Discovery of ultrafast spontaneous spin switching in an antiferromagnet by femtosecond noise correlation spectroscopy.

Owing to their high magnon frequencies, antiferromagnets are key materials for future high-speed spintronics. Picosecond switching of antiferromagnetic spin systems has been viewed a milestone for decades and pursued only by using ultrafast external perturbations. Here, we show that picosecond spin switching occurs spontaneously due to thermal fluctuations in the antiferromagnetic orthoferrite Sm0.7Er0.3FeO3. By analysing the correlation between the pulse-to-pulse polarisation fluctuations of two femtosecond optical probes, we extract the autocorrelation of incoherent magnon fluctuations. We observe a strong enhancement of the magnon fluctuation amplitude and the coherence time around the critical temperature of the spin reorientation transition. The spectrum shows two distinct features, one corresponding to the quasi-ferromagnetic mode and another one which has not been previously reported in pump-probe experiments. Comparison to a stochastic spin dynamics simulation reveals this new mode as smoking gun of ultrafast spontaneous spin switching within the double-well anisotropy potential.

Metachronous hepatic resection for liver only pancreatic metastases.

BACKGROUND: The value of liver resection (LR) for metachronous pancreatic ductal adenocarcinoma (PDAC) metastases remains controversial. However, in light of increasing safety of liver resections, surgery might be a valuable option for metastasized PDAC in selected patients. METHODS: We performed a retrospective, multicenter study including patients undergoing hepatectomy for metachronous PDAC liver metastases between 2004 and 2015 to analyze postoperative outcome and overall survival. All patients were operated with curative intent. Patients with oligometastatic metachronous liver metastasis with definitive chemotherapy (n = 8) served as controls. RESULTS: Overall 25 patients in seven centers were included in this study. The median age at the time of LR was 63.8 years (56.9-69.9) and the median number of metastases in the liver was 1 (IQR 1-2). There were eight non-anatomical resections (32%), 15 anatomical minor (60%) and 2 major LR (8%). Postoperative complications occurred in eleven patients (eight Clavien-Dindo grade I complications (32%) and three grade IIIa complications (12%), respectively). The 30-day mortality was 0%. The median length of stay was 8.6 days (IQR 5-11). Median overall survival following LR was 36.8 months compared to 9.2 months in patients with metachronous liver metastasis with chemotherapy (p = 0007). DISCUSSION: Liver resection for metachronous PDAC metastasis is safe and feasible in selected patients. To address general applicability and to find factors for patient selection, larger trials are urgently warranted.

The Time Deviation in Packet-Based Synchronization.

The telecommunications industry has used the time deviation (TDEV) very effectively for specifying network equipment clock performance as well as the performance of timing signals generated by Central Office equipment such as primary reference clocks and building integrated timing supplies (BITS) and synchronization supply units (SSUs). We discuss here the development of TDEV, and the variations of TDEV motivated by the advent of packet-switching and the steady transformation of the telecom network from circuit-switched-based to packet-switched-based. We illustrate these with simulation of the performance of the precise time protocol (PTP) across a packet-switched network. We then apply published methods to automatically determine noise types, and use these to predict time dispersion from a master clock for a slave clock using these PTP packets to stay synchronized. The result shows how TDEV and the other deviations provide an extensive array of tools for telecom networks, as well as for general time and frequency applications.

Design of non-standard insulin analogs for the treatment of diabetes mellitus.

