Joel Tolentino Jr. | Bataan Peninsula State University (original) (raw)
Papers by Joel Tolentino Jr.
Kimika, Dec 20, 2016
Saccharomycopsis (Syn. Endomycopsis) bubodii 2066 is an isolate from bubod, a starter used in mak... more Saccharomycopsis (Syn. Endomycopsis) bubodii 2066 is an isolate from bubod, a starter used in making rice wine in northern Philippines. We have shown that the yeast has amylolytic activity on raw sago starch. In our attempt to identify the putative raw starch-digesting amylase in S. bubodii, we determined the cDNA sequence of a glucoamylase gene. One primer pair that was designed based on a glucoamylase of Saccharomycopsis fibuligera HUT7212 (GLU1, NCBI Accession Number L25641.1) produced a sequence of 1234 base pairs. To obtain a wider coverage, a primer walking strategy was carried out using four primer pairs designed based on GLU1 gene. The generated sequence of 1535 base pairs shows 98.7 to 100% homology when aligned with glucoamylase genes from four strains of S. fibuligera suggesting that this glucoamylase is highly conserved between the Saccharomycopsis species. This work further reports a gene sequence of glucoamylase derived from Philippine-isolated yeast. The sequence is deposited in GenBank and assigned the accession number KP068007.1. The gene may be heterologously expressed in Saccharomyces cerevisiae for possible utilization in the direct conversion of raw sago starch to bioethanol.
... MUTAGENESIS STUDIES OF SINGLE AND TANDEM DNA DAMAGES BY SITE-SPECIFIC APPROACH Presented by J... more ... MUTAGENESIS STUDIES OF SINGLE AND TANDEM DNA DAMAGES BY SITE-SPECIFIC APPROACH Presented by Joel Hassan G. Tolentino, BS Major Advisor ... To the undergraduates I have worked with: Kushan, Joe, Charlayne and Marie, for being good students and for the ...
... MUTAGENESIS STUDIES OF SINGLE AND TANDEM DNA DAMAGES BY SITE-SPECIFIC APPROACH Presented by J... more ... MUTAGENESIS STUDIES OF SINGLE AND TANDEM DNA DAMAGES BY SITE-SPECIFIC APPROACH Presented by Joel Hassan G. Tolentino, BS Major Advisor ... To the undergraduates I have worked with: Kushan, Joe, Charlayne and Marie, for being good students and for the ...
Complete eradication of CML has not been possible in patients because of the presence of minimal ... more Complete eradication of CML has not been possible in patients because of the presence of minimal residual disease (MRD) in sanctuary sites like the bone marrow (BM). One of the reasons for MRD is the milieu of cytokines and growth factors present in the BM microenvironment, that contribute to BCR-ABL independent drug resistance in CML. For example, in the present study, we demonstrate the importance of STAT3-mediated drug resistance in the BM microenvironment by showing that conditioned media (CM) derived from both normal and patient-derived mesenchymal stem cells and osteoblasts leads to STAT3 phosphorylation (pSTAT3-Y705) and concomitant drug resistance to Nilotinib in CML cells. Inhibiting the activity or reducing the expression of JAK2 and TYK2 was necessary for sensitizing cells to Nilotinib in CM. Moreover, increased pSTAT3-Y705 levels were associated with increased STAT3 transcriptional activity and up-regulation of Mcl-1 and cyclin D1. Our study indicates that there is an inherent redundancy in CM-mediated STAT3 activation pathway because concomitant neutralization of two potent activators of STAT3, IL-6 and G-CSF, does not reverse CM-mediated protection against Nilotinib. Furthermore, utilizing a SCID-hu bone implant in vivo model, we show that K562 cells with reduced STAT3 showed significantly lower tumor burden, which could be attributed to not only the slower proliferation rate, but also to the observation that these cells underwent cell death in BM stromal derived CM. Finally, CD34+ cells from CML patients when exposed to CM showed an increase in STAT3 phosphorylation which correlated with the development of de novo resistance to Nilotinib-mediated cell death. Taken together our data indicate that STAT3 is an important target in CML and its direct inhibition, along with BCR-ABL inhibitors, will likely be the most effective therapeutic strategy for reversing resistance within the BM microenvironment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5033. doi:10.1158/1538-7445.AM2011-5033
Ciencia Administrativa, 2015
La marginacion que prevalece en una buena parte de los municipios de Mexico exige el diseno de po... more La marginacion que prevalece en una buena parte de los municipios de Mexico exige el diseno de politicas y estrategias que promuevan la organizacion de los productores agropecuarios y su participacion activa en el desarrollo economico y social de sus ambitos de competencia. El diseno de estas estrategias debe sustentarse en diagnosticos eficientes que identifiquen sus fortalezas y debilidades para dar atencion a sus necesidades prioritarias y aprovechar su potencial. En 2011 se realizo un diagnostico de las organizaciones agropecuarias, forestales y turisticas en el municipio de Soteapan, Veracruz, con el objetivo de identificar sus capacidades de organizacion, gestion, produccion y comercializacion, y determinar los factores que limitan su desarrollo, con base en el marco legal en el que estan constituidas. Los resultados muestran que las organizaciones estudiadas mantienen sistemas de produccion tradicionales, con una capacidad de gestion baja, y un mercado de corto alcance a nive...
