Abstract 3360: Phototheranostics of cancer associated fibroblasts by targeting fibroblast activation protein-α

Introduction: Stromal cells such as cancer associated fibroblasts (CAFs) mediate many of the aggressive characteristics of cancer1 and have an ever-replenishing supply that is largely left intact by our current therapeutic strategies.2 Fibroblast activation protein-α (FAP-α) is a target antigen that been reported to be selectively expressed in tumors by a subset of immunosuppressive stromal fibroblasts. Here, we extended our previous near-infrared photoimmunotherapy (NIR-PIT) study,3 to develop a FAP-α-targeted monoclonal antibody (mAb) photosensitizer conjugate. We developed FAP-α overexpressing MDA-MB-231 and HT-1080 cells to test the feasibility of targeting FAP-α expressing populations in cells and tumors in vivo, in terms of the specificity of the conjugate to bind to, detect, and eliminate FAP-α expressing populations.

Method: FAP-α monoclonal antibody (AF3715) and its IgG isotype control were conjugated with a NIR phthalocyanine dye, IR700, to form FAP-α-IR700 and IgG-IR700. FAP-α overexpression was achieved by transducing MDA-MB-231 and HT-1080 cells with lentivirus encoding the gene for human FAP (Accession No. NM_004460.3) that was subcloned into lentiviral vector pMA3211 to obtain 231-FAP and HT-1080-FAP cells. Cell viability was measured by using CCK-8 assay. Bilateral tumor models were established by inoculating 1×106 MDA-MB-231 cells or 1×106 231-FAP cells in 0.05 ml of Hank's balanced salt solution on either side in the mammary fat pads of athymic Balb/c (nu/nu) female mice. A similar number of HT-1080 or HT-1080-FAP cells were inoculated bilaterally in the flank. 50 μg of FAP-α-IR700 or IgG-IR700 was injected i.v., and fluorescence images of IR700 in mice were obtained over a 24-h period (n = 3 per group). At 24 h post injection, mice were euthanized, and tumors were isolated for imaging. For PIT, tumor-bearing mice (n = 4 per group) received two i.v. injections of 100 μg of FAP-α-IR700 at a one-week interval, and tumors were exposed to NIR irradiation at 200 J/cm2 at 24h p.i. Tumor diameters were measured over 2 weeks. IgG-IR700 and PBS-injected mice were used as controls.

Results and Discussion: We confirmed FAP-α overexpression in 231-FAP and HT-1080-FAP cells. FAP-α-IR700 was activated by NIR light, causing FAP-α-specific cell death. FAP-α-IR700-mediated phototoxicity was dependent on the conjugate concentration and NIR light dose; and it was inhibited by excess AF3715. We observed the preferential accumulation of FAP-α-IR700 in FAP-α-overexpressing 231-FAP and HT-1080-FAP tumors compared to their wild-type counterparts. The mean fluorescence intensity of FAP-α-IR700 in FAP-α-overexpressing tumors was approximately two to threefold higher than the wild type tumors. FAP-α-IR700 injection together with NIR light exposure resulted in the highest tumor growth delay in 231-FAP tumors and HT-1080-FAP tumors. Our results evaluate and confirm the ability of FAP-α-IR700 to target and eliminate FAP-α-overexpressing cell populations, providing novel opportunities to selectively deplete FAP-α high CAFs in cancers.

References: 1. Horimoto, Y. et al. Cell Adh Migr. 2012; 2. Eyden, B. et al. J Cell Mol Med. 2008; 3. Jin, J. et al. Sci.Rep. 2016. Supported by NIH R35 CA209960, P41 EB024495, and Emerson Collective Cancer Research Fund.

Citation Format: Jiefu Jin, James D. Barnett, Balaji Krishnamachary, Yelena Mironchik, Hisataka Kobayashi, Zaver Bhujwalla. Phototheranostics of cancer associated fibroblasts by targeting fibroblast activation protein-α [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3360.

