Additive effects of TPMT and NUDT15 on thiopurine toxicity in children with acute lymphoblastic leukemia across multiethnic populations

BACKGROUND

Thiopurines such as mercaptopurine (MP) are widely used to treat acute lymphoblastic leukemia (ALL). Thiopurine-S-methyltransferase (TPMT) and Nudix hydrolase 15 (NUDT15) inactivate thiopurines, and no-function variants are associated with drug-induced myelosuppression. Dose adjustment of MP is strongly recommended in patients with intermediate or complete loss of activity of TPMT and NUDT15. However, the extent of dosage reduction recommended for patients with intermediate activity in both enzymes is currently not clear.

METHODS

MP dosages during maintenance were collected from 1768 patients with ALL in Singapore, Guatemala, India, and North America. Patients were genotyped for TPMT and NUDT15, and actionable variants defined by the Clinical Pharmacogenetics Implementation Consortium were used to classify patients as TPMT and NUDT15 normal metabolizers (TPMT/NUDT15 NM), TPMT or NUDT15 intermediate metabolizers (TPMT IM or NUDT15 IM), or TPMT and NUDT15 compound intermediate metabolizers (TPMT/NUDT15 IM/IM). In parallel, we evaluated MP toxicity, metabolism, and dose adjustment using a Tpmt/Nudt15 combined heterozygous mouse model (Tpmt+/-/Nudt15+/-).

RESULTS

Twenty-two patients (1.2%) were TPMT/NUDT15 IM/IM in the cohort, with the majority self-reported as Hispanics (68.2%, 15/22). TPMT/NUDT15 IM/IM patients tolerated a median daily MP dose of 25.7 mg/m2 (interquartile range = 19.0-31.1 mg/m2), significantly lower than TPMT IM and NUDT15 IM dosage (P < .001). Similarly, Tpmt+/-/Nudt15+/- mice displayed excessive hematopoietic toxicity and accumulated more metabolite (DNA-TG) than wild-type or single heterozygous mice, which was effectively mitigated by a genotype-guided dose titration of MP.

CONCLUSION

We recommend more substantial dose reductions to individualize MP therapy and mitigate toxicity in TPMT/NUDT15 IM/IM patients.

Molecular and long-term behavioral consequences of neonatal opioid exposure and withdrawal in mice

Introduction

Infants exposed to opioids in utero are at high risk of exhibiting Neonatal Opioid Withdrawal Syndrome (NOWS), a combination of somatic withdrawal symptoms including high pitched crying, sleeplessness, irritability, gastrointestinal distress, and in the worst cases, seizures. The heterogeneity of in utero opioid exposure, particularly exposure to polypharmacy, makes it difficult to investigate the underlying molecular mechanisms that could inform early diagnosis and treatment of NOWS, and challenging to investigate consequences later in life.

Methods

To address these issues, we developed a mouse model of NOWS that includes gestational and post-natal morphine exposure that encompasses the developmental equivalent of all three human trimesters and assessed both behavior and transcriptome alterations.

Results

Opioid exposure throughout all three human equivalent trimesters delayed developmental milestones and produced acute withdrawal phenotypes in mice reminiscent of those observed in infants. We also uncovered different patterns of gene expression depending on the duration and timing of opioid exposure (3-trimesters, in utero only, or the last trimester equivalent only). Opioid exposure and subsequent withdrawal affected social behavior and sleep in adulthood in a sex-dependent manner but did not affect adult behaviors related to anxiety, depression, or opioid response.

Discussion

Despite marked withdrawal and delays in development, long-term deficits in behaviors typically associated with substance use disorders were modest. Remarkably, transcriptomic analysis revealed an enrichment for genes with altered expression in published datasets for Autism Spectrum Disorders, which correlate well with the deficits in social affiliation seen in our model. The number of differentially expressed genes between the NOWS and saline groups varied markedly based on exposure protocol and sex, but common pathways included synapse development, the GABAergic and myelin systems, and mitochondrial function.

