Patient-reported outcomes (PROs) in KEYLYNK-010: Pembrolizumab (pembro) plus olaparib (ola) vs abiraterone acetate (abi) or enzalutamide (enza) for patients (pts) with previously treated metastatic castration-resistant prostate cancer (mCRPC)

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Background: The phase 3, randomized KEYLYNK-010 trial (NCT03834519) of pembro + ola vs next-generation hormonal agent (NHA) abi or enza did not significantly improve rPFS or OS in molecularly unselected pts with mCRPC treated with prior NHA and docetaxel. The study was stopped for futility after the second prespecified interim analysis. PROs for pembro + ola vs NHA in KEYLYNK-010 are presented. Methods: Pts were randomly assigned 2:1 to receive pembro 200 mg IV Q3W for ≤35 cycles (~2 y) + ola 300 mg orally BID or NHA (either abi 1000 mg orally QD + prednisone 5 mg orally BID, if pt previously received enza, or enza 160 mg orally QD if pt previously received abi). PROs were evaluated in pts who received ≥1 dose of study treatment and had ≥1 PRO assessment. FACT-P and BPI-SF were administered at baseline, Q3W until wk 24, Q6W until wk 72, and Q12W thereafter for ≤2 y. Time to pain progression (TTPP) based on BPI-SF was a prespecified secondary end point. Prespecified exploratory end points included least squares mean (LSM) change from baseline to wk 15 for FACT-P total and subscales scores (FACT-G total, TOI, FAPSI-6, FWB, PWB, and PCS) and BPI-SF scores (pain interference, pain severity, and worst pain), and time to deterioration (TTD) and overall improvement rate in FACT-P total and subscale scores. Differences were evaluated using 2-sided nominal P values not controlled for multiplicity. Results: A total of 793 pts were randomly assigned to pembro + ola (n = 529) or NHA (n = 264). As of January 18, 2022, median follow-up was 18.7 mo (range, 6.1-31.7). In all randomized pts, completion rate for FACT-P and BPI-SF at baseline and wk 15 was >84% and >57%, respectively. No differences were observed in the median TTPP for pembro + ola (13.5 mo [95% CI, 9.7-NR]) vs NHA (12.0 mo [95% CI, 10.1-NR]; HR, 0.95 [0.72-1.26]). No LSM differences were observed in FACT-P total scores (pembro + ola, –4.62 [95% CI, –6.47 to –2.77] vs NHA, –5.86 [95% CI, –8.58 to –3.13]) or BPI-SF scores (Table). There were no differences in TTD in FACT-P total, FACT-G total, TOI, FAPSI-6, FWB, PWB, and PCS scores between groups. A numerically higher proportion of pts had improved + stable FACT-P total scores for pembro + ola (44.0%) vs NHA (39.0%). FACT-P and BPI-SF scores were generally maintained across all evaluated time points up to wk 81. Conclusions: No clinically meaningful changes from baseline were observed in HRQoL or disease-related symptom scores with either pembro + ola or NHA. PRO scores were generally similar between pembro + ola and NHA at all analyzed time points, suggesting HRQoL was maintained in heavily pretreated pts receiving pembro + ola. Clinical trial information: NCT03834519 . [Table: see text]

Phase I-II study to evaluate safety and efficacy of niraparib plus cabozantinib in patients with advanced urothelial/kidney cancer (NICARAGUA trial): Preliminary data of phase I study

