Development, Characterization, and Evaluation of SLN-Loaded Thermoresponsive Hydrogel System of Topotecan as Biological Macromolecule for Colorectal Delivery.

BACKGROUND: Chemotherapeutic drugs cause severe toxicities if administered unprotected, without proper targeting, and controlled release. In this study, we developed topotecan- (TPT-) loaded solid lipid nanoparticles (SLNs) for their chemotherapeutic effect against colorectal cancer. The TPT-SLNs were further incorporated into a thermoresponsive hydrogel system (TRHS) (TPT-SLNs-TRHS) to ensure control release and reduce toxicity of the drug. Microemulsion technique and cold method were, respectively, used to develop TPT-SLNs and TPT-SLNs-TRHS. Particle size, polydispersive index (PDI), and incorporation efficiency (IE) of the TPT-SLNs were determined. Similarly, gelation time, gel strength, and bioadhesive force studies of the TPT-SLNs-TRHS were performed. Additionally, in vitro release and pharmacokinetic and antitumour evaluations of the formulation were done. RESULTS: TPT-SLNs have uniformly distributed particles with mean size in nanorange (174 nm) and IE of ~90%. TPT-SLNs-TRHS demonstrated suitable gelation properties upon administration into the rat's rectum. Moreover, drug release was exhibited in a control manner over an extended period of time for the incorporated TPT. Pharmacokinetic studies showed enhanced bioavailability of the TPT with improved plasma concentration and AUC. Further, it showed significantly enhanced antitumour effect in tumour-bearing mice as compared to the test formulations. CONCLUSION: It can be concluded that SLNs incorporated in TRHS could be a potential source of the antitumour drug delivery with better control of the drug release and no toxicity.

[Significance of v-raf murine sarcoma viral oncogene homologue B1 in rheumatoid arthritis].

OBJECTIVE: To detect serum v-raf murine sarcoma viral oncogene homologue B1 (BRAF) protein levels and to investigate their clinical significance in rheumatoid arthritis (RA) patients. METHODS: Serum samples were obtained from 78 RA patients, 32 osteoarthritis (OA) patients, 16 systemic lupus erythematosus (SLE) patients, 16 gout patients, 16 ankylosing spondylitis (AS) patients, 16 Sjogren syndrome (SS) patients and 30 healthy controls. BRAF protein in the sera was examined by enzyme-linked immunosorbent assay (ELISA). The associations between BRAF levels and the clinical features including age, sex, disease duration, swelling joints, tenderness joints, duration of moning stiffness, joint deformity, visual assessment scale (VAS) and extra articular manifestations and laboratory parameters including erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor (RF), disease activity score in 28 joints (DAS28), anti-cyclic citrullinated peptide (CCP) antibody, antikeratin antibody, antnuclear antibody (ANA), immunoglobulin and cytokines, such as TNF-α, IL-1ß, IL-6 and IL-17A in RA patients were evaluated. Data analyses were performed by using SPSS 19.0 program. RESULTS: The serum BRAF protein levels in the RA patients were significantly higher than those of other rheumatic diseases groups including OA, SLE, AS, SS, gout patients and healthy controls, the P value was 0.002, <0.001, <0.001, <0.001, 0.001 and <0.001 respectively. The level of serum BRAF protein in the RA patients showed a positive correlation with the rheumatoid factor (P=0.009) and IgA levels (P=0.006), but no correlation with clinical features, such as age and duration or other laboratory parameters, including CRP, ESR, anti-CCP antibody, IgM, IgG, TNF-α, IL-1ß, IL-6 and IL-17A. The RA patients were further divided into normal levels of BRAF protein group and elevated levels of BRAF protein group. Compared with the clinical features and laboratory indexes of normal and elevated levels of BRAF protein groups in the RA patients, there was no significant difference between the two groups in age, duration, DAS28, CRP, ESR, RF, anti-CCP, IgA, IgG, IgM, TNF-α or IL-6. CONCLUSION: The elevated level of BRAF protein in the RA patients showed that BRAF might play a role in the pathogenesis of RA. Further researches on BRAF gene expression may help to clarify the role of BRAF in RA.

Radiation-enhancing effect of sodium glycididazole in patients suffering from non-small cell lung cancer with multiple brain metastases: A randomized, placebo-controlled study.