Blood, Nov 16, 2012
Abstract 869 We previously reported that the linear peptide referred to as HYD1 induces necrotic ... more Abstract 869 We previously reported that the linear peptide referred to as HYD1 induces necrotic cell death in myeloma cell lines (Nair RR et al. Mol Cancer Ther. 2009 Aug;8(8):2441-51). We have now developed a more potent cyclic analog based on the active core region of the linear peptide which we now refer to as MTI-101. MTI-101, as a single agent, induces cell death in AML cell lines U937 and HL-60 with an IC50 value of 23.03 ± 0.67 and 36.06 ± 4.99 μM, respectively. Interestingly, unlike the conventional drugs therapies that succumb to cell adhesion mediated-drug resistance (CAM-DR), we found that MTI-101 kills U937 and HL-60 cells co-cultured with bone marrow stromal cells, with increased sensitivity and an IC50 value of 17.89 ± 2.47 and 24.61 ± 3.06 μM, respectively. Furthermore, again unlike the conventional drug therapies, MTI-101-mediated cell death was accompanied by oncosis and ATP depletion along with no observable caspase-3 activation indicative of a necrotic mode of cell death. More importantly, MTI-101 was able to induce cell death in relapsed primary AML patient CD34 progenitor cells but was devoid of activity in the CD34 progenitor cells obtained from healthy individuals. We have established that MTI-101 has robust activity as a single agent using multiple myeloma in vivo models. Our laboratory is currently pursuing the activity of MTI-101 using AML specific animal model. To delineate the cell surface targets responsible for MTI-101 actions in AML, we utilized biotin-conjugated MTI-101 as bait to pull down protein complexes involved in MTI-101 cell surface binding. Follow-up immuno-precipitation and western blotting studies confirmed that CD44 and ITGA4 are two proteins that are present in the MTI-101 cell surface binding complexes. Also, in addition to causing cell death, binding of MTI-101 to the cell surface, lead to activation of several cell survival pathways including induction of autophagy, activation of ERK ½ and PyK2. In order to determine if inhibition of these survival signals will lead to a better therapeutic outcome when utilizing MTI-101, we pretreated U937 cells with inhibitors of autophagy (chloroquine), ERK ½ (PD 98059) and Pyk2 (PF 562271) followed by MTI-101. We found that, pretreatment of cells with each inhibitor individually synergized with MTI-101 in inducing cell death in U937 cells. Taken together, MTI-101 is a peptidomimetic with a novel mechanism of action that can be exploited for the treatment of relapsed AML. Our studies provide preclinical rationale for continued development of this class of compounds for the treatment of relapsed AML and set the stage for designing rationale combination strategies for increasing the efficacy of MTI-101. Disclosures: McLaughlin: Modulation Therapeutics Inc: Patents & Royalties, Vice-President and Co-founder Other. Hazlehurst:Modulation Therapeutics Inc: Patents & Royalties, President and Co-founder Other.