Structure-based protein design has enabled the engineering of insulin analogs with improved pharmacokinetic and pharmacodynamic properties. Exploiting classical structures of zinc insulin hexamers, the first insulin analog products focused on destabilization of subunit interfaces to obtain rapid-acting (prandial) formulations. Complementary efforts sought to stabilize the insulin hexamer or promote higher-order self-assembly within the subcutaneous depot toward the goal of enhanced basal glycemic control with reduced risk of hypoglycemia. Current products either operate through isoelectric precipitation (insulin glargine, the active component of Lantus; Sanofi-Aventis, Paris, France) or employ an albumin-binding acyl tether (insulin detemir, the active component of Levemir; Novo-Nordisk, Basværd, Denmark). In the past year second-generation basal insulin analogs have entered clinical trials in an effort to obtain ideal flat 24-hour pharmacodynamic profiles. The strategies employ non-standard protein modifications. One candidate (insulin degludec; Novo-Nordisk a/s) undergoes extensive subcutaneous supramolecular assembly coupled to a large-scale allosteric reorganization of the insulin hexamer (the TR transition). Another candidate (LY2605541; Eli Lilly and Co., Indianapolis, IN, USA) utilizes coupling to polyethylene glycol to delay absorption and clearance. On the other end of the spectrum, advances in delivery technologies (such as microneedles and micropatches) and excipients (such as the citrate/zinc-ion chelator combination employed by Biodel, Inc., Danbury, CT, USA) suggest strategies to accelerate PK/PD toward ultra-rapid-acting insulin formulations. Next-generation insulin analogs may also address the feasibility of hepatoselective signaling. Although not in clinical trials, early-stage technologies provide a long-range vision of "smart insulins" and glucose-responsive polymers for regulated hormone release.

Varying ratios of wavelengths in dual wavelength LED photomodulation alters gene expression profiles in human skin fibroblasts.

BACKGROUND AND OBJECTIVE: LED photomodulation has been shown to profoundly influence cellular behavior. A variety of parameters with LED photomodulation can alter cellular response in vitro. The effects of one visible and one infrared wavelength were evaluated to determine the optimal ratio to produce a net increase in dermal collagen by altering the ratio of total energy output of each wavelength. The ratio between the two wavelengths (590 and 870 nm) was shifted in 25% increments. STUDY DESIGN/MATERIALS AND METHODS: Human skin fibroblasts in culture were exposed to a 590/870 nm LED array with total combined energy density fixed at 4.0 mW/cm.. The ratio of 590/870 nm tested parameters were: 100/0%, 75/25%, 50/50%, 25/75%, and 0/100%. These ratios were delivered using pulsed duty cycle of exposure (250 milliseconds "on" time/100 milliseconds "off" time/100 pulses) for a total energy fluence of 0.1 J/cm.. Gene expression was examined using commercially available extra cellular matrix and adhesion molecule RT PCR Arrays (SA Biosciences, Frederick, MD) at 24 hours post-exposure. RESULTS: Different expression profiles were noticed for each of the ratios studied. Overall, there was an average (in an 80 gene array) of 6% expression difference in up or downregulation between the arrays. The greatest increase in collagen I and decrease in collagenase (MMP-1) was observed with 75/25% ratio of 590/870 nm. The addition of increasing proportions of IR wavelengths causes alteration in gene expression profile. The ratios of the wavelengths caused variation in magnitude of expression. CONCLUSIONS: Cell metabolism and gene expression can be altered by simultaneous exposure to multiple wavelengths of low energy light. Varying the ratios of specific wavelength intensity in both visible and near infrared light therapy can strongly influence resulting fibroblast gene expression patterns.

Human sex reversal due to impaired nuclear localization of SRY. A clinical correlation.

SRY, an architectural transcription factor encoded by the sex-determining region of the Y chromosome, initiates testicular differentiation in mammalian embryogenesis. The protein contains a high-mobility group (HMG) box, a DNA-bending motif conserved among a broad class of nuclear proteins. Mutations causing human sex reversal (46, XY pure gonadal dysgenesis) are clustered in this domain. Basic N- and C-terminal regions of the HMG box are each proposed to provide nuclear localization signals. The significance of the C-terminal basic cluster (SRY residues 130-134) is uncertain, however, as its activity in cell culture varies with assay conditions. To test its importance, we have investigated a C-terminal sex-reversal mutation (R133W, position 78 of the HMG box). This de novo mutation impairs nuclear localization but not specific DNA binding or sharp DNA bending. Correlation between these properties and the phenotype of the patient suggests that nuclear localization of SRY is required for testicular differentiation and directed in part by the C-terminal basic cluster. To our knowledge, these results provide the first example of impaired organogenesis due to a nuclear localization signal mutation.