PURPOSE: Median survival of patients with brain metastases from non-small cell lung cancer is poor. This study was to investigate the radiation-enhancing effect of sodium glycididazole combined with whole-brain radiotherapy of multiple brain metastases from non-small cell lung cancer. PATIENTS AND METHODS: Sixty-four patients with multiple brain metastases from non-small cell lung cancer were included: the study group (n=32) received whole-brain radiotherapy combined with sodium glycididazole at a dose of 700mg/m(2) intravenous infusion 30minutes before radiotherapy, three times a week; the control group (n=32) only received whole-brain radiotherapy. The primary end point was central nervous system (CNS) progression-free survival and overall survival. The treatment-related toxicity was also recorded. RESULTS: The CNS disease control rate was better (90.6% vs 65.6%, P=0.016) in the study group than in the control group at 3 month of follow-up. The median CNS progression-free survival time was longer in the study group than in the control group (7.0 months vs 4.0 months, P=0.038). There was no significant difference of the median overall survival time between the study group and the control group (11.0 months vs 9.0 months, P=0.418). On the other hand, the treatment-related toxicity showed no statistically significant difference between these two groups (P>0.05). CONCLUSIONS: The study indicated that sodium glycididazole was an effective, promising radiation-enhancing agent that improved CNS disease control rate, extended the median CNS progression-free survival time and was well tolerated in patients suffering from non-small cell lung cancer with multiple brain metastases.

Copy number variations of HLA-I and activation of NKp30 pathway determine the sensitivity of gastric cancer cells to the cytotoxicity of natural killer cells.

Nude mice are important in vivo model for characterization of cell malignancy behavior; however, many cancer cells fail to form tumors in it. Understanding this defective mechanism may provide novel insights into tumorigenesis and how tumor cells escape innate immunity. Whole-genome sequencing was conducted on two gastric cancer (GC) cells, BGC823 and AGS, which do and do not form tumors in nude mice, to identify their genomic differences relevant to natural killer (NK) cells. We found that the tumorigenic capacity of human GC cell lines was dependent on the recruitment and activation of NK cells in xenograft tumors. We used whole-genome sequence (WGS) on GC cell lines to identify potential genes controlling susceptibility to NK-mediated killing. The tumorigenic cell line BGC823 expressed high levels of HLA-I because of copy gain and was resistant to NK cell killing. In contrast, another cell line AGS expressing low levels of HLA-I with activated NKp30/MAPK/IL-12 (interleukin-12) or IL-2 (interleukin-2) pathway was susceptible to NK lysis. Treatment of tumor bearing mice with systemic administration of IL-12 in combination with intratumor injection of anti-HLA-I antibody significantly increased NK cell recruitment into xenograft tumors, which became sensitive to NK killing, resulting in reduced tumor progression. In human GC specimens, decreased HLA-I expression and increased NK cells surrounding tumor cells were correlated with decreased metastasis potential and better prognosis of patients. Our results provide a mechanistic basis for GC cells to escape NK lysis and a promising prospect of NK immunotherapy for GC cells.

Interleukin-21 Induces Proliferation and Proinflammatory Cytokine Profile of Fibroblast-like Synoviocytes of Patients with Rheumatoid Arthritis.

Fibroblast-like synoviocytes (FLS) play a pivotal role in the pathogenesis of rheumatoid arthritis (RA) through aggressive proliferation and invasion, and certain proinflammatory cytokines may affect synoviocyte proliferation. To evaluate whether interleukin-21 (IL-21) could promote proliferation and proinflammatory cytokine production by RA-FLS, immunohistochemistry and immunoblotting were performed to observe the expression of IL-21 receptor (IL-21R) in synovial tissues and FLS from RA and osteoarthritis (OA) patients. The MTS assay was used to analyse RA-FLS proliferation. The concentrations of IL-6 and tumour necrosis factor-α (TNF-α) in culture supernatants were determined by enzyme-linked immunosorbent assay (ELISA). The signalling pathways triggered by IL-21 were characterized by immunoblotting. IL-21R was upregulated in the synovial tissues and FLS of RA patients as compared with OA patients. IL-21 stimulated RA-FLS proliferation and promoted the production of TNF-α and IL-6 and blockade of IL-21/IL-21R pathway with IL-21R.Fc attenuated IL-21-induced proliferation and secretion of TNF-α and IL-6. Moreover, IL-21 induced activation of the ERK1/2, PI3K/AKT and STAT3 pathways, and blockade of these pathways attenuated IL-21-induced proliferation and secretion of TNF-α and IL-6. These results suggest that IL-21 could promote RA-FLS proliferation and production of proinflammatory cytokines. Therefore, therapeutic strategies targeting IL-21 might be effective for the treatment of RA.

