A risk-reward examination of sample multiplexing reagents for single cell RNA-Seq

Single-cell RNA sequencing (scRNA-Seq) has emerged as a powerful tool for understanding cellular heterogeneity and function. However the choice of sample multiplexing reagents can impact data quality and experimental outcomes. In this study, we compared various multiplexing reagents, including MULTI-Seq, Hashtag antibody, and CellPlex, across diverse sample types such as human peripheral blood mononuclear cells (PBMCs), mouse embryonic brain and patient-derived xenografts (PDXs). We found that all multiplexing reagents worked well in cell types robust to ex vivo manipulation but suffered from signal-to-noise issues in more delicate sample types. We compared multiple demultiplexing algorithms which differed in performance depending on data quality. We find that minor improvements to laboratory workflows such as titration and rapid processing are critical to optimal performance. We also compared the performance of fixed scRNA-Seq kits and highlight the advantages of the Parse Biosciences kit for fragile samples. Highly multiplexed scRNA-Seq experiments require more sequencing resources, therefore we evaluated CRISPR-based destruction of non-informative genes to enhance sequencing value. Our comprehensive analysis provides insights into the selection of appropriate sample multiplexing reagents and protocols for scRNA-Seq experiments, facilitating more accurate and cost-effective studies.

PI3K/mTOR is a therapeutically targetable genetic dependency in diffuse intrinsic pontine glioma

Diffuse midline glioma (DMG), including tumors diagnosed in the brainstem (diffuse intrinsic pontine glioma; DIPG), are uniformly fatal brain tumors that lack effective treatment. Analysis of CRISPR/Cas9 loss-of-function gene deletion screens identified PIK3CA and MTOR as targetable molecular dependencies across patient derived models of DIPG, highlighting the therapeutic potential of the blood-brain barrier-penetrant PI3K/Akt/mTOR inhibitor, paxalisib. At the human-equivalent maximum tolerated dose, mice treated with paxalisib experienced systemic glucose feedback and increased insulin levels commensurate with patients using PI3K inhibitors. To exploit genetic dependence and overcome resistance while maintaining compliance and therapeutic benefit, we combined paxalisib with the antihyperglycemic drug metformin. Metformin restored glucose homeostasis and decreased phosphorylation of the insulin receptor in vivo, a common mechanism of PI3K-inhibitor resistance, extending survival of orthotopic models. DIPG models treated with paxalisib increased calcium-activated PKC signaling. The brain penetrant PKC inhibitor enzastaurin, in combination with paxalisib, synergistically extended the survival of multiple orthotopic patient-derived and immunocompetent syngeneic allograft models; benefits potentiated in combination with metformin and standard-of-care radiotherapy. Therapeutic adaptation was assessed using spatial transcriptomics and ATAC-Seq, identifying changes in myelination and tumor immune microenvironment crosstalk. Collectively, this study has identified what we believe to be a clinically relevant DIPG therapeutic combinational strategy.

Tumor cell-derived spermidine promotes a pro-tumorigenic immune microenvironment in glioblastoma via CD8+ T cell inhibition

The glioblastoma microenvironment is enriched in immunosuppressive factors that potently interfere with the function of cytotoxic T lymphocytes. Cancer cells can directly impact the immune system, but the mechanisms driving these interactions are not completely clear. Here we demonstrate that the polyamine metabolite spermidine is elevated in the glioblastoma tumor microenvironment. Exogenous administration of spermidine drives tumor aggressiveness in an immune-dependent manner in pre-clinical mouse models via reduction of CD8+ T cell frequency and phenotype. Knockdown of ornithine decarboxylase, the rate-limiting enzyme in spermidine synthesis, did not impact cancer cell growth in vitro but did result in extended survival. Furthermore, glioblastoma patients with a more favorable outcome had a significant reduction in spermidine compared to patients with a poor prognosis. Our results demonstrate that spermidine functions as a cancer cell-derived metabolite that drives tumor progression by reducing CD8+T cell number and function.

Matrix Selection for the Visualization of Small Molecules and Lipids in Brain Tumors Using Untargeted MALDI-TOF Mass Spectrometry Imaging

Matrix-assisted laser desorption/ionization mass spectrometry imaging allows for the study of metabolic activity in the tumor microenvironment of brain cancers. The detectable metabolites within these tumors are contingent upon the choice of matrix, deposition technique, and polarity setting. In this study, we compared the performance of three different matrices, two deposition techniques, and the use of positive and negative polarity in two different brain cancer types and across two species. Optimal combinations were confirmed by a comparative analysis of lipid and small-molecule abundance by using liquid chromatography-mass spectrometry and RNA sequencing to assess differential metabolites and enzymes between normal and tumor regions. Our findings indicate that in the tumor-bearing brain, the recrystallized α-cyano-4-hydroxycinnamic acid matrix with positive polarity offered superior performance for both detected metabolites and consistency with other techniques. Beyond these implications for brain cancer, our work establishes a workflow to identify optimal matrices for spatial metabolomics studies.

Discovery of a highly potent, selective, orally bioavailable inhibitor of KAT6A/B histone acetyltransferases with efficacy against KAT6A-high ER+ breast cancer

KAT6A, and its paralog KAT6B, are histone lysine acetyltransferases (HAT) that acetylate histone H3K23 and exert an oncogenic role in several tumor types including breast cancer where KAT6A is frequently amplified/overexpressed. However, pharmacologic targeting of KAT6A to achieve therapeutic benefit has been a challenge. Here we describe identification of a highly potent, selective, and orally bioavailable KAT6A/KAT6B inhibitor CTx-648 (PF-9363), derived from a benzisoxazole series, which demonstrates anti-tumor activity in correlation with H3K23Ac inhibition in KAT6A over-expressing breast cancer. Transcriptional and epigenetic profiling studies show reduced RNA Pol II binding and downregulation of genes involved in estrogen signaling, cell cycle, Myc and stem cell pathways associated with CTx-648 anti-tumor activity in ER-positive (ER+) breast cancer. CTx-648 treatment leads to potent tumor growth inhibition in ER+ breast cancer in vivo models, including models refractory to endocrine therapy, highlighting the potential for targeting KAT6A in ER+ breast cancer.

Correlating MRI features with additional genetic markers and patient survival in histological grade 2-3 IDH-mutant astrocytomas

PURPOSE

The increasing importance of molecular markers for classification and prognostication of diffuse gliomas has prompted the use of imaging features to predict genotype ("radiogenomics"). CDKN2A/B homozygous deletion has only recently been added to the diagnostic paradigm for IDH[isocitrate dehydrogenase]-mutant astrocytomas; thus, associated radiogenomic literature is sparse. There is also little data on whether different IDH mutations are associated with different imaging appearances. Furthermore, given that molecular status is now generally obtained routinely, the additional prognostic value of radiogenomic features is less clear. This study correlated MRI features with CDKN2A/B status, IDH mutation type and survival in histological grade 2-3 IDH-mutant brain astrocytomas.

METHODS

Fifty-eight grade 2-3 IDH-mutant astrocytomas were identified, 50 with CDKN2A/B results. IDH mutations were stratified into IDH1-R132H and non-canonical mutations. Background and survival data were obtained. Two neuroradiologists independently assessed the following MRI features: T2-FLAIR mismatch (<25%, 25-50%, >50%), well-defined tumour margins, contrast-enhancement (absent, wispy, solid) and central necrosis.

