Analysis of the Effector Functions of Vδ2 γδ T Cells and NK Cells against Cholangiocarcinoma Cells.

Cholangiocarcinoma (CCA) is a rare disease characterized by malignant cells derived from the epithelial cells of the biliary duct system. Despite extensive treatments, the prognosis for CCA remains poor, emphasizing the critical need for the development of novel treatments. Considerable attention has been directed towards innate immune effector cells, which can recognize tumor cells independently of the major histocompatibility complex, laying the foundation for the development of off-the-shelf drugs. In this study, we cultured innate immune cells obtained from the peripheral blood of healthy adults and conducted a comparative analysis of the effector functions against CCA cell lines by Vδ2 γδ T cells and NK cells. This analysis was performed using standard short- and long-term cytotoxicity assays, as well as ELISA for IFN-γ. Vδ2 γδ T cells demonstrated cytotoxicity and IFN-γ production in response to CCA cells in a TCR-dependent manner, particularly in the presence of tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1-bisphosphonate, a bisphosphonate prodrug. In contrast, direct killing and antibody-dependent cellular cytotoxicity were relatively slow and weak. Conversely, NK cells displayed potent, direct cytotoxicity against CCA cells. In summary, both Vδ2 γδ T cells and NK cells show promise as innate immune effector cells for adoptive transfer therapy in the context of CCA.

Three distinct mechanisms underlying human γδ T cell-mediated cytotoxicity against malignant pleural mesothelioma.

Introduction: Malignant pleural mesothelioma (MPM) is a rare and highly aggressive thoracic tumor with poor prognosis and limited therapeutic options. Although immune checkpoint inhibitors exhibit a promising effect in some patients with unresectable MPM in clinical trials, the majority of MPM patients show only modest response rates to the currently available treatments. It is thus imperative to develop novel and innovative therapeutic modalities for MPM, including immune effector cell-based therapies. Methods: γδ T cells were expanded using tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino) ethylidene-1,1-bisphosphonate (PTA) and interleukin-2, and the therapeutic potential of γδ T cells was examined through analyzing cell surface markers and cellular cytotoxicity against MPM in vitro using a europium chelate-based time-resolved fluorescence assay system and a luciferase-based luminescence assay system. Results and discussion: We successfully expanded γδ T cells from peripheral blood mononuclear cells of healthy donors and MPM patients. γδ T cells expressed natural killer receptors such as NKG2D and DNAM-1 and exhibited a moderate level of cytotoxicity to MPM cells in the absence of antigens. The inclusion of PTA, (E)-4-hydroxy-3- methylbut-2-enyl diphosphate (HMBPP) or zoledronic acid (ZOL) induced a TCR-dependent cytotoxicity in γδ T cells and secreted interferon-γ (IFN-γ). In addition, γδ T cells expressing CD16 exhibited a significant level of cytotoxicity against MPM cells in the presence of an anti-epidermal growth factor receptor (EGFR) mAb, at lower concentrations than in clinical settings, whereas a detectable level of IFN-γ was not produced. Taken together, γδ T cells showed cytotoxic activity against MPM in three distinct mechanisms through NK receptors, TCRs and CD16. Since major histocompatibility complex (MHC) molecules are not involved in the recognition, both autologous and allogeneic γδ T cells could be used for the development of γδ T cell-based adoptive immunotherapy for MPM.

Surgical intervention for non-small-cell lung cancer with minimal malignant pleural effusion.