Abstract 3444: Intratumor regulatory T cells prevent IFN-gamma-dependent tumor vessel regression and can be selectively targeted by anti-CD25 near-infrared photoimmunotherapy

Regulatory T cells (Tregs) play pivotal roles in inhibiting anti-tumor immunity at different phases and locations (priming phase in lymph node and effector phase in tumor tissue) through their ability to suppress the function of T, NK, and antigen-presenting cells. However, our knowledge about the roles of Tregs in tumor immunity has largely derived from analyses after systemic depletion of Tregs or systemic manipulation of Treg functions in murine tumor models. The specific roles that intra- and extra-tumor Tregs play remain unclear due to technical difficulties to deplete or manipulate Tregs in a spatially specific manner. In order to achieve spatially specific depletion of Tregs in a clinically applicable manner, we have previously developed an anti-CD25 F(ab')2 near-infrared photoimmunotherapy (NIR-PIT), in which an intravenous injection of IR700-conjugated anti-CD25 F(ab')2 followed by irradiation of near-infrared light on tumors achieves selective depletion of intratumor Tregs and suppresses tumor growth. The suppression of tumor growth by the anti-CD25 F(ab')2 NIR-PIT depends on CD8 T and NK cells and their production of IFN-γ; however, the exact target of IFN-γ and the mechanisms of tumor regression remain to be elucidated. In this study, we aimed to dissect the mechanisms of the anti-tumor effect of intratumor Treg depletion by anti-CD25 F(ab')2 NIR-PIT using a series of Ifngr1 knockout mice models including bone-marrow chimera and conditional knockout models. Unexpectedly, we found that the target of IFN-γ in anti-CD25 F(ab')2 NIR-PIT was endothelial cells of tumor vessels. In both MC38 and EO771 tumor models (murine colon and breast cancer, respectively), CD8 T cells, NK cells, and Tregs were mainly located along the tumor vessels, and depletion of intratumor Tregs by anti-CD25 F(ab')2 NIR-PIT induced IFN-γ expression from these perivascular CD8 T and NK cells for up to 6 hours. This transient but synchronized induction of IFN-γ/STAT1 signaling along tumor vessels caused rapid vessel regression, intratumor ischemia, and apoptotic death of tumor cells. Combination with IL-15 treatment further eradicated residual tumor cells to achieve complete remission of MC38 and EO771 tumors.

Citation Format: Yutaka Kurebayashi, Peter L. Choyke, Hisataka Kobayashi, Noriko Sato. Intratumor regulatory T cells prevent IFN-gamma-dependent tumor vessel regression and can be selectively targeted by anti-CD25 near-infrared photoimmunotherapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3444.

Conjugation Ratio, Light Dose, and pH Affect the Stability of Panitumumab-IR700 for Near-Infrared Photoimmunotherapy

Near-infrared photoimmunotherapy (NIR-PIT), a newly developed cancer-cell-specific therapy, relies on a monoclonal antibody-photoabsorber conjugate (APC) and is based on a photoinduced ligand release reaction. Local exposure of the tumor to NIR light induces rapid immunogenic necrotic cell death. The molecular properties of APCs, including their stability and aggregation properties, have important implications for the long-term stability and shelf life. In this study, panitumumab was conjugated with IRDye700DX (IR700) as a model for other NIR-PIT agents. Higher IR700-to-mAb conjugation ratios correlated with increased in vitro cell death up to a ratio of 2.5 dye molecules per antibody. Conjugation ratios higher than 2.5 did not improve cell killing activity. APC aggregation was induced in a light-dose-dependent manner. A near-room-level light dose was sufficient to induce aggregation of APCs. Solvent pH lower than 4 induced aggregation, but higher pH did not induce aggregation. The IR700-to-mAb conjugation ratio, light irradiation dose, and solvent pH affect the APC stability and efficacy.

Abstract A09: Photoimmunotherapy (PIT) for treatment of bladder cancer

Introduction: The use of light as a means of therapy for bladder cancer (BC) has a long history but has been hampered by a lack of tumor specificity and therefore, damage to the normal bladder mucosa. Here, we describe a targeted form of phototherapy called photoimmunotherapy (PIT). To begin with, anti-EGFR antibody panitumumab (pan) was labeled with the photo-absorber (PA), IRDye 700Dx (IR700), to create pan IR700, an antibody-PA conjugate that is activated by near-infrared radiation (NIR). However, PIT may be less effective when a tumor lacks “overwhelming” expression of a single target such as EGFR. Hence, a combinatorial PIT approach for targeting BC expressing EGFR and HER2, using PA-labeled pan and trastuzumab (tra), respectively.

