A Cohort Study to Evaluate Genetic Predictors for Aromatase Inhibitor Musculoskeletal Symptoms (AIMSS): Results from ECOG-ACRIN E1Z11

PURPOSE

Aromatase Inhibitor-Associated Musculoskeletal Symptoms (AIMSS) are common and frequently lead to AI discontinuation. Single nucleotide polymorphisms (SNPs) in candidate genes have been associated with AIMSS and AI discontinuation. E1Z11 is a prospective cohort study designed to validate associations between 10 SNPs and AI discontinuation due to AIMSS.

PATIENTS AND METHODS

Postmenopausal women with stage I-III hormone receptor-positive breast cancer received anastrozole 1 mg daily and completed patient-reported outcomes (PRO) to assess AIMSS (Stanford Health Assessment Questionnaire; HAQ) at baseline, 3, 6, 9, and 12 months. We estimated that 40% of participants would develop AIMSS, and 25% would discontinue AI treatment within 12 months. Enrollment of 1,000 women with a fixed number per racial strata provided 80% power to detect an effect size of 1.5-4. SNPs were in ESR1 (rs2234693, rs2347868, rs9340835), CYP19A1 (rs1062033, rs4646), TCL1A (rs11849538, rs2369049, rs7158782, rs7159713), and HTR2A (rs2296972).

RESULTS

Of 970 evaluable women, 43% developed AIMSS and 12% discontinued AI therapy within 12 months. While more Black and Asian women developed AIMSS compared to White women (49% vs 39%, p=0.017; 50% vs 39%, p=0.004, respectively), AI discontinuation rates were similar across groups. None of the SNPs were significantly associated with AIMSS or AI discontinuation in the overall population, or in distinct cohorts. The odds ratio for rs2296972 (HTR2A) approached significance for developing AIMSS.

CONCLUSION

We were unable to prospectively validate candidate SNPs previously associated with AI discontinuation due to AIMSS. Future analyses will explore additional genetic markers, PRO predictors of AIMSS, and differences by race.

Tolerability of Olaparib Combined with Abiraterone in Patients with Metastatic Castration-resistant Prostate Cancer: Further Results from the Phase 3 PROpel Trial

BACKGROUND

The PROpel study (NCT03732820) demonstrated a statistically significant progression-free survival benefit with olaparib plus abiraterone versus placebo plus abiraterone in the first-line metastatic castration-resistant prostate cancer (mCRPC) setting, irrespective of homologous recombination repair mutation status.

OBJECTIVE

We report additional safety analyses from PROpel to increase clinical understanding of the adverse-event (AE) profiles of olaparib plus abiraterone versus placebo plus abiraterone.

DESIGN, SETTING, AND PARTICIPANTS

A randomised (1:1), double-blind, placebo-controlled trial was conducted at 126 centres in 17 countries (October 2018-January 2020). Patients had mCRPC and no prior systemic mCRPC treatment.

INTERVENTION

Olaparib (300 mg bid) or placebo with abiraterone (1000 mg od) plus prednisone/prednisolone (5 mg bid).

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The data cut-off date was July 30, 2021. Safety was assessed by AE reporting (Common Terminology Criteria for Adverse Events v4.03) and analysed descriptively.

RESULTS AND LIMITATIONS

The most common AEs (all grades) for olaparib plus abiraterone versus placebo plus abiraterone were anaemia (46.0% vs 16.4%), nausea (28.1% vs 12.6%), and fatigue (27.9% vs 18.9%). Grade ≥3 anaemia occurred in 15.1% versus 3.3% of patients in the olaparib plus abiraterone versus placebo plus abiraterone arm. The incidences of the most common AEs for olaparib plus abiraterone peaked early, within 2 mo, and were managed typically by dose modifications or standard medical practice. Overall, 13.8% versus 7.8% of patients discontinued treatment with olaparib plus abiraterone versus placebo plus abiraterone because of an AE; 3.8% versus 0.8% of patients discontinued because of anaemia. More venous thromboembolism events were observed in the olaparib plus abiraterone arm (any grade, 7.3%; grade ≥3, 6.8%) than in the placebo plus abiraterone arm (any grade, 3.3%; grade ≥3, 2.0%), most commonly pulmonary embolism (6.5% vs 1.8% for olaparib plus abiraterone vs placebo plus abiraterone).

CONCLUSIONS

Olaparib plus abiraterone has a manageable and predictable safety profile.

PATIENT SUMMARY

The PROpel trial showed that in patients who had not received any previous treatment for metastatic castration-resistant prostate cancer, olaparib combined with abiraterone was more effective in delaying progression of the disease than abiraterone alone. Most side effects caused by combining olaparib with abiraterone could be managed with supportive care methods, by pausing olaparib administration for a short period of time and/or by reducing the dose of olaparib.

Updated efficacy and safety of entrectinib in NTRK fusion-positive non-small cell lung cancer

OBJECTIVES

NTRK fusions result in constitutively active oncogenic TRK proteins responsible for ∼ 0.2 % of non-small cell lung cancer (NSCLC) cases. Approximately 40 % of patients with advanced NSCLC develop CNS metastases; therefore, treatments with intracranial (IC) efficacy are needed. In an integrated analysis of three phase I/II studies (ALKA-372-001: EudraCT 2012-000148-88; STARTRK-1: NCT02097810; STARTRK-2: NCT02568267), entrectinib, a potent, CNS-active, TRK inhibitor, demonstrated efficacy in patients with NTRK fusion-positive (fp) NSCLC (objective response rate [ORR]: 64.5 %; 2 August 2021 data cut-off). We present updated data for this cohort.

MATERIALS AND METHODS

Eligible patients were ≥ 18 years with locally advanced/metastatic, NTRK-fp NSCLC with ≥ 12 months of follow-up. Tumor responses were assessed by blinded independent central review (BICR) per RECIST v1.1 at Week 4 and every eight weeks thereafter. Co-primary endpoints: ORR; duration of response (DoR). Secondary endpoints included progression-free survival (PFS); overall survival (OS); IC efficacy; safety. Enrolment cut-off: 2 July 2021; data cut-off: 2 August 2022.

RESULTS

The efficacy-evaluable population included 51 patients with NTRK-fp NSCLC. Median age was 60.0 years (range 22-88); 20 patients (39.2 %) had investigator-assessed baseline CNS metastases. Median survival follow-up was 26.3 months (95 % CI 21.0-34.1). ORR was 62.7 % (95 % CI 48.1-75.9), with six complete and 26 partial responses. Median DoR and PFS were 27.3 months (95 % CI 19.9-30.9) and 28.0 months (95 % CI 15.7-30.4), respectively. Median OS was 41.5 months. In patients with BICR-assessed baseline CNS metastases, IC-ORR was 64.3 % (n = 9/14; 95 % CI 35.1-87.2), including seven complete responders, and IC-DoR was 55.7 months. In the safety-evaluable population (n = 55), most treatment-related adverse events were grade 1/2; no treatment-related deaths were reported.

