Promalignant effects of antiangiogenics in the tumor microenvironment.

Antiangiogenic therapies are considered a promising strategy against solid tumors. Their aim is to inhibit the formation of new blood vasculature, thereby reducing the oxygen and nutrient supply to prevent further tumor growth and spreading. However, the strategy has seen limitations, as survival benefits are modest and often accompanied with increased tumor aggressiveness in form of invasion and metastasis. Antiangiogenic induced changes in the tumor microenvironment, such as hypoxia, mechanical stress or extracellular acidification can activate different receptors of tumoral and stromal cells and induce an extensive remodeling of the entire tumor microenvironment, with the overall goal to invade nearby tissues and regain access to the vasculature. In this regard, receptor tyrosine kinases have been studied intensively and especially the inhibition of c-Met has given promising results, characterized by a reduction in invasiveness and prolonged survival. Receptors that sense changes in the extracellular matrix like integrins or proteoglycans can also induce downstream signaling that stimulates the expression of remodeling factors such as new matrix components, enzymes or chemoattractants. Targeting multiple receptors and sensors of cancer cells simultaneously might represent an effective second line treatment that prevents the formation of malignant side effects.

Phase II Study of Everolimus and Octreotide LAR in Patients with Nonfunctioning Gastrointestinal Neuroendocrine Tumors: The GETNE1003_EVERLAR Study.

BACKGROUND: Antitumor activity of the combination of somatostatin analogues (SSAs) and the mammalian target of rapamycin (mTOR) inhibitor everolimus in patients with neuroendocrine tumors (NETs) has been reported but not confirmed in prospective trials. MATERIALS AND METHODS: This prospective, multicenter, single-arm phase II EVERLAR study evaluated everolimus 10 mg/day and the SSA octreotide 30 mg every 28 days in patients with advanced nonfunctioning well-differentiated gastrointestinal NETs (GI-NETs) that progressed in the last 12 months (ClinicalTrials.gov NCT01567488). Prior treatment with SSAs and any systemic or locoregional therapy was allowed except for mTOR inhibitors. Patients continued treatment until disease progression or unacceptable adverse events (AEs). The primary endpoint was progression-free survival (PFS) at 12 months; secondary endpoints included early biochemical response, objective response rate (ORR) by RECIST v1.0, overall survival (OS), AEs, activation of mTOR pathway (insulin-like growth factor 1 receptor [IGF1R] and phosphoS6 [pS6] expression). RESULTS: Forty-three patients were included in the intent-to-treat analyses. After 12 months of treatment, 62.3% (95% confidence interval [CI] 48%-77%) of patients had not progressed or died. The 24-month PFS rate was 43.6% (95% CI 29%-58%). The confirmed ORR was 2.3%, and stable disease was 58.1%. Median OS was not reached after 24 months of median follow-up. Dose reductions and temporary interruptions due to AEs were required in 14 (33%) and 33 (77%) patients, respectively. The most frequent AEs were diarrhea, asthenia, mucositis, rash, and hyperglycemia. No correlation was observed between IGFR1 and pS6 expression and PFS/OS. CONCLUSION: The everolimus-octreotide combination provided clinically relevant efficacy in nonfunctioning GI-NETs, similar to the results of RADIANT-2 in functioning setting. IMPLICATIONS FOR PRACTICE: The EVERLAR study reports prospective data of somatostatin analogue in combination with everolimus in nonfunctioning gastrointestinal neuroendocrine tumors suggesting meaningful activity and favorable toxicity profile that supports drug combination in this setting.

ALK1 Loss Results in Vascular Hyperplasia in Mice and Humans Through PI3K Activation.

OBJECTIVE: ALK1 (activin-receptor like kinase 1) is an endothelial cell-restricted receptor with high affinity for BMP (bone morphogenetic protein) 9 TGF-ß (transforming growth factor-ß) family member. Loss-of-function mutations in ALK1 cause a subtype of hereditary hemorrhagic telangiectasia-a rare disease characterized by vasculature malformations. Therapeutic strategies are aimed at reducing potential complications because of vascular malformations, but currently, there is no curative treatment for hereditary hemorrhagic telangiectasia. APPROACH AND RESULTS: In this work, we report that a reduction in ALK1 gene dosage (heterozygous ALK1+/- mice) results in enhanced retinal endothelial cell proliferation and vascular hyperplasia at the sprouting front. We found that BMP9/ALK1 represses VEGF (vascular endothelial growth factor)-mediated PI3K (phosphatidylinositol 3-kinase) by promoting the activity of the PTEN (phosphatase and tensin homolog). Consequently, loss of ALK1 function in endothelial cells results in increased activity of the PI3K pathway. These results were confirmed in cutaneous telangiectasia biopsies of patients with hereditary hemorrhagic telangiectasia 2, in which we also detected an increase in endothelial cell proliferation linked to an increase on the PI3K pathway. In mice, genetic and pharmacological inhibition of PI3K is sufficient to abolish the vascular hyperplasia of ALK1+/- retinas and in turn normalize the vasculature. CONCLUSIONS: Overall, our results indicate that the BMP9/ALK1 hub critically mediates vascular quiescence by limiting PI3K signaling and suggest that PI3K inhibitors could be used as novel therapeutic agents to treat hereditary hemorrhagic telangiectasia.

