultaneously grab PEGylated liposomal DiD increasing the internalization ability up to 60% in 24 h. We further showed that the combination of CD20 Ab-mPEG scFv and PLD successfully led to a ninefold increase in tumor cytotoxicity (LC50: 0.38 nM) compared to the CD20 Ab-DNS scFv and PLD (lC50: 3.45 nM) in vitro. Importantly, a combination of CD20 Ab-mPEG scFv and PLD had greater anti-liquid tumor efficacy (P = 0.0005) in Raji-bearing mice than CD20 Ab-DNS scFv and PLD. CONCLUSION: Our results indicate that this "double-attack" strategy using CD20 Ab-mPEG scFv and PLD can retain the tumor targeting (first attack) and confer PLD tumor-selectivity (second attack) to enhance PLD internalization and improve therapeutic efficacy in liquid tumors.

Gut Fecal Microbiota Transplant in a Mouse Model of Orthotopic Rectal Cancer.

The gut microbiota is reported to play an important role in carcinogenesis and the treatment of CRC. SW480 and SW620 colon cancer cells integrated with infrared fluorescent proteins were injected into the rectal submucosa of nude mice. In the subsequent 30 days, we observed tumor growth weekly using an in vivo imaging system. The bacterial solution was infused anally into the mice to perform bacterial transplant. Phosphate-buffered saline, Acinetobacter lwoffii, and Bifidobacterium longum solutions were infused individually. The 16S ribosomal DNA (rDNA) and polymerase chain reaction of murine feces were investigated to confirm the colonization of target bacteria. In the SW620 orthotopic xenograft rectal cancer model, 4 of 5 mice developed rectal cancer by 30 days after submucosal injection. In the SW480 orthotopic xenograft rectal cancer model, 2 of 6 mice developed rectal cancer by 30 days after submucosal injection. For the 16S rDNA analysis, the mice receiving the bacterial solution infusion demonstrated positive findings for A. lwoffii and B. longum. With the successful establishment of a mouse model of orthotopic rectal cancer and transplant of target bacteria, we can further explore the relationship between gut microbiota and CRC. The role of fecal microbiota transplant in the treatment and alleviation of adverse events of chemotherapy in CRC could be clarified in subsequent studies.

Humanized bispecific antibody (mPEG × HER2) rapidly confers PEGylated nanoparticles tumor specificity for multimodality imaging in breast cancer.

BACKGROUND: Developing a universal strategy to improve the specificity and sensitivity of PEGylated nanoaparticles (PEG-NPs) for assisting in the diagnosis of tumors is important in multimodality imaging. Here, we developed the anti-methoxypolyethylene glycol (mPEG) bispecific antibody (BsAb; mPEG × HER2), which has dual specificity for mPEG and human epidermal growth factor receptor 2 (HER2), with a diverse array of PEG-NPs to confer nanoparticles with HER2 specificity and stronger intensity. RESULT: We used a one-step formulation to rapidly modify the nanoprobes with mPEG × HER2 and optimized the modified ratio of BsAbs on several PEG-NPs (Lipo-DiR, SPIO, Qdot and AuNP). The αHER2/PEG-NPs could specifically target MCF7/HER2 cells (HER2++) but not MCF7/neo1 cells (HER2+/-). The αHER2/Lipo-DiR and αHER2/SPIO could enhance the sensitivity of untargeted PEG-NPs on MCF7/HER2 (HER2++). In in vivo imaging, αHER2/Lipo-DiR and αHER2/SPIO increased the specific targeting and enhanced PEG-NPs accumulation at 175% and 187% on 24 h, respectively, in HER2-overexpressing tumors. CONCLUSION: mPEG × HER2, therefore, provided a simple one-step formulation to confer HER2-specific targeting and enhanced sensitivity and contrast intensity on HER2 positive tumors for multimodality imaging.

Bispecific antibody (HER2 × mPEG) enhances anti-cancer effects by precise targeting and accumulation of mPEGylated liposomes.

