Clear cell renal cell carcinoma (ccRCC) is a highly immunogenic malignancy, yet the contribution of exhausted CD4+ T-cells to therapeutic response remains poorly understood. We investigated whether cabozantinib, a multi-kinase inhibitor used in metastatic ccRCC, modulates the dysfunctional state of tumor-conditioned CD4+ T-cells. In a human co-culture model with 786-O cells, exhausted CD4+ T-cells displayed marked induction of AXL, together with upregulation of key exhaustion-associated molecules. Cabozantinib suppressed AXL , CD274 , and other gene expression at the transcript level and reduced total PD-1 and PD-L1 protein abundance, while exerting no measurable effect on CD+ T-cell yield. Functionally, cabozantinib attenuated the inflammatory program of exhausted CD4+ T-cells by reducing IL-1β and IL-6 expression and secretion and by reshaping the extracellular cytokine milieu. This effect was accompanied by increased TGFβ2 and IDO1 expression, indicating immune reprogramming rather than simple restoration of effector function. In clinical specimens, AXL was detected in both tumor cells and TILs in ccRCC. Additionally, patients with metastatic RCC treated with cabozantinib exhibited reduced systemic inflammatory indices during therapy. Together, these findings identify AXL-associated exhausted CD4+ T-cells as a previously underappreciated target of cabozantinib and highlight CD4+ T-cell reprogramming as a potential component of its immunomodulatory activity in ccRCC.

Recent discoveries shed light on molecular mechanisms responsible for classical Hodgkin lymphoma (HL) development and progression, along with features of Hodgkin – Reed and Sternberg cells (HRS). Here, we summarize current knowledge on characteristic molecular alterations in HL, as well as existing targeted therapies and potential novel treatments for this disease. We discuss the importance of cluster of differentiation molecule 30 (CD30) and the programmed cell death-1 protein (PD-1) and ligands (PD-L1/2), and other molecules involved in immune modulation in HL. We highlight emerging evidence indicating that the altered function of SWI/SNF-type chromatin remodeling complexes, PRC2, and other epigenetic modifiers, contribute to variations in chromatin status, which are typical for HL. We postulate that despite of the existence of plentiful molecular data, the understanding of HL development remains incomplete. We therefore propose research directions involving analysis of reverse signaling in the PD-1/PD-L1 mechanism, chromatin remodeling, and epigenetics-related alterations, in order to identify HL features at the molecular level. Such attempts may lead to the identification of new molecular targets, and thus will likely substantially contribute to the future development of more effective targeted therapies.

About 40% of clear cell renal cell carcinoma (ccRCC) cases carry the pbrm1 mutation inactivating BAF180 subunit of the SWI/SNF chromatin remodeling complex (CRC). Here we show that the majority of transcriptomic changes appear at the stage I of ccRCC development. By contrast, the stage II ccRCC exhibits hyperactivation of DNA replication demonstrated by the overexpression of several genes, e.g., RRM1 and RRM2 genes encoding subunits of ribonucleotide reductase (RNR) complex. We found that the degree of RRM1 and RRM2 upregulation in ccRCC patients depends on pbrm1 mutation. We show that the BAF180 protein product of the PBRM1 gene directly binds to RRM1 and RRM2 loci. The BAF180 binding regions are targeted by regulatory proteins previously reported as SWI/SNF CRC interacting partners. BAF180 binding to RRMs loci correlates with enrichment of H3K27me3 in case of RRM1 and H3K14Ac on RRM2, indicating the existence of differential regulatory mechanism controlling expression of these genes. We found that the strong overexpression of RRM2 in ccRCC patient samples correlates with T cell infiltration. Surprisingly, the majority of tumor infiltrating lymphocytes (TILs) consisted of CD4+ T cells. Furthermore, we show that exhausted CD4+ T cells induced the expression of the RRM2 gene in the primary ccRCC cell line. Collectively, our results provide the link between PBRM1 loss, RRM2 expression and T cell infiltration, which may lead to the establishment of new treatment of this disease.

