Biomedical subjects

S B Howell

Publications and source records attributed to S B Howell.

At least 19 recordsLinked to original sources

PubMed2004

Improved targeting of platinum chemotherapeutics. the antitumour activity of the HPMA copolymer platinum agent AP5280 in murine tumour models.

AP5280 is a novel N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-bound platinum (Pt) therapeutic designed to increase the therapeutic index relative to conventional, small-molecule platinum agents. The platinum-polymer construct accumulates in solid tumours on the basis of increased capillary permeability. The bound platinum moiety is present as an N,O-Pt chelate at the distal end of a tetrapeptide linker, glycine-phenylalanine-leucine-glycine, and the weight-average molecular weight (Mw) of the construct is 22 kDa. The antitumour activity and toxicity of AP5280 were assessed in the syngeneic murine B16F10 and Lewis lung tumour models, and in the human ovarian carcinoma 2008 and head and neck squamous carcinoma UMSCC10b xenograft models. The maximum tolerated dose (MTD) of AP5280 was 6-fold greater than that of carboplatin (CBDCA) in vivo. AP5280 was active in all four tumour models, and it displayed a higher therapeutic index than CBDCA in each of these tumour models. The antitumour effect of AP5280 given at 16% of its MTD was equivalent to that produced by a MTD of CBDCA. Thus, consistent with the design goal for this drug, and despite being less potent than CBDCA, AP5280 produced less systemic toxicity relative to its antitumour activity and thus has a greater therapeutic index. On the basis of the improved therapeutic index evidenced in these models, AP5280 has been advanced into clinical trials.

Acrylamides↗

PubMed2003

Loss of atm sensitises p53-deficient cells to topoisomerase poisons and antimetabolites.

BACKGROUND: Ataxia-telangiectasia is a pleiotropic autosomal recessive disorder caused by mutations in the ATM gene. In addition to a profound cancer predisposition, another hallmark of ataxia-telangiectasia is radiosensitivity. Recently, p53-null mouse fibroblasts have been reported to be radiosensitised by the concurrent loss of ATM. MATERIALS AND METHODS: We compared the sensitivity of atm(+/+)/p53(-/-) and atm(-/-)/p53(-/-) mouse embryonic fibroblasts to different classes of chemotherapeutic agents using the MTT assay, Trypan Blue exclusion and fluorescence-activated cell sorting for cell cycle and apoptosis analyses. RESULTS: Loss of ATM function in p53-deficient cells resulted in a 2- to 4-fold increase in sensitivity to the topoisomerase I poisons camptothecin and topotecan, to the topoisomerase II poisons doxorubicin, epirubicin and etoposide, and to the antimetabolites 5-fluorouracil and gemcitabine, but not to the platinum compounds cisplatin, carboplatin and oxaliplatin, the taxanes docetaxel and paclitaxel, or to busulfan. Loss of ATM function did not result in increased apoptosis, but resulted in increased Trypan Blue staining in response to epirubicin, suggesting that processes other than apoptosis may mediate cytotoxicity. ATM deficiency did not alter the extent of G(1)/S or G(2)/M cell cycle phase accumulation produced by epirubicin, suggesting that enhanced sensitivity was not due to failure of checkpoint activation. CONCLUSIONS: We provide further evidence that ATM is involved in regulating cellular defences against some cytotoxic agents in the absence of p53. Tumour-targeted functional inhibition of ATM may be a valuable strategy for increasing the efficacy of anticancer agents in the treatment of p53-mutant cancers.

Animals↗

PubMed2002

The cellular pharmacology of oxaliplatin resistance.

