Outcomes of Targeted Therapy Plus Immunotherapy and High-Dose Stereotactic Ablative Body Radiotherapy (SABR) for Metastatic Renal Cell Cancer Patients

PURPOSE/OBJECTIVE(S)

Stereotactic ablative body radiotherapy (SABR) is one of the treatment options for metastatic renal cell carcinoma (mRCC) but is limited by a lack of data to evaluate targeted therapy plus immunotherapy concurrently with high-dose SABR to multiple sites. We evaluated the safety and disease control for mRCC patients who concurrently received the above tri-modality treatment.

MATERIALS/METHODS

Patients were treated with SABR (40-70 Gy/5-10 fractions) for small lesions or partial-SABR (tumor center boosted with 6-8 Gy/3-5 fractions with 50-60 Gy/20-25 fractions to the whole tumor volume) for bulky tumors or tumors adjacent to critical organs. When SABR/partial-SABR was not feasible, a moderate fractionated radiotherapy plan, usually 60Gy/20 fractions were applied. of Targeted therapy plus immunotherapy (PD-1 inhibitor) was not interrupted during or after radiotherapy (RT). Adverse events (AEs) were evaluated. Disease control rate (DCR), objective response rate (ORR), progression-free survival (PFS) and overall survival (OS) were calculated. The PFS1 was defined as the first progression since the start of RT. The PFS2 was defined as the second progression after the second RT course, if new metastases occurred after first RT were all re-irradiated, and the systemic therapy was not changed. The Kaplan-Meier method was used for time-to-event endpoints.

RESULTS

A total of 51 patients, with a median age of 57 yr, were enrolled. The median follow-up was 12 months. There were 75% of patients with intermediate-risk and 18% with favorable-risk disease. 61% of the patients were oligometastatic. 71% had clear cell renal cancer. There were 241 metastases while 161 (67%) were irradiated. 80% of the lesions received SABRP/partial SABR. 1 patient with 14 lesions irradiated received proton therapy. All the surviving patients are continuing using targeted therapy while 81% patients complete at least 1-year PD-1 therapy. 10 patients (20%) had grade 3 drug-related AEs: pneumonitis (n = 2), elevated alanine transaminase (n = 4), myositis (n = 1), hand-foot syndrome myositis (n = 1), enteritis (n = 1), fatigue (n = 1). There were 1 grade 4 AEs of upper gastrointestinal bleeding. No grade 3-5 RT-related AEs was found. ORR and DCR for irradiated lesion were 51% and 98%. Median OS and PFS2 was not reached. Median PFS1 was 14(6-22) months. Estimated 1- and 2-yr OS, PFS1 and PFS2 were 90% and 90%, 56% and 38%, 74% and 51% respectively. Univariate analysis showed that an PFS1 benefit was found in patients who received radiation before systemic therapy failure (p = 0.038).

CONCLUSION

We investigated the high-dose RT in combination of concurrent targeted and immunotherapy in patients with metastatic RCC. We found that this treatment regimen was well tolerated, with good cancer control. Early use of high-dose RT to multi-lesions may improve PFS. Partial-SABR for bulky lesions close to critical organs could be safely and effectively applied under certain circumstances. These encouraging findings warrant further investigation.

Delineation of the distinct inflammatory signaling roles of TAK1 and JAK1/3 in the CIA model of rheumatoid arthritis

Rheumatoid arthritis (RA) is a complex autoimmune disease characterized by hyperactive immune cells within the joints, which leads to inflammation, bone degeneration, and chronic pain. For several decades, frontline immunomodulators such as the anti-tumor necrosis factor (TNF) biologics adalimumab (Humira), etanercept (Enbrel), and infliximab (Remicade) have successfully managed disease progression for many patients. However, over time, patients become refractory to these treatments requiring chronic disease to be managed with conventional and more problematic disease modifying antirheumatic drugs such as methotrexate and hydroxychloroquine, and corticosteroids. Due to the large proportion of patients who continue to fail on frontline biologic therapies, there remains an unmet need to derive novel alternative targets with improved efficacy and safety profiles to treat RA. Recent advances in the field have defined novel targets that play important roles in RA pathology, including the Janus activated kinase (JAK) and transforming growth factor beta activated kinase-1 (TAK1). Although three inhibitors of the JAK signaling pathway have been approved for the treatment of moderately to severely active RA in patients who failed on one or more anti-TNFs, at present, no FDA approved TAK1 treatments exist. Our recent discovery of a highly potent and selective, orally bioavailable TAK1 inhibitor has provided insight into the therapeutic potential of this protein kinase as a novel target for RA. Here, we show the distinct cytokine signaling of tofacitnib (Xeljanz; JAK1/3 inhibitor) compared to HS-276 (TAK1 inhibitor) in lipopolysaccharide (LPS) challenged THP-1 cells. Furthermore, in the collagen induced arthritis pre-clinical mouse model of RA, both tofacintib and HS-276 attenuated disease activity score and inflammatory cytokines in the serum. Overall, our results delineate the distinct cytokine signaling of JAK1/3 and TAK1 targeted therapies in vitro and in vivo and suggest that selective TAK1 inhibitors may provide superior therapeutic relief in RA with fewer adverse events.