Targeted antibodies and methoxy-PEGylated nanocarriers have gradually become a mainstream of cancer therapy. To increase the anti-cancer effects of targeted antibodies combined with mPEGylated liposomes (mPEG-liposomes), we describe a bispecific antibody in which an anti-methoxy-polyethylene glycol scFv (αmPEG scFv) was fused to the C-terminus of an anti-HER2 (αHER2) antibody to generate a HER2 × mPEG BsAb that retained the original efficacy of a targeted antibody while actively attracting mPEG-liposomes to accumulate at tumor sites. HER2 ×mPEG BsAb can simultaneously bind to HER2-high expressing MCF7/HER2 tumor cells and mPEG molecules on mPEG-liposomal doxorubicin (Lipo-Dox). Pre-incubation of HER2 × mPEG BsAb with cells increased the endocytosis of Lipo-DiD and enhanced the cytotoxicity of Lipo-Dox to MCF7/HER2 tumor cells. Furthermore, pre-treatment of HER2 × mPEG BsAb enhanced the tumor accumulation and retention of Lipo-DiR 2.2-fold in HER2-high expressing MCF7/HER2 tumors as compared to HER2-low expressing MCF7/neo1 tumors. Importantly, HER2 × mPEG BsAb plus Lipo-Dox significantly suppressed tumor growth as compared to control BsAb plus Lipo-Dox in MCF7/HER2 tumor-bearing mice. These results indicate that HER2 × mPEG BsAb can enhance tumor accumulation of mPEG-liposomes to improve the therapeutic efficacy of combination treatment. Anti-mPEG scFv can be fused to any kind of targeted antibody to generate BsAbs to actively attract mPEG-drugs and improve anti-cancer efficacy. STATEMENT OF SIGNIFICANCE: Antibody targeted therapy and PEGylated drugs have gradually become the mainstream of cancer therapy. To enhance the anti-cancer effects of targeted antibodies combined with PEGylated drugs is very important. To this aim, we fused an anti-PEG scFv to the C-terminal of HER2 targeted antibodies to generate a HER2×mPEG bispecific antibody (BsAb) to retain the original efficacy of targeted antibody whilst actively attract mPEG-liposomal drugs to accumulate at tumor sites. The present study demonstrates pre-treatment of HER2×mPEG BsAb can enhance tumor accumulation of mPEG-liposomal drugs to improve the therapeutic efficacy of combination treatment. Anti-mPEG scFv can be fused to any kind of targeted antibody to generate BsAbs to actively attract mPEG-drugs and improve anti-cancer efficacy.

Use of syngeneic cells expressing membrane-bound GM-CSF as an adjuvant to induce antibodies against native multi-pass transmembrane protein.

Membrane antigens (mAgs) are important targets for the development of antibody (Ab) drugs. However, native mAgs are not easily prepared, causing difficulties in acquiring functional Abs. In this study, we present a platform in which human mAgs were expressed in native form on cell adjuvants made with membrane-bound cytokines that were then used immunize syngeneic mice directly. The membrane-bound cytokines were used as immune stimulators to enhance specific Ab responses against the desired mAgs. Then, mAgs-expressing xenogeneic cells were used for Ab characterization to reduce non-specific binding. We established cell adjuvants by expressing membrane-bound cytokines (mIL-2, mIL-18, or mGM-CSF) on BALB/3T3 cells, which were effective in stimulating splenocyte proliferation in vitro. We then transiently expressed ecotropic viral integration site 2B (EVI2B) on the adjuvants and used them to directly immunize BALB/c mice. We found that 3T3/mGM-CSF cells stimulated higher specific anti-EVI2B Ab response in the immunized mice than the other cell adjuvants. A G-protein coupled receptor (GPCR), CXCR2, was then transiently expressed on 3T3/mGM-CSF cell adjuvant to immunize mice. The immune serum exhibited relatively higher binding to xenogeneic 293 A/CXCR2 cells than 293 A cells (~3.5-fold). Several hybridoma clones also exhibited selective binding to 293 A/CXCR2 cells. Therefore, the cell adjuvant could preserve the native conformation of mAgs and exhibit anti-mAg Ab stimulatory ability, providing a more convenient and effective method to generate functional Abs, thus possibly accelerating Ab drug development.

Specific activation of pro-Infliximab enhances selectivity and safety of rheumatoid arthritis therapy.