Hierarchical protein folding: asymmetric unfolding of an insulin analogue lacking the A7-B7 interchain disulfide bridge.

The landscape paradigm of protein folding can enable preferred pathways on a funnel-like energy surface. Hierarchical preferences may be manifest as a nonrandom pathway of disulfide pairing. Stepwise stabilization of structural subdomains among on-pathway intermediates is proposed to underlie the disulfide pathway of proinsulin and related molecules. Here, effects of pairwise serine substitution of insulin's exposed interchain disulfide bridge (Cys(A7)-Cys(B7)) are characterized as a model of a late intermediate. Untethering cystine A7-B7 in an engineered monomer causes significantly more marked decreases in the thermodynamic stability and extent of folding than occur on pairwise substitution of internal cystine A6-A11 [Weiss, M. A., Hua, Q. X., Jia, W., Chu, Y. C., Wang, R. Y., and Katsoyannis, P. G. (2000) Biochemistry 39, 15429-15440]. Although substantially disordered and without significant biological activity, the untethered analogue contains a molten subdomain comprising cystine A20-B19 and a native-like cluster of hydrophobic side chains. Remarkably, A and B chains make unequal contributions to this folded moiety; the B chain retains native-like supersecondary structure, whereas the A chain is largely disordered. These observations suggest that the B subdomain provides a template to guide folding of the A chain. Stepwise organization of insulin-like molecules supports a hierarchic view of protein folding.

Activities of monomeric insulin analogs at position A8 are uncorrelated with their thermodynamic stabilities.

Previous studies have demonstrated that the potency and thermodynamic stability of human insulin are enhanced in concert by substitution of Thr(A8) by arginine or histidine. These surface substitutions stabilize the N-terminal alpha-helix of the A chain, a key element of hormone-receptor recognition. Does enhanced stability necessarily imply enhanced activity? Here, we test by structure-based mutagenesis the relationship between the stability and activity of the hormone. To circumvent confounding effects of insulin self-association, A chain analogs were combined with a variant B chain (Asp(B10), Lys(B28), and Pro(B29) (DKP)) to create a monomeric template. Five analogs were obtained by chain combination; disulfide pairing proceeded in each case with native yield. CD and (1)H NMR spectra of the DKP analogs are essentially identical to those of DKP-insulin, indicating a correspondence of structures. Receptor binding affinities were determined by competitive displacement of (125)I-insulin from human placental membranes. Thermodynamic stabilities were measured by CD titration; unfolding was monitored as a function of guanidine concentration. In this broader collection of analogs receptor binding affinities are uncorrelated with stability. We suggest that receptor binding affinities of A8 analogs reflect local features of the hormone-receptor interface rather than the stability of the free hormone or the intrinsic C-capping propensity of the A8 side chain.

The dimerization domain of HNF-1alpha: structure and plasticity of an intertwined four-helix bundle with application to diabetes mellitus.

