Circulating miRNAs as non-invasive biomarkers to predict aggressive prostate cancer after radical prostatectomy.

BACKGROUND: Prostate cancer is an extremely heterogeneous disease. Despite being clinically similar, some tumours are more likely to recur after surgery compared to others. Distinguishing those that need adjuvant or salvage radiotherapy will improve patient outcomes. The goal of this study was to identify circulating microRNA that could independently predict prostate cancer patient risk stratification after radical prostatectomy. METHODS: Seventy-eight prostate cancer patients were recruited at the Odette Cancer Centre in Sunnybrook Health Sciences Centre. All patients had previously undergone radical prostatectomy. Blood samples were collected simultaneously for PSA testing and miRNA analysis using NanoString nCounter technology. Of the 78 samples, 75 had acceptable miRNA quantity and quality. Patients were stratified into high- and low-risk categories based on Gleason score, pathological T stage, surgical margin status, and diagnostic PSA: patients with Gleason ≥ 8; pT3a and positive margin; pT3b and any margin; or diagnostic PSA > 20 µg/mL were classified as high-risk (n = 44) and all other patients were classified as low-risk (n = 31). RESULTS: Using our patient dataset, we identified a four-miRNA signature (miR-17, miR-20a, miR-20b, miR-106a) that can distinguish high- and low-risk patients, in addition to their pathological tumour stage. High expression of these miRNAs is associated with shorter time to biochemical recurrence in the TCGA dataset. These miRNAs confer an aggressive phenotype upon overexpression in vitro. CONCLUSIONS: This proof-of-principle report highlights the potential of circulating miRNAs to independently predict risk stratification of prostate cancer patients after radical prostatectomy.

Validation of a Metastatic Assay using biopsies to improve risk stratification in patients with prostate cancer treated with radical radiation therapy.

Background: Radiotherapy is an effective treatment of intermediate/high-risk locally advanced prostate cancer, however, >30% of patients relapse within 5 years. Clinicopathological parameters currently fail to identify patients prone to systemic relapse and those whom treatment intensification may be beneficial. The purpose of this study was to independently validate the performance of a 70-gene Metastatic Assay in a cohort of diagnostic biopsies from patients treated with radical radiotherapy and androgen deprivation therapy. Patients and methods: A bridging cohort of prostate cancer diagnostic biopsy specimens was profiled to enable optimization of the Metastatic Assay threshold before further independent clinical validation in a cohort of diagnostic biopsies from patients treated with radical radiotherapy and androgen deprivation therapy. Multivariable Cox proportional hazard regression analysis was used to assess assay performance in predicting biochemical failure-free survival (BFFS) and metastasis-free survival (MFS). Results: Gene expression analysis was carried out in 248 patients from the independent validation cohort and the Metastatic Assay applied. Ten-year MFS was 72% for Metastatic Assay positive patients and 94% for Metastatic Assay negative patients [HR = 3.21 (1.35-7.67); P = 0.003]. On multivariable analysis the Metastatic Assay remained predictive for development of distant metastases [HR = 2.71 (1.11-6.63); P = 0.030]. The assay retained independent prognostic performance for MFS when assessed with the Cancer of the Prostate Assessment Score (CAPRA) [HR = 3.23 (1.22-8.59); P = 0.019] whilst CAPRA itself was not significant [HR = 1.88, (0.52-6.77); P = 0.332]. A high concordance [100% (61.5-100)] for the assay result was noted between two separate foci taken from 11 tumours, whilst Gleason score had low concordance. Conclusions: The Metastatic Assay demonstrated significant prognostic performance in patients treated with radical radiotherapy both alone and independent of standard clinical and pathological variables. The Metastatic Assay could have clinical utility when deciding upon treatment intensification in high-risk patients. Genomic and clinical data are available as a public resource.

Systemic therapy in men with metastatic castration-resistant prostate cancer: a systematic review.