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Background: Niraparib (N) is a (PARP)-1/-2 inhibitor and Cabozantinib (C) is a tyrosine kinase (TK) inhibitor that targets VEGF signalling via inhibition of multiple TK receptors including c-MET and TAM kinases (TYRO3, AXL, MER). The c-Met receptor TK is abnormally activated and could be decrease response to PARP inhibitors. Preclinical data reveals that treatment with c-Met inhibitors renders cells more sensitive to PARP inhibition. A phase (Ph) I-II study was designed to explore the safety and efficacy of the combination of N + C in genitourinary cancers. Methods: Multicenter, open-label Ph I-II study (NCT03425201). Confirmed histopathological diagnosis of either metastatic urothelial carcinoma (mUC) or advanced clear cell renal cell carcinoma previously treated with a maximum of two previous regimens. Adequate bone marrow, liver and renal functions were required. The Ph I portion aimed to identify the maximum tolerated dose (MTD) and recommended ph II dose (RP2D). Pt received N and C p.o. once daily in 28-day cycles: Dose level 1 (DL1) N/C 100/20 mg; DL2 200/20 mg; DL3 200/40 mg; DL4 200/60 mg. A further amendment developed DL1.1 100/40 mg. Pt were accrued to each dose level in cohorts of 6 pt until the MTD was achieved (defined as highest dose at which ≤1 out of 6 pt experience a DLT, evaluated during the first 2 cycles). Results: Nineteen evaluable pt for DLT were included, 14 of them had UC. There was no DLT at DL1. Two out of the first 6 evaluable pt in DL2 had DLT (G3 thrombopenia and anemia and G3 diarrhea respectively). Upon analysis of these pt it was agreed to include 3 additional new pt for evaluation. Two pt were included with one presenting a DLT (G3 hepatic toxicity). Enrolment then continued in a new DL 1.1 cohort and 1 of 6 pts had DLT (G3 mucositis), being then considered the RP2D. No toxic deaths were reported. Six pt (32%) received at least 10 cycles and 9 pt (47%) received at least 6 cycles. Three patients (16%) achieved partial response (all of them with mUC disease) and 14 (74%) stable disease. Conclusions: N plus C combination can be safely administered with a manageable toxicity profile and preliminary efficacy was reported in mUC heavily pretreated pts. The RP2D is N 100 mg plus C 40 mg qd. Ph II study is now recruiting mUC patients. Clinical trial information: NCT03425201. [Table: see text]

Spermidine is essential for normal proliferation of trypanosomatid protozoa

Trypanosomatid parasites containing a metabolically unstable ornithine decarboxylase (ODC) are naturally resistant to high levels of alpha-difluoromethylornithine (DFMO) because this ODC inhibitor, though causing a drastic reduction of intracellular putrescine, elicits only a moderate decrease of the spermidine endogenous pool. In this study we have used a combination of DFMO with cyclohexylamine (CHA; bis-cyclohexylammonium sulfate), an inhibitor of spermidine synthase, to reach a more complete depletion of spermidine. Under these conditions we have observed the arrest of proliferation not only in trypanosomatids with stable ODC but also in parasites with an enzyme of high turnover rate. In all cases the reinitiation of proliferation occurred only after the addition of exogenous spermidine, and neither putrescine nor spermine were able to induce the same effect.

Sensitivity of trypanosomatid protozoa to DFMO and metabolic turnover of ornithine decarboxylase

alpha-Difluoromethylornithine (DFMO), the specific and irreversible inhibitor of ornithine decarboxylase (ODC), was able to induce the arrest of proliferation in Leishmania mexicana and ODC-transformed Trypanosoma cruzi cultures grown in a semi-defined medium essentially free of polyamines. Conversely, Crithidia fasciculata and Phytomonas 274 were not affected by the inhibitor. The drug-resistance of Crithidia and Phytomonas was neither caused by an impairment of DFMO uptake nor by a decrease of the enzyme affinity for the inhibitor. We were also able to rule out the possibility of ODC overexpression in the drug-tolerant parasites. The measurements of ODC metabolic turnover indicated that the enzymes from Crithidia and Phytomonas have a short half-life of 20-40 min, while ODC from Leishmania and transgenic Trypanosoma cruzi are rather stable with a half-life longer than 6 hours. Analyses of polyamine internal pools under different growth conditions have shown that DFMO was able to markedly decrease the levels of putrescine and spermidine in all parasites, but the depletion of spermidine was higher in trypanosomatids containing an ODC with slow turnover. Our results suggest that in these parasites cultivated in the presence of the drug, spermidine might decrease below critical levels needed to maintain trypanothione concentrations or other conditions essential for normal proliferation.

Trypanosoma cruzi epimastigotes lack ornithine decarboxylase but can express a foreign gene encoding this enzyme

Trypanosoma cruzi, a pathogenic protozoan causing Chagas disease, lacks ornithine decarboxylase (ODC), the enzyme catalyzing the first step of polyamine biosynthetic pathway in eukaryotic cells. Our results indicate that the auxotrophy for diamines of T. cruzi epimastigotes is due to the absence of an active ODC gene in these parasites and not to the inability for the expression of this gene. The introduction of an exogenous complete coding region from Crithidia fasciculata ODC gene inserted in an expression vector specific for trypanosomatids induces the normal expression of the foreign genetic information allowing the transformed T. cruzi to overcome the exogenous polyamine requirement for growth. The enzyme expressed in the transformed parasites has shown a considerably extended metabolic stability. The loss of ODC activity in T. cruzi might be related to the parasite adaptation to the intracellular stages of its life cycle.