Maturity-onset diabetes mellitus of the young (MODY) is a human genetic syndrome most commonly due to mutations in hepatocyte nuclear factor-1alpha (HNF-1alpha). Here, we describe the crystal structure of the HNF-1alpha dimerization domain at 1.7 A resolution and assess its structural plasticity. The crystal's low solvent content (23%, v/v) leads to tight packing of peptides in the lattice. Two independent dimers, similar in structure, are formed in the unit cell by a 2-fold crystallographic symmetry axis. The dimers define a novel intertwined four-helix bundle (4HB). Each protomer contains two alpha-helices separated by a sharp non-canonical turn. Dimer-related alpha-helices form anti-parallel coiled-coils, including an N-terminal "mini-zipper" complementary in structure, symmetry and surface characteristics to transcriptional coactivator dimerization cofactor of HNF-1 (DCoH). A confluence of ten leucine side-chains (five per protomer) forms a hydrophobic core. Isotope-assisted NMR studies demonstrate that a similar intertwined dimer exists in solution. Comparison of structures obtained in multiple independent crystal forms indicates that the mini-zipper is a stable structural element, whereas the C-terminal alpha-helix can adopt a broad range of orientations. Segmental alignment of the mini-zipper (mean pairwise root-mean-square difference (rmsd) in C(alpha) coordinates of 0.29 A) is associated with a 2.1 A mean C(alpha) rmsd displacement of the C-terminal coiled-coil. The greatest C-terminal structural variation (4.1 A C(alpha) rmsd displacement) is observed in the DCoH-bound peptide. Diabetes-associated mutations perturb distinct structural features of the HNF-1alpha domain. One mutation (L12H) destabilizes the domain but preserves structural specificity. Adjoining H12 side-chains in a native-like dimer are predicted to alter the functional surface of the mini-zipper involved in DCoH recognition. The other mutation (G20R), by contrast, leads to a dimeric molten globule, as indicated by its 1H-NMR features and fluorescent binding of 1-anilino-8-naphthalene sulfonate. We propose that a glycine-specific turn configuration enables specific interactions between the mini-zipper and the C-terminal coiled-coil.

Novel treatment strategies in chronic lymphocytic leukemia.

The recent introduction of new active agents has led to a renaissance of clinical investigation in chronic lymphocytic leukemia (CLL). These agents include three purine analogues, (pentostatin, fludarabine, and cladribine) and two monoclonal antibodies (rituximab and CAMPATH I-H). Careful clinical studies have allowed for the development of novel combinations of two and even three non-cross- resistant agents. These preliminary studies indicate that such combinations can induce complete responses in a larger proportion of patients than can single-agent therapy. In CLL, survival is superior for patients achieving a complete response compared with patients achieving a partial response. Therefore, strategies designed to induce high-quality responses in the majority of patients may one day lead to improved survival or possibly even cure in patients with chronic lymphocytic leukemia.

A thermophilic mini-chaperonin contains a conserved polypeptide-binding surface: combined crystallographic and NMR studies of the GroEL apical domain with implications for substrate interactions.

A homologue of the Escherichia coli GroEL apical domain was obtained from thermophilic eubacterium Thermus thermophilus. The domains share 70 % sequence identity (101 out of 145 residues). The thermal stability of the T. thermophilus apical domain (Tm>100 degrees C as evaluated by circular dichroism) is at least 35 degrees C greater than that of the E. coli apical domain (Tm=65 degrees C). The crystal structure of a selenomethione-substituted apical domain from T. thermophilus was determined to a resolution of 1.78 A using multiwavelength-anomalous-diffraction phasing. The structure is similar to that of the E. coli apical domain (root-mean-square deviation 0.45 A based on main-chain atoms). The thermophilic structure contains seven additional salt bridges of which four contain charge-stabilized hydrogen bonds. Only one of the additional salt bridges would face the "Anfinsen cage" in GroEL. High temperatures were exploited to map sites of interactions between the apical domain and molten globules. NMR footprints of apical domain-protein complexes were obtained at elevated temperature using 15N-1H correlation spectra of 15N-labeled apical domain. Footprints employing two polypeptides unrelated in sequence or structure (an insulin monomer and the SRY high-mobility-group box, each partially unfolded at 50 degrees C) are essentially the same and consistent with the peptide-binding surface previously defined in E. coli GroEL and its apical domain-peptide complexes. An additional part of this surface comprising a short N-terminal alpha-helix is observed. The extended footprint rationalizes mutagenesis studies of intact GroEL in which point mutations affecting substrate binding were found outside the "classical" peptide-binding site. Our results demonstrate structural conservation of the apical domain among GroEL homologues and conservation of an extended non-polar surface recognizing diverse polypeptides.

