Clozapine alone versus clozapine and risperidone for refractory schizophrenia.
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Agranulocytosis↗
Biomedical subjects
Stanton L Gerson
Publications and source records attributed to Stanton L Gerson.
Targeted modulation of MGMT: clinical implications.
O(6)-Methylguanine DNA methyltransferase (MGMT) has been studied for >20 years as a gene that is associated with the mutagenicity and cytotoxicity induced by either methylating carcinogens or alkylating (methylating and chloroethylating) therapeutic agents. Pioneering studies of alkylating agents identified alkylated guanine at the O(6) position, the substrate of MGMT, as a potentially promutagenic and lethal toxic DNA lesion. MGMT plays a prominent role in DNA adduct repair that limits the mutagenic and cytotoxic effect of alkylating agents. Because of its role in cancer etiology and chemotherapy resistance, MGMT is of particular interest. In this article, the clinical effect of MGMT expression and targeted modulation of MGMT will be summarized.
Antineoplastic Agents, Alkylating↗
Peritransplant use of ultraviolet-B irradiation (UV-B) therapy is detrimental to allogeneic stem cell transplantation outcome.
Whole-body UV-B phototherapy has been used for the treatment of graft-versus-host disease (GVHD) of the skin and has systemic immunosuppressive and tolerogenic effects. We hypothesized that whole-body UV-B therapy would improve donor engraftment and decrease the incidence and severity of GVHD that is associated with decreased intensity allogeneic hematopoietic stem cell transplantation. This study tested the feasibility of using UV-B phototherapy that was initiated before grafting and continued until engraftment to determine its effect on transplantation outcome. Eight patients (median age, 55.5 years; range, 32-65 years) with hematologic malignancies were included. Allogeneic peripheral blood stem cells were obtained from matched related (n=5) or matched unrelated (n=3) donors. Conditioning regimen was fludarabine 30 mg/m2 intravenously for 5 days, cyclophosphamide 1 g/m2/d intravenously for 2 days, and equine antithymocyte globulin 30 mg/kg/d for 2 days. GVHD prophylaxis included cyclosporine, methylprednisolone, and escalating doses of narrowband UV-B (311 nm) according to skin tolerance, 3 days a week, from 10 days before to 28 days after transplantation. The conditioning regimen and the UV-B therapy were well tolerated. Two patients received all 14 prescribed UV-B treatments (cumulative doses of 2000 and 3260 mJ/cm2, respectively) and 6 patients received 8 to 13 treatments with a cumulative dose range of 528-3465 mJ/cm2. There was a rapid decrease in epidermal CD1a+ cells by day of transplantation. Myeloid engraftment was rapid. One patient had secondary engraftment failure at 3 months and another had mixed chimerism at day 100. Seven of 8 patients developed severe acute GVHD (grade III, n=5; grade IV, n=2). Six had skin involvement, 5 had gastrointestinal involvement, and 1 had liver involvement. Four patients died (2 from sepsis, 1 from acute GVHD, and 1 from chronic GVHD). Four patients are alive (130-287 days), 3 with extensive chronic GVHD. We conclude that extended peritransplant UV-B therapy at the standard minimally erythemogenic dose is detrimental to the outcome of allogeneic stem cell transplantation. It is unclear how UV-B at this immunsuppressive dose might have altered skin and systemic cytokine and immune cell compositions in the host and increased GVHD- and treatment-related mortalities. Different UV-B dose and schedules should be further explored. However, although other phototherapeutic modalities may be effective against GVHD, extended UV-B therapy should not be used during early phases of decreased conditioning allogeneic transplantation.
Adult↗
Randomised comparison of two B-cell purging protocols for patients with B-cell non-Hodgkin lymphoma: in vivo purging with rituximab versus ex vivo purging with CliniMACS CD34 cell enrichment device.