Notch-dependent VEGFR3 upregulation allows angiogenesis without VEGF-VEGFR2 signalling.

Developing tissues and growing tumours produce vascular endothelial growth factors (VEGFs), leading to the activation of the corresponding receptors in endothelial cells. The resultant angiogenic expansion of the local vasculature can promote physiological and pathological growth processes. Previous work has uncovered that the VEGF and Notch pathways are tightly linked. Signalling triggered by VEGF-A (also known as VEGF) has been shown to induce expression of the Notch ligand DLL4 in angiogenic vessels and, most prominently, in the tip of endothelial sprouts. DLL4 activates Notch in adjacent cells, which suppresses the expression of VEGF receptors and thereby restrains endothelial sprouting and proliferation. Here we show, by using inducible loss-of-function genetics in combination with inhibitors in vivo, that DLL4 protein expression in retinal tip cells is only weakly modulated by VEGFR2 signalling. Surprisingly, Notch inhibition also had no significant impact on VEGFR2 expression and induced deregulated endothelial sprouting and proliferation even in the absence of VEGFR2, which is the most important VEGF-A receptor and is considered to be indispensable for these processes. By contrast, VEGFR3, the main receptor for VEGF-C, was strongly modulated by Notch. VEGFR3 kinase-activity inhibitors but not ligand-blocking antibodies suppressed the sprouting of endothelial cells that had low Notch signalling activity. Our results establish that VEGFR2 and VEGFR3 are regulated in a highly differential manner by Notch. We propose that successful anti-angiogenic targeting of these receptors and their ligands will strongly depend on the status of endothelial Notch signalling.

The TGFß pathway stimulates ovarian cancer cell proliferation by increasing IGF1R levels.

In a search for new therapeutic targets for treating epithelial ovarian cancer, we analyzed the Transforming Growth Factor Beta (TGFß) signaling pathway in these tumors. Using a TMA with patient samples we found high Smad2 phosphorylation in ovarian cancer tumoral cells, independently of tumor subtype (high-grade serous or endometrioid). To evaluate the impact of TGFß receptor inhibition on tumoral growth, we used different models of human ovarian cancer orthotopically grown in nude mice (OVAs). Treatment with a TGFßRI&II dual inhibitor, LY2109761, caused a significant reduction in tumor size in all these models, affecting cell proliferation rate. We identified Insulin Growth Factor (IGF)1 receptor as the signal positively regulated by TGFß implicated in ovarian tumor cell proliferation. Inhibition of IGF1R activity by treatment with a blocker antibody (IMC-A12) or with a tyrosine kinase inhibitor (linsitinib) inhibited ovarian tumoral growth in vivo. When IGF1R levels were decreased by shRNA treatment, LY2109761 lost its capacity to block tumoral ovarian cell proliferation. At the molecular level TGFß induced mRNA IGF1R levels. Overall, our results suggest an important role for the TGFß signaling pathway in ovarian tumor cell growth through the control of IGF1R signaling pathway. Moreover, it identifies anti-TGFß inhibitors as being of potential use in new therapies for ovarian cancer patients as an alternative to IGF1R inhibition.

A novel role for an RCAN3-derived peptide as a tumor suppressor in breast cancer.

