Abstract P2-01-12: Development of prediction model for omission of sentinel lymph node biopsy in T1 breast cancer

INTRODUCTION

Axillary sentinel lymph node (SLN) biopsy is a standard method for axillary nodal staging in the treatment of breast cancer. However, along with the trends to SLN performed only without additional axillary lymph node dissection, it's time to be considered omission of SLN for selective patients. We developed a prediction model to assess the negative probability of sentinel lymph node metastasis, specifically focus on the patients with clinical T1 breast cancer.

METHODS and MATERIALS

The study group consisted of 513 consecutive patients with clinical T1 breast cancer, who had undergone primary surgery between 2007 and 2012. The clinicopathologic factors and imaging modalities including breast ultrasound (US), magnetic resonance imaging (MRI), chest computed tomography (CT), and positron emission tomography (PET) were evaluated. Patients who fulfilled our inclusion criteria were randomized into experimental and validation set by 3:1 ratio. In the experimental group (n = 256), multivariate logistic regression analysis was used to analyze the association of each variable with the likelihood of SLN metastases. A prediction model was developed based on the patients in the experimental group and was validated with internal patient cohorts.

RESULTS

Of the 513 patients, 119 (23.1%) were found to have SLN metastases. In univariate analysis, presence of lymphovascular invasion (P < 0.001) and suspicious finding of preoperative image studies (US, PET, and MRI, P < 0.001) were independent positive predictors of SLN metastases. In multivariate analysis of experimental group, estrogen receptor status (P = 0.012), presence of lymphatic invasion (P < 0.001), and suspicious finding of preoperative image studies (US, PET, and MRI, P < 0.001) were each associated with involvement of SLN. A prediction model based on this analysis consists of 9 rows including 6 variables (age, estrogen receptor status, presence of lymphatic invasion, and results of preoperative US, PET or CT, MRI). The sum of assigned points for all six variables made corresponding value of negative probability of SLN metastasis. The accuracy of prediction model applied to the validation group, as measured by the area under the receiver operating curve was 0.789.

CONCLUSIONS

The prediction model developed here may be a useful tool to assess SLN involvement for clinical T1 breast cancer patients. And prospective study for additional validation of the prediction model is currently in preparation, exploring the possibility of SLN biopsy omission.

Citation Format: Cho JN, Song EJ, Lee MH, Jung S-Y, Lee S, Kang H-S, Sim SH, Park IH, Lee KS, Kim YJ, Kim S-K, Kwon Y, Nam B-H, Lee ES. Development of prediction model for omission of sentinel lymph node biopsy in T1 breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-01-12.

Abstract P4-10-12: Psychosocial health of disease-free breast cancer survivors compared with cancer-free general population: Korean health examinee cohort study

Background/purpose: The number of long-term breast cancer survivors is increasing rapidly due to the growing rates of detection, incidence and improved survival. Quality of life (QOL) of physical and psychosocial health outcomes vary across the breast cancer survivors including diagnosis at different stages of breast cancer. There is little data regarding the psychosocial health of disease-free breast cancer survivors compared with those of general population. We conducted to assess the QOL, especially psychosocial health, of disease-free female survivors over 2 year after breast cancer diagnosis compared with cancer-free control women.

Methods: We used baseline data from the health examinee cohort, a part of the Korea Genome Epidemiology Study which is a large scaled cohort study established since 2001. This cohort has collected data of past medical history, socioeconomical factors (income, education, marital status and current employment status) and health behavioral factors (smoking, drinking, physical activity, BMI, menopausal status and subjective health status) of participants while they underwent regular health examination. The disease-free breast cancer survivors were defined as those who answered that they were ≥2 years from the initial diagnosis of breast cancer without recurrence and current treatment. Among the participants female subjects without history of any type cancer were randomly selected at 1:4 ratio by 5-year age groups, educational attainment level and household income as a comparison group. We analyzed Psychosocial Well-being Index-Short Form (PWI-SF) in these two groups. Subjects with score ≤8, 9–26, and 27 were classified as the 'healthy group', 'latent stress group', and 'stress group,' respectively.