We investigated the feasibility, safety and efficacy of two B-cell purging methods in patients with CD20+ non-Hodgkin lymphoma (NHL) receiving autologous stsem cell transplantation. Myeloid and immune recoveries between the methods were compared. Twenty-seven patients were randomised to either in vivo purging with rituximab or ex vivo purging by CD34+ cell selection. Both purging methods were efficient at eliminating B-cells in infusates. When compared with in vivo purging, ex vivo purging was associated with CD34+ cell loss and delayed median neutrophil (10 d vs. 11 d) and platelet (12.5 d vs. 17 d) count recoveries. Lymphocyte recovery was similar in both groups, but immunoglobulin recovery was delayed after in vivo purging. Late-infectious complications were few in both arms. At a median follow-up of 27 months, 2-year probabilities of event-free survival (EFS) rates were 81% for in vivo purging and 76% for ex vivo purging (P = 0.66). When compared with 53 unpurged patients, all 27 purged patients had improved 3-year probabilities of overall survival (89% vs. 70%, P = 0.014) and a trend for improved EFS (78% vs. 57%, P = 0.075). In conclusion, although both purging methods were feasible and safe, rituximab purging was superior as it did not impair CD34+ cell mobilisation and was associated with faster myeloid recovery. Further studies are needed to determine whether rituximab purging is more effective than the use of unpurged autografts.
Adult↗
Long-term-infected telomerase-immortalized endothelial cells: a model for Kaposi's sarcoma-associated herpesvirus latency in vitro and in vivo.
Kaposi's sarcoma-associated herpesvirus (KSHV) is associated with Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman's disease. Most KS tumor cells are latently infected with KSHV and are of endothelial origin. While PEL-derived cell lines maintain KSHV indefinitely, all KS tumor-derived cells to date have lost viral genomes upon ex vivo cultivation. To study KSHV latency and tumorigenesis in endothelial cells, we generated telomerase-immortalized human umbilical vein endothelial (TIVE) cells. TIVE cells express all KSHV latent genes 48 h postinfection, and productive lytic replication could be induced by RTA/Orf50. Similar to prior models, infected cultures gradually lost viral episomes. However, we also obtained, for the first time, two endothelial cell lines in which KSHV episomes were maintained indefinitely in the absence of selection. Long-term KSHV maintenance correlated with loss of reactivation in response to RTA/Orf50 and complete oncogenic transformation. Long-term-infected TIVE cells (LTC) grew in soft agar and proliferated under reduced-serum conditions. LTC, but not parental TIVE cells, formed tumors in nude mice. These tumors expressed high levels of the latency-associated nuclear antigen (LANA) and expressed lymphatic endothelial specific antigens as found in KS (LYVE-1). Furthermore, host genes, like those encoding interleukin 6, vascular endothelial growth factor, and basic fibroblast growth factor, known to be highly expressed in KS lesions were also induced in LTC-derived tumors. KSHV-infected LTCs represent the first xenograft model for KS and should be of use to study KS pathogenesis and for the validation of anti-KS drug candidates.
Animals↗
Differential competitive resistance to methylating versus chloroethylating agents among five O6-alkylguanine DNA alkyltransferases in human hematopoietic cells.
P140K-MGMT and G156A-MGMT genes encode two O(6)-benzylguanine-resistant O(6)-alkylguanine DNA alkyltransferase proteins that confer a high degree of O(6)-benzylguanine and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) or O(6)-benzylguanine and temozolomide resistance to primary hematopoietic cells. In this study, we directly compared these and three other O(6)-benzylguanine-resistant MGMT genes for their ability to protect the human erythroleukemia cell line, K562, using a direct competitive selection strategy to identify the mutation that conferred the greatest degree of protection from O(6)-benzylguanine and either BCNU or temozolomide. MFG retroviral vector plasmids for each of these mutants [G156A-MGMT (ED(50) for O(6)-benzylguanine, 60 micromol/L); and P140K-MGMT, MGMT-2 (S152H, A154G, Y158H, G160S, L162V), MGMT-3 (C150Y, A154G, Y158F, L162P, K165R), and MGMT-5 (N157T, Y158H, A170S; ED(50) for benzylguanine, >1,000 micromol/L)] were mixed, and the virus produced from Phoenix cells was transduced into K562 cells. Stringent selection used high doses of O(6)-benzylguanine (800 micromol/L) and temozolomide (1,000 micromol/L) or BCNU (20 micromol/L) administered twice, and following regrowth, surviving clones were isolated, and the MGMT transgene was sequenced. None of the mutants was lost during selection. Using temozolomide, the enrichment factor was greatest for P140K-MGMT (1.7-fold). Using BCNU selection, the greatest enrichment was observed with MGMT-2 (1.5-fold). G156A-MGMT, which is the least O(6)-benzylguanine-resistant MGMT gene of the mutants tested, was not lost during selection but was selected against. The optimal mutant MGMT useful as a drug resistance gene may depend on whether a methylating or chloroethylating agent is used for drug selection.
