The link between cancer metabolism and immunosuppression, inflammation and immune escape has generated major interest in investigating the effects of low pH on tumor immunity. Indeed, microenvironmental acidity may differentially impact on diverse components of tumor immune surveillance, eventually contributing to immune escape and cancer progression. Although the molecular pathways underlying acidity-related immune dysfunctions are just emerging, initial evidence indicates that antitumor effectors such as T and NK cells tend to lose their function and undergo a state of mostly reversible anergy followed by apoptosis, when exposed to low pH environment. At opposite, immunosuppressive components such as myeloid cells and regulatory T cells are engaged by tumor acidity to sustain tumor growth while blocking antitumor immune responses. Local acidity could also profoundly influence bioactivity and distribution of antibodies, thus potentially interfering with the clinical efficacy of therapeutic antibodies including immune checkpoint inhibitors. Hence tumor acidity is a central regulator of cancer immunity that orchestrates both local and systemic immunosuppression and that may offer a broad panel of therapeutic targets. This review outlines the fundamental pathways of acidity-driven immune dysfunctions and sheds light on the potential strategies that could be envisaged to potentiate immune-mediated tumor control in cancer patients.

Exosomes are endosome-derived nanovesicles actively released into the extracellular environment and biological fluids, both under physiological and pathological conditions, by different cell types. We characterized exosomes constitutively secreted by HER2-overexpressing breast carcinoma cell lines and analyzed in vitro and in vivo their potential role in interfering with the therapeutic activity of the humanized antibody Trastuzumab and the dual tyrosine kinase inhibitor (TKI) Lapatinib anti-HER2 biodrugs. We show that exosomes released by the HER2-overexpressing tumor cell lines SKBR3 and BT474 express a full-length HER2 molecule that is also activated, although to a lesser extent than in the originating cells. Release of these exosomes was significantly modulated by the growth factors EGF and heregulin, two of the known HER2 receptor-activating ligands and naturally present in the surrounding tumor microenvironment. Exosomes secreted either in HER2-positive tumor cell-conditioned supernatants or in breast cancer patients' serum bound to Trastuzumab. Functional assays revealed that both xenogeneic and autologous HER2-positive nanovesicles, but not HER2-negative ones, inhibited Trastuzumab activity on SKBR3 cell proliferation. By contrast, Lapatinib activity on SKBR3 cell proliferation was unaffected by the presence of autologous exosomes. Together, these findings point to the role of HER2-positive exosomes in modulating sensitivity to Trastuzumab, and, consequently, to HER2-driven tumor aggressiveness.

Purpose: To elucidate the mechanism by which trastuzumab, a humanized monoclonal antibody against HER2 with proven survival benefit in women with HER2-positive metastatic breast cancer, mediates its antitumor activity.Experimental Design: A pilot study including 11 patients with HER2-positive tumors treated in a neo-adjuvant setting with trastuzumab was performed. Trastuzumab was administered i.v. at a dose of 4 mg/kg followed by three weekly i.v. doses of 2 mg/kg. The primary tumor was surgically removed 7 days after the last treatment. Surgical samples, tumor biopsies, and lymphocytes from these patients were collected for biological studies.Result: Clinical data indicated one complete pathological remission and four partial remissions using RECIST (Response Evaluation Criteria in Solid Tumors). Trastuzumab was well tolerated and neither serious adverse events nor changes in cardiac function were observed during this short-term treatment and after surgery. The biological data showed that, independent of response, (a) all patients showed high levels of circulating trastuzumab; (b) saturating level of trastuzumab was present in all of the tumors; (c) no down-modulation of HER2 was observed in any tumors; (d) no changes in vessel diameter was observed in any tumors; (e) no changes in proliferation was observed in any tumors; and (f) a strong infiltration by lymphoid cells was observed in all cases. Patients with complete remission or partial remission were found to have a higher in situ infiltration of leukocytes and a higher capability to mediate in vitro antibody-dependent cellular cytotoxicity activity.Conclusions: The results of this pilot study argue against trastuzumab activity in patients through downmodulation of HER2 but in favor of antibody-dependent cellular cytotoxicity guiding efforts to optimize the use of trastuzumab in breast cancer patients.

The candidate tumor suppressor gene, FHIT, encompasses the common human chromosomal fragile site at 3p14.2, the hereditary renal cancer translocation breakpoint, and cancer cell homozygous deletions. Fhit hydrolyzes dinucleotide 5,5ٟ-P 1 ,P 3 -triphosphate in vitro and mutation of a central histidine abolishes hydrolase activity. To study Fhit function, wild-type and mutant FHIT genes were transfected into cancer cell lines that lacked endogenous Fhit. No consistent effect of exogenous Fhit on growth in culture was observed, but Fhit and hydrolase ''dead'' Fhit mutant proteins suppressed tumorigenicity in nude mice, indicating that 5,5ٟ-P 1 ,P 3 -triphosphate hydrolysis is not required for tumor suppression.The structure and expression of the FHIT gene encompassing the FRA3B common fragile site frequently are altered in primary or cultured esophageal, head and neck, lung, gastric, breast, and cervical carcinomas (1-8). Structural alterations tend to be because of deletion within both FHIT alleles, resulting in loss of exons and concomitant absence of full-length FHIT transcript and protein (ref. 6; for review, ref. 9). It has been argued that the FHIT gene may be altered in cancer cells simply because it encompasses the fragile region and is likely to be very susceptible to breakage (7). We agree that the locus is highly susceptible to carcinogen damage, explaining why deletion is much more frequent than point mutation in the gene, but we argue that loss of Fhit function provides a selective advantage for the tumor cell; otherwise, frequent expansion of the deleted FHIT clones in tumors and tumor-derived cell lines would be difficult to explain.Fhit-related proteins have been found in mammals and yeasts (1, 10, 11) and constitute a branch of the histidine triad (HIT) superfamily (12). The Fhit branch includes the Schizosaccharomyces pombe diadenosine tetraphosphate hydrolase [dinucleoside 5Ј,5ٞ-P 1 ,P 4 -tetraphosphate (Ap 4 A) hydrolase] (10) to which Fhit is similar. Barnes et al. (13) have shown that Fhit behaves in vitro as a typical dinucleoside 5Ј,5ٞ-P 1 ,P 3 -triphosphate (Ap 3 A) hydrolase (EC 3.6.1.29); site-directed mutagenesis of FHIT demonstrated that the conserved histidines are required for full activity, and the central histidine of the triad is essential for Ap 3 A hydrolase activity.To investigate mechanisms for a selective growth advantage of Fhit negative tumors, we have prepared vectors for expression of Fhit in cancer-derived cells and have examined the phenotypes of the Fhit-expressing clones relative to the Fhit negative parental cells. To determine if the in vitro enzymatic activity was associated with a role in tumor suppression, the hydrolase ''dead'' mutant gene, FHITH96N, with the central histidine codon of the HIT changed to an asparagine codon, also was expressed in Fhit negative cancer cells. MATERIALS AND METHODSCells. The MKN74 cell line (kindly provided by Eiichi Tahara, University of Hiroshima, Japan), was derived from a gastric carcinoma (14) and forms tumors rapidly ...