Police épistémologique : l’enquête « streptomycine »

Pas d’ouvrage de méthodologie des essais cliniques sans une référence historique à la streptomycine. Deux études simultanées, l’une britannique, l’autre américaine, annoncent la médecine moderne : randomisation et rigueur du groupe témoin. Curieusement, la référence citée varie en fonction de la nationalité de l’utilisateur, qui évoque soit le statisticien britannique Austin Bradford Hill, soit la Veteran Administration, et qui élude l’une ou l’autre dans sa bibliographie. L’étude historique permet d’appréhender la lente genèse des essais cliniques et la permanence des difficultés rencontrées dans leur réalisation.The discovery of streptomycin is attributed to a microbiologist, Selman Waksman, Nobel Prize 1952, a paternity that was disputed by his collaborator Albert Schatz, who was the first author of the princeps article. Two pioneering clinical studies involved streptomycin, both of which have been widely used as reference works. The first one was English, under the name of Austin Bradford Hill. It inaugurated a randomization in medicine. The second trial was American, and carried out by the Veteran Administration. It made use for the first time of the « control group ». The present article analyses the genesis of clinical trials and illustrates the recurrent difficulties encountered in their implementation

Macrophage depletion reduces postsurgical tumor recurrence and metastatic growth in a spontaneous murine model of melanoma

International audienceSurgical resection of tumors is often followed by regrowth at the primary site and metastases may emerge rapidly following removal of the primary tumor. Macrophages are important drivers of tumor growth, and here we investigated their involvement in postoperative relapse as well as explore macrophage depletion as an adjuvant to surgical resection. RETAAD mice develop spontaneous metastatic melanoma that begins in the eye. Removal of the eyes as early as 1 week of age did not prevent the development of metastases; rather, surgery led to increased proliferation of tumor cells locally and in distant metastases. Surgery-induced increase in tumor cell proliferation correlated with increased macrophage density within the tumor. Moreover, macrophages stimulate tumor sphere formation from tumor cells of post-surgical but not control mice. Macrophage depletion with a diet containing the CSF-1R specific kinase inhibitor Ki20227 following surgery significantly reduced postoperative tumor recurrence and abrogated enhanced metastatic outgrowth. Our results confirm that tumor cells disseminate early, and show that macrophages contribute both to post-surgical tumor relapse and growth of metastases, likely through stimulating a population of tumor-initiating cells. Thus macrophage depletion warrants exploration as an adjuvant to surgical resection

Melanoma-initiating cells exploit M2 macrophage TGFβ and arginase pathway for survival and proliferation

International audienceM2 macrophages promote tumor growth and metastasis, but their interactions with specific tumor cell populations are poorly characterized. Using a mouse model of spontaneous melanoma, we showed that CD34 -but not CD34 + tumor-initiating cells (TICs) depend on M2 macrophages for survival and proliferation. Tumor-associated macrophages (TAMs) and macrophage-conditioned media protected CD34 -TICs from chemotherapy in vitro. In vivo, while inhibition of CD115 suppressed the macrophage-dependent CD34 -TIC population, chemotherapy accelerated its development. The ability of TICs to respond to TAMs was acquired during melanoma progression and immediately preceded a surge in metastatic outgrowth. TAM-derived transforming growth factor-β (TGFβ) and polyamines produced via the Arginase pathway were critical for stimulation of TICs and synergized to promote their growth

How to develop better screens for anti-cancer therapies?

The clinical efficacy of chemotherapy relies in part on its ability to potentiate anti-tumor immune responses. Recent work shows that several chemotherapeutic drugs induce intra-tumoral expression of lymphocyte-attracting chemokines, leading to clinical responses. Here, we argue that such knowledge should be used to screen for novel anti-tumor treatments

In vitro template-change PCR to create single crossover libraries: a case study with B. thuringiensis Cry2A toxins

During evolution the creation of single crossover chimeras between duplicated paralogous genes is a known process for increasing diversity. Comparing the properties of homologously recombined chimeras with one or two crossovers is also an efficient strategy for analyzing relationships between sequence variation and function. However, no well-developed in vitro method has been established to create single-crossover libraries. Here we present an in vitro template-change polymerase change reaction that has been developed to enable the production of such libraries. We applied the method to two closely related toxin genes from B. thuringiensis and created chimeras with differing properties that can help us understand how these toxins are able to differentiate between insect species

Absence of MutSβ leads to the formation of slipped-DNA for CTG/CAG contractions at primate replication forks

Typically disease-causing CAG/CTG repeats expand, but rare affected families can display high levels of contraction of the expanded repeat amongst offspring. Understanding instability is important since arresting expansions or enhancing contractions could be clinically beneficial. The MutSβ mismatch repair complex is required for CAG/CTG expansions in mice and patients. Oddly, by unknown mechanisms MutSβ-deficient mice incur contractions instead of expansions. Replication using CTG or CAG as the lagging strand template is known to cause contractions or expansions respectively; however, the interplay between replication and repair leading to this instability remains unclear. Towards understanding how repeat contractions may arise, we performed in vitro SV40-mediated replication of repeat-containing plasmids in the presence or absence of mismatch repair. Specifically, we separated repair from replication: Replication mediated by MutSβ- and MutSα-deficient human cells or cell extracts produced slipped-DNA heteroduplexes in the contraction- but not expansion-biased replication direction. Replication in the presence of MutSβ disfavoured the retention of replication products harbouring slipped-DNA heteroduplexes. Post-replication repair of slipped-DNAs by MutSβ-proficient extracts eliminated slipped-DNAs. Thus, a MutSβ-deficiency likely enhances repeat contractions because MutSβ protects against contractions by repairing template strand slip-outs. Replication deficient in LigaseI or PCNA-interaction mutant LigaseI revealed slipped-DNA formation at lagging strands. Our results reveal that distinct mechanisms lead to expansions or contractions and support inhibition of MutSβ as a therapeutic strategy to enhance the contraction of expanded repeats