SMAC Mimetics for the Treatment of Lung Carcinoma: Present Development and Future Prospects.

BACKGROUND: Uncontrolled cell growth and proliferation, which originate from lung tissue often lead to lung carcinoma and are more likely due to smoking as well as inhaled environmental toxins. It is widely recognized that tumour cells evade the ability of natural programmed death (apoptosis) and facilitates tumour progression and metastasis. Therefore investigating and targeting the apoptosis pathway is being utilized as one of the best approaches for decades. OBJECTIVE: This review describes the emergence of SMAC mimetic drugs as a treatment approach, its possibilities to synergize the response along with current limitations as well as future perspective therapy for lung cancer. METHOD: Articles were analysed using search engines and databases namely Pubmed and Scopus. RESULT: Under cancerous circumstances, the level of Inhibitor of Apoptosis Proteins (IAPs) gets elevated, which suppresses the pathway of programmed cell death, plus supports the proliferation of lung cancer. As it is a major apoptosis regulator, natural drugs that imitate the IAP antagonistic response like SMAC mimetic agents/Diablo have been identified to trigger cell death. SMAC i.e. second mitochondria activators of caspases is a molecule produced by mitochondria, stimulates apoptosis by neutralizing/inhibiting IAP and prevents its potential responsible for the activation of caspases. Various preclinical data have proven that these agents elicit the death of lung tumour cells. Apart from inducing apoptosis, these also sensitize the cancer cells toward other effective anticancer approaches like chemo, radio, or immunotherapies. There are many SMAC mimetic agents such as birinapant, BV-6, LCL161, and JP 1201, which have been identified for diagnosis as well as treatment purposes in lung cancer and are also under clinical investigation. CONCLUSION: SMAC mimetics acts in a restorative way in the prevention of lung cancer.

Tumor-associated macrophages employ immunoediting mechanisms in colorectal tumor progression: Current research in Macrophage repolarization immunotherapy.

Tumor-associated macrophages (TAMs) constitute the most prolific resident of the tumor microenvironment (TME) that regulate its TME into tumor suppressive or progressive milieu by utilizing immunoediting machinery. Here, the tumor cells construct an immunosuppressive microenvironment that educates TAMs to polarize from anti-tumor TAM-M1 to pro-tumor TAM-M2 phenotype consequently contributing to tumor progression. In colorectal cancer (CRC), the TME displays a prominent pro-tumorigenic immune profile with elevated expression of immune-checkpoint molecules notably PD-1, CTLA4, etc., in both MSI and ultra-mutated MSS tumors. This authenticated immune-checkpoint inhibition (ICI) immunotherapy as a pre-requisite for clinical benefit in CRC. However, in response to ICI, specifically, the MSIhi tumors evolved to produce novel immune escape variants thus undermining ICI. Lately, TAM-directed therapies extending from macrophage depletion to repolarization have enabled TME alteration. While TAM accrual implicates clinical benefit in CRC, sustained inflammatory insult may program TAMs to shift from M1 to M2 phenotype. Their ability to oscillate on both facets of the spectrum represents macrophage repolarization immunotherapy as an effective approach to treating CRC. In this review, we briefly discuss the differentiation heterogeneity of colonic macrophages that partake in macrophage-directed immunoediting mechanisms in CRC progression and its employment in macrophage re-polarization immunotherapy.

Role of PARP Inhibitors in Glioblastoma and Perceiving Challenges as Well as Strategies for Successful Clinical Development.

Glioblastoma multiform is the most aggressive primary type of brain tumor, representing 54% of all gliomas. The average life span for glioblastoma multiform is around 14-15 months instead of treatment. The current treatment for glioblastoma multiform includes surgical removal of the tumor followed by radiation therapy and temozolomide chemotherapy for 6.5 months, followed by another 6 months of maintenance therapy with temozolomide chemotherapy (5 days every month). However, resistance to temozolomide is frequently one of the limiting factors in effective treatment. Poly (ADP-ribose) polymerase (PARP) inhibitors have recently been investigated as sensitizing drugs to enhance temozolomide potency. However, clinical use of PARP inhibitors in glioblastoma multiform is difficult due to a number of factors such as limited blood-brain barrier penetration of PARP inhibitors, inducing resistance due to frequent use of PARP inhibitors, and overlapping hematologic toxicities of PARP inhibitors when co-administered with glioblastoma multiform standard treatment (radiation therapy and temozolomide). This review elucidates the role of PARP inhibitors in temozolomide resistance, multiple factors that make development of these PARP inhibitor drugs challenging, and the strategies such as the development of targeted drug therapies and combination therapy to combat the resistance of PARP inhibitors that can be adopted to overcome these challenges.