RESULTS

8/50 tumours with CDKN2A/B results demonstrated homozygous deletion; slightly shorter survival was not significant (p=0.571). IDH1-R132H mutations were present in 50/58 (86%). No MRI features correlated with CDKN2A/B status or IDH mutation type. T2-FLAIR mismatch did not predict survival (p=0.977), but well-defined margins predicted longer survival (HR 0.36, p=0.008), while solid enhancement predicted shorter survival (HR 3.86, p=0.004). Both correlations remained significant on multivariate analysis.

CONCLUSION

MRI features did not predict CDKN2A/B homozygous deletion, but provided additional positive and negative prognostic information which correlated more strongly with prognosis than CDKN2A/B status in our cohort.

BRAF-mediated brain tumors in adults and children: A review and the Australian and New Zealand experience

The mitogen-activated protein kinase (MAPK) pathway signaling pathway is one of the most commonly mutated pathways in human cancers. In particular, BRAF alterations result in constitutive activation of the rapidly accelerating fibrosarcoma-extracellular signal-regulated kinase-MAPK significant pathway, leading to cellular proliferation, survival, and dedifferentiation. The role of BRAF mutations in oncogenesis and tumorigenesis has spurred the development of targeted agents, which have been successful in treating many adult cancers. Despite advances in other cancer types, the morbidity and survival outcomes of patients with glioma have remained relatively stagnant. Recently, there has been recognition that MAPK dysregulation is almost universally present in paediatric and adult gliomas. These findings, accompanying broad molecular characterization of gliomas, has aided prognostication and offered opportunities for clinical trials testing targeted agents. The use of targeted therapies in this disease represents a paradigm shift, although the biochemical complexities has resulted in unexpected challenges in the development of effective BRAF inhibitors. Despite these challenges, there are promising data to support the use of BRAF inhibitors alone and in combination with MEK inhibitors for patients with both low-grade and high-grade glioma across age groups. Safety and efficacy data demonstrate that many of the toxicities of these targeted agents are tolerable while offering objective responses. Newer clinical trials will examine the use of these therapies in the upfront setting. Appropriate duration of therapy and durability of response remains unclear in the glioma patient cohort. Longitudinal efficacy and toxicity data are needed. Furthermore, access to these medications remains challenging outside of clinical trials in Australia and New Zealand. Compassionate access is limited, and advocacy for mechanism of action-based drug approval is ongoing.

Flow Cytometry Identification of Cell Compartments in the Murine Brain

Glioma can be modelled in the murine brain through the induction of genetically engineered mouse models or intracranial transplantation. Gliomas (oligodendroglioma and astrocytoma) are thought to arise from neuronal and glial progenitor populations in the brain and are poorly infiltrated by immune cells. An improved understanding of oligodendrocytes, astrocytes, and the immune environment throughout tumor development will enhance the analysis and development of brain cancer models. Here, we describe the isolation and analysis of murine brain cell types using a combination of flow cytometry and quantitative RT-PCR strategies to analyze these individual cell populations in vivo.

How has the COVID-19 pandemic impacted clinical care and research in Neuro-Oncology?

The COVID-19 pandemic has challenged the continued delivery of healthcare globally. Due to disease risk, clinicians were forced to re-evaluate the safety and priorities of pre-pandemic care. Neuro-oncology presents unique challenges, as patients can deteriorate rapidly without intervention. These challenges were also observed in countries with reduced COVID-19 burden with centres required to rapidly develop strategies to maintain efficient and equitable care. This review aims to summarise the impact of the pandemic on clinical care and research within the practice of Neuro-oncology. A narrative review of the literature was performed using MEDLINE and EMBASS and results screened using PRISMA guidelines with relevant inclusion and exclusion criteria. Search strategies included variations of ‘Neuro-oncology’ combined with COVID-19 and other clinical-related terms. Most adult and paediatric neurosurgical centres experienced reductions in new referrals and operations for brain malignancies, and those who did present for treatment frequently had operations cancelled or delayed. Many radiation therapy and medical oncology centres altered treatment plans to mitigate COVID-19 risk for patients and staff. New protocols were developed that aimed to reduce in-person visits and reduce the risk of developing severe complications from COVID-19. The COVID-19 pandemic has presented many challenges to the provision of safe and accessible healthcare. Despite these challenges, some benefits to healthcare provision such as the use of telemedicine are likely to remain in future practice. Neuro-oncology staff must remain vigilant to ensure patient and staff safety.

Adult medulloblastoma in an Australian population

Medulloblastoma in adult patients is a rare condition with limited contemporary demographic and treatment outcome data available in an Australian population. We conducted a retrospective review of patterns of care and outcomes of adult patients diagnosed with medulloblastoma treated at major neuro-oncology centres across Australia between January 2010 and December 2019. A total of 80 patients were identified and the median follow-up after diagnosis was 59.2 (range 0.5-204) months. A variety of chemotherapy regimens were used in the adjuvant and recurrent settings. The median overall survival (mOS) was 78 months (IQR 17.5-94.8). Patients who had no residual disease post-resection or with SHH-subtype tumours had a numerically longer 5-year survival rate than those with residual disease post resection or non-SHH subtypes respectively. The median time to recurrence from diagnosis was 18.4 months. The median OS from 1st relapse was 22.1 months (95% CI 11.7-31.4) and mOS from second relapse was 10.2 months (95% CI 6.6 - NR). This is the largest dataset examining patterns of care of adult patients with medulloblastoma in an Australian population. Substantial variation existed in the chemotherapy agents used in the adjuvant and recurrent setting. As has been demonstrated in a paediatric population, trials such as the upcoming EORTC 1634-BTG/NOA-23 trial (PersoMed-1 study) which are tailoring treatments to molecular profiles are likely to improve outcome in adult medulloblastoma.

PALVEN: phase Ib trial of palbociclib, letrozole and venetoclax in estrogen receptor- and BCL2-positive advanced breast cancer

The addition of a CDK4/6 inhibitor to endocrine therapy improves progression-free and overall survival in women with metastatic estrogen receptor-positive breast cancer. In that setting, CDK4/6 inhibitors induce a potent cell-cycle arrest (which may be accompanied by tumor senescence) but fail to induce apoptotic cell death. Venetoclax is a potent inhibitor of BCL2, a pro-survival protein overexpressed in the majority of estrogen receptor-positive cancers. Pre-clinical findings indicate that venetoclax augments tumor response to the CDK4/6 inhibitor palbociclib by triggering apoptosis, including in senescent cells. The PALVEN phase Ib trial will further examine this finding. The primary objective is to identify the maximum tolerated dose and determine the recommended phase II dose for palbociclib, letrozole and venetoclax combination therapy. Clinical Trial Registration: NCT03900884 (ClinicalTrials.gov).