PURPOSE: We assessed the clinical significance of minimal malignant pleural effusion (MPE) using liquid-based cytology (LBC) and immunocytochemistry and reviewed the postoperative outcomes of patients with non-small-cell lung cancer (NSCLC). METHODS: We reviewed 240 patients with cM0 NSCLC who underwent lobectomy. Carcinoembryonic antigen (CEA) immunocytochemistry was performed with LBC to aid in the diagnosis of minimal MPE. We assessed the efficacy of this diagnostic method, relevant clinical factors, and postoperative outcomes. RESULTS: LBC showed positive results in two patients and suspicious results in 21. Of the 21 patients, immunocytochemistry showed minimal MPE in 10 (47.6%); therefore, a total of 12 patients (5%) showed minimal MPE. Minimal MPE is associated with an older age, increased consolidation tumor ratio, and adenocarcinoma histology. The 12 patients with minimal MPE had a 3-year overall survival rate of 90%. Postoperative recurrence was observed in seven patients (58.3%), four of whom were treated with epidermal growth factor receptor-tyrosine kinase inhibitors or immune checkpoint inhibitors, while three are still undergoing treatment, with a survival of 2.2, 2.5 and 5.5 years. CONCLUSIONS: CEA immunocytochemistry offers high sensitivity for the diagnosis of minimal MPE. Surgical intervention may be considered for select patients with NSCLC showing minimal MPE.

Prognostic Impact of Using Combined Plasma Fibrinogen Level and Neutrophil-to-Lymphocyte Ratio in Resectable Non-small Cell Lung Cancer.

BACKGROUND: Both plasma fibrinogen level and neutrophil-to-lymphocyte ratio (NLR) are associated with malignant potential in different cancer types. The current study evaluated the use of combined plasma fibrinogen level and NLR (F-NLR) as a prognostic predictor in patients with non-small cell lung cancer (NSCLC). METHODS: Data collected from 279 patients with resectable NSCLC were retrospectively reviewed. Patients were divided into three groups based on the F-NLR score: score 2, high fibrinogen level (≥350 mg/dL) and high NLR (≥2.5); score 1, either high fibrinogen level or high NLR; and score 0, neither abnormal. Overall survival (OS) and relapse-free survival (RFS) were evaluated using the Kaplan-Meier method and log-rank test. Cox proportional hazard model was used to assess prognostic factors. RESULTS: Numbers of patients with F-NLR score of 0, 1, and 2 were 122 (43.7%), 105 (37.6%), and 52 (18.6%), respectively. The F-NLR was found to be significantly associated with age, male sex, heavy smoking history, high pT status and pathological stage, and nonadenocarcinoma. Moreover, the OS and RFS significantly differed according to the F-NLR score (P < 0.001, P = 0.003). A multivariate analysis revealed that a high F-NLR score (≥1) was an independent poor prognostic factor for OS (P = 0.027). In subgroup analyses, an adverse prognostic impact of the F-NLR score on OS was identified regardless of nodal involvement or pathological stage. CONCLUSIONS: The F-NLR score, which is based on histological inflammation and coagulability, could be a potential prognostic indicator in patients with resectable NSCLC.

Establishment of serum-free adapted Chinese hamster ovary cells with double knockout of GDP-mannose-4,6-dehydratase and GDP-fucose transporter.

Although antibodies have attracted attention as next-generation biopharmaceuticals, the costs of purifying the products and of arranging the environment for cell cultivation are high. Therefore, there is a need to increase antibody efficacy and improve product quality as much as possible. Since antibodies are glycoproteins, their glycan structures have been found to affect the function of antibodies. Especially, afucosylation of the N-linked glycan in the Fc region is known to significantly increase antibody-dependent cellular cytotoxicity. In this study, we established a double-mutant ΔGMDΔGFT in which GDP-mannose 4,6-dehydratase and GDP-fucose transporter were knocked out in Chinese hamster ovary cells, a platform for biopharmaceutical protein production. By adapting ΔGMDΔGFT cells to serum-free medium and constructing suspension-cultured cells, we established host CHO cells with no detected fucosylated glycans and succeeded in production of afucosylated antibodies. We also demonstrated that, in culture in the presence of serum, fucosylation occurs due to contamination from serum components. Furthermore, we found that afucosylation of glycans does not affect cell growth after adaptation to serum-free medium as compared to wild-type CHO cells growth and does not significantly affect the expression levels of other endogenous fucose metabolism-related enzyme genes. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10616-021-00501-3.