Floppy SOX: mutual induced fit in hmg (high-mobility group) box-DNA recognition.

The high-mobility group (HMG) box defines a DNA-bending motif of broad interest in relation to human development and disease. Major and minor wings of an L-shaped structure provide a template for DNA bending. As in the TATA-binding protein and a diverse family of factors, insertion of one or more side chains between base pairs induces a DNA kink. The HMG box binds in the DNA minor groove and may be specific for DNA sequence or distorted DNA architecture. Whereas the angular structures of non-sequence-specific domains are well ordered, free SRY and related autosomal SOX domains are in part disordered. Observations suggesting that the minor wing lacks a fixed tertiary structure motivate the hypothesis that DNA bending and stabilization of protein structure define a coupled process. We further propose that mutual induced fit in SOX-DNA recognition underlies the sequence dependence of DNA bending and enables the induction of promoter-specific architectures.

SRYand architectural gene regulation: the kinetic stability of a bent protein-DNA complex can regulate its transcriptional potency.

Protein-directed DNA bending is proposed to regulate assembly of higher-order DNA-multiprotein complexes (enhanceosomes and repressosomes). Because transcriptional initiation is a nonequilibrium process, gene expression may be modulated by the lifetime of such complexes. The human testis-determining factor SRY contains a specific DNA-bending motif, the high-mobility group (HMG) box, and is thus proposed to function as an architectural factor. Here, we test the hypothesis that the kinetic stability of a bent HMG box-DNA complex can in itself modulate transcriptional potency. Our studies employ a cotransfection assay in a mammalian gonadal cell line as a model for SRY-dependent transcriptional activation. Whereas sex-reversal mutations impair SRY-dependent gene expression, an activating substitution is identified that enhances SRY's potency by 4-fold. The substitution (I13F in the HMG box; fortuitously occurring in chimpanzees) affects the motif's cantilever side chain, which inserts between base pairs to disrupt base pairing. An aromatic F13 cantilever prolongs the lifetime of the DNA complex to an extent similar to its enhanced function. By contrast, equilibrium properties (specific DNA affinity, specificity, and bending; thermodynamic stability and cellular expression) are essentially unchanged. This correlation between potency and lifetime suggests a mechanism of kinetic control. We propose that a locked DNA bend enables multiple additional rounds of transcriptional initiation per promoter. This model predicts the occurrence of a novel class of clinical variants: bent but unlocked HMG box-DNA complexes with native affinity and decreased lifetime. Aromatic DNA-intercalating agents exhibit analogous kinetic control of transcriptional elongation whereby chemotherapeutic potencies correlate with drug-DNA dissociation rates.

Hierarchical protein "un-design": insulin's intrachain disulfide bridge tethers a recognition alpha-helix.