In vivo genome-editing screen identifies tumor suppressor genes that cooperate with Trp53 loss during mammary tumorigenesis

Breast cancer is a heterogeneous disease that comprises multiple histological and molecular subtypes. To gain insight into mutations that drive breast tumorigenesis, we describe a pipeline for the identification and validation of tumor suppressor genes. Based on an in vivo genome‐wide CRISPR/Cas9 screen in Trp53^+/– heterozygous mice, we identified tumor suppressor genes that included the scaffold protein Axin1, the protein kinase A regulatory subunit gene Prkar1a, as well as the proof‐of‐concept genes Pten, Nf1, and Trp53 itself. Ex vivo editing of primary mammary epithelial organoids was performed to further interrogate the roles of Axin1 and Prkar1a. Increased proliferation and profound changes in mammary organoid morphology were observed for Axin1/Trp53 and Prkar1a/Trp53 double mutants compared to Pten/Trp53 double mutants. Furthermore, direct in vivo genome editing via intraductal injection of lentiviruses engineered to express dual short‐guide RNAs revealed that mutagenesis of Trp53 and either Prkar1a, Axin1, or Pten markedly accelerated tumor development compared to Trp53‐only mutants. This proof‐of‐principle study highlights the application of in vivo CRISPR/Cas9 editing for uncovering cooperativity between defects in tumor suppressor genes that elicit mammary tumorigenesis.

Perioperative clinical trials for glioma: Raising the bar

Gliomas are a heterogeneous group of primary brain cancers with poor survival despite multimodality therapy that includes surgery, radiation and chemotherapy. Numerous clinical trials have investigated systemic therapies in glioma, but have largely been negative. Multiple factors have contributed to the lack of progress including tumour heterogeneity, the tumour micro-environment and presence of the blood-brain barrier, as well as extrinsic factors relating to trial design, such as the lack of a contemporaneous biopsy at the time of treatment. A number of strategies have been proposed to progress new agents into the clinic. Here, we review the progress of perioperative, including phase 0 and 'window of opportunity', studies and provide recommendations for trial design in the development of new agents for glioma. The incorporation of pre- and post-treatment biopsies in glioma early phase trials will provide valuable pharmacokinetic and pharmacodynamic data and also determine the target or biomarker effect, which will guide further development of new agents. Perioperative 'window of opportunity' studies must use drugs with a recommended-phase-2-dose, known safety profile and adequate blood-brain barrier penetration. Drugs shown to have on-target effects in perioperative trials can then be evaluated further in a larger cohort of patients in an adaptive trial to increase the efficiency of drug development.

Abstract OT-27-01: PALVEN: A phase 1b study of palbociclib, letrozole and venetoclax in estrogen receptor, BCL2-positive metastatic breast cancer

Background: CDK4/6 inhibitors are integral to the treatment of Estrogen Receptor (ER) positive metastatic breast cancer (MBC). Although they are potent inhibitors of proliferation, tumor cell death (by apoptosis) may be curtailed. Venetoclax, an inhibitor of the pro-survival protein BCL2, has shown promise in an early phase clinical trial in ER+ MBC1. Moreover, preclinical studies suggest that venetoclax could improve tumor response to endocrine therapy and a CDK4/6 inhibitor by triggering apoptosis, including in growth arrested/senescent cells2. PALVEN is a phase 1b study (NCT NCT03900884), aiming to combine venetoclax with letrozole and the CDK4/6 inhibitor palbociclib. Trial Design: Eligible patients will be treated with letrozole (2.5 mg), palbociclib (75-125 mg) and venetoclax (100-800 mg) using a 3+3 dose escalation study design, with a maximum of 6 patients per dose cohort. Both palbociclib and venetoclax will be administered on day 1-21 of a 28 day cycle. Dose limiting toxicity (DLT) will be evaluated in the first 4 weeks of treatment. Tumor assessment will be performed every 8 weeks for 24 weeks and then every 12 weeks until progression. The primary endpoint is to describe DLTs reported within the first 4 weeks of treatment and determine the maximum tolerated dose (MTD), in order to define a recommended phase 2 dose (RP2D). Secondary endpoints include type and worst grade adverse events per patient (CTCAE v5.0), tumor response (RECIST v1.1), clinical benefit rate (CBR), progression free and overall survival (PFS, OS) as well as patient reported outcomes. Exploratory endpoints include metabolic response (using FDG-PET), changes in circulating tumor DNA (ctDNA), peripheral blood leukocyte subsets, and tumor phenotype in paired and progression biopsies. Eligibility Women with ER+ (≥10% positively stained carcinoma cells) and BCL2+ (≥50% cells with at least moderate cytoplasmic staining; intensity 2-3 on a 0-3 scale), unresectable locally advanced or MBC are eligible. Patients must have measurable or evaluable disease as per RECIST v1.1 and ECOG performance score of 0-1. Participants must not have had &gt;2 prior lines of treatment in the metastatic setting and no previous treatment with CDK4/6 inhibitor or venetoclax in the adjuvant or metastatic setting. Statistical methods This is a proof-of-concept, dose escalation study and any statistical analysis of responses will be exploratory. Analysis will be focused primarily on adverse events, particularly DLTs reported in the DLT observation period. All secondary endpoints will be analysed separately combining all dosing cohorts. The response rate and CBR will be estimated with 95% confidence intervals calculated using exact methods based on the binomial distribution. Time-to-event endpoints (PFS and OS) will be described using Kaplan-Meier methods to calculate the median survival. Response rate, CBR and time-to-event endpoints (PFS and OS) will also be described for patients treated in the 1st versus 2nd and 3rd line setting. Accrual Target accrual is 6-36, depending on the number of dose cohorts required to reach DLT. Recruitment is active at 2 sites in Australia. References 1 Lok, S.W., et al. (2019). Cancer Discov 9, 354-369. 2 Whittle, J.R., et al. (2020). Clin Cancer Res Advance online.

Citation Format: Christine Muttiah, Avraham Travers, James R Whittle, Sarah-Jane Dawson, Belinda Yeo, Jane E Visvader, Catherine Oakman, Geoffrey J Lindeman. PALVEN: A phase 1b study of palbociclib, letrozole and venetoclax in estrogen receptor, BCL2-positive metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-27-01.

Modeling Breast Cancer Using CRISPR-Cas9-Mediated Engineering of Human Breast Organoids

Breast cancer is characterized by histological and functional heterogeneity, posing a clinical challenge for patient treatment. Emerging evidence suggests that the distinct subtypes reflect the repertoire of genetic alterations and the target cell. However, the precise initiating events that predispose normal epithelium to neoplasia are poorly understood. Here, we demonstrate that breast epithelial organoids can be generated from human reduction mammoplasties (12 out of 12 donors), thus creating a tool to study the clonal evolution of breast cancer. To recapitulate de novo oncogenesis, we exploited clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 for targeted knockout of four breast cancer-associated tumor suppressor genes (P53, PTEN, RB1, NF1) in mammary progenitor cells from six donors. Mutant organoids gained long-term culturing capacity and formed estrogen-receptor positive luminal tumors on transplantation into mice for one out of six P53/PTEN/RB1-mutated and three out of six P53/PTEN/RB1/NF1-mutated lines. These organoids responded to endocrine therapy or chemotherapy, supporting the potential utility of this model to enhance our understanding of the molecular events that culminate in specific subtypes of breast cancer.

Dual Targeting of CDK4/6 and BCL2 Pathways Augments Tumor Response in Estrogen Receptor-Positive Breast Cancer

PURPOSE

Although cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors significantly extend tumor response in patients with metastatic estrogen receptor-positive (ER⁺) breast cancer, relapse is almost inevitable. This may, in part, reflect the failure of CDK4/6 inhibitors to induce apoptotic cell death. We therefore evaluated combination therapy with ABT-199 (venetoclax), a potent and selective BCL2 inhibitor.