Growing tumors avoid recognition and destruction by the immune system. During continuous stimulation of tumor-infiltrating lymphocytes (TILs) by tumors, TILs become functionally exhausted; thus, they become unable to kill tumor cells and to produce certain cytokines and lose their ability to proliferate. This collectively results in the immune escape of cancer cells. Here, we show that breast cancer cells expressing PD-L1 can accelerate exhaustion of persistently activated human effector CD4+ T cells, manifesting in high PD-1 and PD-L1 expression level son T cell surfaces, decreased glucose metabolism genes, strong downregulation of SWI/SNF chromatin remodeling complex subunits, and p21 cell cycle inhibitor upregulation. This results in inhibition of T cell proliferation and reduction of T cell numbers. The RNAseq analysis on exhausted CD4+ T cells indicated strong overexpression of IDO1 and genes encoding pro-inflammatory cytokines and chemokines. Some interleukins were also detected in media from CD4+ T cells co-cultured with cancer cells. The PD-L1 overexpression was also observed in CD4+ T cells after co-cultivation with other cell lines overexpressing PD-L1, which suggested the existence of a general mechanism of CD4+ T cell exhaustion induced by cancer cells. The ChIP analysis on the PD-L1 promoter region indicated that the BRM recruitment in control CD4+ T cells was replaced by BRG1 and EZH2 in CD4+ T cells strongly exhausted by cancer cells. These findings suggest that epi-drugs such as EZH2 inhibitors may be used as immunomodulators in cancer treatment.

Conventional cytotoxic drugs preferentially eliminate differentiated cancer cells but spare relatively more resistant stem-like cancer cells capable to initiate recurrence. Due to cancer cell plasticity, the stem-like phenotype can be also acquired by cancer cells refractory to treatment with cytotoxic drugs. We investigated whether drugs inhibiting receptor tyrosine kinases could be used to target human colon cancer cells initiating cancer regrowth following conventional cytotoxic treatment. The moderately differentiated cell line HT-29 and poorly differentiated cell line HCT-116 were exposed to 5-fluorouracil (5-FU). Cells that resisted the exposure to 5-FU were subsequently treated with imatinib or sunitinib. Both drugs reduced clonogenicity of 5-FU-refractory cells under normoxic and hypoxic culture conditions. The expression of numerous stemness-related genes was upregulated in cancer cells following the exposure to 5-FU, and remained at a high level in 5-FU-refractory cells undergoing renewal under normoxia, but decreased spontaneously under hypoxia. Imatinib downregulated the expression of stemness-related genes in cells undergoing renewal under normoxia. A combination of imatinib with PRI-2191, an analogue of 1,25-dihydroxyvitamin D3, downregulated stemness-related genes in HCT-116/5-FU cells more efficiently than imatinib alone. A synthetic analogue of 1,25-dihydroxyvitamin D2 (PRI-1906) abolished the effect of imatinib on gene expression in HCT-116/5-FU cells undergoing renewal under normoxia. Sunitinib promoted shift of phenotype of HT-29/5-FU cells undergoing renewal toward stem-like one. It suggests that the phenotype shift toward stemness induced by sequential sunitinib treatment following 5-FU treatment could increase a risk of cancer recurrence. In contrast to sunitinib, imatinib could be used both to interfere with cancer regrowth after conventional chemotherapy and to downregulate the expression of stemness-related genes in residual colon cancer cells capable to initiate cancer recurrence. The findings suggest that imatinib could also be combined with vitamin D analogue PRI-2191 to prevent recurrence more efficiently than imatinib alone and to compensate for vitamin D deficiency resulting from imatinib treatment.

Inhibition of spleen tyrosine kinase (SYK) in tonic B-cell receptor (BCR) signal-dependent diffuse large B-cell lymphomas (DLBCLs) inhibits cellular proliferation, decreases cholesterol biosynthesis, and triggers apoptosis, at least in part via a mechanism involving decreased activity of phosphatidylinositol 3-kinase/AKT axis. Because forkhead box O1 (FOXO1) is a major effector of this pathway, we investigated the role of FOXO1 in toxicity of BCR pathway inhibition. Inhibition of SYK in DLBCL cells with tonic BCR signaling decreased phospho-AKT and phospho-FOXO1 levels and triggered FOXO1-driven gene expression. Introduction of constitutively active FOXO1 mutant triggered cell cycle arrest and apoptosis, indicating that increased FOXO1 activity is toxic to these DLBCL cells. Depletion of FOXO1 with short hairpin RNA led to almost complete resistance to chemical SYK inhibitor R406, demonstrating that FOXO1 is also required for R406-induced cell death. FOXO1 in these cells is also involved in regulation of expression of the critical master regulator of cholesterol biosynthesis, SREBP1. Because HRK is the key effector of SYK inhibition, we characterized a mechanism linking FOXO1 activation and HRK induction that involves caspase-dependent cleavage of HRK's transcriptional repressor DREAM. Because AKT in lymphoma cells can be regulated by other signals than BCR, we assessed the combined effects of the AKT inhibitor MK-2206 with R406 and found markedly synergistic FOXO1-dependent toxicity. In primary DLBCLs, FOXO1 expression was present in 80% of tumors, correlated with SYK activity, and was associated with longer overall survival. These results demonstrate that FOXO1 is required for SYK and AKT inhibitor-induced toxicity.