Results: Total 347 survivors of breast cancer and 1,388 matched participants without cancer history were selected for analysis. Even after being matched for education and household income status, breast cancer survivors showed better psychosocial health status and health behaviors compared with matched comparison group. The prevalence of latent stress and stress group (vs healthy group) by PWI-SF score was 88.2% in breast cancer survivors and 89.9% in the matched female controls, showing borderline significant differences (p = 0.057). The prevalence rates of ever drinkers and smokers or obese women were lower and of those who exercised ≥150 min/week were higher in breast cancer survivors (p < 0.05). The total PWI-SF score was lower in breast cancer survivors, suggesting lower level of psychosocial stress level in breast cancer survivors. After adjusting for effects of other sociodemographic variables, breast cancer survivors were less likely to be included in stress group by 36% (OR = 0.64; 95% confidence interval [CI], 0.42–0.98).

Conclusions: The disease-free breast cancer survivors with regular health examination showed better psychosocial health status compared with matched general population. The better health behaviors in cancer survivors such as less alcohol drinking, low BMI, less history of smoking and more regular exercise, which have been identified in several previous cancer survivors studies might be attributed to their better psychosocial health status.

Citation Format: Lee MH, Park B, Song EJ, Park SJ, Kong S-Y, Lee ES. Psychosocial health of disease-free breast cancer survivors compared with cancer-free general population: Korean health examinee cohort study. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-10-12.

EFFECTS OF RESISTANCE EXERCISES AND COMPLEX DECONGESTIVE THERAPY ON ARM FUNCTION AND MUSCULAR STRENGTH IN BREAST CANCER RELATED LYMPHEDEMA

The incorporation of resistance exercises into the lifestyle of patients with lymphedema is understudied and an emerging interest. We investigated the effectiveness and results of adding a moderate intensity resistance exercise program for 8 weeks in conjunction with intensive CDT for 1 or 2 weeks (depending on severity) on arm volume, arm function, QOL, and muscular strength in patients with breast cancer-related lymphedema. This prospective, pilot trial included forty-four patients with a history of breast cancer who were beginning complex decongestive therapy for lymphedema. They were assigned to either the intervention (n = 22) or control (n = 22). groups. The intervention comprised of resis- tance band exercises 5 times a week for 8 weeks. These were initially supervised during the intensive lymphedema treatment, but performed independently during the study period. Limb volume, muscular strength, and the European Organization for Research and Treatment of Cancer QOL Questionnaire C30 (EORTC QLQ-C30), EORTC-Breast Cancer-Specific QOL Questionnaire (EORTC QLQ-BR23), and Disabilities of Arm, Shoulder, and Hand (DASH) questionnaires were assessed at baseline and at 8 weeks. After 8 weeks, the intervention group demonstrated statistically significant differences (p < 0.05) in the DASH score and muscular strength compared to the control group. Our results indicate that upper body resistance exercise demonstrates a positive effect on arm function and muscular strength without increasing arm volume in breast cancer related lymphedema during and shortly post intensive CDT lymphedema treatment.

Accurate genotyping of hepatitis C virus through nucleotide sequencing and identification of new HCV subtypes in China population