Driver Mutations in Leukemia Promote Disease Pathogenesis through a Combination of Cell-Autonomous and Niche Modulation.

Studies of patients with acute myeloid leukemia (AML) have led to the identification of mutations that affect different cellular pathways. Some of these have been classified as preleukemic, and a stepwise evolution program whereby cells acquire additional mutations has been proposed in the development of AML. How the timing of acquisition of these mutations and their impact on transformation and the bone marrow (BM) microenvironment occurs has only recently begun to be investigated. We show that constitutive and early loss of the epigenetic regulator, TET2, when combined with constitutive activation of FLT3, results in transformation of chronic myelomonocytic leukemia-like or myeloproliferative neoplasm-like phenotype to AML, which is more pronounced in double-mutant mice relative to mice carrying mutations in single genes. Furthermore, we show that in preleukemic and leukemic mice there are alterations in the BM niche and secreted cytokines, which creates a permissive environment for the growth of mutation-bearing cells relative to normal cells.

SHP2 inhibition reduces leukemogenesis in models of combined genetic and epigenetic mutations.

In patients with acute myeloid leukemia (AML), 10% to 30% with the normal karyotype express mutations in regulators of DNA methylation, such as TET2 or DNMT3A, in conjunction with activating mutation in the receptor tyrosine kinase FLT3. These patients have a poor prognosis because they do not respond well to established therapies. Here, utilizing mouse models of AML that recapitulate cardinal features of the human disease and bear a combination of loss-of-function mutations in either Tet2 or Dnmt3a along with expression of Flt3ITD, we show that inhibition of the protein tyrosine phosphatase SHP2, which is essential for cytokine receptor signaling (including FLT3), by the small molecule allosteric inhibitor SHP099 impairs growth and induces differentiation of leukemic cells without impacting normal hematopoietic cells. We also show that SHP099 normalizes the gene expression program associated with increased cell proliferation and self-renewal in leukemic cells by downregulating the Myc signature. Our results provide a new and more effective target for treating a subset of patients with AML who bear a combination of genetic and epigenetic mutations.

Inhibition of Inflammatory Signaling in Tet2 Mutant Preleukemic Cells Mitigates Stress-Induced Abnormalities and Clonal Hematopoiesis.

Inflammation is a risk factor for cancer development. Individuals with preleukemic TET2 mutations manifest clonal hematopoiesis and are at a higher risk of developing leukemia. How inflammatory signals influence the survival of preleukemic hematopoietic stem and progenitor cells (HSPCs) is unclear. We show a rapid increase in the frequency and absolute number of Tet2-KO mature myeloid cells and HSPCs in response to inflammatory stress, which results in enhanced production of inflammatory cytokines, including interleukin-6 (IL-6), and resistance to apoptosis. IL-6 induces hyperactivation of the Shp2-Stat3 signaling axis, resulting in increased expression of a novel anti-apoptotic long non-coding RNA (lncRNAs), Morrbid, in Tet2-KO myeloid cells and HSPCs. Expression of activated Shp2 in HSPCs phenocopies Tet2 loss with regard to hyperactivation of Stat3 and Morrbid. In vivo, pharmacologic inhibition of Shp2 or Stat3 or genetic loss of Morrbid in Tet2 mutant mice rescues inflammatory-stress-induced abnormalities in HSPCs and mature myeloid cells, including clonal hematopoiesis.

Comparative evaluation of hemodynamic, vasoconstrictive, and SpO2 variability during different stages of periodontal surgery performed using 0.5% ropivacaine or 2% lignocaine HCl (1:80,000 adrenaline) local anesthesia: A randomized, double-blind, split-mouth pilot study.