Relevance of E-cadherin expression to EGFR-TKI molecular targeted therapy sensitivity/resistance and its clinical significance.

We examined the effect of E-cadherin expression on epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) molecular targeted therapy sensitivity/resistance. We treated MCF-7, MDA-MB-231, T24, SiHa, H460, SK-HEP-1, MHCC97-H, and THP-1 cells with the EGFR-TKIs PD153035 and gefitinib, and then tested the drug-resistance and sensitivity using the MTT method, calculated IC50 values for each cell line, and compared the results to E-cadherin content. The MTT assay was used to determine the survival rates of MCF-7, MDA-MB-231, T24, SiHa, H460, SK-HEP-1, MHCC97-H, and THP-1 cells upon the action of EGFR-TKI (PD153035, gefitinib). For PD153035, the IC50 in MCF-7, MDA-MB-231, T24, and SiHa cells differed from that of H460, SK-HEP-1, MHCC97-H, and THP-1 (P < 0.05). Following gefitinib treatment, the IC50 values of MCF-7, MDA-MB-231, T24, and SiHa cells differed from those of H460, SK-HEP-1, MHCC97-H, and THP-1 cells (P < 0.01). The survival rate of MCF-7, MDA-MB-231, T24, and SiHa cells clearly decreased with increasing drug concentration, indicating the cells were sensitive to the drugs and that E-cadherin expression was positive; however, H460, SK-HEP-1, MHCC97-H, and THP-1 cells showed no significant decreased with increasing drug concentration, indicating that they were resistant to the drugs and that E-cadherin expression was negative. The survival rate of epithelial tumor cells through the action of EGFR-TKI is related to E-cadherin expression. E-cadherin may play a significant role in the sensitivity regulation of EGFR molecular targeting treatment. E-cadherin may provide important clues for selecting proper EGFR-TKI molecular targeting treatment.

Serum C-reactive protein predicts poor prognosis in patients with locoregionally advanced nasopharyngeal carcinoma treated with chemoradiotherapy.

BACKGROUND: We aimed to evaluate the association of serum C-reactive protein (crp) with prognosis in patients with locoregionally advanced nasopharyngeal carcinoma treated with chemoradiotherapy. METHODS: We retrospectively reviewed 79 patients with locoregionally advanced nasopharyngeal carcinoma (cT3-4N0-3M0) treated with chemoradiotherapy. Chemoradiotherapy consisted of external-beam radiotherapy to the nasopharynx (70-80 Gy), the lymph node-positive area (60-70 Gy), and the lymph node-negative area (50-60 Gy) combined with 3 cycles of various platinum-based regimens delivered at 3-week intervals. Elevated crp was defined as more than 8 mg/L. The survival rate was calculated using the Kaplan-Meier method, and univariate and multivariate analyses (Cox proportional hazards model) were used to identify factors significantly associated with prognosis. RESULTS: During the median follow-up of 3.9 years (range: 1-5.5 years), 23 patients died from nasopharyngeal cancer. The 5-year cancer-specific survival (css) rate was 62.90%. Before chemoradiotherapy, 18 patients had high serum crp; the css rate in that subgroup was significantly worse than the rate in the remaining patients (p = 0.0002). Multivariate analysis showed that crp was an independent prognostic indicator of css, with a hazard ratio of 3.04 (95% confidence interval: 1.22 to 7.55; p = 0.017). Among the 18 patients with elevated serum crp, 9 achieved normal serum crp after chemoradiotherapy, of whom 5 remained living with no evidence of recurrence or metastasis during follow-up. By contrast, the remaining 9 patients in whom serum crp did not normalize after chemoradiotherapy died within 4.2 years. CONCLUSIONS: Elevated serum crp before treatment predicts poor prognosis in patients with locoregionally advanced nasopharyngeal carcinoma treated with chemoradiotherapy.

Construction of recombinant adenoviruses carrying the optimal shRNA template against goat PTHrP and successful suppression of PTHrP expression in mammary epithelial cells.