A hierarchical pathway of protein folding can enable segmental unfolding by design. A monomeric insulin analogue containing pairwise substitution of internal A6-A11 cystine with serine [[Ser(A6),Ser(A11),Asp(B10),Lys(B28),Pro(B29)]insulin (DKP[A6-A11](Ser))] was previously investigated as a model of an oxidative protein-folding intermediate [Hua, Q. X., et al. (1996) J. Mol. Biol. 264, 390-403]. Its structure exhibits local unfolding of an adjoining amphipathic alpha-helix (residues A1-A8), leading to a 2000-fold reduction in activity. Such severe loss of function, unusual among mutant insulins, is proposed to reflect the cost of induced fit: receptor-directed restoration of the alpha-helix and its engagement in the hormone's hydrophobic core. To test this hypothesis, we have synthesized and characterized the corresponding alanine analogue [[Ala(A6),Ala(A11),Asp(B10),Lys(B28), Pro(B29)]insulin (DKP[A6-A11](Ala))]. Untethering the A6-A11 disulfide bridge by either amino acid causes similar perturbations in structure and dynamics as probed by circular dichroism and (1)H NMR spectroscopy. The analogues also exhibit similar decrements in thermodynamic stability relative to that of the parent monomer as probed by equilibrium denaturation studies (Delta Delta G(u) = 3.0 +/- 0.5 kcal/mol). Despite such similarities, the alanine analogue is 50 times more active than the serine analogue. Enhanced receptor binding (Delta Delta G = 2.2 kcal/mol) is in accord with alanine's greater helical propensity and more favorable hydrophobic-transfer free energy. The success of an induced-fit model highlights the applicability of general folding principles to a complex binding process. Comparison of DKP[A6-A11](Ser) and DKP[A6-A11](Ala) supports the hypothesis that the native A1-A8 alpha-helix functions as a preformed recognition element tethered by insulin's intrachain disulfide bridge. Segmental unfolding by design provides a novel approach to dissecting structure-activity relationships.

Treatment of poikiloderma of Civatte with an intense pulsed light source.

BACKGROUND: Effective treatment of poikiloderma of Civatte combines elimination of both the vascular and pigmented components simultaneously. A broad spectrum, noncoherent, intense pulsed light (IPL) source delivers multiple wavelengths with software controlled pulse durations and sequencing, which permits treatment of both vascular and pigmented lesions simultaneously. OBJECTIVE: To determine response and side effects of poikiloderma of Civatte of the neck and chest when treated by IPL. METHODS: One hundred and thirty-five patients randomly selected with typical changes of poikiloderma of Civatte on the neck and/or upper chest were treated with one to five treatments using IPL. RESULTS: Clearance of more than 75% of telangiectasias and hyperpigmentation comprising poikiloderma was observed. The incidence of side effects was 5%, including pigment changes. In many cases, improved skin texture was noted both by physician and patient. CONCLUSION: IPL is an effective mode of therapy for poikiloderma of Civatte. It offers a reduction of pigment and telangiectasias with a low risk profile. Additional benefits include subjective changes of improvement in skin texture.

Consolidation therapy with high-dose cyclophosphamide improves the quality of response in patients with chronic lymphocytic leukemia treated with fludarabine as induction therapy.

Fludarabine is the most active agent in the treatment of chronic lymphocytic leukemia (CLL). Despite this activity only a minority of patients treated with fludarabine achieve a complete response. We evaluated a new treatment program of sequential therapy with fludarabine followed by high-dose cyclophosphamide in previously untreated patients with CLL. This report details the results in 25 patients with previously untreated CLL. Patients received fludarabine (25 mg/m2/day x 5 days every 4 weeks for six cycles) as induction followed by consolidation with high-dose cyclophosphamide at one of three dose levels 1.5 g/m2, 2.25 g/m2, or 3 g/m2 administered every 2 weeks for three doses. High-dose cyclophosphamide was given with G-CSF support (5 microg/kg/day days 3-12). Complete response (CR) required a normal physical examination, normal CBC, a normal bone marrow evaluation including no residual lymphoid nodules on biopsy. A nodular response was defined as a complete response with the exception of an occasional residual nodule seen on bone marrow biopsy. Flow cytometric analysis for CD5:CD19 dual staining and kappa/lambda clonal excess was performed in all patients as a sensitive measure of minimal residual disease (MRD). Selected patients had patient/tumor-specific oligonucleotides generated that were subsequently used in a polymerase chain reaction as an extremely sensitive measure of MRD. There were no treatment-related deaths and no patient encountered unacceptable toxicity. After completion of this sequential regimen 76% (95% confidence interval: 59-93%) of patients had a major response: eight (32%) achieved a CR, four (16%) a nodular response, seven (28%) a PR, and six patients (24%) failed. Four patients withdrew from study during induction with fludarabine and did not receive at least one cycle of cyclophosphamide. Of the 21 patients who received consolidation with cyclophosphamide 10 (48%) had an improved quality of response when compared to that achieved with fludarabine. Two patients (8%) had no disease detectable by flow cytometry ('flow cytometric' CR) after six cycles of fludarabine. This improved to nine patients (36%) after high-dose cyclophosphamide. Following consolidation with high-dose cyclophosphamide three patients (12%) tested negative by PCR. All of these patients had morphologic evidence of residual disease after six cycles of fludarabine. Consolidation with high-dose cyclophosphamide increased the fraction of patients achieving a nodular response or CR three-fold (16% to 48%). This appears to be clinically relevant because with a median follow-up of 52 (range 34-78) months the projected 6-year survival for patients achieving a CR or NR is 91% compared to 41% for all others (P = 0.012). We conclude that sequential therapy with fludarabine followed by high-dose cyclophosphamide in previously untreated patients with CLL is safe and can improve the quality of response in a large proportion of patients compared to therapy with fludarabine alone.