EXPERIMENTAL DESIGN

BCL2 family member expression was assessed following treatment with endocrine therapy and the CDK4/6 inhibitor palbociclib. Functional assays were used to determine the impact of adding ABT-199 to fulvestrant and palbociclib in ER⁺ breast cancer cell lines, patient-derived organoid (PDO), and patient-derived xenograft (PDX) models. A syngeneic ER⁺ mouse mammary tumor model was used to study the effect of combination therapy on the immune system.

RESULTS

Triple therapy was well tolerated and produced a superior and more durable tumor response compared with single or doublet therapy. This was associated with marked apoptosis, including of senescent cells, indicative of senolysis. Unexpectedly, ABT-199 resulted in Rb dephosphorylation and reduced G₁-S cyclins, most notably at high doses, thereby intensifying the fulvestrant/palbociclib-induced cell-cycle arrest. Interestingly, a CRISPR/Cas9 screen suggested that ABT-199 could mitigate loss of Rb (and potentially other mechanisms of acquired resistance) to palbociclib. ABT-199 did not abrogate the favorable immunomodulatory effects of palbociclib in a syngeneic ER⁺ mammary tumor model and extended tumor response when combined with anti-PD1 therapy.

CONCLUSIONS

This study illustrates the potential for targeting BCL2 in combination with CDK4/6 inhibitors and supports investigation of combination therapy in ER⁺ breast cancer.

Abstract PD7-07: Synergistic targeting of CDK4/6 and BCL-2 pathways in estrogen receptor positive breast cancer

Background: Despite incremental advances in chemotherapy and endocrine therapy, survival outcomes for patients with ER-positive (ER+) metastatic breast cancer (MBC) remain poor. The majority of relapsing tumors exhibit deregulation of the cyclin-dependent kinase 4 and 6 (CDK4/6)/cyclin D1 (CCND1)/Rb signaling pathway. CDK4/6 inhibitors (such as palbociclib) in combination with endocrine therapy have been shown to significantly improve progression free survival in patients who are in 1st or 2nd line relapse, although overall survival benefit has yet to be demonstrated. This may reflect their largely cytostatic mechanism of action, with minimal induction of tumor cell death. Thus, combinatorial strategies that also induce apoptosis could be beneficial. Notably, the pro-survival protein BCL-2 is overexpressed in the majority of ER+ tumors and the potent and specific BCL-2 inhibitor venetoclax (ABT-199) has been found to synergize with endocrine therapy in patient derived xenograft (PDX) models. Promising activity has also been observed in an early phase clinical trial. We therefore investigated dual targeting of the CDK4/6 and BCL-2 pathways in pre-clinical models of ER+ and BCL-2+ breast cancer.

Results: We first examined endocrine sensitive or resistant cell-lines and found that pro-survival BCL-2 proteins were upregulated in resistant cells. BCL-2 family protein levels were also found to be elevated in palbociclib resistant cells, suggesting that BCL-2 could represent a therapeutic target. We next determined whether venetoclax improved response to dual therapy comprising the selective estrogen receptor degrader fulvestrant and palbociclib. In clonogenic assays of endocrine sensitive breast cancer cell lines, triple therapy containing venetoclax significantly reduced the number and size of colonies, when compared to double therapy. The addition of venetoclax to fulvestrant/palbociclib also augmented cell death in tumor organoid models derived from either ER+ BCL-2+ primary tumors or PDX models. Moreover, triple therapy improved tumor response and overall survival in mice bearing ER+ BCL-2+ PDX tumors. Mechanistically, this was accompanied by increased apoptosis and reduced cellular proliferation (as determined by cleaved caspase-3 and Ki67 levels, respectively). As CDK4/6 inhibitors have recently been shown to promote anti-tumor immunity, we evaluated immune modulation using the ER+ 67NR cell line in a syngeneic (BALB/c) mouse mammary tumor model. Similar to the PDX models, triple therapy comprising fulvestrant, palbociclib and venetoclax was more effective than double therapy comprising either fulvestrant/palbociclib or fulvestrant/venetoclax. Flow cytometric analysis of tumors revealed that this was accompanied by a reduced intratumoral FOXP3+:cytotoxic CD8 T-cell ratio.

Conclusions: The addition of the BCL-2 inhibitor venetoclax to conventional therapy comprising endocrine therapy and a CDK4/6 inhibitor augments tumor response and elicits a favorable intratumoral immune profile. Collectively, these findings support investigation of combination therapy in the clinic for patients with ER+ BCL-2+ MBC.

Citation Format: Whittle JR, Vaillant F, Policheni AN, Liu K, Pal B, Giner G, Fernandez K, Gray DH, Caldon CE, Smyth GK, Visvader JE, Lindeman GJ. Synergistic targeting of CDK4/6 and BCL-2 pathways in estrogen receptor positive breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD7-07.

Abstract PD1-06: A phase 1b dose-escalation and expansion study of the BCL-2 inhibitor venetoclax combined with tamoxifen in ER and BCL-2–positive metastatic breast cancer (MBC)

Background: Venetoclax, a potent and selective inhibitor of the survival protein BCL-2 (recently approved in CLL and in development in other hematopoietic malignancies), has yet to be evaluated in pts with solid tumors. BCL-2 is overexpressed in ˜85% of ER+ breast cancer. Pre-clinical findings using patient-derived xenograft breast tumor models suggest that venetoclax synergizes with endocrine therapy by increasing apoptosis. Here we report mBEP, an investigator-initiated phase 1b study of venetoclax with tamoxifen in 33 pts with ER+ (&gt;1%), BCL-2+ (&gt;10%, 2-3+ intensity) and HER2– MBC.

Methods: We conducted a 3+3 dose escalation study comprising cohorts receiving venetoclax 200, 400, 600 or 800 mg/d with tamoxifen 20 mg/d (continued until progression). The primary endpoint was to determine the maximum tolerated dose (MTD), define dose-limiting toxicities (DLTs) and identify the recommended phase 2 dose (RP2D). In a dose expansion phase (at the RP2D), secondary endpoints including safety and tolerability, response at 24 wks (RECIST v1.1), clinical benefit rate (CBR) and progression-free survival (PFS) were studied.

Results: In the escalation phase (n=15 pts), treatment was well tolerated with no DLTs or high-grade (Gd 3/4) adverse events observed, apart from asymptomatic on-target lymphopenia (Gd 3, 2/15 pts). MTD was not reached. The 800 mg/d dose was selected as the RP2D and the cohort expanded to include 24 pts with ≥24 wks follow up (range 24-105 wks). Fifteen pts had received prior regimens for MBC (median 3, range 1-9) that included tamoxifen in 5/15.

For the RP2D cohort (n=24), overall responses (OR) included 1 CR (4%) and 12 PR (50%), with 5 SD (21%), corresponding to a CBR of 75%. The 9 pts treated in the first line setting experienced a 78% OR (7/9 pts) and 11% SD (1/9 pts), equating to an 89% CBR. The data are immature for determining median PFS for the RP2D cohort (currently 40+ wks).