Nucleotide sequencing of the phylogenetically informative region of NS5B remains the gold standard for hepatitis C virus (HCV) genotyping. Here we developed a new methodology for sequencing new NS5B regions to increase the accuracy and sensitivity of HCV genotyping and subtyping. The eight new primers were identified by scanning the full-length NS5B regions from 1127 HCV genomic sequences found in HCV databases. The ability of each pair of primers to amplify HCV subtypes was scored, and the new primers were able to amplify the NS5B region better than the previously used primers, therefore more accurately subtyping HCV strains. Sequencing the DNA amplified by the new primer pairs can specifically and correctly detect the five standard HCV subtypes (1a, 2a, 3b, 6a and 1b). We further examined patient samples and found that the new primers were able to identify HCV subtypes in clinical samples with high sensitivity. This method was able to detect all subtypes of HCV in 567 clinical samples. Importantly, three novel HCV subtypes (1b-2a, 1b-2k and 6d-6k) were identified in the samples, which have not been previous reported in China. In conclusion, sequencing the NS5B region amplified by the new NS5B primers is a more reliable method of HCV genotyping and a more sensitive diagnostic tool than sequencing using the previously described primers, and could identify new HCV subtypes. Our research is useful for clinical diagnosis, guidance of clinical treatment, management of clinical patients, and studies on the epidemiology of HCV.

Abstract P1-01-19: Role of axillary clearance with tumor positive sentinel node in mastectomy group: Is the results of ACOSOG Z0011 trial adaptable to mastectomy patient?

Background: Recent data from ACOSOG Z0011 trial or AMAROS trial suggest that axillary lymph node dissection(ALND) may be unnecessary for patients with positive sentinel lymph node biopsy(SLNB) receiving breast conserving surgery(BCS) with irradiation. However, consensus statements and guidelines until recently recommended that patients with mastectomy and tumor positive sentinel node undergo completion ALND. In this preliminary study, we compared these patients who did not undergo ALND with the patients who received BCS with SLNB only and irradiation and we analyzed the locoregional recurrence rate to show no differences of outcomes between two groups.

Method: We identified 6,163 women with invasive breast cancer who underwent surgical resection at the National Cancer Center (Goyang,Gyeonggi-do,Korea) between January 2000 to December 2011. Clinico-pathological data obtained from prospective collecting medical database of our institution were analyzed retrospectively. The mastectomy with positive SLNB group was 47 patients and BCS with positive SLNB and irradiation group was 172 patients. The primary end point was loco-regional recurrence rate.

Result : Clinical and tumor characteristics were similar between two groups except T stage and receptor status. The mean tumor size was 5.5cm with mastectomy group and 3.5cm with BCS group. The median number of nodes removed was three. There was not a single case of locoregional recurrence in both groups. At a median follow-up of 53.5 months (last follow-up, May 2013), 5-year overall survival was 85.7% with mastectomy and 97.3% with BCS group.

Conclusion : In our study, there was no case of locoregional recurrence as above. This results lend weight to the argument that SLNB without ALND may be reasonable management for selected patients with appropriate surgery and adjuvant systemic therapy. This study can be regarded as a preliminary study with a sufficient value despite of the prognosis showed some statistical differences between two groups. It resides in the difference of initial stage of patients of two groups. We will present additional data compared with the mastectomy with axillary clearance group at the meeting.

Acknowledgement This work was supported by grant from the National Cancer Center Korea (1210331-2).

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-01-19.

Abstract P3-08-14: Could the preoperative systemic therapy be a risk factor for breast cancer-related lymphedema in stage II/III breast cancer?

Background: The breast cancer-related lymphedema (LE) has been known to be closely related to axillary lymph nodes dissection (ALND), chemotherapy, and radiation therapy. In this study, we evaluated whether the sequence of systemic chemotherapy and surgery could be a predictive factor in stage II/III breast cancer.

Methods and Materials: A total of 867 patients with stage II/III breast cancer, who underwent curative surgery with adequate systemic therapy from 2004 to 2009, were retrospectively analyzed. Adjuvant chemotherapy (ACT) was performed in 571 patients (65.9%) and preoperative systemic chemotherapy (PSC) in 296 (34.1%). We evaluated the incidence of LE by clinicopathologic factors and treatments.