CONCLUSION

Entrectinib has continued to demonstrate deep and durable systemic and IC responses in patients with NTRK-fp NSCLC.

Real-World Clinical Outcomes of Bevacizumab-awwb Biosimilar versus Bevacizumab Reference Product in Patients with Metastatic Colorectal Cancer

BACKGROUND

Bevacizumab-awwb was the first biosimilar approved for cancer treatment in the USA. Limited information is available on the real-world comparative safety and effectiveness of bevacizumab biosimilars, especially for indications granted approval through extrapolation.

OBJECTIVE

To evaluate the real-world outcomes of patients with metastatic colorectal cancer (mCRC) initiated on bevacizumab-awwb versus bevacizumab reference product.

PATIENTS AND METHODS

This was an observational, longitudinal cohort study of US adult patients with mCRC from four integrated care delivery systems who were newly initiated on bevacizumab-awwb between 1 July 2019 and 30 March 2020 or bevacizumab reference product between 1 July 2015 and 30 June 2018. Patients were followed until 1 year after treatment initiation, end of plan membership, or death, whichever occurred first. The primary outcome of overall survival (OS) was analyzed using a binary non-inferiority test with lower margin of 10% and adjusted Cox proportional hazards regression analysis to assess all-cause mortality if non-inferiority was met. Secondary outcomes included counts of doses received, treatment duration, all-cause hospitalizations, and incidence of serious adverse events.

RESULTS

A total of 1445 patients initiated on either bevacizumab-awwb (n = 239) or bevacizumab reference product (n = 1206) were included in the analysis. The mean overall age was 60 ± 13 years, 46% of patients were female, and 51% were white. The OS rate was 72.8% and 73.1% for patients receiving bevacizumab-awwb and bevacizumab reference product, respectively (p < 0.01 for non-inferiority). The adjusted hazard ratio for mortality was 1.01 (0.77-1.33, p = 0.93). There were no statistically significant differences in secondary outcomes between the study groups.

CONCLUSIONS

These findings suggest that bevacizumab-awwb is as effective and safe as bevacizumab reference product for the real-world treatment of mCRC.

Validation of Immunotherapy Response Score as Predictive of Pan-solid Tumor Anti-PD-1/PD-L1 Benefit

Immunotherapy response score (IRS) integrates tumor mutation burden (TMB) and quantitative expression biomarkers to predict anti-PD-1/PD-L1 [PD-(L)1] monotherapy benefit. Here, we evaluated IRS in additional cohorts. Patients from an observational trial (NCT03061305) treated with anti-PD-(L)1 monotherapy were included and assigned to IRS-High (-H) versus -Low (-L) groups. Associations with real-world progression-free survival (rwPFS) and overall survival (OS) were determined by Cox proportional hazards (CPH) modeling. Those with available PD-L1 IHC treated with anti-PD-(L)1 with or without chemotherapy were separately assessed. Patients treated with PD-(L)1 and/or chemotherapy (five relevant tumor types) were assigned to three IRS groups [IRS-L divided into IRS-Ultra-Low (-UL) and Intermediate-Low (-IL), and similarly assessed]. In the 352 patient anti-PD-(L)1 monotherapy validation cohort (31 tumor types), IRS-H versus IRS-L patients had significantly longer rwPFS and OS. IRS significantly improved CPH associations with rwPFS and OS beyond microsatellite instability (MSI)/TMB alone. In a 189 patient (10 tumor types) PD-L1 IHC comparison cohort, IRS, but not PD-L1 IHC nor TMB, was significantly associated with anti-PD-L1 rwPFS. In a 1,103-patient cohort (from five relevant tumor types), rwPFS did not significantly differ in IRS-UL patients treated with chemotherapy versus chemotherapy plus anti-PD-(L)1, nor in IRS-H patients treated with anti-PD-(L)1 versus anti-PD-(L)1 + chemotherapy. IRS associations were consistent across subgroups, including both Europeans and non-Europeans. These results confirm the utility of IRS utility for predicting pan-solid tumor PD-(L)1 monotherapy benefit beyond available biomarkers and demonstrate utility for informing on anti-PD-(L)1 and/or chemotherapy treatment.

Significance

This study confirms the utility of the integrative IRS biomarker for predicting anti-PD-L1/PD-1 benefit. IRS significantly improved upon currently available biomarkers, including PD-L1 IHC, TMB, and MSI status. Additional utility for informing on chemotherapy, anti-PD-L1/PD-1, and anti-PD-L1/PD-1 plus chemotherapy treatments decisions is shown.

Abiraterone and Olaparib for Metastatic Castration-Resistant Prostate Cancer

Abiraterone and Olaparib for Metastatic Prostate CancerPatients with metastatic castration-resistant prostate cancer, regardless of homologous recombination repair gene mutation status, received either abiraterone and olaparib or abiraterone and placebo in the first-line setting. Imaging-based progression-free survival was 24.8 months for patients treated with abiraterone and olaparib versus 16.6 months for those receiving abiraterone alone.

NSABP FC-11: A phase II study of neratinib (N) plus trastuzumab (T) or N plus cetuximab (C) in patients (pts) with "quadruple wild-type" metastatic colorectal cancer (mCRC) based on HER2 status

3564

Background: Patients (pts) with KRAS wild-type (WT) mCRC treated with single agent anti-EGFR therapy (tx) have improved OS compared to BSC but only a 10-15% response rate. Prior EGFR tx may upregulate HER amplification. For pts with quadruple WT mCRC (KRAS, NRAS, BRAF, PIC3KA), data suggest that dual targeting of the MAPK pathway, specifically EGFR and HER2, may be more effective. The purpose of this study was to evaluate the activity of dual MAPK pathway inhibition based on HER2 status: amplified (amp), non-amplified (non-amp), or mutated (mt). Methods: This 2-arm phase II trial enrolled pts with quad WT mCRC with ECOG PS 0-2, adequate organ function, prior oxaliplatin- and irinotecan-based regimens, and known HER2 status. Arm 1: HER2 amp (confirmed as >2.14 copy number by Guardant 360) and prior anti-EGFR tx or HER2 mt (with qualifying mt) with or without prior anti-EGFR tx; Arm 2: HER2 non-amp or HER2 amp without prior anti-EGFR tx. Tx included T 4 mg/kg IV loading dose → 2 mg/kg/wk and N 240 mg po daily (Arm 1) or C 400 mg/m2 IV loading dose → 250 mg/m2/wk and N 240 mg po daily (Arm 2). Imaging was performed every 8 wks with response per RECIST 1.1. Primary end point (EP) of each arm was 6 mo PFS (PFS6). Secondary EPs: Response rate (ORR), clinical benefit rate (CBR), toxicity and exploratory assessments of N pharmacokinetics, genetic and molecular analyses, and evaluation of multiple drug combinations in PDX/PDXO models. We tested H0: PFS6 <0.13 v HA: PFS6 >0.47 (α=0.05; power=0.90 to reject HA). Treating 15 pts in each arm, if ≥5 pts are alive and progression free (PFS6 0.33), the arm is worth further testing. Results: From Jul 2018 - Mar 2021, 25 pts enrolled from 9 different centers. Arm 1 closed due to poor accrual (n=4). Those pts have been excluded from further analysis. Arm 2 enrolled 21 pts. with 15 evaluable for response by imaging. Early discontinuation occurred in 6 of 21 pts: 2 withdrew consent, 3 due to toxicity, and 1 physician withdrawal. Of the 15 evaluable pts, there were 6 PR, 5 of 13 HER2 non-amp, 1 of 2 HER2 amp, (duration 120-171 days; mean 140) and 5 SD (duration 59-231 days; mean 124). The ORR (CR/PR) in all pts who received at least one dose of tx is 33% (6/20). 8 of 15 evaluable pts (53%) were progression free at cycle 6. Common grade 3+ AEs (>5%) included diarrhea (24%), rash (8%), and abdominal pain/distension (8%), without any grade 5 AEs. Conclusions: The combination of C+N was reasonably well tolerated with expected toxicities of diarrhea and rash. The ORR, CBR, and PFS compare favorably to pts previously relapsed following oxaliplatin and irinotecan and treated with single-agent anti-EGFR tx. Upon entry, biopsies for PDX implantation had an engraftment success rate of ̃80%. We anticipate using these grafts to establish PDXO models for molecular analyses and further drug testing. Support: NSABP Foundation, Puma Biotechnology. Clinical trial information: NCT03457896.