Expression of membrane Hsp90 is a molecular signature of T cell activation

Heat shock protein 90 (Hsp90) maintains cellular proteostasis during stress and has been under investigation as a therapeutic target in cancer for over two decades. We and others have identified a membrane expressed form of Hsp90 (mHsp90) that previously appeared to be restricted to rapidly proliferating cells exhibiting a metastatic phenotype. Here, we used HS-131, a fluor-tethered mHsp90 inhibitor, to quantify the effect of T cell activation on the expression of mHsp90 in human and mouse T cells. In cell-based assays, stimulation of human T cells induced a 20-fold increase in mHsp90 expression at the plasma membrane, suggesting trafficking of mHsp90 is regulated by TCR and inflammatory mediated signaling. Following injection of HS-131 in mouse models of human rheumatoid arthritis and inflammatory bowel disease, we detected localization of the probe at sites of active disease, consistent with immune cell invasion. Moreover, despite rapid hepatobiliary clearance, HS-131 demonstrated efficacy in reducing the mean clinical score in the CIA arthritis model. Our results suggest mHsp90 expression on T cells is a molecular marker of T cell activation and potentially a therapeutic target for chronic diseases such as rheumatoid arthritis.

Expression of ectopic heat shock protein 90 in male and female primary afferent nociceptors regulates inflammatory pain

ABSTRACT

Heat shock protein 90 (Hsp90) is a ubiquitously expressed integral cellular protein essential for regulating proteomic stress. Previous research has shown that Hsp90 regulates critical signaling pathways underlying chronic pain and inflammation. Recent discovery of membrane bound ectopic Hsp90 (eHsp90) on tumor cells has shown that Hsp90 induction to the plasma membrane can stabilize disease-relevant proteins. Here, we characterize eHsp90 expression in a mouse model of inflammation and demonstrate its role in nociception and pain. We found that intraplantar complete Freund adjuvant (CFA) induced robust expression of eHsp90 on the cell membranes of primary afferent nociceptors located in the L3-L5 dorsal root ganglia (DRG), bilaterally, with minimal to no expression in other tissues. Complete Freund adjuvant-induced increases in eHsp90 expression on lumbar DRG were significantly greater in females compared with males. Furthermore, exogenous Hsp90 applied to primary Pirt-GCaMP3 nociceptors induced increases in calcium responses. Responses were estrogen-dependent such that greater activity was observed in female or estrogen-primed male nociceptors compared with unprimed male nociceptors. Treatment of mice with the selective eHsp90 inhibitor HS-131 (10 nmol) significantly reversed CFA-induced mechanical pain, thermal heat pain, and hind paw edema. Notably, a higher dose (20 nmol) of HS-131 was required to achieve analgesic and anti-inflammatory effects in females. Here, we provide the first demonstration that inflammation leads to an upregulation of eHsp90 on DRG nociceptors in a sex-dependent manner and that inhibition of eHsp90 reduces nociceptor activity, pain, and inflammation. Thus, eHsp90 represents a novel therapeutic axis for the development of gender-tailored treatments for inflammatory pain.

TAK1: a potent tumour necrosis factor inhibitor for the treatment of inflammatory diseases

Aberrant tumour necrosis factor (TNF) signalling is a hallmark of many inflammatory diseases including rheumatoid arthritis (RA), irritable bowel disease and lupus. Maladaptive TNF signalling can lead to hyper active downstream nuclear factor (NF)-κβ signalling in turn amplifying a cell's inflammatory response and exacerbating disease. Within the TNF intracellular inflammatory signalling cascade, transforming growth factor-β-activated kinase 1 (TAK1) has been shown to play a critical role in mediating signal transduction and downstream NF-κβ activation. Owing to its role in TNF inflammatory signalling, TAK1 has become a potential therapeutic target for the treatment of inflammatory diseases such as RA. This review highlights the current development of targeting the TNF-TAK1 signalling axis as a novel therapeutic strategy for the treatment of inflammatory diseases.