Endoscopic Surgery Using Ultrasonic Energy Device for Tracheal Metastatic Tumor.

We describe a rare case of tracheal metastasis from endometrial carcinoma obstructing the central airway. A 57-year-old woman who underwent previous surgery for endometrial serous adenocarcinoma presented with severe tracheal stenosis caused by a stalked tracheal tumor. Urgent debulking surgery was performed under rigid bronchoscopy. The tumor stem was dissected using ultrasonically activated device blades. Rigid bronchoscopy combined with an ultrasonically activated device is an effective option for relieving tracheal stenosis and resecting the intratracheal tumor.

Volume-Based Consolidation-to-Tumor Ratio Is a Useful Predictor for Postoperative Upstaging in Stage I and II Lung Adenocarcinomas.

BACKGROUND: We investigated the postoperative upstaging of stage I and II lung adenocarcinoma patients to identify useful predictors for accurate staging. METHODS: We retrospectively reviewed data from 80 consecutive patients undergoing lobectomy and mediastinal lymph node dissection for clinical stage I and II lung adenocarcinomas. We evaluated clinical variables, including the preoperative serum carcinoembryonic antigen (CEA), tumor diameter, consolidation-to-tumor ratio (CTR), maximum standardized uptake value (SUVmax) on FDG- PET, expression of epithelial growth factor receptor mutations, and pathological invasion to the pleura (pl), lymph duct (ly), and vein (v). RESULTS: Eleven patients (13.8%) showed postoperative upstaging. Three cases had pN1 migrating from cN0, four cases had pN2 from cN0, and four cases showed malignant pleural effusion. The CEA level and CTR were significantly higher in the upstaging group. The tumors in the upstaging group showed more frequent pathological invasion to the visceral pleura and vein. In patients with 3 cm or smaller consolidation, two-dimensional (2D)-CTR and volume-based CTR were independent predictors of upstaging. CONCLUSIONS: Volume-based CTR could be a useful predictor for accurate clinical staging in stage I and II adenocarcinoma patients in addition to consolidation size, serum CEA level, and 2D-CTR. Both volume-based and 2D-CTRs might be especially useful in T1 diseases.

The Role of Cardio-Ankle Vascular Index as a Predictor of Mortality in Patients on Maintenance Hemodialysis.

AIM: Mortality rate of maintenance hemodialysis patients is known to be high. Cardio-ankle vascular index (CAVI) is an index reflecting the proper stiffness of the arterial tree from the origin of the aorta to the ankle. We aimed to clarify the utility of CAVI as a predictor of mortality in hemodialysis patients. The roles of age and nutritional conditions on survival were also examined. METHODS: We followed 242 patients undergoing hemodialysis for 6 consecutive years. Data from 209 patients (mean age was 60 ± 11 years) excluding those with ankle-brachial index <0.90 were then analyzed. CAVI and heart to ankle pulse wave velocity (haPWV) were measured using Vasera 1500. RESULTS: Thirty-eight hemodialysis patients who died during the 6-year period had higher age, cardiothoracic ratio (CTR), CAVI, and haPWV, and lower diastolic blood pressure, albumin, phosphate, and calcium phosphate product. The Kaplan-Meier curves for cumulative survival among the tertile groups showed that the mortality rate was higher in the highest tertile (T3) compared to T1/T2 for both CAVI and haPWV. Receiver operating characteristic (ROC) analysis revealed that CAVI had better discriminatory power for all-cause mortality compared to haPWV. In the Cox-proportional hazards analyses, 1 SD increase in both parameters contributed independently to all-cause mortality [CAVI: HR 1.595 (95% CI 1.108-2.297), haPWV: HR 1.695 (95% CI 1.185-2.425)], as well as age and CTR. Both parameters above the cut-offs estimated in the ROC analysis (CAVI ≥ 9.2, haPWV ≥ 8.9) also had independent contributions to mortality. CONCLUSION: Through the 6 consecutive years of follow-up in 209 HD patients, increased CAVI might represent a major modifiable risk factor for all-cause mortality. Further research is needed to examine whether CAVI-lowering interventions contribute to improved prognosis.