Treatment responses were pre-empted by metabolic responses (FDG-PET) at 4 wks (seen in 13/16 (81%) pts studied), and correlated with serial changes in circulating tumor DNA (ctDNA). Intriguingly, responses and clinical benefit were observed in pts with plasma-detected ESR1 mutations (4/10 and 7/10, respectively).

The most common treatment-related AEs (CTCAE v4.0) for all pts were lymphopenia in 29/33 (88%; 57% Gd 1-2, 30% Gd 3-4), neutropenia in 24/33 (73%; 67% Gd 1-2, 6% Gd 3), nausea in 22/33 (67%; all ≤Gd 2), anemia in 13/33 (39%; 33% Gd 1-2, 6% G3), thrombocytopenia in 11/33 (33%; all ≤Gd 2), vomiting in 11/33 (33%, all ≤Gd 2), diarrhea in 10/33 (30%; 24% Gd 1-2, 6% Gd 3), infection in 9/33 (27%; 18% Gd 2, 9% Gd 3) and fatigue in 7/33 (21%; all ≤Gd 2). There was one possible treatment-related SAE (infection).

Conclusions: In the first clinical study to evaluate venetoclax in a solid tumor, we demonstrate that combining venetoclax with endocrine therapy has a tolerable safety profile and elicits remarkable activity in ER+ and BCL-2+ MBC. These findings support further investigation of combination therapy for patients with BCL-2-positive breast cancer.

Sponsor: The Royal Melbourne Hospital (ACTRN12615000702516)

Citation Format: Lindeman GJ, Lok SW, Whittle JR, Siow ZR, Bergin AR, Dawson S-J, Desai J, Gray DH, Liew D, Mann GB, Murugasu A, Roberts AW, Rosenthal MA, Shackleton K, Sherman P, Silva MJ, Teh C, Travers A, Vaillant F, Visvader JE. A phase 1b dose-escalation and expansion study of the BCL-2 inhibitor venetoclax combined with tamoxifen in ER and BCL-2–positive metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD1-06.

Synergistic action of the MCL-1 inhibitor S63845 with current therapies in preclinical models of triple-negative and HER2-amplified breast cancer

The development of BH3 mimetics, which antagonize prosurvival proteins of the BCL-2 family, represents a potential breakthrough in cancer therapy. Targeting the prosurvival member MCL-1 has been an area of intense interest because it is frequently deregulated in cancer. In breast cancer, MCL-1 is often amplified, and high expression predicts poor patient outcome. We tested the MCL-1 inhibitor S63845 in breast cancer cell lines and patient-derived xenografts with high expression of MCL-1. S63845 displayed synergistic activity with docetaxel in triple-negative breast cancer and with trastuzumab or lapatinib in HER2-amplified breast cancer. Using S63845-resistant cells combined with CRISPR (clustered regularly interspaced short palindromic repeats)-Cas9 (CRISPR-associated 9) technology, we identified deletion of BAK and up-regulation of prosurvival proteins as potential mechanisms that confer resistance to S63845 in breast cancer. Collectively, our findings provide a strong rationale for the clinical evaluation of MCL-1 inhibitors in breast cancer.

Vaccine-Induced Antibodies that Neutralize Group 1 and Group 2 Influenza A Viruses

Antibodies capable of neutralizing divergent influenza A viruses could form the basis of a universal vaccine. Here, from subjects enrolled in an H5N1 DNA/MIV-prime-boost influenza vaccine trial, we sorted hemagglutinin cross-reactive memory B cells and identified three antibody classes, each capable of neutralizing diverse subtypes of group 1 and group 2 influenza A viruses. Co-crystal structures with hemagglutinin revealed that each class utilized characteristic germline genes and convergent sequence motifs to recognize overlapping epitopes in the hemagglutinin stem. All six analyzed subjects had sequences from at least one multidonor class, and-in half the subjects-multidonor-class sequences were recovered from >40% of cross-reactive B cells. By contrast, these multidonor-class sequences were rare in published antibody datasets. Vaccination with a divergent hemagglutinin can thus increase the frequency of B cells encoding broad influenza A-neutralizing antibodies. We propose the sequence signature-quantified prevalence of these B cells as a metric to guide universal influenza A immunization strategies.

Abstract IA19: Targeting the BCL-2 family in breast cancer

The steps taken to evade cell death are a recognized hallmark of cancer. Intense efforts over the last three decades have provided important insights into the molecular mechanisms that govern programmed cell death and how tumors recalibrate key survival pathways to sustain their growth. The pro-survival protein BCL-2 is overexpressed in approximately 75% of breast cancer, where it is has emerged as an important prognostic marker. Indeed, BCL-2 expression is a key component of the Oncotype DX assay. BCL-2 overexpression is even more prominent in luminal tumors (~85%), reflecting its estrogen-responsiveness. Other key pro-survival family members, MCL-1 and BCL-XL, are also commonly expressed across breast cancer subtypes. This group of pro-survival guardian proteins play a critical role in keeping pro-apoptotic effector proteins (such as BAX and BAK) in check. The effector proteins are essential for commitment to apoptosis, which occurs following mitochondrial cytochrome c release and caspase activation, resulting in cell death. BCL-2 guardian proteins also neutralize a group of sensor proteins (such as BIM). The sensor proteins are triggered by distinct cytotoxic stimuli (such as chemotherapy) to activate the effectors BAX and BAK. The sensor proteins are termed BH3 only proteins, as they lack the BCL-2 Homology (BH) domains BH1, BH2 and BH4 found in the two other subgroups.

While BCL-2 is an important prognostic marker in breast cancer, its precise role as a predictive marker of tumor response has yet to be properly clarified. Nevertheless, there is increasing evidence that augmented levels of pro-survival BCL-2 proteins can prime tumors for death induced by conventional chemotherapy or endocrine therapy. This is due to the high occupation of pro-survival BCL-2 proteins by pro-apoptotic BH3 proteins, which can be activated by therapy, thereby committing tumor cells to apoptosis.

Small molecule inhibitors termed BH3 mimetics that bind and neutralize BCL-2 pro-survival proteins have recently been described. These are showing considerable promise in early phase studies of lymphoid malignancies. We recently explored the feasibility of targeting luminal B tumors in combination therapy comprising endocrine therapy (tamoxifen) and a BH3 mimetic (ABT-737 or ABT-199) using patient derived xenograft (PDX) models of primary breast cancer. Tumor response and overall survival were significantly improved by combination therapy, when compared to tamoxifen alone. Moreover, synergy between BH3 mimetics and PI3K/mTOR inhibitors could be exploited by concomitant targeting of both survival pathways, a strategy that appeared both safe and effective. Since the potent and selective BCL-2 inhibitor ABT-199 was effective in these models (despite abundant BCL-XL expression), BCL-2 may be a crucial target for some luminal tumors, where we speculate it could provide a suitable companion biomarker for patient selection. This work has formed the basis for a Phase 1b study of BCL-2 inhibition with ABT-199 (venetoclax) in combination with tamoxifen in metastatic ER-positive breast cancer (ISRCTN98335443). The prospects for the development of BCL-XL and MCL-1 inhibitors will also be discussed.

Citation Format: Geoffrey J. Lindeman, Delphine Merino, François Vaillant, James R. Whittle, Sheau Wen Lok, Kylie Shackleton, Jane E. Visvader. Targeting the BCL-2 family in breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr IA19.