Nucleic Acids Research, 2007
Comparative mutagenesis of 1,N 6-ethenoadenine (eA) and 8-oxoguanine (8-oxoG), two endogenous DNA... more Comparative mutagenesis of 1,N 6-ethenoadenine (eA) and 8-oxoguanine (8-oxoG), two endogenous DNA lesions that are also formed by exogenous DNA damaging agents, have been evaluated in HeLa and xeroderma pigmentosum variant (XPV) cell extracts. Two-dimensional gel electrophoresis of the duplex M13mp2SV vector containing these lesions established that there was significant inhibition of replication fork movement past eA, whereas 8-oxoG caused only minor stalling of fork progression. In extracts of HeLa cells, eA was weakly mutagenic inducing all three base substitutions in approximately equal frequency, whereas 8-oxoG was 10-fold more mutagenic inducing primarily G!T transversions. These data suggest that 8-oxoG is a miscoding lesion that presents a minimal, if any, block to DNA replication in human cells. We hypothesized that bypass of eA proceeded principally by an error-free mechanism in which the undamaged strand was used as a template, since this lesion strongly blocked fork progression. To examine this, we determined the sequence of replication products derived from templates in which a G was placed across from the eA. Consistent with our hypothesis, 93% of the progeny were derived from replication of the undamaged strand. When translesion synthesis occurred, eA!T mutations increased 3-fold in products derived from the mismatched eA: G construct compared with those derived from the eA: T construct. More efficient repair of eA in the eA: T construct may have been responsible for lower mutation frequency. Primer extension studies with purified pol g have shown that this polymerase is highly error-prone when bypassing eA. To examine if pol g is the primary mutagenic translesion polymerase in human cells, we determined the lesion bypass characteristics of extracts derived from XPV cells, which lack this polymerase. The eA: T construct induced eA!G and eA!C mutant frequencies that were approximately the same as those observed using the HeLa extracts. However, eA!T events were increased 5-fold relative to HeLa extracts. These data support a model in which pol g-mediated translesion synthesis past this adduct is error-free in the context of semiconservative replication in the presence of fidelity factors such as PCNA.
Frontiers in Oncology, 2012
Chronic myeloid leukemia (CML) is initially driven by the bcr-abl fusion oncoprotein. The identif... more Chronic myeloid leukemia (CML) is initially driven by the bcr-abl fusion oncoprotein. The identification of bcr-abl led to the discovery and rapid translation into the clinic of bcr-abl kinase inhibitors. Although, bcr-abl inhibitors are efficacious, experimental evidence indicates that targeting bcr-abl is not sufficient for elimination of minimal residual disease found within the bone marrow (BM). Experimental evidence indicates that the failure to eliminate the leukemic stem cell contributes to persistent minimal residual disease. Thus curative strategies will likely need to focus on strategies where bcr-abl inhibitors are given in combination with agents that specifically target the leukemic stem cell or the leukemic stem cell niche. One potential target to be exploited is the Janus kinase (JAK)/signal transducers and activators of transcription 3 (STAT3) pathway. Recently using STAT3 conditional knockout mice it was shown that STAT3 is critical for initiating the disease. Interestingly, in the absence of treatment, STAT3 was not shown to be required for maintenance of the disease, suggesting that STAT3 is required only in the tumor initiating stem cell population (Hoelbl et al., 2010). In the context of the BM microenvironment, STAT3 is activated in a bcr-abl independent manner by the cytokine milieu. Activation of JAK/STAT3 was shown to contribute to cell survival even in the event of complete inhibition of bcr-abl activity within the BM compartment. Taken together, these studies suggest that JAK/STAT3 is an attractive therapeutic target for developing strategies for targeting the JAK-STAT3 pathway in combination with bcr-abl kinase inhibitors and may represent a viable strategy for eliminating or reducing minimal residual disease located in the BM in CML.
Leukemia Research, 2012
In this study, we show that conditioned media (CM) generated from bone marrow (BM)-derived mesenc... more In this study, we show that conditioned media (CM) generated from bone marrow (BM)-derived mesenchymal stromal cells lead to BCR-ABL independent STAT3 activation. Activation of STAT3 is important not only for survival of CML cells but also for its protection against Nilotinib (NI), within the BM microenvironment. Reducing the expression of both JAK2 and TYK2 or utilizing a pan-JAK inhibitor blocked CM-mediated STAT3 activation and sensitized CML cells to NI-mediated cell death. Finally, we demonstrate that in patient-derived primitive leukemic cells, co-cultured with BM stromal cells, inhibition of BCR-ABL and JAK activity was a successful strategy to potentiate their elimination.