The members of the human regulators of calcineurin (RCAN) protein family are endogenous regulators of the calcineurin (CN)-cytosolic nuclear factor of activated T-cells (NFATc) pathway activation. This function is explained by the presence of a highly conserved calcipressin inhibitor of calcineurin (CIC) motif in RCAN proteins, which has been shown to compete with NFATc for the binding to CN and therefore are able to inhibit NFATc dephosphorylation and activation by CN. Very recently, emerging roles for NFATc proteins in transformation, tumor angiogenesis and metastasis have been described in different cancer cell types. In this work, we report that the overexpression of RCAN3 dramatically inhibits tumor growth and tumor angiogenesis in an orthotopic human breast cancer model. We suggest that RCAN3 exerts these effects in a CN-dependent manner, as mutation of the CIC motif in RCAN3 abolishes the tumor suppressor effect. Moreover, the expression of the EGFP-R3(178-210) peptide, spanning the CIC motif of RCAN3, is able to reproduce all the antitumor effects of RCAN3 full-length protein. Finally, we show that RCAN3 and the EGFP-R3(178-210) peptide inhibit the CN-NFATc signaling pathway and the induction of the NFATc-dependent gene cyclooxygenase-2. Our work suggests that the EGFP-R3(178-210) peptide possess potent tumor suppressor properties and therefore constitutes a novel lead for the development of potent and specific antitumoral agents. Moreover, we propose the targeting of the CN-NFATc pathway in the tumor cells constitutes an effective way to hamper tumor progression by impairing the paracrine network among tumor, endothelial and polymorphonucleated cells.

Small molecule enoxacin is a cancer-specific growth inhibitor that acts by enhancing TAR RNA-binding protein 2-mediated microRNA processing.

MicroRNAs (miRNAs) are small RNA molecules that regulate gene expression at the posttranscriptional level and are critical for many cellular pathways. The disruption of miRNAs and their processing machineries also contributes to the development of human tumors. A common scenario for miRNA expression in carcinogenesis is emerging that shows that impaired miRNA production and/or down-regulation of these transcripts occurs in many neoplasms. Several of these lost miRNAs have tumor-suppressor features, so strategies to restore their expression globally in malignancies would be a welcome addition to the current therapeutic arsenal against cancer. Herein, we show that the small molecule enoxacin, a fluoroquinolone used as an antibacterial compound, enhances the production of miRNAs with tumor suppressor functions by binding to the miRNA biosynthesis protein TAR RNA-binding protein 2 (TRBP). The use of enoxacin in human cell cultures and xenografted, orthotopic, and metastatic mouse models reveals a TRBP-dependent and cancer-specific growth-inhibitory effect of the drug. These results highlight the key role of disrupted miRNA expression patterns in tumorigenesis, and suggest a unique strategy for restoring the distorted microRNAome of cancer cells to a more physiological setting.

Metronomic chemotherapy following the maximum tolerated dose is an effective anti-tumour therapy affecting angiogenesis, tumour dissemination and cancer stem cells.

In this article, the effectiveness of a multi-targeted chemo-switch (C-S) schedule that combines metronomic chemotherapy (MET) after treatment with the maximum tolerated dose (MTD) is reported. This schedule was tested with gemcitabine in two distinct human pancreatic adenocarcinoma orthotopic models and with cyclophosphamide in an orthotopic ovarian cancer model. In both models, the C-S schedule had the most favourable effect, achieving at least 80% tumour growth inhibition without increased toxicity. Moreover, in the pancreatic cancer model, although peritoneal metastases were observed in control and MTD groups, no dissemination was observed in the MET and C-S groups. C-S treatment caused a decrease in angiogenesis, and its effect on tumour growth was similar to that produced by the MTD followed by anti-angiogenic DC101 treatment. C-S treatment combined an increase in thrombospondin-1 expression with a decrease in the number of CD133+ cancer cells and triple-positive CD133+/CD44+/CD24+ cancer stem cells (CSCs). These findings confirm that the C-S schedule is a challenging clinical strategy with demonstrable inhibitory effects on tumour dissemination, angiogenesis and CSCs.

Effectivity of pazopanib treatment in orthotopic models of human testicular germ cell tumors.

BACKGROUND: Cisplatin (CDDP) resistance in testicular germ cell tumors (GCTs) is still a clinical challenge, and one associated with poor prognosis. The purpose of this work was to test pazopanib, an anti-tumoral and anti-angiogenic multikinase inhibitor, and its combination with lapatinib (an anti-ErbB inhibitor) in mouse orthotopic models of human testicular GCTs. METHODS: We used two different models of human testicular GCTs orthotopically grown in nude mice; a CDDP-sensitive choriocarcinoma (TGT38) and a new orthotopic model generated from a metastatic GCT refractory to first-line CDDP chemotherapy (TGT44). Nude mice implanted with these orthotopic tumors were treated with the inhibitors and the effect on tumoral growth and angiogenesis was evaluated. RESULTS: TGT44 refractory tumor had an immunohistochemical profile similar to the original metastasis, with characteristics of yolk sac tumor. TGT44 did not respond when treated with cisplatin. In contrast, pazopanib had an anti-angiogenic effect and anti-tumor efficacy in this model. Pazopanib in combination with lapatinib in TGT38, an orthotopic model of choriocarcinoma had an additive effect blocking tumor growth. CONCLUSIONS: We present pazopanib as a possible agent for the alternative treatment of CDDP-sensitive and CDDP-refractory GCT patients, alone or in combination with anti-ErbB therapies.