AIMS: Since 2004, docetaxel-based chemotherapy has been the standard of care for men with metastatic castration-resistant prostate cancer (mCRPC), but recently randomised controlled trials (RCTs) of novel agents have shown promise in extending overall survival. These trials have evaluated agents delivered before chemotherapy, to replace or supplement docetaxel, or addressed treatment options for men who have progressed on docetaxel therapy. This review was undertaken to determine which systemic therapies improve cancer- or patient-related outcomes in men with mCRPC. MATERIALS AND METHODS: Searches were carried out in MEDLINE, EMBASE, the Cochrane Library and relevant conference proceedings. Eligible articles included RCTs comparing systemic therapy or combination (excluding primary or secondary androgen deprivation therapy, bone protective agents or radionuclides) with placebo or other agents in men with mCRPC. RESULTS: Twenty-five RCTs met the selection criteria. In chemotherapy-naive patients, targeted therapy with tasquinimod conferred a benefit in progression-free survival. Immunotherapy with sipuleucel-T extended overall survival and was well tolerated, but had no effect on the time to disease progression. Hypercastration with abiraterone extended progression-free survival, whereas overall survival was improved but not statistically proven. In the chemotherapy setting, updated and new trials of docetaxel alone confirmed the survival benefit seen in previous studies. A survival benefit with the addition of estramustine to docetaxel shown in a previous study did not lead to an improvement in pain palliation or quality of life. Trials of combining targeted therapies with docetaxel generally did not extend survival. The addition of bevacizumab improved progression-free survival, but not overall survival. The addition of GVAX immunotherapy or calcitriol was harmful. In the post-chemotherapy setting, progression-free and overall survival benefits were detected with cabazitaxel, abiraterone and enzalutamide. Cabazitaxel was associated with greater toxicity, whereas abiraterone and enzalutamide had less severe adverse effects. Satraplatin and sunitinib both extended progression-free survival, but did not improve overall survival. CONCLUSION: Docetaxel-based chemotherapy remains the standard of care in men with mCRPC who are candidates for palliative systemic therapy. Promising results are emerging with sipuleucel-T and abiraterone in the pre-docetaxel setting and cabazitaxel, abiraterone and enzalutamide in patients who progress on or after docetaxel. Further research to determine the optimal choice, sequence or even the combination of these agents is necessary.

Intra-fraction motion during extreme hypofractionated radiotherapy of the prostate using pre- and post-treatment imaging.

AIMS: To determine intra-fraction displacement of the prostate during extreme hypofractionated radiotherapy using pre- and post-treatment orthogonal images with three implanted gold seed fiducial markers. MATERIALS AND METHODS: In total, 265 image pairs were obtained from 53 patients who underwent extreme hypofractionated radiotherapy to a dose of 35 Gy in five fractions on standard linear accelerators. Position verification was obtained with orthogonal X-rays before and after treatment and were used to determine intra-fraction prostate displacement. RESULTS: The mean intra-fraction prostate displacements were -0.03 ± 0.61 mm (one standard deviation), 0.21 ± 1.50 mm and -0.86 ± 1.73 mm in the left-right, superior-inferior and anterior-posterior directions, respectively. The mean intra-fraction displacement during the first two fractions was moderately correlated with the displacement in the remaining three fractions, with correlation coefficients of 0.63 (95% confidence interval 0.43-0.77) and 0.47 (95% confidence interval 0.22-0.65) in the superior-inferior and anterior-posterior directions, respectively. There was no significant correlation in the left-right direction with a coefficient of -0.04 (95% confidence interval -0.31-0.23). CONCLUSIONS: The mean intra-fraction prostate displacement during a course of extreme hypofractionated radiotherapy is small. A strategy using the first two fractions to predict future displacements >5 mm warrants further validation.

Androgen deprivation therapy for prostate cancer-review of indications in 2010.

The discovery of androgen deprivation therapy (ADT) has been one of the most important advances in the treatment of prostate cancer. Here, the indications for the use of ADT are reviewed, together with the data supporting each indication. The settings for ADT use include cytoreduction; combined ADT and radiotherapy; pathologic node-positive disease; and recurrent, metastatic, or progressive prostate cancer.

Phase I/II study of a five-fraction hypofractionated accelerated radiotherapy treatment for low-risk localised prostate cancer: early results of pHART3.