Life-threatening extrapleural hematoma in an anticoagulated patient 2 weeks after lobectomy.

We report a case of an anticoagulated patient with sudden onset pleural hematoma after straining at defecation to cardiac arrest on 2 weeks after lobectomy for lung cancer. We decided to perform an emergent operation for an evacuation of extrapleural hematoma immediately after resuscitation. The bleeding point was revealed on the extrapleural thoracic apex. We should be aware that extrapleural hematoma can occur because of increased intrathoracic pressure such as straining during defecation in patients on anticoagulation.

Negative-pressure wound therapy in combination with bronchial occlusion to treat bronchopleural fistula: a case report.

BACKGROUND: Bronchopleural fistula, which usually accompanies bronchial fistula and empyema, is a severe complication of lung cancer surgery. Negative-pressure wound therapy can enhance drainage and reduce the empyema cavity, potentially leading to early recovery. This therapy is not currently indicated for bronchopleural fistulas because of the risk of insufficient respiration due to air loss from the fistula. CASE PRESENTATION: A 73-year-old man, who was malnourished because of peritoneal dialysis, was referred to our hospital for the treatment of lung cancer. Right lower lobectomy with mediastinal lymph node dissection was performed via posterolateral thoracotomy, and the bronchial stump was covered with the intercostal muscle flap. His postoperative course was uneventful and he was discharged. However, he was readmitted to our hospital because of respiratory failure and diagnosed as having bronchopleural fistula on the basis of the bronchoscopic finding of a 10-mm hole at the membranous portion of the inlet of the remnant lower lobe bronchus. Thus, thoracotomy debridement and open window thoracostomy were immediately performed. After achieving infection control, bronchial occlusion was performed using fibrin glue and a polyglycolic acid sheet was inserted through a fenestrated wound. Bronchial fistula closure was observed on bronchoscopy; therefore, a negative-pressure wound therapy system was applied to close the fenestrated wound. The collapsed lung was re-expanded and the granulation tissue around the wound increased; therefore, thoracic cavity size decreased and thoracoplasty using the latissimus dorsi was performed. CONCLUSIONS: This bronchopleural fistula was treated successfully after a right lower lobectomy using an extra-pleural bronchial occlusion and negative-pressure wound therapy.

Comparison of a Novel Bisphosphonate Prodrug and Zoledronic Acid in the Induction of Cytotoxicity in Human Vγ2Vδ2 T Cells.

Increasing attention has been paid to human γδ T cells expressing Vγ2Vδ2 T cell receptor (also termed Vγ9Vδ2) in the field of cancer immunotherapy. We have previously demonstrated that a novel bisphosphonate prodrug, tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1-bisphosphonate (PTA), efficiently expands peripheral blood Vγ2Vδ2 T cells to purities up to 95-99% in 10-11 days. In the present study, we first examined the effect of PTA on farnesyl diphosphate synthase (FDPS) using liquid chromatography mass spectrometry (LC-MS) to analyze the mechanism underlying the PTA-mediated expansion of Vγ2Vδ2 T cells. We find that the prodrug induced the accumulation of both isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), direct upstream metabolites of FDPS. This indicates that not only IPP but also DMAPP plays an important role in PTA-mediated stimulation of Vγ2Vδ2 T cells. We next analyzed TCR-independent cytotoxicity of Vγ2Vδ2 T cells. When human lung cancer cell lines were challenged by Vγ2Vδ2 T cells, no detectable cytotoxicity was observed in 40 min. The lung cancer cell lines were, however, significantly killed by Vγ2Vδ2 T cells after 4-16 h in an effector-to-target ratio-dependent manner, demonstrating that Vγ2Vδ2 T cell-based cell therapy required a large number of cells and longer time when tumor cells were not sensitized. By contrast, pulsing tumor cell lines with 10-30 nM of PTA induced significant lysis of tumor cells by Vγ2Vδ2 T cells even in 40 min. Similar levels of cytotoxicity were elicited by ZOL at concentrations of 100-300 µM, which were much higher than blood levels of ZOL after infusion (1-2 µM), suggesting that standard 4 mg infusion of ZOL was not enough to sensitize lung cancer cells in clinical settings. In addition, Vγ2Vδ2 T cells secreted interferon-γ (IFN-γ) when challenged by lung cancer cell lines pulsed with PTA in a dose-dependent manner. Taken together, PTA could be utilized for both expansion of Vγ2Vδ2 T cells ex vivo and sensitization of tumor cells in vivo in Vγ2Vδ2 T cell-based cancer immunotherapy. For use in patients, further studies on drug delivery are essential because of the hydrophobic nature of the prodrug.