Tolerability of abiraterone (abi) combined with olaparib (ola) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC): Further results from the phase III PROpel trial

5019

Background: The Phase III PROpel (NCT03732820) trial demonstrated at interim analysis a statistically significant clinical benefit from combining ola + abi in the first-line (1L) mCRPC setting vs placebo (pbo) + abi. Benefit was seen irrespective of a pt’s homologous recombination repair mutation (HRRm) status; median radiographic progression-free survival (rPFS) 24.8 for ola + abi vs 16.6 months for pbo + abi (hazard ratio [HR] 0.66, 95% confidence interval [CI] 0.54–0.81; P<0.0001). The safety profile of ola + abi was shown to be consistent with that for the individual drugs. We report additional interim safety analysis from PROpel. Methods: Eligible pts were ≥18 years with mCRPC, had received no prior chemotherapy or next-generation hormonal agent treatment at mCRPC stage, and were unselected by HRRm status. Pts were randomized 1:1 to abi (1000 mg qd) plus prednisone/prednisolone with either ola (300 mg bid) or pbo. Primary endpoint was investigator-assessed rPFS. Safety was assessed in all pts receiving ≥1 dose of study treatment by adverse event (AE) reporting (CTCAE v4.03). Results: 398 pts received ola + abi and 396 pbo + abi (safety analysis set). At data cut-off (July 30, 2021), median total duration of exposure for ola was 17.5 vs 15.7 months for pbo, and for abi 18.2 months in the ola + abi arm and 15.7 in the pbo + abi arm. Anemia (n=183) was the most common AE in the ola + abi arm, and 34% of these 183 events were managed by dose interruption, 23% by dose reduction, and 8% resulted in treatment discontinuation. Anemia and pulmonary embolism (PE) were the only Grade ≥3 AEs in ≥5% of pts (anemia: ola + abi, 15.1% vs pbo + abi, 3.3%; PE: 6.5% vs 1.8%, respectively). Most PEs were detected incidentally on radiographic imaging (69.2% and 71.4% in the ola + abi and pbo + abi arms, respectively) and no pts discontinued. More pts in the ola + abi arm experienced venous thromboembolism (Table). Arterial thromboembolism and cardiac failure AEs were balanced between the treatment arms. No AE of myelodysplastic syndrome/acute myeloid leukemia was reported in either treatment arm. COVID-19 was reported more frequently with ola + abi (8.3% vs 4.5%). Conclusions: PROpel demonstrated a predictable safety profile for ola + abi given in combination to pts with 1L mCRPC unselected by HRRm status. AEs of cardiac failure and arterial thromboembolism were reported at similar frequency in both treatment arms. The majority of PEs were asymptomatic. The safety profile of abiraterone was not adversely impacted by its combination with olaparib. Clinical trial information: NCT03732820. [Table: see text]

Real-world outcomes of biosimilar bevacizumab-awwb versus reference bevacizumab in patients with metastatic colorectal cancer

3552

Background: Bevacizumab-awwb was the first biosimilar approved by the U.S. Food and Drug Administration (FDA) for treatment of cancer and became available for use in July 2019. Clinical comparative efficacy and safety of bevacizumab-awwb to bevacizumab was established in a single study of adult patients with advanced non-squamous non-small cell lung cancer. Approval based on extrapolation was granted by the FDA for all other indications, including metastatic colorectal cancer (mCRC). The objective of this study was to evaluate the real-world effectiveness and safety outcomes of patients with mCRC initiated on bevacizumab-awwb versus bevacizumab in an integrated healthcare delivery system. Methods: This was an observational cohort study of patients with mCRC in Kaiser Permanente California, Colorado, and Mid-Atlantic States who were initiated on bevacizumab-awwb between July 2019 and March 2020 or reference bevacizumab between July 2015 and June 2018. Patients with history of bevacizumab use in the 6 months prior to the index treatment date were excluded. Patients were followed until 12 months after treatment initiation, end of plan membership, or death, whichever occurred first. The primary outcome of overall survival (OS) was analyzed using a non-inferiority test with lower margin of 10% and Cox proportional-hazards modeling. Secondary outcomes included count of doses received, treatment duration, all-cause hospitalizations, and incidence of serious adverse events. Results: A total of 1,445 patients initiated on either bevacizumab-awwb (n=239) or bevacizumab (n=1,206) were included in the analysis. The mean overall age was 60 ± 13 years and 54% of patients were male. The OS rate was 72.8% and 73.1% for patients receiving bevacizumab-awwb and bevacizumab, respectively ( p<0.01 for non-inferiority). The adjusted hazard ratio for mortality was 1.01 (0.77-1.33, p=0.93). There were no statistically significant differences in secondary outcomes between the 2 study groups (Table). Conclusions: Bevacizumab-awwb is a safe and effective option when compared to the reference bevacizumab in the treatment of mCRC. Future studies should evaluate outcomes after longer follow-up time and in different cancer types. [Table: see text]

KRYSTAL-1: Updated activity and safety of adagrasib (MRTX849) in patients (Pts) with unresectable or metastatic pancreatic cancer (PDAC) and other gastrointestinal (GI) tumors harboring a KRASG12C mutation