AIM: The aim of this study is to compare anesthetic, hemodynamic, vasoconstrictive, and SpO2 variability of 0.5% ropivacaine to the "gold standard" lignocaine (2%) with epinephrine (1:80,000) during periodontal surgery. MATERIALS AND METHODS: A total of 20 systemically healthy controls meeting the inclusion criteria were selected from the Outpatient Department of Sri Sai College of Dental Surgery. Preoperatively, all participants were infiltrated with 0.5 ml of 0.5% ropivacaine intradermally as test solution to record any allergic reaction. Open flap debridement was performed using local anesthesia containing 2% lignocaine hydrochloride with 1:80,000 epinephrine or 0.5% ropivacaine. Recordings were made of the time of onset, duration of action, the intensity, and depth of anesthesia and various hemodynamic changes throughout the surgical procedure. In addition, blood loss volume and postoperative pain were also assessed. RESULTS: Ropivacaine showed statistically longer duration of action (mean±SD =5.3±0.71 hrs) than lignocaine with epinephrine (mean=2.14±0.98 hrs). Blood loss during flap surgery was comparatively less when performed under ropivacaine. No statistical differences were observed in systolic BP, diastolic BP, SpO2 and heart rate during different stages of periodontal surgery between either of the local anesthetic agents. CONCLUSION: Ropivacaine demonstrates comparable efficacy as lignocaine with added advantage of longer duration of action and superior postoperative pain control. No adverse events from this newer anesthetic were noted, and hence, it can be used safely as a viable local anesthetic for periodontal surgical procedures.

Role of SHP2 in hematopoiesis and leukemogenesis.

PURPOSE OF REVIEW: SH2 domain-containing tyrosine phosphatase 2 (SHP2), encoded by PTPN11 plays an important role in regulating signaling from cell surface receptor tyrosine kinases during normal development as well as oncogenesis. Herein we review recently discovered roles of SHP2 in normal and aberrant hematopoiesis along with novel strategies to target it. RECENT FINDINGS: Cell autonomous role of SHP2 in normal hematopoiesis and leukemogenesis has long been recognized. The review will discuss the newly discovered role of SHP2 in lineage specific differentiation. Recently, a noncell autonomous role of oncogenic SHP2 has been reported in which activated SHP2 was shown to alter the bone marrow microenvironment resulting in transformation of donor derived normal hematopoietic cells and development of myeloid malignancy. From being considered as an 'undruggable' target, recent development of allosteric inhibitor has made it possible to specifically target SHP2 in receptor tyrosine kinase driven malignancies. SUMMARY: SHP2 has emerged as an attractive target for therapeutic targeting in hematological malignancies for its cell autonomous and microenvironmental effects. However a better understanding of the role of SHP2 in different hematopoietic lineages and its crosstalk with signaling pathways activated by other genetic lesions is required before the promise is realized in the clinic.

RAG-mediated DNA double-strand breaks activate a cell type-specific checkpoint to inhibit pre-B cell receptor signals.

DNA double-strand breaks (DSBs) activate a canonical DNA damage response, including highly conserved cell cycle checkpoint pathways that prevent cells with DSBs from progressing through the cell cycle. In developing B cells, pre-B cell receptor (pre-BCR) signals initiate immunoglobulin light (Igl) chain gene assembly, leading to RAG-mediated DNA DSBs. The pre-BCR also promotes cell cycle entry, which could cause aberrant DSB repair and genome instability in pre-B cells. Here, we show that RAG DSBs inhibit pre-BCR signals through the ATM- and NF-κB2-dependent induction of SPIC, a hematopoietic-specific transcriptional repressor. SPIC inhibits expression of the SYK tyrosine kinase and BLNK adaptor, resulting in suppression of pre-BCR signaling. This regulatory circuit prevents the pre-BCR from inducing additional Igl chain gene rearrangements and driving pre-B cells with RAG DSBs into cycle. We propose that pre-B cells toggle between pre-BCR signals and a RAG DSB-dependent checkpoint to maintain genome stability while iteratively assembling Igl chain genes.

MntR(Rv2788): a transcriptional regulator that controls manganese homeostasis in Mycobacterium tuberculosis.

The pathogenic mycobacterium Mycobacterium tuberculosis encodes two members of the DtxR/MntR family of metalloregulators, IdeR and SirR. IdeR represses gene expression in response to ferrous iron, and we here demonstrate that SirR (Rv2788), although also annotated as an iron-dependent repressor, functions instead as a manganese-dependent transcriptional repressor and is therefore renamed MntR. MntR regulates transporters that promote manganese import and genes that respond to metal ion deficiency such as the esx3 system. Repression of manganese import by MntR is essential for survival of M. tuberculosis under conditions of high manganese availability, but mntR is dispensable during infection. In contrast, manganese import by MntH and MntABCD was found to be indispensable for replication of M. tuberculosis in macrophages. These results suggest that manganese is limiting in the host and that interfering with import of this essential metal may be an effective strategy to attenuate M. tuberculosis.

