A genetic variant in Rassf1a predicts outcome in mCRC patients treated with cetuximab plus chemotherapy: results from FIRE-3 and JACCRO 05 and 06 trials.

The Hippo pathway is involved in colorectal cancer (CRC) development and progression. The Hippo regulator Rassf1a is also involved in the Ras signaling cascade. In this work, we tested single nucleotide polymorphisms within Hippo components and their association with outcome in CRC patients treated with cetuximab. Two cohorts treated with cetuximab plus chemotherapy were evaluated (198 RAS wild-type (WT) patients treated with first-line FOLFIRI plus Cetuximab within the FIRE-3 trial and 67 Ras WT patients treated either with first-line mFOLFOX6 or SOX plus Cetuximab). In these two populations, Rassf1a rs2236947 was associated with overall survival (OS), as patients with a CC genotype had significantly longer OS compared with those with CA or AA genotypes. This association was stronger in patients with left-side CRC (hazard ratio (HR): 1.79 (1.01-3.14); P=0.044 and HR: 2.83 (1.14-7.03); P=0.025, for Fire 3 and JACCRO cohorts, respectively). Rassf1a rs2236947 is a promising biomarker for patients treated with cetuximab plus chemotherapy.

Genetic variants of DNA repair-related genes predict efficacy of TAS-102 in patients with refractory metastatic colorectal cancer.

Background: Tri-phosphorylated trifluridine (FTD) incorporation into DNA is TAS-102's main anti-tumor action. We tested whether genetic polymorphisms in homologous recombination (HR) and cell cycle checkpoint pathway for DNA repair is associated with outcomes in refractory metastatic colorectal cancer (mCRC) patients treated with TAS-102. Patients and methods: We analyzed genomic DNA extracted from 233 samples of three cohorts: an evaluation cohort of 52 patients receiving TAS-102, a validation cohort of 129 patients receiving TAS-102 and a control cohort of 52 patients receiving regorafenib. Single nucleotide polymorphisms of genes involved in HR (ATM, BRCA1, BRCA2, XRCC3, FANCD2, H2AX, RAD51) and cell cycle checkpoint (ATR, CHEK1, CHEK2, CDKN1A, TP53, CHE1, PIN1, PCNA) were analyzed by PCR-based direct sequencing. Results: In univariate analysis for the evaluation cohort, patients with any G allele in ATM rs609429 had longer overall survival (OS) than those with the C/C variant (8.7 vs. 4.4 months, HR 0.37, 95% CI: 0.14-0.99, P = 0.022). Patients carrying any A allele in XRCC3 rs861539 had significantly longer progression-free survival (PFS) (3.8 vs. 2.3 months, HR 0.44, 95% CI: 0.21-0.92, P = 0.024) and OS (15.6 vs. 6.3 months, HR 0.25, 95% CI: 0.08-0.79, P = 0.012) than those with the G/G variant. In multivariable analysis, ATM rs609429 remained significant for OS (P = 0.020). In the validation cohort, patients having ATM rs609429 with any G allele showed longer OS and PFS; the G/A variant in XRCC3 rs861539 showed longer OS, though without statistical significance. Conclusion: Genetic variants in the HR pathway may predict clinical outcome in mCRC patients receiving TAS-102.

Prostatectomy at high-volume centers improves outcomes and lowers the costs of care for prostate cancer.

BACKGROUND: High-volume surgeons with ⩾250 radical prostatectomies provide superior oncological outcomes as evidenced by a lower rate of PSA recurrence (PSAR). The financial benefits of performing prostatectomies at high-volume centers (HVC) are unexplored. METHODS: A base case--referent scenario--where the share of prostatectomies at high- and low-volume centers were evenly divided at 50% was defined. Additional scenarios with increasing shares of prostatectomies at HVC with 10% increments were also modeled. Using a lower probability of PSAR as the only advantage of more experienced surgeons, the savings that would result from fewer recurrences, avoidance of salvage radiation therapy (SRT) and management of fewer men with metastatic cancer were calculated. RESULTS: The savings associated with performing 80% of radical prostatectomy at HVC were $177, $357 and $559 per prostatectomy at 5, 10 and 20 years, respectively. These savings would offset referral costs of up to $1833 per prostatectomy referral at no additional total societal costs. Given the longer average biochemical failure-free survival with prostatectomies at HVC, referral costs of more than $1833 may be cost effective. CONCLUSIONS: Under the conservative assumption of accounting for lower rates of PSAR as the only benefit of surgery in an HVC, performing prostatectomies at an HVC was associated with savings that may offset part of the initial referral costs.