519

Background: KRAS, the most frequently mutated oncogene in cancer, is a key mediator of the RAS/MAPK signaling cascade that promotes cellular growth and proliferation. KRAS mutations occur in approximately 90% of pancreatic cancer, and approximately 2% of these are KRASG12C mutations. Adagrasib, an investigational agent, is a KRASG12C inhibitor that irreversibly and selectively binds KRASG12C, locking it in its inactive state; adagrasib has been optimized for favorable pharmacokinetic (PK) properties, including long half-life (̃24 h), extensive tissue distribution, dose-dependent PK, as well as CNS penetration. Methods: KRYSTAL-1 (NCT03785249) is a multicohort Phase 1/2 study evaluating adagrasib as monotherapy or in combinations in pts with advanced solid tumors harboring a KRASG12C mutation. Here we report preliminary data from pts enrolled in a Phase 2 cohort evaluating single-agent adagrasib administered orally at 600 mg BID in previously treated pts with unresectable or metastatic solid tumors (excluding NSCLC and CRC), including pancreatic and other GI cancers. Study endpoints include clinical activity, safety, and PK. Results: The data cutoff was 10 September 2021. A total of 42 pts were enrolled in this cohort (median age 63.5 years, range 21–89; 52% female; 71% white; 29%/71% ECOG PS 0/1; median 2 prior lines of therapy, range 1–7; median follow-up 6.3 months), of whom 30 pts had KRASG12C-mutant GI tumors (12 PDAC, 8 biliary tract, 5 appendiceal, 2 gastro-esophageal junction, 2 small bowel, and 1 esophageal). In a preliminary analysis, 27 pts with GI tumors were evaluable for clinical activity; partial responses (PRs) were seen in 41% (11/27, including 3 unconfirmed PRs); the disease control rate (DCR) was 100% (27/27). Of the 12 pts with PDAC (median 3 prior lines of therapy; median follow-up 8.1 months), 10 were evaluable for clinical activity; PRs were seen in 50% (5/10, including 1 unconfirmed PR); the DCR was 100% (10/10). Median progression-free survival (PFS) was 6.6 months (95% CI 1.0–9.7), and treatment was ongoing in 50% of pts with PDAC. Among the 17 evaluable pts with other GI tumors, 6 achieved PR (35%; 2 unconfirmed) with a DCR of 100% (17/17); 11 pts were still receiving treatment. In the overall cohort, treatment-related adverse events of any grade occurred in 91% (38/42), the most frequent being nausea (48%), diarrhea (43%), vomiting (43%), and fatigue (29%); grade 3/4 events occurred in 21% of pts, with no grade 5 events. Conclusions: Adagrasib monotherapy is well tolerated and demonstrates encouraging clinical activity in pretreated pts with PDAC and other GI tumors harboring a KRASG12C mutation. Further exploration of adagrasib is ongoing in this pt population (NCT03785249). Clinical trial information: NCT03785249.

First-line pembrolizumab plus chemotherapy versus chemotherapy in advanced esophageal cancer: Longer-term efficacy, safety, and quality-of-life results from the phase 3 KEYNOTE-590 study

241

Background: At interim analysis of the phase 3, randomized, double-blind KEYNOTE-590 (NCT03189719) study, 1L pembrolizumab (pembro) + chemotherapy (chemo) vs chemo alone provided superior OS, PFS, and ORR with a manageable safety profile in patients (pts) with untreated, advanced/unresectable or metastatic adenocarcinoma or esophageal squamous cell carcinoma (ESCC) or Siewert type 1 esophagogastric junction adenocarcinoma (EGJ). We report efficacy, safety, and health-related quality of life (HRQoL) results with an additional 12 months (mo) of follow-up. Methods: 749 eligible pts were randomized 1:1 to pembro 200 mg or placebo Q3W for up to 2 yr + chemo. Randomization was stratified by geographic region, histology, and performance status. Treatment continued until progression, unacceptable toxicity, or withdrawal, or 2 yr. No crossover was permitted. Primary endpoints were OS in pts with ESCC PD-L1 combined positive score (CPS) ≥10 tumors, and OS and PFS (RECIST v1.1; by INV) in ESCC, PD-L1 CPS ≥10, and all pts. Secondary endpoints included ORR, DOR, safety, and HRQoL. HRQol was assessed in 711 treated pts with ≥1 HRQoL assessment (356 pembro + chemo; 355 chemo). Data cutoff was July 9, 2021. Results: At data cutoff, median follow-up (randomization to data cutoff) was 34.8 mo. Median OS was longer with pembro + chemo vs chemo in pts with ESCC CPS ≥10 (HR 0.59; 95% CI, 0.45-0.76), ESCC (HR 0.73; 95% CI, 0.61-0.88), CPS ≥10 (HR 0.64; 95% CI, 0.51-0.80), and all pts (HR 0.73, 95% CI, 0.63-0.86). In pts with adenocarcinoma OS HR was 0.73 (95% CI, 0.55-0.99). The 24-mo OS rate in all pts was 26.3% vs 16.1%. Median PFS was longer with pembro + chemo vs chemo in ESCC (HR 0.65; 95% CI, 0.54-0.78), CPS ≥10 (HR 0.51; 95% CI, 0.41-0.65), and all pts (HR 0.64; 95% CI, 0.55-0.75). The 24-mo PFS rate in all pts was 11.6% vs 3.3%. Confirmed ORR was 45.0% (25 CR [6.7%]) vs 29.3% (9 CR [2.4%]), with median DOR of 8.3 vs 6.0 mo. Approximately 20% vs 6% of pts had response duration ≥24 months. Grade 3-5 drug-related AE rates were 72% vs 68%. Discontinuation rates from drug-related AEs were 21% vs 12%. There was no significant difference in least square mean (LSM) change from baseline to wk 18 between arms in EORTC QLQ-C30 global health status/quality-of-life (LSM difference -0.10; 95% CI, -3.40-3.20). LSM change from baseline to wk 18 was better with pembro + chemo vs chemo for QLQ-OES 18 pain (-2.94; 95% CI, -5.86 to -0.02) and dysphagia (-5.54; 95% CI, -10.92 to -0.16). Conclusions: With an additional 12 months of follow-up, pembro + chemo continued to provide significant and clinically meaningful improvement in OS, PFS, and ORR vs chemo with a manageable safety profile, and stable quality-of-life for pts with untreated, advanced esophageal and EGJ cancer. These data continue to support 1L pembro + chemo as a new standard of care in these patients. Clinical trial information: NCT03189719.

Atezolizumab with enzalutamide versus enzalutamide alone in metastatic castration-resistant prostate cancer: a randomized phase 3 trial

Early clinical data indicate that some patients with castration-resistant prostate cancer may benefit from program death ligand-1 (PD-L1) inhibition, especially with enzalutamide. The IMbassador250 trial (no. NCT03016312) enrolled 759 men with metastatic castration-resistant prostate cancer whose disease progressed on abiraterone. The addition of atezolizumab to enzalutamide in an open-label randomized trial did not meet the primary endpoint of improved overall survival in unselected patients (stratified hazard ratio 1.12, 95% confidence interval (0.91, 1.37), P = 0.28), despite an acceptable safety profile. In archival tumor samples, prostate tumors showed comparatively low expression of key immune biomarkers. DNA damage-response alterations, phosphatase and tensin homolog status and PD-L1 expression levels were similar between hormone-sensitive and castration-resistant prostate cancers. In planned biomarker analysis, longer progression-free survival was seen with atezolizumab in patients with high PD-L1 IC2/3, CD8 expression and established immune gene signatures. Exploratory analysis linked progression-free survival in the atezolizumab arm with immune genes such as CXCL9 and TAP1, together with other potentially relevant biomarkers including phosphatase and tensin homolog alterations. Together these data indicate that the expected biology associated with response to immune checkpoint inhibitors is present in prostate cancer, albeit in fewer patients. Careful patient selection may be required for immune checkpoint inhibitors to identify subgroups of patients who may benefit from this treatment approach.