Oxaliplatin is a third generation platinum compound that differs from cisplatin and carboplatin in having a broader spectrum of antitumour activity. Molecular studies suggest that oxaliplatin adducts are recognised and processed differently than those produced by the earlier generation Pt-containing drugs. We report here studies on the kinetics of the development of oxaliplatin resistance, and the changes in the cellular pharmacology of oxaliplatin that accompany the emergence of the resistant phenotype in five parental human tumour cell lines and their sub-lines selected for acquired oxaliplatin resistance in vitro. During selection, resistance did not substantially increase until after at least six cycles of oxaliplatin treatment. Oxaliplatin demonstrated schedule-dependency with a 1-h exposure being substantially less cytotoxic than a continuous exposure. Whole cell uptake was linear with concentration, but uptake in the resistant cells averaged only 27+/-10 S.D.% of that in the sensitive cells. Pt accumulation in DNA was markedly reduced in four of the five resistant cell lines, but this did not correlate with either IC(50) or total cellular accumulation. Four of the five resistant sub-lines also demonstrated increased tolerance to adducts in DNA that ranged from 3.1 to 7.6-fold. We conclude that development of acquired resistance to oxaliplatin is accompanied by independent defects in both whole cell uptake and in adduct formation.

Antineoplastic Agents↗

PubMed2001

Hypoxia-induced enrichment and mutagenesis of cells that have lost DNA mismatch repair.

Loss of DNA mismatch repair (MMR) increases the risk of spontaneous mutations. We sought to determine whether there was an interaction between hypoxia and MMR deficiency that might contribute to the phenomenon of tumor progression. Human colon carcinoma HCT116+ch2 (MMR-deficient) and HCT116+ch3 (MMR-proficient) sublines were exposed for varying periods of time to an environment of <0.1% O2 and pH as low as 6.1. When a population containing 5% MMR-deficient cells and 95% MMR-proficient cells was subjected to hypoxia for 72 h, the MMR-deficient cells were enriched by a factor of 2-fold in the surviving population, whereas no enrichment was detected in cells maintained under aerobic conditions. The potential of hypoxia to destabilize the genome was determined by measuring the frequency of clones in the surviving population resistant to very high concentrations of 6-thioguanine or cisplatin. A 72-h exposure to hypoxia did not increase the frequency of resistant clones in the MMR-proficient cells but produced a 7.8-fold increase in 6-thioguanine-resistant clones and a 2.5-fold increase in cisplatin-resistant clones in the MMR-deficient cells. Loss of MMR increased the frequency of mutations in a reporter vector sensitive to frameshift mutations in a microsatellite sequence. Exposure to hypoxia for a time period as short as 48 h further increased the number of mutations in both cell types, but the absolute number of mutants was higher in the MMR-deficient cells. These results indicate that hypoxia and its accompanying low pH enrich for MMR-deficient cells and that loss of MMR renders human colon carcinoma cells hypersensitive to the ability of hypoxia to induce microsatellite instability and generate highly drug-resistant clones in the surviving population.

Adenocarcinoma↗

PubMed2001

Enhanced expression and activity of DNA polymerase beta in human ovarian tumor cells: impact on sensitivity towards antitumor agents.

DNA polymerase beta, one of the most inaccurate DNA synthesizing enzymes, has been shown to confer genetic instability when up-regulated in cells, a situation found in several human cancers. Here, we demonstrated that enhanced activity and expression of this enzyme occur in the human ovarian tumor 2008/C13*5.25 cells, which are resistant to the antitumor agent cisplatin and hypersensitive to 6-thioguanine. We found that translesion synthesis across platinated DNA crosslinks as well as increased incorporation into DNA of 6-thioguanine took place in the 2008/C13*5.25 cells compared to the parental 2008 cells. Such features being molecular signatures of DNA polymerase beta, these findings suggest that deregulation of its expression in cancer cells may contribute to the modulation of the response to antitumor treatments and therefore to tumor progression.

Antimetabolites, Antineoplastic↗

PubMed2001

Quantification of tumor cell injury in vitro and in vivo using expression of green fluorescent protein under the control of the GADD153 promoter.