TAK1 regulates the tumor microenvironment through inflammatory, angiogenetic and apoptotic signaling cascades

Transforming growth factor beta-activated kinase 1 (TAK1) has been implicated for its role in inflammatory signaling and as an important mediator of cellular apoptosis and necroptosis in various cell types. Our recent discovery of a first-in-class, potent and selective TAK1 inhibitor, takinib, represents a novel pharmacological tool to evaluate TAK1’s role in cancer. In this study we evaluated the potential therapeutic capacity of TAK1 inhibition on tumor growth and on tumor microenvironment remodeling. In a screen of 16 cancer cell lines, takinib in combination with tumor necrosis factor (TNF) was found to induce cell death (>20%) in 6 out of 16 cell lines. Furthermore, knocking out of TAK1 in MDA-MB-231 cells dramatically increased their sensitization to TNF-mediated apoptosis. In vivo xenographs of MDA-MB-231 TAK1^KO tumors displayed delayed tumor growth and increased overall survival compared to TAK1^WT controls. Histological and proteomic analysis of TAK1^KO tumors showed altered angiogenic signaling and inflammatory signaling via immune cells. Overall, these findings suggest that the targeting of TAK1 in immune mediated cancers may be a novel therapeutic axis.

A highly selective inhibitor of interleukin-1 receptor-associated kinases 1/4 (IRAK-1/4) delineates the distinct signaling roles of IRAK-1/4 and the TAK1 kinase

Interleukin-1 receptor-associated kinase-1 (IRAK-1) and IRAK-4, as well as transforming growth factor β-activated kinase 1 (TAK1), are protein kinases essential for transducing inflammatory signals from interleukin receptors. IRAK family proteins and TAK1 have high sequence identity within the ATP-binding pocket, limiting the development of highly selective IRAK-1/4 or TAK1 inhibitors. Beyond kinase activity, IRAKs and TAK1 act as molecular scaffolds along with other signaling proteins, complicating the interpretation of experiments involving knockin or knockout approaches. In contrast, pharmacological manipulation offers the promise of targeting catalysis-mediated signaling without grossly disrupting the cellular architecture. Recently, we reported the discovery of takinib, a potent and highly selective TAK1 inhibitor that has only marginal activity against IRAK-4. On the basis of the TAK1-takinib complex structure and the structure of IRAK-1/4, here we defined critical contact sites of the takinib scaffold within the nucleotide-binding sites of each respective kinase. Kinase activity testing of takinib analogs against IRAK-4 identified a highly potent IRAK-4 inhibitor (HS-243). In a kinome-wide screen of 468 protein kinases, HS-243 had exquisite selectivity toward both IRAK-1 (IC50 = 24 nm) and IRAK-4 (IC50 = 20 nm), with only minimal TAK1-inhibiting activity (IC50 = 0.5 μm). Using HS-243 and takinib, we evaluated the consequences of cytokine/chemokine responses after selective inhibition of IRAK-1/4 or TAK1 in response to lipopolysaccharide challenge in human rheumatoid arthritis fibroblast-like synoviocytes. Our results indicate that HS-243 specifically inhibits intracellular IRAKs without TAK1 inhibition and that these kinases have distinct, nonredundant signaling roles.

Pharmacological inhibition of TAK1, with the selective inhibitor takinib, alleviates clinical manifestation of arthritis in CIA mice

OBJECTIVES

To examine the ability of takinib, a selective transforming growth factor beta-activated kinase 1 (TAK1) inhibitor, to reduce the severity of murine type II collagen-induced arthritis (CIA), and to affect function of synovial cells.

METHODS

Following the induction of CIA, mice were treated daily with takinib (50 mg/kg) and clinical scores assessed. Thirty-six days post-CIA induction, histology was performed on various joints of treated and vehicle-treated animals. Inflammation, pannus, cartilage damage, bone resorption, and periosteal bone formation were quantified. Furthermore, pharmacokinetics of takinib were evaluated by LC-MS in various tissues. Rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS) cells were cultured with 10 μM takinib and cytokine secretion analyzed by cytokine/chemokine proteome array. Cytotoxicity of takinib for RA-FLS was measured with 24 to 48 h cultures in the presence or absence of tumor necrosis factor (TNF).