Results: At a median follow-up of 5.1 years (range, 3.0-8.3 years), 360 patients (41.5%) had experienced LE, 244 patients have retained LE (permanent LE), and 116 patents were normalized. The overall 5-year cumulative incidence of LE was 17%. LE occurred in 188 patients (32.9%) in patients with ACT, 172 patients (58.1%) with PSC (P&lt;0.001), permanent LE in 121 (21.2%) with ACT, 123 (41.6%) with PSC (P&lt;0.001), respectively. Multivariate analysis showed that PSC (hazard ratio [HR], 1.65; P&lt;.001), radiotherapy (HR, 2.24; P&lt;0.01), ALND (HR, 1.41; P = 0.04), and nodal stage (HR, 1.93; P = 0.04) were independent risk factors for LE occurrence. For the permanent LE, PSC (HR, 1.44; P = 0.05), radiotherapy (HR, 2.79; P&lt;0.01), ALND (HR, 1.77; P&lt;0.01), and nodal stage (HR, 3.01; P = 0.02) showed the associations.

Conclusions: The risk factors associated with LE were advanced stage, ALND and radiotherapy. PSC was one of predictors for transients LE. However, further evaluation should be done whether it is a risk factor for permanent LE.

This research was supported by National Cancer Center Grant NCC-1210181-2 by the National Cancer Center, Republic of Korea.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-08-14.

Rac1 regulates heat shock responses by reorganization of vimentin filaments: identification using MALDI-TOF MS

Rac1 has been implicated in a wide variety of biological processes, including actin remodeling and various signaling cascades. Here we have examined whether Rac1 might be involved in heat shock-induced cell signaling. We found that Rat2 stable cells expressing a dominant negative Rac1 mutant, RacN17 (Rat2-RacN17), were significantly more tolerant to heat shock than control Rat2 cells, and simultaneously inhibited the activation of SAPK/JNK by heat shock compared to control Rat2 cells. However, no discernible effect was observed in typical heat shock responses including total protein synthesis and heat shock protein synthesis. To identify the proteins involved in this difference, we separated the proteins of both Rat2 and Rat2-RacN17 cell lines after heat shock using two-dimensional gel electrophoresis and identified the differentially expressed proteins by matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) after in-gel trypsin digestion. Differentially expressed proteins between two cell lines were identified as vimentin. Rat2-RacN17 cells showed significant changes in vimentin as well as marked changes in vimentin reorganization by heat shock. The vimentin changes were identified as N-terminal head domain cleavage. These results suggest that Rac1 plays a pivotal role in the heat shock-induced signaling cascade by modifying intermediate vimentin filaments.

[Identification of proteome molecules by proteomics using two-dimensional gel electrophoresis and MALDI-TOF MS]

Genomic technologies have enabled rapid accumulation of information from complex biological systems over the last two decades. The complete DNA sequence is now known for many organisms and the informational database obtained from genome sequencing projects has provided the base for the specification of proteome - the protein complement of genome. Genomic functions can be inferred from the analysis of gene structure and gene expression profiles because proteins are the functional molecules of an organism. Integrated technologies including protein separation, identification, characterization and information manage system are essential to analyze the proteins in complex cellular matrix. This study is focusing on the strategies of proteome analysis using sample preparation, 2-dimensional gel electrophoresis, processing of protein spots and identification of proteins, protein-protein interaction and posttranslational modification using MALDI-TOF-MS. 2-D gel electrophoresis is currently the most powerful protein separation technique and MALDI-TOF MS is powerful identification technique for protein and peptides as a sensitive, rapid, and high resolution analytical method. The developed integrated proteome technologies are very useful to understand the biological phenomena at molecular level by identifying the new molecules and their modifications in various cellular processes, and can be applied for biotechnology including medical science.

Mapping of the locus for cholestasis-lymphedema syndrome (Aagenaes syndrome) to a 6.6-cM interval on chromosome 15q

Patients with cholestasis-lymphedema syndrome (CLS) suffer severe neonatal cholestasis that usually lessens during early childhood and becomes episodic; they also develop chronic severe lymphedema. The genetic cause of CLS is unknown. We performed a genome screen, using DNA from eight Norwegian patients with CLS and from seven unaffected relatives, all from an extended pedigree. Regions potentially shared identical by descent in patients were further characterized in a larger set of Norwegian patients. The patients manifest extensive allele and haplotype sharing over the 6.6-cM D15S979-D15S652 region: 30 (83.3%) of 36 chromosomes of affected individuals carry a six-marker haplotype not found on any of the 32 nontransmitted parental chromosomes. All Norwegian patients with CLS are likely homozygous for the same disease mutation, inherited from a shared ancestor.