Methods: Human BC tissue microarray (TMAs) and BC cell lines were analyzed for expression of EGFR and HER2. Mechanism of PIT-induced cell death was studied using proliferation assays, transmission electron microscopy (TEM), and production of reactive and singlet oxygen species (ROS/SOS). Finally, efficacy of PA-labeled antibodies singly and in combination was analyzed in vitro and in vivo.

Results: Most BC tissues have some expression of EGFR, but squamous cell carcinoma (SCC) of bladder has maximum EGFR expression. About 45% of BC tissues stain for both EGFR and HER2. Pan IR700 activated by NIR light rapidly killed UMUC-5 cells, a bladder SCC line. Pan alone, pan IR700 without NIR, or NIR alone had no effect on cells. TEM demonstrated that cell death is due to necrosis. Singlet oxygen species (SOS) had a substantially larger contribution towards cell death than reactive oxygen species (ROS). NIR-PIT with pan IR700 demonstrated reduced growth compared to only pan IR700-treated UMUC-5 xenograft tumors. In non-SCC BCs we used a combinatorial PIT approach using pan IR700 and tra IR700 to target EGFR and HER2, respectively. In vitro, PIT in the presence of combination pan IR700 and tra IR700 was more efficacious than either agent alone with lethal dose 50 (LD50) of 28.66 J/cm2 for combination PIT compared to 71.55 J/cm2 for the PanIR700 alone. In vivo, tumor xenografts treated with combination PIT showed significant tumor growth retardation compared to single-agent therapy.

Conclusion: PIT is a new targeted treatment for BC. Our data demonstrate that pan IR700-induced PIT selectively kills EGFR-expressing bladder cancer. Combination PIT is a promising approach for treating BC by selectively inducing death in BC cells with low/moderate expression of surface receptors.

Citation Format: Reema Railkar, Mohammad Rashid Siddiqui, Thomas Sanford, Hisataka Kobayashi, Peter L. Choyke, Piyush K. Agarwal. Photoimmunotherapy (PIT) for treatment of bladder cancer [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2019 May 18-21; Denver, CO. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(15_Suppl):Abstract nr A09.

Effect of Short PEG on Near-Infrared BODIPY-Based Activatable Optical Probes

Targeted near-infrared (NIR) fluorescence probes are playing a significant role in biomedical imaging because NIR penetrates deeper into tissues and is associated with reduced autofluorescence compared to visible light fluorescence probes. Long-wavelength emitting 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is an attractive platform for synthesizing NIR fluorophores because of its high photostability, high molar absorption coefficient, and sharp absorption and emission spectra. However, its lipophilicity hampers the conjugation chemistry necessary to add targeting moieties. In this study, we synthesized a novel NIR BODIPY derivative, NMP14. Substitutions of ethylene-bridged pyrrole units at the 3- or 5-position of the parent BODIPY chromophore result in a red shift of more than 200 nm. However, NMP14 cannot be conjugated to antibodies because of its hydrophobicity. Therefore, we synthesized NMP13 by adding short poly(ethylene glycol) to NMP14 and successfully conjugated NMP13 to cetuximab and trastuzumab. In vitro microscopic studies showed that NMP13 conjugated antibodies were activated after internalization and lysosomal processing, which means that NMP13 acts as an activatable probe only turning on after cellular internalization. After the administration of NMP13 conjugated antibodies, mice tumors were detected with high tumor to background ratios for a long period. These results suggest that NMP13 has potential as an activatable fluorescence probe for further clinical applications.

Wound healing after excision of subcutaneous tumors treated with near-infrared photoimmunotherapy

