Combining nilotinib and PD-L1 blockade reverses CD4+ T-cell dysfunction and prevents relapse in acute B-cell leukemia

Patients with acute lymphoblastic leukemia have experienced significantly improved outcomes due to the advent of chimeric antigen receptor (CAR) T cells and bispecific T-cell engagers, although a proportion of patients still relapse despite these advances. T-cell exhaustion has been recently suggested to be an important driver of relapse in these patients. Indeed, phenotypic exhaustion of CD4+ T cells is predictive of relapse and poor overall survival in B-cell acute lymphoblastic leukemia (B-ALL). Thus, therapies that counter T-cell exhaustion, such as immune checkpoint blockade, may improve leukemia immunosurveillance and prevent relapse. Here, we used a murine model of Ph+ B-ALL as well as human bone marrow biopsy samples to assess the fundamental nature of CD4+ T-cell exhaustion and the preclinical therapeutic potential for combining anti-PD-L1 based checkpoint blockade with tyrosine kinase inhibitors targeting the BCR-ABL oncoprotein. Single-cell RNA-sequence analysis revealed that B-ALL induces a unique subset of CD4+ T cells with both cytotoxic and helper functions. Combination treatment with the tyrosine kinase inhibitor nilotinib and anti-PD-L1 dramatically improves long-term survival of leukemic mice. Depletion of CD4+ T cells prior to therapy completely abrogates the survival benefit, implicating CD4+ T cells as key drivers of the protective anti-leukemia immune response. Indeed, treatment with anti-PD-L1 leads to clonal expansion of leukemia-specific CD4+ T cells with the aforementioned helper/cytotoxic phenotype as well as reduced expression of exhaustion markers. These findings support efforts to use PD1/PD-L1 checkpoint blockade in clinical trials and highlight the importance of CD4+ T-cell dysfunction in limiting the endogenous anti-leukemia response.

321 PD-L1 checkpoint blockade eradicates residual leukemia in a mouse model of acute lymphoblastic leukemia by countering exhaustion of cytotoxic and effector CD4+ T-cells

Background

Phenotypic exhaustion of CD4+ T-cells is a strong negative prognostic factor in acute lymphoblastic leukemia (ALL).1–3 Despite this, PD1/PD-L1 immune checkpoint therapy has shown little activity in this disease setting to date. Factors influencing the responsiveness of the T-cell compartment to checkpoint blockade are unknown.

Methods

An established murine model of BCR-ABL+ ALL was used. Leukemia was established by tail vein injection, and mice were treated with the BCR-ABL tyrosine kinase inhibitor nilotinib with or without PD-L1 mAb therapy. scRNAseq/TCRseq was performed using multiple treatment groups.

Results

Treatment of leukemia-bearing mice with a combination of the BCR-ABL tyrosine kinase inhibitor nilotinib and PD-L1 immune checkpoint blockade led to eradication of leukemia in 70% of treated mice (figure 1). Efficacy was dependent on the presence of CD4+ T-cells, while CD8+ T-cells appeared to play a lesser role. Direct cytotoxicity by CD4+ T-cells was confirmed in live cell-killing assays (figure 2). Mice that were treated with PD-L1 blockade and survived to day 100 were found to have no detectable residual leukemia. They were also protected from leukemia rechallenge, suggesting the elicitation of a memory response. scRNAseq analysis revealed that CD44hi CD4+ T-cells were highly heterogeneous, with regulatory, effector, and stem-like TCF7+ precursor subsets present (figures 3–4). A unique population of CD4+ T-cells was elicited by live leukemia challenge (clusters 6 and 7 in figure 3) but not by vaccination with heat-killed leukemia cells. This subset was characterized by relatively low levels of expression of TCF7, but high levels of expression of Granzyme B, TOX, the effector cytokines IFNγ and TNFα, the inhibitory receptors PD1, TIM3, and LAG3, and the chemokine CCL5 (figure 5). PD-L1 checkpoint blockade was associated with early narrowing of the clonality of this population (figure 6), decreased markers of exhaustion, and more robust synthesis of TNFα.