Oxidative modification of nucleoside diphosphate kinase and its identification by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Nucleoside diphosphate kinase (NDPK, Nm23) has been implicated as a multifunctional protein. However, the regulatory mechanism of NDPK is poorly understood. We have examined the modification of NDPK in oxidative stresses. We found that oxidative stresses including diamide and H(2)O(2) treatment cause disulfide cross-linking of NDPK inside cells. This cross-linking was reversible in response to mild oxidative stress, and irreversible to strong stress. This suggests that disulfide cross-linked NDPK may be a possible mechanism in the modification of cellular regulation. To confirm this idea, oxidative modification of NDPK has been performed in vitro using purified human NDPK H(2)O(2) inactivated the nucleoside diphosphate (NDP) kinase activity of NDPK by producing intermolecular disulfide bonds. Disulfide cross-linking of NDPK also dissociated the native hexameric structure into a dimeric form. The oxidation sites were identified by the analysis of tryptic peptides of oxidized NDPK, using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Intermolecular cross-linking between Cys109-Cys109, which is highly possible based on the X-ray crystal structure of NDPK-A, and oxidations of four methionine residues were identified in H(2)O(2)-treated NDPK. This cross-linkng was confirmed using mutant C109A (NDPK-A(C109A)) which had similar enzymatic activity as a wild NDPK-A. Mutant NDPK-A(C109A) was not cross-linked and was not easily denatured by the oxidant. Therefore, enzymatic activity and the quaternary structure of NDPK appear to be regulated by cross-linking with oxidant. These findings suggest one of the regulatory mechanisms of NDPK in various cellular processes.

Effects of cytoskeletal inhibitors on the accumulation of vincristine in a resistant human lung cancer cell line with high level of polymerized tubulin

We have previously established a vincristine resistant human lung cancer cell line (PC-9/VCR) by a stepwise exposure of parental line PC-9 to vincristine. In this study the resistant cells showed enhanced vincristine cytotoxicity in the presence of cytochalasin B and D. The increase in cytotoxicity was associated with an enhanced accumulation and a reduced efflux of vincristine. Colchicine and taxol had no effects on vincristine accumulation. Several cytoplasmic proteins were overexpressed in the resistant cells. The two major ones, with molecular weights of 58.8 kDa and 83.2 kDa, were shown by western blotting to be beta-tubulin and actin, respectively. The polymerized tubulin level in the resistant cells was significantly (p < 0.05) higher than that in the parental cells. These results suggest that the cellular cytoskeletons might play an important role in VCR resistance in the PC-9/VCR human lung cancer cell line.

Functional identification of the mouse circadian Clock gene by transgenic BAC rescue

As a complementary approach to positional cloning, we used in vivo complementation with bacterial artificial chromosome (BAC) clones expressed in transgenic mice to identify the circadian Clock gene. A 140 kb BAC transgene completely rescued both the long period and the loss-of-rhythm phenotypes in Clock mutant mice. Analysis with overlapping BAC transgenes demonstrates that a large transcription unit spanning approximately 100,000 base pairs is the Clock gene and encodes a novel basic-helix-loop-helix-PAS domain protein. Overexpression of the Clock transgene can shorten period length beyond the wild-type range, which provides additional evidence that Clock is an integral component of the circadian pacemaking system. Taken together, these results provide a proof of principle that "cloning by rescue" is an efficient and definitive method in mice.