Disparities in clinical trials participation in a vertically integrated care delivery system

128

Background: Sparse data exists on the diversity clinical trial enrollment in community settings. This information is important to ensure equity of care and generalizability of results. Methods: We conducted a retrospective cohort study of members of an integrated healthcare system diagnosed with invasive malignancies (excluding non-melanoma skin cancers) between 2013-2017 to examine demographics of the oncology population compared to those who enrolled in a clinical trial. Logistic regression was used to assess correlates of clinical trial participation, comparing general and screened samples to enrolled sample. Odds ratios were adjusted for gender, geocoded median household income, cancer type, and stage. Results: Of the 84,977 patients with a cancer diagnosis, N = 2606 were screened for clinical trial participation and consented, and of those N = 1372 enrolled. The percent of Latinx (25.8% vs 24.0%; OR 0.9? CI 0.72-1.05) and African American/Black (10.9% vs 11.1%; OR 0.92 CI 0.75-1.11) clinical trial participation mirrored that of the general oncology population, respectively using Non-Hispanic Whites as reference. Asian/Pacific Islander had equal odds of clinical trial enrollment (OR 1.08 CI 0.92-1.27). The enrolled population was younger than the general oncology population. Conclusions: This study suggests that in an integrated healthcare system with equal access to care, the clinical trials population is well representative of its general oncology population.[Table: see text]

Ipatasertib plus abiraterone and prednisolone in metastatic castration-resistant prostate cancer (IPATential150): a multicentre, randomised, double-blind, phase 3 trial

BACKGROUND

The PI3K/AKT and androgen-receptor pathways are dysregulated in metastatic castration-resistant prostate cancers (mCRPCs); tumours with functional PTEN-loss status have hyperactivated AKT signalling. Dual pathway inhibition with AKT inhibitor ipatasertib plus abiraterone might have greater benefit than abiraterone alone. We aimed to compare ipatasertib plus abiraterone with placebo plus abiraterone in patients with previously untreated mCRPC with or without tumour PTEN loss.

METHODS

We did a randomised, double-blind, phase 3 trial at 200 sites across 26 countries or regions. Patients aged 18 years or older with previously untreated asymptomatic or mildly symptomatic mCRPC who had progressive disease and Eastern Collaborative Oncology Group performance status of 0 or 1 were randomly assigned (1:1; permuted block method) to receive ipatasertib (400 mg once daily orally) plus abiraterone (1000 mg once daily orally) and prednisolone (5 mg twice a day orally) or placebo plus abiraterone and prednisolone (with the same dosing schedule). Patients received study treatment until disease progression, intolerable toxicity, withdrawal from the study, or study completion. Stratification factors were previous taxane-based therapy for hormone-sensitive prostate cancer, type of progression, presence of visceral metastasis, and tumour PTEN-loss status by immunohistochemistry. Patients, investigators, and the study sponsor were masked to the treatment allocation. The coprimary endpoints were investigator-assessed radiographical progression-free survival in the PTEN-loss-by-immunohistochemistry population and in the intention-to-treat population. This study is ongoing and is registered with ClinicalTrials.gov, NCT03072238.

FINDINGS

Between June 30, 2017, and Jan 17, 2019, 1611 patients were screened for eligibility and 1101 (68%) were enrolled; 554 (50%) were assigned to the placebo-abiraterone group and 547 (50%) to the ipatasertib-abiraterone group. At data cutoff (March 16, 2020), median follow-up duration was 19 months (range 0-33). In the 521 (47%) patients who had tumours with PTEN loss by immunohistochemistry (261 in the placebo-abiraterone group and 260 in the ipatasertib-abiraterone group), median radiographical progression-free survival was 16·5 months (95% CI 13·9-17·0) in the placebo-abiraterone group and 18·5 months (16·3-22·1) in the ipatasertib-abiraterone group (hazard ratio [HR] 0·77 [95% CI 0·61-0·98]; p=0·034; significant at α=0·04). In the intention-to-treat population, median progression-free survival was 16·6 months (95% CI 15·6-19·1) in the placebo-abiraterone group and 19·2 months (16·5-22·3) in the ipatasertib-abiraterone group (HR 0·84 [95% CI 0·71-0·99]; p=0·043; not significant at α=0·01). Grade 3 or higher adverse events occurred in 213 (39%) of 546 patients in the placebo-abiraterone group and in 386 (70%) of 551 patients in the ipatasertib-abiraterone group; adverse events leading to discontinuation of placebo or ipatasertib occurred in 28 (5%) in the placebo-abiraterone group and 116 (21%) in the ipatasertib-abiraterone group. Deaths due to adverse events deemed related to treatment occurred in two patients (<1%; acute myocardial infarction [n=1] and lower respiratory tract infection [n=1]) in the placebo-abiraterone group and in two patients (<1%; hyperglycaemia [n=1] and chemical pneumonitis [n=1]) in the ipastasertb-abiraterone group.

INTERPRETATION

Ipatasertib plus abiraterone significantly improved radiographical progression-free survival compared with placebo plus abiraterone among patients with mCRPC with PTEN-loss tumours, but there was no significant difference between the groups in the intention-to-treat population. Adverse events were consistent with the known safety profiles of each agent. These data suggest that combined AKT and androgen-receptor signalling pathway inhibition with ipatasertib and abiraterone is a potential treatment for men with PTEN-loss mCRPC, a population with a poor prognosis.

FUNDING

F Hoffmann-La Roche and Genentech.