Parathyroid hormone-related protein (PTHrP) is a protein member of the parathyroid hormone family that regulates the dynamic balance between blood and bone calcium during lactation. However, the mechanism of its regulation is not very clear. In order to establish a framework for further functional studies of the PTHrP gene in goat mammary gland epithelial cells during the lactation period, PTHrP cDNA was isolated from Xinong Saanen dairy goats. Its coding sequence is 534 bp in size. We also designed a short hairpin RNA (shRNA) to efficiently inhibit PTHrP expression and constructed recombinant adenoviruses carrying a template encoding this shRNA (AD-PTHrP-322) using the Block-iT shRNA interference system. Finally, the inhibition of PTHrP expression by the recombinant adenoviruses was confirmed by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and Western blotting. qRT-PCR results showed that the expression of PTHrP mRNA in mammary epithelial cells was downregulated by 29.2, 68.1, and 82.6% 24, 48, and 72 h after the cells were infected with AD-PTHrP-322, respectively. Western blotting also showed that the expression of PTHrP was reduced in a time-dependent manner. These results suggest that AD-PTHrP-322 significantly inhibits the expression of PTHrP.

ANXA2 remodels the microstructures of caco2 cells.

ANXA2 was reported as a multiple tumors relevant gene expressed excessively in many tumor tissue types, especially in the cancers from digestion system, and its aberrant expression enhances the malignant properties of cancer cells. We suppose that the microstructure heterogeneity is important to maintain the malignancy of cancer cells, and excessive ANXA2 expression enhance the malignancy by remodeling the microstructures of cancer cells. To validate the proposal, the ANXA2-/-caco2 cell line was generated and the changes of the microstructures in the ANXA2 deleted and wild type caco2 cells were observed under fluorescence microscope, laser scanning confocal microscope and electron microscope. We found that ANXA2 deletion induced the pseudopodia shorted and spared, non-stained areas increased, mitochondria decreased, and the expression and polymerization of F-actin and ß-tubulin changed. By the findings above, it is firstly reported in this paper that the ANXA2 excessive expression induces the significant changes of the microstructures in cancer cells. Combining our previous data together, our results indicate that ANXA2 excessive expression enhances the malignancy of cancers partially by remodeling the cell microstructures.

Serum soluble CD44v6 levels in patients with oral and maxillofacial malignancy.

OBJECTIVE: To determine the levels of serum sCD44v6 in patients with oral cancer and evaluate the value of serum sCD44v6 in adjuvant diagnosis, staging and monitoring treatment response in these patients. MATERIALS AND METHODS: A total of 112 hospitalized patients with oral and maxillofacial malignancy and 28 healthy individuals were examined for serum sCD44v6 levels. Venous blood was collected from these patients and the healthy individuals. One week after treatment, venous blood was collected once again in 60 patients with oral and maxillofacial squamous cell carcinoma (OSCC). RESULTS: The sCD44v6 concentration was not significantly different between patients with oral and maxillofacial malignancy and control group (P > 0.05). The levels of serum sCD44v6 in patients with OSCC and salivary carcinoma showed no difference with those in control group (P > 0.05). The sCD44v6 level in patients with stage III and IV disease was higher than that of patients with stage I and II and that of the control group, but the difference was not significant (P > 0.05). Serum sCD44v6 levels in patients with OSCC after treatment became lower than that prevailed during pretreatment (P < 0.05). CONCLUSION: The possible roles of CD44v6 in the diagnosis of oral and maxillofacial malignancy deserve further elucidation and evaluation. Serum sCD44v6 may be a valuable marker in monitoring treatment response in patients with OSCC.

Regulation of urokinase production by androgens in human prostate cancer cells: effect on tumor growth and metastases in vivo.