RESULTS

Here, we show takinib's ability to reduce the clinical score in the CIA mouse model of rheumatoid arthritis (RA) (p < 0.001). TAK1 inhibition reduced inflammation (p < 0.01), cartilage damage (p < 0.01), pannus, bone resorption, and periosteal bone formation and periosteal bone width in all joints of treated mice compared to vehicle treated. Significant reduction of inflammation (p < 0.004) and cartilage damage (p < 0.004) were observed in the knees of diseased treated animals, with moderate reduction seen in the forepaws and hind paws. Furthermore, the pharmacokinetics of takinib show rapid plasma clearance (t_½ = 21 min). In stimulated RA-FLS cells, takinib reduced GROα, G-CSF, and ICAM-1 pro-inflammatory cytokine signaling.

CONCLUSION

Our findings support the hypothesis that TAK1 targeted therapy represents a novel therapeutic axis to treat RA and other inflammatory diseases.

[Clinical features analysis of metanephric adenoma: a series of 16 cases]

Objective: To study the clinical characteristics, image findings, therapeutic method and prognosis of metanephric adenoma. Method: The clinical characteristic, image findings, operation methods and prognosis of 16 metanephric adenoma patients treated at Department of Urology, Peking University First Hospital from January 2004 to March 2016 were analyzed retrospectively. Results: There were 6 male and 10 female patients in the study. The mean age of patients was 33.7 years (ranging from 14 to 83 years). Two patients came to the hospital because of fever, while other 14 patients had no symptoms and found renal tumor by medical examination. One case was found polythemia vera and another 1 case showed mild anemia. Serum creatine of all the cases were in normal range. The tumor of 11 cases were at left side and 5 cases were at right. All patients took urinary tract ultrasound. Fifteen patients took CT examination. Among them, 14 cases were solid mass and 1 case was cystosolid.CT value was (41±4) HU. CT scan showed that the tumor was slight enhanced and CT value increased to (77±9) HU. Six patients took MRI examination. The MRI showed high or low signal of T1WI or T2WI scans.Tumor size was (4.7±3.9)cm (ranging from 1.7 to 17.5 cm). All 16 patients took operation and 11 of them took laparoscopic surgery while the other 5 cases took open surgery. Eleven cases took partial nephrectomy, 4 cases took nephrectomy and 1 case took nephroureterectomy. The surgical procedures were all successful and no complications occured during perioperative period. All cases were all confirmed metanephric adenoma by postoperative pathology and surgery cut edge were all negative. Immunohistochemical study showed that the positive rate of Vimentin, CD57, AE1/AE3, WT1, CK7 and AMACR respectively were 16/16, 15/16, 12/16, 10/16, 3/16 and 2/16. The median follow-up time of 16 cases was 44 months (ranging from 8 to 125 months) and none had recurrence or metastasis.One case died 125 months after surgery because of advanced age(83 years old). Conclusions: Metanephric adenoma is difficult to be diagnosed relying on clinical characteristics and image features. Pathology can help confirm the diagnosis. Partial nephrectomy is the first choice for operation and can achieve good prognosis. But it still needs a regular follow-up.

[The impact to operation safety of preoperative renal artery embolization for management of diameter≥10 cm renal cell carcinoma]

Objective: To study the impact to operation safety of preoperative renal artery embolization for management of ≥10 cm renal cell carcinoma. Methods: The clinical data of 239 cases with ≥10 cm renal cell carcinoma which all had underwent operation in Department of Urology, Peking University First Hospital from January 2002 to December 2014 were retrospectively analyzed. Fifty-three patients underwent preoperative renal artery embolization (therapeutic group) and 186 patients did not (control group). The effect of embolization on operative time, transfusion requirements, hospitalization, ICU stay and perioperative complications were analyzed by comparing the two groups using rank sum test and χ(2) test or Fisher exact test. Results: Comparing the therapeutic group and control group, there was significant difference in tumor location (on the left or right). The mean age, sex, mean primary tumor size, and TNM stage were similar in both groups. Comparing the therapeutic group and control group, there were more open surgeries in therapeutic group (96.2% vs. 82.3%, χ(2)=6.438, P=0.013). There were no significant differences in mean operative time (238 (525) minutes vs. 208 (583) minutes, Z=-2.182, P=0.062). The mean blood transfusion (700 (1 900) ml vs. 925 (8 800) ml, Z=-1.064, P=0.006) had significant difference. The therapeutic group had a longer mean hospitalization (21 (50) days vs. 15 (79) days, Z=-4.322, P=0.000) and higher rate of intensive care unit stay (54.7% vs. 34.4%, χ(2)=6.103, P=0.027). There was no significant difference in perioperative complications between two groups (0 vs.3.2%, P=0.408). Conclusion: Preoperative renal artery embolization in ≥10 cm renal cell carcinoma patients undergoing operation provides benefit in increasing operation safety and reducing perioperative death.