Alkylating Agents↗
Phase II trial of the O6-alkylguanine DNA alkyltransferase inhibitor O6-benzylguanine and 1,3-bis(2-chloroethyl)-1-nitrosourea in advanced melanoma.
PURPOSE: 1,3-Bis(2-chloroethyl)-1-nitrosourea (BCNU) induces DNA damage via a chloroethyl adduct at the O(6) position of guanine, which can be repaired by O(6)-alkylguanine DNA alkyltransferase (AGT) expressed in melanoma. We postulated that the addition of O(6) benzylguanine (O(6)BG), a potent inactivator of AGT, would improve the clinical response to BCNU in melanoma. EXPERIMENTAL DESIGN: Patients had measurable disease, adequate organ function, and a corrected Diffusing capacity of the lung for carbon monoxide (DLCO) of > or =70% predicted. They were accrued into two cohorts based on prior chemotherapy. O(6)BG (120 mg/m(2)) was administered i.v. followed by BCNU (40 mg/m(2)) on an outpatient basis. Peripheral blood mononuclear cells (PBMC) were collected pre- and 18 hours post-O(6)BG to analyze AGT depletion. Treatment was every 6 weeks, and clinical response was assessed after every two cycles. RESULTS: Forty-two patients were enrolled, 22 of these patients were chemotherapy-naïve. In the chemotherapy-naïve cohort, there was a patient with a complete response (CR), 4 with stable disease (SD), 13 with progressive disease (PD), and 4 nonevaluable patients; the median time to progression was 80 days and the median survival was 211 days. In the prior-chemotherapy cohort, there were no responses, 3 SD, 15 PD, and 2 nonevaluable patients; median time to progression was 54 days and median survival was 120 days. AGT was depleted from PBMC in the 15 patients tested. Grades 3 to 4 myelosuppression was seen in 57% of patients; toxicities were similar between the two cohorts. CONCLUSIONS: O(6)BG/BCNU was successfully administered on an outpatient basis and depleted AGT from PBMC. However, significant myelosuppression was observed and the clinical outcome was not improved. Alternative mechanisms of resistance to melanoma cell death need to be investigated.
Adult↗
High-dose carmustine, etoposide, and cisplatin for autologous stem cell transplantation with or without involved-field radiation for relapsed/refractory lymphoma: an effective regimen with low morbidity and mortality.
Over a 10-year period (January 1993 to October 2002), 101 relapsed or refractory non-Hodgkin lymphoma patients were treated at our center with high-dose chemotherapy and autologous transplantation. The median patient age was 54 years (range, 25-70 years). Thirty-two patients had indolent (low-grade), 42 had aggressive (intermediate-grade), and 27 had very aggressive (high-grade) non-Hodgkin lymphoma. Thirty-six patients had primary refractory disease, 20 had a chemoresistant relapse, 35 patients had a chemosensitive relapse, and 10 patients were "initial high risk" patients. The median number of prior chemotherapy regimens was 2 (range, 1-5). The preparative regimen (BEP) was bischloroethylnitrosourea (BCNU) 600 mg/m 2 , etoposide 2400 mg/m 2 , and Platinol (cisplatin) 200 mg/m 2 given intravenously over 5 days. Within 3 weeks before transplantation, 70 patients received involved-field radiotherapy (IFR) 20 Gy to sites of currently active (>2 cm) or prior bulky (>5 cm) disease. Most patients (n = 93) received mobilized peripheral blood stem cells (median CD34 + cell dose, 6.7 x 10 6 /kg). Median neutrophil (>500/microL) and platelet (>20 000/microL, untransfused) recoveries were 11 days (range, 7-19 days) and 14 days (range, 7-36 days), respectively. At a median follow-up of 41 months (range, 4 to 118 months) for survivors, Kaplan-Meier 5-year probabilities of overall survival (OS) and disease-free survival (DFS) were 58.6% and 51.1%, respectively. Four patients (4%) died within 30 days of stem cell infusion (1 pulmonary embolism, 2 septicemias with multiorgan failure, and 1 progressive lymphoma). Two patients (2%) developed interstitial pneumonitis most likely secondary to high-dose BCNU. Three cases (3%) of secondary acute myelogenous leukemia occurred. On multivariate analysis, age (<60 or > or =60 years), histologic grade (low versus intermediate or high), the use of IFR, and chemotherapy response at baseline did not affect OS or DFS. Of 70 patients given IFR, 27 relapsed: 10 (37%) within and 17 (63%) outside the radiation field. The use of IFR did not affect either OS or DFS, probably because IFR was offered to patients with bulky or chemoresistant disease. BEP with or without IFR is a highly effective and well-tolerated regimen in the relapsed/refractory lymphoma setting. It has low morbidity and transplant-related mortality and a low incidence (3%) of posttransplantation malignancy.
