Recombinant Mouse Transmembrane protein 97 (Tmem97)

What is Transmembrane Protein 97 (Tmem97) and what are its alternative nomenclatures?

Transmembrane protein 97 (Tmem97) is a member of the insulin-like growth factor-binding protein family that has garnered significant research interest in recent years . The protein is also widely known as sigma-2 receptor (σ2R/TMEM97) in neuroscience research contexts and as meningioma-associated protein (MAC30) in some cancer research literature . This diversity in nomenclature reflects the protein's discovery in different research contexts and its multifunctional nature across various biological systems. The identification of TMEM97 as the sigma-2 receptor resolved a long-standing question in pharmacology, as the molecular identity of this receptor had been elusive for many years despite numerous pharmacological studies implicating it in various pathological processes . Understanding the various names used in literature is crucial for comprehensive literature searches and avoiding confusion when interpreting cross-disciplinary research on this protein.

What is the expression pattern of Tmem97 in normal mouse tissues?

In mouse tissues, Tmem97 demonstrates a specific expression pattern that provides important clues about its physiological functions. In the retina, σ2R/TMEM97 immunoreactivity has been detected in retinal ganglion cells (RGCs), photoreceptor inner segments, retinal pigment epithelium (RPE), cells in the inner nuclear layer, and sparsely in the outer nuclear layer . This retinal expression pattern suggests important roles in visual processing and retinal cell function. The protein's expression has also been documented in the central nervous system, which aligns with its implicated roles in modulating affective behaviors and pain processing . Notably, when validating expression patterns, it's essential to confirm antibody specificity, as studies have shown no σ2R/TMEM97 immunoreactivity was detected in the retina of TMEM97−/− knockout mice, providing an important negative control for immunohistochemical studies . Researchers should consider using multiple detection methods including immunohistochemistry, in situ hybridization, and RT-PCR to comprehensively map expression patterns in their tissues of interest.

How can researchers confirm the specificity of their Tmem97 detection methods?

Confirming the specificity of Tmem97 detection methods is critical for experimental validity. The gold standard approach involves parallel testing in wild-type and Tmem97 knockout tissues. Studies have demonstrated that while σ2R/TMEM97 immunoreactivity is detected across multiple retinal cell types in wild-type mice, no such reactivity is observed in retinas from TMEM97−/− mice . This provides conclusive evidence for antibody specificity. For RNA detection methods, similar validation using knockout tissues should be performed. Additionally, researchers should use multiple antibodies targeting different epitopes of the protein and compare expression patterns to enhance confidence in detection specificity. When recombinant Tmem97 is used as a positive control, it's important to verify its identity through mass spectrometry and assess its functional activity to ensure it represents the native conformation of the protein. Cross-validation between protein and mRNA detection methods can provide further confidence in the specificity and reliability of detection approaches.

What phenotypes are observed in Tmem97 knockout mice under normal physiological conditions?

TMEM97−/− knockout mice are viable and fertile with no visible gross abnormalities, suggesting that the protein is not essential for embryonic development or basic physiological functions . Detailed examination of retinal structure in TMEM97−/− mice shows no discernible differences compared to wild-type animals under normal conditions . Furthermore, functional assessments using electroretinograms (ERGs) reveal that both scotopic and photopic responses in TMEM97−/− mice are comparable to those of wild-type mice, with scotopic b-waves being reliably recorded at flash intensities as low as −4.4 log cd s/m² . Visual acuity measurements using an optomotor system have shown that TMEM97−/− mice maintain normal visual function, with an average visual acuity of 0.45 ± 0.024 cycles per degree, which falls within the reported normal range for wild-type mice . These findings indicate that under baseline conditions, the absence of Tmem97 does not significantly impact retinal development or visual function, suggesting potential compensatory mechanisms or redundant pathways that maintain normal physiology in the absence of this protein.

How does Tmem97 contribute to breast cancer progression through Wnt signaling pathway modulation?

Tmem97 plays a critical role in breast cancer progression by functioning as a positive modulator of the canonical Wnt signaling pathway, a key oncogenic mechanism . At the molecular level, TMEM97 has been identified as an LRP6-interacting protein that enhances LRP6-mediated Wnt signaling in a CK1δ/ε-dependent manner . This interaction is particularly significant as LRP6 is a co-receptor for Wnt ligands and a central component of canonical Wnt pathway activation. The binding of TMEM97 to the LRP6 intracellular domain facilitates the recruitment of CK1δ/ε to the LRP6 complex, resulting in LRP6 phosphorylation at Ser1490 and subsequent stabilization of β-catenin . This mechanism effectively amplifies Wnt signaling output in cancer cells.