Cancer Research, 2010
Soluble factors and extracellular matrices from the bone marrow stroma, provides the essential mi... more Soluble factors and extracellular matrices from the bone marrow stroma, provides the essential microenvironment that contributes to the persistence of minimal residual disease found in patients with Chronic Myeloid Leukemia (CML), under treatment with tyrosine kinase inhibitors. We previously showed that in CML cells, bone marrow stroma-derived conditioned medium (CM) is sufficient to cause resistance to BCR-ABL inhibitors in a STAT3-dependent manner. In this study, we show that development of resistance in CM correlated with increased STAT3 phosphorylation and increased STAT3 DNA binding in CML cells. The activation of Stat3 in the context of CM was persistent even in the presence of BCR-ABL inhibitors. Moreover, the increase in DNA binding resulted in increased transcriptional activity of STAT3 and increased expression of MCL-1, Bcl-xl and Cyclin D1 in cells exposed to CM. We also found that CM-mediated increase in STAT3 activation requires JAK activity, since use of a pan JAK inh...
Biochemical Pharmacology, 2010
Bcr-abl kinase inhibitors have provided proof of principal that targeted therapy holds great prom... more Bcr-abl kinase inhibitors have provided proof of principal that targeted therapy holds great promise for the treatment of cancer. However, despite the success of these agents in treating chronic myelogenous leukemia (CML), the majority of patients continue to present with minimal residual disease contained within the bone marrow microenvironment. These clinical observations suggest that the bone marrow microenvironment may provide survival signals that contribute to the failure to eliminate minimal residual disease. The bone marrow microenvironment is comprised of multiple sub-domains which vary in cellular composition and gradients of soluble factors and matrix composition. Experimental evidence indicates that exposure of tumor cells to either bone marrow derived soluble factors or matrixes can confer a multi-drug resistance phenotype. Together, these data indicate that targeting such pathways may be a viable approach for increasing the efficacy of chemotherapy. Moreover, we propose that personalized medicine must go beyond understanding predictive models inherent to tumors but rather build predictive models that consider diversity in response due to interactions with the tumor microenvironment. This review will focus on CML, however, understanding the contribution of the bone marrow microenvironment could contribute to rationale combination therapy in other types of leukemia, multiple myeloma and solid tumors which metastasize to the bone.
Kimika, Dec 20, 2016
Saccharomycopsis (Syn. Endomycopsis) bubodii 2066 is an isolate from bubod, a starter used in mak... more Saccharomycopsis (Syn. Endomycopsis) bubodii 2066 is an isolate from bubod, a starter used in making rice wine in northern Philippines. We have shown that the yeast has amylolytic activity on raw sago starch. In our attempt to identify the putative raw starch-digesting amylase in S. bubodii, we determined the cDNA sequence of a glucoamylase gene. One primer pair that was designed based on a glucoamylase of Saccharomycopsis fibuligera HUT7212 (GLU1, NCBI Accession Number L25641.1) produced a sequence of 1234 base pairs. To obtain a wider coverage, a primer walking strategy was carried out using four primer pairs designed based on GLU1 gene. The generated sequence of 1535 base pairs shows 98.7 to 100% homology when aligned with glucoamylase genes from four strains of S. fibuligera suggesting that this glucoamylase is highly conserved between the Saccharomycopsis species. This work further reports a gene sequence of glucoamylase derived from Philippine-isolated yeast. The sequence is deposited in GenBank and assigned the accession number KP068007.1. The gene may be heterologously expressed in Saccharomyces cerevisiae for possible utilization in the direct conversion of raw sago starch to bioethanol.
... MUTAGENESIS STUDIES OF SINGLE AND TANDEM DNA DAMAGES BY SITE-SPECIFIC APPROACH Presented by J... more ... MUTAGENESIS STUDIES OF SINGLE AND TANDEM DNA DAMAGES BY SITE-SPECIFIC APPROACH Presented by Joel Hassan G. Tolentino, BS Major Advisor ... To the undergraduates I have worked with: Kushan, Joe, Charlayne and Marie, for being good students and for the ...
... MUTAGENESIS STUDIES OF SINGLE AND TANDEM DNA DAMAGES BY SITE-SPECIFIC APPROACH Presented by J... more ... MUTAGENESIS STUDIES OF SINGLE AND TANDEM DNA DAMAGES BY SITE-SPECIFIC APPROACH Presented by Joel Hassan G. Tolentino, BS Major Advisor ... To the undergraduates I have worked with: Kushan, Joe, Charlayne and Marie, for being good students and for the ...