Variations in genes involved in dormancy associated with outcome in patients with resected colorectal liver metastases.

BACKGROUND: Tumor dormancy has been described as a state of hibernation. Dormancy can be switched to proliferation by different pathways, which may play a critical role in tumor recurrence. In this study, we investigated genetic variations within genes involved in tumor dormancy and their association with recurrence and outcome in patients with colorectal liver metastases (CLM) who underwent neoadjuvant bevacizumab-based chemotherapy. PATIENTS AND METHODS: Genomic DNA was extracted from resected CLM (FFPE) from 149 patients. Single-nucleotide polymorphisms (SNPs) in 14 genes associated with dormancy were analyzed by direct Sanger DNA sequencing and evaluated for response, recurrence-free survival (RFS), overall survival (OS) and recurrence patterns. RESULTS: NME1 rs34214448 C>A was significantly associated with RFS in univariable analysis (P = 0.039) and with intrahepatic recurrence (P = 0.014). NOTCH3 rs1044009 T>C and CD44 rs8193 C>T showed a significant difference in 3-year OS rates (P = 0.004 and P = 0.042, respectively). With respect to radiological response, CD44 rs8193 C>T variant genotypes were associated with a significantly higher response rate (P = 0.033). Recursive partitioning analyses revealed that Dll4 rs12441495 C>G, NME1 rs34214448 C>A and NOTCH3 rs1044009 T>C were the dominant SNPs predicting histological response, RFS and OS, respectively. CONCLUSION: Our data suggest that gene variations within genes involved in tumor dormancy pathways are associated with response and outcome in patients with resected CLM. These data may lead to new and more effective treatment strategies targeting tumor dormancy.

Association of variants in genes encoding for macrophage-related functions with clinical outcome in patients with locoregional gastric cancer.

BACKGROUND: Nuclear factor-kappaB (NF-κB) and CCL2/CCR2 chemokine axis play a central role in tumor progression such as stimulation of angiogenesis, acceleration of tumor invasion and migration, and suppression of innate immunosurveillance in the macrophage-related functions. There have been few reports regarding association of the macrophage function-related genes with the clinical outcome in gastric cancer. We hypothesized that variants in genes encoding for NF-κB and CCL2/CCR2 axis may predict prognosis in gastric cancer and tested whether the functional single-nucleotide polymorphisms (SNPs) will be associated with clinical outcome in patients with gastric cancer across two independent groups. PATIENTS AND METHODS: This study enrolled two cohorts which consisted of 160 Japanese patients and 104 US patients with locoregional gastric cancer. Genomic DNA was analyzed for association of 11 SNPs in NFKB1, RELA, CCL2, and CCR2 with clinical outcome using PCR-based direct DNA sequencing. RESULTS: The univariable analysis showed four SNPs had significant association with clinical outcome in the Japanese cohort, NFKB1 rs230510 remained significant upon multivariable analysis. The patients with the A allele of the NFKB1 rs230510 had significantly longer overall survival (OS) compared with those with the T/T genotype in both the Japanese and US cohort in the univariable analysis. In contrast, genotypes with the T allele of CCL2 rs4586 were significantly associated with shorter OS compared with the C/C genotype in the US cohort [hazard ratio (HR) 2.43; P = 0.015] but longer OS in the Japanese cohort (HR 0.58; P = 0.021), resulting in the statistically significant opposite impact on OS (P = 0.001). CONCLUSIONS: Our study provides the first evidence that the NFKB1 rs230510 and CCL2 rs4586 are significantly associated with the clinical outcome in patients with locoregional gastric cancer. These results also suggest that the genetic predisposition of the host may dictate the immune-related component of the tumor for progression in gastric cancer.

Distinct gene expression profiles of proximal and distal colorectal cancer: implications for cytotoxic and targeted therapy.