Near‐infrared photoimmunotherapy (NIR‐PIT) is a novel cancer therapy that employs a combination of infrared light and tumor‐targeted monoclonal antibody‐photoabsorber conjugates to cause both direct tumor necrosis and immunogenic cell death. NIR‐PIT may have potential in the perioperative setting before surgery, and therefore it is important to know the effect of NIR‐PIT on wound healing. Fifty mice were implanted with subcutaneous xenografts of N87 human gastric cancer cells, and tumors were excised after reaching a predetermined size. After excision, 30 mice were split into three groups: Controls, NIR‐PIT 1 day prior to surgery and NIR‐PIT 3 days prior to surgery. The quantity of reactive oxygen species (ROS) in each wound was measured on Postoperative Days 2 and 4, and mice were monitored weekly for 4 weeks for evidence of local tumor recurrence as well as clinical evidence of wound healing complications (eg, dehiscence, infection). The remaining 20 mice (10 controls, 10 treated with NIR‐PIT 1 day prior to surgery) were sacrificed on either Postoperative Day 7 or 14, the skin around wounds were excised, and tensile strength was measured with a digital force gauge. There were no significant differences between treatment and control groups with respect to wound ROS levels, wound tensile strength, local tumor recurrence, or postoperative complication rates (P > .05). In conclusion, neoadjuvant (pre‐operative) NIR‐PIT shows no evidence of adverse wound healing effects, and it is likely a safe adjunctive treatment to surgery. Postoperative use of NIR‐PIT merits investigation.

A near-infrared light-mediated cleavable linker strategy using the heptamethine cyanine chromophore

Optical methods offer the potential to manipulate living biological systems with exceptional spatial and temporal control. Caging bioactive molecules with photocleavable functional groups is an important strategy that could be applied to a range of problems, including the targeted delivery of otherwise toxic therapeutics. However existing approaches that require UV or blue light are difficult to apply in organismal settings due to issues of tissue penetration and light toxicity. Photocaging groups built on the heptamethine cyanine scaffold enable the targeted delivery of bioactive molecules using near-IR light (up to 780nm) in live animal settings. Here we provide a detailed procedure demonstrating the utility of the heptamethine cyanine caging group to create a light-cleavable linker between an antibody, panitumumab, and a therapeutic small molecule in the duocarmycin class of natural products. Descriptions of the design and synthesis of the small molecule component, assembly of the antibody conjugate, in vitro analysis of uncaging, in vivo imaging, and impact on tumor progression are provided.

P1496Impact of electrical reverse remodeling by cardiac resynchronization therapy on adverse cardiac events in patients of heart failure with reduced ejection fraction

Background

Recently, structural reverse remodeling (SRR) and electrical reverse remodeling (ERR) after cardiac resynchronization therapy (CRT) have been reported in patients of heart failure with reduced ejection fraction (HFrEF). However the relationship between ERR and subsequent adverse cardiac events is still unknown. We aimed to elucidate the impact of ERR after CRT on the occurrence of heart failure events and ventricular arrhythmias.

Methods

A total of 36 HFrEF patients who underwent newly CRT implantation were investigated retrospectively. The intrinsic QRS duration (iQRSd) had been recorded before and more than 6 months after CRT implantation. Biventricular pacing was temporarily turned off during measurement of iQRSd. ERR was defined as positive shortening of iQRSd and SRR was defined as reduction of left ventricular end systolic volume by more than 15% after CRT implantation. The primary endpoint was a composite of all cause death, heart failure hospitalizations and ventricular tachyarrhythmia events.

Results

ERR was observed in 17 patients (47.2%) and SRR in 22 patients (61.1%). The group with ERR included more patients with lower NYHA class prior to CRT and patients with SRR. The primary endpoint was observed in 15 patients (51.4 %) for a median of 181 [63, 367] days during follow-up. Kaplan-Meier analysis revealed that the group without ERR was poor prognosis compared with the group with ERR (p = 0.022, Log-rank test).

Conclusion

Patients of HFrEF with ERR after CRT may have fewer adverse cardiac events such as worsening heart failure or ventricular arrhythmia events from this short-term study.

Abstract Figure. Adverse cardiac events and ERR

THU0293 PREDICTORS OF LONG-TERM THERAPY WITH GLUCOCORTICOID IN POLYMYALGIA RHEUMATICA

Background:

Polymyalgia rheumatica (PMR) is a common inflammatory condition of elderly persons. Clinical symptoms respond to low-dose glucocorticoids (GC), but treatment is often required for several years. 2015 EULAR/ACR recommendations1)recommend considering early introduction of methotrexate (MTX) in addition to GC, particularly in patients at a high risk for relapse and/or prolonged therapy. However, risk factors for prolonged therapy are not clear yet.

Objectives:

We investigated predictive factors which corresponded to the long-term GC therapy.