First in human nanotechnology doxorubicin delivery system to target epidermal growth factor receptors in recurrent glioblastoma

There are limited treatment options for patients with recurrent glioblastoma (GBM). The EnGeneIC delivery vehicle (EDV) is a novel nanocellular (minicell) compound which packages theoretically effective concentrations of chemotherapeutic drugs that are designed to target tumors via minicell-surface attached bispecific proteins (EnGeneIC, Lane Cove West, NSW, Australia). Epidermal growth factor receptor (EGFR) is overexpressed in 40-50% of patients with GBM and is a promising target for new therapeutics. (V)EDVDox contains doxorubicin (Dox) within the minicells and targets EGFR through Vectibix (V; Amgen Biologicals, Thousand Oaks, CA, USA). We conducted a first in human Phase I study of (V)EDVDox in adults with recurrent GBM expressing EGFR on immunohistochemistry, following standard therapy including radiation and temozolomide, to establish a safe maximum tolerated dose and determine a recommended Phase II dose (RPTD). (V)EDVDox was administered weekly in an 8week cycle, with dose escalation in successive cohorts of patients using a standard 3+3 design. In total, 14 patients were treated at three dose levels, and the RPTD was identified as 5×10(9)(V)EDVDox. Overall (V)EDVDox was well tolerated, with no dose limiting toxicity and no withdrawals from the study due to adverse events. The most common adverse events were nausea, fever, and chills or rigors, experienced in seven, five and five patients, respectively. Transient uncomplicated hypophosphatemia was seen in seven patients and was not dose-related. Our results demonstrate that (V)EDVDox, up to a dose of 5×10(9)(V)EDVDox weekly, is well tolerated in patients with recurrent GBM.

Patient-derived xenograft models of breast cancer and their predictive power

Despite advances in the treatment of patients with early and metastatic breast cancer, mortality remains high due to intrinsic or acquired resistance to therapy. Increased understanding of the genomic landscape through massively parallel sequencing has revealed somatic mutations common to specific subtypes of breast cancer, provided new prognostic and predictive markers, and highlighted potential therapeutic targets. Evaluating new targets using established cell lines is limited by the inexact correlation between responsiveness observed in cell lines versus that elicited in the patient. Patient-derived xenografts (PDXs) generated from fresh tumor specimens recapitulate the diversity of breast cancer and reflect histopathology, tumor behavior, and the metastatic properties of the original tumor. The high degree of genomic preservation evident across primary tumors and their matching PDXs over serial passaging validate them as important preclinical tools. Indeed, there is accumulating evidence that PDXs can recapitulate treatment responses of the parental tumor. The finding that tumor engraftment is an independent and poor prognostic indicator of patient outcome represents the first step towards personalized medicine. Here we review the utility of breast cancer PDX models to study the clonal evolution of tumors and to evaluate novel therapies and drug resistance.

Sirtuins, nuclear hormone receptor acetylation and transcriptional regulation

Endocrine signaling via nuclear receptors (NRs) is known to play an important role in normal physiology as well as in human tumor progression. Hormones regulate gene expression by altering local chromatin structure and, thereby, accessibility of transcriptional co-regulators to DNA. Recently it has been shown that non-histone proteins involved in hormone signaling, such as nuclear receptors and NR co-activators, are regulated by acetylation, resulting in their altered transcriptional activity. NAD-dependent protein deacetylases, the sirtuins (Sir2-related enzymes), directly modify NRs. Because sirtuins have been shown to regulate tumor cellular growth, aging, metabolic signaling and endocrine hormone signaling, they might play a role in cancer progression. This review focuses on the role of acetylation and the sirtuins in nuclear hormone receptor signaling.

Wingless signaling leads to an asymmetric response to decapentaplegic-dependent signaling during sense organ patterning on the notum of Drosophila melanogaster

Wnt and Decapentaplegic cell signaling pathways act synergistically in their contribution to macrochaete (sense organ) patterning on the notum of Drosophila melanogaster. The Wingless-signaling pathway was ectopically activated by removing Shaggy activity (the homologue of vertebrate glycogen synthase kinase 3) in mosaics. Proneural activity is asymmetric within the Shaggy-deficient clone of cells and shows a fixed "polarity" with respect to body axis, independent of the precise location of the clone. This asymmetric response indicates the existence in the epithelium of a second signal, which we suggest is Decapentaplegic. Ectopic expression of Decapentaplegic induces extra macrochaetes only in cells which also receive the Wingless signal. Activation of Hedgehog signaling generates a long-range signal which can promote macrochaete formation in the Wingless activity domain. This signal depends upon decapentaplegic function. Autonomous activation of the Wingless signal response in cells causes them to attenuate or sequester this signal. Our results suggest a novel patterning mechanism which determines sense organ positioning in Drosophila.

How is developmental stability sustained in the face of genetic variation?

The number and arrangement of scutellar bristles on the thorax of Drosophila melanogaster is largely invariant in wild-type stocks. This character therefore appears to be buffered against changes in phenotype, and has previously been described as a canalized character. Mutations that do alter this phenotype increase the variability in bristle number and can reveal otherwise cryptic genetic differences at other loci. This phenomenon is examined and possible mechanisms contributing to stability of this developmental event are discussed, but the notion that the character is canalized is found not to be heuristic.

Genetic relationships between the mutations spade and Sternopleural and the wingless gene in Drosophila development

In Drosophila melanogaster, there are cases in which gene products contributing to the same developmental event may derive from closely adjacent transcription units and may even share cis-regulatory sequences. Correct recognition of such genomic organization is central to an understanding of developmental mechanisms. The adult phenotypes of combinations between the mutations spade, Sternopleural, and wingless suggest that they are lesions in functionally related genes within the same chromosomal region. wingless mutations fail to complement the recessive mutation spade. The spade mutation, as previously shown, behaves as a lesion in a regulatory site of wingless, sited 5' to the transcription unit, and is concerned with particular postembryonic functions of wingless. While showing wingless-like phenotypes in combination with Sternopleural, even lethal alleles of wingless complement the recessive lethality of Sternopleural alleles. Mutations in Sternopleural increase the severity of wingless phenotypes in many wingless-dependent processes during postembryonic development, and this interaction can occur when the only functional copies of Sp or wg are located in either opposing chromosomes or the same chromosome. This is inconsistent with previous attempts to define Sp as a regulatory allele of wg and explain the phenotypes that result from combinations of Sp and wg by means of transvection. We have analyzed a new EMS-induced allele of Sternopleural that is more severe than the original allele, which also argues for Sp being a separate, mutable genetic locus rather than a regulatory allele of wg. Finally, we have a revertant of Sternopleural (Sp[Rv1]) that behaves as a genetic null allele of wg, but causes ventral-to-dorsal transformations in combination with wg(P), which is not observed in combinations of wg null alleles with wg(P). Because wg(P) is the result of an inversion and because inversions inhibit transvection, the increased severity observed in Sp(Rv1)/wg(P) in comparison to wg(null)/Sp(Rv1) animals cannot be explained by an absence of transvection. Therefore, the two Sternopleural mutations most reasonably define an independent gene located 3' to the wingless gene and having strong functional synergism with it.