The GADD153 gene is strongly transcriptionally activated by many types of cellular injury and the magnitude of the change in GADD153 expression is proportional to the extent of damage. We developed a novel reporter system in which a chimeric gene containing the GADD153 promoter linked to the coding region of an enhanced green fluorescent protein (EGFP) gene was stably integrated into the genome of a clone of UMSCC10b head and neck carcinoma cells. Activation of the exogenous GADD153 promoter was quantified using flow cytometric measurement of EGFP expression following drug exposure. The exogenous GADD153 promoter in this clone was activated by N-methl-N'-nitro-N-nitrosoguanidine (MNNG) in a concentration-dependent manner with kinetics that closely paralleled perturbation of cell cycle phase distribution. EGFP expression was strongly activated by a variety of genotoxic agents including DNA cross-linking and methylating agents, oxygen free radicals, DNA intercalator, UV and gamma-radiation and hypoxia. When grown as a xenograft in nude mice, the stably transfected clone also demonstrated dose-dependent EGFP expression when measured 4 days after cisplatin treatment. The reporter system accurately categorized the relative potency of adducts produced by 6 related platinum-containing drugs. In conclusion, this reporter system can facilitate in vitro and in vivo screening for agents capable of producing cytotoxicity via a wide variety of different mechanisms, and can be utilized to investigate the relative potency of structurally related DNA adducts.

Animals↗

PubMed2001

P53 modulates the effect of loss of DNA mismatch repair on the sensitivity of human colon cancer cells to the cytotoxic and mutagenic effects of cisplatin.

This study examined how the DNA mismatch repair (MMR) system and p53 interact to maintain genomic integrity in the presence of the mutagenic stress induced by cisplatin (DDP). Sensitivity to the cytotoxic and mutagenic effect of DDP was assessed using a panel of sublines of the MMR-deficient HCT116 colon carcinoma cells in which MMR function had been restored by transfer of a copy of MLH1 on chromosome 3 or in which p53 function had been disabled by expression of HPV-16 E6. Loss of p53 function by expression of E6 in MMR-proficient HCT116+ ch3 cells conferred only 1.1-2.0-fold resistance to a panel of commonly used chemotherapeutic agents, whereas disruption of p53 in MMR-deficient HCT116 cells resulted in substantial levels of resistance to some agents (paclitaxel, 1.9-fold; gemcitabine, 2.7-fold; 6-thioguanine, 3.3-fold; and etoposide, 4.4-fold) but sensitization to other agents (topotecan, 2.5-fold; and DDP, 3.3-fold). Loss of MMR or p53 alone had only a minor effect on sensitivity to the mutagenic effect of DDP as measured by the appearance of variants resistant to 6-thioguanine, etoposide, topotecan, gemcitabine, and paclitaxel in the population 10 days later (1.0-2.4-fold), whereas loss of both p53 and MMR had a more profound effect (1.7-6.5-fold). Loss of both p53 and MMR increased the basal frequency insertion/deletion mutations detected by a shuttle vector-based assay to a greater extent than loss of either alone. In association with DDP-induced injury, loss of p53 or MMR alone resulted in 1.2- and 1.7-fold more mutations, whereas loss of both resulted in a 5.1-fold increase in mutant frequency. Examination of the impact of loss of p53 and/or MMR on the DDP-induced cell cycle checkpoint activation, p53 induction, ability of the cell to tolerate adducts in its DNA, and the rate of disappearance of platinum from genomic DNA indicated the effects of the loss of p53 and/or MMR on all of these parameters, suggesting a multifactorial etiology for the changes in sensitivity to the cytotoxic and mutagenic effects of DDP. These results indicate that p53 and MMR can cooperate to control sensitivity to the cytotoxic effect of DDP and to limit its mutagenic potential in the colon cancer cells.

Antineoplastic Agents↗

PubMed2001

Use of the ratio of time to progression following first- and second-line therapy to document the activity of the combination of oxaliplatin with 5-fluorouracil in the treatment of colorectal carcinoma.