Prospective validation of genetic predictors of aromatase inhibitor-associated musculoskeletal symptoms (AIMSS) in a racially diverse cohort: Results from ECOG-ACRIN E1Z11

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Background: AIMSS are common and frequently lead to early discontinuation of adjuvant AI therapy. Single nucleotide polymorphisms (SNPs) in candidate genes have been associated with AIMSS and AI discontinuation. The primary objective of E1Z11 was to validate previously identified associations between 10 specific SNPs in candidate genes and AI discontinuation due to AIMSS in a community-based, racially diverse cohort. Methods: Postmenopausal women with hormone receptor-positive stage I-III breast cancer enrolled onto a prospective multi-site cohort study, the majority through the NCI Community Oncology Research Program (NCORP). Participants received anastrozole 1 mg oral daily, and completed patient-reported outcomes (PROs) at baseline, 3, 6, 9, and 12 months. AIMSS was defined as >20% increase in Stanford Health Assessment Questionnaire (HAQ) score over baseline occurring within 1 year of AI therapy. We projected 40% would develop AIMSS and 25% would discontinue AI treatment within 1 year, informing a planned enrollment of 1000 women with a fixed number per strata (600 Caucasian, 200 African-American [AA] & 200 Asian) to provide 80% power to detect an effect size of 1.5-4. SNPs include ESR1 (rs2234693, rs2347868, rs9340835), CYP19A1 (rs1062033, rs4646), TCL1A (rs11849538, rs2369049, rs7158782, rs7159713), and HTR2A (rs2296972). Hardy-Weinberg equilibrium (HWE) was evaluated within each racial subset. SNP genotypes were coded as additive effects on the log odds ratio by coding as 0, 1 or 2 for the count of the minor allele. A Cochran-Armitage trend test was used with a 1-sided alpha of 0.0025 (Bonferroni correction for 10 tests). Results: We enrolled 999 evaluable women (616 Caucasian, 184 AA, 199 Asian). Genotyping was successful in 974 (98%). AIMSS developed in 43%, and AI therapy was discontinued in 12% within 1 year. While more AA and Asians developed AIMSS compared to Caucasians (48% vs 38%, p=0.017; 50% vs 38%, p=0.004), AI discontinuation rates were similar across racial groups. HWE was satisfied for all SNPs at the 5% alpha level, except for TCL1A/rs11849538 (p=0.002) in the AA cohort. None of the 10 SNPs were significantly associated with AI discontinuation or development of AIMSS in the overall population, or in any of the 3 cohorts. Conclusions: Although AIMSS were more common in AA and Asians, AI discontinuation rates were similar in the 3 cohorts. We were unable to prospectively validate 10 SNPs in 4 genes previously associated with AI discontinuation due to AIMSS. Future analyses will include other predictors of AIMSS, PROs, and additional genetic markers for the entire cohort and by race. Support: NCI UG1CA189828, UG1CA233196, UG1CA233277, UG1CA233320, UG1CA233178, UG1CA233160, UG1CA232760, UG1CA233341, UG1CA233329, U10CA180821, UG1CA189821, UG1CA189830, U10CA180888, UG1CA189859, UG1CA189863, UG1CA189971. Clinical trial information: NCT01824836.

Entrectinib in patients with advanced or metastatic NTRK fusion-positive solid tumours: integrated analysis of three phase 1-2 trials

BACKGROUND

Entrectinib is a potent inhibitor of tropomyosin receptor kinase (TRK) A, B, and C, which has been shown to have anti-tumour activity against NTRK gene fusion-positive solid tumours, including CNS activity due to its ability to penetrate the blood-brain barrier. We present an integrated efficacy and safety analysis of patients with metastatic or locally advanced solid tumours harbouring oncogenic NTRK1, NTRK2, and NTRK3 gene fusions treated in three ongoing, early-phase trials.

METHODS

An integrated database comprised the pivotal datasets of three, ongoing phase 1 or 2 clinical trials (ALKA-372-001, STARTRK-1, and STARTRK-2), which enrolled patients aged 18 years or older with metastatic or locally advanced NTRK fusion-positive solid tumours who received entrectinib orally at a dose of at least 600 mg once per day in a capsule. All patients had an Eastern Cooperative Oncology Group performance status of 0-2 and could have received previous anti-cancer therapy (except previous TRK inhibitors). The primary endpoints, the proportion of patients with an objective response and median duration of response, were evaluated by blinded independent central review in the efficacy-evaluable population (ie, patients with NTRK fusion-positive solid tumours who were TRK inhibitor-naive and had received at least one dose of entrectinib). Overall safety evaluable population included patients from STARTRK-1, STARTRK-2, ALKA-372-001, and STARTRK-NG (NCT02650401; treating young adult and paediatric patients [aged ≤21 years]), who received at least one dose of entrectinib, regardless of tumour type or gene rearrangement. NTRK fusion-positive safety evaluable population comprised all patients who have received at least one dose of entrectinib regardless of dose or follow-up. These ongoing studies are registered with ClinicalTrials.gov, NCT02097810 (STARTRK-1) and NCT02568267 (STARTRK-2), and EudraCT, 2012-000148-88 (ALKA-372-001).

FINDINGS

Patients were enrolled in ALKA-372-001 from Oct 26, 2012, to March 27, 2018; in STARTRK-1 from Aug 7, 2014, to May 10, 2018; and in STARTRK-2 from Nov 19, 2015 (enrolment is ongoing). At the data cutoff date for this analysis (May 31, 2018) the efficacy-evaluable population comprised 54 adults with advanced or metastatic NTRK fusion-positive solid tumours comprising ten different tumour types and 19 different histologies. Median follow-up was 12.9 months (IQR 8·77-18·76). 31 (57%; 95% CI 43·2-70·8) of 54 patients had an objective response, of which four (7%) were complete responses and 27 (50%) partial reponses. Median duration of response was 10 months (95% CI 7·1 to not estimable). The most common grade 3 or 4 treatment-related adverse events in both safety populations were increased weight (seven [10%] of 68 patients in the NTRK fusion-positive safety population and in 18 [5%] of 355 patients in the overall safety-evaluable population) and anaemia (8 [12%] and 16 [5%]). The most common serious treatment-related adverse events were nervous system disorders (three [4%] of 68 patients and ten [3%] of 355 patients). No treatment-related deaths occurred.

INTERPRETATION

Entrectinib induced durable and clinically meaningful responses in patients with NTRK fusion-positive solid tumours, and was well tolerated with a manageable safety profile. These results show that entrectinib is a safe and active treatment option for patients with NTRK fusion-positive solid tumours. These data highlight the need to routinely test for NTRK fusions to broaden the therapeutic options available for patients with NTRK fusion-positive solid tumours.

FUNDING

Ignyta/F Hoffmann-La Roche.

NSABP FC-11: A phase II study of neratinib (N) plus trastuzumab (T) or n plus cetuximab (C) in patients (pts) with "quadruple wild-type (WT)" (KRAS/NRAS/BRAF/PIK3CA WT) metastatic colorectal cancer (mCRC) based on HER2 status—Amplified (amp), non-amplified (non-amp), WT, or mutated (mt)