Abstract CT137: A pilot pharmacokinetic study of VAL413 in patients with recurrent pediatric solid tumors

Background: Ewing's sarcoma (EWS) is the second most common malignant bone tumor affecting children, adolescents and young adults. Intravenous irinotecan hydrochloride (IRN-IV) is approved for the treatment of adult colorectal cancer. IRN-IV is also widely used off-label as salvage therapy for patients with recurrent EWS, rhabdomyosarcoma, neuroblastoma, hepatoblastoma, and medulloblastoma. Prior adult and pediatric trials demonstrate that the combination of intravenous irinotecan and temozolomide has significant antitumor activity in advanced EWS. Recently, commercially available intravenous irinotecan has been administered orally (IRN-IVPO) in pediatric patients to reduce intravenous administration-related side effects, improve convenience and reduce clinic time and costs. Unfortunately, the taste of the iv preparation can be limiting, leading to poor compliance especially in pediatric patients. Development of an advanced formulation to improve tolerability and patient compliance is an important unmet need. Methods: VAL-413 is novel formulation developed to improve tolerability of oral irinotecan for the treatment of cancer. This study (USIND#135675) aims to establish the recommended phase II dose of VAL-413 when given in combination with temozolomide. Secondary objectives include characterization of the pharmacokinetics of VAL-413 vs. conventional irinotecan given orally (IRN-IVPO), evaluating palatability of VAL-413, assessing the toxicity profile of VAL-413 in combination with temozolomide, and assessment of tumor response. Up to 20 patients &gt= 1 to &lt= 30 years of age with recurrent pediatric solid tumors will be enrolled at two different dose levels of VAL-413 in combination with fixed-dose temozolomide using a standard 3 + 3 design. During the first cycle of treatment, each patient will receive 4 daily doses of VAL-413 and one daily dose of IRN-IVPO, together with 5 days of concurrent temozolomide. During all subsequent cycles, only VAL-413 will be given with temozolomide in 5-day courses administered every 21 days. Up to 17 cycles of treatment may be administered on this study. This study design will test the hypothesis that VAL-413 will not have significant pharmacokinetic differences from IRN-IVPO using intra-patient comparison of pharmacokinetic profiles. The evaluation of two dose levels will help to formally define a recommended Phase II dose for further studies. Toxicity will be evaluated based on CTCAEv5 and tumor response based on RECISTv1.1.

Citation Format: James I. Geller, Dennis Brown, Jeffrey Bacha, Neil Sankar, Sarath Kanekal, Mark Leggas, Lars Wagner. A pilot pharmacokinetic study of VAL413 in patients with recurrent pediatric solid tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT137.

Phase II trial of carfilzomib and irinotecan in relapsed small cell lung cancer (NCT01941316)

8513

Background: Relapsed small cell lung cancer (SCLC) is incurable with limited therapeutic options. This phase II study evaluated efficacy and tolerability of carfilzomib + irinotecan in SCLC pts who progressed after prior platinum-based therapy, based on expected synergy of proteosome inhibitor carfilzomib and topisomerase 1 inhibitor irinotecan. Methods: SCLC pts who progressed after one platinum-containing regimen (no maintenance therapy allowed) for recurrent/metastatic disease were eligible. Pts were stratified by response to platinum-based therapy: sensitive (progressive disease (PD) > 90 days after chemo) versus refractory (PD 30 to 90 days after chemo). Pts were treated with up to 6 cycles of carfilzomib (20/36 mg.m2 D1, 2, 8, 9, 15, 16 q28D) and irinotecan (125 mg/m2 D1, 8, 15 q28D), imaging was performed every 2 cycles. The primary efficacy endpoint was 6-month overall survival (OS). Results: 62 pts enrolled and were evaluable for efficacy and adverse events. The 6-month OS was 59% in the platinum sensitive stratum and 54% in the platinum refractory stratum. Overall response rate: sensitive stratum 21.6% (1.6% CR + 16.4% PR) and refractory stratum 12.5% (all PR). Disease control (SD+PR+CR) was 68% in platinum sensitive and 56% in refractory patients. Progression free survival and OS were 3.6 months (95% CI 2.6 - 4.6) and 6.9 months (95% CI 4.3 - 12.3) in the sensitive stratum, and 3.3 months (95% CI 1.8 – 3.9) and 6.8 months (95% CI 4.1-11) in the refractory stratum. Twenty-nine pts (47%) experienced at least one grade 3 AE and 8 subjects had grade 4 toxicities: decreased neutrophils, leukocytes, and lymphocytes, diarrhea, vomiting, sepsis, hypokalemia, hypocalcemia, and dehydration. There were three treatment related deaths: myocardial infarction (possible), lung infection (possible), sepsis (probable). Conclusions: In previously treated pts with relapsed SCLC, irinotecan and carfilzomib was effective in platinum-sensitive and, notably, platinum-refractory pts with similar toxicity profile. This combination is a viable option in relapsed SCLC, can be considered following progression on immunotherapy (IO) or in subjects who cannot receive IO, and should be further explored in a randomized phase III trial. Clinical trial information: NCT01941316.