BACKGROUND: It has been proposed that the activity of a second-line treatment regimen can be documented by showing that the time to progression (TTP) following second-line therapy is longer than the TTP following first-line therapy in the same patients. PATIENTS AND METHODS: The ratio of TTP during first and second-line therapy, identified as the growth modulation index (GMI), was determined in 34 patients with advanced colorectal cancer. First-line chemotherapy consisted of one of several schedules of leucovorin (LV)-modulated 5-fluorouracil (5-FU) or raltitrexed. Second-line therapy consisted of the combination of LV-modulated 5-FU and oxaliplatin (1-OHP). Patients were switched to second-line therapy upon evidence of progressive disease following first-line therapy. RESULTS: Median TTP following first-line therapy was 13 weeks (95% confidence interval (CI): 7.6-18.7), while median TTP following second-line therapy was 31 weeks (95% CI: 21.3-41.0). Sixteen patients (47%; 95% CI: 35%-59%), showed a GMI > or = 1.33, while the remaining 18 patients (53%; 95% CI: 40%-66%) had a GMI < 1.33. Log-rank analysis of the Kaplan-Meier curves of TTP following first- versus second-line therapy demonstrated a statistically significant difference in favour of second-line therapy (P = 0.0081). CONCLUSIONS: This study demonstrates the utility of the GMI as a tool for assessing the activity of novel second-line therapeutic programs.

Adult↗

PubMed2001

Intrathecal treatment of neoplastic meningitis due to breast cancer with a slow-release formulation of cytarabine.

DepoCyte is a slow-release formulation of cytarabine designed for intrathecal administration. The goal of this multi-centre cohort study was to determine the safety and efficacy of DepoCyte for the intrathecal treatment of neoplastic meningitis due to breast cancer. DepoCyte 50 mg was injected once every 2 weeks for one month of induction therapy; responding patients were treated with an additional 3 months of consolidation therapy. All patients had metastatic breast cancer and a positive CSF cytology or neurologic findings characteristic of neoplastic meningitis. The median number of DepoCyte doses was 3, and 85% of patients completed the planned 1 month induction. Median follow up is currently 19 months. The primary endpoint was response, defined as conversion of the CSF cytology from positive to negative at all sites known to be positive, and the absence of neurologic progression at the time the cytologic conversion was documented. The response rate among the 43 evaluable patients was 28% (CI 95%: 14-41%); the intent-to-treat response rate was 21% (CI 95%: 12-34%). Median time to neurologic progression was 49 days (range 1-515(+)); median survival was 88 days (range 1-515(+)), and 1 year survival is projected to be 19%. The major adverse events were headache and arachnoiditis. When drug-related, these were largely of low grade, transient and reversible. Headache occurred on 11% of cycles; 90% were grade 1 or 2. Arachnoiditis occurred on 19% of cycles; 88% were grade 1 or 2. DepoCyte demonstrated activity in neoplastic meningitis due to breast cancer that is comparable to results reported with conventional intrathecal agents. However, this activity was achieved with one fourth as many intrathecal injections as typically required in conventional therapy. The every 2 week dose schedule is a major advantage for both patients and physicians.

Adult↗

PubMed2001

Identification of genes that mediate sensitivity to cisplatin.

Cisplatin (cDDP) is effective against some human tumors, but many are intrinsically resistant and, even among initially sensitive tumors, acquired resistance develops commonly during treatment. It has not been possible to prove which biochemical mechanisms control sensitivity to cDDP. Gene knockout studies in yeast, Dictyostelium discoideum, and mammalian cells have begun to unambiguously identify genes whose products function to modulate the cytotoxicity of cDDP. This review summarizes information currently available about the function of these genes. This comprehensive compilation points to the involvement of regulatory pathways known to mediate apoptosis, cell cycle checkpoint activation, and transcriptional rescue as regulators of cDDP sensitivity. Elucidation of the molecular mechanisms that mediate cDDP resistance holds promise for the design of pharmacological strategies for preventing, overcoming, or reversing this form of drug resistance.

Antineoplastic Agents↗

PubMed2000

Synthesis, conformational analysis and bioactivity of Lan-7, a lanthionine analog of TT-232.