In experimental models using breast cancer cells, knockout of TMEM97 has been shown to attenuate the Wnt/β-catenin signaling cascade specifically by reducing LRP6 phosphorylation, which leads to decreased expression of Wnt target genes including AXIN2, LEF1, and survivin . This downregulation of Wnt pathway activity has profound functional consequences, as TMEM97 deficiency suppresses multiple cancer hallmarks including cell viability, proliferation, colony formation, migration, invasion, and cancer stem cell-like properties in breast cancer cells . Importantly, these in vitro findings translate to in vivo models, where TMEM97 knockout has been demonstrated to suppress tumor growth through downregulation of the Wnt/β-catenin signaling pathway in breast cancer xenograft models . These findings collectively establish TMEM97 as a potential therapeutic target in breast cancer, particularly in tumors with aberrant Wnt pathway activation.

What is the relationship between Tmem97 and estrogen receptor signaling in breast cancer?

The relationship between Tmem97 and estrogen receptor (ER) signaling represents a significant axis in breast cancer biology that has important implications for treatment approaches. TMEM97/sigma 2 receptor has been identified as a novel regulator of estrogen receptor activation, establishing a direct link between these two signaling systems . Clinical data support this relationship, as TMEM97 is highly expressed in ER-positive breast tumors and its expression strongly correlates with the presence of estrogen receptors and progesterone receptors, but not with HER2 status . This pattern suggests a specific functional relationship with hormone receptor signaling rather than with growth factor receptor pathways.

What methodologies are most effective for studying Tmem97 function in neuropathic pain and affective behavior models?

Studying Tmem97 function in neuropathic pain and affective behavior models requires a comprehensive methodological approach that combines genetic manipulation with sophisticated behavioral assessments. The most effective research strategy utilizes TMEM97 knockout mice alongside wild-type controls to definitively establish the role of this protein in specific behavioral phenotypes . For investigating affective behaviors, a battery of complementary tests should be employed to assess different aspects of anxiety and depression-like behaviors, including open field test, light/dark preference test, elevated plus maze, elevated zero maze, forced swim test, and tail suspension test . This multi-test approach is crucial because single tests may yield inconsistent results due to the intrinsic variability of behavioral assays and the complex nature of affective behaviors in rodent models.

How does genetic ablation of Tmem97 affect retinal ganglion cell survival following ischemic injury?

Genetic ablation of Tmem97 significantly enhances retinal ganglion cell (RGC) survival following ischemic injury, revealing a critical role for this protein in neurodegeneration pathways . In wild-type mice subjected to retinal ischemia, a substantial loss of RGCs is observed seven days post-injury when compared to the untouched contralateral eye . In striking contrast, TMEM97−/− knockout mice maintain significantly higher numbers of RGCs after the same ischemic challenge . This neuroprotective effect is specifically attributable to the absence of the σ2R/TMEM97 protein, as all other aspects of retinal structure and function appear normal in these knockout mice under baseline conditions.

The experimental approach to quantify this neuroprotective effect involves inducing transient retinal ischemia in one eye while leaving the contralateral eye untouched as an internal control . Seven days post-ischemia, RGCs are identified through immunostaining for RBPMS (RNA binding protein with multiple splicing), a specific RGC marker . The survival rate is calculated as the ratio of RBPMS-positive cells in the ischemic eye versus those in the control eye within the same animal, providing a robust quantitative measure that controls for inter-animal variability . This experimental paradigm provides compelling evidence that σ2R/TMEM97 plays a role in facilitating RGC death following ischemic injury, and that inhibiting the function of this protein confers significant neuroprotection . These findings have important implications for developing novel therapeutic approaches for RGC degenerative conditions such as glaucoma and ischemic optic neuropathies.

What experimental design considerations are important when developing pharmacological modulators of Tmem97?