Vaccination with an Attenuated Ferritin Mutant Protects Mice against Virulent Mycobacterium tuberculosis.

Mycobacterium tuberculosis the causative agent of tuberculosis affects millions of people worldwide. New tools for treatment and prevention of tuberculosis are urgently needed. We previously showed that a ferritin (bfrB) mutant of M. tuberculosis has altered iron homeostasis and increased sensitivity to antibiotics and to microbicidal effectors produced by activated macrophages. Most importantly, M. tuberculosis lacking BfrB is strongly attenuated in mice, especially, during the chronic phase of infection. In this study, we examined whether immunization with a bfrB mutant could confer protection against subsequent infection with virulent M. tuberculosis in a mouse model. The results show that the protection elicited by immunization with the bfrB mutant is comparable to BCG vaccination with respect to reduction of bacterial burden. However, significant distinctions in the disease pathology and host genome-wide lung transcriptome suggest improved containment of Mtb infection in animals vaccinated with the bfrB mutant, compared to BCG. We found that downmodulation of inflammatory response and enhanced fibrosis, compared to BCG vaccination, is associated with the protective response elicited by the bfrB mutant.

Targeting phosphatidylinositol-3-kinase pathway for the treatment of Philadelphia-negative myeloproliferative neoplasms.

Myeloproliferative neoplasms (MPN) are a diverse group of chronic hematological disorders that involve unregulated clonal proliferation of white blood cells. Sevearl of them are associated with mutations in receptor tyrosine kinases or cytokine receptor associated tyrosine kinases rendering them independent of cytokine-mediated regulation. Classically they have been broadly divided into BCR-ABL1 fusion + ve (Ph + ve) or -ve (Ph-ve) MPNs. Identification of BCR-ABL1 tyrosine kinase as a driver of chronic myeloid leukemia (CML) and successful application of small molecule inhibitors of the tyrosine kinases in the clinic have triggered the search for kinase dependent pathways in other Ph-ve MPNs. In the past few years, identification of mutations in JAK2 associated with a majority of MPNs raised the hopes for similar success with specific targeting of JAK2. However, targeting JAK2 kinase activity has met with limited success. Subsequently, mutations in genes other than JAK2 have been identified. These mutations specifically associate with certain MPNs and can drive cytokine independent growth. Therefore, targeting alternate molecules and pathways may be more successful in management of MPNs. Among other pathways, phosphatidylinositol -3 kinase (PI3K) has emerged as a promising target as different cell surface receptor induced signaling pathways converge on the PI3K signaling axis to regulate cell metabolism, growth, proliferation, and survival. Herein, we will review the clinically relevant inhibitors of the PI3K pathway that have been evaluated or hold promise for the treatment of Ph-ve MPNs.

IdeR is required for iron homeostasis and virulence in Mycobacterium tuberculosis.

Iron is an essential but potentially harmful nutrient, poorly soluble in aerobic conditions, and not freely available in the human host. To acquire iron, bacteria have evolved high affinity iron acquisition systems that are expressed under iron limitation often in conjunction with virulence determinants. Because excess iron can be dangerous, intracellular iron must be tightly controlled. In mycobacteria, IdeR functions as a global iron dependent transcriptional regulator, but because inactivation of ideR is lethal for Mycobacterium tuberculosis, it has not been possible to use genetics to fully characterize this protein's function or examine the requirement of iron regulation during tuberculosis infection. In this work, a conditional M. tuberculosis ideR mutant was generated and used to study the basis of IdeR's essentiality. This investigation uncovered positive regulation of iron storage as a critical aspect of IdeR's function in regular culture and a prominent factor for survival under stresses associated with life in macrophages. Moreover, this study demonstrates that IdeR is indispensable in the mouse model of tuberculosis, thereby linking iron homeostasis to virulence in M. tuberculosis.

Role of glutathione in augmenting the anticancer activity of pyrroloquinoline quinone (PQQ).