A sandostatin analog, TT-232 (D-Phe-c[Cys-Tyr-D-Trp-Lys-Cys]-Thr-NH2), exhibits strong antitumor effects both in vitro and in vivo. In order to study the structure-activity relationships of TT-232, we designed and synthesized an analog of TT-232, namely Lan-7, in which the disulfide bridge is replaced by a lanthionine monosulfide bridge. Conformational analysis by NMR spectroscopy and computer simulations revealed that Lan-7 and TT-232 adopt very similar conformations in solution, which are quite different from the preferred conformations of sandostatin. Lan-7 has significant growth inhibition effects on a number of human tumor cell lines. It can also induce apoptosis in human ovarian carcinoma 2008 cells. At the same time, Lan-7 produced no toxicity to normal human hematopoietic progenitor cells. All of these results indicate that the modification we made does not alter the anti-tumor activity of TT-232.

Antineoplastic Agents↗

PubMed2000

Targeted chemoradiation for advanced head and neck cancer: analysis of 213 patients.

BACKGROUND: To determine the survival results, patterns of relapse, and organ preservation effects of a targeted chemoradiation protocol for patients with advanced (stage III-IV) carcinoma of the head and neck. METHODS: Analysis of 213 patients with stage III-IV squamous cell carcinoma treated at UT Memphis between June 1993 and March 1998. Treatment included weekly intra-arterial infusions of cisplatin (150 mg/m(2)/ week x 4) rapidly delivered to the tumor bulk, simultaneous intravenous thiosulfate for systemic drug neutralization, and conventional external-beam irradiation (180-200 cGy/fraction) to a total dose of 68-72 Gy. RESULTS: Tumor response, toxicity, disease control above the clavicle, pattern of relapse, and survival. There were 89 events of grade III-IV toxicity and 6 treatment-related deaths (grade V). Complete response in the primary and regional sites was obtained in 171 of 213 (80%) and 92 of 151 (61%), respectively. The rate of clearance of regional disease after neck dissection was 98%. There were 51 of 195 recurrences (26%): 11 local (5.6%), 5 regional (2.6%), and 35 distant (17.9%). The Kaplan Meier plot projections for overall and cancer-related 5-year survival was 38.8% and 53.6%, respectively, whereas disease control above the clavicle was 74.3%. CONCLUSIONS: We believe this chemoradiation protocol represents an effective management scheme for patients with advanced head and neck cancer with a high rate of organ preservation and possibly improved survival.

Adult↗

PubMed2000

Increase in tumor GADD153 mRNA level following treatment correlates with response to paclitaxel.

PURPOSE: We investigated the relationship between the basal and treatment-induced change in the tumor expression of the drug resistance gene MDR1 and the cellular injury response gene GADD153, and clinical response to paclitaxel treatment. METHODS: MDR1 and GADD153 mRNA levels were measured by reverse transcriptase polymerase chain reaction (RT-PCR) in tumor samples obtained by fine needle aspiration biopsy from 14 patients before and 24 h after paclitaxel infusion. RESULTS: There was no difference between responders and non-responders with respect to either the basal MDR1 mRNA level or the change in MDR1 mRNA level at 24 h after treatment (P = 0.464). Likewise, there was no difference in basal GADD153 mRNA level between responders and non-responders. However, there was a significantly greater increase in GADD153 mRNA at 24 h in responders compared with non-responders (P = 0.005). An increase in GADD153 mRNA level of 1.5-fold or higher predicted response with a sensitivity of 86% and a specificity of 100%. CONCLUSIONS: An increase in GADD153 mRNA level reflects chemotherapy-induced damage sufficient to be manifest as a clinically detectable reduction in tumor volume. Measurement of the change in GADD153 mRNA level successfully identified patients destined to respond as early as 24 h post-treatment.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2000

Depletion of protein kinase C (PKC) by 12-O-tetradecanoylphorbol-13-acetate (TPA) enhances platinum drug sensitivity in human ovarian carcinoma cells.