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Background: HER2 has been shown to be a validated therapeutic target for the treatment of mCRC. Preclinical and clinical evidence supports the use of HER2-targeted agents in each of these mCRC cohorts. In HERACLES, treatment–refractory, KRAS exon 2 (codons 12 and 13) WT, HER2 amp mCRC pts were treated with T and lapatinib (L). Objective response rate (CR or PR) was 8/27 and disease control rate (CR, PR, and SD > 16 wks) was 16/27. Duration of response ranged from 24-94+ wks. Anecdotal reports have shown activity of N in HER2 mts from several cancer types. In mCRC PDX models with qualifying HER2 mts, T plus N is more active than either drug alone. In quad WT, HER2 non-amp PDX models, C plus TKI resulted in major tumor regressions not seen with C monotherapy. In NSABP FC-7, a trial of C + N in cetuximab refractory pts, HER2 amp was observed in 2/23 primary tissue samples; after C exposure, HER2 amp was seen in 5/17 samples, presumably signal upregulation under selective pressure of C. HER2 amp was concordant in tissue (CISH) and blood using cfDNA. Methods: This multi-center 3-cohort phase II trial is currently enrolling pts (total planned N = 35). Pts with quad WT, HER2 amp (n = 15) with prior anti-EGFR therapy and/or HER2 mt mCRC (n = 5) will receive T 4 mg/kg iv loading dose followed by 2 mg/kg/wk and N 240 mg po daily (Arm 1). Pts with quad WT, HER2 non-amp (n = 15) with no prior anti-EGFR therapy will receive C 400 mg/m2 iv loading dose followed by 250 mg/m2/wk, and N 240 mg (Arm 2). Specific pt eligibility for quad WT and HER2 status are defined below: Arm 1: HER2 amp confirmed in blood by Guardant360 assay, and prior treatment with C or panitumumab (P). HER2 mt (with qualifying mt) with or without prior treatment with C or P. Arm 2: HER2 non-amp or HER2 amp and no prior therapy with C or P. The primary aim is 6-mos progression-free survival for each cohort. Secondary aims: response rates and toxicity. Exploratory aims: genetic and molecular analyses. Specific drug combinations will be evaluated in PDX models. NCT03457896. Support: Puma Biotechnology, Inc.; NSABP Foundation, Inc. Clinical trial information: NCT03457896.

Triweekly carboplatin alone in the treatment of oropharyngeal carcinoma with definitive concurrent chemoradiation: Outcomes of 120 unselected patients and a comparison to the RTOG 0129 regimen results

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Background: In 2002, due to the significant toxicities associated with triweekly high-dose cisplatin, we decided to routinely use triweekly carboplatin in the treatment of locally advanced head and neck cancer patients as our standard definitive concurrent chemoradiation drug, the outcomes of which are reported here. Methods: From August of 2002 through May of 2009, newly diagnosed patients with stage III (22%) or IVA/B (78%) oropharyngeal squamous carcinoma were treated with carboplatin (AUC=5) x 3 on days 1, 22 and 43 along with concurrent conventional RT (N=67) or IMRT (N=53) to 70 Gy. Individuals treated with induction chemotherapy or definitive surgery of any kind prior to concurrent chemoradiation, and surviving/recurrence-free patients with less than 24 months of follow-up were excluded, leaving 120 patients for this analysis. The median age was 58 (range 42-85). Feeding tubes were not placed prophylactically. Planned post chemoRT neck dissections were not performed. HPV/P16 status was not determined in any patients prior to treatment. Seventy-one patients (59%) had a significant history of tobacco use, 38 of whom were current smokers. Results: With a median follow-up of 64 months (range 32-108) for surviving patients, 15 (12.5%) had a loco-regional recurrence (LR), and a total of 9 patients (7.5%) failed distantly, including one with simultaneous LR. Only 26 (22%) patients required feeding tubes during or shortly after (< 90 days) chemoRT; 90% received 3 cycles of carboplatin and planned RT dose was delivered in 98%. The 3-year loco-regional control and overall survival rates for the entire group were 88% and 82%, respectively; these rates for 92 patients eligible for RTOG 0129 (T2N2-3, T3-4 any N) were 86% and 77%. At last follow-up, only 3% were feeding-tube dependent. Conclusions: This first ever report of concurrent triweekly carboplatin alone with radiotherapy at a large U.S. institution for locally advanced oropharyngeal carcinoma suggests that it is better tolerated and more feasible than concurrent triweekly high-dose cisplatin, with similar/favorable disease control and survival rates.

Introduction to retroviruses and retroviral vectors

As various viral vector systems for gene transfer are developed, interest in using such systems in applied settings continues to grow. This Chapter is designed to provide background information for readers interested in learning about lentiviral vector systems for gene transfer applications but who lack a background in retrovirology. To assist those readers who are unfamiliar with retroviral vector systems, basic outlines of the retroviral replication cycle and of characteristics of retroviral vector systems are introduced here in order to present and define concepts and terms that are discussed in subsequent Chapters.

Approaches to gene therapy for human immunodeficiency virus infection

Much progress has been made in developing new and more efficient treatments for human immunodeficiency virus (HIV) infection, the cause of acquired immunodeficiency syndrome (AIDS). However, the scope of the HIV epidemic and the limitations of existing treatments necessitate the continued development of novel treatment strategies. Gene therapy is one such forward-looking strategy. Gene therapy approaches for HIV infection include efforts to interfere with viral replication directly by engineering HIV-resistant cells or indirectly by eliminating infected cells from the body, primarily by eliciting a therapeutic immune response to destroy HIV-infected cells. Although the prospect of gene therapy as a routine treatment for HIV infection remains distant, continuous progress is being made, which should also have implications for gene therapy strategies for a variety of other diseases. This article reviews some of the strategies for investigating the feasibility of gene transfer for the treatment of HIV infection.

Development of lentiviral vectors for gene therapy for human diseases

Retroviral vectors derived from murine retroviruses are being used in several clinical gene therapy trials. Recently, progress has been made in the development of vectors based on the lentivirus genus of retroviruses, which ironically includes a major human pathogen, human immunodeficiency virus (HIV). As these vector systems for clinical gene transfer are developed, it is important to understand the rationale behind their design and development. This article reviews the fundamental features of retrovirus replication and of the elements necessary for development of a retroviral vector system, and it discusses why vector systems based on HIV or other lentiviruses have the potential to become important tools in clinical gene therapy. (Blood. 2000;95:2499-2504)

Association of murine leukemia virus pol with virions, independent of Gag-Pol expression

During the replication cycle of murine leukemia virus (MLV), Pol is normally synthesized as part of a Gag-Pol fusion protein. In this study, the ability of free MLV Pol to be incorporated into virions was examined. When MLV Gag and MLV Pol were coexpressed from separate plasmids in cells, reverse transcriptase (RT) activity associated with Gag core particles at a slightly lower level than did RT activity generated from wild-type Gag-Pol expression. Particles produced in this manner were somewhat less infectious than those produced with wild-type Gag-Pol. A smaller amount of MLV Pol also associated with heterologous human immunodeficiency virus type 1 Gag cores.

Effects of second-site mutations on dominant interference by a human immunodeficiency virus type 1 envelope glycoprotein mutant

We have demonstrated previously that a human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein containing a Val-to-Glu substitution at the second amino acid of the transmembrane glycoprotein gp41 (termed the 41.2 mutant) dominantly interferes with wild-type envelope-mediated syncytium formation and virus infectivity. To understand the mechanism by which the 41.2 mutant exerts the dominant interfering phenotype and thereby determine further how the mutant might be used as an inhibitor of viral spread, additional mutations were made in the envelope gene, and the effects of these mutations on interference were determined. It was found that processing of the 41.2 mutant glycoprotein in gp120 and gp41 subunits and a functional CD4-binding domain are necessary for the interfering phenotype to be exhibited fully. However, neither a wild-type V3 loop nor the gp41 cytoplasmic tail is necessary for efficient interference. In addition, it was determined that the dominant interfering phenotype is not conferred exclusively by the glutamate substitution at amino acid 2 of gp41, since a substitution with a basic residue at this position also results in a dominant interfering envelope glycoprotein.