Colorectal cancer (CRC) is a heterogeneous disease with genetic profiles and clinical outcomes dependent on the anatomic location of the primary tumor. How location has an impact on the molecular makeup of a tumor and how prognostic and predictive biomarkers differ between proximal versus distal colon cancers is not well established. We investigated the associations between tumor location, KRAS and BRAF mutation status, and the messenger RNA (mRNA) expression of proteins involved in major signaling pathways, including tumor growth (epidermal growth factor receptor (EGFR)), angiogenesis (vascular endothelial growth factor receptor 2 (VEGFR2)), DNA repair (excision repair cross complement group 1 (ERCC1)) and fluoropyrimidine metabolism (thymidylate synthase (TS)). Formalin-fixed paraffin-embedded tumor specimens from 431 advanced CRC patients were analyzed. The presence of seven different KRAS base substitutions and the BRAF V600E mutation was determined. ERCC1, TS, EGFR and VEGFR2 mRNA expression levels were detected by reverse transcriptase-PCR. BRAF mutations were significantly more common in the proximal colon (P<0.001), whereas KRAS mutations occurred at similar frequencies throughout the colorectum. Rectal cancers had significantly higher ERCC1 and VEGFR2 mRNA levels compared with distal and proximal colon tumors (P=0.001), and increased TS levels compared with distal colon cancers (P=0.02). Mutant KRAS status was associated with lower ERCC1, TS, EGFR and VEGFR2 gene expression in multivariate analysis. In a subgroup analysis, this association remained significant for all genes in the proximal colon and for VEGFR2 expression in rectal cancers. The mRNA expression patterns of predictive and prognostic biomarkers, as well as associations with KRAS and BRAF mutation status depend on primary tumor location. Prospective studies are warranted to confirm these findings and determine the underlying mechanisms.

Correlation of corpus callosal morphometry with cognitive and motor function in periventricular leukomalacia.

PURPOSE: We aim to correlate size and shape of corpus callosum with severity of motor and cognitive impairments in children with periventricular leukomalacia (PVL). METHODS: Children with PVL were stratified based on the severity of their motor and cognitive impairments. An age-matched control group was established. The corpus callosum was identified on mid-sagittal T (1)-weighted spin-echo (TR/TE: 550/15) MR images. The shape characteristics of the corpus callosum were measured with respect to a template via a shape transformation. The degree of callosal-shape transformation was quantified by a deformation function, which in turn was compared, using point-wise T-tests, for controls versus patients, diplegic versus quadriplegic patients, and patients with mild versus severe cognitive impairment. RESULTS: 29 children with spastic cerebral palsy and PVL and 32 age-matched controls were identified. In the PVL group, the entire corpus callosum was significantly smaller than in the control group (p value = 0.001). Significant differences existed in the shape of the corpus callosum between patients with diplegic versus quadriplegic and between patients with severe versus mild cognitive impairment. CONCLUSION: Global and regional corpus callosal morphology can be quantified using deformation functions.

Second surgery for recurrent pilocytic astrocytoma in children.

Pilocytic astrocytoma (PA) is the most common childhood brain tumor. In cases where the tumor progresses or recurs following primary surgical resection, the appropriate treatment is unclear. Options include chemotherapy, radiation therapy, surgical resection or a combination thereof. To analyze the utility of further surgery, we performed a retrospective, single-institution review of pediatric patients with recurrent PAs from 1990 to 1999 who were treated with a second surgical resection. Patients were excluded if they received adjuvant chemotherapy or radiation therapy. Twenty cases were identified. Tumor locations included: cerebral hemisphere (3), cerebellum (7), optic pathway/hypothalamus (5), thalamus (1) and brainstem (4). The indication for 4 surgeries included an enlarging tumor-associated cyst. At second surgery, 10 of 20 patients had a gross total resection (GTR), 2 a near total resection (NTR), and the remaining 8 patients had a subtotal resection (STR). No patients have died. Two of 10 tumors after GTR, 0 of 2 tumors after NTR, and 7 of 8 tumors after STR had second recurrence/progression at a mean of 15 months (range 4-33 months) following second surgery. The remaining 11 patients are recurrence/progression-free at a mean of 40.7 months (range 19-119 months). Surgery for tumors or midline structures rarely resulted in a GTR (1 of 10 cases). Surgery for tumors located in the cerebral hemispheres or cerebellum resulted in GTR or NTR in all cases and can result in long periods of progression-free survival without further adjuvant treatment.

Decision support system for medical triage.

The paper explains the application of an artificial intelligence tool for the purpose of medical decision-making. The first product of this application is a triage engine, available on the Internet, to help laypersons make a decision about the urgency of their situation by providing tailored and accurate information. The expansion of this tool can lead to diagnostic tools for professionals or for educational purposes.

Intelligent system and risk of different diseases in the general population.