Drug resistance by evasion of antiangiogenic targeting of VEGF signaling in late-stage pancreatic islet tumors.

Function-blocking antibodies to VEGF receptors R1 and R2 were used to probe their roles in controlling angiogenesis in a mouse model of pancreatic islet carcinogenesis. Inhibition of VEGFR2 but not VEGFR1 markedly disrupted angiogenic switching, persistent angiogenesis, and initial tumor growth. In late-stage tumors, phenotypic resistance to VEGFR2 blockade emerged, as tumors regrew during treatment after an initial period of growth suppression. This resistance to VEGF blockade involves reactivation of tumor angiogenesis, independent of VEGF and associated with hypoxia-mediated induction of other proangiogenic factors, including members of the FGF family. These other proangiogenic signals are functionally implicated in the revascularization and regrowth of tumors in the evasion phase, as FGF blockade impairs progression in the face of VEGF inhibition.

High FGFR1-4 mRNA Expression Levels Correlate with Response to Selective FGFR Inhibitors in Breast Cancer.

PURPOSE: FGFR1 amplification (FGFR1amp) is recurrent in metastatic breast cancer (MBC) and is associated with resistance to endocrine therapy and CDK4/6 inhibitors (CDK4/6is). Multi-tyrosine kinase inhibitors (MTKIs) and selective pan-FGFR inhibitors (FGFRis) are being developed for FGFR1amp breast cancer. High-level FGFR amplification and protein expression by IHC have identified breast cancer responders to FGFRis or MTKIs, respectively. EXPERIMENTAL DESIGN: Here, we used preclinical models and patient samples to identify predictive biomarkers to these drugs. We evaluated the antitumor activity of an FGFRi and an MTKI in a collection of 17 breast cancer patient-derived xenografts (PDXs) harboring amplification in FGFR1/2/3/4 and in 10 patients receiving either an FGFRi/MTKI. mRNA levels were measured on FFPE tumor samples using two commercial strategies. Proliferation and angiogenesis were evaluated by detecting Ki-67 and CD31 in viable areas by immunofluorescence. RESULTS: High FGFR1-4 mRNA levels but not copy-number alteration (CNA) is associated with FGFRi response. Treatment with MTKIs showed higher response rates than with FGFRis (86% vs. 53%), regardless of the FGFR1-4 mRNA levels. FGFR-addicted PDXs exhibited an antiproliferative response to either FGFRis or MTKIs, and PDXs exclusively sensitive to MTKI exhibited an additional antiangiogenic response. Consistently, the clinical benefit of MTKIs was not associated with high FGFR1-4 mRNA levels and was observed in patients previously treated with antiangiogenic drugs. CONCLUSIONS: Tailored therapy with FGFRis in molecularly selected MBC based on high FGFR1-4 mRNA levels warrants prospective validation in patients with CDK4/6i-resistant luminal breast cancer and in patients with TNBC without targeted therapeutic options.

Filamin B plays a key role in vascular endothelial growth factor-induced endothelial cell motility through its interaction with Rac-1 and Vav-2.

Actin-binding proteins filamin A (FLNA) and B (FLNB) are expressed in endothelial cells and play an essential role during vascular development. In order to investigate their role in adult endothelial cell function, we initially confirmed their expression pattern in different adult mouse tissues and cultured cell lines and found that FLNB expression is concentrated mainly in endothelial cells, whereas FLNA is more ubiquitously expressed. Functionally, small interfering RNA knockdown of endogenous FLNB in human umbilical vein endothelial cells inhibited vascular endothelial growth factor (VEGF)-induced in vitro angiogenesis by decreasing endothelial cell migration capacity, whereas FLNA ablation did not alter these parameters. Moreover, FLNB-depleted cells increased their substrate adhesion with more focal adhesions. The molecular mechanism underlying this effect implicates modulation of small GTP-binding protein Rac-1 localization and activity, with altered activation of its downstream effectors p21 protein Cdc42/Rac-activated kinase (PAK)-4/5/6 and its activating guanine nucleotide exchange factor Vav-2. Moreover, our results suggest the existence of a signaling complex, including FLNB, Rac-1, and Vav-2, under basal conditions that would further interact with VEGFR2 and integrin alphavbeta5 after VEGF stimulation. In conclusion, our results reveal a crucial role for FLNB in endothelial cell migration and in the angiogenic process in adult endothelial cells.