Deregulated hepatic metabolism exacerbates impaired testosterone production in Mrp4-deficient mice

The physiological role of multidrug resistance protein 4 (Mrp4, Abcc4) in the testes is unknown. We found that Mrp4 is expressed primarily in mouse and human Leydig cells; however, there is no current evidence that Mrp4 regulates testosterone production. We investigated its role in Leydig cells, where testosterone production is regulated by cAMP, an intracellular messenger formed when the luteinizing hormone (LH) receptor is activated. Because Mrp4 regulates cAMP, we compared testosterone levels in Mrp4(-/-) and Mrp4(+/+) mice. Young Mrp4(-/-) mice had significantly impaired gametogenesis, reduced testicular testosterone, and disruption of Leydig cell cAMP homeostasis. Both young and adult mice had impaired testosterone production. In Mrp4(-/-) primary Leydig cells treated with LH, intracellular cAMP production was impaired and cAMP-response element-binding protein (CREB) phosphorylation was strongly attenuated. Notably, expression of CREB target genes that regulate testosterone biosynthesis was reduced in Mrp4(-/-) Leydig cells in vivo. Therefore, Mrp4 is required for normal Leydig cell testosterone production. However, adult Mrp4(-/-) mice are fertile, with a normal circulating testosterone concentration. The difference is that in 3-week-old Mrp4(-/-) mice, disruption of gonadal testosterone production up-regulates hepatic Cyp2b10, a known testosterone-metabolizing enzyme. Therefore, defective testicular testosterone production de-regulates hepatic Cyp-mediated testosterone metabolism to disrupt gametogenesis. These findings have important implications for understanding the side effects of therapeutics that disrupt Mrp4 function and are reported to alter androgen production.

An HPLC assay for the lipophilic camptothecin analog AR-67 carboxylate and lactone in human whole blood

AR-67 (7-t-butyldimethylsilyl-10-hydroxycamptothecin, DB-67) is a camptothecin analog currently in early stage clinical trials. The lactone moiety of camptothecins hydrolyzes readily in blood to yield the pharmacologically inactive carboxylate form. However the lactone form of third-generation lipophilic congeners, such as AR-67, is more stable, possibly due to partitioning into red cell membranes. This prompted us to develop a reverse-phase HPLC method with fluorescence detection (excitation 380 nm/emission 560 nm), which could quantitate the concentration of AR-67 lactone and carboxylate in whole blood. Samples were prepared by red cell lysis, protein precipitation with methanol and centrifugation to remove denatured materials. Recovery was estimated to be >85%. Analytes were eluted isocratically with 0.15 m ammonium acetate buffer containing 10 mm TBAP (pH 6.5) and acetonitrile (65:35, v/v) on a Nova-Pak C(18) column (4 µm; 3.9 × 150 mm). The assay was linear in the ranges 0.5-300 and 2.5-300 ng/mL for carboxylate and lactone, respectively. Accuracy and precision were acceptable. AR-67 forms were stable in whole blood and in methanolic supernatants. This assay has been successfully applied to measure AR-67 concentrations in whole blood of patients enrolled in a phase I study.