Properties of xanthine dehydrogenase variants from rosy mutant strains of Drosophila melanogaster and their relevance to the enzyme's structure and mechanism

Xanthine dehydrogenase, a molybdenum, iron-sulfur flavoenzyme encoded in the fruit fly Drosophila melanogaster by the rosy gene, has been characterised both from the wild-type and mutant files. Enzyme assays, using a variety of different oxidising and reducing substrates were supplemented by limited molecular characterisation. Four rosy strains showed no detectable activity in any enzyme assay tried, whereas from four wild-type and three rosy mutant strains, those for the [E89K], [L127F] and [L157P]xanthine dehydrogenases (in all of which the mutation is in the iron-sulfur domain), the enzyme molecules, although present at different levels, had extremely similar or identical properties. This was confirmed by purification of one wild-type and one mutant enzyme. [E89K]xanthine dehydrogenase. These both had ultraviolet-visible absorption spectra similar to milk xanthine oxidase. Both were found to be quite stable molecules, showing very high catalytic-centre activities and with little tendency to become degraded by proteolysis or modified by conversion to oxidase or desulfo forms. In three further rosy strains, giving [G353D]xanthine dehydrogenase and [S357F]xanthine dehydrogenase mutated in the flavin domain, and [G1011E]xanthine dehydrogenase mutated in the molybdenum domain, enzyme activities were selectively diminished in certain assays. For the G353D and S357F mutant enzymes activities to NAD+ as oxidising substrate were diminished, to zero for the latter. In addition for [G353D]xanthine dehydrogenase, there was an increase in apparent Km values both for NAD+ and NADH. These findings indicate involvement of this part of the sequence in the NAD(+)-binding site. The G1011E mutation has a profound effect on the enzyme. As isolated and as present in crude extracts of the files, this xanthine dehydrogenase variant lacks activity to xanthine or pterin as reducing substrate, indicating an impairment of the functioning of its molybdenum centre. However, it retains full activity to NADH with dyes as oxidising substrate. Mild oxidation of the enzyme converts it, apparently irreversibly, to a form showing full activity to xanthine and pterin. The nature of the group that is oxidised is discussed in the light of redox potential data. It is proposed that the process involves oxidation of the pterin of the molybdenum cofactor from the tetrahydro to a dihydro oxidation state. This conclusion is fully consistent with recent information [Romäo, M. J., Archer, M., Moura, I., Moura. J.J.G., LeGall, J., Engh, R., Schneider, M., Hof, P. & Huber, R. (1995) Science 270. 1170-1176) from X-ray crystallography on the structure of a closely related enzyme from Desulfovibrio gigas. It is proposed, that apparent irreversibility of the oxidative activating process for [G1011E]xanthine dehydrogenase, is due to conversion of its pterin to the tricyclic derivative detected by these workers. The data thus provide the strongest evidence available, that the oxidation state of the pterin can have a controlling influence on the activity of a molybdenum cofactor enzyme. Implications regarding pterin incorporation into xanthine dehydrogenase and in relation to other molybdenum enzymes are discussed.

wingless expression mediates determination of peripheral nervous system elements in late stages of Drosophila wing disc development

We have used conditional wingless genotypes to dissect the role of this gene in late stages of wing disc development. One of these genotypes (wgIL/wg-lacZ) is simultaneously a reporter of wingless transcription and temperature-sensitive for wingless function, and has allowed us to define its pattern of transcription in the absence of wingless activity. The primordia of a subset of the bristles of the notum, which develop in or immediately adjacent to wingless-expressing cells, depend upon wingless activity. The time-course of this contribution and the effect on proneural gene expression together suggest that wingless may regulate the activity of products of the achaete-scute complex in proneural clusters. wingless activity is also required at the presumptive wing margin and is a necessary precondition for the change in proliferation pattern in this region. The involvement of wingless in transducing or mediating positional signals for spatial patterning in imaginal disc development is discussed.

Use of rosy mutant strains of Drosophila melanogaster to probe the structure and function of xanthine dehydrogenase

The usefulness in structure/function studies of molybdenum-containing hydroxylases in work with rosy mutant strains of Drosophila melanogaster has been investigated. At least 23 such strains are available, each corresponding to a single known amino acid change in the xanthine dehydrogenase sequence. Sequence comparisons permit identification, with some certainty, of regions associated with the iron-sulphur centres and the pterin molybdenum cofactor of the enzyme. Procedures have been developed and rigorously tested for the assay in gel-filtered extracts of the flies, of different catalytic activities of xanthine dehydrogenase by the use of various oxidizing and reducing substrates. These methods have been applied to 11 different rosy mutant strains that map to different regions of the sequence. All the mutations studied cause characteristic activity changes in the enzyme. In general these are consistent with the accepted assignment of the cofactors to the different domains and with the known reactivities of the molybdenum, flavin and iron-sulphur centres. Most results are interpretable in terms of the mutation affecting electron transfer to or from one redox centre only. The activity data provide evidence that FAD and the NAD+/NADH binding sites are retained in mutants mapping to the flavin domain. Therefore, despite some indications from sequence comparisons, it is concluded that the structure of this domain of xanthine dehydrogenase cannot be directly related to that of other flavoproteins for which structural data are available. The data also indicate that the artificial electron acceptor phenazine methosulphate acts at the iron-sulphur centres and suggest that these centres may not be essential for electron transfer between molybdenum and flavin. The work emphasizes the importance of combined genetic and biochemical study of rosy mutant xanthine dehydrogenase variants in probing the structure and function of enzymes of this class.

Establishment of imaginal discs and histoblast nests in Drosophila

In Drosophila the homeotic genes of the bithorax-complex (BX-C) and Antennapedia-complex (ANT-C) specify the identity of segments. Adult segment primordia are established in the embryo as the histoblast nests of the abdomen and the imaginal discs of the head, thorax and terminalia. We have used a molecular probe for the limb primordia and in vivo culture to describe the nature of the adult primordia in mutants in which the pattern of homeotic gene expression was altered. The results suggest that the histoblast or disc 'mode' of development is initiated by the extended germ band stage through activity of the BX-C and ANT-C and is relatively inflexible thereafter [corrected].

The Drosophila segment polarity gene patched is involved in a position-signalling mechanism in imaginal discs

We demonstrate the role of the segment polarity gene patched (ptc) in patterning in the cuticle of the adult fly. Genetic mosaics of a lethal allele of patched show that the contribution of patched varies in a position-specific manner, defining three regions in the wing where ptc clones, respectively, behave as wild-type cells, affect vein formation, or are rarely recovered. Analysis of twin clones demonstrates that the reduced clone frequency results from a proliferation failure or cell loss. In the region where clones upset venation, they autonomously fail to form veins and also non-autonomously induce ectopic veins in adjacent wild-type cells. In heteroallelic combinations with lethal alleles, two viable alleles produce distinct phenotypes: (1) loss of structures and mirror-image duplications in the region where patched clones fail to proliferate; (2) vein abnormalities in the anterior compartment. We propose that these differences reflect independently mutable functions within the gene. We show the pattern of patched transcription in the developing imaginal wing disc in relation to the expression of certain other reporter genes using a novel double-labelling method combining non-radioactive detection of in situ hybridization with beta-galactosidase detection. The patched transcript is present throughout the anterior compartment, with a stripe of maximal intensity along the A/P compartment border extending into the posterior compartment. We propose that the patched product is a component of a cell-to-cell position-signalling mechanism, a proposal consistent with the predicted structure of the patched protein.