Abstract 321 Figure 1

Survival analysis. BCR-ABL+ ALL was established by tail vein injection on day 0. Nilotinib (75 mg/kg) was administered via oral gavage. mAbs targeting PD-L1 with or without depleting antibodies towards CD4 or CD8 were administered via intraperitoneal injection. p-value derived by log-rank analysis

Abstract 321 Figure 2

Analysis of the increase in the number of dead cells (y-axis) over time (x-axis) from a live killing assay (Incucyte) using splenic CD4+ or CD8+ T-cells from experimental arms as treated in figure 3. Control traces from separate wells with LM138 target cells only are included. Experiments were done using Cytotox NIR

Abstract 321 Figure 3

(Left) Experimental approach. 5 groups (n=4 mice/group) were treated in parallel with the indicated conditions. CD44hi CD4+ T-cells from the spleen and bone marrow of mice in each group were labelled with oligo-conjugated hashtag antibodies (Biolegend) and CITE-SEQ antibodies towards PD1, TIM3, LAG3, CD25, and TIGIT, prior to FACs-sorting. scRNAseq/TCRseq analysis (10x Genomics) was performed on 5,349 individual cells after multiplet removal. (Right) UMAP plots of all cells combined. Clusters were identified by differential expression of canonical gene products

Abstract 321 Figure 4

Feature plots demonstrating expression of canonical gene products projected onto the UMAP plot in figure 3. Antibody derived tags (ADTs; bottom row) indicate expression level of surface proteins profiled using CITESEQ antibodies

Abstract 321 Figure 5

Heatmap of select gene product expression levels in exhausted (cluster 6) CD4+ T-cells across treatment conditions

Abstract 321 Figure 6

Simpsons diversity index of the TCR repertoire across treatment arms. Lower values indicate relatively decreased clonality

Conclusions

PDL1 immune checkpoint blockade is effective at eradicating residual disease in preclinical models of BCR-ABL+ ALL. ALL elicits a unique CD4+ memory/effector subset characterized by the potential for both chemotactic and cytotoxic functions. Leukemia induces early exhaustion of this subset, which is countered by PDL1 blockade. Efforts to extend these observations to human specimens are underway and will be reported.

References

Hohtari H, Brück O, Blom S, et al. Immune cell constitution in bone marrow microenvironment predicts outcome in adult ALL. Leukemia 2019;33(7):1570–1582.

Blaeschke F, Willier S, Stenger D, et al. Leukemia-induced dysfunctional TIM-3. Leukemia 2020;34(10):2607–2620.

Liu L, Chang YJ, Xu LP, et al. T cell exhaustion characterized by compromised MHC class I and II restricted cytotoxic activity associates with acute B lymphoblastic leukemia relapse after allogeneic hematopoietic stem cell transplantation. Clin Immunol 2018;190:32–40.

Targeted Chemotherapy and Checkpoint Blockade Mediate Synergistic Protection Against BCR-ABL+ B Cell Leukemia

Immunotherapy using anti-PDL1/anti-CTLA4 checkpoint blockade has been successfully employed for cancers with many non-synonymous mutations. Whether checkpoint blockade-based approaches can be adapted to cancers with low mutational burden, such as BCR-ABL+ B cell leukemia, is still unclear. We have previously demonstrated that the endogenous anti-tumor T cell response, although important for initial control of leukemia, is unable to control leukemia by itself. We show here that leukemia induces an exhaustion phenotype in activated T cells, as well as an associated loss of effector function, that could contribute to the inability to clear leukemia. However, checkpoint blockade therapy using aPDL1 and aCTLA4 by themselves had no impact on survival in leukemic mice. Combining aPDL1 blockade with targeted chemotherapy using the BCR-ABL inhibitor nilotinib had a significant synergistic therapeutic effect. The effectiveness of the aPDL1-nilotinib dual therapy was primarily dependent on CD4 T cells, indicating a key role for endogenous anti-tumor CD4 T cells in leukemia clearance. Indeed, a significant proportion of long-term surviving nilotinib + aPDL1-treated mice were protected against a secondary leukemia re-challenge; indicative of an effective memory T cell responses. Thus, combination therapeutic approaches involving checkpoint blockade can elicit potent anti-tumor CD4 T cell responses that induce long-term protection against leukemia. Future studies will explore the mechanisms by which CD4 T cells orchestrate protective anti-leukemia responses.