AIMS: Most men with low-risk localised prostate cancer prefer treatments with high control rates and minimal disruption to their lives. Hypofractionating external radiation treatments can theoretically maintain high bioequivalent tumour doses, decrease treatment visits and decrease acute and late toxicities. The aim of this study was to assess the toxicity and feasibility of a hypofractionated accelerated regimen for these patients. MATERIALS AND METHODS: The present study was a phase I/II study in which patients with T1-2b, Gleason < or = 6 and prostate-specific antigen (PSA) < or = 10 ng/ml prostate cancer received 35Gy in five fractions, once a week over 29 days. Treatment was delivered with intensity-modulated radiotherapy on standard linear accelerators, with daily image guidance using gold seed fiducials, and a 4mm clinical target volume to planning target volume margin. RESULTS: As of January 2008, the target accrual of 30 patients had been reached and all had completed treatment and at least 6 months of follow-up. Dose-volume histogram objectives were achievable in all patients. Treatment was very well tolerated with no grade 3 or 4 genitourinary toxicity, gastrointestinal toxicity nor fatigue observed (95% confidence interval 0-12%). As a group, compared with baseline, the following additional grade 2 toxicities were observed: 13% genitourinary, 7% gastrointestinal and 10% fatigue. At 6 months all scores had returned to or improved over baseline. The median PSA before treatment was 6.0 ng/ml. At 6 months, the median PSA was 1.8 ng/ml and 75% had a PSA < or = 3.0 ng/ml. CONCLUSIONS: This novel technique using standard linear accelerators seems feasible and is well tolerated. Further follow-up will be carried out to document late toxicity and efficacy.

A phase I/II study to evaluate the toxicity and efficacy of accelerated fractionation radiotherapy for the palliation of dysphagia from carcinoma of the oesophagus.

AIMS: We hypothesised that accelerated fractionated radiotherapy may provide a good palliative approach for dysphagia relief in patients with incurable oesophageal cancer, significantly reducing the overall duration of treatment, while providing symptom response with an acceptable toxicity profile. A phase I/II accelerated fractionation study was conducted to evaluate the efficacy and toxicity of this approach. MATERIALS AND METHODS: Patients with incurable oesophageal cancer, symptomatic with dysphagia, Eastern Cooperative Oncology Group performance statusor=6 h apart), 5 days a week, over 2 weeks. RESULTS: Of the 39 evaluable patients, the dysphagia response rate was 69% (27/39) with a median response duration of 5.5 months. The median time to response was 4 weeks. Twenty-eight per cent (11/39) of patients had transient worsening in their dysphagia scores. Acute toxicity (weeks 1-8) occurred in 41% (16/39) of patients. An improvement in global quality of life by week 8 was seen in 42% of patients. There were no late neurological sequelae. The median overall survival was 8 (range 1.7-58+) months. CONCLUSION: The ideal palliative regimen should be relatively short, with minimal toxicity, while offering a favourable response profile. Accelerated fractionation fulfils these criteria and is a suitable treatment alternative for the palliation of dysphagia, especially if the goal is to deliver a higher total biological dose within a shorter (2 week) period of time.

A genome-wide association screen identifies regions on chromosomes 1q25 and 7p21 as risk loci for sporadic prostate cancer.

We conducted a genome-wide association study of 3090 sporadic prostate cancer patients and controls using the Affymetrix 10 000 SNP GeneChip. Initial screening of 40 prostate cancer cases and 40 non-cancer controls revealed 237 SNPs to be associated with prostate cancer (P<0.05). Among these SNPs, 33 were selected for further association analysis of 2069 men who had undergone a cancer-screening prostate biopsy. Results identified five loci as being significantly associated with increased prostate cancer risk in this larger sample (rs 1930293, OR=1.7, P=0.03; rs 717809-2p12, OR=1.3, P=0.03; rs 494770-4q34, OR=1.3, P=0.01; rs 2348763-7p21, OR=1.5, P=0.01; rs 1552895-9p22, OR=1.5, P=0.002). To validate these association data, 61 additional HapMap tagSNPs spanning the latter five loci were genotyped in this subject cohort and an additional 1021 men (total subject number=3090). This analysis revealed tag SNP rs 4568789 (chromosome 1q25) and tag SNP rs 13225697 (chromosome 7p21) to be significantly associated with prostate cancer (P-values 0.009 and 0.008, respectively). Haplotype analysis revealed significant associations of prostate cancer with two allele risk haplotypes on both chromosome 1q25 (adjusted OR of 2.7 for prostate cancer, P=0.0003) and chromosome 7p21 (adjusted OR of 1.3, P=0.0004). As linkage data have identified a putative prostate cancer gene on chromosome 1q25 (HPC1), and microarray data have revealed the ETV1 oncogene to be overexpressed in prostate cancer tissue, it appears that chromosome 1q25 and 7p21 may be sites of gene variants conferring risk for sporadic and inherited forms of prostate cancer.

Expression of the TMPRSS2:ERG fusion gene predicts cancer recurrence after surgery for localised prostate cancer.