This is a new approach to define the risk of the general population for a specific disease. We use Bayesian theory to define the risk of the population. Analyzing the major risk factors of a disease, how they affect the incidence and/or prevalence of the disease, and the statistics of each risk factor in the population, along with the power of the Bayes theorem helps us define the risk of that population for that disease. To find out what the risk of the general population for a disease is, prospective epidemiological studies in the population shown are needed. These studies usually lead to the identification of the major risk factors for a disease and their impacts which are quite costly and requires a long time to get to the results. Also a large personnel is needed to perform effectively in the study. The result of the risk of the general population for a first heart attack using our software is in agreement with the result of the Framingham heart study. Large studies like Framingham is not available for other diseases to enable us to evaluate the accuracy of our software precisely. To overcome this shortage we have sought medical experts' evaluation of the predicted risk of the general population for other disease by this software, which needs to be completed.

Design and synthesis of modified quinolones as antitumoral acridones.

The bacterial topoisomerase II (DNA gyrase) and the mammalian topoisomerase II represent the cellular targets for quinolone antibacterials and a wide variety of anticancer drugs, respectively. In view of the mechanistic similarities and sequence homologies exhibited by the two enzymes, tentative efforts to selectively shift from an antibacterial to an antitumoral activity was made by synthesizing a series of modified tricyclic quinolones, in which the essential 3-carboxylic function is surrogated by phenolic OH and the classic C-6 fluorine atom is replaced by a NH2 group. The resulting 7-amino-9-acridone derivatives were assayed for their antibacterial as well as cytotoxic activities. No antibacterial activity was found. On the other hand, many derivatives showed significant cytotoxic activity against both HL-60 and P388 leukemias and a wide panel of human and rodent solid tumor cells, derivatives 25 and 26 displaying the best overall antiproliferative activity. Against the LoVo cell line, derivative 25 exhibited higher cytotoxic effects than etoposide.

Antitumor activity of 2,2'-bipyridyl-6-carbothioamide: a ribonucleotide reductase inhibitor.

1. 2,2'-Bipyridyl-6-carbothioamide (BPYTA) is a synthesized compound with chelating properties demonstrating in vitro and in vivo antitumor activity. 2. The BPYTA cytotoxic effect is mainly due to the inhibition of ribonucleotide reductase (RR), a key enzyme in proliferating cells. The active form of BPYTA is its iron chelate [BPYTA-Fe(II), molar ratio 2:1], which destroys the tyrosyl radical of RR small subunit (R2). 3. The copper chelate of BPYTA [BPYTA-Cu(II), molar ratio 2:1] also has antiproliferative activity, but RR is not the only intracellular target. 4. BPYTA potently synergizes in vitro with hydroxyurea, the most widely used R2 inhibitor.

Malignant metastatic eccrine poroma. Proposal for a new therapeutic protocol.

BACKGROUND: Malignant metastatic eccrine poroma is a very rare cutaneous neoplasm, and consequently the references in the literature regarding the treatment of this tumor, known also as porocarcinoma, are very poor. OBJECTIVE: To call attention to a new therapeutic protocol in the treatment of metastatic porocarcinoma, as well as to underline an antineoplastic efficacy of vitamin A analogues. METHODS: The results are presented on the basis of the clinical case of a malignant eccrine poroma with metastatic regional lymph nodes. RESULTS: With our new chemotherapeutic protocol, arrest of the metastatic progression was achieved after 3 months and the remission was maintained until the 10th month of therapy. CONCLUSIONS: A new chemotherapy protocol consisting of isotretinoin and interferon alpha has confirmed the advantages of polychemotherapy in the treatment of metastatic malignant eccrine poroma. On the basis of the considerably long, although incomplete, remission with good drug tolerance in spite of the high doses used as well as the undoubtedly major antineoplastic strength of the latest generation of synthetic retinoids, we feel that these findings could be a good starting point for further experimental verifications of the therapy of this aggressive cutaneous neoplasm.

The 2,2'-bipyridyl-6-carbothioamide copper (II) complex differs from the iron (II) complex in its biochemical effects in tumor cells, suggesting possible differences in the mechanism leading to cytotoxicity.