During rheumatoid arthritis (RA) treatment, long-term injection of antitumor necrosis factor α antibodies (anti-TNFα Abs) may induce on-target toxicities, including severe infections (tuberculosis [TB] or septic arthritis) and malignancy. Here, we used an immunoglobulin G1 (IgG1) hinge as an Ab lock to cover the TNFα-binding site of Infliximab by linking it with matrix metalloproteinase (MMP) -2/9 substrate to generate pro-Infliximab that can be specifically activated in the RA region to enhance the selectivity and safety of treatment. The Ab lock significantly inhibits the TNFα binding and reduces the anti-idiotypic (anti-Id) Ab binding to pro-Infliximab by 395-fold, 108-fold compared with Infliximab, respectively, and MMP-2/9 can completely restore the TNFα neutralizing ability of pro-Infliximab to block TNFα downstream signaling. Pro-Infliximab was only selectively activated in the disease site (mouse paws) and presented similar pharmacokinetics (PKs) and bio-distribution to Infliximab. Furthermore, pro-Infliximab not only provided equivalent therapeutic efficacy to Infliximab but also maintained mouse immunity against Listeria infection in the RA mouse model, leading to a significantly higher survival rate (71%) than that of the Infliximab treatment group (0%). The high-selectivity pro-Infliximab maintains host immunity and keeps the original therapeutic efficiency, providing a novel strategy for RA therapy.

Enhanced drug internalization and therapeutic efficacy of PEGylated nanoparticles by one-step formulation with anti-mPEG bispecific antibody in intrinsic drug-resistant breast cancer.

For those patients with HER2-overexpressing breast cancer, treatment with PEGylated liposomal doxorubicin (PLD) is inefficacious due to the intrinsic low sensitivity to doxorubicin. A very large increase in drug accumulation by active targeting may enhance the therapeutic efficacy of PLD. We established a humanized bispecific antibody (BsAb; mPEG × HER2) which has dual specificity for methoxy-polyethylene glycol (mPEG) and human epidermal growth factor receptor 2 (HER2) to enhance the specificity, internalization and anticancer activity of PLD for cancer cells that overexpress HER2. One-step formulation of PLD with mPEG × HER2 converted the PLD into HER2 targeted liposomes that were stable at 4 °C in PBS as well as at 37 °C in the presence of serum. αHER2/PLD induced receptor-mediated endocytosis and enhanced doxorubicin accumulation in MCF7/HER2 (HER2-amplified) breast cancer cells. αHER2/PLD also displayed more than 200-fold increased cytotoxicity to MCF7/HER2 cells and 28-fold increased cytotoxicity to drug-resistant MDA-MB-361 cells with a physical deletion of the TOP2A gene. αHER2/PLD specifically accumulated doxorubicin in the nucleus of cancer cells in tumor-bearing mice and produced significantly greater antitumor activity against MCF7/HER2 (P < 0.0001) and MDA-MB-361 (P < 0.05) tumors as compared to untargeted PLD. Furthermore, the cardiotoxicity of αHER2/PLD was similar to that of PLD in human cardiomyocytes and in mice. Our results indicate that the one-step formulation of PLD by mPEG × HER2 is a simple method to confer tumor specificity, increase drug internalization and enhance the anticancer activity of PLD against HER2-overexpressing and doxorubicin-resistant breast cancer.

Pharmacological inhibition of bacterial ß-glucuronidase prevents irinotecan-induced diarrhea without impairing its antitumor efficacy in vivo.

Irinotecan (CPT-11), a first-line chemotherapy for advanced colorectal cancer, causes serious diarrhea in patients receiving treatment. The underlying mechanism has been shown that the active metabolite of CPT-11, SN-38, is metabolized to the inactive metabolite SN-38 glucuronide (SN-38 G) during hepatic glucuronidation, and subsequently is exported into the intestine, where SN-38 G is hydrolyzed by bacterial ß-glucuronidase (ßG) to be SN-38, thus leading to intestinal toxicity. Thus, inhibition of the intestinal bacterial ßG activity is expected to prevent CPT-11-induced diarrhea. However, the effects of such inhibition on serum pharmacokinetics of SN-38, the key determinant of CPT-11 treatment, are uncertain. Here, we determined the effects of a potent E. coli ßG (eßG)-specific inhibitor pyrazolo[4,3-c]quinoline derivative (TCH-3562) for the potential use in preventing CPT-11-induced diarrhea. TCH-3562 exhibited efficacious inhibitory potency of endogenous ßG activity in two anaerobes, Eubacteriumsp. and Peptostreptococcus anaerobius. Oral administration of TCH-3562 also effectively reduced the bacterial ßG activity in mice intestine. Moreover, pharmacokinetic analysis of TCH-3562 revealed a relatively low amount of TCH-3562 was detected in the plasma whereas the majority of TCH-3562 was found in the feces. Importantly, co-treatment of CPT-11 and TCH-3562 did not decrease active SN-38 level in mice plasma. Finally, we established that TCH-3562 as an adjuvant treatment showed protective effects on CPT-11-induced diarrhea and had no negative effects on the therapeutic efficacy of CPT-11 in tumor-bearing mice. Therefore, inhibition of the intestinal bacterial ßG activity by the specific inhibitor, TCH-3562, is promising to prevent CPT-11-induced diarrhea while maintaining its anti-tumor efficacy that may have clinical potentials for the treatment with CPT-11.