[Prognostic factors of patients with T3N0M0 renal cell carcinoma: a single-center retrospective study of 182 patients]

OBJECTIVE

To evaluate the impacts of clinical, pathological, and laboratory factors on oncological outcomes of patients with T3N0M0 renal cell carcinoma.

METHODS

The clinical data, laboratory exam results, and follow-up outcomes of 182 patients with T3N0M0 renal cell carcinoma who underwent nephrectomy from 2007 to 2012 in Peking University First Hospital were retrospectively collected. The 5-year cancer-specific survival and 5-year recurrence-free survival of all the patients were calculated using Kaplan-Meier method, and the statistical significance between the survival curves were compared using the Log-rank test. Variables with significant differences in the univariate analysis were subjected to the multivariate analysis by Cox regression model. All the comparisons were conducted using two-tailed test and P<0.05 was considered statistically significant.

RESULTS

A total of 182 patients were included in this study. Of all the 182 patients, 126 were male (69.23%) and 56 were female (30.77%). The mean age was (56.75±12.45) years. The median follow-up time was 48 months (3-99 months). At the end of the follow-up, 50 patients (27.47%) died due to the disease after a median of 29.74 months and 59 patients (32.42%) had tumor recurrence after a median of 22.12 months. The 5-year cancer-specific survival of all patients was 68.30% (95% CI: 60.16%-75.84%); the 5-year recurrence-free survival was 60.70% (95% CI: 53.16%-68.84%). In the univariate analysis, diabetes mellitus, tumor invasion status, Fuhrman grade, serum album, serum cholestenone, anemia, and neutrophils percentage were associated with the cancer-specific survival and Fuhrman grade, serum album and anemia were associated with the recurrence-free survival. Variables with significant differences on univariate analysis were included in Cox multivariate regression analysis. Multivariate Logistic regression analysis showed that diabetes mellitus (HR=2.434, 95% CI: 1.243-4.769, P=0.010), hypoalbuminemia (HR=2.188, 95% CI: 1.074-1.074, P=0.031), and anemia (HR=3.320, 95% CI: 1.839-5.991, P<0.001) were independent risk factors significantly associated with cancer-specific survival; and higher Fuhrman grade (HR=2.552, 95% CI: 1.433-4.545, P=0.001), anemia (HR=2.535, 95% CI: 1.497-4.293, P=0.001) were independent factors significantly associated with recurrence-free survival.

CONCLUSION

Diabetes mellitus, hypoalbuminemia, and anemia were independent risk factors significantly associated with cancer-specific survival of T3N0M0 renal cell carcinoma patients; higher Fuhrman grade and anemia were independent risk factors significantly associated with tumor recurrence of T3N0M0 renal cell carcinoma patients.

The differential inhibitory effects of genistein on the growth of cervical cancer cells in vitro

The biological effect of genistein on cervical cancer was studied on two cervical cancer cell lines with different cellular characteristics. Here we report that genistein exhibits inhibitory effects on the growth of HeLa and ME-180 cells. The IC50 was 35 microM and 60 microM for HeLa and ME-180 cells, respectively. ME-180 cells showed obvious G2/M arrest with genistein treatment while most of the HeLa cells were accumulated in S phase. The underlying molecular mechanism was further elucidated by apoptosis analysis and expression levels of cell cycle regulatory proteins. Treatment of the cell lines with genistein also resulted in suppression of invasion through a surrogate membrane in a dose-dependent manner, particularly the HeLa cells. While the underlying mechanism needs to be further studied, the higher suppressive effect on invasion of HeLa cells, an adenocarcinoma cell line, are noteworthy. This in vitro observation may have clinical implication to improve the treatment of cervical adenocarcinoma.