Adult↗
Cotransplantation of HLA-identical sibling culture-expanded mesenchymal stem cells and hematopoietic stem cells in hematologic malignancy patients.
Mesenchymal stem cells (MSCs) are found in a variety of tissues, including human bone marrow; secrete hematopoietic cytokines; support hematopoietic progenitors in vitro; and possess potent immunosuppressive properties. We hypothesized that cotransplantation of culture-expanded MSCs and hematopoietic stem cells (HSCs) from HLA-identical sibling donors after myeloablative therapy could facilitate engraftment and lessen graft-versus-host disease (GVHD); however, the safety and feasibility of this approach needed to be established. In an open-label, multicenter trial, we coadministered culture-expanded MSCs with HLA-identical sibling-matched HSCs in hematologic malignancy patients. Patients received either bone marrow or peripheral blood stem cells as the HSC source. Patients received 1 of 4 study-specified transplant conditioning regimens and methotrexate (days 1, 3, and 6) and cyclosporine as GVHD prophylaxis. On day 0, patients were given culture-expanded MSCs intravenously (1.0-5.0 x 10(6)/kg) 4 hours before infusion of either bone marrow or peripheral blood stem cells. Forty-six patients (median age, 44.5 years; range, 19-61 years) received MSCs and HLA-matched sibling allografts. MSC infusions were well tolerated, without any infusion-related adverse events. The median times to neutrophil (absolute neutrophil count > or = 0.500 x 10(9)/L) and platelet (platelet count > or = 20 x 10(9)/L) engraftment were 14.0 days (range, 11.0-26.0 days) and 20 days (range, 15.0-36.0 days), respectively. Grade II to IV acute GVHD was observed in 13 (28%) of 46 patients. Chronic GVHD was observed in 22 (61%) of 36 patients who survived at least 90 days; it was extensive in 8 patients. Eleven patients (24%) experienced relapse at a median time to progression of 213.5 days (range, 14-688 days). The probability of patients attaining disease- or progression-free survival at 2 years after MSC infusion was 53%. Cotransplantation of HLA-identical sibling culture-expanded MSCs with an HLA-identical sibling HSC transplant is feasible and seems to be safe, without immediate infusional or late MSC-associated toxicities. The optimal MSC dose and frequency of administration to prevent or treat GVHD during allogeneic HSC transplantation should be evaluated further in phase II clinical trials.
Adult↗
N-benzoylstaurosporine (PKC412) inhibits Akt kinase inducing apoptosis in multiple myeloma cells.
Multiple myeloma is a clonal malignancy of plasma cells that invariably progresses to a chemoresistant state. The PI3K/Akt pathway mediates signals downstream of several growth factors involved in myeloma pathogenesis, and constitutive activation of Akt was observed in myeloma cells. We now report that a staurosporine derivative, N-benzoylated staurosporine or PKC412, induces cell death in myeloma cell lines (RPMI8226S, U266, MM1S and MM1R) with loss of mitochondrial membrane potential Delta psi m, caspase 3 and PARP cleavage. ZVAD.fmk, but not interleukin-6, rescued these cells from PKC412 effects. Upstream of the mitochondria, PKC412 inhibited Bad phosphorylation and attenuated Akt kinase activity by suppressing its phosphorylation on serine residue in its activation loop. Reduced phosphorylation of downstream Akt substrates GSK3 alpha/beta and FKHR was also noted. Stable transfection of 8226S cells with constitutively active Akt (8226S-myAkt) partially protected against PKC412 cytotoxicity. Primary myeloma cells isolated from refractory myeloma patients (n=4), were equally sensitive to PKC412 treatment. More importantly, PKC412 did not affect CFU-GM or BFU-E colony formation. In summary, our results demonstrate that PKC412 suppresses Akt kinase activation and induces apoptosis in myeloma cell lines, as well as primary resistant cells. PKC412 is an appropriate candidate for novel treatment protocols for multiple myeloma.