The prostate-specific gene, TMPRSS2 is fused with the gene for the transcription factor ERG in a large proportion of human prostate cancers. The prognostic significance of the presence of the TMPRSS2:ERG gene fusion product remains controversial. We examined prostate cancer specimens from 165 patients who underwent surgery for clinically localised prostate cancer between 1998 and 2006. We tested for the presence of TMPRSS2:ERG gene fusion product, using RT-PCR and direct sequencing. We conducted a survival analysis to determine the prognostic significance of the presence of the TMPRSS2:ERG fusion gene on the risk of prostate cancer recurrence, adjusting for the established prognostic factors. We discovered that the fusion gene was expressed within the prostate cancer cells in 81 of 165 (49.1%) patients. Of the 165 patients, 43 (26.1%) developed prostate-specific antigen (PSA) relapse after a mean follow-up of 28 months. The subgroup of patients with the fusion protein had a significantly higher risk of recurrence (58.4% at 5 years) than did patients who lacked the fusion protein (8.1%, P<0.0001). In a multivariable analysis, the presence of gene fusion was the single most important prognostic factor; the adjusted hazard ratio for disease recurrence for patients with the fusion protein was 8.6 (95% CI=3.6-20.6, P<0.0001) compared to patients without the fusion protein. Among prostate cancer patients treated with surgery, the expression of TMPRSS2:ERG fusion gene is a strong prognostic factor and is independent of grade, stage and PSA level.

Functional and pharmacokinetic outcomes after a single intravenous infusion of recombinant human erythropoietin in patients with malignant extradural spinal cord compression.

AIMS: To determine the cerebrospinal fluid concentrations and the functional and pain outcomes after a single intravenous infusion of erythropoietin at the start of a standard radiotherapy and steroid protocol. MATERIALS AND METHODS: Ten paraparetic patients with malignant extradural spinal cord compression who were eligible for radiotherapy, lumbar puncture and intravenous epoetin alpha were enrolled. The patients received epoetin alpha 1500 IU/kg intravenously over 30 min followed by a standardised dexamethasone and radiotherapy protocol. A lumbar puncture and venipuncture were carried out 24-30 h after the epoetin alpha infusion. The patients were followed closely at defined intervals. RESULTS: Erythropoietin was detectable in the cerebrospinal fluid in all eight patients sampled (median 92.5 mIU/ml, range 17.8-214.0 mIU/ml). Before treatment, eight patients were non-ambulatory and two patients were ambulatory with assistance. After treatment, eight (80%, 95% confidence interval [CI] 44-97%) improved at least one functional class and recovered or maintained ambulation. Five of seven patients (71%; 95% CI 29-96%) with objective sensory deficits and one of seven (14%; 95% CI 0-58%) catheter-dependent patients recovered. Overall, 78% (95% CI 40-97%) had a pain response. CONCLUSIONS: After an intravenous infusion of epoetin alpha, radiotherapy and steroids, high concentrations of erythropoietin were detectable in the cerebrospinal fluid. Patients with malignant extradural spinal cord compression showed encouraging improvements in neurological function and pain.

A population-based study of malignant spinal cord compression in Ontario.

DESIGN: Population-based cohort study. BACKGROUND: Malignant spinal cord compression (MSCC) has long been recognized as an important complication of cancer, but its incidence is unknown. OBJECTIVES: To describe the incidence, the management, and the outcome of MSCC in the cancer population of the Canadian province of Ontario. METHODS: Episodes of MSCC, and treatments used for each episode, were identified by linking electronic hospital separation records and cancer centre records to Ontario's population-based cancer registry. The cumulative frequency of MSCC in the last 5 years of life was described in the 121435 patients who died of cancer in Ontario between 1990 and 1995. Survival after the first episode of MSCC, and duration of hospitalization with MSCC, was described. RESULTS: The cumulative probability of experiencing at least one episode of MSCC in the 5 years preceding death from cancer was 2.5% overall, and ranged from 0.2% in cancer of the pancreas to 7.9% in myeloma. Overall, 60.2% of first episodes of MSCC were treated with primary radiotherapy, and 16.1% with surgery +/- postoperative radiotherapy, while in the remaining 23.7%, there was no record of radiotherapy or surgery. Overall, the median survival following the first episode of MSCC was 2.9 months. The diagnosis of MSCC was associated with a doubling of the time spent in hospital in the last year of life. CONCLUSION: MSCC is a fairly common occurrence among patients dying of cancer. There is a 40-fold variation in the cumulative incidence of MSCC among different types of cancer.

Disseminated intravascular coagulation and PC-SPES: a case report and literature review.