Ten hub genes associated with progression and prognosis of pancreatic carcinoma identified by co-expression analysis.

Since the five-year survival rate is less than 5%, pancreatic ductal adenocarcinoma (PDAC) remains the 4th cause of cancer-related death. Although PDAC has been repeatedly researched in recent years, it is still predicted to be the second leading cause of cancer death by year 2030. In our study, the differentially expressed genes in dataset GSE62452 were used to construct a co-expression network by WGCNA. The yellow module related to grade of PDAC was screened. Combined with co-expression network and PPI network, 36 candidates were screened. After survival and regression analysis by using GSE62452 and TCGA dataset, we identified 10 real hub genes (CCNA2, CCNB1, CENPF, DLGAP5, KIF14, KIF23, NEK2, RACGAP1, TPX2 and UBE2C) tightly related to progression of PDAC. According to Oncomine database and The Human Protein Atlas (HPA), we found that all real hub genes were overexpressed in pancreatic carcinoma compared with normal tissues on transcriptional and translational level. ROC curve was plotted and AUC was calculated to distinguish recurrent and non-recurrent PDAC and every AUC of the real hub gene was greater than 0.5. Finally, functional enrichment analysis and gene set enrichment (GSEA) was performed and both of them showed the cell cycle played a vital role in PDAC.

Selective antibody activation through protease-activated pro-antibodies that mask binding sites with inhibitory domains.

Systemic injection of therapeutic antibodies may cause serious adverse effects due to on-target toxicity to the antigens expressed in normal tissues. To improve the targeting selectivity to the region of disease sites, we developed protease-activated pro-antibodies by masking the binding sites of antibodies with inhibitory domains that can be removed by proteases that are highly expressed at the disease sites. The latency-associated peptide (LAP), C2b or CBa of complement factor 2/B were linked, through a substrate peptide of matrix metalloproteinase-2 (MMP-2), to an anti-epidermal growth factor receptor (EGFR) antibody and an anti-tumor necrosis factor-α (TNF-α) antibody. Results showed that all the inhibitory domains could be removed by MMP-2 to restore the binding activities of the antibodies. LAP substantially reduced (53.8%) the binding activity of the anti-EGFR antibody on EGFR-expressing cells, whereas C2b and CBa were ineffective (21% and 9.3% reduction, respectively). Similarly, LAP also blocked 53.9% of the binding activity of the anti-TNF-α antibody. Finally, molecular dynamic simulation showed that the masking efficiency of LAP, C2b and CBa was 33.7%, 10.3% and -5.4%, respectively, over the binding sites of the antibodies. This strategy may aid in designing new protease-activated pro-antibodies that attain high therapeutic potency yet reduced systemic on-target toxicity.

Enhancement Effect of a Variable Topology of a Membrane-Tethered Anti-Poly(ethylene glycol) Antibody on the Sensitivity for Quantifying PEG and PEGylated Molecules.

