[Lani]

Sarah--it is a complicated process of gene therapy via genetic engineering

done in petri dishes

These experiments were done by/for Dr. Weinberg, who most attendees at AACR meetings year after year seem to think is THE MOST TALENTED CANCER RESEARCHER ALIVE

here is how they did it to get regression of long mets which were already established:

Acute miR-31 expression drives regression of established spontaneous lung metastases
In order to determine the consequences of expressing miR-31 in a temporally controlled manner, we used a doxycycline (dox)-inducible miR-31 expression vector system (Supplemental Fig. 1A). As anticipated (Valastyan et al. 2009b), when these vectors were introduced into otherwise metastatic MDA-MB-231 (231) human breast cancer cells, which are essentially devoid of endogenous miR-31 expression (Valastyan et al. 2009b), we observed dox-dependent inhibition of several in vitro cell biological traits (invasiveness, motility, and resistance to anoikis-mediated cell death) that serve as surrogate markers of metastatic proficiency (Supplemental Fig. 1B–D). These effects arose in the absence of altered in vitro proliferation kinetics and therefore did not represent cytostatic or cytotoxic influences (Supplemental Fig. 1E). These findings established that our dox-inducible system closely recapitulated the known influences of constitutive miR-31 expression on malignant cellular behaviors in vitro.

We exploited this ability to precisely control the timing of miR-31 expression to gauge the impact of activating miR-31 function in already-seeded 231 cell lung metastases and primary tumors at various time points after implantation. Accordingly, we implanted the dox-inducible 231 cells orthotopically in the mammary fat pads of mice and activated miR-31 either (1) at no point during the experiment, (2) for the entire course of the 2-mo study, (3) only after relatively modest numbers of micrometastases had formed in the lungs at 1 mo post-implantation, (4) subsequent to the formation of large numbers of pulmonary metastases at 6 wk after implantation, or (5) only following the establishment of an overwhelming metastatic burden in the lungs at 7 wk post-implantation (Fig. 1A). The consequences of acute miR-31 expression on primary mammary tumor development and metastatic progression in the lungs were then assessed.



Activation of miR-31 at any of the assayed time points failed to alter 231 cell primary mammary tumor growth (Fig. 1B). The absence of an effect on primary tumor size did not arise due to failure of dox-mediated up-regulation of miR-31 (Supplemental Fig. 2). Moreover, the miR-31 molecules produced upon dox treatment were indeed functionally active, as gauged by their ability to suppress the levels of three known (Valastyan et al. 2009b) miR-31 downstream target genes: integrin-α5 (ITGA5), radixin (RDX), and RhoA (Supplemental Fig. 3). Hence, miR-31 induction did not elicit general cytostatic or cytotoxic responses.

Despite the lack of changes in their overall sizes, histological examination of the orthotopically arising 231 cell primary mammary tumors revealed stark differences following miR-31 activation. Consistent with prior observations (Valastyan et al. 2009b), 231 cells lacking miR-31 yielded primary tumors that displayed extensive histopathological evidence of local stromal invasion (Fig. 1C,D). In contrast, primary tumors formed by cells that expressed miR-31 for the entire duration of the experiment had a well-encapsulated appearance and were largely noninvasive (Fig. 1C,D).

Interestingly, if miR-31 was not expressed for the first month of the experiment in order to allow the formation of invasive, poorly encapsulated primary mammary tumors, and was then activated for the remainder of the study, the histological appearance of these primary tumors was converted from an invasive phenotype to one that was largely noninvasive (Fig. 1C,D). Similarly, reversal of the invasiveness of 231 cell primary tumors was observed when miR-31 was acutely expressed in even more advanced primary lesions beginning at 6 wk post-implantation (Fig. 1C,D). In contrast, however, no significant change in primary tumor histology occurred when miR-31 was expressed for only the final 7 d of the experiment (Fig. 1C,D). These changes in invasiveness arose in the absence of alterations in the differentiation state of these primary tumors (Supplemental Fig. 4). Together, these observations revealed that activation of miR-31 in established primary mammary tumors was capable of reversing their already-acquired invasiveness

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Hope this helps!