Pyrroloquinoline quinone (PQQ), a bacterial redox co-factor and antioxidant, is highly reactive with nucleophilic compounds present in biological fluids. PQQ induced apoptosis in human promonocytic leukemia U937 cells and this was accompanied by depletion of the major cellular antioxidant glutathione and increase in intracellular reactive oxygen species (ROS). Treatment with glutathione (GSH) or N-acetyl-L-cysteine (NAC) did not spare PQQ toxicity but resulted in a 2-5-fold increase in PQQ-induced apoptosis in U937 cells. Cellular GSH levels increased following treatment by NAC alone but were severely depleted by co-treatment with NAC and PQQ. This was accompanied by an increase in intracellular ROS. Alternatively, depletion of glutathione also resulted in increased PQQ cytotoxicity. However, the cells underwent necrosis as evidenced by dual labeling with annexin V and propidium iodide. PQQ-induced cytotoxicity is thus critically regulated by the cellular redox status. An increase in GSH can augment apoptosis and its depletion can switch the mode of cell death to necrosis in the presence of PQQ. Our data suggest that modulation of intracellular GSH can be used as an effective strategy to potentiate cytotoxicity of quinones like PQQ.

A novel N-alkylated prodigiosin analogue induced death in tumour cell through apoptosis or necrosis depending upon the cell type.

PURPOSE: To investigate the mechanism of cell death induced by the N-alkylated prodigiosin analogue, 2,2'-[3-methoxy-1'amyl-5'-methyl-4-(1''-pyrryl)] dipyrryl-methene (MAMPDM) in S-180 and EL-4 tumour cell lines. METHODS: Effect of MAMPDM on cell viability was assessed by MTT dye conversion. Induction of apoptosis was assessed by monitoring caspase 3 activity using a fluorogenic substrate, fragmentation of DNA by gel electrophoresis and sub-diploid DNA containing cells by flowcytometry. Necrosis was estimated by flowcytometric analysis of the uptake of propidium iodide. RESULTS: MAMPDM inhibited the proliferation of murine fibrosarcoma, S-180 cells and induced cell death. Investigations into the mechanism of cell death by MAMPDM in S-180 cells showed absence of hallmarks of apoptotic cell death such as activation of caspase 3, DNA fragmentation and presence of cells with sub-diploid DNA content. However, there was a rapid loss of membrane integrity as assessed by uptake of propidium iodide, which is characteristic of necrosis. In contrast to induction of necrosis in S-180 cells, MAMPDM induced apoptotic cell death in EL-4 cells as evident by activation of caspase 3, fragmentation of DNA and sub-diploid DNA containing cells. CONCLUSIONS: MAMPDM could induce cell death by either apoptosis or necrosis depending upon the cell type. This would be of advantage in elimination of tumor cells defective in apoptotic pathway and therefore, refractory to the conventional therapies.

Role of interleukin-2 regulated proteins in immunosuppression by the N-alkylated prodigiosin analogue.

Prodigiosins have emerged as a novel family of tripyrrole compounds with significant T cell specific immunosuppressive potential. We had previously reported the immunosuppressive activity of a novel N-alkylated prodigiosin analogue, 2,2'-[3-methoxy-1'amyl-5'-methyl-4-(1''-pyrryl)] dipyrryl-methene (MAMPDM) in mitogen stimulated spleen cells. There was an increase in the accumulation of IL-2 and induction of apoptotic cell death. Since IL-2 regulates both cellular proliferation and activation induced cell death (AICD), we have investigated the effect of MAMPDM on the expression of IL-2 regulated genes that are involved in these two opposite processes. The mitogen stimulated mouse spleen cells did not undergo a single division in presence of proliferation inhibitory concentrations of MAMPDM. An increase in the percentage of apoptotic cells was observed in the undivided cell population. The cells were arrested in G1 phase independent of the p53 expression. Expression of IL-2 regulated genes such as CD71, proliferating cell nuclear antigen (PCNA) and cyclin D was suppressed while that of Fas was not. Thus, in the presence of MAMPDM there was selective inhibition of only the pro-mitogenic signaling and not that of pro-apoptotic signaling by IL-2. The induction of apoptosis in presence of MAMPDM was the effect rather than cause for the anti-proliferative activity.

3,3'-diselenodipropionic acid, an efficient peroxyl radical scavenger and a GPx mimic, protects erythrocytes (RBCs) from AAPH-induced hemolysis.