Sunitinib inhibits tumor growth and synergizes with cisplatin in orthotopic models of cisplatin-sensitive and cisplatin-resistant human testicular germ cell tumors.

PURPOSE: Germ cell tumors (GCT) of the testis are highly curable, but those patients who are refractory to cisplatin (CDDP)-based combination chemotherapy have a poor prognosis. Therefore, identifying new alternatives for treatment remains a priority. Several studies support an important role for angiogenesis in GCTs, suggesting that antiangiogenic treatment might be a good alternative. Sunitinib is an oral multitarget tyrosine kinase receptor inhibitor with antiangiogenic and antitumor activities. In the present study, we evaluated the effect of sunitinib, CDDP, or the combination of both drugs using an orthotopic model of human testicular GCT. EXPERIMENTAL DESIGN: Mice were implanted with four different testicular tumors: a yolk sac, two choriocarcinomas, and a CDDP-resistant choriocarcinoma variant induced in mice by continuous exposure to CDDP. Mice were treated with vehicle, CDDP, sunitinib, or the combination of both drugs and their effects on tumors were analyzed. RESULTS: We observed a significant inhibition in tumor growth accompanied by longer survival after sunitinib treatment. Combination therapy with CDDP significantly enhanced these effects. Sunitinib induced apoptosis, reduced tumor cell proliferation and tumor vasculature, and inhibited vascular endothelial growth factor receptor 1, 2, and 3 and platelet-derived growth factor receptor alpha phosphorylation without affecting phosphorylation of other tyrosine kinase receptors. More importantly, tumor growth inhibition induced by sunitinib was also observed in the induced CDDP-resistant choriocarcinoma model. CONCLUSIONS: Taken together, these results suggest that sunitinib might be a new alternative for treatment of CDDP-refractory patients.

EVI1 as a Prognostic and Predictive Biomarker of Clear Cell Renal Cell Carcinoma.

The transcription factor EVI1 plays an oncogenic role in several types of neoplasms by promoting aggressive cancer features. EVI1 contributes to epigenetic regulation and transcriptional control, and its overexpression has been associated with enhanced PI3K-AKT-mTOR signaling in some settings. These observations raise the possibility that EVI1 influences the prognosis and everolimus-based therapy outcome of clear cell renal cell carcinoma (ccRCC). Here, gene expression and protein immunohistochemical studies of ccRCC show that EVI1 overexpression is associated with advanced disease features and with poorer outcome-particularly in the CC-e.3 subtype defined by The Cancer Genome Atlas. Overexpression of an oncogenic EVI1 isoform in RCC cell lines confers substantial resistance to everolimus. The EVI1 rs1344555 genetic variant is associated with poorer survival and greater progression of metastatic ccRCC patients treated with everolimus. This study leads us to propose that evaluation of EVI1 protein or gene expression, and of EVI1 genetic variants may help improve estimates of prognosis and the benefit of everolimus-based therapy in ccRCC.

Kidney cancer PDOXs reveal patient-specific pro-malignant effects of antiangiogenics and its molecular traits.

An open debate in antiangiogenic therapies is about their consequence on tumor invasiveness and metastasis, which is undoubtedly relevant for patients currently treated with antiangiogenics, such as renal cell carcinoma patients. To address, this we developed an extensive series of 27 patient biopsy-derived orthotopic xenograft models (Ren-PDOX) that represent inter-patient heterogeneity. In specific tumors, antiangiogenics produced increased invasiveness and metastatic dissemination, while in others aggressiveness remained unchanged. Mechanistically, species-discriminative RNA sequencing identified a tumor cell-specific differential expression profile associated with tumor progression and aggressivity in TCGA RCC patients. Gene filtering using an invasion-annotated patient series pinpointed two candidate genes, of which ALDH1A3 differentiated the pro-invasive subtype of Ren-PDOXs. Validation in an independent series of 15 antiangiogenic-treated patients confirmed that pre-treatment ALDH1A3 can significantly discriminate patients with pro-aggressive response upon treatment. Overall, results confirm that effects of antiangiogenic drugs on tumor invasion and metastasis are heterogeneous and may profoundly affect the natural progression of tumors and promote malignancy. Furthermore, we identify a specific molecular biomarker that could be used to select patients that better benefit from treatment.