When developing pharmacological modulators of Tmem97, several critical experimental design considerations must be addressed to ensure scientific rigor and translational relevance. First, target specificity must be rigorously established through binding assays comparing affinity between wild-type and TMEM97−/− tissues or cells . The selective, high-affinity σ2R/TMEM97 ligand DKR-1677 exemplifies this approach, as it has been shown to protect RGCs from ischemia damage in wild-type mice, providing a pharmacological complement to genetic knockout studies . Pharmacokinetic and pharmacodynamic properties must be carefully assessed, particularly blood-brain barrier penetration for compounds targeting central nervous system indications.

Dose-response relationships should be comprehensively characterized across multiple model systems to establish effective concentration ranges and therapeutic windows . For neuropathic pain and affective disorder applications, compounds should be evaluated in both preventive and therapeutic treatment paradigms to determine if they can both prevent and reverse established pathology . Previous studies with compounds like siramesine HCl have demonstrated potency comparable to or exceeding clinical anxiolytic drugs like diazepam and lorazepam in reversing anxiety-like behaviors, establishing important benchmarks for novel compounds . For cancer applications, compounds should be tested both as monotherapies and in combination with standard-of-care treatments like tamoxifen for ER-positive breast cancer to assess potential synergistic effects . Long-term safety studies are particularly important given Tmem97's widespread expression across multiple tissues and its involvement in fundamental cellular processes like the Wnt signaling pathway . Together, these design considerations form a comprehensive framework for developing and validating Tmem97-targeted therapeutics across multiple disease indications.

What techniques are most effective for generating and validating Tmem97 knockout mouse models?

Generating and validating Tmem97 knockout mouse models requires careful consideration of multiple technical factors to ensure the creation of reliable research tools. CRISPR/Cas9 gene editing has emerged as the preferred method for generating constitutive TMEM97−/− knockout mice due to its efficiency and precision . When designing targeting strategies, researchers should consider whether a complete null allele or a conditional knockout is more appropriate for their research questions, particularly given Tmem97's involvement in multiple physiological systems. For conditional knockout approaches, Cre-loxP systems targeting specific tissues or cell types (such as retinal ganglion cells or mammary epithelium) allow for more precise dissection of tissue-specific functions while avoiding potential developmental compensation mechanisms.

Rigorous validation of knockout models is essential and should include multiple complementary approaches. Genetic validation should confirm the targeted mutation at the DNA level through PCR and sequencing . Transcriptional validation should demonstrate the absence of Tmem97 mRNA through RT-PCR and/or in situ hybridization . Protein validation is critical and should confirm the absence of Tmem97 protein through Western blotting and immunohistochemistry, with wild-type tissues serving as positive controls . The absence of σ2R/TMEM97 immunoreactivity in knockout mouse tissues provides a crucial validation of both the knockout model and the specificity of detection antibodies . Functional validation should confirm alterations in known Tmem97-dependent pathways, such as Wnt signaling in relevant tissues . Phenotypic characterization should include comprehensive assessment of viability, fertility, gross morphology, and baseline physiological parameters to identify any unexpected developmental or physiological consequences of Tmem97 deletion . This multi-layered validation approach ensures the generation of reliable models that can substantially advance our understanding of Tmem97 function.

How can researchers accurately measure Tmem97-mediated effects on Wnt/β-catenin signaling in experimental models?

Accurately measuring Tmem97-mediated effects on Wnt/β-catenin signaling requires a multi-faceted experimental approach that captures various aspects of this complex pathway. At the protein level, Western blot analysis should be employed to assess the phosphorylation state of LRP6 at Ser1490, as TMEM97 has been shown to enhance this specific phosphorylation event in a CK1δ/ε-dependent manner . Additionally, measurement of β-catenin stabilization and nuclear translocation provides a direct readout of canonical Wnt pathway activation and can be assessed through subcellular fractionation followed by Western blotting or through immunofluorescence microscopy to visualize β-catenin localization . Co-immunoprecipitation assays should be used to detect the physical interaction between TMEM97 and LRP6, as well as the recruitment of CK1δ/ε to this complex, which represents the mechanistic basis for TMEM97's enhancement of Wnt signaling .