Amino Acid Chloromethyl Ketones↗
DNA repair defects in stem cell function and aging.
Cellular DNA is under constant challenge by exogenous and endogenous genotoxic stress, which results in both transient and accumulated DNA damage and genomic instability. All cells are equipped with DNA damage response pathways that trigger DNA repair, cell cycle arrest, and, if need be, apoptosis, to eliminate DNA damage or damaged cells. The consequences of these processes for stem cells can be profound: diminution in stem cell pools, or, because of altered gene expression, an increased chance for stem cell differentiation or malignant transformation. Furthermore, a number of DNA repair abnormalities are linked to premature aging syndromes, and these are associated with defects in the stem cell population. The specific DNA repair systems for which there are data regarding the impact of repair defects on stem cell function include O(6)-alkylguanine DNA alkyltransferase, nucleotide excision repair, base excision repair, mismatch repair, non-homologous DNA end-joining Fanconi's anemia protein complex, and homologous recombination. It has recently become clear that deficiencies of these processes are associated not only with cancer and/or aging but also with stem cell defects. This discovery raises the possibility of a link between aging and stem cell dysfunction. In this review, we provide evidence for a link between DNA repair systems and the maintenance and longevity of stem cells.
Aging, Premature↗
A phase I and pharmacodynamic study of fludarabine, carboplatin, and topotecan in patients with relapsed, refractory, or high-risk acute leukemia.
PURPOSE: A novel regimen designed to maximize antileukemia activity of carboplatin through inhibiting repair of platinum-DNA adducts was conducted in poor prognosis, acute leukemia patients. EXPERIMENTAL DESIGN: Patients received fludarabine (10 to 15 mg/m(2) x 5 days), carboplatin (area under the curve 10 to 12 by continuous infusion over 5 days), followed by escalated doses of topotecan infused over 72 hours (fludarabine, carboplatin, topotecan regimen). Twenty-eight patients had acute myelogenous leukemia (7 untreated secondary acute myelogenous leukemia, 11 in first relapse, and 10 in second relapse or refractory), 1 patient had refractory/relapsed acute lymphoblastic leukemia, and 2 patients had untreated chronic myelogenous leukemia blast crisis. Six patients had failed an autologous stem cell transplant. Patients ranged from 19 to 76 (median 54) years. Measurement of platinum-DNA adducts were done in serial bone marrow specimens. RESULTS: Fifteen of 31 patients achieved bone marrow aplasia. Clinical responses included 2 complete response, 4 complete response with persistent thrombocytopenia, and 2 partial response. Prolonged myelosuppression was observed with median time to blood neutrophils >/=200/microl of 28 (0 to 43) days and time to platelets >/=20,000/microl (untransfused) of 40 (24 to 120) days. Grade 3 or greater infections occurred in all of the patients, and there were 2 infection-related deaths. The nonhematologic toxicity profile was acceptable. Five patients subsequently received allografts without early transplant-related mortality. Maximum tolerated dose of fludarabine, carboplatin, topotecan regimen was fludarabine 15 mg/m(2) x 5, carboplatin area under the curve 12, and topotecan 2.55 mg/m(2) over 72 hours. An increase in bone marrow, platinum-DNA adduct formation between the end of carboplatin infusion and 48 hours after the infusion correlated with bone marrow response. CONCLUSIONS: Fludarabine, carboplatin, topotecan regimen is a promising treatment based on potential pharmacodynamic interactions, which merits additional study in poor prognosis, acute leukemia patients.
Adult↗
A randomized phase I and pharmacological trial of sequences of 1,3-bis(2-chloroethyl)-1-nitrosourea and temozolomide in patients with advanced solid neoplasms.