Methods:

This was a retrospective study in a single general hospital in Japan. We reviewed the medical records of the Japanese patients with PMR between April 2011 and January 2020. Diagnosis of PMR was based on Bird’s criteria or 2012 EULAR/ACR Classification Criteria2). All patients were treated with prednisolone (PSL), according to the BSR and BHPR guidelines3), for more than 6 months. Patients treated with MTX and accompanied by the giant cell arteritis were excluded from this study. Relapse was defined as the reappearance of symptoms associated with elevated C-reactive protein (CRP) levels in patients receiving GC that required an increase in GC dose. Remission was defined as the absence of clinical symptoms and normal CRP with discontinuation of GC. We compared the clinical findings, laboratory data at baseline and clinical course between those who achieved remission within 2 years (early-remission group) and those who required GC therapy for more than 2 years (long-therapy group). Comparisons between groups were made using Student’s t-test and chi-square test (IBM SSPE statistics version 26). This study was approved by the ethics committee of Tokyo Medical University (T2019-0079).

Results:

As of January 2020, 89 patients have been treated with PSL for more than 6 months. 50 patients have achieved a remission, 29 were undergoing treatment, and 10 have transferred to other hospitals or died (Table 1). The median time required for the patients to achieve remission was 16 months (Interquartile Range 12-21). After one-year GC therapy, remission was achieved in 14% (11/77), 66% (41/62) after 2-year, 84% (47/56) after 3-year, and 91.0% (49/54) after 4-years. Forty-one patients, who achieved remission within 2 years, were included in the early-remission group. Twenty-one were included in the long therapy group (Table 1). There were no differences in sex, age at onset, body mass index, clinical features, and serum albumin at diagnosis. Serum CRP of long-therapy group was significantly higher than those of the early-remission group (Table 2). Mean relapse times in the full follow-up times were 0.4 in the early-remission group and 3.1 in the long-therapy group. Multivariate logistic regression analysis showed that history of relapse till 6 months was significant predictors of the long-term GC therapy (odds ratio, 6.48; 95%CI 1.44-29.12).

Conclusion:

The remission rates of our study are lower than those of the previous reports. We have tapered GC gradually according to the BSR and BHPR guidelines3). However, some patients need the long-term therapy for more than 2 years. We might consider additional MTX therapy in patients who experience a relapse during the first six months.

References:

[1]Dejaco C, et al. 2015 recommendations for the management of polymyalgia rheumatica: a European League against Rheumatism/American College of Rheumatology collaborative initiative. Ann Rheum Dis 2015; 74:1799-1807.

[2]Dasgupta B, et al: 2012 provisional classification criteria for polymyalgia rheumatica: a European League against Rheumatism/American College of Rheumatology collaborative initiative. Ann Rheum Dis 2012;71: 484-492.

[3]Dasgupta, B, et al. BSR and BHPR guidelines for the management of polymyalgia rheumatica. Rheumatology 2010; 49:186-190.

Disclosure of Interests:

None declared

P1353Echocardiographic predictor of sick sinus syndrome following catheter ablation of persistent atrial fibrillation

Funding Acknowledgements

Abbott Medical Japan, Medtronic Japan, Boston Scientific Japan, Biotronic Japan, Japan Life Line

Background / Introduction

Although sick sinus syndrome(SSS) can be associated with atrial fibrillation(AF), predictive factors of SSS following catheter ablation(CA) of persistent atrial fibrillation(perAF) are not well known.

Purpose

We investigated echocardiographic parameters to predict occurrence of SSS after restoration of sinus rhythm by CA for perAF patients.

Methods

Ninety-eight consecutive perAF patients from June 2014 to May 2018 treated with CA were retrospectively reviewed. Twelve patients(12%, SSS group) developed SSS after successful CA and 86 patients(88%, non-SSS group) did not. Baseline characteristics, blood exam, and echocardiographic findings(RA area size, LA area size, EF, etc) before AF CA were analyzed using Student’s t test, Mann-Whitney test, Chi-square test and Univariate analysis. Multivariate logistic analysis was then performed using those parameters. The atrial area size was calculated from 4 chamber view at the atrial end- systole.

Results

The multivariate analysis for predictive factors of SSS is shown in the table. Right atrium(RA) area could predict SSS(17.3 ± 4.8cm2 vs. 14.7 ± 3.6cm2, odds ratio 1.468; 95% confidence interval 1.088 to 1.981, p = 0.012). Gender (female) was also an independent predictor(4/12 (33%) vs. 8/86 (9%), odds ratio 39.832; 95% confidence interval 2.589 to 612.938, p = 0.008). The other echocardiographical findings(LA area size, EF, etc), baseline characteristics and blood exam results were not related to SSS after successful CA of perAF patients.