BACKGROUND: PC-SPES is a herbal remedy gaining acceptance amongst prostate cancer patients and health care providers due to credible laboratory and clinical studies. However, PC-SPES has not been assessed in the standard rigorous approval process mandated for conventional agents. OBJECTIVES: To present a case of a patient with prostate cancer who, while using PC-SPES, developed disseminated intravascular coagulation (DIC). A review of the literature was conducted to determine if there is a relationship between PC-SPES and hemorrhagic disorders. METHODS: Searches were conducted in MEDLINE (1966-December 2000) and the Cochrane Collaboration's database. RESULTS: There are 116 clinical and laboratory based studies of PC-SPES published to date. There are no randomized controlled trials. Clinical studies have demonstrated a significant reduction in prostate specific antigen (PSA) levels within 6 weeks. Improved quality-of-life, reduction in the volume of tumor deposits and reduction in analgesic use has been demonstrated in hormone refractory patients. Laboratory studies suggest that the beneficial effects of PC-SPES are unrelated to physiologic estrogens. However, PC-SPES has a side-effect profile similar to diethylstilbestrol. There is data demonstrating a <5% risk of thromboembolic events, but this is the first report of DIC. CONCLUSION: The study of PC-SPES is in its infancy. This case may serve as a cautionary note to health care providers and patients regarding herbal remedies. Those using PC-SPES should have an increased level of surveillance for bleeding disorders.

Brachytherapy in patients with small prostate glands.

PURPOSE: To better define the role of small prostate volume in selecting patients for brachytherapy. MATERIALS AND METHODS: Thirty patients with a transrectal ultrasound (TRUS)-based prostate volumes less than 20 cc were treated at the University of Washington by permanent isotope implantation for prostatic carcinoma. Preimplant TRUS studies were taken at 0.5-cm intervals from the base of the gland to the apex. Planning margins of 1 to 5 mm were added to the prostatic margins, and sources were routinely planned to be placed as much as 5 mm outside of the prostatic margin. The prescription dose was 144 and 115 Gy for full-dose iodine 125 and palladium 103 monotherapy, respectively. For patients receiving supplemental external-beam irradiation, the implant doses were 120 and 90 Gy for 125I and 103Pd, respectively. The morning following the implant, axial computed tomographic (CT) images of the prostate were obtained at 0.5-cm intervals with patients in the supine position. Follow-up ranged from 11 to 28 months (median 21 months). RESULTS: The median coverage of the postimplant prostate volume by the prescription dose was 92%. To calculate the incidence of source migration, the number of sources placed at the time of implant was compared with the number identified on postimplant CT scan. The median number of sources implanted was 84 (range 65-103) compared to an average of 82 identified postoperatively, which is consistent with a source migration rate of two. A median of 31 sources appeared to be outside of the prostatic margins, as identified on postimplant CT scan (range 14-53). Of the 23 patients contacted at the time of this report, one had developed acute postimplant urinary retention that resolved within 2 weeks of implantation. At last follow-up, patient pre- and postimplant AUA scores were not substantially different, with the median AUA score increasing from 7 (range 2-21) to 8 (range 1-27). CONCLUSIONS: Patients with small prostate volumes appear to have acceptable morbidity and target coverage with prostate brachytherapy. Based on the data reported here, we do not believe that a small prostate volume in itself is a contraindication to brachytherapy.

Development and testing of a visit-specific patient satisfaction questionnaire: the Princess Margaret Hospital Satisfaction With Doctor Questionnaire.

PURPOSE: To develop a psychometrically sound patient-satisfaction-with-physician questionnaire that can be used in an outpatient oncology setting. PATIENTS AND METHODS: The questionnaire was developed by a four-step process involving a total of 277 cancer patients. The item-generation process utilized input from 95 oncology outpatients, three medical researchers, and the relevant literature. Items were tested by 70 of the above patients. Initial item reduction was achieved by input from another eight patients. Factor analysis and validity testing used data derived from a different group of 174 oncology outpatients. Convergent validity was tested by correlating the Princess Margaret Hospital Patient Satisfaction with Doctor Questionnaire (PMH/PSQ-MD) with Rubin et al's Physician subscale of the Patient's Viewpoint Questionnaire (PS-PVQ) and Smith et al's Patient-Doctor Interaction Scale (PDIS). Divergent validity was tested by comparing these questionnaires with Spitzer's quality of life (QOL) questionnaire. RESULTS: The final PMH/PSQ-MD is a 29-item self-administered questionnaire with four response categories and a "does not apply" category. Four domains were confirmed by factor analysis: (1) information exchange, (2) interpersonal skills, (3) empathy, and (4) quality of time. The questionnaire has an overall Cronbach's alpha of 0.97; the values for each domain are, respectively, 0.92, 0.90, 0. 88, and 0.88. The PMH/PSQ-MD correlated well with both the PDIS and the PS-PVQ (P <.001 for both). Divergent validity was confirmed with Spitzer's QOL questionnaire. CONCLUSION: The PMH/PSQ-MD is an outpatient satisfaction questionnaire specific to the patient-physician interaction that has shown excellent internal consistency, is feasible, and has strong support for validity in this oncology population.