Thymic regulatory T cells arise via two distinct developmental programs

The developmental programs that generate a broad repertoire of regulatory T cells (T_reg cells) able to respond to both self antigens and non-self antigens remain unclear. Here we found that mature T_reg cells were generated through two distinct developmental programs involving CD25⁺ T_reg cell progenitors (CD25⁺ T_regP cells) and Foxp3^lo T_reg cell progenitors (Foxp3^lo T_regP cells). CD25⁺ T_regP cells showed higher rates of apoptosis and interacted with thymic self antigens with higher affinity than did Foxp3^lo T_regP cells, and had a T cell antigen receptor repertoire and transcriptome distinct from that of Foxp3^lo T_regP cells. The development of both CD25⁺ T_regP cells and Foxp3^lo T_regP cells was controlled by distinct signaling pathways and enhancers. Transcriptomics and histocytometric data suggested that CD25⁺ T_regP cells and Foxp3^lo T_regP cells arose by coopting negative-selection programs and positive-selection programs, respectively. T_reg cells derived from CD25⁺ T_regP cells, but not those derived from Foxp3^lo T_regP cells, prevented experimental autoimmune encephalitis. Our findings indicate that T_reg cells arise through two distinct developmental programs that are both required for a comprehensive T_reg cell repertoire capable of establishing immunotolerance.

Dasatinib Changes Immune Cell Profiles Concomitant with Reduced Tumor Growth in Several Murine Solid Tumor Models

Dasatinib, a broad-range tyrosine kinase inhibitor, induces rapid mobilization of lymphocytes and clonal expansion of cytotoxic cells in leukemia patients. Here, we investigated whether dasatinib could induce beneficial immunomodulatory effects in solid tumor models. The effects on tumor growth and on the immune system were studied in four different syngeneic mouse models (B16.OVA melanoma, 1956 sarcoma, MC38 colon, and 4T1 breast carcinoma). Both peripheral blood (PB) and tumor samples were immunophenotyped during treatment. Although in vitro dasatinib displayed no direct cytotoxicity to B16 melanoma cells, a significant decrease in tumor growth was observed in dasatinib-treated mice compared with vehicle-treated group. Further, dasatinib-treated melanoma-bearing mice had an increased proportion of CD8⁺ T cells in PB, together with a higher amount of tumor-infiltrating CD8⁺ T cells. Dasatinib-mediated antitumor efficacy was abolished when CD4⁺ and CD8⁺ T cells were depleted with antibodies. Results were confirmed in sarcoma, colon, and breast cancer models, and in all cases mice treated daily with dasatinib had a significant decrease in tumor growth. Detailed immunophenotyping of tumor tissues with CyTOF indicated that dasatinib had reduced the number of intratumoral regulatory T cells in all tumor types. To conclude, dasatinib is able to slow down the tumor growth of various solid tumor models, which is associated with the favorable blood/tumor T-cell immunomodulation. The assessment of synergistic combinatorial therapies with other immunomodulatory drugs or targeted small-molecule oncokinase inhibitors is warranted in future clinical trials. Cancer Immunol Res; 5(2); 157-69. ©2017 AACR.

Abstract 2587: Dasatinib-induced reduction of tumor growth is accompanied by the changes in the immune profile in melanoma B16.OVA mouse model

Dasatinib, a tyrosine kinase inhibitor used in the treatment of chronic myeloid leukemia and acute lymphoblastic leukemia, has been shown to exert immunomodulatory effects in addition to direct oncokinase inhibition. Recently, we observed that dasatinib induces a rapid (within one hour after oral administration) and marked mobilization of lymphocytes (up to 8-fold increase in lymphocyte count), which closely follows the drug plasma concentration. In addition, in a subgroup of patients a clonal expansion of large granular lymphocytes occurs, which is correlated with good therapy response.

As dasatinib-induced immunomodulatory effects are not leukemia specific, we aimed to exploit this activity to slow down or inhibit the growth of a syngeneic murine melanoma model and to characterize in detail the anti-tumor immune responses.

Ovalbumin expressing murine melanoma cell line B16.OVA was grown under the skin of immunocompetent mice. The mice (n=6/group) were treated daily i.g. either with 30 mg/kg dasatinib or vehicle only. Blood was collected before tumor transplantation, before treatment, and on treatment days 4, 7 and 10. Tumor volumes were measured manually and specific growth rate was calculated based on the first and the last day of the treatment. In addition to white blood cell differential counts, immunophenotyping of blood and tumor homogenate was done by flow cytometry using antibodies against CD45.1, CD3, CD4, CD8b and NK1.1, and SIINFEKL-pentamer to detect B16.OVA-specific cells. To assess the functional properties of lymphocytes, we used antibodies against immune checkpoint inhibitors CTLA-4 and PD-1, and a degranulation marker CD107.