2,2'-bipyridyl-6-carbothioamide (BPYTA) is an antitumor agent with chelating properties. It has previously been shown that the R2 subunit of ribonucleotide reductase (RR) is its major cellular target, but RR inhibition is observed only in the presence of ferrous iron (BPYTA-Fe, molar ratio 2:1). Because the copper (II) complex of BPYTA (BPYTA-Cu, molar ratio 1:1)) has in vitro antitumor activity comparable to that of BPYTA-Fe, we studied the mechanism of action of this new metal complex. Spectorphotometric and HPLC studies demonstrated that, at pH 7.5, BPYTA-Cu is stable at molar ratio 2:1 and copper is in its favored oxidized form [BPYTA-Cu(II)]. Electron paramagnetic resonance (EPR) studies with mouse recombinant R2 demonstrated that BPYTA-Cu destroys the R2 tyrosyl radical at the same concentration at which BPYTA-Fe does (78% vs 73% destruction at 200 microM, with 5 min of contact), but R2 inhibition is not time-dependent. Studies of the metabolism of [14C] cytidine suggest that the cytotoxic activity of BPYTA-Cu can be explained in terms of RR inhibition. However, the significant inhibition of RNA synthesis and the lack of cross-resistance to BPYTA-Cu of cell lines resistant to other RR inhibitors suggest that BPYTA-Cu may have more than one cellular target. Moreover, cell proliferation studies suggest that, unlike BPYTA-Fe, BPYTA-Cu displays its activity immediately after contact with the target cells. Our study demonstrates that significant differences in the biochemical effects of BPYTA and, perhaps, also its mechanism of action are due solely to the bonded transition metalloelement. This might also be the case with other chelators that demonstrate cytotoxic activity following metalloelement chelation.

A predictive screening model for in vitro selection of agents with potential antitumor activity.

In vitro methods are often used to pre-select compounds with potential antitumor activity before animal testing. This study presents a second stage screening model used to further evaluate compounds which demonstrate interesting antiproliferative activity towards tumor cell lines. The model is based on an antiproliferative assay evaluating 125I-5-iodo-2'-deoxyuridine incorporation in DNA after 66 h compound-cells contact, carried out on a human leukemic cell line (HL-60) and bone marrow cells (BM) from healthy donors. The model identifies compounds which are more toxic against normal cells than tumor cells (unsuitable compounds) and focuses attention on the highly selective compounds. Compounds belonging to a third group identified by the model need to be further studied to ascertain their anticancer properties.

Furanfurin and thiophenfurin: two novel tiazofurin analogues. Synthesis, structure, antitumor activity, and interactions with inosine monophosphate dehydrogenase.

The syntheses of furan and thiophene analogues of tiazofurin (furanfurin and thiophenfurin, respectively) are described. Direct stannic chloride-catalyzed C-glycosylation of ethyl 3-furan-carboxylate (6) or ethyl 3-thiophencarboxylate (18) with 1,2,3,5-tetra-O-acetyl-D-ribofuranose gave 2- and 5-glycosylated regioisomers, as a mixture of alpha- and beta-anomers, and the beta-2,5-diglycosylated derivatives. Deprotection of ethyl 5-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)furan-3-carboxylate (9 beta) and ethyl 5-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)thiophene-3-carboxylate (20 beta) with sodium ethoxide afforded ethyl 5-beta-D-ribofuranosylfuran-3-carboxylate (12 beta) and ethyl 5-beta-D-ribofuranosylthiophene-3-carboxylate (23 beta) which were converted into 5-beta-D-ribofuranosylfuran-3-carboxamide (furanfurin, 4) and 5-beta-D-ribofuranosylthiophene-3-carboxamide (thiophenfurin, 5) by reaction with ammonium hydroxide. The anomeric configuration and the site of glycosylation were established by 1H-NMR and proton-proton nuclear Overhauser effect difference spectroscopy. The structure of compound 23 beta was confirmed by X-ray crystallography. Thiophenfurin was found to be cytotoxic in vitro toward murine lymphocytic leukemia P388 and L1210, human myelogenous leukemia K562, human promyelocytic leukemia HL-60, human colon adenocarcinoma LoVo, and B16 melanoma at concentrations similar to that of tiazofurin. In the same test furanfurin proved to be inactive. Thiophenfurin was found active in vivo in BD2F1 mice inoculated with L1210 cells with a % T/C of 168 at 25 mg/kg. K562 cells incubation with thiophenfurin resulted in inhibition of inosine monophosphate (IMP) dehydrogenase (63%) and an increase in IMP pools (6-fold) with a concurrent decrease in GTP levels (42%). Incubation of adenosine-labeled K562 cells with tiazofurin, thiophenfurin, and furanfurin resulted in a 2-fold higher NAD analogue formulation by thiophenfurin than by tiazofurin. Furanfurin was converted to the NAD analogue with only 10% efficiency. The results obtained support the hypothesis that the presence of S in the heterocycle in position 2 with respect to the glycosidic bond is essential for the cytotoxicity and IMP dehydrogenase activity of tiazofurin, while the N atom is not.