This study was aimed to determine whether hypocalcemic analogs of active forms of vitamins D modulate expression of genes related to stem-like phenotype in colon cancer cell lines HT-29 and HCT-116 undergoing renewal after the treatment with 5-fluorouracil (5-FU). Both lines express vitamin D receptor, but differ in differentiation stage and vitamin D sensitivity. Cells that resisted the 5-FU exposure were treated with synthetic analog of 1,25-dihydroxyvitamin D2 (PRI-1906) and analogs of 1,25-dihydroxyvitamin D3 (PRI-2191 and PRI-2205). Proliferative activity was more profoundly affected by vitamin D analogs in HT-29/5-FU than in HCT-116/5-FU cells. In HT-29/5-FU cells, analogs PRI-1906 and PRI-2191 downregulated the expression of genes related to survival, re-growth, and invasiveness during renewal, while PRI-2205 increased expression of genes related to differentiation only. In HCT-116/5-FU cells, PRI-2191 decreased the expression of stemness- and angiogenesis-related genes, whereas PRI-1906 augmented their expression. The effects in HCT-116/5-FU cells were observed at higher concentrations of the analogs than those used for HT-29/5-FU cells. Out of the series of analogs studied, PRI-2191 might be used to counteract the renewal of both moderately and poorly differentiated cancer cells following conventional treatment.

Resistance to glucocorticosteroids (GCs) is a major adverse prognostic factor in B-ALL, but the molecular mechanisms leading to GC resistance are not completely understood. Herein, we sought to elucidate the molecular background of GC resistance in B-ALL and characterize the therapeutic potential of targeted intervention in these mechanisms. Using exploratory bioinformatic approaches, we found that resistant cells exhibited significantly higher expression of MEK/ERK (MAPK) pathway components. We found that GC-resistant ALL cell lines had markedly higher baseline activity of MEK and small-molecule MEK1/2 inhibitor selumetinib increased GCs-induced cell death. MEK inhibitor similarly increased in vitro dexamethasone activity in primary ALL blasts from 19 of 22 tested patients. To further confirm these observations, we overexpressed a constitutively active MEK mutant in GC-sensitive cells and found that forced MEK activity induced resistance to dexamethasone. Since recent studies highlight the role GC-induced autophagy upstream of apoptotic cell death, we assessed LC3 processing, MDC staining and GFP-LC3 relocalization in cells incubated with either DEX, SEL or combination of drugs. Unlike either drug alone, only their combination markedly increased these markers of autophagy. These changes were associated with decreased mTOR activity and blocked 4E-BP1 phosphorylation. In cells with silenced beclin-1 (BCN1), required for autophagosome formation, the synergy of DEX and SEL was markedly reduced. Taken together, we show that MEK inhibitor selumetinib enhances dexamethasone toxicity in GC-resistant B-ALL cells. The underlying mechanism of this interaction involves inhibition of mTOR signaling pathway and modulation of autophagy markers, likely reflecting induction of this process and required for cell death. Thus, our data demonstrate that modulation of MEK/ERK pathway is an attractive therapeutic strategy overcoming GC resistance in B-ALL patients.

Molecular profiling has led to identification of subtypes of diffuse large B-cell lymphomas (DLBCLs) differing in terms of oncogenic signaling and metabolic programs. The OxPhos-DLBCL subtype is characterized by enhanced mitochondrial oxidative phosphorylation. As increased oxidative metabolism leads to overproduction of potentially toxic reactive oxygen species (ROS), we sought to identify mechanisms responsible for adaptation of OxPhos cells to these conditions. Herein, we describe a mechanism involving the FOXO1–TXN–p300 redox-dependent circuit protecting OxPhos-DLBCL cells from ROS toxicity. We identify a BCL6-dependent transcriptional mechanism leading to relative TXN overexpression in OxPhos cells. We found that OxPhos cells lacking TXN were uniformly more sensitive to ROS and doxorubicin than control cells. Consistent with this, the overall survival of patients with high TXN mRNA expression, treated with doxorubicin-containing regimens, is significantly shorter than of those with low TXN mRNA expression. TXN overexpression curtails p300-mediated FOXO1 acetylation and its nuclear translocation in response to oxidative stress, thus attenuating FOXO1 transcriptional activity toward genes involved in apoptosis and cell cycle inhibition. We also demonstrate that FOXO1 knockdown in cells with silenced TXN expression markedly reduces ROS-induced apoptosis, indicating that FOXO1 is the major sensor and effector of oxidative stress in OxPhos-DLBCLs. These data highlight dynamic, context-dependent modulation of FOXO1 tumor-suppressor functions via acetylation and reveal potentially targetable vulnerabilities in these DLBCLs.