Down-regulation of protein kinase C (PKC) by 12-Otetradecanoylphorbol-13-acetate (TPA) enhances the sensitivity of human ovarian carcinoma 2008 cells to various types of platinum compounds such as cisplatin (DDP), carboplatin and (-)-(R)-2-aminomethylpyrrolidine (1,1-cyclobutanedicarboxylato)-platinum(II) monohydrate (DWA) by a factor of two- to threefold. TPA enhanced the sensitivity of the DDP-resistant 2008/C13*5.25 subline to each of these three drugs to the same extent as for the 2008 cells. The extent of PKC down-regulation and drug sensitization depended on the duration of TPA exposure; maximum effect was achieved with a 48 h pretreatment. Sensitization was TPA concentration-dependent and was maximal at 0.05 microM TPA. 2008 cells expressed only the PKCalpha and PKCzeta isoforms. Western blot analysis revealed that whereas the expression of PKCalpha was reduced by TPA the level of PKCzeta was not affected. These results suggest that PKCalpha is the isotype responsive to TPA in these cells and that platinum drug sensitivity can be modulated by this isoform alone. In parallel to its effect on PKCalpha, TPA decreased cellular glutathione content by 30 +/- 3 (standard deviation (s.d.) % in 2008 cells and by 41 +/- 3 (s.d.) % in 2008/C13*5.25 cells. TPA also increased accumulation of DDP and DWA by 70%, although this effect was limited to the 2008/C13*5.25 cells. TPA rendered 2008 and 2008/C13*5.25 cells resistant to cadmium chloride by a factor of 3.7 and 3.6-fold respectively, suggesting a significant increase in cellular metallothionein content. Although the mechanism of TPA induced sensitization is not yet fully understood, this study points to a central role for PKCalpha in modulating platinum drug sensitivity.

Antineoplastic Agents↗

PubMed2000

Identification of genes differentially expressed in association with acquired cisplatin resistance.

The goal of this study was to identify genes whose mRNA levels are differentially expressed in human cells with acquired cisplatin (cDDP) resistance. Using the parental UMSCC10b head and neck carcinoma cell line and the 5.9-fold cDDP-resistant subline, UMSCC10b/Pt-S15, two suppressive subtraction hybridization (SSH) cDNA libraries were prepared. One library represented mRNAs whose levels were increased in the cDDP resistant variant (the UP library), the other one represented mRNAs whose levels were decreased in the resistant cells (the DOWN library). Arrays constructed with inserts recovered from these libraries were hybridized with SSH products to identify truly differentially expressed elements. A total of 51 cDNA fragments present in the UP library and 16 in the DOWN library met the criteria established for differential expression. The sequences of 87% of these cDNA fragments were identified in Genbank. Among the mRNAs in the UP library that were frequently isolated and that showed high levels of differential expression were cytochrome oxidase I, ribosomal protein 28S, elongation factor 1alpha, alpha-enolase, stathmin, and HSP70. The approach taken in this study permitted identification of many genes never before linked to the cDDP-resistant phenotype.

Cisplatin↗

PubMed2000

p53 interacts with the DNA mismatch repair system to modulate the cytotoxicity and mutagenicity of hydrogen peroxide.

This study focused on the question of how the DNA mismatch repair (MMR) system and p53 interact to maintain genomic integrity in the presence of the mutagenic stress induced by hydrogen peroxide (H(2)O(2)). The cytotoxic and mutagenic effects of H(2)O(2) were compared in four colon carcinoma sublines: HCT116, HCT116/E6, HCT116+ch3, and HCT116+ch3/E6, representing MMR(-)/p53(+), MMR(-)/p53(-), MMR(+)/p53(+), and MMR(+)/p53(-) phenotypes, respectively. Loss of p53 in MMR-proficient cells did not significantly alter cellular sensitivity to H(2)O(2), but disruption of p53 in MMR-deficient cells resulted in substantial resistance to H(2)O(2) (IC(50) values of 203.8 and 66.2 microM for MMR(-)/p53(-) and MMR(-)/p53(+) cells, respectively). The effect of loss of p53 and MMR function on sensitivity to the mutagenic effect of H(2)O(2) paralleled the effects on cytotoxic sensitivity. In MMR-deficient cells, loss of p53 resulted in a 3.5- and 2.2-fold increase in the generation of 6-thiogunaine and ouabain-resistant clones, respectively. Loss of MMR in combination with loss of p53 synergistically increased the frequency of frameshift mutations in the CA repeat tracts of the out-of-frame shuttle vector pZCA29 and further promoted instability of microsatellite sequences under H(2)O(2) stress. Flow cytometric analysis showed that H(2)O(2) treatment produced a G(l) and G(2)/M phase arrest in MMR(+)/p53(+) cells. Loss of MMR did not alter the ability of H(2)O(2) to activate either checkpoint; loss of p53 in either the MMR-proficient or deficient cells resulted in impairment of the G(l) arrest and a more pronounced G(2)/M arrest. H(2)O(2) caused a greater and more longed increase in p53 protein levels in MMR-proficient than in the MMR-deficient cells. The results demonstrate that the effect of disabling p53 function is modulated by the proficiency of the MMR system (and vice versa) and that there is an overlap between the functions of p53 and the MMR system with respect to the activation of apoptosis and mutagenesis after an oxidative stress.