Complete eradication of CML has not been possible in patients because of the presence of minimal ... more Complete eradication of CML has not been possible in patients because of the presence of minimal residual disease (MRD) in sanctuary sites like the bone marrow (BM). One of the reasons for MRD is the milieu of cytokines and growth factors present in the BM microenvironment, that contribute to BCR-ABL independent drug resistance in CML. For example, in the present study, we demonstrate the importance of STAT3-mediated drug resistance in the BM microenvironment by showing that conditioned media (CM) derived from both normal and patient-derived mesenchymal stem cells and osteoblasts leads to STAT3 phosphorylation (pSTAT3-Y705) and concomitant drug resistance to Nilotinib in CML cells. Inhibiting the activity or reducing the expression of JAK2 and TYK2 was necessary for sensitizing cells to Nilotinib in CM. Moreover, increased pSTAT3-Y705 levels were associated with increased STAT3 transcriptional activity and up-regulation of Mcl-1 and cyclin D1. Our study indicates that there is an inherent redundancy in CM-mediated STAT3 activation pathway because concomitant neutralization of two potent activators of STAT3, IL-6 and G-CSF, does not reverse CM-mediated protection against Nilotinib. Furthermore, utilizing a SCID-hu bone implant in vivo model, we show that K562 cells with reduced STAT3 showed significantly lower tumor burden, which could be attributed to not only the slower proliferation rate, but also to the observation that these cells underwent cell death in BM stromal derived CM. Finally, CD34+ cells from CML patients when exposed to CM showed an increase in STAT3 phosphorylation which correlated with the development of de novo resistance to Nilotinib-mediated cell death. Taken together our data indicate that STAT3 is an important target in CML and its direct inhibition, along with BCR-ABL inhibitors, will likely be the most effective therapeutic strategy for reversing resistance within the BM microenvironment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5033. doi:10.1158/1538-7445.AM2011-5033
Ciencia Administrativa, 2015
La marginacion que prevalece en una buena parte de los municipios de Mexico exige el diseno de po... more La marginacion que prevalece en una buena parte de los municipios de Mexico exige el diseno de politicas y estrategias que promuevan la organizacion de los productores agropecuarios y su participacion activa en el desarrollo economico y social de sus ambitos de competencia. El diseno de estas estrategias debe sustentarse en diagnosticos eficientes que identifiquen sus fortalezas y debilidades para dar atencion a sus necesidades prioritarias y aprovechar su potencial. En 2011 se realizo un diagnostico de las organizaciones agropecuarias, forestales y turisticas en el municipio de Soteapan, Veracruz, con el objetivo de identificar sus capacidades de organizacion, gestion, produccion y comercializacion, y determinar los factores que limitan su desarrollo, con base en el marco legal en el que estan constituidas. Los resultados muestran que las organizaciones estudiadas mantienen sistemas de produccion tradicionales, con una capacidad de gestion baja, y un mercado de corto alcance a nive...