This study aimed to evaluate the capacity of hypocalcemic analogues of 1α,25-dihydroxyvitamin D2 (1,25D2) and 1α,25-dihydroxyvitamin D3 (1,25D3) to inhibit regrowth and regulate the stemness-related gene expression in colon cancer cells undergoing renewal after exposure to 5-fluorouracil (5-FU). All of the tested analogues of 1,25D2 equally potently decreased the clonogenicity and the proliferative activity of HT-29 cells which survived the exposure to 5-FU, but differently regulated gene expression of these cells during their renewal. 1,25D2 and analogues (PRI-1907 and PRI-1917), as well as 1,25D3 and analogue PRI-2191, decreased the relative expression level of several stemness-related genes, such as NANOG, OCT3/4, PROM1, SOX2, ALDHA1, CXCR4, in HT-29/5-FU cells during their renewal, in comparison to untreated HT-29/5-FU cells. The other 1,25D2 analogues (PRI-1906 and PRI-1916) were not capable of downregulating the expression of these stemness-related genes as the analogues PRI-1907 and PRI-1917 did. All of the tested vitamin D analogues upregulated CDH1, the gene encoding E-cadherin associated with epithelial phenotype. Out of the series of analogues studied, side-chain branched analogues of 1,25D2 (PRI-1907, PRI-1917) and the analogue of 1,25D3 (PRI-2191) might be used to target cancer cells with stem-like phenotypes that survive conventional chemotherapy.

Conventional anti-cancer drugs preferentially eliminate differentiated cancer cells but those cells that are spared (i. e. cancer stem cells: CSC), initiate recurrence. We tested whether drugs that target receptor tyrosine kinases (RTKs) involved in developmental signaling cascades and activated in CSC, could be used to silence and/or to eliminate colorectal cancer cells refractory to conventional treatment with cytoreductive drugs. A sequential treatment model was thereby developed with doxorubicin (DOX) and imatinib. CT-26 mouse colon carcinoma cells were pretreated with DOX to select DOX-refractory cells with CSC properties, which were then subsequently treated with RTK inhibitor imatinib, where their regrowth was found to be inhibited. Under both normoxic and hypoxic conditions, imatinib potently inhibited clonogenicity of DOX-refractory CT-26 cells. Treatment with DOX did not eliminate tumorigenic CT-26 cells, since CT-26 cells pre-exposed to DOX in vitro, when inoculated subcutaneously, induced tumors in 90 % of mice, as opposed to a 100 % rate in the case of chemonaive CT-26 cells. In mice inoculated with chemonaive CT-26 cells, tumor formation was not prevented by imatinib. However, imatinib prevented tumor formation in 50 % of mice inoculated with CT-26 cells pre-exposed to DOX in vitro, with the remaining 50 % mice showing delayed tumor formation. These results suggest that the sequential use of the drug imatinib, as a drug targeting cancer cells expressing stem cell features after conventional cytoreductive treatment, is a promising future strategy for preventing tumor recurrence.