Base Pair Mismatch↗

PubMed2000

Analysis of MLH1 and MSH2 expression in ovarian cancer before and after platinum drug-based chemotherapy.

Preclinical studies have demonstrated a relationship between DNA mismatch repair (MMR) status and sensitivity to cisplatin and carboplatin. MMR-deficient cells are resistant to both drugs, and selection for cisplatin resistance in vitro is sometimes accompanied by loss of MMR protein expression. We used immunohistochemical staining techniques to investigate hMLH1 and hMSH2 expression in paired ovarian tumor sections from 54 ovarian cancer patients before and after platinum-based therapy. We sought associations between hMLH1 and hMSH2 protein expression and clinical parameters known to be of prognostic significance as well as response to treatment and overall survival. hMLH1 and hMSH2 staining decreased significantly after platinum-based therapy. The percent of malignant cells that stained positive correlated with the intensity of nuclear staining for both proteins; staining for hMLH1 correlated well with staining for hMSH2. Unexpectedly, expression of nuclear hMLH1 correlated negatively with response to treatment. Expression of nuclear hMLH1 and hMSH2 was positively correlated with pretreatment CA125 level, and expression of nuclear hMSH2 was positively correlated with change in CA125 level after treatment. Tumor stage was associated with expression of nuclear hMSH2, and tumor histological subtype was associated with both hMLH1 and hMSH2 staining. No association was found between expression of either protein and overall survival. These results indicate that the tumor is biologically altered after chemotherapy consistent with treatment-induced selection for cells expressing lower hMLH1 and hMSH2 levels. However, immunohistochemical staining for either hMLH1 or hMSH2 was not highly predictive of drug sensitivity as measured by response or survival.

Adaptor Proteins, Signal Transducing↗

PubMed2000

Resistance to apoptosis in prostate cancer cells.

Androgen-independent prostate cancer cells are remarkably resistant to therapeutic agents that work by triggering apoptosis via the caspase cascade. The recent sequencing of the entire genome of one of the most radiation-resistant organisms known, Deinococcus radiodurans, yields some insight into how prostate cancer cells might mount such resistance to apoptosis. Rather than being attributable to any one mechanism, the extreme radiation resistance of D. radiodurans appears to reflect the expression of a large number of different systems capable of preventing, repairing, or tolerating DNA damage and a very high degree of redundancy in these systems. Many molecular alterations that may influence the threshold for apoptosis have already been described in advanced prostate cancer; changes in bcl-2, p53, and the androgen receptor have been the most extensively studied. Current information is consistent with the concept that individual prostate cancer cells express multiple antiapoptotic mechanisms. This conclusion implies that it will not be possible to enhance cellular sensitivity to therapeutics that activate apoptosis by disabling just one target in a pathway, because other proteins are likely to be available to assume its function. Likewise, even elimination of a whole pathway may have little effect on sensitivity because cellular viability is protected by so many different mechanisms. However, where molecular changes have a phenotypic consequence, they offer a window of opportunity for the development of novel therapeutic strategies. One such example is a recently identified small organic compound that can inhibit p53 function and thus protect normal tissues against radiation-induced apoptosis without impairing killing of p53-deficient tumor cells.

Androgen Antagonists↗