Sensitive quantification of the pharmacokinetics of poly(ethylene glycol) (PEG) and PEGylated molecules is critical for PEGylated drug development. Here, we developed a sensitive sandwich enzyme-linked immunosorbent assay (ELISA) for PEG by tethering an anti-PEG antibody (AGP3) via tethers with different dimensions on the surface of 293T cells (293T/S-αPEG, short-type cells; 293T/L-αPEG, long-type cells; 293T/SL-αPEG, hybrid-type cells) to improve the binding capacity and detection limit for free PEG and PEGylated molecules. The binding capacity of hybrid-type cells for PEG-like molecules (CH3-PEG5K-FITC (FITC = fluorescein isothiocyanate) and eight-arm PEG20K-FITC) was at least 10-80-fold greater than that of 293T cells expressing anti-PEG antibodies with uniform tether lengths. The detection limit of free PEG (OH-PEG3K-NH2 and CH3-PEG5K-NH2) and PEG-like molecule (CH3-PEG5K-FITC, CH3-PEG5K-SHPP, and CH3-PEG5K-NIR797) was14-137 ng mL-1 in the hybrid-type cell-based sandwich ELISA. 293T/SL-αPEG cells also had significantly higher sensitivity for quantification of a PEGylated protein (PegIntron) and multiarm PEG macromolecules (eight-arm PEG20K-NH2 and eight-arm PEG40K-NH2) at 3.2, 16, and 16 ng mL-1, respectively. Additionally, the overall binding capacity of 293T/SL-αPEG cells for PEGylated macromolecules was higher than that of 293T/S-αPEG or 293T/L-αPEG cells. Anchoring anti-PEG antibodies on cells via variable-length tethers for cell-based sandwich ELISA, therefore, provides a sensitive, high-capacity method for quantifying free PEG and PEGylated molecules.

Optimization of an Anti-poly(ethylene glycol) (anti-PEG) Cell-Based Capture System To Quantify PEG and PEGylated Molecules.

Sensitive determination of the pharmacokinetics of PEGylated molecules can accelerate the process of drug development. Here, we combined different anti-PEG Fab expressing 293T cells as capture cells (293T/3.3, 293T/6.3, and 293T/15-2b cells) with four detective anti-PEG antibodies (3.3, 6.3, 7A4, or 15-2b) to optimize an anti-PEG cell-based sandwich ELISA. Then, we quantified free PEG (mPEG2K-NH2 and mPEG5K-NH2) or PEG-conjugated small molecules (mPEG5K-biotin and mPEG5K-NIR797), proteins (PegIntron and Pegasys), and nanoparticles (Liposomal-Doxorubicin and quantum-dots). The combination of 293T/15-2b cells and the 7A4 detection antibody was best sensitivity for free PEG, PEG-like molecules, and PEGylated proteins with detection at ng mL-1 levels. On the other hand, 293T/3.3 cells combined with the 15-2b antibody had the highest sensitivity for quantifying Lipo-Dox at 2 ng mL-1. All three types of anti-PEG cells combined with the 15-2b antibody had high sensitivity for quantum dot quantification down to 7 pM. These results suggest that the combination of 293T/15-2b cells and 7A4 detection antibody is the optimal pair for sensitive quantification of free PEG, PEG-like molecules, and PEGylated proteins, whereas the 293T/3.3 cells combined with 15-2b are more suitable for quantifying PEGylated nanoparticles. The optimized anti-PEG cell-based sandwich ELISA can provide a sensitive, precise, and convenient tool for the quantification of a range of PEGylated molecules.

Possible sources of neuroprotection following subretinal silicon chip implantation in RCS rats.

Current retinal prosthetics are designed to stimulate existing neural circuits in diseased retinas to create a visual signal. However, implantation of retinal prosthetics may create a neurotrophic environment that also leads to improvements in visual function. Possible sources of increased neuroprotective effects on the retina may arise from electrical activity generated by the prosthetic, mechanical injury due to surgical implantation, and/or presence of a chronic foreign body. This study evaluates these three neuroprotective sources by implanting Royal College of Surgeons (RCS) rats, a model of retinitis pigmentosa, with a subretinal implant at an early stage of photoreceptor degeneration. Treatment groups included rats implanted with active and inactive devices, as well as sham-operated. These groups were compared to unoperated controls. Evaluation of retinal function throughout an 18 week post-implantation period demonstrated transient functional improvements in eyes implanted with an inactive device at 6, 12 and 14 weeks post-implantation. However, the number of photoreceptors located directly over or around the implant or sham incision was significantly increased in eyes implanted with an active or inactive device or sham-operated. These results indicate that in the RCS rat localized neuroprotection of photoreceptors from mechanical injury or a chronic foreign body may provide similar results to subretinal electrical stimulation at the current output evaluated here.