PURPOSE: O(6)-alkylguanine-DNA alkyltransferase (AGAT) is modulated by methylating agents, which, in turn, abrogates nitrosourea resistance in preclinical studies. The feasibility of administering various sequences of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and temozolomide (TEM) in patients with advanced solid neoplasms was evaluated in this Phase I and pharmacological study to assess this premise in the clinical setting. The study also sought to determine the maximum tolerated dose (MTD) levels of BCNU and TEM as a function of Seq, to characterize the pharmacokinetic (PK) behavior of TEM administered both before and after BCNU, assess AGAT fluctuations in peripheral blood mononuclear cells (PBMCs), and seek preliminary evidence of anticancer activity. EXPERIMENTAL DESIGN: Sixty-three patients were randomized to receive treatment with oral TEM daily on days 1-5 and BCNU administered i.v., either on day 1 before TEM [Sequence (Seq) B-->T] or day 5 after TEM (Seq T-->B). Treatment was repeated every 6 weeks. Blood sampling for PK studies was performed on both days 1 and 5 of course one. PBMCs were sampled to evaluate major sequence-dependent effects on AGAT levels. RESULTS: Neutropenia and thrombocytopenia were the principal dose-limiting toxicities of the BCNU/TEM regimen. These effects were more prominent in patients receiving Seq T-->B, resulting in a much lower MTD of 80/100 mg/m(2)/day compared with 150/110 mg/m(2)/day for Seq B-->T. Notable antitumor activity was observed in patients with glioblastoma multiforme, sarcoma, and ovarian carcinoma. No sequence-dependent PK effects were noted to account for sequence-dependent toxicological effects. At the MTD level, AGAT activity in PBMCs decreased 3-fold, on average, and AGAT fluctuations did not appear to be sequence-dependent. CONCLUSIONS: The principal toxicities of the BCNU/TEM regimen were neutropenia and thrombocytopenia, which were consistent and predictable, albeit sequence-dependent. Seq T-->B was substantially more myelosuppressive, resulting in disparate MTDs and dose levels recommended for subsequent disease-directed evaluations (150/110 and 80/100 mg/m(2)/day for Seq B-->T and T-->B, respectively). Sequence-dependent differences in TEM PK do not account for this clinically relevant magnitude of sequence-dependent toxicity. The characteristics of the myelosuppressive effects of BCNU/TEM, the paucity of severe nonhematological toxicities, and antitumor activity at tolerable doses warrant disease-directed evaluations on this schedule.
Adult↗
Limited lentiviral transgene expression with increasing copy number in an MGMT selection model: lack of copy number selection by drug treatment.
Retroviral vector integration into the human genome carries increased risk of oncogenesis with increasing integrations. To boost transgene expression for gene therapy, multiple integrations are often sought. We studied the relationship between the number of vector integrations and transgene expression and the effect that drug selection in an MGMT-selection model would have on vector copy number. K562 cells were transduced using a lentiviral vector and a library of clones was generated. Median proviral copy number was 4 and a positive correlation with transgene expression was observed. Transgene expression increased at a linear rate between 1 and 4 vector copies/cell, but was unpredictable at >4 integrations/cell. When lentivirus MGMT(P140K)-transduced K562 cells were treated with O(6)-benzylguanine (BG)/BCNU, there was no selection for increased median copy number in colony-forming units, despite strong selection pressure and an increase in transgene expression and activity. These data show a direct and linear correlation between MGMT(P140K) transgene expression and vector copy number. Strong BG/BCNU selective pressure does not result in preferential survival of high-copy-number clones but does select for strong transgene expression. Thus drug selection would not be expected to increase the risk of oncogenesis due to exaggerated selection in favor of high-copy-number vector integration.
Alkyl and Aryl Transferases↗
MGMT: its role in cancer aetiology and cancer therapeutics.
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Animals↗
Therapeutic impact of methoxyamine: blocking repair of abasic sites in the base excision repair pathway.
A major obstacle to effective treatment with alkylating agents in cancer is the presence of elaborate mechanisms of DNA repair. For instance, the methylating therapeutic agent, temozolomide forms O6-methylguanine (O6mG), 7-methylguanine (N7mG) and 3-methyladenine (N3mA) DNA adducts that are repaired by at least two mechanisms. The O6mG DNA adduct, a cytotoxic and genotoxic lesion, is repaired by O6-methylguanine DNA-methyltransferase (MGMT). Thus, MGMT is a major mechanism of resistance to methylating agents. Meanwhile, cell death caused by O6mG adducts is promoted by mismatch repair (MMR) system, such that deficiency in MMR is associated with pronounced resistance to methylating agents. N7mG, the dominant lesions formed by methylating therapeutic agents, and N3mA DNA adducts are removed by the base excision repair (BER) pathway. Efficient BER repair minimizes the impact of these lesions in normal and tumor cells. Thus, only when BER is disrupted, do these abundant N-methylated DNA adducts become highly cytotoxic. Most importantly, BER disruption is able to bypass other resistance factors such as MMR defects and high MGMT activity. BER, in fact, is an important drug-resistant factor because of its variety of substrates and the ability to rapidly and efficiently repair these DNA lesions. However, the impact of both active BER and inactive BER on anticancer therapy has yet to be fully studied. This review will establish the premise that targeting abasic sites formed during BER will disrupt this pathway and enhance the therapeutic efficacy of alkylating agents.