Conclusions

The large RA area size and gender (female) could predict SSS in perAF patients after restoration of sinus rhythm by successful CA. We may need to inform possible SSS after CA to female patients with a large RA before CA.

Multivariate Logistic analysis Total(N = 98) SSS group (N = 12) Non SSS group (N = 86) Odds ratio 95% CI P-value Age 64(58-69) 68(60-72) 63(57-69) 1.032 0.929-1.145 0.560 Gender/Female 12(12%) 4(33%) 8(9%) 39.832 2.589-612.938 0.008 CKD 27(28%) 6(50%) 21(24%) 1.264 0.179-8.945 0.814 BNP 91(53-180) 206(167-304) 82(48-169) 1.003 0.993-1.012 0.609 RDW 45.1 ± 3.9 46.4 ± 4.8 44.9 ± 3.8 1.242 0.971-1.588 0.085 RA area 15.1 ± 3.8 17.3 ± 4.8 14.7 ± 3.6 1.468 1.088-1.981 0.012 LA area 24.2(17.0-24.9) 24.4(17.7-26.3) 24.1(16.8-24.4) 0.967 0.803-1.165 0.726 Right atrium area and gender were the independent predictor of SSS in persistent atrial fibrillation patients after restoration of sinus rhythm

Colorectal cancer treated by resection and extended lymphadenectomy: patterns of spread in left- and right-sided tumours

BACKGROUND

Whether tumour side affects the anatomical extent and distribution of lymph node metastasis in colon cancer is unknown. The impact of tumour side on the anatomical pattern of lymphatic spread in colon cancer was assessed.

METHODS

Patients with stage III colon cancer from a Japanese multi-institutional database who underwent extensive (D3) lymphadenectomy, which is similar in concept to complete mesocolic excision with central venous ligation, were divided into groups with right- and left-sided tumours. Based on location, mesenteric lymph nodes were categorized as paracolic (L1), intermediate (L2) or central (L3). The Kaplan-Meier method was used to evaluate disease-free survival (DFS) and overall survival (OS), and multivariable Cox models were used to evaluate the association between anatomical lymph node level, metastatic pattern and outcome.

RESULTS

A total of 4034 patients with stage III colon cancer (right 1618, left 2416) were included. Unadjusted OS was worse in patients with right colon cancer (hazard ratio 1·23, 95 per cent c.i. 1·08 to 1·40; P = 0·002), but DFS was similar. Right-sided tumours more frequently invaded L3 nodes than left-sided lesions (8·5 versus 3·7 per cent; P < 0·001). The proportion of patients with a skipped pattern of lymphatic spread was higher in right than in left colon cancer (13·7 versus 9·0 per cent; P < 0·001). In multivariable analysis, invasion of L3 nodes was associated with worse OS in left but not in right colon cancer. The presence of skipped metastasis was associated with worse DFS in left, but not right, colon cancer.

CONCLUSION

There are significant differences in the pattern of lymph node invasion between right- and left-sided stage III colon cancer, and in their prognostic significance, suggesting that tumour side may dictate the operative approach.

Site-Specific PEGylation of Anti-Mesothelin Recombinant Immunotoxins Increases Half-life and Antitumor Activity

Recombinant immunotoxins (RIT) are chimeric proteins containing an Fv that binds to tumor cells, fused to a fragment of Pseudomonas exotoxin (PE) that kills the cell. Their efficacy is limited by their short half-life in the circulation. Chemical modification with polyethylene glycol (PEG) is a well-established method to extend the half-lives of biologics. Our goal was to engineer RITs with an increase in half-life and high cytotoxic activity. We introduced single cysteines at different locations in five anti-mesothelin RITs and employed site-specific PEGylation to conjugate them to 20-kDa PEG. Because our previous PEGylation method using β-mercaptoethanol reduction gave poor yields of PEG-modified protein, we employed a new method using tris(2-carboxyethyl)phosphine to reduce the protein and could PEGylate RITs at approximately 90% efficiency. The new proteins retained 19% to 65% of cytotoxic activity. Although all proteins are modified with the same PEG, the radius of hydration varies from 5.2 to 7.1, showing PEG location has a large effect on protein shape. The RIT with the smallest radius of hydration has the highest cytotoxic activity. The PEGylated RITs have a 10- to 30-fold increase in half-life that is related to the increase in hydrodynamic size. Biodistribution experiments indicate that the long half-life is due to delayed uptake by the kidney. Antitumor experiments show that several PEG-RITs are much more active than unmodified RIT, and the PEG location greatly affects antitumor activity. We conclude that PEGylation is a useful approach to improve the half-life and antitumor activity of RITs.