We have previously found that ex vivo expanded human CD4+CD25+Treg cells suppress proliferation of lymphoma B-cell lines. Here we demonstrate that the immunomodulatory drug lenalidomide potentiates suppression of lymphoma B-cell proliferation by freshly isolated CD4+CD25+Tregs, as well as suppression by Tregs expanded polyclonally in the presence of rapamycin from CD4+CD25+T cells or CD4+CD25+CD127loT cells. The regulation of lymphoma cell proliferation by Tregs pre-expanded with "third-party" allogeneic MoDCs in the presence of rapamycin was also potentiated by lenalidomide. Lenalidomide contributed to the suppression exerted by Tregs despite concomitant downregulation of Treg proliferation. Lenalidomide did not reduce the suppression of conventional T cells by expanded Tregs. The exposure of polyclonally expanded Tregs to lenalidomide did not significantly alter their phenotype. There was no uniform pattern of lenalidomide effect on Treg-mediated regulation of lymphoma B cells freshly isolated from patients. Freshly isolated lymphoma cells activated with multimeric CD40L and IL-4 to support their survival in vitro varied in their sensitivity to lenalidomide, and the regulatory effect of Tregs on such lymphoma cells ranged from suppression to help in individual patients. Lenalidomide potentiated or attenuated Treg effects on the survival of freshly isolated lymphoma cells. A combination of lenalidomide treatment with adoptive transfer of CD4+CD25+Tregs or CD4+CD25+CD127loTregs expanded ex vivo could be used to suppress proliferation of residual lymphoma in select patients with lymphoma responsive to the regulation by Tregs and sensitive to lenalidomide.

Activated regulatory T cells (Tregs) suppress proliferation and differentiation of normal B cells. In our study, allogeneic polyclonal CD4(+)CD25(+)Tregs and CD4(+)CD25(+)CD127(lo)Tregs expanded in vitro in the presence of rapamycin and low dose IL-2 suppressed proliferation of 11 out of 12 established lymphoma B-cell lines. The effect of expanded CD4(+)CD25(+)Tregs on survival of freshly isolated lymphoma B cells maintained in culture with soluble multimeric CD40L and IL-4 was variable across lymphoma entities. The survival of freshly isolated follicular lymphoma cells usually decreased in cocultures with CD4(+)CD25(+)Tregs. Treg effect on chronic lymphocytic leukemia/small lymphocytic lymphoma cells ranged from suppression to help in individual patients. CD4(+)CD25(+)Tregs or CD4(+)CD25(+)CD127(lo)Tregs expanded ex vivo with rapamycin could be used to suppress regrowth of residual lymphoma after autologous hematopoietic cell transplantation (HCT), and to counteract both graft-versus-host disease and lymphoma re-growth after allogeneic HCT in select patients with lymphoma susceptible to the regulation by Tregs.

Introduction: In normal B lymphocytes, B-cell receptor (BCR)-induced activation of PI3K-AKT kinases and subsequent inactivation of FOXO1 is a critical pro-survival component of tonic BCR signaling. In murine models, conditional deletion of FOXO1 protected quiescent peripheral B cells from apoptosis mediated by inducible loss of the BCR, demonstrating that PI3K-AKT-FOXO1 axis plays a central role in B-cell homeostasis. Disruption of the BCR signaling by SYK inhibitor leads also to the apoptosis of BCR-dependent DLBCLs, at least in part via a mechanism involving decreased activity of PI3K/AKT axis. Herein, we investigated the role of FOXO1 in toxicity of BCR pathway/SYK inhibition in human BCR-dependent lymphomas.

Glucocorticoids (GC) have been used for decades in the treatment of B-cell acute lymphoblastic leukemia (B-ALL) in children and adults. Induction of apoptosis is thought to be the principal effector mechanism of GC's action, but recent studies highlight the role of autophagy upstream of apoptotic cell death (Laane et al 2009). Resistance to GCs is a major adverse prognostic factor, however the molecular mechanisms leading to GC resistance are not completely understood. Herein, we sought to elucidate the molecular mechanisms driving GC-resistance in precursor B-cell acute lymphoblastic leukemia cells and in vitro characterize the therapeutic potential of targeted intervention in these mechanisms.