Identification and localization of K+ channels in the mouse retina

Voltage-gated potassium channels are differentially expressed in the brain, and recent studies have shown that K+ channels show subcellular localization. We characterized the distribution of five different K+ channels in the mouse retina. Each channel was distributed in a unique pattern in the retina and was localized to specific subcellular domains within a given retinal neuron. Kv1.4 and Kv4.2 were consistently found in axonal and somatodendritic portions, respectively, consistent with previous studies in brain. In contrast, Kv1.2, Kv1.3, and Kv2.1 showed variable subcellular distribution depending upon cellular context. These results suggest that no one K+ channel is distributed over the entire length of the neuron to provide a "housekeeping" level of membrane potential stabilization. Instead, we propose that each K+ channel is associated with a specific subcellular functional module, and each local K+ conductance responds uniquely to local voltage and second messenger signals.

The Shaker-like potassium channels of the mouse rod bipolar cell and their contributions to the membrane current

RT PCR on mRNA from enzymatically dissociated, isolated bipolar cells showed that these neurons express the Shaker-like K+ channels Kv1.1, Kv1.2, and Kv1.3. Immunohistochemical localization showed each channel to have a unique subcellular distribution: Kv1.1 immunoreactivity was detected in the dendrites and axons terminal, whereas Kv1.2 and Kv1.3 subunits were localized to the axon and the postsynaptic membrane of the rod ribbon synapse, respectively. Whole-cell patch-clamp recordings indicated that the activation voltage of the delayed rectifier current of the isolated bipolar cell and the inhibitory constants for current blockade by TEA, 4-AP, and Ba2+ were similar to these same properties measured for Kv1.1 expressed in oocytes. However, the TEA and 4-AP inhibitory constants for the bipolar cell current differed from the inhibitory constants for Kv1.2 or Kv1.3. These results suggest that the current of the isolated rod bipolar cell is most similar to Kv1.1 but that all three channels may function in the intact retina to allow complex modulation of retinal synaptic signals.

Potentiation of growth inhibition due to vincristine by ascorbic acid in a resistant human non-small cell lung cancer cell line

A human cell subline (PC-9/VCR) resistant to vincristine was established from non-small cell lung cancer PC-9 cells by incremental exposure of the cells to vincristine. The resistant cells showed phenotypic resistance to vincristine (10-fold), colchicine (6.9-fold) and cisplatin (1.4-fold) but they showed sensitivity to other chemotherapeutic agents including melphalan and etoposide VP-16. The characteristics of the vincristine resistance was partially inhibited (5-7-fold) by co-treatment of PC-9/VCR cells with a nontoxic concentration of L-ascorbic acid (25 micrograms/ml). Co-treatment or 96 h pre-treatment with ascorbic acid resulted in potentiation of the vincristine effect on the resistant, but not on the sensitive, cell line. The growth inhibition due to vincristine treatment after 24 or 96 h growth in ascorbic acid-free medium was decreased in the resistant as well as in the sensitive cell line. In both cell lines, enhanced growth rate has been shown after ascorbic acid treatment. Similarly, cross-resistance of PC-9/VCR cells to colchicine could also be blocked by ascorbic acid. In addition, a nontoxic concentration of verapamil, a known multidrug resistance inhibitor, did not affect the resistant phenotype of PC-9/VCR cells. These findings suggest that an ascorbic acid-sensitive mechanism may be involved in drug resistance per se in the human lung cancer cells, which differs from the classical phosphoglycoprotein-mediated or previously reported non-phosphoglycoprotein-mediated multidrug resistance.