Clinical and pharmacokinetic (PK) findings in a phase I study of 7-t-butyldimethylsilyl-10-hydroxycamptothecin (AR-67) in patients with refractory solid tumors

2534

Background: AR-67 is a 3rd generation camptothecin analog selected for development based on the high in vitro stability of its pharmacologically active lactone form and high potency in preclinical models. This report describes the initial phase I study of intravenous AR-67 in adults with refractory solid tumors. Methods: AR-67 was infused over 1 hour for 5 days of a 21-day cycle using an accelerated titration phase I trial design. PK was performed on the 1st and 4th day of cycle 1. AR-67 was assayed with a validated chromatography method. Toxicity and response were assessed using NCI CTC (v3) grading scale and RECIST. Results: In total, 26 patients were treated at 9 dose levels (mg/m2/day): 1.2 (n=2), 1.67 (n=3), 2.34 (n=3), 3.2 (n=3); 4.5 (n=1), 6.3 (n=1), 7.5 (n=7), 8.9 (n=4) and 12.4 (n=2). Median age 62 (range 31–79), 15M/11F, median prior therapies 3 (range 1 to 6). Tumor types included: colorectal (8), non-small cell lung (NSCLC) (4), small cell lung (3), soft tissue sarcoma, (3), head and neck (2), prostate (2), and other (4). 21 subjects completed 2 or more cycles of therapy, 5 subjects received 1 cycle of therapy and had rapid disease progression (1 received 2d of drug prior to PD), 1 subject is still under treatment after 9 cycles. DLTs were observed in 5 patients: 2 of 2 at 12.4 mg/m2/day (Gr 4 febrile neutropenia, Gr 3 fatigue); 2 of 4 at 8.9 mg/m2/day (Gr 4 thrombocytopenia), 1 of 7 at 7.5 mg/m2/day (Gr 4 thrombocytopenia). Common C1 worst-grade drug related toxicities (CTC I/II % vs III/IV %): Hg (27/8), WBC (11/19), ANC (19/8), platelets (19/12), fatigue (15/8) insomnia (8/0), flushing (15//0), constipation (8/0), nausea (23/0), ALT elevation (12/0), hiccups (8/0). Antitumor activity, assessed by development of PR and SD, was observed in NSCLC, SCLC, colon and bladder cancer. The lactone form was predominant in plasma (>85% of AUC) at all time points. Clearance was constant with increasing dose and exposure (AUC) correlated with toxicity. Conclusions: AR-67 has superior lactone stability compared to approved analogs, has a predictable toxicity profile that did not include diarrhea and has activity in NSCLC. The RP2D is 7.5 mg/m2/day for 5 days of a 21-day cycle. This work was supported by R21-CA-123867 and Arno Therapeutics.

[Table: see text]

Metabolism and transport pathways of the blood stable camptothecin AR-67 (7-t-butyldimethylsilyl-10-hydroxycamptothecin)