For functional assessment of Wnt pathway activation, luciferase reporter assays using TOPFlash/FOPFlash constructs provide a quantitative readout of β-catenin-dependent transcriptional activity . This should be complemented by qRT-PCR analysis of endogenous Wnt target genes such as AXIN2, LEF1, and survivin, which have been shown to be downregulated following TMEM97 knockout in breast cancer cells . To establish causality in observed phenotypes, rescue experiments are crucial - for example, determining whether constitutively active β-catenin can reverse the effects of TMEM97 knockout would confirm that the observed phenotypes are indeed mediated through the Wnt pathway . In vivo models such as breast cancer xenografts provide the most physiologically relevant context for assessing TMEM97's impact on Wnt signaling, and immunohistochemical analysis of tumor sections should include markers for both pathway activity (phospho-LRP6, nuclear β-catenin) and functional outcomes (proliferation markers like Ki-67) . This comprehensive approach allows for robust characterization of Tmem97's role in modulating this crucial signaling pathway.

What behavioral testing protocols best detect Tmem97-dependent changes in anxiety and depression-like phenotypes?

Developing effective behavioral testing protocols for detecting Tmem97-dependent changes in anxiety and depression-like phenotypes requires careful consideration of test selection, methodological consistency, and integrated analysis approaches. A comprehensive behavioral test battery should include multiple complementary assays that assess different aspects of anxiety and depression-like behaviors . For anxiety assessment, the light/dark preference test has shown particular sensitivity to Tmem97-dependent effects, with female TMEM97 KO mice demonstrating reduced anxiety-like behaviors compared to wild-type counterparts . This should be supplemented with additional tests such as open field, elevated plus maze, and elevated zero maze to provide a more complete anxiety profile . For depression-like behaviors, the tail suspension test has demonstrated significant genotype-dependent differences, with TMEM97 KO female mice showing reduced immobility compared to wild-type mice, indicating an antidepressant-like phenotype . The forced swim test provides a complementary measure of behavioral despair, though it may not always yield consistent results with the tail suspension test .

How might findings on Tmem97 in mouse models inform therapeutic strategies for human diseases?

Findings on Tmem97 in mouse models provide promising avenues for developing therapeutic strategies across multiple human disease areas. In oncology, particularly breast cancer, the identification of TMEM97 as a positive modulator of canonical Wnt signaling suggests that targeting this protein could effectively suppress tumor growth and progression . The demonstration that TMEM97 knockout attenuates multiple cancer hallmarks including proliferation, migration, invasion, and stemness properties in breast cancer cells provides compelling pre-clinical evidence for this approach . Additionally, the discovery that TMEM97 enhances estrogen receptor α activity and contributes to tamoxifen resistance suggests that inhibiting TMEM97 might sensitize resistant tumors to endocrine therapies, potentially overcoming a major clinical challenge in breast cancer management .

In neurological conditions, the finding that female TMEM97 KO mice show reduced anxiety-like and depressive-like behaviors suggests that inhibiting TMEM97 might have anxiolytic and antidepressant effects . This is particularly significant for pain management, as TMEM97 KO mice did not develop the neuropathic pain-induced depressive-like phenotype that was observed in wild-type mice following nerve injury . This suggests that TMEM97 inhibitors could potentially address both neuropathic pain and its common psychiatric comorbidities . Similarly, the observation that TMEM97 knockout or pharmacological inhibition with the selective ligand DKR-1677 protects retinal ganglion cells from ischemia-induced degeneration offers a novel neuroprotective strategy for conditions like glaucoma and ischemic optic neuropathies . The conservation of TMEM97 structure and function between mice and humans supports the translational potential of these findings, though species differences in expression patterns and signaling interactions must be carefully considered during therapeutic development . Moving forward, developing high-specificity pharmacological modulators of TMEM97 with favorable pharmacokinetic profiles will be crucial for translating these promising preclinical findings into clinical applications.

What are the challenges and considerations in developing selective Tmem97 modulators for different disease indications?

Developing selective Tmem97 modulators for different disease indications presents several unique challenges that researchers must address. Target selectivity stands as a primary concern, as Tmem97/sigma-2 receptor ligands must demonstrate high specificity to avoid off-target effects, particularly with the closely related sigma-1 receptor which has distinct functions . The multifunctional nature of Tmem97 across different tissues necessitates careful consideration of potential side effects; for instance, while inhibiting Tmem97 may provide neuroprotection in retinal cells, it could potentially disrupt normal ER signaling in hormonal tissues . This complexity requires disease-specific benefit/risk assessments and possibly tissue-targeted drug delivery strategies.