Antiangiogenic effect of gemcitabine following metronomic administration in a pancreas cancer model.

Gemcitabine shows a marked antitumor effect as a result of its cytotoxic action toward proliferative cells. In this article, we aim to investigate the potential antitumor and antiangiogenic effect of gemcitabine following a metronomic schedule that involves the regular administration of cytotoxic drugs at doses lower than standard treatment. In vitro results showed that human endothelial cells are more sensitive to gemcitabine (IC(50) 3 nmol/L) than pancreatic tumor cells (IC(50) 20 nmol/L). For in vivo studies, we used an orthotopic implantation model of human pancreatic carcinoma in nude mice. Gemcitabine was administered i.p. following a low-dose schedule (1 mg/kg/d for a month) and compared with the conventional schedule (100 mg/kg days 0, 3, 6, and 9 postimplantation). Metronomic treatment effect on established tumor was equivalent to standard administration. The measure of CD31 endothelial marked area allowed us to show an in vivo antiangiogenic effect of this drug that was further enhanced by using metronomic administration. This effect correlated with an induction of thrombospondin-1, a natural inhibitor of angiogenesis. Our results allow us to hypothesize that, in addition to a direct antiproliferative or cytotoxic antiendothelial cell effect, a secondary effect involving thrombospondin-1 induction might provide an explanation for the specificity of the effects of metronomic gemcitabine treatment.

Uveal Melanoma, Angiogenesis and Immunotherapy, Is There Any Hope?

Uveal melanoma is considered a rare disease but it is the most common intraocular malignancy in adults. Local treatments are effective, but the systemic recurrence rate is unacceptably high. Moreover, once metastasis have developed the prognosis is poor, with a 5-year survival rate of less than 5%, and systemic therapies, including immunotherapy, have rendered poor results. The tumour biology is complex, but angiogenesis is a highly important pathway in these tumours. Vasculogenic mimicry, the ability of melanomas to generate vascular channels independently of endothelial cells, could play an important role, but no effective therapy targeting this process has been developed so far. Angiogenesis modulates the tumour microenvironment of melanomas, and a close interplay is established between them. Therefore, combining immune strategies with drugs targeting angiogenesis offers a new therapeutic paradigm. In preclinical studies, these approaches effectively target these tumours, and a phase I clinical study has shown encouraging results in cutaneous melanomas. In this review, we will discuss the importance of angiogenesis in uveal melanoma, with a special focus on vasculogenic mimicry, and describe the interplay between angiogenesis and the tumour microenvironment. In addition, we will suggest future therapeutic approaches based on these observations and mention ways in which to potentially enhance current treatments.

Quantification of gold nanoparticle accumulation in tissue by two-photon luminescence microscopy.

Nanomedicine has emerged as a promising strategy to address some of the limitations of traditional biomedical sensing, imaging and therapy modalities. Its applicability and efficacy are, in part, hindered by the difficulty in both controllably delivering nanoparticles to specific regions and accurately monitoring them in tissue. Gold nanoparticles are among the most extensively used inorganic nanoparticles which benefit from high biocompatibility, flexible functionalization, strong and tunable resonant absorption, and production scalability. Moreover, their capability to enhance optical fields at their plasmon resonance enables local boosting of non-linear optical processes, which are otherwise very inefficient. In particular, two-photon induced luminescence (TPL) in gold offers high signal specificity for monitoring gold nanoparticles in a biological environment. In this article, we demonstrate that TPL microscopy provides a robust sub-micron-resolution technique able to quantify accumulated gold nanorods (GNRs) both in cells and in tissues. First, the temporal accumulation of GNRs with two different surface chemistries was measured in 786-O cells during the first 24 hours of incubation, and at different nanoparticle concentrations. Subsequently, GNR accumulation in mice, 6 h and 24 hours after tail vein injection, was quantified by TPL microscopy in biopsied tissue from kidney, spleen, liver and clear cell renal cell carcinoma (ccRCC) tumors, in good agreement with inductively coupled mass spectroscopy. Our data suggest that TPL microscopy stands as a powerful tool to understand and quantify the delivery mechanisms of gold nanoparticles, highly relevant to the development of future theranostic medicines.