2553

Background: AR-67 is a 3rd generation camptothecin analog with superior stability of its active lactone form (>85%). This stability has been credited in part to the -R10 hydroxyl group (-OH); a group also present on the two clinically approved analogs, topotecan and irinotecan. As with SN-38, the active metabolite of irinotecan, the -OH of AR-67 may be a site for glucuronidation by a UDP glucuronosyltransferase. Moreover, many camptothecins are substrates for the efflux transporter BCRP (ABCG2) and the anionic carboxylate may be a substrate for the liver uptake transporter OATP1B1 (SLCO1B1). Pharmacogenetic studies have established that significant portions of the population have polymorphisms in these genes, which lead to altered pharmacokinetics and toxicity profiles of their substrates. This report describes in-vitro metabolism and transport studies with AR-67 as well as identification of metabolites in plasma and urine from patients enrolled in a phase I study. Methods: AR-67 and its metabolites were detected using chromatography methods with fluorescence or MS/MS detection. In vitro metabolism studies were done with UGT and CYP450 enzyme isoforms expressed in Sf9 cells. In vivo AR-67 metabolic products were identified in clinical plasma and urine specimens. Collection of clinical specimens has been described (control #09-AB-30336-ASCOAM). AR-67 uptake and efflux studies were performed in cells transfected with ABCG2 or SLCO1B1. Results: AR-67 glucuronidation was demonstrated to occur in vitro, primarily by UGT1A8. AR-67 was also found to be a substrate of CYP3A4 and CYP3A5. Only limited glucuronide and oxidation metabolite peaks were observed in patient samples at the highest concentrations. Diminished accumulation of AR-67 lactone was observed in BCRP expressing Saos-2 cells and significant uptake of AR-67 carboxylate was observed in OATP1B1 expressing cells. Conclusions: Unlike SN-38, AR-67 was not found to be a major substrate of UGT1A1, but was rapidly processed by UGT1A8, an isoform that is highly expressed in the GI tract. These data may explain the absence of diarrhea during this phase I study. The pharmacologic significance of ABCG2 and SLCO1B1 polymorphisms should be explored further in the context of population studies.

[Table: see text]

Pharmacokinetics (PK) of the highly lipophilic and blood stable camptothecin AR-67 (7-t-butyldimethylsilyl-10- hydroxycamptothecin) in adult patients with solid malignancies

2546

Background: Camptothecin analogs possess a labile lactone ring, which readily undergoes a pH dependent, albeit reversible, hydrolysis in plasma to yield a carboxylate moiety. The latter is considered inactive due to its electronegative charge that impedes transport into cells. Furthermore, the carboxylate is cleared rapidly and causes toxicity in eliminating organs due to lactonation. AR-67 is a highly lipophilic 3rd generation analog with superior stability of its lactone form in preclinical models. This report describes the PK of AR-67 in patients with refractory solid tumors enrolled in a phase I study. Methods: AR-67 was infused over 1 hr for 5 days every 21-days. PK was performed on the 1st and 4th day of cycle 1. Blood, plasma, and urine were collected (0–24 hrs) from 26 patients (see 09-AB-30336-ASCOAM) treated at 9 dose levels: 1.2–12.4 (mg/m2/day). AR-67 carboxylate and lactone were assayed with a validated chromatography method. Results: AR-67 was detectable at all dose levels. Blood concentrations mirrored those in plasma and were superimposable when adjusted by the hematocrit. AR-67 concentration peaked at the end of the 1-hr infusion and declined biexponentially with a terminal t1/2 of 1.4 hr (plasma lactone). A linear relationship was observed between dose and AUC. The lactone clearance on Day 1 was 16.6 (±5.5) vs. 19.6 (±6.3) L/hr/m2 on Day 5. The carboxylate clearance was ∼ 6-fold higher. Lactone was the major form in all samples and its area under the time vs. concentration curve (AUC) was 85.5% (range 74.0%-94.1%) of the total AUC. Urine (0–24 hr) contained 2.5% (0.3%-6.7%) of the dose on Day 1 vs. 2.7% (0.9–11.1%) on Day 4. Extensive metabolite peaks were not observed in plasma, blood, or urine samples. Plasma protein binding of the carboxylate was 90% (range 80%-96%) vs. 95% (range 90%-98%) for the lactone. Conclusions: AR-67 is a lipophilic camptothecin with a unique PK profile. Unlike other clinically approved analogs with lower lactone stability (35%-65%), over 85% of the AR-67 AUC is in the active lactone form. This high lactone-low carboxylate exposure coupled with the apparently limited metabolism of AR-67 may result in increased activity and decreased toxicity.