Blood, Nov 16, 2012
Abstract 869 We previously reported that the linear peptide referred to as HYD1 induces necrotic ... more Abstract 869 We previously reported that the linear peptide referred to as HYD1 induces necrotic cell death in myeloma cell lines (Nair RR et al. Mol Cancer Ther. 2009 Aug;8(8):2441-51). We have now developed a more potent cyclic analog based on the active core region of the linear peptide which we now refer to as MTI-101. MTI-101, as a single agent, induces cell death in AML cell lines U937 and HL-60 with an IC50 value of 23.03 ± 0.67 and 36.06 ± 4.99 μM, respectively. Interestingly, unlike the conventional drugs therapies that succumb to cell adhesion mediated-drug resistance (CAM-DR), we found that MTI-101 kills U937 and HL-60 cells co-cultured with bone marrow stromal cells, with increased sensitivity and an IC50 value of 17.89 ± 2.47 and 24.61 ± 3.06 μM, respectively. Furthermore, again unlike the conventional drug therapies, MTI-101-mediated cell death was accompanied by oncosis and ATP depletion along with no observable caspase-3 activation indicative of a necrotic mode of cell death. More importantly, MTI-101 was able to induce cell death in relapsed primary AML patient CD34 progenitor cells but was devoid of activity in the CD34 progenitor cells obtained from healthy individuals. We have established that MTI-101 has robust activity as a single agent using multiple myeloma in vivo models. Our laboratory is currently pursuing the activity of MTI-101 using AML specific animal model. To delineate the cell surface targets responsible for MTI-101 actions in AML, we utilized biotin-conjugated MTI-101 as bait to pull down protein complexes involved in MTI-101 cell surface binding. Follow-up immuno-precipitation and western blotting studies confirmed that CD44 and ITGA4 are two proteins that are present in the MTI-101 cell surface binding complexes. Also, in addition to causing cell death, binding of MTI-101 to the cell surface, lead to activation of several cell survival pathways including induction of autophagy, activation of ERK ½ and PyK2. In order to determine if inhibition of these survival signals will lead to a better therapeutic outcome when utilizing MTI-101, we pretreated U937 cells with inhibitors of autophagy (chloroquine), ERK ½ (PD 98059) and Pyk2 (PF 562271) followed by MTI-101. We found that, pretreatment of cells with each inhibitor individually synergized with MTI-101 in inducing cell death in U937 cells. Taken together, MTI-101 is a peptidomimetic with a novel mechanism of action that can be exploited for the treatment of relapsed AML. Our studies provide preclinical rationale for continued development of this class of compounds for the treatment of relapsed AML and set the stage for designing rationale combination strategies for increasing the efficacy of MTI-101. Disclosures: McLaughlin: Modulation Therapeutics Inc: Patents & Royalties, Vice-President and Co-founder Other. Hazlehurst:Modulation Therapeutics Inc: Patents & Royalties, President and Co-founder Other.
Nucleic Acids Research, 2007
Comparative mutagenesis of 1,N 6-ethenoadenine (eA) and 8-oxoguanine (8-oxoG), two endogenous DNA... more Comparative mutagenesis of 1,N 6-ethenoadenine (eA) and 8-oxoguanine (8-oxoG), two endogenous DNA lesions that are also formed by exogenous DNA damaging agents, have been evaluated in HeLa and xeroderma pigmentosum variant (XPV) cell extracts. Two-dimensional gel electrophoresis of the duplex M13mp2SV vector containing these lesions established that there was significant inhibition of replication fork movement past eA, whereas 8-oxoG caused only minor stalling of fork progression. In extracts of HeLa cells, eA was weakly mutagenic inducing all three base substitutions in approximately equal frequency, whereas 8-oxoG was 10-fold more mutagenic inducing primarily G!T transversions. These data suggest that 8-oxoG is a miscoding lesion that presents a minimal, if any, block to DNA replication in human cells. We hypothesized that bypass of eA proceeded principally by an error-free mechanism in which the undamaged strand was used as a template, since this lesion strongly blocked fork progression. To examine this, we determined the sequence of replication products derived from templates in which a G was placed across from the eA. Consistent with our hypothesis, 93% of the progeny were derived from replication of the undamaged strand. When translesion synthesis occurred, eA!T mutations increased 3-fold in products derived from the mismatched eA: G construct compared with those derived from the eA: T construct. More efficient repair of eA in the eA: T construct may have been responsible for lower mutation frequency. Primer extension studies with purified pol g have shown that this polymerase is highly error-prone when bypassing eA. To examine if pol g is the primary mutagenic translesion polymerase in human cells, we determined the lesion bypass characteristics of extracts derived from XPV cells, which lack this polymerase. The eA: T construct induced eA!G and eA!C mutant frequencies that were approximately the same as those observed using the HeLa extracts. However, eA!T events were increased 5-fold relative to HeLa extracts. These data support a model in which pol g-mediated translesion synthesis past this adduct is error-free in the context of semiconservative replication in the presence of fidelity factors such as PCNA.