Successful thoracoscopic evacuation of an extrapleural hematoma with delayed symptomatic pleural effusion: a case report.

BACKGROUND: Traumatic extrapleural hematoma is a rare condition and is usually managed conservatively until spontaneous resolution unless active bleeding or expansion is found. CASE PRESENTATION: An 80-year-old man taking an anticoagulant medication was referred to our hospital after accidentally falling in a street ditch while riding a bike. Chest X-ray and computed tomography (CT) scan showed multiple fractures on ribs 7-9, hemothorax, and extrapleural hematoma in the posterior chest wall. Though the patient's hemothorax was improved by chest tube drainage, the extrapleural hematoma still remained. He was transferred to another hospital for rehabilitation, but he was readmitted to our hospital because of dyspnea with accumulation of left pleural effusion, including a subpopulation of neutrophils, but without bacterial infection. We performed thoracoscopic evacuation of the hematoma on day 57 after the initial blunt chest trauma. The patient has had no recurrence of pleuritis for 6 months after surgery. CONCLUSION: Since posttraumatic extrapleural hematoma may result in delayed secondary intractable pleural effusion causing dyspnea, careful observation is necessary when considering indications of surgical intervention.

Bioluminescence Microplate Assay of Cyanide with Escherichia coli Harboring a Plasmid Responsible for Cyanide-dependent Light Emission in Alginate Microenvironment.

We describe the bioluminescence of a genetically engineered Escherichia coli harboring a recombined plasmid with a catalase gene promoter fused lux gene cluster, responsible for the generation of photons closely associated with respiratory inhibition, with the aim of applying it for cyanide sensing. This E. coli construct was favorably utilized for the microplate assay of cyanide by leveraging the microenvironment of the biocompatible alginate. The brightness of the bioluminescence, induced by cyanide stimulation of the respiration causative of the production of hydrogen peroxide, positively correlates with its concentration. Moreover, visualization of cyanide with a consumer digital camera, ranging in concentration from about 0.01 mg CN·L-1 in the alginate sol to around 100 mg CN·L-1 in its gel, was attained.

Synthesis and Immunomodulatory Activity of Fluorine-Containing Bisphosphonates.

Immune checkpoint blockade using anti-PD-1/PD-L1 or anti-CTLA-4 monoclonal antibodies (mAbs) has revolutionized cancer treatment. However, many types of cancer do not respond and for those that do, only a minority of patients achieve durable remissions. Therefore, oncoimmunologists are working to develop adoptive cell therapies for non-hematopoietic tumors by harnessing immune effector cells such as αß T cells and γδ T cells. In contrast to conventional αß T cells that recognize peptides in the context of MHC class I or II molecules, γδ T cells expressing Vγ2Vδ2 T cell receptors (also termed Vγ9Vδ2) are stimulated by isoprenoid metabolites (phosphoantigens) such as isopentenyl diphosphate in a butyrophilin-3A1-dependent manner. Vγ2Vδ2 T cells kill almost all types of tumor cells that have been treated with bisphosphonates. In this study, we synthesized a series of fluorine-containing bisphosphonates based on current drugs and found that they stimulated Vγ2Vδ2 T cell killing of tumor cells. A fluorine-containing prodrug analogue of zoledronate where phosphonate moieties were masked with pivaloyloxymethyl groups markedly enhanced Vγ2Vδ2 T-cell-mediated cytotoxicity, and also promoted the expansion of peripheral blood Vγ2Vδ2 T cells. These results demonstrate that a prodrug of a fluorine-containing zoledronate analogue can sensitize tumor cells for killing as well as expand Vγ2Vδ2 T cells for adoptive cell therapy.