On the 10th day of treatment, the tumor volumes were smaller in dasatinib group compared to control group, and there was a significant decrease in the tumor growth rate (0.06 vs. 0.18, p=0.01). Furthermore, dasatinib treated mice had increased proportion of CD8+ cells in the circulation (21% vs. 14%, p=0.04) and the CD4/CD8 ratio was significantly decreased (1.39 vs. 1.52, p= 0.04). During the tumor growth the mean CTLA-4 expression on CD8+ cells increased from 1.2% to 9% in the control group, whereas, in dasatinib group the increase was more modest (1.2% to 5.7%). Interestingly, 80% of tumor infiltrating CD8+ cells expressed PD1 antigen compared to <5% of PD1 positive CD8+ cells in the peripheral blood suggesting lymphocyte anergy or exhaustion induced by tumor cells.

To conclude, dasatinib treatment slowed down the tumor growth in B16.OVA mouse model, which could be associated with the immunomodulatory effects of dasatinib. However, combinatorial treatment regimens may be needed as dasatinib is not able to fully break the immune cell anergy induced by tumor cells.

Citation Format: Can Hekim, Mette Ilander, Markus Vähä-Koskela, Paula Savola, Siri Tähtinen, Akseli Hemminki, Kimmo Porkka, Satu Mustjoki. Dasatinib-induced reduction of tumor growth is accompanied by the changes in the immune profile in melanoma B16.OVA mouse model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2587. doi:10.1158/1538-7445.AM2014-2587

Proteolytic activity of prostate-specific antigen (PSA) towards protein substrates and effect of peptides stimulating PSA activity

Prostate-specific antigen (PSA or kallikrein-related peptidase-3, KLK3) exerts chymotrypsin-like proteolytic activity. The main biological function of PSA is the liquefaction of the clot formed after ejaculation by cleavage of semenogelins I and II in seminal fluid. PSA also cleaves several other substrates, which may explain its putative functions in prostate cancer and its antiangiogenic activity. We compared the proteolytic efficiency of PSA towards several protein and peptide substrates and studied the effect of peptides stimulating the activity of PSA with these substrates. An endothelial cell tube formation model was used to analyze the effect of PSA-degraded protein fragments on angiogenesis. We showed that PSA degrades semenogelins I and II much more efficiently than other previously identified protein substrates, e.g., fibronectin, galectin-3 and IGFBP-3. We identified nidogen-1 as a new substrate for PSA. Peptides B2 and C4 that stimulate the activity of PSA towards small peptide substrates also enhanced the proteolytic activity of PSA towards protein substrates. Nidogen-1, galectin-3 or their fragments produced by PSA did not have any effect on endothelial cell tube formation. Although PSA cleaves several other protein substrates, in addition to semenogelins, the physiological importance of this activity remains speculative. The PSA levels in prostate are very high, but several other highly active proteases, such as hK2 and trypsin, are also expressed in the prostate and may cleave protein substrates that are weakly cleaved by PSA.

Evaluation of peptides as protease inhibitors and stimulators

Changes in proteolytic activity are associated with several diseases, including cancer. Proteases are potential drug targets and targeting of proteases is used for treatment of various conditions/diseases, like high blood pressure and HIV. We present here detailed protocols for basic evaluation of the effects of peptides on the activity of proteases, using kallikrein-related peptidases KLK2 and KLK3 (also known as hK2 and PSA), and trypsin as examples. KLK2 and KLK3 are major prostatic proteases, and they are potential targets for prostate cancer treatment. KLK2 has trypsin-like activity and KLK3 chymotrypsin-like activity. By phage display technology, we have developed peptides that specifically stimulate KLK3-activity and other peptides that inhibit KLK2 or trypsin. The effect of the peptides on the proteolytic activity of proteases can be studied using substrates, the cleavage of which generates detectable signal, allowing rapid evaluation of protease activity. The cleavage of protein substrates can be detected by SDS-PAGE, followed by staining of the proteins. We also describe graphical analysis of the IC50-value, the effect of a peptide on Michaelis-Menten constant (K(m)) and the maximal reaction rate (V(max)).

Pseudopeptides with a centrally positioned alkene-based disulphide bridge mimetic stimulate kallikrein-related peptidase 3 activity

First successful pseudopeptides of the KLK3-activating bicyclic peptide “C-4” are reported.