Ascorbic acid increases drug accumulation and reverses vincristine resistance of human non-small-cell lung-cancer cells

A human lung-cancer PC-9 subline with acquired resistance to vincristine (VCR), a chemotherapeutic agent, was established with incremental increases of the drug. The resistant PC-9 subline (PC-9/VCR) shows a 12-fold increase in resistance to VCR and a unique cross-resistance pattern: high cross-resistance to the potent VCR analogue colchicine (6.9-fold) and vinblastine (2.5-fold); lower cross-resistance to actinomycin D (1.8-fold), cisplatin (1.2-fold) and adriamycin (1.3-fold) and a sensitivity to melphalan and VP-16 which is similar to that of the parental cell line. A reduced accumulation of VCR in the resistant cells was demonstrated. Interestingly, the VCR resistance of the PC-9/VCR cell line was partially reversed by ascorbic acid, and the drug uptake was enhanced. In contrast, ascorbic acid had no effect on drug tolerance and drug accumulation was not observed in either PC-9 parental cells or known multidrug-resistant (MDR) cells, suggesting that VCR resistance in PC-9/VCR cells results essentially from reduced drug accumulation. It is worth noting that, whereas reduced drug accumulation in the PC-9/VCR cells was susceptible to modulation by ascorbic acid, the increased efflux rate characteristic of the resistant cells was not. Further, there was a higher efflux rate in resistant cells than in parental cells. DNA Southern- and RNA Northern-blot hybridization analyses indicate that PC-9/VCR cells do not contain amplified mdr genes or overexpress P-glycoprotein. In addition, the calcium-channel blocker verapamil, which acts as a competitive inhibitor of drug binding and efflux, did not affect the resistant phenotype of PC-9/VCR cells. These findings suggest an ascorbic acid-sensitive drug uptake mechanism which is important in mediating VCR resistance per se in human lung-cancer cells; this differs from the P-glycoprotein-mediated MDR mechanism.

[The efflux of intracellular vincristine in drug-resistant human lung cancer cells is not mediated by P-glycoprotein]

A subline (PC-9/VCR) of the human lung adenocarcinoma cell line (PC-9), derived by in vitro exposure to vincristine (VCR), exhibited a 10-12-fold resistance to VCR by MTT and HTCA assay. Compared to the parental cell line (PC-9), PC-9/VCR-resistant cells displayed a reduced accumulation of VCR. The rate of VCR efflux was shown to be enhanced by PC-9/VCR. Unlike multidrug resistance, this efflux was independent of P-glycoprotein overexpression as determined by the Northern blotting method. In addition, PC-9/VCR showed no collateral sensitivity to verapamil. This resistant subline only showed 6.9-fold and 2.5-fold cross resistance to colchicine and vinblastine, respectively. This preliminary result indicates that defective drug accumulation in PC-9/VCR is due to other mechanisms possibly involving the microtubule assembly.

The potassium channel MBK1 (Kv1.1) is expressed in the mouse retina

1. The neurons of the retina have electrical properties that are different from those of most of the other neurons of the central nervous system. To identify the voltage-gated ion channels found in the retina, we screened mouse retinal cDNA libraries with oligonucleotide probes homologous to the mammalian K+ channel MBK1 (Kv1.1) and ligated two partial clones to produce a full-length clone with no significant differences from MBK1. 2. Expression of MBK1 mRNA was determined by RNAse protection. MBK1 mRNA was detected in retinal RNA and was also detected in brain, liver, and heart RNAs. 3. We transcribed the full-length clone, injected it into oocytes of Xenopus laevis, and measured the membrane currents 2 to 6 days later. Depolarization from a holding voltage of -90mV induced a slowly activated outward current with a peak value as large as 20 microA. The current inactivated very slowly with a single exponential time course [mean time constant, 6.5 +/- 0.4 sec (SEM) for activation voltage of -10mV]. 4. The outward current was reduced to half-maximal by 0.42 mM tetraethylammonium, 1.1 mM 4-aminopyridine, and 3.2 mM Ba2+ but was not significantly attenuated by Co2+ (1 mM). 5. The reversal potential (measured with tail currents) changed by 53mV per decade change of [K+] from 1 to 77 mM. 6. The voltage for half-maximal activation of the conductance was -26.6mV (+/- 1.7mV), and the voltage required for an e-fold increase in conductance was 6.9mV (+/- 0.5mV). 7. Thus, the mRNA for MBK1 found in the mouse retina causes the expression of a voltage-dependent K+ current which has properties suitable for may retinal neurons.