Animals↗
Phase I and correlative study of combination bryostatin 1 and vincristine in relapsed B-cell malignancies.
PURPOSE: Bryostatin 1 activates protein kinase C (PKC) with short-term exposure and results in depletion of PKC with prolonged exposure. Preclinical in vitro and in vivo studies demonstrate synergistic activity and increased tumor apoptosis in B-cell malignancies when a prolonged infusion of bryostatin 1 is followed by vincristine. EXPERIMENTAL DESIGN: We embarked on a Phase I trial of bryostatin 1 as a 24-h continuous infusion followed by bolus vincristine in patients with refractory B-cell malignancies other than acute leukemias. Twenty-four evaluable patients were enrolled. RESULTS: The dose-limiting toxicity was myalgia. The MTD and recommended Phase II dose of bryostatin 1 was 50 microg/m2/24 h followed by vincristine 1.4 mg/m2 (maximum total dose of 2 mg) repeated every 2 weeks. Significant antitumor activity was observed in this relapsed population, including patients who had failed high-dose chemotherapy. This included 5 durable complete and partial responses and 5 patients with stable disease lasting > or =6 months (range, 6-48+ months). Median time to response was 8 months. Correlative studies demonstrated a progressive increase in serum interleukin-6 with bryostatin 1 infusion followed by an additional increase after vincristine. Flow cytometry for detection of apoptosis in B and T cells showed an initial decrease in apoptotic frequency in CD5+ cells within 6 h of bryostatin 1 infusion compatible with its known increase in PKC activity in the majority of patients followed by a return to baseline or overall increase in apoptotic frequency after completion of infusion. All (5 of 5) patients who had an overall increase in apoptotic frequency in CD5+ cells achieved either a clinical response or prolonged stable disease. Four of these 5 patients did not have the initial decrement in apoptosis at 6 h. CONCLUSIONS: Given the lack of myelosuppression and early evidence of clinical efficacy, additional exploration of this regimen in non-Hodgkin's lymphoma and multiple myeloma is warranted.
Adult↗
Measurement of anti-cancer agent methoxyamine in plasma by tandem mass spectrometry with on-line sample extraction.
In this work, we present the development and validation of a tandem mass spectrometry method for the quantitative determination of methoxyamine (CH3ONH2), a potential new chemotherapeutic agent, in human and mouse plasma. Methoxyamine together with the internal standard (I.S.) methoxyl-D3-amine was directly derivatized in plasma sample with a novel chemical agent 4-(N,N-diethylamino)benzaldehyde. The product solution was injected into an on-line Oasis HLB extraction column (2.1 mm x 20 mm) for analyte extraction. After the elution of extractives, the derivatized analytes were monitored by the positive-electrospray-ionization mass spectrometry (ESI-MS-MS). The structures of derivatized analytes were elucidated by fragmentation. Quantitation of plasma methoxyamine was carried out by the multiple reaction monitoring (MRM) mode. This method had a linear calibration range of 1.00-1000 ng/ml with a correlation coefficient of 0.9999 for methoxyamine in both human and mouse plasma. The limit of detection (LOD) and limit of quantification (LOQ) for methoxyamine in plasma were 0.150 and 0.500 ng/ml, respectively. It was demonstrated that the method had high recovery and accuracy (90.1-94.7 and 90.1-96.3%), as well as excellent intra- and inter-assay precision (2.2 and 3.7%), at three concentration levels (5.00, 50.0, 500 ng/ml). This method has been used to analyze the plasma levels of methoxyamine in samples obtained from male CD1 mice after bolus intraperitoneal injection of 2, 5 and 20mg methoxyamine hydrochloride (CH3ONH2.HCl) per kilogram mouse.
Animals↗