2,2'-Bipyridyl-6-carbothioamide and its ferrous complex: their in vitro antitumoral activity related to the inhibition of ribonucleotide reductase R2 subunit.

2,2'-Bipyridyl-6-carbothioamide (BPYTA), a synthetic compound with antitumoral activity, is characterized by chelating properties because of the N*-N*-S* tridentate ligand system and is therefore comparable to alpha-(N)-heterocyclic carboxaldehyde thiosemicarbazones which are potent inhibitors of ribonucleotide reductase (RR). Electron paramagnetic resonance studies on the small subunit of mouse recombinant RR (R2) demonstrated that BPYTA can destroy the R2 tyrosyl radical only if Fe(II) is present (73% destruction at 50 microM, after 20 min of contact). The R2 inhibition was reversible and time dependent. Studies on tumoral lines confirmed that the main cell target of BPYTA is RR and demonstrated that the iron-complexed form compared to the nonchelated form has some difficulty in crossing the cell membrane. Spectrophotometric and electron paramagnetic resonance studies clearly indicated that BPYTA chelates iron only when this is reduced and that the BPYTA-Fe(II) complex is stable in the presence of oxygen. From reported results we conclude that BPYTA is a powerful RR inhibitor (R2 subunit) which has a different mechanism of action from that of Desferal. It has some properties in common with alpha-(N)-heterocyclic carboxaldehyde thiosemicarbazones, but they are not identical. It would be interesting to do further studies on the BPYTA mechanism of action and evaluate the in vivo antitumoral activity of the preformed complex.

In vitro synergistic activity of PDN-IFN alpha and NM + IFN alpha combinations on fresh bone-marrow samples from multiple myeloma patients.

The differential staining cytotoxicity (DiSC) assay was used to evaluate the in vitro sensitivity of tumour and normal bone-marrow cells from 21 multiple myeloma (MM) patients to antitumour agents methylprednisolone (PDN), nitrogen mustard (NM) and recombinant interferon alpha-2b (IFN alpha) tested singly and in the combinations PDN + IFN alpha and NM + IFN alpha. Both the PDN-IFN alpha and NM-IFN alpha associations were more efficacious than any agents used singly in reducing the percentage of myeloma cell survival. However, whereas NM, alone and in combination with IFN alpha, provoked a severe reduction in normal bone-marrow population, PDN and PDN + IFN alpha induced an increase percentage survival of normal bone-marrow cells. These findings indicate that, at least in vitro, the PDN-IFN alpha combination exerts a great antitumor effect which is not associated with a relevant cytotoxic activity on normal myeloid cells.

In vitro chemosensitivity of newly diagnosed and relapsing acute non-lymphoid leukemia patients.

We evaluated the in vitro sensitivity of circulating blasts from 25 newly diagnosed and 7 relapsing ANLL patients to drugs employed in vivo for inducing remission. Ten of the 14 newly diagnosed complete responders were in vitro sensitive to cytosine arabinoside and daunorubicin, whereas 10/11 non-responders were resistant to both agents. Although cells from all 7 relapsing patients were in vitro sensitive to the remission inducing agents, only 4 entered complete remission. Even if only indicative, these findings suggest that the poor prognosis of relapsing patients may be due, at least in part, to factors other than drug resistance. Moreover, the chemosensitivity test adopted is a better predictor in newly diagnosed than relapsing patients, as indicated by the concordance between in vitro and in vivo results.

Isolation of two cellular lines resistant to ribonucleotide reductase inhibitors to investigate the inhibitory activity of 2,2'-bipyridyl-6-carbothioamide.

The mechanism of action of a synthetic compound--2,2'-bipyridyl-6-carbothioamide--was investigated by developing tumor lines resistant to it (P388-R1.5 and P388-R4). P388-R4 is resistant to inhibitors of ribonucleotide reductase (RR) while no resistance was observed to antitumor drugs having other targets (except to bleomycin). The resistance to inhibitors of the RR M2 subunit is higher than that to compounds active on the RR M1 subunit. Moreover, murine chromosome 12, in which the M2 structural gene was recently localized, was trisomic in the resistant lines. We conclude that it is possible to consider BPYTA a new inhibitor of the RR M2 subunit.