Re-irradiation for locally recurrent nasopharyngeal carcinoma.

Since 1989, 17 patients have undergone re-irradiation for locally recurrent nasopharyngeal cancer (NPC). The dose currently administered externally is 39.6 Gy in 36 fractions (BID) followed by an intracavitary boost (15-20 Gy). Disease persisted in five out of five patients treated palliatively. Eleven of 12 patients treated with curative intent achieved local control.

Emergency treatment of malignant extradural spinal cord compression: an evidence-based guideline.

PURPOSE: To review the literature for malignant extradural spinal cord compression (MSCC), produce evidence-based recommendations based on the criteria used by the Canadian Task Force on the Periodic Health Examination, and make suggestions regarding future research directives. METHODS: A systematic review of the literature with explicit study selection and evaluation criteria was performed. Primary outcome measure was posttreatment ambulation rate. RESULTS: There is good evidence to support the use of high-dose dexamethasone (96 mg/d), but inconclusive evidence for the use of moderate-dose steroids (16 mg/d) in conjunction with radiotherapy (RT) for the treatment of MSCC. Fair evidence exists for not using steroids in patients who are nonparetic and ambulatory pretreatment, and to give radiation to patients with subclinical spinal cord compression (SCC). The remainder of the recommendations are based on inconclusive evidence: RT alone should be the first-line treatment for ambulatory patients except when there is spinal instability, bony compression, or paraplegia on presentation, in which case surgery should be performed. Either modality can be used for paraparetic patients who are nonambulatory. Postoperative RT should be considered for tumor in residua. Ambulatory, undiagnosed patients should have needle biopsy attempted first. Patients should be aggressively screened and educated about SCC. CONCLUSION: In general, there were very few papers of high methodologic quality found in the literature. More studies are needed to satisfy the validity of many of the clinical decisions that are made today with regard to the management of MSCC.

Cytotoxic effect of RB 6145 in human tumour cell lines: dependence on hypoxia, extra- and intracellular pH and drug uptake.

Low pH and hypoxia are a common feature of many solid tumours. This study examined the effect of these two conditions on the cytotoxic properties of the bifunctional agent RB 6145, the prodrug of RSU 1069. The effect of acidic pH on RB 6145 toxicity was examined in six human tumour cell lines under hypoxic conditions and was found to have little effect in HT 29, A549, U373 and HT 144 cells. Treatment was for 1 h at 37 degrees C, pH 6.4 or 7.4. Significant potentiation of RB 6145 toxicity was observed in SiHa cells (enhancement ratio; ERpH approximately 1.6) and in U1 cells (ERpH approximately 1.4). In these two cell lines the potentiation of RB 6145 toxicity arising from hypoxia was large, with ERHyp approximately 11 and 15 in SiHa and U1 cells respectively. SiHa cells, which show a pH effect and HT 29 cells, which do not, were chosen for further comparative studies of drug uptake )nd regulation of intracellular pH. High-performance liquid chromatography (HPLC) determinations of the uptake of RB 6145 and its dervatives showed that in SiHa cells, intracellular to extracellular drug concentration ratio (Ci/Ce) at 1 h was approximately 40% higher at pH 6.4 than at pH 7.4, whereas in HT 29 cells Ci/Ce was approximately 25% lower. Under conditions of acidic extracellular pH, regulation of pH was somewhat less effective in SiHa cells, where pHi dropped to within 0.2 pH units of the extracellular pH over a 2.5 h treatment at pH 6.4. It seems likely that increased drug uptake was at least part of the basis for the observed potentiation of RB 6145 toxicity in SiHa cells. A model which would better explain the results for both cell lines might also include the possibility that low pH per se potentiates cytotoxic damage to a modest extent and that it is offset or augmented by altered uptake in HT 29 and SiHa cells respectively.