Diffuse large B-cell lymphoma (DLBCL) is a clinically and molecularly heterogeneous disease. The comparison of DLBCLs transcriptional profiles using multiple clustering algorithms led to the identification of distinct DLBCL subtypes reflecting tumor-intrinsic features. The OxPhos-DLBCL subtype is characterized by enhanced mitochondrial oxidative phosphorylation, a major source of potentially toxic reactive oxygen species (ROS). Therefore, we investigated the role of potential mechanisms attenuating ROS toxicity in this DLBCL subtype. We found significantly increased thioredoxin (TXN) mRNA abundance in DLBCLs classified as OxPhos subtype compared to other subtypes. The overall survival (OS) of patients with high TXN mRNA expression was significantly shorter than of those with low TXN mRNA expression, regardless of treatment regimen (R-CHOP and CHOP). TXN overexpression in OxPhos-DLBCLs was also confirmed in a cell line panel at protein level using immunoblotting. To explain transcriptional mechanisms responsible for differential TXN expression in different DLBCLs, we analyzed the TXN promoter and identified two BCL6 binding sites within 1kb upstream of TXN transcription start site. Unlike in other molecular subtypes, BCL6 does not exhibit a repressor activity in OxPhos-DLBCLs (PNAS, 2007; 104: 3207-12). Using luciferase reporter assays and shRNA-mediated gene expression knock-down, we demonstrated that relative differences in TXN abundance between DLBCL subtypes are at least in part caused by the lack of BCL6 transcription repressor activity. We next tested the consequences of TXN depletion in DLBCLs. We found that OxPhos cells with silenced TXN expression were uniformly more sensitive to apoptosis induced by ROS production than control cells. TXN inhibition sensitized all tested cell lines to doxorubicin, the fundamental drug used in DLBCL chemotherapy acting in part as a ROS inducer. In addition to its role in maintaining redox homeostasis, TXN also regulates transcriptional responses to ROS. For example, TXN reduces disulfide bonds between FOXO4 and acetyltransferase p300, which results in reduced FOXO4 acetylation and impaired proapoptotic signaling. For this reason, we assessed whether p300 and TXN are involved in acetylation of FOXO1, a major FOXO member expressed in DLBCLs. In cells with blocked TXN activity, FOXO1 acetylation was significantly higher compared to cells overexpressing wild-type TXN. TXN decreased p300-mediated FOXO1 acetylation, reduced its proapoptotic activity and expression of FOXO1-dependent genes (TRAIL, p27, BIM). We found that FOXO1 and p300 interact in redox and TXN-dependent manner and identified a conserved FOXO1's Cys612 to be responsible for FOXO1-p300 binding. We mutated FOXO1 C612 to Ala and found that when cotransfected with p300, C612A FOXO1 exhibited dramatically suppressed ROS-induced acetylation. Blockade of FOXO1 acetylation resulted in markedly lower expression of FOXO1 target genes, higher cellular proliferation and lower apoptosis. Furthermore, TXN inhibited FOXO1 nuclear translocation in response to oxidative stress in OxPhos-DLBCLs. Finally, silencing FOXO1 in OxPhos cells with knocked-down TXN expression markedly inhibited DLBCL cell line apoptosis in response to oxidative stress, suggesting that FOXO1 is an essential TXN-regulated sensor and effector of ROS toxicity in OxPhos-DLBCL cells. Taken together, these results demonstrate that TXN is overexpressed in a subset of DLBCLs, and high TXN mRNA abundance is related to shorter OS of DLBCL patients. TXN knock-down enhances oxidative stress toxicity in OxPhos cell lines at least in part by facilitating FOXO1 nuclear retention and increasing acetylation of this transcription factor, thus augmenting its proapoptotic activity. Disclosures No relevant conflicts of interest to declare.

The primary function of hair and fur covering mammalian skin is to provide mechanical and thermal protection for the body. The proteins that constitute hair are extremely resistant to degradation by environmental factors. However, even durable materials can be slowly broken down by mechanical stresses, biodegradation mediated by endogenous enzymes in the skin or host microbes. We hypothesised that the biodegradation products of hair may possess bioprotective properties, which supplement their physical protective properties. Although evolutionary processes have led to a reduction in the amount of hair on the human body, it is possible that the bioprotective properties of hair biodegradation products have persisted. The human skin is exposed to various environmental carcinogenic factors. Therefore, we hypothesised that the potential bioprotective mechanisms of hair degradation products affect melanoma growth. We used pepsin to partially digest hair enzymatically, and this process produced a water-soluble lysate containing a mixture of peptides, including fragments of keratin and keratin-associated proteins. We found out that the mixtures of soluble peptides obtained from human hair inhibited the proliferation of human melanoma cells in vitro. Moreover, the hair-derived peptide mixtures also inhibited the proliferation of B lymphoma cells and urinary bladder cancer cells. Normal human cells varied in their susceptibility to the effects of the lysate; the hair-derived peptide mixtures modulated the proliferation of normal human fibroblasts but did not inhibit the proliferation of human mesenchymal cells derived from umbilical cord stromal cells. These results suggest that hair-derived peptides may represent a new class of anti-proliferative factors derived from basically structural proteins. Identification of active regulatory compounds and recognition of the mechanism of their action might pave the way to elaboration of new anticancer drugs.