Pattern formation in imaginal discs

Imaginal discs are sacs of folded epithelium arising during embryogenesis. They proliferate during the larval instars, and at metamorphosis secrete the adult cuticle, therefore being responsible for the characteristic surface patterning of this insect. Each disc has intrinsic growth controls and their cell lineage shows constraints known as compartments. Spatial patterns emerge through interaction between adjacent cells. Molecular genetic analysis of mutants with changed pattern has implicated transcription factors, secreted, membrane-bound and growth factor related proteins in the position-signalling mechanism. Their accessibility to contemporary cell biological techniques makes imaginal discs a model system for investigating patterning in animal tissues.

A protein with several possible membrane-spanning domains encoded by the Drosophila segment polarity gene patched

The patterning of cells in insect segments requires the exchange of information between cells, which in Drosophila depends on the activity of members of the segment-polarity class of genes. Here we report the molecular characterization of one such gene, patched. We find that patched encodes a large protein with several possible membrane-spanning domains and is expressed in a complex pattern during embryogenesis.

Chromosomal continuity in the abdominal region of the bithorax complex of Drosophila is not essential for its contribution to metameric identity

We have examined the developmental consequences for larval and imaginal segmental cuticular structure of a chromosomal translocation involving a breakpoint in the abdominal region of the bithorax complex (BX-C). This complex makes an essential contribution to the development of metameric differences in part of the thorax and in all abdominal segments. The breakpoint is proximal to the most distal (iab-7) homeobox, and results in the translocation to the Y chromosome of the Ultrabithorax (Ubx) and abdominal-A (abd-A) domains. The genotype deficient for the distal part of the complex shows normal function for Ubx and abd-A but has a phenotype typical for severe Abd-B mutations. Conversely, the distal fragment retains a segment identity function which must represent a contribution from Abd-B in parasegments 13 and 14; the latter metamere is wild type, indicating that it does not require the contribution of Ubx or abd-A. We also constructed a genotype comprising the proximal fragment of this translocation together with an overlapping distal fragment of the BX-C derived from Df(3R)Ubx109. It therefore contained all sequences of the BX-C though in the abdominal region the abd-A and Abd-B domains were not adjacent to each other in the chromosome. This genotype was phenotypically normal and demonstrates that DNA sequences in the abd-A and Abd-B regions do not require cis-arrangement for their activity.

The effect of lethal mutations and deletions within the bithorax complex upon the identity of caudal metameres in the Drosophila embryo

Mutations and deletions of the abdA and AbdB functions in the bithorax complex of Drosophila melanogaster have been examined for their effect upon the hypodermal derivatives of the caudal segments of the embryo, employing light- and scanning electron microscopy. No cuticular structures located posterior to the denticle belt of abdominal segment 8 are affected in abdA- embryos. Embryos of AbdB- genotype no longer have six of the seven pairs of sense organs present in this region, lack posterior spiracles but instead have sclerotized cuticle and sense organs typical of the head region and a rudimentary extra ventral denticle belt. The anal pads, tuft and sense organ 1 do not require BX-C functions for their specification. We discuss the provenance of these cuticular structures and the domain of function of elements within the bithorax complex in terms of parasegmental metameric units.

Recessive lethal mutations within the bithorax-complex in Drosophila

Genetic deficiencies of the bithorax-complex (BX-C) in Drosophila, have been used to recover recessive lethal mutations in this chromosome region following mutagenesis. Complementation analysis separates these lethal mutations into five groups within a smaller deficiency, thought to remove the entire BX-C, and into 20 to the left and 4 to the right of the region. Homozygotes for each of only three groups of lethals, Ubx, abdA and AbdB, produce homoeotic segmental transformations in embryos. The functional domains of abdA and AbdB have been defined by changes in the appearance of larval hypodermal structures and of clones in imaginal tissue. The function abdA is required in all the compartments caudal to the anteroposterior border of abdominal segment 1 up to and including the anterior region of abdominal segment 8, whilst AbdB is required in abdominal segments 5 to 9. One allele of AbdB produces a ninth abdominal setal band and structures characteristic of head segments posterior to A8. Rare adult survivors hemizygous for an AbdB allele have eight abdominal segments in both sexes, and lack genitalia in females. Our findings are discussed in the context of the organisation of genetic functions within the BX-C.

Replacement of posterior by anterior structures in the Drosophila wing caused by the mutation apterous-blot

The recessive mutation apterous-blot in Drosophila melanogaster causes replacement of posterior wing structures by anterior ones, with variable penetrance and expressivity. Extreme transformations resemble mirror-image duplicate anterior wings as in the mutant engrailed. Anterior structures in the posterior wing only appear on the dorsal surface. Duplications solely of posterior structures are also seen. Clonal analysis shows that extra cell proliferation occurs in the posterior area but is complete by 108 h after egg deposition. Lineage analysis is consistent with a clonal perpetuation of the transformation. Genetic mosaics to test the cell-autonomy of apterous-blot show that it is not autonomously expressed in clones. The results of lineage analysis, the phenotypes of combinations of apterous-blot with other apterous alleles including a deletion for the locus and with various other homoeotic mutations, are together used to distinguish three alternative modes of action of this mutation. It is concluded that apterous-blot is unlikely to be a selector gene mutation but instead may cause the transformation by an event like transdetermination following a local failure in cell function in the wing disc.

Genetic analysis of the mutation female-lethal in Drosophila melanogaster

A genetic analysis was made of theFemale-lethal(Fl) locus ofDrosophila melanogaster. This is anX-linked mutation which causes lethality only in females. Other alleles do not complementFland are either lethal or sterile when homozygous in females. Complementation studies onFlalleles demonstrate that there is no simple ranking of these alleles in terms of severity of phenotypic effect. Dosage manipulation ofFlalleles indicates that the sex-specificity is not a consequence of gene dosage effects. Viability studies on males carryingFlalleles show thatFlalleles have no effect on viability regardless of the presence or absence of aYchromosome. TheFllocus is therefore sex-specific. The hypothesis thatFl+ is involved in the establishment of imaginal phenotypic sex cannot be substantiated on the basis of experiments utilizing sex-change mutations.

Cortical morphogenesis in Paramecium aurelia: mutants affecting cell shape

In order to investigate the importance of the nuclear genotype during morphogenesis of the cortex inParamecium aurelia, a search was made for conditional and unconditional mutants affecting cell shape. Ten different mutants were readily recovered following mutagenesis withN-methyl-N-nitro-N-nitrosoguanidine on stock 51s of syngen 4. The detailed pattern of surface units remained unchanged in these mutants but each one can be described as resembling a normal cell twisted about its long axis. Nine of the mutants complement each other and show no linkage. The remaining mutant, a ‘chain former’, has conditional expression, and is only recognizable at 35 °C. The penetrance of this mutant is affected by the food organism used. The conditional mutant also interacts with seven of the other mutants in pairwise homozygous combinations so that in these genotypes it can be classified after growth at 25 °C. The mutants are discussed in relation to the search for genie effects on the cortical pattern.