Determination of human γδ T cell-mediated cytotoxicity using a non-radioactive assay system.

The adoptive transfer of immune effector cells, such as CD8+ killer αß T cells, γδ T cells, NK (natural killer) cells, and genetically-modified T cells, has been receiving increasing attention. It is essential to determine cellular cytotoxicity so as to monitor the function and quality of ex vivo-expanded immune effector cells before infusion. The most common method is the [51Cr]-sodium chromate release assay. It is, however, preferable to avoid the use of radioactive materials in clinical laboratories. In order to establish a non-radioactive alternative to the standard radioactive assay, we previously synthesized a chelate-forming prodrug (BM-HT) and demonstrated that a combination of BM-HT and europium (Eu3+) was useful to determine NK cell-mediated cytotoxicity. In the present study, we examined whether or not this improved assay system could be used to determine the cellular cytotoxicity exhibited by Vγ2Vδ2+ γδ T cells. In addition, we compared Eu3+ and terbium (Tb3+) in the measurement of cellular cytotoxicity. Our assay system using BM-HT could be used successfully for the analysis of both γδ T cell receptor (TCR)- and CD16-mediated cytotoxicity. When the intensity of fluorescence was compared between Eu3+ and Tb3+, Tb3+ chelate was more sensitive than Eu3+ chelate, suggesting that the detection system using Tb3+ is superior to Eu3+ when tumor cells are not efficiently labeled with BM-HT. The method established herein is expected to promote the development of novel adoptive cell therapies for cancer.

Intractable pneumothorax due to rupture of subpleural rheumatoid nodules: a case report.

BACKGROUND: In rare cases, rheumatoid pleural nodules can rupture into the pleural cavity to cause pneumothorax or empyema. We report successful surgical treatment of a patient with an intractable secondary pneumothorax due to rupture of a subpleural rheumatoid nodule into the pleural cavity. CASE PRESENTATION: A 75-year-old man with a medical history of rheumatoid arthritis, acute coronary syndrome, and diabetes was admitted to our hospital because of left chest pain and dyspnea. A chest X-ray and chest computed tomography (CT) scan showed a left pneumothorax and several small subpleural nodules with cavitation. Repeated pleurodesis via a chest tube failed to improve the pneumothorax, so we decided to perform thoracoscopic surgery. Air leakage was detected in the left upper lobe where the subpleural nodule was visible on chest CT. Resection of the lesion successfully resulted in resolution of the air leakage. The final pathological diagnosis of the subpleural nodule was a pulmonary rheumatoid nodule. The patient has had no evidence of recurrence of pneumothorax after surgery. CONCLUSIONS: We obtained a final pathological diagnosis of a rheumatoid nodule that caused an intractable pneumothorax. Pneumothorax associated with rupture of rheumatoid nodules in the subpleural cavitary is difficult to treat with thoracoscopic surgery as a second-line treatment.

Expansion of human γδ T cells for adoptive immunotherapy using a bisphosphonate prodrug.