The problem of a solvent exposable disulfide when preparing Co(II)-substituted metallo-beta-lactamase L1 from Stenotrophomonas maltophilia

In an effort to prepare Co(II)-substituted metallo-beta-lactamase L1 from Stenotrophomonas maltophilia for future spectroscopic and mechanistic studies, two methods for the preparation of Co(II)-L1 were tested. Method A involved adding CoCl2 directly to apo-L1 under anaerobic conditions. The resulting enzyme contained 1.9 moles of cobalt and exhibited very little activity, and UV-Vis, 1H NMR, and EPR studies indicated that most of the cobalt in this sample was Co(III). Method B involved reducing the single and unique disulfide bridge in L1 with tris(carboxyethyl)phosphine prior to adding CoCl2. The resulting enzyme was pink, contained 2.5 moles of cobalt per mole of enzyme, and exhibited kcat and Km values of 18+1 s(-1) and 10+/-1 microM, respectively, when using nitrocefin as the substrate. UV-Vis, 1H NMR, and EPR studies revealed that this enzyme sample contained high-spin Co(II). The UV-Vis spectra also provided evidence for Co(II) bound to one or both of the reduced cysteines. Efforts to block this non-specific Co(II) binding site using a chemical modification agent or site-directed mutagenesis were unsuccessful. The data presented here demonstrate the problem of solvent-exposed disulfides when preparing Co(II)-substituted enzymes and offers a convenient method to circumvent the problem.

Phosphonamidate and phosphothioate dipeptides as potential inhibitors of VanX

In an effort to prepare novel inhibitors of VanX, N-[(1-aminoethyl)hydroxyphosphinyl]-D-alanine 1 and S-[(aminoethyl)hydroxyphosphinyl]-thiolacetic acid 2 were synthesized and evaluated as inhibitors of VanX. Phosphonamidate 1 was shown to be a partial competitive inhibitor of VanX with a Ki of 36+/-3 microM, and phosphothioate 2 was shown not to inhibit VanX.

Inhibition studies on the metallo-beta-lactamase L1 from Stenotrophomonas maltophilia

In an effort to identify a competitive inhibitor that can be used in future spectroscopic and crystallographic studies and to better understand the interaction of a mercaptoacetic acid-thiolester-containing compound with metallo-beta-lactamase L1 from Stenotrophomonas maltophilia, inhibition studies using two thiol-containing compounds were conducted. N-(2'-Mercaptoethyl)-2-phenylacetamide is a competitive inhibitor of L1 with a K(i) of 50 +/- 3 microM, and this compound is not a time-dependent inactivator of L1. N-Benzylacetyl-d-alanylthioacetic acid is a competitive inhibitor of L1 with a K(i) of 1.6 +/- 0.3 microM. Matrix-assisted laser desorption ionization time-of-flight mass spectrometric studies revealed that 2 mol of mercaptoacetate covalently bind to L1 upon incubation of the enzyme with N-benzylacetyl-d-alanylthioacetic acid; however, this covalently modified enzyme has the same activity as wild-type L1. Last, inhibition studies were used to demonstrate that 4-morpholinoethanesulfonic acid does not inhibit L1, even at concentrations up to 300 mM. This work identifies two possible competitive inhibitors which can be used in future structural studies and further demonstrates inhibitory heterogeneity among the metallo-beta-lactamases.

Continuous assay for VanX, the D-alanyl-D-alanine dipeptidase required for high-level vancomycin resistance

The reaction of L-alanine-p-nitroanilide with VanX was studied in an effort to develop a continuous assay for VanX activity for future kinetic and inhibition studies. VanX, containing Zn(II), Co(II), Fe(II), or Ni(II), catalyzes the hydrolysis of L-alanine-p-nitroanilide producing L-alanine and p-nitroaniline as products; the formation of the latter product (epsilon(404nm) = 10, 700 M(-1) cm(-1)) can be continuously monitored using UV-VIS spectrophotometry. Zn(II)-, Co(II)-, Fe(II)-, and Ni(II)-containing VanX exhibit saturation kinetics when L-alanine-p-nitroanilide is used as the substrate with K(m) and k(cat) values ranging from 300 to 700 microM and 0.028 to 0.080 s(-1), respectively. Inhibition studies using O-[(1S)-aminoethylhydroxyphosphinyl]-D-lactic acid as the inhibitor and L-alanine-p-nitroanilide as the substrate yielded a K(i) of 400 +/- 8 microM at pH 7.0. These studies reveal a continuous assay of VanX activity which could be used to further study the kinetic mechanism of VanX and to allow for the development of high-throughput screening for inhibitors of VanX.