During the complex multistep process of tumor progression, prostate cancer is initiated as an androgen-sensitive, nonmetastatic cancer, followed by a gradual transition into a highly metastatic and androgen-insensitive variety that lacks the expression of functional androgen receptors (AR). Urokinase (uPA), a member of the serine protease family, has been implicated in the progression of various human malignancies, including prostate cancer. Although uPA production is regulated by various growth factors and cytokines, the role of sex steroids (androgens) in regulating uPA gene expression in prostate cancer is poorly understood. In the current study, we have examined the role of androgens in regulating uPA production and the invasive capacity of the androgen insensitive PC-3 cells transfected with the full-length human AR complementary DNA (PC-3T). Restoration of androgen responsiveness in PC-3T cells caused a marked decrease in cell doubling time. Treatment of PC-3T cells with dihydroxytestosterone (DHT) caused a dose-dependent decrease in uPA messenger RNA and protein production, resulting in their decreased ability to invade through the Matrigel. Nuclear runoff assays revealed that these effects were attributable to the ability of DHT to inhibit uPA gene transcription. AR antagonist flutamide (Flu) reversed the effect of DHT on proliferation and invasion of PC-3T cells. Both control (PC-3) and experimental (PC-3T) cells were injected into the right flank of male BALB/c nu/nu mice. Control animals developed palpable tumors and microscopic tumor metastases at lymph nodes, lungs, and liver at 6-week posttumor cell inoculation. In contrast to this, because of androgen sensitivity of PC-3T cells, palpable tumors were observed only at week 12, with occasional tumor metastases in lungs. Furthermore, inoculation of PC-3T cells into surgically castrated host animals resulted in the development of tumors at a much earlier time (week 10) and a high incidence of metastases, compared with regular animals receiving PC-3T cells. Collectively, these results demonstrate the ability of androgen to regulate uPA production, which may directly effect prostate cancer growth, invasion, and metastasis in vitro and in vivo.

Transcriptional regulation of urokinase (uPA) gene expression in breast cancer cells: role of DNA methylation.

Carcinoma of the breast is a leading hormone-dependent malignancy, resulting in a high rate of morbidity and mortality. During the complex multi-step process of tumor promotion, this common cancer is initiated as hormone-responsive (HR), non-metastatic cancer, followed by a gradual transition into a highly metastatic hormone-insensitive (HI) variety which lacks the functional estrogen receptor. This transition of cancer cells causes them to become refractory to hormonal treatment. Urokinase (uPA), a member of the serine protease family has been implicated in the progression of several malignancies including breast cancer. In the current study, we have examined the correlation between hormone sensitivity and uPA expression in HR normal mammary epithelial cells (HMEC) and in MCF-7 and T-47D breast cancer cell lines. Comparison was made with HI breast cancer cells MDA-231. uPA mRNA expression was seen only in the highly invasive, HI breast cancer cells MDA-231. Lack of uPA expression in HR normal (HMEC) and in minimally invasive, HR cells (MCF-7 and T-47D) was due to transcriptional suppression of uPA gene expression as determined by nuclear run-off assays. Since alteration of the DNA methylation status of CpG island in the 5' sequence of oncogenes and tumor suppressor genes has been demonstrated to change their expression, we examined DNA methylation as a potential molecular mechanism for regulating uPA gene transcription in these cancer cells. Southern blot analysis using methylation sensitive enzymes revealed that CpG island of uPA gene are methylated in HR, HMEC, MCF-7 and T-47D cells, whereas they are hypomethylated in HI and MDA-231 cells. Treatment of HR MCF-7 cells with cytosine DNA methyltransferase inhibitor 5' azacytidine caused a dose-dependent induction of uPA mRNA due to demethylation of the CpG island of the uPA gene which led to increased invasive ability of these HR cancer cells. Our results demonstrate that DNA methylation can regulate the transcription of the uPA gene to alter the invasive behaviour of these HR breast cancer cells.

[Apoptosis of human melanoma cell line WM-983A by p16 gene transduction].

OBJECTIVE: To further understand the mechanism of action of the tumor-suppressor gene p16. METHODS: An adenoviral expression vector with full length cDNA of p16 gene insert was constructed (Ad-p16) and transfected into WM-983A cells, the p16 gene of which was point mutated at codon 126. The effect of exogenous p16 gene on the growth of WM-983A cells was examined in vitro and in vivo. RESULTS: Expression of p16 gene in WM-983A cells was confirmed by Western blot. The in vitro growth of the Ad-p16 transfected WM-983A cells was significantly inhibited (inhibition rate: 78%) as compared to mock (Ad-LacZ) transfected WM-983A cells. Colony-forming activity in vitro of the Ad-p16 transfected WM-983A cells was completely inhibited. Morphologically, the Ad-p16 transfected cells appeared apoptotic which was confirmed by the appearance of pre-G1 on flow cytometry and DNA fragmentation. The growth of WM-983A xenografts in nude mice was retarded by intra-tumoral injection of Ad-p16. CONCLUSION: p16 gene participates in the induction of cell apoptosis. It is promising to use it for gene therapy of cancer, especially when combined with other apopptosis-inducing agents.