Cancer immunotherapy with human γδ T cells expressing Vγ2Vδ2 T cell receptor (also termed Vγ9Vδ2) has shown promise because of their ability to recognize and kill most types of tumors in a major histocombatibility complex (MHC) -unrestricted fashion that is independent of the number of tumor mutations. In clinical trials, adoptive transfer of Vγ2Vδ2 T cells has been shown to be safe and does not require preconditioning. In this report, we describe a method for preparing highly enriched human Vγ2Vδ2 T cells using the bisphosphonate prodrug, tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1-bisphosphonate (PTA). PTA stimulated the expansion of Vγ2Vδ2 cells to purities up to 99%. These levels were consistently higher than those observed after expansion with zoledronic acid, the most commonly used stimulator for clinical trials. Cell numbers also averaged more than those obtained with zoledronic acid and the expanded Vγ2Vδ2 cells exhibited high cytotoxicity against tumor cells. The high purity of Vγ2Vδ2 cells expanded by PTA increased engraftment success in immunodeficient NOG mice. Even low levels of contaminating αß T cells resulted in some mice with circulating human αß T cells rather than Vγ2Vδ2 cells. Vγ2Vδ2 cells from engrafted NOG mice upregulated CD25 and secreted tumor necrosis factor-α and interferon-γ in response to PTA-treated tumor cells. Thus, PTA expands Vγ2Vδ2 T cells to higher purity than zoledronic acid. The high purities allow the successful engraftment of immunodeficient mice without further purification and may speed up the development of allogeneic Vγ2Vδ2 T cell therapies derived from HLA-matched normal donors for patients with poor autologous Vγ2Vδ2 T cell responses.

Anti-Tumor Activity and Immunotherapeutic Potential of a Bisphosphonate Prodrug.

Bisphosphonates have benefits in breast cancer and multiple myeloma patients and have been used with adoptive immunotherapy with γδ T cells expressing Vγ2 Vδ2 TCRs. Although treatment with γδ T cells is safe, it has shown limited efficacy. Present bisphosphonates stimulate γδ T cells but were designed to inhibit bone resorption rather than treating cancer and have limited oral absorption, tumor cell entry, and cause bone side effects. The development of phosphate and phosphonate nucleotide prodrugs has led to important drugs for hepatitis C and HIV. Using a similar approach, we synthesized bisphosphonate prodrugs and found that they efficiently limit tumor cell growth. Pivoxil bisphosphonate esters enter cells where esterases convert them to their active acids. The bisphosphonate esters stimulated γδ T cells to secrete TNF-α in response to a variety of tumor cells more efficiently than their corresponding acids. The most active compound, tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1- bisphosphonate (7), specifically expanded γδ T cells and stimulated them to secrete interferon-γ and kill tumor cells. In preclinical studies, combination therapy with compound 7 and γδ T cells prolonged survival of mice inoculated with either human bladder cancer or fibrosarcoma cells. Therefore, bisphosphonate prodrugs could enhance the effectiveness of adoptive cancer immunotherapy with γδ T cells.

Targeting Cancer Cells with a Bisphosphonate Prodrug.

Nitrogen-containing bisphosphonates have antitumor activity in certain breast cancer and myeloma patients. However, these drugs have limited oral absorption, tumor cell entry and activity, and cause bone side effects. The potencies of phosphorylated antiviral drugs have been increased by administering them as prodrugs, in which the negative charges on the phosphate moieties are masked to make them lipophilic. We synthesized heterocyclic bisphosphonate (BP) prodrugs in which the phosphonate moieties are derivatized with pivaloyloxymethyl (pivoxil) groups and that lack the hydroxy "bone hook" on the geminal carbon. When the lipophilic BP prodrugs enter tumor cells, they are converted into their active forms by intracellular esterases. The most active BP prodrug, tetrakispivaloyloxymethyl 2-(thiazole-2-ylamino)ethylidene-1,1-bisphosphonate (7), was found to potently inhibit the in vitro growth of a variety of tumor cell lines, especially hematopoietic cells, at nanomolar concentrations. Consistent with this fact, compound 7 inhibited the prenylation of the RAP1A small GTPase signaling protein at concentrations as low as 1-10 nm. In preclinical studies, 7 slowed the growth of human bladder cancer cells in an immunodeficient mouse model. Thus, 7 is significantly more active than zoledronic acid, the most active FDA-approved BP, and a potential anticancer therapeutic.