3,3'-diselenodipropionic acid (DSePA), a derivative of selenocystine, has been synthesized and examined for antioxidant activity, glutathione peroxidase (GPx) activity, and cytotoxicity. The effect of DSePA on membrane lipid peroxidation, release of hemoglobin, and intracellular K+ ion as a consequence of erythrocyte (red blood cells or RBCs) oxidation by free radicals generated by 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH) were used to evaluate the antioxidant ability. Lipid peroxidation, hemolysis, and K+ ion loss in RBCs were assessed, respectively, by formation of thiobarbituric acid reactive substances (TBARS), absorbance of hemoglobin at 532 nm and flame photometry. The IC50 values for lipid peroxidation, hemolysis, and K+ ion leakage were 45+/-5, 20+/-2, and 75+/-8 microM, respectively. DSePA treatment prevented the depletion of glutathione (GSH) levels in RBCs from free-radical-induced stress. DSePA is a good peroxyl radical scavenger and the bimolecular rate constant for the reaction of DSePA with a model peroxyl radical, trichloromethyl peroxyl radical (CCl 3O2*), was determined to be 2.7x10(8) M(-1) s(-1) using a pulse radiolysis technique. DSePA shows GPx activity with higher substrate specificity towards peroxides than thiols. The cytotoxicity of DSePA was studied in lymphocytes and EL4 tumor cells and the results showed that DSePA is nontoxic to these cells at the concentrations employed. These results when compared with two well-known selenium compounds, sodium selenite and ebselen, indicated that DSePA, although it shows lesser GPx activity, has higher free radical scavenging ability and lesser toxicity.

Prodigiosins: a novel family of immunosuppressants with anti-cancer activity.

Prodigiosins (PrGs) are a family of promising therapeutic molecules, isolated mostly from Gram-negative bacteria and characterized by a common pyrryldipyrrylmethene structure with varying side chains. They show a broad spectrum of activities such as anti-microbial, anti-malarial, anti-cancer and immunosuppressive. PrGs are attracting increasing attention due to the ongoing research for less toxic, but effective agents for cancer chemotherapy and immunosuppression for preventing allograft rejection and autoimmunity. Different analogues have been synthesized and evaluated. This review discusses the immunosuppressive and anti-cancer activities of this class of compounds, as both involve inhibition of cell proliferation. The main focus is on the in vitro and in vivo immunosuppressive activity of the different PrGs and the mechanisms involved. PrGs primarily target the T cells, though some effects are observed on other cell types also. Unlike the well-known immunosuppressant cyclosporin A, PrGs do not inhibit the secretion of IL-2 but inhibit the mitogenic signaling from IL-2, suggesting a different mechanism of action. Janus tyrosine kinase 3 (Jak3) that associates with IL-2R upon activation is considered as the molecular target for PrGs. Its restricted expression makes Jak3 as an attractive target for immunosuppressive therapy. However, the available literature suggests that some other pathways are also influenced by the PrGs. These may be important for the anti-cancer activity, as well as immunosuppressive action. Therefore, PrGs appear to be potential candidates for pharmaceutical development as immunosuppressants and also as anti-cancer agents.

Radiation-induced bystander effects and adaptive response in murine lymphocytes.

PURPOSE: To study the bystander effects of gamma-radiation in murine lymphocytes using irradiated conditioned medium (ICM) generated from irradiated lymphocytes. METHODS: Proliferation response of unirradiated lymphocytes to mitogen concanavalin A (con A) in presence of ICM, collected from gamma-irradiated lymphocytes (60Co source; 0.35 Gy/min; 0.1-1 Gy), was studied by 3H-thymidine incorporation and also by dye dilution using carboxyfluorescein succinimidyl ester (CFSE). Expression of proliferation markers, interleukin 2 receptor alpha chain (CD25) and cyclin D in ICM treated lymphocytes was analyzed by labeling with specific antibodies. Intracellular reactive oxygen species (ROS) and apoptosis were estimated by flow cytometry using dichlorodihydrofluorescein diacetate (H2DCFDA) and propidium iodide, respectively. Nitric oxide (NO) was measured using Griess reagent. RESULTS: Proliferation response to con A in unirradiated lymphocytes was enhanced in the presence of ICM with maximum enhancement observed in the presence of 0.5 Gy ICM. Augmentation of proliferation in the presence of ICM was accompanied by an increase in CD25 and cyclin D expression, enhanced ROS and NO generation. ICM pretreated lymphocytes showed adaptive response to radiation which was not abrogated by wortmannin, a phosphatidyl inositol 3-kinase (PI3K) inhibitor. CONCLUSION: Soluble factors released from irradiated lymphocytes initiate a signaling cascade in unirradiated lymphocytes resulting in increased response to mitogen and radioresistance which may have an important role in radiation-induced immunomodulation.