Pharmacokinetic considerations are critical, particularly blood-brain barrier penetration for central nervous system indications like neuropathic pain and anxiety disorders . For retinal applications, ocular bioavailability presents its own set of challenges, potentially requiring specialized formulations or delivery methods . The distinct roles of Tmem97 in different disease contexts may necessitate different pharmacological approaches: antagonists appear beneficial for neuroprotection and pain management, while in cancer contexts, the specific disruption of Tmem97-LRP6 interaction might be more selective than complete inhibition . Furthermore, therapeutic timing must be carefully considered, as preventive versus therapeutic applications may require different pharmacological profiles, particularly in progressive conditions like neuropathic pain where early intervention may be crucial . Finally, patient stratification will be essential for clinical development, especially in breast cancer where Tmem97 expression correlates with ER positivity and could serve as a biomarker for selecting patients most likely to benefit from Tmem97-targeted therapies . Addressing these challenges will require integrated approaches combining medicinal chemistry, pharmacology, and disease-specific expertise to realize the therapeutic potential of Tmem97 modulation.

What are the optimal conditions for expressing and purifying recombinant mouse Tmem97 protein for structural and functional studies?

Expressing and purifying recombinant mouse Tmem97 protein presents significant technical challenges due to its transmembrane nature. For successful expression, researchers should consider multiple expression systems including bacterial (E. coli), insect cell (Sf9, High Five), and mammalian cell (HEK293, CHO) platforms, with mammalian and insect systems generally yielding better results for transmembrane proteins due to their advanced post-translational modification capabilities. When using bacterial systems, specialized E. coli strains designed for membrane protein expression (such as C41/C43(DE3) or Lemo21(DE3)) can significantly improve yields. The protein should be engineered with affinity tags (such as His6 or FLAG) positioned to avoid interference with protein folding, and fusion partners like MBP (maltose-binding protein) or SUMO can enhance solubility and expression levels.

For purification, detergent selection is critical - mild non-ionic detergents like DDM (n-dodecyl-β-D-maltoside) or LMNG (lauryl maltose neopentyl glycol) often provide a good balance between effective solubilization and preservation of protein structure and function. Alternatively, membrane mimetics such as nanodiscs, amphipols, or styrene-maleic acid lipid particles (SMALPs) can provide a more native-like environment for the purified protein. Multi-step purification approaches combining affinity chromatography, ion exchange, and size exclusion chromatography yield the highest purity. Quality control is essential and should include SDS-PAGE, Western blotting, mass spectrometry, and functional binding assays with known ligands to confirm proper folding and activity. For structural studies, thermal stability assays can identify buffer conditions that maximize protein stability. When studying Tmem97's interactions with partners like LRP6, co-expression and co-purification strategies should be considered to capture physiologically relevant protein complexes . These optimized conditions are crucial for advancing structural understanding and developing selective pharmacological modulators of this important protein.

How can researchers accurately compare Tmem97 expression levels across different experimental models and tissue samples?

Accurately comparing Tmem97 expression levels across different experimental models and tissue samples requires a multi-faceted approach combining quantitative techniques with appropriate controls and normalization methods. For mRNA quantification, quantitative real-time PCR (qRT-PCR) remains the gold standard, but requires careful primer design targeting conserved regions of Tmem97 and validation across different mouse strains to account for potential polymorphisms . Multiple reference genes should be used for normalization, with GAPDH, β-actin, and 18S rRNA being common choices, though tissue-specific reference genes may provide more accurate normalization in certain contexts. Digital PCR offers an alternative that provides absolute quantification without standard curves and may be less affected by PCR inhibitors present in certain tissue extracts.

For protein quantification, Western blotting with carefully validated antibodies is essential, ideally using antibodies recognizing different epitopes to confirm specificity . Loading controls should be selected based on the experimental context - for example, β-actin may be appropriate for cell lines but can vary across tissues, making total protein normalization (through stain-free gels or Ponceau staining) a more reliable approach for tissue comparisons. Absolute quantification can be achieved using recombinant Tmem97 protein standards of known concentration. For tissue localization studies, immunohistochemistry should always include TMEM97 knockout tissues as negative controls, as demonstrated in retinal studies where no σ2R/TMEM97 immunoreactivity was detected in knockout mice . For cross-species comparisons, species-specific antibodies or conserved-epitope antibodies with demonstrated cross-reactivity should be used. When comparing expression across disease states (such as cancer vs. normal tissue), matched samples from the same individual provide the most reliable comparisons. Finally, computational approaches for integrated analysis of multi-omic data can provide comprehensive insights, particularly when correlating Tmem97 expression with functional pathway activity as demonstrated in studies linking Tmem97 expression with estrogen receptor status in breast tumors .