Frontiers in Oncology, 2012
Chronic myeloid leukemia (CML) is initially driven by the bcr-abl fusion oncoprotein. The identif... more Chronic myeloid leukemia (CML) is initially driven by the bcr-abl fusion oncoprotein. The identification of bcr-abl led to the discovery and rapid translation into the clinic of bcr-abl kinase inhibitors. Although, bcr-abl inhibitors are efficacious, experimental evidence indicates that targeting bcr-abl is not sufficient for elimination of minimal residual disease found within the bone marrow (BM). Experimental evidence indicates that the failure to eliminate the leukemic stem cell contributes to persistent minimal residual disease. Thus curative strategies will likely need to focus on strategies where bcr-abl inhibitors are given in combination with agents that specifically target the leukemic stem cell or the leukemic stem cell niche. One potential target to be exploited is the Janus kinase (JAK)/signal transducers and activators of transcription 3 (STAT3) pathway. Recently using STAT3 conditional knockout mice it was shown that STAT3 is critical for initiating the disease. Interestingly, in the absence of treatment, STAT3 was not shown to be required for maintenance of the disease, suggesting that STAT3 is required only in the tumor initiating stem cell population (Hoelbl et al., 2010). In the context of the BM microenvironment, STAT3 is activated in a bcr-abl independent manner by the cytokine milieu. Activation of JAK/STAT3 was shown to contribute to cell survival even in the event of complete inhibition of bcr-abl activity within the BM compartment. Taken together, these studies suggest that JAK/STAT3 is an attractive therapeutic target for developing strategies for targeting the JAK-STAT3 pathway in combination with bcr-abl kinase inhibitors and may represent a viable strategy for eliminating or reducing minimal residual disease located in the BM in CML.
Leukemia Research, 2012
In this study, we show that conditioned media (CM) generated from bone marrow (BM)-derived mesenc... more In this study, we show that conditioned media (CM) generated from bone marrow (BM)-derived mesenchymal stromal cells lead to BCR-ABL independent STAT3 activation. Activation of STAT3 is important not only for survival of CML cells but also for its protection against Nilotinib (NI), within the BM microenvironment. Reducing the expression of both JAK2 and TYK2 or utilizing a pan-JAK inhibitor blocked CM-mediated STAT3 activation and sensitized CML cells to NI-mediated cell death. Finally, we demonstrate that in patient-derived primitive leukemic cells, co-cultured with BM stromal cells, inhibition of BCR-ABL and JAK activity was a successful strategy to potentiate their elimination.
Cancer Research, 2010
Soluble factors and extracellular matrices from the bone marrow stroma, provides the essential mi... more Soluble factors and extracellular matrices from the bone marrow stroma, provides the essential microenvironment that contributes to the persistence of minimal residual disease found in patients with Chronic Myeloid Leukemia (CML), under treatment with tyrosine kinase inhibitors. We previously showed that in CML cells, bone marrow stroma-derived conditioned medium (CM) is sufficient to cause resistance to BCR-ABL inhibitors in a STAT3-dependent manner. In this study, we show that development of resistance in CM correlated with increased STAT3 phosphorylation and increased STAT3 DNA binding in CML cells. The activation of Stat3 in the context of CM was persistent even in the presence of BCR-ABL inhibitors. Moreover, the increase in DNA binding resulted in increased transcriptional activity of STAT3 and increased expression of MCL-1, Bcl-xl and Cyclin D1 in cells exposed to CM. We also found that CM-mediated increase in STAT3 activation requires JAK activity, since use of a pan JAK inh...
Biochemical Pharmacology, 2010
Bcr-abl kinase inhibitors have provided proof of principal that targeted therapy holds great prom... more Bcr-abl kinase inhibitors have provided proof of principal that targeted therapy holds great promise for the treatment of cancer. However, despite the success of these agents in treating chronic myelogenous leukemia (CML), the majority of patients continue to present with minimal residual disease contained within the bone marrow microenvironment. These clinical observations suggest that the bone marrow microenvironment may provide survival signals that contribute to the failure to eliminate minimal residual disease. The bone marrow microenvironment is comprised of multiple sub-domains which vary in cellular composition and gradients of soluble factors and matrix composition. Experimental evidence indicates that exposure of tumor cells to either bone marrow derived soluble factors or matrixes can confer a multi-drug resistance phenotype. Together, these data indicate that targeting such pathways may be a viable approach for increasing the efficacy of chemotherapy. Moreover, we propose that personalized medicine must go beyond understanding predictive models inherent to tumors but rather build predictive models that consider diversity in response due to interactions with the tumor microenvironment. This review will focus on CML, however, understanding the contribution of the bone marrow microenvironment could contribute to rationale combination therapy in other types of leukemia, multiple myeloma and solid tumors which metastasize to the bone.