Alpha-difluoromethylornithine-resistant cell lines obtained after one-step selection of Leishmania mexicana promastigote cultures

Proliferation of Leishmania mexicana promastigotes in synthetic medium can be blocked by the depletion of intracellular polyamine pools induced by the presence of D,L-alpha-difluoromethylornithine (DFMO), a specific and irreversible inhibitor of ornithine decarboxylase (ODC). Here we report that DFMO-resistant cell lines growing normally at DFMO levels of 10 mM have been obtained from non-proliferating cultures after a single-step selection in the presence of high concentrations of the drug. The DFMO-resistant promastigotes underwent a morphological transformation into an 'amastigote-like' form after incubation for several hours at gradually increasing temperatures up to 35 degrees C. The uptake of DFMO was not significantly altered in the drug-resistant cell lines but in both cases (promastigote and 'amastigote-like' forms) the ODC specific activity was increased approx. 15-fold over the normal enzymic levels found in the wild-type Leishmania. The enzyme affinities for its substrate and for DFMO gave very similar values in the drug-resistant promastigotes and the wild-type parasites. In contrast, ODC from the 'amastigote-like' Leishmania showed a higher affinity for ornithine and a decreased capacity for the binding of DFMO. An 80-fold amplification of the ODC gene and a corresponding increase in its transcripts have been detected in both DFMO-resistant Leishmania cell lines. The drug-resistant phenotypes with their characteristic morphologies, the increased levels of ODC activity and the amplification of the ODC gene have been stable for at least 6 months in the absence of selective pressure.

Ornithine decarboxylase from Leishmania mexicana promastigotes: interaction with pyridoxal 5'-phosphate and alpha-difluoromethylornithine

The catalytic properties of ornithine decarboxylase (ODC) from Leishmania mexicana as well as the interaction with its cofactor pyridoxal 5'-phosphate (PLP) and the irreversible inhibitor alpha-difluoromethylornithine (DFMO) have been studied using partially purified preparations of the enzyme obtained from parasite promastigotes. Leishmania extracts prepared in the presence of saturating concentrations of PLP yielded an enzyme considerably more resistant to heat inactivation and with a three-fold higher activity than the ODC obtained without the addition of cofactor. The complete removal of PLP by treatment with hydroxylamine yielded the apoenzyme which shows an absolute requirement for PLP to recover its enzymatic activity. The Km values for L-ornithine and PLP were 0.7 mM and 25 microM, respectively, while Ki for DFMO was 0.2 mM. The restoration of ODC activity from apoenzyme and cofactor seems to involve time and temperature-dependent activation processes. L. mexicana ODC has an apparent molecular mass of 240 +/- 20 kDa.

Differential regulation of putrescine uptake in Trypanosoma cruzi and other trypanosomatids

Putrescine uptake in Trypanosoma cruzi epimastigotes is 10 to 50-fold higher than in Leishmania mexicana or Crithidia fasciculata. Polyamine transport in all these trypanosomatids is an energy-dependent process strongly inhibited by the presence of 2,4-dinitrophenol or KCN. Putrescine uptake in T. cruzi and L. mexicana was markedly decreased by the proton ionophore carbonylcyanide m-chlorophenylhydrazone but it was not affected by ouabain, a Na(+)-K+ pump inhibitor. The depletion of intracellular polyamines by treatment of parasite cultures with alpha-difluoromethylornithine elicited a marked induction of putrescine uptake in L. mexicana and C. fasciculata by increasing considerably the Vmax of this process. Conversely, the uptake of putrescine in T. cruzi was essentially unchanged by the same treatment. The differential regulation of putrescine transport in T. cruzi might be related to some distinctive features of polyamine metabolism in this parasite.

Ornithine decarboxylase from Crithidia fasciculata is metabolically unstable and resistant to polyamine down-regulation

Ornithine decarboxylase (ODC) of Crithidia fasciculata extracts shows maximal activity during exponential growth of the parasite and decreases markedly in the stationary phase. The inhibition of protein synthesis by cycloheximide evoked a rapid loss of enzyme activity with a half-life of about 30 min. Upon removal of DFMO from Crithidia cultures treated with the drug for 24 h, the ODC activity increased at the same rate as total protein synthesis. The addition of putrescine at high concentrations to parasites cultivated in a synthetic medium showed that Crithidia ODC levels were not reduced by polyamines.