Sexual dimorphism in diverse metazoans is regulated by a novel class of intertwined zinc fingers.

Sex determination is regulated by diverse pathways. Although upstream signals vary, a cysteine-rich DNA-binding domain (the DM motif) is conserved within downstream transcription factors of Drosophila melanogaster (Doublesex) and Caenorhabditis elegans (MAB-3). Vertebrate DM genes have likewise been identified and, remarkably, are associated with human sex reversal (46, XY gonadal dysgenesis). Here we demonstrate that the structure of the Doublesex domain contains a novel zinc module and disordered tail. The module consists of intertwined CCHC and HCCC Zn(2+)-binding sites; the tail functions as a nascent recognition alpha-helix. Mutations in either Zn(2+)-binding site or tail can lead to an intersex phenotype. The motif binds in the DNA minor groove without sharp DNA bending. These molecular features, unusual among zinc fingers and zinc modules, underlie the organization of a Drosophila enhancer that integrates sex- and tissue-specific signals. The structure provides a foundation for analysis of DM mutations affecting sexual dimorphism and courtship behavior.

A phase I and II study of pentostatin (Nipent) with cyclophosphamide for previously treated patients with chronic lymphocytic leukemia.

Purine analogs and alkylating agents are the most active drugs in the treatment of patients with chronic lymphocytic leukemia (CLL). Although fludarabine is the most widely tested purine analog in CLL, myelosuppression has limited its use in combination chemotherapy regimens. Because pentostatin (Nipent; SuperGen, San Ramon, CA), a related purine analog with proven activity in CLL, has less myelosuppression, we postulated that it would prove advantageous and could be more readily combined with alkylating agents. We are conducting a phase I/II trial of combination chemotherapy with pentostatin and cyclophosphamide for previously treated patients with CLL. Patients need to have Rai high-risk disease or "active" intermediate-risk disease. The treatment regimen consists of a fixed dose of pentostatin (4 mg/m2) combined with an increasing dose of cyclophosphamide. We plan to treat cohorts of three patients each at cyclophosphamide dose levels of 600, 900, 1,200, 1,500, and 2,000 mg/m2. Cycles will be repeated every 21 days. If unacceptable toxicity is encountered at one dose level, then three additional patients (total of six patients) will be accrued to that dose level before further dose escalations will be permitted. A second instance of unacceptable toxicity will close that dose level and identify the preceding level as the phase II dose. Additional patients will be accrued to the phase II dose level to better assess response. Supportive measures include the use of granulocyte colony-stimulating factor (5 microg/kg/d) to limit neutropenia. Sulfamethoxazole/trimethoprim will be given as prophylaxis against Pneumocystis carinii pneumonia and acyclovir will be administered as prophylaxis for herpes zoster. Response will be assessed according to standard criteria, and flow cytometry and fluorescent in situ hybridization will be used to assess for minimal residual disease in patients with trisomy 12.