Cloning and characterization of the altA alpha-tubulin gene of Physarum

A cDNA clone derived from the altA locus, encoding one of several alpha-tubulins in Physarum, was sequenced and used to determine the developmental and cell cycle expression patterns of its corresponding gene. The predicted amino acid sequence of the altA gene product, alpha 1A-tubulin, is 92% identical to the other known Physarum alpha-tubulins, alpha 1B and alpha 2B, which are products of two tightly linked genes at the altB locus. The nucleotide sequence of the altA coding region is 82% identical to the two altB genes. Expression of the altA gene was found in all three cell types examined - amoeba, flagellate and plasmodium - but at substantially different levels in each. The peak level of altA message detected in flagellates was 14-fold higher than in amoebae, while the peak level in plasmodia was 5-fold lower than in amoebae. The expression pattern of altA and the predicted amino acid sequence of the alpha-tubulin it encodes suggest that alpha 1A is the substrate for post-translational acetylation, giving rise to the alpha 3-tubulin isoform found specifically in amoebae and flagellates. Northern blot analysis of plasmodial RNA samples from specific times in the cell cycle showed that the level of altA message varies over the cell cycle in a pattern similar to transcripts from other tubulin genes, with a peak at mitosis and little or no message detected during most of interphase.

Cells induced to express a human immunodeficiency virus type 1 envelope gene mutant inhibit the spread of wild-type virus

The feasibility of using a trans-dominant interfering human immunodeficiency virus type 1 (HIV-1) envelope mutant for inducible gene therapy of HIV infection was investigated. Genes encoding wild-type or mutant glycoproteins were introduced into CD4+ cells, where they were stably maintained but not expressed until induced. Envelope (env) gene expression was dependent upon the viral regulatory protein Tat. Induction of the mutant env resulted in resistance to cytopathic effects mediated by wild-type envelope and decreased infectious vector virus production. When cells containing the mutant env gene were infected with wild-type virus, viral spread was inhibited. The fact that maintenance of the env gene was stable over time suggests that inducible gene therapy using the dominantly interfering env mutant may be a feasible approach to slowing the progression of HIV-1 disease.

Analysis of HIV-1 envelope mutants and pseudotyping of replication-defective HIV-1 vectors by genetic complementation

Infectious HIV-1 particles containing replication-defective vectors that express the hygromycin B phosphotransferase gene were generated by transient complementation in COS-1 cells. A defective vector dependent only on trans-complementation with an env gene and a small vector containing a deletion of almost all of the trans region were used to examine pseudotyping of HIV-1 by an amphotropic murine retrovirus. Although pseudotyping by the heterologous envelope glycoprotein occurred with efficiency, no pseudotyping at the RNA level was observed. Genetic complementation was used to rapidly analyze the effect of env mutations in the V3, proteolytic processing site, fusion domain, and cytoplasmic tail on viral infectivity. Mutations decreasing syncytium formation usually also lowered infectivity. However, a mutation in the cytoplasmic tail and a separate mutation adjacent to the fusion domain dramatically decreased viral particle infectivity but did not appreciably decrease envelope glycoprotein-mediated cell-to-cell fusion. These results may indicate that these regions of the transmembrane peptide are necessary for acquisition of envelope glycoprotein by budding virus particles or for virus entry.

Human immunodeficiency virus vectors for inducible expression of foreign genes

Tat-dependent expression of an endogenous lethal or deleterious foreign gene might be useful for abrogating the production of human immunodeficiency virus (HIV) from cells. This type of HIV-induced cellular killing, as well as other approaches to gene therapy for HIV infection, would be facilitated by simple HIV vectors that express introduced genes in a Tat-inducible manner. As part of studies to examine the feasibility of this concept, we constructed HIV-1 vectors that express the hygromycin B phosphotransferase gene (Hygr) in a Tat-dependent manner. Comparison of the efficiency of propagation of each vector indicates that sequences extending into the gag open reading frame are necessary in cis for efficient vector propagation. Southern blot analysis of genomic DNA isolated from vector-infected cells demonstrated that the vectors were capable of being propagated as expected without gross rearrangements or deletions. A fragment of the influenza A virus hemagglutinin (H5 HA) gene, capable of eliciting antibody and cytotoxic T-cell responses, was used as a marker for further characterization of the vector system. A Tat-dependent vector conferring the H5 HA+ phenotype was assayed by indirect immunofluorescence, and cells which contained but did not express the H5 HA gene were isolated. The activation of H5 HA expression following HIV infection of Tat- cells that stably contained but did not express the H5 HA construct was determined to be an efficient process.

Preferential expression of one beta-tubulin gene during flagellate development in Physarum

The microbial eukaryote Physarum polycephalum displays several distinct cell types in its life cycle, including amoebae, flagellates and plasmodia. Despite its relative simplicity, Physarum has a tubulin gene family of complexity comparable to that of Drosophila. We have identified beta-tubulin cDNAs from Physarum that are derived from the betA beta-tubulin locus and encode beta 1A tubulin. We have also identified a partial cDNA for the unlinked betB beta-tubulin gene, which encodes beta 1B tubulin. The polypeptide sequences encoded by betA and betB show 99% identity, but the nucleotide sequences show only 85% identity, consistent with an ancient duplication of these genes. The betB gene is expressed in amoebae, flagellates and plasmodia, whereas betA is expressed only in amoebae and flagellates. During the amoeba-flagellate transition the level of betA transcript increases over 100-fold, while the level of betB transcript changes very little. Thus Physarum has a mechanism for regulating the level of discrete beta-tubulin transcripts differentially during flagellate development. A need for this differential regulation could account for the maintenance of the virtually isocoding betA and betB beta-tubulin genes.

A mutation in the human immunodeficiency virus type 1 transmembrane glycoprotein gp41 dominantly interferes with fusion and infectivity

Several domains of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein have been identified that are involved in HIV-1-mediated membrane fusion. One domain that is involved in membrane fusion is the hydrophobic amino terminus of the HIV-1 transmembrane glycoprotein gp41. Here we show that a polar substitution at gp41 amino acid 2 (the 41.2 mutation) results in an envelope glycoprotein that dominantly interferes with both syncytium formation and infection mediated by the wild-type HIV-1 envelope glycoprotein. The interference by the 41.2 mutant is not a result of aberrant envelope glycoprotein synthesis, processing, or transport. The 41.2 mutant elicits a dominant interfering effect even in the presence of excess wild-type glycoprotein, suggesting that a higher-order envelope glycoprotein complex is involved in membrane fusion. These results shed light on the process by which the HIV-1 envelope glycoproteins induce membrane fusion reactions and present a possible approach to anti-HIV therapy.