Abstract 2828: Characterization of protein substrates of PSA: effect of PSA stimulating peptides

Increased proteolytic activity is associated with cancer, where proteases play a major role in tumor spread and formation of metastases. However, proteases may also inhibit tumor growth. The prostate produces several proteases, the most abundant one being prostate-specific antigen (PSA or kallikrein-related peptidase-3, KLK3). The role of PSA in the prostate, and in particular in prostate cancer, is not well known. However, several functions have been proposed, most of which are based on the protein substrates, which PSA cleaves in vitro. These include both tumor growth promoting and inhibiting activities, e.g., antiangiogenic activity of PSA. We have previously used phage display technology to develop peptides, the synthetic analogs of which stimulate the activity of PSA. These peptides are useful for studying the significance of PSA-activity and potentially for prostate cancer treatment. We analyzed the cleavage of different protein substrates of PSA and found that physiological substrates, semenogelin-1 and −2, are cleaved much more efficiently than other substrates, such as IGFBP-3, fibronectin and galectin-3. The peptides increased the proteolytic activity of PSA towards these protein substrates, but the extent of stimulation and the relative efficiency of peptides were different than with small peptide substrates. We conclude that the peptides can be used to stimulate the activity of PSA towards natural protein substrates. Thus, they may be potential lead molecules for drug development. As most of the studied protein substrates are cleaved with very low efficiency, their relevance as PSA substrates is questionable, especially as prostate produces several other highly active proteases, including several kallikreins and trypsin. As compared to other substrates, semenogelins are very efficiently cleaved by PSA, highlighting the substrate specificity of PSA.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2828. doi:1538-7445.AM2012-2828

Identification of IGFBP-3 fragments generated by KLK2 and prevention of fragmentation by KLK2-inhibiting peptides

Kallikrein-related peptidase 2 (KLK2) degrades insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) in vitro. IGFBP-3 forms complexes with IGFs, preventing them from binding to their receptors and stimulating cell proliferation and survival. IGF-independent actions have also been described for IGFBP-3. The degradation of IGFBP-3 by KLK2 or other proteases in the prostate may promote the growth of prostate cancer. We studied IGFBP-3 degradation by immunoblotting and two specific immunoassays, one recognizing only native non-fragmented IGFBP-3 and the other one recognizing both intact and proteolytically cleaved IGFBP-3. Peptides were used to inhibit the enzyme activity of KLK2 and cleavage sites in IGFBP-3 were identified by mass spectrometry. KLK2 proteolyzed IGFBP-3 into several small fragments, mostly after Arg residues, in keeping with the trypsin-like activity of KLK2. The fragmentation could be inhibited by KLK2-inhibiting peptides in a dose-dependent fashion. As degradation of IGFBP-3 could lead to a more aggressive cancer phenotype, inhibition of KLK2 activity might be useful for treatment of prostate cancer and other diseases associated with increased KLK2 activity.

Complex formation between human prostate-specific antigen and protease inhibitors in mouse plasma

BACKGROUND

When secreted from the prostate, most of prostate-specific antigen (PSA) is free and enzymatically active. Upon reaching circulation, active PSA is inactivated by complex formation with protease inhibitors. To justify the use of mouse models for evaluation of the function of PSA and for studies on therapeutic modalities based on modulation of PSA activity, it is important to know whether PSA complexation is similar in mouse and man.

METHODS

To characterize the circulating forms of PSA in mouse, we used subcutaneous LNCaP and 22RV1 human prostate cancer cell xenograft tumor models. We also added PSA directly to mouse serum. Free and total PSA were measured by immunoassay, and PSA complexes were extracted by immunopurification followed by SDS-PAGE, in-gel trypsin digestion and identification of signature peptides by mass spectrometry.

RESULTS

In mice bearing xenograft tumors, 68% of the immunoreactive PSA occurred in complex, and when added to mouse serum, over 70% of PSA forms complexes that comprises alpha(2)-macroglobulin and members of the alpha(1)-antitrypsin (AAT) family.

CONCLUSION

In mouse plasma, PSA forms complexes similar to those in man, but the major immunoreactive complex contains AAT rather than alpha(1)-antichymotrypsin, which is the main complex forming serpin in man. The complex formation of PSA produced by xenograft tumor models in mice is similar to that of human prostate tumors with respect to the complexation of PSA.