Adenovirus-mediated transfer of RA538 gene and its antitumor effect.

The RA538 cDNA was transferred into human ovarian cancer cell line SK-OV-3 and human melanoma cell line WM-983A by its recombinant adenoviral vector constructed through homologous recombination. It was demonstrated that the recombinant adenovirus could transfer RA538 gene with high efficiency, and could obviously inhibit tumor growth, with the inhibiting rates of 85% and 73% respectively, at the same time greatly repress the colony forming ability of the cells. The therapeutic experiments on transplanted subcutaneous tumor model in nude mice demonstrated that RA538 could significantly inhibit tumor growth. Flow cytometry and DNA fragmentation analysis indicated that RA538 could induce the cell cycle G1 arrest/apoptosis of the tumor cells. The expression of c-myc gene was found pronouncedly reduced by Western blot analysis. These results suggest that the RA538 recombinant adenovirus could be a promising drug in cancer gene therapy.

Design of a transferrin-proteinase inhibitor conjugate to probe for active cysteine proteinases in endosomes.

A new technique has been developed to identify active proteinases in endosomes that does not require prior isolation of organelles and extraction of the active enzymes. [125I]Iodotyrosylalanyldiazomethane was reversibly conjugated to transferrin to selectively deliver it to endosomes. The protein was conjugated to the inhibitor via a disulphide bond using N-succinimidyl 3-(2-pyridyldithio)propionate. The inhibitor portion of the conjugate bound irreversibly to active cathepsins B and L, and subsequently the reacted enzymes were separated from the transferrin after SDS/PAGE under reducing conditions. Uptake of the protein-inhibitor conjugate and incorporation of inhibitor into cathepsins was blocked at 4 degreesC, demonstrating that the conjugate enters cells by receptor-mediated endocytosis. Furthermore, endocytosed transferrin-inhibitor conjugate could be recycled back to the extracellular medium and binding to the transferrin receptor could be blocked by native transferrin. Labelling of the enzymes was not blocked by incubating cells at 16 degreesC, consistent with the majority of the reagent being targeted to endosomes. The inhibited enzymes remained conjugated to transferrin, showing that the disulphide bond between the transferrin and inhibitor was not reduced in the endosome. Results from these studies show that endosomes contain both intermediate and late biosynthetic forms of active cathepsin B, which are indistinguishable from those found in mature lysosomes. These results indicate that the active enzymes in endosomes are not early biosynthetic forms in transit to lysosomes but most probably enter the endosome via retrograde traffic from the lysosome.

Quantification of cathepsins B and L in cells.

A method for quantifying active cysteine proteinases in mammalian cells has been developed using an active-site-directed inhibitor. Fluoren-9-ylmethoxycarbonyl(di-iodotyrosylalanyl)-diaz omethane (Fmoc-[I2]Tyr-Ala-CHN2) was prepared and shown to react irreversibly with cathepsins B and L, but not with cathepsin S. The non- and mono-iodo forms of the inhibitor reacted with all three enzymes. These results demonstrate that, unlike cathepsins B and L, cathepsin S has a restricted S2-binding site that cannot accommodate the bulky di-iodotyrosine. Fmoc-[I2]Tyr-Ala-CHN2 was able to penetrate cells and react with active enzymes within the cells. A radiolabelled form of the inhibitor was synthesized and the concentration of functional inhibitor was established by titration with papain. This inhibitor was used to quantify active cysteine proteinases in cultured cells. Active cathepsin B was found to be expressed by all of the cells studied, consistently with a housekeeping role for this enzyme. Active forms of cathepsin L were also expressed by all of the cells, but in different quantities. Two additional proteins were labelled in some of the cells, and these may represent other non-characterized proteinases. Higher levels of active cathepsins B and L, and an unidentified protein of Mr 39000, were found in breast tumour cells that are invasive, compared with those that are not invasive. From the data obtained, it can be calculated that the concentrations of both active cathepsins B and L in lysosomes can be as high as 1 mM, each constituting up to 20% of total protein in the organelle. This new technique provides a more direct procedure for determining the proteolytic potential of cellular lysosomes.