[Table: see text]

Effects of dexamethasone (Dex) pretreatment on toxicity and efficacy of carboplatin and gemcitabine (Carbo/Gem) in patients with non-small cell lung cancer (NSCLC)

18124

Background: Our preclinical data showed that treating mice with Dex 4 days prior to chemotherapy increased efficacy and decreased toxicity of Carbo/Gem in nude mice bearing human NSCLC by increasing drug concentration in tumors, and decreasing drug concentration in normal tissue without altering plasma pharmacokinetics (PK). Thus, we undertook a Phase I/II trial to determine the optimal dose of Dex, and the effect of Dex on Carbo/Gem plasma PK. Methods: Patients (n=30) with untreated, stage IV NSCLC and PS =2 received Gem, 1g/m2 days 1&8, and Carbo, AUC 5.5 on day 1. Patients were randomized (1:2:2) to receive no Dex (arm 1), or Dex at 8 and 16 mg bid po 4 days before and on day 1 (arms 2 and 3). Dex was administered in courses 2, 3, and 4 (only) to allow course 1 vs course 2 intra-patient toxicity and Carbo/Gem plasma PK assessment. Plasma samples were analyzed by HPLC for Carbo/Gem. Plasma PK analysis was performed with NONMEM v5 using a 5-compatment or 2-compartment structural models for Gem and Carbo. Results: Patients in arms 1, 2, and 3 were similar in PS, age, gender, and histology. In arms 1, 2, and 3, patients completing 4 planned courses of therapy: 1/6, 6/12, 9/12; partial responses (RECIST): 2/6, 7/12, and 8/12. Hematologic toxicity in arms 1 (no Dex), 2, and 3 (Dex) was compared. Platelet nadirs (course2÷course1): 0.6±0.2, 3.77±2.0, 3.4±0.72 (p<0.02); AGC nadirs: 1.1±0.3, 2.32±0.4, 4.95±1.04 (p< 0.01); Change in median time to recovery from day 1 (course 2-course 1) of AGC to 1,500 mm3 in days: +9, -15, -19; Change in median time to recovery of platelets to 100,000 mm3: +5, -1, -1.5. Comparison of nadir AGC and platelets between courses 2, 3, and 4 consistently demonstrated superiority of arm 3 over arm 2. No significant differences in non-hematologic toxicities were seen between arms 1, 2 and 3. Gem and Carbo clearance values were not significantly different among arms or courses. Area under the time-concentration curves (course2÷course1): 0.91±0.18, 0.77±0.15, 0.80±0.16. Conclusions: Dex pretreatment appears to reduce toxicity and improve efficacy of Carbo/Gem in NSCLC patients, with arm 3>2. These effects are not due to alteration of plasma PK since no significant decrease in chemotherapy exposure was observed in arms 2 and 3.

[Table: see text]

Topotecan Combination Chemotherapy in Two New Rodent Models of Retinoblastoma

Chemotherapy combined with laser therapy and cryotherapy has improved the ocular salvage rate for children with bilateral retinoblastoma. However, children with late-stage disease often experience recurrence shortly after treatment. To improve the vision salvage rate in advanced bilateral retinoblastoma, we have developed and characterized two new rodent models of retinoblastoma for screening chemotherapeutic drug combinations. The first model is an orthotopic xenograft model in which green fluorescent protein- or luciferase-labeled human retinoblastoma cells are injected into the eyes of newborn rats. The second model uses a replication-incompetent retrovirus (LIA-E(E1A)) encoding the E1A oncogene. Clonal, focal tumors arise from mouse retinal progenitor cells when LIA-E(E1A) is injected into the eyes of newborn p53-/- mice. Using these two models combined with pharmacokinetic studies and cell culture experiments, we have tested the efficacy of topotecan combined with carboplatin and of topotecan combined with vincristine for the treatment of retinoblastoma. The combination of topotecan and carboplatin most effectively halted retinoblastoma progression in our rodent models and was superior to the current triple drug therapy using vincristine, carboplatin, and etoposide. Vincristine had the lowest LC50 in culture but did not reduce tumor growth in our preclinical retinoblastoma models. Taken together, these data suggest that topotecan may be a suitable replacement for etoposide in combination chemotherapy for the treatment of retinoblastoma.