Combined CD44- and CD25-Targeted Near-Infrared Photoimmunotherapy Selectively Kills Cancer and Regulatory T Cells in Syngeneic Mouse Cancer Models

Near-infrared photoimmunotherapy (NIR-PIT) is a newly developed and selective cancer treatment that induces necrotic and immunogenic cell death and utilizes a mAb conjugated to a photo-absorber dye, IR700DX, activated by NIR light. Although CD44 is a surface cancer marker associated with drug resistance, anti-CD44-IR700 NIR-PIT results in inhibited cell growth and prolonged survival in multiple tumor types. Meanwhile, CD25-targeted NIR-PIT has been reported to achieve selective and local depletion of FOXP3⁺CD25⁺CD4⁺ regulatory T cells (Treg), which are primary immunosuppressive cells in the tumor microenvironment (TME), resulting in activation of local antitumor immunity. Combined NIR-PIT with CD44- and CD25-targeted agents has the potential to directly eliminate tumor cells and also amplify the immune response by removing FOXP3⁺CD25⁺CD4⁺ Tregs from the TME. We investigated the difference in therapeutic effects of CD44-targeted NIR-PIT alone, CD25-targeted NIR-PIT alone, and the combination of CD44- and CD25-targeted NIR-PIT in several syngeneic tumor models, including MC38-luc, LL/2, and MOC1. The combined NIR-PIT showed significant tumor growth inhibition and prolonged survival compared with CD44-targeted NIR-PIT alone in all tumor models and showed prolonged survival compared with CD25-targeted NIR-PIT alone in MC38-luc and LL/2 tumors. Combined CD44- and CD25-targeted NIR-PIT also resulted in some complete remissions. Therefore, combined NIR-PIT simultaneously targeting cancer antigens and immunosuppressive cells in the TME may be more effective than either type of NIR-PIT alone and may have potential to induce prolonged immune responses in treated tumors.

Near-Infrared Photoimmunotherapy: Photoactivatable Antibody-Drug Conjugates (ADCs)

Cancer treatment has been founded traditionally on the three approaches of surgery, radiation, and chemotherapy with the latter recognized as the obvious systemic treatment approach applicable to disease that has spread. Although significant progress has been made over nearly 100 years of developing systemic treatments, it remains clear that use of the toxic agents involved is a two-edged sword with normal organ toxicities always needing to be balanced with and against administration of relevant therapeutic doses. With the advent of monoclonal antibodies targeted against tumor-associated antigens that could be used as carriers of potently toxic chemotherapy drugs, it was thought that such antibody-drug conjugates (ADCs) could engender the answer to the toxicity/therapeutic equation by shifting the equation more toward beneficial therapeutic efficacy. However, over 40 or so years, antibody-drug conjugates have not significantly affected the toxicity/therapy balance paradigm in most cancer indications, especially in solid tumors. Ideally, a further step may be required in that a non-tumor-targeted antibody-drug conjugate should be essentially nontoxic in its native administered form, with toxic effects unleashed only at the site of targeted tumors. A new approach that employs this principle is the use of an antibody-drug conjugate that is essentially nontoxic to normal tissues by virtue of requiring an extra step of light activation to become potent. We describe the preclinical data and first clinical results gained over the past few years by use of antibody-drug conjugates wherein the drug comprises a near-infrared photoactivatable dye delivered to tumors by a monoclonal antibody and is subsequently activated to a toxic entity solely at sites of tumors.