Control of Leishmania mexicana proliferation by modulation of polyamine intracellular levels

Repeated treatments of Leishmania mexicana promastigote cultures with a-difluoromethylornithine could not block proliferation when the parasite was grown in a rich medium. Although the irreversible inhibitor of ornithine decarboxylase was able to abolish the enzymatic activity under these conditions, polyamine depletion was only partial probably due to the uptake of these substances from the external medium. Conversely, when Leishmania was cultivated in a defined medium essentially free of polyamines, a-difluoromethylornithine was able to decrease the growth rate and proliferation was arrested after several passages in the presence of the drug. Parasite multiplication could be resumed by addition of exogenous polyamines, and a strict correlation between Leishmania promastigote growth and intracellular levels of spermidine was observed.

Stable ornithine decarboxylase in promastigotes of Leishmania mexicana mexicana

Studies on the decarboxylation of ornithine in Leishmania mexicana have shown that this activity corresponds to a true ornithine decarboxylase rather than to an oxidative decarboxylation or aminotransferase reaction, both of which also give rise to the release of CO2. The stoichiometric relationship between substrate and products has indicated that extracts of L. mexicana were able to catalyse the formation of an unknown compound besides putrescine and CO2. The addition of cycloheximide to cultures of L. mexicana allowed us to demonstrate that ornithine decarboxylase degradation in vivo was extremely slow in this parasite. This remarkable stability of the enzyme is only comparable to that found in Trypanosoma brucei and contrasts with the high turnover rate of ornithine decarboxylases of different mammalian cells.

Association of ribosomal subunits. IV. Polyamines as active components of the association factor from Bacillus stearothermophilus

The association of ribosomal subparticles induced by several associating agents has been studied under different conditions. The following observations were made: 1. Spermidine was able to produce the association of subunits, and the concentration and temperature curves of this reaction were similar to those obtained with association factor. The product formed in the latter case was more stable. 2. The association at low Mg2+ concentration was higher with association factor than with polyamines. 3. The temperature-dependent binding of spermidine to 30-S subunits formed an active complex, which was converted into the 30S-50S couples by the addition of 50-S subparticles at low temperature. A similar behaviour has been previously shown for the complete association factor and its low molecular weight fraction. 4. The same unstable form of 30S-50S couples has been obtained either with spermidine or with the low molecular weight component (AFII) of the association factor. In both cases the protein fraction AFI was able to complete the reaction by stabilizing the subunit couple. 5. After glutaraldehyde fixation the products of the reactions with spermidine or association factor behaved in a similar way when they were submitted to long sucrose-gradient centrifugations. 6. The analysis of association factor preparations has shown that they contain spermidine as well as spermine. The polyamine levels in association factor could account for part of the total associating activity.

Isolation of heterogeneous circular DNA from induced lysogens of bacteriophage Mu-1

Covalently-closed circular DNA molecules are formed after induction of phage Mu cts4 and after infection with phage Mu cts4. The circular molecules obtained after induction have a molecular length range from 36.5 to 156.7 kilobases as measured by electron microscopic techniques. These heterogeneous molecules have no consistent correlation to exact multiples of a Mu genome equivalent (37.3 +/- 1.2 kilobases). Direct evidence is given that these molecules contain phage Mu DNA that is covalently linked to other DNA sequences.

Dissociation of 70S ribosomes: some properties of the dissociating factor from Bacillus stearothermophilus and Escherichia coli

A protein factor which produces in vitro dissociation of 70S particles into 30S and 50S subunits has been obtained from Bacillus stearothermophilus and Escherichia coli. The factor could be extracted from ribosomes, polyribosomes, and S100 supernatant. The kinetics and temperature curve of the dissociation process in the B. stearothermophilus system have been studied and compared with the reaction in the E. coli system. No species specificity was observed when hybrid mixtures of ribosomes and dissociating factor from both bacteria were used. The wide variations of dissociating activity in cells at different stages of growth and the capacity of the liberated subunits to carry out polypeptide synthesis suggest that the dissociating factor has a physiological role.