What are the most promising future research directions for understanding Tmem97 function in neurodegenerative conditions?

Future research on Tmem97 in neurodegenerative conditions should pursue several promising directions that build upon recent discoveries. Investigation of Tmem97's role across different neurodegenerative diseases beyond retinal degeneration is a critical priority, particularly in conditions like Alzheimer's, Parkinson's, and amyotrophic lateral sclerosis where neuroprotective strategies are urgently needed . The discovery that Tmem97 knockout protects retinal ganglion cells from ischemia-induced degeneration and that selective ligands like DKR-1677 have neuroprotective effects suggests potential therapeutic applications across multiple neurodegenerative contexts . Molecular mechanism studies should focus on identifying the downstream effectors of Tmem97 in neuronal death pathways, examining whether its pro-degenerative effects involve alterations in calcium signaling, mitochondrial function, oxidative stress responses, or programmed cell death pathways.

Cell-type specific manipulation of Tmem97 through conditional knockout or viral approaches would help distinguish between its functions in neurons versus support cells like glia and vascular components, providing more precise therapeutic targeting strategies . Development of improved pharmacological tools with enhanced selectivity for Tmem97 over related proteins and favorable blood-brain barrier penetration would facilitate both mechanistic studies and therapeutic development . Long-term studies examining whether chronic Tmem97 inhibition maintains its neuroprotective effects without compensatory adaptations or adverse effects are essential for therapeutic applications. The discovery that female TMEM97 KO mice show reduced anxiety and depression-like behaviors, combined with protection from neuropathic pain-induced affective changes, suggests exploring Tmem97's role in the intersection between neurodegeneration, pain, and psychiatric conditions . Finally, translational studies examining Tmem97 expression and polymorphisms in human neurodegenerative disease cohorts would help establish clinical relevance and identify patient populations most likely to benefit from Tmem97-targeted therapies . These research directions promise to substantially advance our understanding of Tmem97's role in neurodegenerative processes and accelerate therapeutic development for conditions with significant unmet medical needs.

How might combining Tmem97 inhibition with other targeted therapies create novel therapeutic approaches for breast cancer?

Combining Tmem97 inhibition with other targeted therapies holds considerable promise for creating novel therapeutic approaches for breast cancer with enhanced efficacy and reduced resistance development. For hormone receptor-positive breast cancers, the discovery that TMEM97 enhances estrogen receptor α activity and contributes to tamoxifen resistance suggests that combining TMEM97 inhibitors with endocrine therapies could overcome or prevent resistance mechanisms . Specifically, TMEM97 inhibition might resensitize resistant tumors to tamoxifen or aromatase inhibitors, potentially extending the duration of response to these well-established treatments . The finding that MCF7 and T47D cells with increased TMEM97 expression show enhanced growth under estrogen-depleted conditions further supports this combinatorial approach .

For cancers with aberrant Wnt pathway activation, combining TMEM97 inhibitors with other Wnt pathway modulators could provide synergistic effects through multi-level pathway inhibition . Since TMEM97 enhances LRP6-mediated Wnt signaling and facilitates the recruitment of CK1δ/ε to LRP6, combining TMEM97 inhibitors with other agents targeting different nodes in the Wnt pathway (such as porcupine inhibitors or β-catenin/TCF interaction disruptors) might achieve more complete pathway suppression . Investigating combinations with standard chemotherapeutic agents is also warranted, as Wnt pathway inhibition has been shown to enhance chemosensitivity in various cancer models . For triple-negative breast cancers, which currently lack targeted therapy options, exploration of TMEM97 expression and function could potentially identify a new therapeutic vulnerability . Careful patient stratification based on TMEM97 expression levels and concomitant pathway alterations will be essential for maximizing therapeutic benefit and designing rational clinical trials for these combination approaches . Emerging technologies like patient-derived organoids and xenografts provide valuable platforms for preclinical testing of these combination strategies in systems that better recapitulate tumor heterogeneity and microenvironment interactions.