Development of peptides specifically modulating the activity of KLK2 and KLK3

The prostate produces several proteases, the most abundant ones being kallikrein-related peptidase 3 (KLK3, PSA) and KLK2 (hK2), which are potential targets for tumor imaging and treatment. KLK3 expression is lower in malignant than in normal prostatic epithelium and it is further reduced in poorly differentiated tumors, in which the expression of KLK2 is increased. KLK3 has been shown to inhibit angiogenesis, whereas KLK2 may mediate tumor growth and invasion by participating in proteolytic cascades. Thus, it may be possible to control prostate cancer growth by modulating the proteolytic activity of KLK3 and KLK2. We have developed peptides that very specifically stimulate the activity of KLK3 or inhibit that of KLK2. Using these peptides we have established peptide-based methods for the determination of enzymatically active KLK3. The first-generation peptides are unstable in vivo and are rapidly cleared from the circulation. Currently we are modifying the peptides to make them suitable for in vivo applications. We have been able to considerably improve the stability of KLK2-binding peptides by cyclization. In this review we summarize the possible roles of KLK3 and KLK2 in prostate cancer and then concentrate on the development of peptides that modulate the activity of these proteases.

Activity and stability of human kallikrein-2-specific linear and cyclic peptide inhibitors

Human glandular kallikrein (KLK2) is a highly prostate-specific serine protease, which is mainly excreted into the seminal fluid, but part of which is also secreted into circulation from prostatic tumors. Since the expression level of KLK2 is elevated in aggressive tumors and it has been suggested to mediate the metastasis of prostate cancer, inhibition of the proteolytic activity of KLK2 is of potential therapeutic value. We have previously identified several KLK2-specific linear peptides by phage display technology. Two of its synthetic analogs, A R R P A P A P G (KLK2a) and G A A R F K V W W A A G (KLK2b), show specific inhibition of KLK2 but their sensitivity to proteolysis in vivo may restrict their potential use as therapeutic agents. In order to improve the stability of the linear peptides for in vivo use, we have prepared cyclic analogs and compared their biological activity and their structural stability. A series of cyclic variants with cysteine bridges were synthesized. Cyclization inactivated one peptide (KLK2a) and its derivatives, while the other peptide (KLK2b) and its derivatives remained active. Furthermore, backbone cyclization of KLK2b improved significantly the resistance against proteolysis by trypsin and human plasma. Nuclear magnetic resonance studies showed that cyclization of the KLK2b peptides does not make the structures more rigid. In conclusion, we have shown that backbone cyclization of KLK2 inhibitory peptides can be used to increase stability without losing biological activity. This should render the peptides more useful for in vivo applications, such as tumor imaging and prostate cancer targeting.

Novel peptide inhibitors of human kallikrein 2

Human kallikrein 2 (hK2) is a serine protease produced by the secretory epithelial cells in the prostate. Because hK2 activates several factors participating in proteolytic cascades that may mediate metastasis of prostate cancer, modulation of the activity of hK2 is a potential way of preventing tumor growth and metastasis. Furthermore, specific ligands for hK2 are potentially useful for targeting and imaging of prostate cancer and for assay development. We have used enzymatically active recombinant hK2 captured by a monoclonal antibody exposing the active site of the enzyme to screen phage display peptide libraries. Using libraries expressing 10 or 11 amino acids long linear peptides, we identified six different peptides binding to hK2. Three of these were shown to be specific and efficient inhibitors of the enzymatic activity of hK2 toward a peptide substrate. Furthermore, the peptides inhibited the activation of the proform of prostate-specific antigen by hK2. Amino acid substitution analyses revealed that motifs of six amino acids were required for the inhibitory activity. These peptides are potentially useful for treatment and targeting of prostate cancer.

Hyperprolactinaemia does not always mean ‘hyperprolactinaemia’!

The presence of macroprolactinaemia was investigated in the symptom-free hyperprolactinaemia cases to reveal its incidence. The serum prolactin (PRL) fractions in 21 female patients with hyperprolactinaemia without any clinical symptoms were analyzed with PEG (polyethylene glycol precipitation) procedure. In 14 of these 21 cases, hyperprolactinaemia was detected with a high fraction of macroprolactin. In cases with asymptomatic hyperprolactinaemia, it is more appropriate to employ the PEG precipitation test to detect the disorder. High levels of serum prolactin, do not essentially indicate the presence of a prolactinoma but may only indicate macroprolactinaemia.