Cancer neovasculature-targeted near-infrared photoimmunotherapy (NIR-PIT) for gastric cancer: different mechanisms of phototoxicity compared to cell membrane-targeted NIR-PIT

BACKGROUND

Near-infrared photoimmunotherapy (NIR-PIT) constitutes a new class of molecular-targeted theranostics utilizing monoclonal antibody (mAb)-photosensitizer conjugates and NIR light. In this study, we developed a new type of NIR-PIT targeting vascular endothelial growth factor receptor 2 (VEGFR-2) expressed on vascular endothelium in an experimental gastric cancer model and evaluated the feasibility by comparing conventional NIR-PIT targeting cancer cell membrane in vitro and in vivo.

METHODS

HER2-positive human gastric cancer cells, NCI-N87, were used for the experiments. Anti-HER2 mAb, trastuzumab and anti-VEGFR-2 mAb, DC101 were conjugated to photosensitizer, IR700. Phototoxicity in response to NIR-PIT were investigated in vitro and in vivo. Microvessel densities, as an indicator of angiogenesis, were counted in harvested xenografts after NIR-PIT to elucidate the mechanism.

RESULTS

DC101-IR700 did not induce phototoxic effect in vitro because of the absence of expression of VEGFR-2 in NCI-N87 cancer cells. However, it induced an antitumor effect in NCI-N87 xenograft tumors accompanied with damage in tumor neovasculature as determined by decreasing tumor microvessel density, which represents a different mechanism than that of conventional NIR-PIT targeting antigens expressed on the tumor cell membrane.

CONCLUSION

We demonstrated a new approach of NIR-PIT utilizing a target on vascular endothelium, such as VEGFR-2, and this treatment might lead to the development of a new therapeutic strategy for human gastric cancer.

Photoimmunotherapy targeting biliary-pancreatic cancer with humanized anti-TROP2 antibody

Photoimmunotherapy (PIT) is a new type of tumor‐specific treatment utilizing monoclonal antibody (mAb)‐photosensitizer conjugates and near‐infrared (NIR) light irradiation. One potential PIT target, the type I transmembrane protein TROP2, is expressed at high levels in many cancers, including pancreatic carcinoma (PC) and cholangiocarcinoma (CC), in which its expression is correlated with poor prognosis and tumor aggressiveness. In this study, we assessed the efficacy of PIT utilizing newly developed humanized anti‐TROP2 mAb conjugated to the photosensitizer IR700 (TROP2‐IR700) for PC and CC. Immunohistochemistry on PC and CC tissue microarrays confirmed that TROP2 is overexpressed in about half of PC and CC specimens. Using cultured PC and CC cells, TROP2‐IR700 localized TROP2‐specific and target‐specific cell killing was observed after NIR light irradiation. In addition, TROP2‐IR700 was localized to mouse xenograft tumors expressing TROP2 after intravenous injection. PC and CC xenograft tumor growth was significantly inhibited by TROP2‐targeted PIT relative to controls. The efficacy of TROP2‐targeted PIT in vitro and against xenografted tumors in vivo suggests promise as a therapy for human PC and CC, both of which currently have dismal prognoses and limited therapeutic options.

Near-infrared photoimmunotherapy through bone

Near‐infrared photoimmunotherapy (NIR‐PIT) is a molecularly targeted cancer phototherapy that is based on injecting a conjugate of a silicon‐phthalocyanine derivative, IRdye 700DX (IR700), and a monoclonal antibody that targets an expressed antigen on the cancer cell surface. Subsequent local exposure to NIR light results in the rapid and highly selective immunogenic cell death of targeted cancer cells. Because many cancers grow in bones through which light does not penetrate well, the goal of this study was to determine if NIR‐PIT can effectively treat cancers in bone. A bovine rib was used as a bone sample. Because the sample’s NIR light transmittance was shown to be approximately 4.52% in preliminary tests, it was hypothesized that a maximum radiation dosage of 128 and 1500 J/cm² would be sufficient to induce cell death in in vitro target cells and in vivo mouse tumor models, respectively. Cell viability was measured through bioluminescence studies comparing relative luciferase activity, as well as a cytotoxicity assay. In the in vitro model, tumor cell viability was significantly decreased after 64 and 128 J/cm² NIR light irradiation through the bone. An in vivo mouse tumor model also showed that 1500 J/cm² NIR light irradiation through the bone significantly reduced tumor viability at both 24 and 48 hours posttreatment compared to the control group (P = .026 and .040 respectively). Therefore, despite limitations in light transmission, NIR‐PIT nevertheless is capable of effectively treating cancers within bone.